119
Kyung-pook National University Display Technology Education Center 경북대학교 디스플레이 기술교육센터 OLED 전문교육과정 OLED 기술 및 발광 원리 2007. 7. 25 [경북대학교 물리학과, 나노과학기술학과 나노물리연구실] E-mail: [email protected] Tel: (053)950-5321 이 형락

OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

Embed Size (px)

Citation preview

Page 1: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

Kyung-pook National University Display Technology Education Center

경북대학교 디스플레이 기술교육센터 OLED 전문교육과정

OLED 기술 및 발광 원리

2007 7 25

[경북대학교 물리학과 나노과학기술학과 나노물리연구실]

E-mail phyhrleeknuackr Tel (053)950-5321

이형락

1OLED 기초공정 이해와 실습

Emissive Display

Electronic Information Displays

Flat Panel Display Projection

Non Emissive Display

Cathode RayTube

Light Valve

FED VFD PDP ELD LED LCD ECD

TN STN TFT MIM FLCD

CRT

디스플레이의디스플레이의 분류분류

2OLED 기초공정 이해와 실습

Growth of Display IndustryGrowth of Display Industry

[디스플레이뱅크 2005]

3OLED 기초공정 이해와 실습

LuminescenceLuminescence Excitation SourceExcitation Source ApplicationApplication

Photoluminescence (PL)Photoluminescence (PL) LightLight PDP 형광등PDP 형광등

Electroluminescence (EL)Electroluminescence (EL) Electric FieldElectric Field OLEDOLED

Cathodoluminescence (CL)Cathodoluminescence (CL) Cathode Ray(electron)

Cathode Ray(electron) CRTCRT

Luminescence and Display

Emission of LightEmission of Light

mnωh

mnωh

mnωh

mnωh

gtm|

gtn|ltAbsorptiongt ltSpontaneous emissiongt ltInduced emissiongt

4OLED 기초공정 이해와 실습

삼성 SDI (2005 3) 102rdquo Full HD (1920X1080) PDP TV

평판평판 디스플레이디스플레이

LG Philips LCD (2006 8 IMID) 100rdquo Full HD (1920X1080) LCD TV

삼성전자 LCD (2007 7 ) 70rdquo Full HD (1920X1080) LCD TV(LED BLU 채용)

5OLED 기초공정 이해와 실습

삼성전자 (2005 5) 40rdquo WXGA (1280X800) AMOLED based on a-Si TFT

삼성SDI (2005 2) 17rdquo UXGA (1600X1200) AMOLED based on LTPS

LPL (2004 10) 201rdquo WXGA (1280X800) AMOLED based on LTPS

OLED OLED 디스플레이디스플레이

22rdquo QVGA (320X240) AMOLED based on a-Si TFT(20073)

6OLED 기초공정 이해와 실습

PMOLEDMobile Phone

Motorola(Pioneer)

Samsung(SNMD)

LG(Pioneer) Sanyo-Kodak

22rdquo AMOLED

AMOLED

OLED OLED 디스플레이디스플레이 상품상품

Sony PDA(65535Color 480ⅹ320 pixels) (2004)

7OLED 기초공정 이해와 실습

Sony Flexible Full Color Display 25rdquo(120X169 03mm 15g) (20075)

Delta Optoelectronics

(231X205) PLED

PLED PLED 디스플레이디스플레이 상품상품

CDT (1280X768 200511) PLED

8OLED 기초공정 이해와 실습

OLED AppplicationsOLED Appplications

9OLED 기초공정 이해와 실습

[J R Sheats et al Science 273 884 (1996)의 자료에 최근 발전을 추가함]

LEDLED의의 발전상황발전상황

10OLED 기초공정 이해와 실습

LCD와비교

자료 한국화학연구원 정보디스플레이 기술개발 사업단

OLED

LTPS TFT

AMOLED

LC

AMLCD

CF

BL a-Si TFT LTPS TFT

SelfSelf--emittingemittingFull color DisplayFull color Display

No Backlight Thin amp Light

Less Cell Process Simple Process

No Liquid Crystal Fast Response TimeWide Viewing Angle

mm 30g 50

(~1μs)

70~80

of LCD

170170

OLED OLED 특성특성

11OLED 기초공정 이해와 실습

Display ComparisonDisplay Comparison

CRT PDP LCD OLEDLarge Size ⊙

High Resolution ⊙ ⊙

ThicknessWeight times ⊙ ⊙

Response Time times ⊙

Viewing Angle ⊙ ⊙ times ⊙

Cost ⊙ times

Color ⊙ ⊙

Power Consumption times times ⊙

Image Sticking ⊙ ⊙

Best ⊙ Good Middle Bad x

OLED

LCD Thickness amp Weight Power Consumption

CRT Cost Color Viewing angle Response time=

+

12OLED 기초공정 이해와 실습

Organic Light Emitting Display

OLED

OLEDOLED의의 분류분류

PLEDPhOLED PMOLED AMOLED

FOLED 구동방식재료(저고분자)

형광성

저분자

발광재료

인광성

저분자

발광재료

형광성

고분자

발광재료

Flexible

기판

OLED

수동구동

OLED

능동구동

OLED

Emission Direction에 따라 Bottom Top amp Transparent OLED가 있음

13OLED 기초공정 이해와 실습

저분자 고분자

박막 성막 방식 진공 열증착 Ink-jet

순도 고순도 재료 용이 고순도 재료 어려움

열 안정성 낮다 높다

작동전압 7-15v 3-7v

NO

NON

OAl

2 Types

Small Molecule

Polymer

OLEDOLED의의 재료재료

n

14OLED 기초공정 이해와 실습

Early OLED (Small Molecule)Early OLED (Small Molecule)

EL emission spectrum is sensitive to thickness of organic layerDiamine layer transports holes and blocks electrons injected from MgAg electrode

bull MgAg ndash 101bull Luminescent film - 600Aringbull Diamine ndash 750Aring

CW Tang amp SA VanSlyke Kodak Research LaboratoriesCW Tang and S A VanSlyke in Kodak Appl Phys Letter 51 913 (1987)

15OLED 기초공정 이해와 실습

Light Emitting PolymersLight Emitting Polymers

First Polymer LED (PVK-polymer)- Partridge polymer 24 733 (1983)----

With conductive polymer anode tooWeak blue light

PPV-LED- The first observation of EL was in

1989 (Burroughs et al)- Friend et al U S Patent 5247190

(1990) Cambridge University andCDT work on polymers

- poly(14-phenylene vinylene) (PPV) poly[2-(2rsquo-ethylhexyloxy)-5-methoxy-

14-phenylene vinylene] (MEH-PPV)

n

PPV

Full colour spectrum

glass substrateITO

polymer layerAl Ca Mg

16OLED 기초공정 이해와 실습

Organic Molecular CrystalsOrganic Molecular Crystals

Inorganic semiconductors Organic semiconductors

2Bohr radius Rydberg

Band transport

Exciton Binding Energy ~25meV Exciton size ~ 50A

Strong Covalent Bond

Strong e-e screening( ~11)

Strong spin-orbit cou

ε ε

εminusprop prop

bull

bull

bull

gt

gt

gt

gt

J is a good quantum numberpling

gt

Hopping transport

Exciton Binding Energy ~ 05 - 1eV E

Exciton localized on singxciton size ~ 5 - 10A

le pol y

Weak Van der Waals interactions

Weak e-e screening( ~3)ε

bull

bull

gt

gt

gt

gt mer chain

Large exchange energy between the lowest singlet and triple

S is a good quantum number

t excitons

Weak spin-orbit couplingbullgt

gt

17OLED 기초공정 이해와 실습

Conjugated PolymerConjugated Polymer

bull sp2 bonding

poly-acetylene (1958)

bull π- electrons delocalized along the chain

bull Dimerization opens an energy gap 2-3 eV (Peierls instability)

18OLED 기초공정 이해와 실습

에너지에너지 밴드밴드 갭갭

Ionization energies of the HOMO levels and binding energies of the LUMO levels for different polyacenes in the gas phase (left solid lines) and in the crystalline state (right double lines) respectively

C C

H

H

nrarrinfin

Eg=14eV

19OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Hopping model

Small polaron model

Poole-Frenkel model

Multiple trapping amp release model

Etc (Exciton model Soliton model Ishiguro modelhellip)

20OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Hopping model

1

00

In most cases T-dep of mobility

exp where = 1 2 3 4TT

αμ μ α

⎡ ⎤⎛ ⎞⎢ ⎥= minus⎜ ⎟⎢ ⎥⎝ ⎠⎣ ⎦

Conventional semiconductor Organic semiconductorconduction band

valence band

LUMO level

HOMO level

delocalized states propagating

Phonon scattering (negative)rarr mobility increases as T darr

localized states hopping

Phonon scattering (positive)rarr mobility decreases as T darr

01 ~ 1 cm2V-1s-1

21OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Small polaron model

In a conjugated molecules a charge is self-trapped by the lattice deformationrarr creation of the localized mid gap states

Ex) A polaron in Polythiophene

32 22( ) exp

2 2

where polaron binding energy electron transfer energy lattice constant

T-dep of the mobility

bB

Bb

b

Eea J k Tk TE

EJa

πμminus ⎛ ⎞

= minus⎜ ⎟⎝ ⎠h

22OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Poole-Frenkel model

Field dependent mobility at high field (E gt 105 Vcm)

- Coulomb potential near localized states is modified by the applied field

( )120

( ) (0)exp

where (0) zero field mobility

Poole-Frenkel factor mag of electric field

T-dep amp field dep of the mobility

B

qF Fk T

eF

μ μ β

μ

β πεε

⎛ ⎞= ⎜ ⎟

⎝ ⎠

=

23OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Multiple trapping amp release model

Narrow delocalized band+ localized trap level (highly concenturated)

Process1) Carriers arrive at a trap and are trapped2) Thermally activated and released

0

0

exp

where mobility in the delocalized bandDensity of delocalized band edge

Concenturation of traps

T-dep of the mobility

tD

B

Ek T

μ μ α

μ

α

⎛ ⎞= minus⎜ ⎟

⎝ ⎠

=

24OLED 기초공정 이해와 실습

무기EL (p-n junction LED)

Light Emission

anode

cathodeETLEMLHTLHIL+

유기EL (polymers or small molecules)

전자수송층(ETL)

발광층(EML)정공

수송층(HTL)

양극(투명전극

ITO 유리 등)

음극(낮은 일함수 금속

Ca AlLi MgAg등)

-전자

정공

+

-+

두께 100 ~ 200 nm

Exciton

OLED OLED 작동원리작동원리

25OLED 기초공정 이해와 실습

Single-layer devices

Unbalanced carrier injection and lower efficiency

dArr

Heterostructures

ITOHILHTLEMLETLCathode(1) Lower the barrier at electrodes

Balanced carrier injection andimproved efficiency

(2) Band offsets between the layers andspace charges build up at hetero-junctionHigh carrier densitieseffective e-h capture

Multilayer StructureMultilayer Structure

Cathode

HILITO

GLASS

HTLEMLETL

-

+

26OLED 기초공정 이해와 실습

Cathode

HILITO

GLASS

HTLEMLETL

-

+

OLED Structure

N N

CH3

H3C

TPD m-MTDATA

N

N N

N

CH3

CH3

H3C

NO

NON

OAl

Alq3

Small Molecules (Fluorescence)

27OLED 기초공정 이해와 실습

OLED StructureSmall Molecules

(Phosphorescence)

NN

N

N

NN

N

N

CuN

N

NN

CuPc MTDATA

Cathode

HILITO

GLASS

HTLEML

ETL-

+

HBL

NNCH3H3C

BCP

28OLED 기초공정 이해와 실습

OLED Structure

Polymers

Cathode

ITO

GLASS

HTLEML

-

+

PEDOT

n

S O3- S O3

-S O3H S O3H S O3H S O3H

SS

SS

SS

O O

OO

O O

OO OO

n

n n

RR

PPV PF

29OLED 기초공정 이해와 실습

Cur

rent

den

sity Lum

inous Intensity

Voltage

ln V

ln J

J = qn0μVd

J = 98 εsμV2d3

Ligh

t

Current

slope = ηexte

Ex)

OLED OLED 특성특성

3 7

Diode Characteristics Rectification ratio 10 - 10 Power efficiency amp drive voltage

Light vs current

optconv ext

elec

opt opt elecext opt ext

elec elec

P hP eV

N s I IIN s I e e

νη η

η η

= =

= = rArr = times

30OLED 기초공정 이해와 실습

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

Vacuum Level

Anode

Cathode

HOMO

LUMO

Φa

Φc

EA

IP

CB

VB

Eg

에너지에너지 준위준위

31OLED 기초공정 이해와 실습

Current - Voltage Characteristics

2

16 17 3

0

0

1

diffusion voltage ~ 13 V

acceptor concentration ~ 10 - 10 cm

(~ 50 - 150 nm

2( )

Width of space charge layer 2 ( )

D

D

A

r DA

r D A

V VCV

N

C A q N V V

w V V qN

ε ε

ε ε

prop minus

= minus

= minus V = 0 )

OLED OLED 전기적전기적 특성특성

( ) Schottky equation

exp 1

ideality factor 1 1 ideal Schottky diodes B ext BJ J eV nk T V V IR

n n

⎡ ⎤= minus = minus⎣ ⎦ge =

Capacitance - Voltage Dependence

32OLED 기초공정 이해와 실습

I - V Characteristics C - V Characteristics

ITOPPVMetal Polymeric Schottky Diode

OLED OLED 전기적전기적 특성특성

33OLED 기초공정 이해와 실습

Injection Dominated Mechanisms

bull Thermionic emission

bull Tunneling

Bulk Dominated Mechanisms

bull Ohmic Conduction

bull Space Charge Limited Current Conduction

bull Space Charge Limited Current Conduction with Traps

Magnitude of Injection Barrier

전하전하 주입주입

34OLED 기초공정 이해와 실습

Thermionic Emission

Fowler-Nordheim Tunneling

2

2 2

3

exp 1 wehere exp

4 120( )

Richardson constant

bns s

B B

n B

eeVJ J J A Tk T k T

em kA m m A cm Kh

φ

π

⎡ ⎤⎛ ⎞ ⎛ ⎞minus= minus =⎢ ⎥⎜ ⎟ ⎜ ⎟

⎝ ⎠ ⎝ ⎠⎣ ⎦

= =

At low field thermionic emission at high field tunneling dominate

전하전하 주입주입

EF

Evac

-eFz(triangular shape)φ

Z=0 Z

Charge accumulationhigher the energy state `

Electron emission (F-N Tunneling)

Electron emission (Thermionic Emission)

2

3212

~ exp

( ) where 8 (2 )3

bJ EE

qb mqh

π

⎛ ⎞minus⎜ ⎟⎝ ⎠

Φ=

35OLED 기초공정 이해와 실습

Applied voltage

Lattice vibration

Localizedelectron

Hopping conductionBand-like conductionDelocalized electron

Lattice vibration(phonon)

Scattered electron

Low Mobility

bull holes μ ~10-4-10-8 Vs due to poor wave function overlap (large hopping distance)

bull electrons μ ~10-6-10-10Vs due to increased disorder and trapping at defect sites caused by impurities such as O2

rArr Build-up of space-charge density (bulk limited current)

전하전하 이동도이동도

36OLED 기초공정 이해와 실습

NoteMobility depends onElectric Field andTemperature

Mobilities of OrganicsMobilities of Organics

Alq3

37OLED 기초공정 이해와 실습

Ohmic conduction

OLEDOLED의의 전류전류

Current Dendity

current depends linearly on the bias voltageo nn qm VJd

=

2

3

0

1

2 1

(no traps)

(exponential trap distributions ( ) exp( )

one of electrodes(Ohmic contact) can supply more carriers per un

98

Current Density

SCLC condition

o

tt

r

m

m tN

VJd

T E N E kTV md T

ε ε μ

+

+ =

=

prop =

it time than can be transported through the dielectric (caused by low mobility)

Space charge limited (SCL) conduction

38OLED 기초공정 이해와 실습

2

2

3

Charge per unit area Q induced by a voltage V

Transit time across the semiconductor

9

Approximate SCLC densi

Child law (Mott- Gu

ty

Elec8

rney law)

o r

r

o rSCLC

r

VQ CVd

d dtE V

VQJt d

ε ε

μ μ

ε ε μ

= =

= =

asymp =

3 2

tric field distribution across the semiconductor

Majority space charges enhance the E field at the

3 3 ( ) at ( )2 2

enhance the injection of the cath

minority carrieode

rs (elect

V x VE x x d E dd d

= = =

rArr rons)

d

(+) (-)

x=0 x=d

Vd

15 Vd232

3)(d

xVxE =

++++

Virtual anode

-

Space Charge Limited CurrentSpace Charge Limited Current

39OLED 기초공정 이해와 실습

2

3

1

2 01

(no traps or discrete traps Mott-Gurney formula)

(exponential trap distributions ( ) exp( )

98

o rSCLC

mt

SCLC m t t

VJd

TVJ N E NmT

E kTd

ε ε μ

+

+

=

prop = =

ECB

EVB

Etrap

Discrete trapping center Exponential distributionof trapping centers

TrapTrap--Limited CurrentLimited Current

40OLED 기초공정 이해와 실습

Shen Burrows Bulovic McCarty Thompson Forrest Jpn J Appl Phys 35 L401 (1996)

ITOTPDAlq3MgAg

12

1

+

+

prop m

m

SCLC dVJ

TrapTrap--Limited CurrentLimited Current

41OLED 기초공정 이해와 실습

0

0

Activation energy at 0 Empirical parameter

Mobility at PF constant

PF

PF

E FT

T Tμβ

Δ =

=

PFPF

B eff

0

3

PFeff 0 0

( ) exp

exp( )

1 1 1with

E FFT μk T

F

qT T T

βμ

μ β

βπεε

⎛ ⎞Δ minus= minus⎜ ⎟⎜ ⎟

⎝ ⎠

equiv

= minus =

Poole Frenkel ModelPoole Frenkel Model

42OLED 기초공정 이해와 실습

1

22 2

0

0

(1)

(2)

EL F S e h

e ee he

T

h he hh

T

T rec rec e h

h eh e

h e

e hEL F S

h e

T rec

h e h e nh e EL F S EL

e h

n nJ n n nedJ n n ned

nJ

ne F

J J Je F

J Jn J J

ed n ed

η η γ

γτ

γτ

τ τ τ γ

μ

η η γμ μ

τ τ

η ηγ

minus

Φ =

minus minus =

minus minus =

lt =

=

Φ = prop

gt

= Φ = prop rArr Φ prop

EL Current RelationEL Current Relation

43OLED 기초공정 이해와 실습

Device Structure ITONPBAlq3Ca

22

21

ZZZ

fdVdQC

+minus

==πφieZiZZZ ||

))=+=

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

V0 independent of the NPB layer thickness

44OLED 기초공정 이해와 실습

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

Dashed line without interfacial charge

Wolfgang Brutting Stefan Berleb Anton G Muckl Organic Electronics 2 (2001)

Device Structure ITONPBAlq3Ca

45OLED 기초공정 이해와 실습

Langevin Recombination of carriers

bull Carriers are statistically independent therefore the e-h recombination is a random process and kinetically bimolecular

bull Total current attracted by a charge into the sphere of Coulombic capture radius rc

2

22

( ) ( )4

(4 ) 14 184

( ) (mean free path A)

n p c n pc

c cB

n p

qJ qp E qpr

qi r J Bqp r nmk T

qB a

μ μ μ μπε

ππε

μ μ λε

= + = +

= = cong asymp minus

there4 = + asympo

TkUd

BeP ~ minusProbability of dissociation

reUπε4

~2

e-

rc

Carrier RecombinationCarrier Recombination

P Langevin Ann Chem Phys 28 289 (1903)

46OLED 기초공정 이해와 실습

Electronic Processes in Organic Crystals and Polymers by MPope and C E Swenberg

ExcitonsExcitons

47OLED 기초공정 이해와 실습

C Adachi et al

Electrons and holesForm excitons

(bound e--h+ pairs)

Exciton Recombination ZoneExciton Recombination Zone

48OLED 기초공정 이해와 실습

MOLECULAR EXCITED STATESAFTER ELECTRICAL EXCITATION

Singletspin anti-symmetric

Tripletspin symmetric

25 75

MOLECULAR GROUND STATEspin anti-symmetric

Relaxation allowedfast efficientFluorescence

Relaxation disallowedslow inefficientPhosphorescence

|χ1χ2 gt = | gt

|χ1χ2 gt = | gt

|χ1χ2 gt

= | gt - | gt2

1

|χ1χ2 gt = | gt + | gt2

1ISC

Spin

OLEDOLED의의 형광형광인광인광

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 2: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

1OLED 기초공정 이해와 실습

Emissive Display

Electronic Information Displays

Flat Panel Display Projection

Non Emissive Display

Cathode RayTube

Light Valve

FED VFD PDP ELD LED LCD ECD

TN STN TFT MIM FLCD

CRT

디스플레이의디스플레이의 분류분류

2OLED 기초공정 이해와 실습

Growth of Display IndustryGrowth of Display Industry

[디스플레이뱅크 2005]

3OLED 기초공정 이해와 실습

LuminescenceLuminescence Excitation SourceExcitation Source ApplicationApplication

Photoluminescence (PL)Photoluminescence (PL) LightLight PDP 형광등PDP 형광등

Electroluminescence (EL)Electroluminescence (EL) Electric FieldElectric Field OLEDOLED

Cathodoluminescence (CL)Cathodoluminescence (CL) Cathode Ray(electron)

Cathode Ray(electron) CRTCRT

Luminescence and Display

Emission of LightEmission of Light

mnωh

mnωh

mnωh

mnωh

gtm|

gtn|ltAbsorptiongt ltSpontaneous emissiongt ltInduced emissiongt

4OLED 기초공정 이해와 실습

삼성 SDI (2005 3) 102rdquo Full HD (1920X1080) PDP TV

평판평판 디스플레이디스플레이

LG Philips LCD (2006 8 IMID) 100rdquo Full HD (1920X1080) LCD TV

삼성전자 LCD (2007 7 ) 70rdquo Full HD (1920X1080) LCD TV(LED BLU 채용)

5OLED 기초공정 이해와 실습

삼성전자 (2005 5) 40rdquo WXGA (1280X800) AMOLED based on a-Si TFT

삼성SDI (2005 2) 17rdquo UXGA (1600X1200) AMOLED based on LTPS

LPL (2004 10) 201rdquo WXGA (1280X800) AMOLED based on LTPS

OLED OLED 디스플레이디스플레이

22rdquo QVGA (320X240) AMOLED based on a-Si TFT(20073)

6OLED 기초공정 이해와 실습

PMOLEDMobile Phone

Motorola(Pioneer)

Samsung(SNMD)

LG(Pioneer) Sanyo-Kodak

22rdquo AMOLED

AMOLED

OLED OLED 디스플레이디스플레이 상품상품

Sony PDA(65535Color 480ⅹ320 pixels) (2004)

7OLED 기초공정 이해와 실습

Sony Flexible Full Color Display 25rdquo(120X169 03mm 15g) (20075)

Delta Optoelectronics

(231X205) PLED

PLED PLED 디스플레이디스플레이 상품상품

CDT (1280X768 200511) PLED

8OLED 기초공정 이해와 실습

OLED AppplicationsOLED Appplications

9OLED 기초공정 이해와 실습

[J R Sheats et al Science 273 884 (1996)의 자료에 최근 발전을 추가함]

LEDLED의의 발전상황발전상황

10OLED 기초공정 이해와 실습

LCD와비교

자료 한국화학연구원 정보디스플레이 기술개발 사업단

OLED

LTPS TFT

AMOLED

LC

AMLCD

CF

BL a-Si TFT LTPS TFT

SelfSelf--emittingemittingFull color DisplayFull color Display

No Backlight Thin amp Light

Less Cell Process Simple Process

No Liquid Crystal Fast Response TimeWide Viewing Angle

mm 30g 50

(~1μs)

70~80

of LCD

170170

OLED OLED 특성특성

11OLED 기초공정 이해와 실습

Display ComparisonDisplay Comparison

CRT PDP LCD OLEDLarge Size ⊙

High Resolution ⊙ ⊙

ThicknessWeight times ⊙ ⊙

Response Time times ⊙

Viewing Angle ⊙ ⊙ times ⊙

Cost ⊙ times

Color ⊙ ⊙

Power Consumption times times ⊙

Image Sticking ⊙ ⊙

Best ⊙ Good Middle Bad x

OLED

LCD Thickness amp Weight Power Consumption

CRT Cost Color Viewing angle Response time=

+

12OLED 기초공정 이해와 실습

Organic Light Emitting Display

OLED

OLEDOLED의의 분류분류

PLEDPhOLED PMOLED AMOLED

FOLED 구동방식재료(저고분자)

형광성

저분자

발광재료

인광성

저분자

발광재료

형광성

고분자

발광재료

Flexible

기판

OLED

수동구동

OLED

능동구동

OLED

Emission Direction에 따라 Bottom Top amp Transparent OLED가 있음

13OLED 기초공정 이해와 실습

저분자 고분자

박막 성막 방식 진공 열증착 Ink-jet

순도 고순도 재료 용이 고순도 재료 어려움

열 안정성 낮다 높다

작동전압 7-15v 3-7v

NO

NON

OAl

2 Types

Small Molecule

Polymer

OLEDOLED의의 재료재료

n

14OLED 기초공정 이해와 실습

Early OLED (Small Molecule)Early OLED (Small Molecule)

EL emission spectrum is sensitive to thickness of organic layerDiamine layer transports holes and blocks electrons injected from MgAg electrode

bull MgAg ndash 101bull Luminescent film - 600Aringbull Diamine ndash 750Aring

CW Tang amp SA VanSlyke Kodak Research LaboratoriesCW Tang and S A VanSlyke in Kodak Appl Phys Letter 51 913 (1987)

15OLED 기초공정 이해와 실습

Light Emitting PolymersLight Emitting Polymers

First Polymer LED (PVK-polymer)- Partridge polymer 24 733 (1983)----

With conductive polymer anode tooWeak blue light

PPV-LED- The first observation of EL was in

1989 (Burroughs et al)- Friend et al U S Patent 5247190

(1990) Cambridge University andCDT work on polymers

- poly(14-phenylene vinylene) (PPV) poly[2-(2rsquo-ethylhexyloxy)-5-methoxy-

14-phenylene vinylene] (MEH-PPV)

n

PPV

Full colour spectrum

glass substrateITO

polymer layerAl Ca Mg

16OLED 기초공정 이해와 실습

Organic Molecular CrystalsOrganic Molecular Crystals

Inorganic semiconductors Organic semiconductors

2Bohr radius Rydberg

Band transport

Exciton Binding Energy ~25meV Exciton size ~ 50A

Strong Covalent Bond

Strong e-e screening( ~11)

Strong spin-orbit cou

ε ε

εminusprop prop

bull

bull

bull

gt

gt

gt

gt

J is a good quantum numberpling

gt

Hopping transport

Exciton Binding Energy ~ 05 - 1eV E

Exciton localized on singxciton size ~ 5 - 10A

le pol y

Weak Van der Waals interactions

Weak e-e screening( ~3)ε

bull

bull

gt

gt

gt

gt mer chain

Large exchange energy between the lowest singlet and triple

S is a good quantum number

t excitons

Weak spin-orbit couplingbullgt

gt

17OLED 기초공정 이해와 실습

Conjugated PolymerConjugated Polymer

bull sp2 bonding

poly-acetylene (1958)

bull π- electrons delocalized along the chain

bull Dimerization opens an energy gap 2-3 eV (Peierls instability)

18OLED 기초공정 이해와 실습

에너지에너지 밴드밴드 갭갭

Ionization energies of the HOMO levels and binding energies of the LUMO levels for different polyacenes in the gas phase (left solid lines) and in the crystalline state (right double lines) respectively

C C

H

H

nrarrinfin

Eg=14eV

19OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Hopping model

Small polaron model

Poole-Frenkel model

Multiple trapping amp release model

Etc (Exciton model Soliton model Ishiguro modelhellip)

20OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Hopping model

1

00

In most cases T-dep of mobility

exp where = 1 2 3 4TT

αμ μ α

⎡ ⎤⎛ ⎞⎢ ⎥= minus⎜ ⎟⎢ ⎥⎝ ⎠⎣ ⎦

Conventional semiconductor Organic semiconductorconduction band

valence band

LUMO level

HOMO level

delocalized states propagating

Phonon scattering (negative)rarr mobility increases as T darr

localized states hopping

Phonon scattering (positive)rarr mobility decreases as T darr

01 ~ 1 cm2V-1s-1

21OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Small polaron model

In a conjugated molecules a charge is self-trapped by the lattice deformationrarr creation of the localized mid gap states

Ex) A polaron in Polythiophene

32 22( ) exp

2 2

where polaron binding energy electron transfer energy lattice constant

T-dep of the mobility

bB

Bb

b

Eea J k Tk TE

EJa

πμminus ⎛ ⎞

= minus⎜ ⎟⎝ ⎠h

22OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Poole-Frenkel model

Field dependent mobility at high field (E gt 105 Vcm)

- Coulomb potential near localized states is modified by the applied field

( )120

( ) (0)exp

where (0) zero field mobility

Poole-Frenkel factor mag of electric field

T-dep amp field dep of the mobility

B

qF Fk T

eF

μ μ β

μ

β πεε

⎛ ⎞= ⎜ ⎟

⎝ ⎠

=

23OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Multiple trapping amp release model

Narrow delocalized band+ localized trap level (highly concenturated)

Process1) Carriers arrive at a trap and are trapped2) Thermally activated and released

0

0

exp

where mobility in the delocalized bandDensity of delocalized band edge

Concenturation of traps

T-dep of the mobility

tD

B

Ek T

μ μ α

μ

α

⎛ ⎞= minus⎜ ⎟

⎝ ⎠

=

24OLED 기초공정 이해와 실습

무기EL (p-n junction LED)

Light Emission

anode

cathodeETLEMLHTLHIL+

유기EL (polymers or small molecules)

전자수송층(ETL)

발광층(EML)정공

수송층(HTL)

양극(투명전극

ITO 유리 등)

음극(낮은 일함수 금속

Ca AlLi MgAg등)

-전자

정공

+

-+

두께 100 ~ 200 nm

Exciton

OLED OLED 작동원리작동원리

25OLED 기초공정 이해와 실습

Single-layer devices

Unbalanced carrier injection and lower efficiency

dArr

Heterostructures

ITOHILHTLEMLETLCathode(1) Lower the barrier at electrodes

Balanced carrier injection andimproved efficiency

(2) Band offsets between the layers andspace charges build up at hetero-junctionHigh carrier densitieseffective e-h capture

Multilayer StructureMultilayer Structure

Cathode

HILITO

GLASS

HTLEMLETL

-

+

26OLED 기초공정 이해와 실습

Cathode

HILITO

GLASS

HTLEMLETL

-

+

OLED Structure

N N

CH3

H3C

TPD m-MTDATA

N

N N

N

CH3

CH3

H3C

NO

NON

OAl

Alq3

Small Molecules (Fluorescence)

27OLED 기초공정 이해와 실습

OLED StructureSmall Molecules

(Phosphorescence)

NN

N

N

NN

N

N

CuN

N

NN

CuPc MTDATA

Cathode

HILITO

GLASS

HTLEML

ETL-

+

HBL

NNCH3H3C

BCP

28OLED 기초공정 이해와 실습

OLED Structure

Polymers

Cathode

ITO

GLASS

HTLEML

-

+

PEDOT

n

S O3- S O3

-S O3H S O3H S O3H S O3H

SS

SS

SS

O O

OO

O O

OO OO

n

n n

RR

PPV PF

29OLED 기초공정 이해와 실습

Cur

rent

den

sity Lum

inous Intensity

Voltage

ln V

ln J

J = qn0μVd

J = 98 εsμV2d3

Ligh

t

Current

slope = ηexte

Ex)

OLED OLED 특성특성

3 7

Diode Characteristics Rectification ratio 10 - 10 Power efficiency amp drive voltage

Light vs current

optconv ext

elec

opt opt elecext opt ext

elec elec

P hP eV

N s I IIN s I e e

νη η

η η

= =

= = rArr = times

30OLED 기초공정 이해와 실습

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

Vacuum Level

Anode

Cathode

HOMO

LUMO

Φa

Φc

EA

IP

CB

VB

Eg

에너지에너지 준위준위

31OLED 기초공정 이해와 실습

Current - Voltage Characteristics

2

16 17 3

0

0

1

diffusion voltage ~ 13 V

acceptor concentration ~ 10 - 10 cm

(~ 50 - 150 nm

2( )

Width of space charge layer 2 ( )

D

D

A

r DA

r D A

V VCV

N

C A q N V V

w V V qN

ε ε

ε ε

prop minus

= minus

= minus V = 0 )

OLED OLED 전기적전기적 특성특성

( ) Schottky equation

exp 1

ideality factor 1 1 ideal Schottky diodes B ext BJ J eV nk T V V IR

n n

⎡ ⎤= minus = minus⎣ ⎦ge =

Capacitance - Voltage Dependence

32OLED 기초공정 이해와 실습

I - V Characteristics C - V Characteristics

ITOPPVMetal Polymeric Schottky Diode

OLED OLED 전기적전기적 특성특성

33OLED 기초공정 이해와 실습

Injection Dominated Mechanisms

bull Thermionic emission

bull Tunneling

Bulk Dominated Mechanisms

bull Ohmic Conduction

bull Space Charge Limited Current Conduction

bull Space Charge Limited Current Conduction with Traps

Magnitude of Injection Barrier

전하전하 주입주입

34OLED 기초공정 이해와 실습

Thermionic Emission

Fowler-Nordheim Tunneling

2

2 2

3

exp 1 wehere exp

4 120( )

Richardson constant

bns s

B B

n B

eeVJ J J A Tk T k T

em kA m m A cm Kh

φ

π

⎡ ⎤⎛ ⎞ ⎛ ⎞minus= minus =⎢ ⎥⎜ ⎟ ⎜ ⎟

⎝ ⎠ ⎝ ⎠⎣ ⎦

= =

At low field thermionic emission at high field tunneling dominate

전하전하 주입주입

EF

Evac

-eFz(triangular shape)φ

Z=0 Z

Charge accumulationhigher the energy state `

Electron emission (F-N Tunneling)

Electron emission (Thermionic Emission)

2

3212

~ exp

( ) where 8 (2 )3

bJ EE

qb mqh

π

⎛ ⎞minus⎜ ⎟⎝ ⎠

Φ=

35OLED 기초공정 이해와 실습

Applied voltage

Lattice vibration

Localizedelectron

Hopping conductionBand-like conductionDelocalized electron

Lattice vibration(phonon)

Scattered electron

Low Mobility

bull holes μ ~10-4-10-8 Vs due to poor wave function overlap (large hopping distance)

bull electrons μ ~10-6-10-10Vs due to increased disorder and trapping at defect sites caused by impurities such as O2

rArr Build-up of space-charge density (bulk limited current)

전하전하 이동도이동도

36OLED 기초공정 이해와 실습

NoteMobility depends onElectric Field andTemperature

Mobilities of OrganicsMobilities of Organics

Alq3

37OLED 기초공정 이해와 실습

Ohmic conduction

OLEDOLED의의 전류전류

Current Dendity

current depends linearly on the bias voltageo nn qm VJd

=

2

3

0

1

2 1

(no traps)

(exponential trap distributions ( ) exp( )

one of electrodes(Ohmic contact) can supply more carriers per un

98

Current Density

SCLC condition

o

tt

r

m

m tN

VJd

T E N E kTV md T

ε ε μ

+

+ =

=

prop =

it time than can be transported through the dielectric (caused by low mobility)

Space charge limited (SCL) conduction

38OLED 기초공정 이해와 실습

2

2

3

Charge per unit area Q induced by a voltage V

Transit time across the semiconductor

9

Approximate SCLC densi

Child law (Mott- Gu

ty

Elec8

rney law)

o r

r

o rSCLC

r

VQ CVd

d dtE V

VQJt d

ε ε

μ μ

ε ε μ

= =

= =

asymp =

3 2

tric field distribution across the semiconductor

Majority space charges enhance the E field at the

3 3 ( ) at ( )2 2

enhance the injection of the cath

minority carrieode

rs (elect

V x VE x x d E dd d

= = =

rArr rons)

d

(+) (-)

x=0 x=d

Vd

15 Vd232

3)(d

xVxE =

++++

Virtual anode

-

Space Charge Limited CurrentSpace Charge Limited Current

39OLED 기초공정 이해와 실습

2

3

1

2 01

(no traps or discrete traps Mott-Gurney formula)

(exponential trap distributions ( ) exp( )

98

o rSCLC

mt

SCLC m t t

VJd

TVJ N E NmT

E kTd

ε ε μ

+

+

=

prop = =

ECB

EVB

Etrap

Discrete trapping center Exponential distributionof trapping centers

TrapTrap--Limited CurrentLimited Current

40OLED 기초공정 이해와 실습

Shen Burrows Bulovic McCarty Thompson Forrest Jpn J Appl Phys 35 L401 (1996)

ITOTPDAlq3MgAg

12

1

+

+

prop m

m

SCLC dVJ

TrapTrap--Limited CurrentLimited Current

41OLED 기초공정 이해와 실습

0

0

Activation energy at 0 Empirical parameter

Mobility at PF constant

PF

PF

E FT

T Tμβ

Δ =

=

PFPF

B eff

0

3

PFeff 0 0

( ) exp

exp( )

1 1 1with

E FFT μk T

F

qT T T

βμ

μ β

βπεε

⎛ ⎞Δ minus= minus⎜ ⎟⎜ ⎟

⎝ ⎠

equiv

= minus =

Poole Frenkel ModelPoole Frenkel Model

42OLED 기초공정 이해와 실습

1

22 2

0

0

(1)

(2)

EL F S e h

e ee he

T

h he hh

T

T rec rec e h

h eh e

h e

e hEL F S

h e

T rec

h e h e nh e EL F S EL

e h

n nJ n n nedJ n n ned

nJ

ne F

J J Je F

J Jn J J

ed n ed

η η γ

γτ

γτ

τ τ τ γ

μ

η η γμ μ

τ τ

η ηγ

minus

Φ =

minus minus =

minus minus =

lt =

=

Φ = prop

gt

= Φ = prop rArr Φ prop

EL Current RelationEL Current Relation

43OLED 기초공정 이해와 실습

Device Structure ITONPBAlq3Ca

22

21

ZZZ

fdVdQC

+minus

==πφieZiZZZ ||

))=+=

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

V0 independent of the NPB layer thickness

44OLED 기초공정 이해와 실습

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

Dashed line without interfacial charge

Wolfgang Brutting Stefan Berleb Anton G Muckl Organic Electronics 2 (2001)

Device Structure ITONPBAlq3Ca

45OLED 기초공정 이해와 실습

Langevin Recombination of carriers

bull Carriers are statistically independent therefore the e-h recombination is a random process and kinetically bimolecular

bull Total current attracted by a charge into the sphere of Coulombic capture radius rc

2

22

( ) ( )4

(4 ) 14 184

( ) (mean free path A)

n p c n pc

c cB

n p

qJ qp E qpr

qi r J Bqp r nmk T

qB a

μ μ μ μπε

ππε

μ μ λε

= + = +

= = cong asymp minus

there4 = + asympo

TkUd

BeP ~ minusProbability of dissociation

reUπε4

~2

e-

rc

Carrier RecombinationCarrier Recombination

P Langevin Ann Chem Phys 28 289 (1903)

46OLED 기초공정 이해와 실습

Electronic Processes in Organic Crystals and Polymers by MPope and C E Swenberg

ExcitonsExcitons

47OLED 기초공정 이해와 실습

C Adachi et al

Electrons and holesForm excitons

(bound e--h+ pairs)

Exciton Recombination ZoneExciton Recombination Zone

48OLED 기초공정 이해와 실습

MOLECULAR EXCITED STATESAFTER ELECTRICAL EXCITATION

Singletspin anti-symmetric

Tripletspin symmetric

25 75

MOLECULAR GROUND STATEspin anti-symmetric

Relaxation allowedfast efficientFluorescence

Relaxation disallowedslow inefficientPhosphorescence

|χ1χ2 gt = | gt

|χ1χ2 gt = | gt

|χ1χ2 gt

= | gt - | gt2

1

|χ1χ2 gt = | gt + | gt2

1ISC

Spin

OLEDOLED의의 형광형광인광인광

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 3: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

2OLED 기초공정 이해와 실습

Growth of Display IndustryGrowth of Display Industry

[디스플레이뱅크 2005]

3OLED 기초공정 이해와 실습

LuminescenceLuminescence Excitation SourceExcitation Source ApplicationApplication

Photoluminescence (PL)Photoluminescence (PL) LightLight PDP 형광등PDP 형광등

Electroluminescence (EL)Electroluminescence (EL) Electric FieldElectric Field OLEDOLED

Cathodoluminescence (CL)Cathodoluminescence (CL) Cathode Ray(electron)

Cathode Ray(electron) CRTCRT

Luminescence and Display

Emission of LightEmission of Light

mnωh

mnωh

mnωh

mnωh

gtm|

gtn|ltAbsorptiongt ltSpontaneous emissiongt ltInduced emissiongt

4OLED 기초공정 이해와 실습

삼성 SDI (2005 3) 102rdquo Full HD (1920X1080) PDP TV

평판평판 디스플레이디스플레이

LG Philips LCD (2006 8 IMID) 100rdquo Full HD (1920X1080) LCD TV

삼성전자 LCD (2007 7 ) 70rdquo Full HD (1920X1080) LCD TV(LED BLU 채용)

5OLED 기초공정 이해와 실습

삼성전자 (2005 5) 40rdquo WXGA (1280X800) AMOLED based on a-Si TFT

삼성SDI (2005 2) 17rdquo UXGA (1600X1200) AMOLED based on LTPS

LPL (2004 10) 201rdquo WXGA (1280X800) AMOLED based on LTPS

OLED OLED 디스플레이디스플레이

22rdquo QVGA (320X240) AMOLED based on a-Si TFT(20073)

6OLED 기초공정 이해와 실습

PMOLEDMobile Phone

Motorola(Pioneer)

Samsung(SNMD)

LG(Pioneer) Sanyo-Kodak

22rdquo AMOLED

AMOLED

OLED OLED 디스플레이디스플레이 상품상품

Sony PDA(65535Color 480ⅹ320 pixels) (2004)

7OLED 기초공정 이해와 실습

Sony Flexible Full Color Display 25rdquo(120X169 03mm 15g) (20075)

Delta Optoelectronics

(231X205) PLED

PLED PLED 디스플레이디스플레이 상품상품

CDT (1280X768 200511) PLED

8OLED 기초공정 이해와 실습

OLED AppplicationsOLED Appplications

9OLED 기초공정 이해와 실습

[J R Sheats et al Science 273 884 (1996)의 자료에 최근 발전을 추가함]

LEDLED의의 발전상황발전상황

10OLED 기초공정 이해와 실습

LCD와비교

자료 한국화학연구원 정보디스플레이 기술개발 사업단

OLED

LTPS TFT

AMOLED

LC

AMLCD

CF

BL a-Si TFT LTPS TFT

SelfSelf--emittingemittingFull color DisplayFull color Display

No Backlight Thin amp Light

Less Cell Process Simple Process

No Liquid Crystal Fast Response TimeWide Viewing Angle

mm 30g 50

(~1μs)

70~80

of LCD

170170

OLED OLED 특성특성

11OLED 기초공정 이해와 실습

Display ComparisonDisplay Comparison

CRT PDP LCD OLEDLarge Size ⊙

High Resolution ⊙ ⊙

ThicknessWeight times ⊙ ⊙

Response Time times ⊙

Viewing Angle ⊙ ⊙ times ⊙

Cost ⊙ times

Color ⊙ ⊙

Power Consumption times times ⊙

Image Sticking ⊙ ⊙

Best ⊙ Good Middle Bad x

OLED

LCD Thickness amp Weight Power Consumption

CRT Cost Color Viewing angle Response time=

+

12OLED 기초공정 이해와 실습

Organic Light Emitting Display

OLED

OLEDOLED의의 분류분류

PLEDPhOLED PMOLED AMOLED

FOLED 구동방식재료(저고분자)

형광성

저분자

발광재료

인광성

저분자

발광재료

형광성

고분자

발광재료

Flexible

기판

OLED

수동구동

OLED

능동구동

OLED

Emission Direction에 따라 Bottom Top amp Transparent OLED가 있음

13OLED 기초공정 이해와 실습

저분자 고분자

박막 성막 방식 진공 열증착 Ink-jet

순도 고순도 재료 용이 고순도 재료 어려움

열 안정성 낮다 높다

작동전압 7-15v 3-7v

NO

NON

OAl

2 Types

Small Molecule

Polymer

OLEDOLED의의 재료재료

n

14OLED 기초공정 이해와 실습

Early OLED (Small Molecule)Early OLED (Small Molecule)

EL emission spectrum is sensitive to thickness of organic layerDiamine layer transports holes and blocks electrons injected from MgAg electrode

bull MgAg ndash 101bull Luminescent film - 600Aringbull Diamine ndash 750Aring

CW Tang amp SA VanSlyke Kodak Research LaboratoriesCW Tang and S A VanSlyke in Kodak Appl Phys Letter 51 913 (1987)

15OLED 기초공정 이해와 실습

Light Emitting PolymersLight Emitting Polymers

First Polymer LED (PVK-polymer)- Partridge polymer 24 733 (1983)----

With conductive polymer anode tooWeak blue light

PPV-LED- The first observation of EL was in

1989 (Burroughs et al)- Friend et al U S Patent 5247190

(1990) Cambridge University andCDT work on polymers

- poly(14-phenylene vinylene) (PPV) poly[2-(2rsquo-ethylhexyloxy)-5-methoxy-

14-phenylene vinylene] (MEH-PPV)

n

PPV

Full colour spectrum

glass substrateITO

polymer layerAl Ca Mg

16OLED 기초공정 이해와 실습

Organic Molecular CrystalsOrganic Molecular Crystals

Inorganic semiconductors Organic semiconductors

2Bohr radius Rydberg

Band transport

Exciton Binding Energy ~25meV Exciton size ~ 50A

Strong Covalent Bond

Strong e-e screening( ~11)

Strong spin-orbit cou

ε ε

εminusprop prop

bull

bull

bull

gt

gt

gt

gt

J is a good quantum numberpling

gt

Hopping transport

Exciton Binding Energy ~ 05 - 1eV E

Exciton localized on singxciton size ~ 5 - 10A

le pol y

Weak Van der Waals interactions

Weak e-e screening( ~3)ε

bull

bull

gt

gt

gt

gt mer chain

Large exchange energy between the lowest singlet and triple

S is a good quantum number

t excitons

Weak spin-orbit couplingbullgt

gt

17OLED 기초공정 이해와 실습

Conjugated PolymerConjugated Polymer

bull sp2 bonding

poly-acetylene (1958)

bull π- electrons delocalized along the chain

bull Dimerization opens an energy gap 2-3 eV (Peierls instability)

18OLED 기초공정 이해와 실습

에너지에너지 밴드밴드 갭갭

Ionization energies of the HOMO levels and binding energies of the LUMO levels for different polyacenes in the gas phase (left solid lines) and in the crystalline state (right double lines) respectively

C C

H

H

nrarrinfin

Eg=14eV

19OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Hopping model

Small polaron model

Poole-Frenkel model

Multiple trapping amp release model

Etc (Exciton model Soliton model Ishiguro modelhellip)

20OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Hopping model

1

00

In most cases T-dep of mobility

exp where = 1 2 3 4TT

αμ μ α

⎡ ⎤⎛ ⎞⎢ ⎥= minus⎜ ⎟⎢ ⎥⎝ ⎠⎣ ⎦

Conventional semiconductor Organic semiconductorconduction band

valence band

LUMO level

HOMO level

delocalized states propagating

Phonon scattering (negative)rarr mobility increases as T darr

localized states hopping

Phonon scattering (positive)rarr mobility decreases as T darr

01 ~ 1 cm2V-1s-1

21OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Small polaron model

In a conjugated molecules a charge is self-trapped by the lattice deformationrarr creation of the localized mid gap states

Ex) A polaron in Polythiophene

32 22( ) exp

2 2

where polaron binding energy electron transfer energy lattice constant

T-dep of the mobility

bB

Bb

b

Eea J k Tk TE

EJa

πμminus ⎛ ⎞

= minus⎜ ⎟⎝ ⎠h

22OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Poole-Frenkel model

Field dependent mobility at high field (E gt 105 Vcm)

- Coulomb potential near localized states is modified by the applied field

( )120

( ) (0)exp

where (0) zero field mobility

Poole-Frenkel factor mag of electric field

T-dep amp field dep of the mobility

B

qF Fk T

eF

μ μ β

μ

β πεε

⎛ ⎞= ⎜ ⎟

⎝ ⎠

=

23OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Multiple trapping amp release model

Narrow delocalized band+ localized trap level (highly concenturated)

Process1) Carriers arrive at a trap and are trapped2) Thermally activated and released

0

0

exp

where mobility in the delocalized bandDensity of delocalized band edge

Concenturation of traps

T-dep of the mobility

tD

B

Ek T

μ μ α

μ

α

⎛ ⎞= minus⎜ ⎟

⎝ ⎠

=

24OLED 기초공정 이해와 실습

무기EL (p-n junction LED)

Light Emission

anode

cathodeETLEMLHTLHIL+

유기EL (polymers or small molecules)

전자수송층(ETL)

발광층(EML)정공

수송층(HTL)

양극(투명전극

ITO 유리 등)

음극(낮은 일함수 금속

Ca AlLi MgAg등)

-전자

정공

+

-+

두께 100 ~ 200 nm

Exciton

OLED OLED 작동원리작동원리

25OLED 기초공정 이해와 실습

Single-layer devices

Unbalanced carrier injection and lower efficiency

dArr

Heterostructures

ITOHILHTLEMLETLCathode(1) Lower the barrier at electrodes

Balanced carrier injection andimproved efficiency

(2) Band offsets between the layers andspace charges build up at hetero-junctionHigh carrier densitieseffective e-h capture

Multilayer StructureMultilayer Structure

Cathode

HILITO

GLASS

HTLEMLETL

-

+

26OLED 기초공정 이해와 실습

Cathode

HILITO

GLASS

HTLEMLETL

-

+

OLED Structure

N N

CH3

H3C

TPD m-MTDATA

N

N N

N

CH3

CH3

H3C

NO

NON

OAl

Alq3

Small Molecules (Fluorescence)

27OLED 기초공정 이해와 실습

OLED StructureSmall Molecules

(Phosphorescence)

NN

N

N

NN

N

N

CuN

N

NN

CuPc MTDATA

Cathode

HILITO

GLASS

HTLEML

ETL-

+

HBL

NNCH3H3C

BCP

28OLED 기초공정 이해와 실습

OLED Structure

Polymers

Cathode

ITO

GLASS

HTLEML

-

+

PEDOT

n

S O3- S O3

-S O3H S O3H S O3H S O3H

SS

SS

SS

O O

OO

O O

OO OO

n

n n

RR

PPV PF

29OLED 기초공정 이해와 실습

Cur

rent

den

sity Lum

inous Intensity

Voltage

ln V

ln J

J = qn0μVd

J = 98 εsμV2d3

Ligh

t

Current

slope = ηexte

Ex)

OLED OLED 특성특성

3 7

Diode Characteristics Rectification ratio 10 - 10 Power efficiency amp drive voltage

Light vs current

optconv ext

elec

opt opt elecext opt ext

elec elec

P hP eV

N s I IIN s I e e

νη η

η η

= =

= = rArr = times

30OLED 기초공정 이해와 실습

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

Vacuum Level

Anode

Cathode

HOMO

LUMO

Φa

Φc

EA

IP

CB

VB

Eg

에너지에너지 준위준위

31OLED 기초공정 이해와 실습

Current - Voltage Characteristics

2

16 17 3

0

0

1

diffusion voltage ~ 13 V

acceptor concentration ~ 10 - 10 cm

(~ 50 - 150 nm

2( )

Width of space charge layer 2 ( )

D

D

A

r DA

r D A

V VCV

N

C A q N V V

w V V qN

ε ε

ε ε

prop minus

= minus

= minus V = 0 )

OLED OLED 전기적전기적 특성특성

( ) Schottky equation

exp 1

ideality factor 1 1 ideal Schottky diodes B ext BJ J eV nk T V V IR

n n

⎡ ⎤= minus = minus⎣ ⎦ge =

Capacitance - Voltage Dependence

32OLED 기초공정 이해와 실습

I - V Characteristics C - V Characteristics

ITOPPVMetal Polymeric Schottky Diode

OLED OLED 전기적전기적 특성특성

33OLED 기초공정 이해와 실습

Injection Dominated Mechanisms

bull Thermionic emission

bull Tunneling

Bulk Dominated Mechanisms

bull Ohmic Conduction

bull Space Charge Limited Current Conduction

bull Space Charge Limited Current Conduction with Traps

Magnitude of Injection Barrier

전하전하 주입주입

34OLED 기초공정 이해와 실습

Thermionic Emission

Fowler-Nordheim Tunneling

2

2 2

3

exp 1 wehere exp

4 120( )

Richardson constant

bns s

B B

n B

eeVJ J J A Tk T k T

em kA m m A cm Kh

φ

π

⎡ ⎤⎛ ⎞ ⎛ ⎞minus= minus =⎢ ⎥⎜ ⎟ ⎜ ⎟

⎝ ⎠ ⎝ ⎠⎣ ⎦

= =

At low field thermionic emission at high field tunneling dominate

전하전하 주입주입

EF

Evac

-eFz(triangular shape)φ

Z=0 Z

Charge accumulationhigher the energy state `

Electron emission (F-N Tunneling)

Electron emission (Thermionic Emission)

2

3212

~ exp

( ) where 8 (2 )3

bJ EE

qb mqh

π

⎛ ⎞minus⎜ ⎟⎝ ⎠

Φ=

35OLED 기초공정 이해와 실습

Applied voltage

Lattice vibration

Localizedelectron

Hopping conductionBand-like conductionDelocalized electron

Lattice vibration(phonon)

Scattered electron

Low Mobility

bull holes μ ~10-4-10-8 Vs due to poor wave function overlap (large hopping distance)

bull electrons μ ~10-6-10-10Vs due to increased disorder and trapping at defect sites caused by impurities such as O2

rArr Build-up of space-charge density (bulk limited current)

전하전하 이동도이동도

36OLED 기초공정 이해와 실습

NoteMobility depends onElectric Field andTemperature

Mobilities of OrganicsMobilities of Organics

Alq3

37OLED 기초공정 이해와 실습

Ohmic conduction

OLEDOLED의의 전류전류

Current Dendity

current depends linearly on the bias voltageo nn qm VJd

=

2

3

0

1

2 1

(no traps)

(exponential trap distributions ( ) exp( )

one of electrodes(Ohmic contact) can supply more carriers per un

98

Current Density

SCLC condition

o

tt

r

m

m tN

VJd

T E N E kTV md T

ε ε μ

+

+ =

=

prop =

it time than can be transported through the dielectric (caused by low mobility)

Space charge limited (SCL) conduction

38OLED 기초공정 이해와 실습

2

2

3

Charge per unit area Q induced by a voltage V

Transit time across the semiconductor

9

Approximate SCLC densi

Child law (Mott- Gu

ty

Elec8

rney law)

o r

r

o rSCLC

r

VQ CVd

d dtE V

VQJt d

ε ε

μ μ

ε ε μ

= =

= =

asymp =

3 2

tric field distribution across the semiconductor

Majority space charges enhance the E field at the

3 3 ( ) at ( )2 2

enhance the injection of the cath

minority carrieode

rs (elect

V x VE x x d E dd d

= = =

rArr rons)

d

(+) (-)

x=0 x=d

Vd

15 Vd232

3)(d

xVxE =

++++

Virtual anode

-

Space Charge Limited CurrentSpace Charge Limited Current

39OLED 기초공정 이해와 실습

2

3

1

2 01

(no traps or discrete traps Mott-Gurney formula)

(exponential trap distributions ( ) exp( )

98

o rSCLC

mt

SCLC m t t

VJd

TVJ N E NmT

E kTd

ε ε μ

+

+

=

prop = =

ECB

EVB

Etrap

Discrete trapping center Exponential distributionof trapping centers

TrapTrap--Limited CurrentLimited Current

40OLED 기초공정 이해와 실습

Shen Burrows Bulovic McCarty Thompson Forrest Jpn J Appl Phys 35 L401 (1996)

ITOTPDAlq3MgAg

12

1

+

+

prop m

m

SCLC dVJ

TrapTrap--Limited CurrentLimited Current

41OLED 기초공정 이해와 실습

0

0

Activation energy at 0 Empirical parameter

Mobility at PF constant

PF

PF

E FT

T Tμβ

Δ =

=

PFPF

B eff

0

3

PFeff 0 0

( ) exp

exp( )

1 1 1with

E FFT μk T

F

qT T T

βμ

μ β

βπεε

⎛ ⎞Δ minus= minus⎜ ⎟⎜ ⎟

⎝ ⎠

equiv

= minus =

Poole Frenkel ModelPoole Frenkel Model

42OLED 기초공정 이해와 실습

1

22 2

0

0

(1)

(2)

EL F S e h

e ee he

T

h he hh

T

T rec rec e h

h eh e

h e

e hEL F S

h e

T rec

h e h e nh e EL F S EL

e h

n nJ n n nedJ n n ned

nJ

ne F

J J Je F

J Jn J J

ed n ed

η η γ

γτ

γτ

τ τ τ γ

μ

η η γμ μ

τ τ

η ηγ

minus

Φ =

minus minus =

minus minus =

lt =

=

Φ = prop

gt

= Φ = prop rArr Φ prop

EL Current RelationEL Current Relation

43OLED 기초공정 이해와 실습

Device Structure ITONPBAlq3Ca

22

21

ZZZ

fdVdQC

+minus

==πφieZiZZZ ||

))=+=

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

V0 independent of the NPB layer thickness

44OLED 기초공정 이해와 실습

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

Dashed line without interfacial charge

Wolfgang Brutting Stefan Berleb Anton G Muckl Organic Electronics 2 (2001)

Device Structure ITONPBAlq3Ca

45OLED 기초공정 이해와 실습

Langevin Recombination of carriers

bull Carriers are statistically independent therefore the e-h recombination is a random process and kinetically bimolecular

bull Total current attracted by a charge into the sphere of Coulombic capture radius rc

2

22

( ) ( )4

(4 ) 14 184

( ) (mean free path A)

n p c n pc

c cB

n p

qJ qp E qpr

qi r J Bqp r nmk T

qB a

μ μ μ μπε

ππε

μ μ λε

= + = +

= = cong asymp minus

there4 = + asympo

TkUd

BeP ~ minusProbability of dissociation

reUπε4

~2

e-

rc

Carrier RecombinationCarrier Recombination

P Langevin Ann Chem Phys 28 289 (1903)

46OLED 기초공정 이해와 실습

Electronic Processes in Organic Crystals and Polymers by MPope and C E Swenberg

ExcitonsExcitons

47OLED 기초공정 이해와 실습

C Adachi et al

Electrons and holesForm excitons

(bound e--h+ pairs)

Exciton Recombination ZoneExciton Recombination Zone

48OLED 기초공정 이해와 실습

MOLECULAR EXCITED STATESAFTER ELECTRICAL EXCITATION

Singletspin anti-symmetric

Tripletspin symmetric

25 75

MOLECULAR GROUND STATEspin anti-symmetric

Relaxation allowedfast efficientFluorescence

Relaxation disallowedslow inefficientPhosphorescence

|χ1χ2 gt = | gt

|χ1χ2 gt = | gt

|χ1χ2 gt

= | gt - | gt2

1

|χ1χ2 gt = | gt + | gt2

1ISC

Spin

OLEDOLED의의 형광형광인광인광

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 4: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

3OLED 기초공정 이해와 실습

LuminescenceLuminescence Excitation SourceExcitation Source ApplicationApplication

Photoluminescence (PL)Photoluminescence (PL) LightLight PDP 형광등PDP 형광등

Electroluminescence (EL)Electroluminescence (EL) Electric FieldElectric Field OLEDOLED

Cathodoluminescence (CL)Cathodoluminescence (CL) Cathode Ray(electron)

Cathode Ray(electron) CRTCRT

Luminescence and Display

Emission of LightEmission of Light

mnωh

mnωh

mnωh

mnωh

gtm|

gtn|ltAbsorptiongt ltSpontaneous emissiongt ltInduced emissiongt

4OLED 기초공정 이해와 실습

삼성 SDI (2005 3) 102rdquo Full HD (1920X1080) PDP TV

평판평판 디스플레이디스플레이

LG Philips LCD (2006 8 IMID) 100rdquo Full HD (1920X1080) LCD TV

삼성전자 LCD (2007 7 ) 70rdquo Full HD (1920X1080) LCD TV(LED BLU 채용)

5OLED 기초공정 이해와 실습

삼성전자 (2005 5) 40rdquo WXGA (1280X800) AMOLED based on a-Si TFT

삼성SDI (2005 2) 17rdquo UXGA (1600X1200) AMOLED based on LTPS

LPL (2004 10) 201rdquo WXGA (1280X800) AMOLED based on LTPS

OLED OLED 디스플레이디스플레이

22rdquo QVGA (320X240) AMOLED based on a-Si TFT(20073)

6OLED 기초공정 이해와 실습

PMOLEDMobile Phone

Motorola(Pioneer)

Samsung(SNMD)

LG(Pioneer) Sanyo-Kodak

22rdquo AMOLED

AMOLED

OLED OLED 디스플레이디스플레이 상품상품

Sony PDA(65535Color 480ⅹ320 pixels) (2004)

7OLED 기초공정 이해와 실습

Sony Flexible Full Color Display 25rdquo(120X169 03mm 15g) (20075)

Delta Optoelectronics

(231X205) PLED

PLED PLED 디스플레이디스플레이 상품상품

CDT (1280X768 200511) PLED

8OLED 기초공정 이해와 실습

OLED AppplicationsOLED Appplications

9OLED 기초공정 이해와 실습

[J R Sheats et al Science 273 884 (1996)의 자료에 최근 발전을 추가함]

LEDLED의의 발전상황발전상황

10OLED 기초공정 이해와 실습

LCD와비교

자료 한국화학연구원 정보디스플레이 기술개발 사업단

OLED

LTPS TFT

AMOLED

LC

AMLCD

CF

BL a-Si TFT LTPS TFT

SelfSelf--emittingemittingFull color DisplayFull color Display

No Backlight Thin amp Light

Less Cell Process Simple Process

No Liquid Crystal Fast Response TimeWide Viewing Angle

mm 30g 50

(~1μs)

70~80

of LCD

170170

OLED OLED 특성특성

11OLED 기초공정 이해와 실습

Display ComparisonDisplay Comparison

CRT PDP LCD OLEDLarge Size ⊙

High Resolution ⊙ ⊙

ThicknessWeight times ⊙ ⊙

Response Time times ⊙

Viewing Angle ⊙ ⊙ times ⊙

Cost ⊙ times

Color ⊙ ⊙

Power Consumption times times ⊙

Image Sticking ⊙ ⊙

Best ⊙ Good Middle Bad x

OLED

LCD Thickness amp Weight Power Consumption

CRT Cost Color Viewing angle Response time=

+

12OLED 기초공정 이해와 실습

Organic Light Emitting Display

OLED

OLEDOLED의의 분류분류

PLEDPhOLED PMOLED AMOLED

FOLED 구동방식재료(저고분자)

형광성

저분자

발광재료

인광성

저분자

발광재료

형광성

고분자

발광재료

Flexible

기판

OLED

수동구동

OLED

능동구동

OLED

Emission Direction에 따라 Bottom Top amp Transparent OLED가 있음

13OLED 기초공정 이해와 실습

저분자 고분자

박막 성막 방식 진공 열증착 Ink-jet

순도 고순도 재료 용이 고순도 재료 어려움

열 안정성 낮다 높다

작동전압 7-15v 3-7v

NO

NON

OAl

2 Types

Small Molecule

Polymer

OLEDOLED의의 재료재료

n

14OLED 기초공정 이해와 실습

Early OLED (Small Molecule)Early OLED (Small Molecule)

EL emission spectrum is sensitive to thickness of organic layerDiamine layer transports holes and blocks electrons injected from MgAg electrode

bull MgAg ndash 101bull Luminescent film - 600Aringbull Diamine ndash 750Aring

CW Tang amp SA VanSlyke Kodak Research LaboratoriesCW Tang and S A VanSlyke in Kodak Appl Phys Letter 51 913 (1987)

15OLED 기초공정 이해와 실습

Light Emitting PolymersLight Emitting Polymers

First Polymer LED (PVK-polymer)- Partridge polymer 24 733 (1983)----

With conductive polymer anode tooWeak blue light

PPV-LED- The first observation of EL was in

1989 (Burroughs et al)- Friend et al U S Patent 5247190

(1990) Cambridge University andCDT work on polymers

- poly(14-phenylene vinylene) (PPV) poly[2-(2rsquo-ethylhexyloxy)-5-methoxy-

14-phenylene vinylene] (MEH-PPV)

n

PPV

Full colour spectrum

glass substrateITO

polymer layerAl Ca Mg

16OLED 기초공정 이해와 실습

Organic Molecular CrystalsOrganic Molecular Crystals

Inorganic semiconductors Organic semiconductors

2Bohr radius Rydberg

Band transport

Exciton Binding Energy ~25meV Exciton size ~ 50A

Strong Covalent Bond

Strong e-e screening( ~11)

Strong spin-orbit cou

ε ε

εminusprop prop

bull

bull

bull

gt

gt

gt

gt

J is a good quantum numberpling

gt

Hopping transport

Exciton Binding Energy ~ 05 - 1eV E

Exciton localized on singxciton size ~ 5 - 10A

le pol y

Weak Van der Waals interactions

Weak e-e screening( ~3)ε

bull

bull

gt

gt

gt

gt mer chain

Large exchange energy between the lowest singlet and triple

S is a good quantum number

t excitons

Weak spin-orbit couplingbullgt

gt

17OLED 기초공정 이해와 실습

Conjugated PolymerConjugated Polymer

bull sp2 bonding

poly-acetylene (1958)

bull π- electrons delocalized along the chain

bull Dimerization opens an energy gap 2-3 eV (Peierls instability)

18OLED 기초공정 이해와 실습

에너지에너지 밴드밴드 갭갭

Ionization energies of the HOMO levels and binding energies of the LUMO levels for different polyacenes in the gas phase (left solid lines) and in the crystalline state (right double lines) respectively

C C

H

H

nrarrinfin

Eg=14eV

19OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Hopping model

Small polaron model

Poole-Frenkel model

Multiple trapping amp release model

Etc (Exciton model Soliton model Ishiguro modelhellip)

20OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Hopping model

1

00

In most cases T-dep of mobility

exp where = 1 2 3 4TT

αμ μ α

⎡ ⎤⎛ ⎞⎢ ⎥= minus⎜ ⎟⎢ ⎥⎝ ⎠⎣ ⎦

Conventional semiconductor Organic semiconductorconduction band

valence band

LUMO level

HOMO level

delocalized states propagating

Phonon scattering (negative)rarr mobility increases as T darr

localized states hopping

Phonon scattering (positive)rarr mobility decreases as T darr

01 ~ 1 cm2V-1s-1

21OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Small polaron model

In a conjugated molecules a charge is self-trapped by the lattice deformationrarr creation of the localized mid gap states

Ex) A polaron in Polythiophene

32 22( ) exp

2 2

where polaron binding energy electron transfer energy lattice constant

T-dep of the mobility

bB

Bb

b

Eea J k Tk TE

EJa

πμminus ⎛ ⎞

= minus⎜ ⎟⎝ ⎠h

22OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Poole-Frenkel model

Field dependent mobility at high field (E gt 105 Vcm)

- Coulomb potential near localized states is modified by the applied field

( )120

( ) (0)exp

where (0) zero field mobility

Poole-Frenkel factor mag of electric field

T-dep amp field dep of the mobility

B

qF Fk T

eF

μ μ β

μ

β πεε

⎛ ⎞= ⎜ ⎟

⎝ ⎠

=

23OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Multiple trapping amp release model

Narrow delocalized band+ localized trap level (highly concenturated)

Process1) Carriers arrive at a trap and are trapped2) Thermally activated and released

0

0

exp

where mobility in the delocalized bandDensity of delocalized band edge

Concenturation of traps

T-dep of the mobility

tD

B

Ek T

μ μ α

μ

α

⎛ ⎞= minus⎜ ⎟

⎝ ⎠

=

24OLED 기초공정 이해와 실습

무기EL (p-n junction LED)

Light Emission

anode

cathodeETLEMLHTLHIL+

유기EL (polymers or small molecules)

전자수송층(ETL)

발광층(EML)정공

수송층(HTL)

양극(투명전극

ITO 유리 등)

음극(낮은 일함수 금속

Ca AlLi MgAg등)

-전자

정공

+

-+

두께 100 ~ 200 nm

Exciton

OLED OLED 작동원리작동원리

25OLED 기초공정 이해와 실습

Single-layer devices

Unbalanced carrier injection and lower efficiency

dArr

Heterostructures

ITOHILHTLEMLETLCathode(1) Lower the barrier at electrodes

Balanced carrier injection andimproved efficiency

(2) Band offsets between the layers andspace charges build up at hetero-junctionHigh carrier densitieseffective e-h capture

Multilayer StructureMultilayer Structure

Cathode

HILITO

GLASS

HTLEMLETL

-

+

26OLED 기초공정 이해와 실습

Cathode

HILITO

GLASS

HTLEMLETL

-

+

OLED Structure

N N

CH3

H3C

TPD m-MTDATA

N

N N

N

CH3

CH3

H3C

NO

NON

OAl

Alq3

Small Molecules (Fluorescence)

27OLED 기초공정 이해와 실습

OLED StructureSmall Molecules

(Phosphorescence)

NN

N

N

NN

N

N

CuN

N

NN

CuPc MTDATA

Cathode

HILITO

GLASS

HTLEML

ETL-

+

HBL

NNCH3H3C

BCP

28OLED 기초공정 이해와 실습

OLED Structure

Polymers

Cathode

ITO

GLASS

HTLEML

-

+

PEDOT

n

S O3- S O3

-S O3H S O3H S O3H S O3H

SS

SS

SS

O O

OO

O O

OO OO

n

n n

RR

PPV PF

29OLED 기초공정 이해와 실습

Cur

rent

den

sity Lum

inous Intensity

Voltage

ln V

ln J

J = qn0μVd

J = 98 εsμV2d3

Ligh

t

Current

slope = ηexte

Ex)

OLED OLED 특성특성

3 7

Diode Characteristics Rectification ratio 10 - 10 Power efficiency amp drive voltage

Light vs current

optconv ext

elec

opt opt elecext opt ext

elec elec

P hP eV

N s I IIN s I e e

νη η

η η

= =

= = rArr = times

30OLED 기초공정 이해와 실습

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

Vacuum Level

Anode

Cathode

HOMO

LUMO

Φa

Φc

EA

IP

CB

VB

Eg

에너지에너지 준위준위

31OLED 기초공정 이해와 실습

Current - Voltage Characteristics

2

16 17 3

0

0

1

diffusion voltage ~ 13 V

acceptor concentration ~ 10 - 10 cm

(~ 50 - 150 nm

2( )

Width of space charge layer 2 ( )

D

D

A

r DA

r D A

V VCV

N

C A q N V V

w V V qN

ε ε

ε ε

prop minus

= minus

= minus V = 0 )

OLED OLED 전기적전기적 특성특성

( ) Schottky equation

exp 1

ideality factor 1 1 ideal Schottky diodes B ext BJ J eV nk T V V IR

n n

⎡ ⎤= minus = minus⎣ ⎦ge =

Capacitance - Voltage Dependence

32OLED 기초공정 이해와 실습

I - V Characteristics C - V Characteristics

ITOPPVMetal Polymeric Schottky Diode

OLED OLED 전기적전기적 특성특성

33OLED 기초공정 이해와 실습

Injection Dominated Mechanisms

bull Thermionic emission

bull Tunneling

Bulk Dominated Mechanisms

bull Ohmic Conduction

bull Space Charge Limited Current Conduction

bull Space Charge Limited Current Conduction with Traps

Magnitude of Injection Barrier

전하전하 주입주입

34OLED 기초공정 이해와 실습

Thermionic Emission

Fowler-Nordheim Tunneling

2

2 2

3

exp 1 wehere exp

4 120( )

Richardson constant

bns s

B B

n B

eeVJ J J A Tk T k T

em kA m m A cm Kh

φ

π

⎡ ⎤⎛ ⎞ ⎛ ⎞minus= minus =⎢ ⎥⎜ ⎟ ⎜ ⎟

⎝ ⎠ ⎝ ⎠⎣ ⎦

= =

At low field thermionic emission at high field tunneling dominate

전하전하 주입주입

EF

Evac

-eFz(triangular shape)φ

Z=0 Z

Charge accumulationhigher the energy state `

Electron emission (F-N Tunneling)

Electron emission (Thermionic Emission)

2

3212

~ exp

( ) where 8 (2 )3

bJ EE

qb mqh

π

⎛ ⎞minus⎜ ⎟⎝ ⎠

Φ=

35OLED 기초공정 이해와 실습

Applied voltage

Lattice vibration

Localizedelectron

Hopping conductionBand-like conductionDelocalized electron

Lattice vibration(phonon)

Scattered electron

Low Mobility

bull holes μ ~10-4-10-8 Vs due to poor wave function overlap (large hopping distance)

bull electrons μ ~10-6-10-10Vs due to increased disorder and trapping at defect sites caused by impurities such as O2

rArr Build-up of space-charge density (bulk limited current)

전하전하 이동도이동도

36OLED 기초공정 이해와 실습

NoteMobility depends onElectric Field andTemperature

Mobilities of OrganicsMobilities of Organics

Alq3

37OLED 기초공정 이해와 실습

Ohmic conduction

OLEDOLED의의 전류전류

Current Dendity

current depends linearly on the bias voltageo nn qm VJd

=

2

3

0

1

2 1

(no traps)

(exponential trap distributions ( ) exp( )

one of electrodes(Ohmic contact) can supply more carriers per un

98

Current Density

SCLC condition

o

tt

r

m

m tN

VJd

T E N E kTV md T

ε ε μ

+

+ =

=

prop =

it time than can be transported through the dielectric (caused by low mobility)

Space charge limited (SCL) conduction

38OLED 기초공정 이해와 실습

2

2

3

Charge per unit area Q induced by a voltage V

Transit time across the semiconductor

9

Approximate SCLC densi

Child law (Mott- Gu

ty

Elec8

rney law)

o r

r

o rSCLC

r

VQ CVd

d dtE V

VQJt d

ε ε

μ μ

ε ε μ

= =

= =

asymp =

3 2

tric field distribution across the semiconductor

Majority space charges enhance the E field at the

3 3 ( ) at ( )2 2

enhance the injection of the cath

minority carrieode

rs (elect

V x VE x x d E dd d

= = =

rArr rons)

d

(+) (-)

x=0 x=d

Vd

15 Vd232

3)(d

xVxE =

++++

Virtual anode

-

Space Charge Limited CurrentSpace Charge Limited Current

39OLED 기초공정 이해와 실습

2

3

1

2 01

(no traps or discrete traps Mott-Gurney formula)

(exponential trap distributions ( ) exp( )

98

o rSCLC

mt

SCLC m t t

VJd

TVJ N E NmT

E kTd

ε ε μ

+

+

=

prop = =

ECB

EVB

Etrap

Discrete trapping center Exponential distributionof trapping centers

TrapTrap--Limited CurrentLimited Current

40OLED 기초공정 이해와 실습

Shen Burrows Bulovic McCarty Thompson Forrest Jpn J Appl Phys 35 L401 (1996)

ITOTPDAlq3MgAg

12

1

+

+

prop m

m

SCLC dVJ

TrapTrap--Limited CurrentLimited Current

41OLED 기초공정 이해와 실습

0

0

Activation energy at 0 Empirical parameter

Mobility at PF constant

PF

PF

E FT

T Tμβ

Δ =

=

PFPF

B eff

0

3

PFeff 0 0

( ) exp

exp( )

1 1 1with

E FFT μk T

F

qT T T

βμ

μ β

βπεε

⎛ ⎞Δ minus= minus⎜ ⎟⎜ ⎟

⎝ ⎠

equiv

= minus =

Poole Frenkel ModelPoole Frenkel Model

42OLED 기초공정 이해와 실습

1

22 2

0

0

(1)

(2)

EL F S e h

e ee he

T

h he hh

T

T rec rec e h

h eh e

h e

e hEL F S

h e

T rec

h e h e nh e EL F S EL

e h

n nJ n n nedJ n n ned

nJ

ne F

J J Je F

J Jn J J

ed n ed

η η γ

γτ

γτ

τ τ τ γ

μ

η η γμ μ

τ τ

η ηγ

minus

Φ =

minus minus =

minus minus =

lt =

=

Φ = prop

gt

= Φ = prop rArr Φ prop

EL Current RelationEL Current Relation

43OLED 기초공정 이해와 실습

Device Structure ITONPBAlq3Ca

22

21

ZZZ

fdVdQC

+minus

==πφieZiZZZ ||

))=+=

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

V0 independent of the NPB layer thickness

44OLED 기초공정 이해와 실습

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

Dashed line without interfacial charge

Wolfgang Brutting Stefan Berleb Anton G Muckl Organic Electronics 2 (2001)

Device Structure ITONPBAlq3Ca

45OLED 기초공정 이해와 실습

Langevin Recombination of carriers

bull Carriers are statistically independent therefore the e-h recombination is a random process and kinetically bimolecular

bull Total current attracted by a charge into the sphere of Coulombic capture radius rc

2

22

( ) ( )4

(4 ) 14 184

( ) (mean free path A)

n p c n pc

c cB

n p

qJ qp E qpr

qi r J Bqp r nmk T

qB a

μ μ μ μπε

ππε

μ μ λε

= + = +

= = cong asymp minus

there4 = + asympo

TkUd

BeP ~ minusProbability of dissociation

reUπε4

~2

e-

rc

Carrier RecombinationCarrier Recombination

P Langevin Ann Chem Phys 28 289 (1903)

46OLED 기초공정 이해와 실습

Electronic Processes in Organic Crystals and Polymers by MPope and C E Swenberg

ExcitonsExcitons

47OLED 기초공정 이해와 실습

C Adachi et al

Electrons and holesForm excitons

(bound e--h+ pairs)

Exciton Recombination ZoneExciton Recombination Zone

48OLED 기초공정 이해와 실습

MOLECULAR EXCITED STATESAFTER ELECTRICAL EXCITATION

Singletspin anti-symmetric

Tripletspin symmetric

25 75

MOLECULAR GROUND STATEspin anti-symmetric

Relaxation allowedfast efficientFluorescence

Relaxation disallowedslow inefficientPhosphorescence

|χ1χ2 gt = | gt

|χ1χ2 gt = | gt

|χ1χ2 gt

= | gt - | gt2

1

|χ1χ2 gt = | gt + | gt2

1ISC

Spin

OLEDOLED의의 형광형광인광인광

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 5: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

4OLED 기초공정 이해와 실습

삼성 SDI (2005 3) 102rdquo Full HD (1920X1080) PDP TV

평판평판 디스플레이디스플레이

LG Philips LCD (2006 8 IMID) 100rdquo Full HD (1920X1080) LCD TV

삼성전자 LCD (2007 7 ) 70rdquo Full HD (1920X1080) LCD TV(LED BLU 채용)

5OLED 기초공정 이해와 실습

삼성전자 (2005 5) 40rdquo WXGA (1280X800) AMOLED based on a-Si TFT

삼성SDI (2005 2) 17rdquo UXGA (1600X1200) AMOLED based on LTPS

LPL (2004 10) 201rdquo WXGA (1280X800) AMOLED based on LTPS

OLED OLED 디스플레이디스플레이

22rdquo QVGA (320X240) AMOLED based on a-Si TFT(20073)

6OLED 기초공정 이해와 실습

PMOLEDMobile Phone

Motorola(Pioneer)

Samsung(SNMD)

LG(Pioneer) Sanyo-Kodak

22rdquo AMOLED

AMOLED

OLED OLED 디스플레이디스플레이 상품상품

Sony PDA(65535Color 480ⅹ320 pixels) (2004)

7OLED 기초공정 이해와 실습

Sony Flexible Full Color Display 25rdquo(120X169 03mm 15g) (20075)

Delta Optoelectronics

(231X205) PLED

PLED PLED 디스플레이디스플레이 상품상품

CDT (1280X768 200511) PLED

8OLED 기초공정 이해와 실습

OLED AppplicationsOLED Appplications

9OLED 기초공정 이해와 실습

[J R Sheats et al Science 273 884 (1996)의 자료에 최근 발전을 추가함]

LEDLED의의 발전상황발전상황

10OLED 기초공정 이해와 실습

LCD와비교

자료 한국화학연구원 정보디스플레이 기술개발 사업단

OLED

LTPS TFT

AMOLED

LC

AMLCD

CF

BL a-Si TFT LTPS TFT

SelfSelf--emittingemittingFull color DisplayFull color Display

No Backlight Thin amp Light

Less Cell Process Simple Process

No Liquid Crystal Fast Response TimeWide Viewing Angle

mm 30g 50

(~1μs)

70~80

of LCD

170170

OLED OLED 특성특성

11OLED 기초공정 이해와 실습

Display ComparisonDisplay Comparison

CRT PDP LCD OLEDLarge Size ⊙

High Resolution ⊙ ⊙

ThicknessWeight times ⊙ ⊙

Response Time times ⊙

Viewing Angle ⊙ ⊙ times ⊙

Cost ⊙ times

Color ⊙ ⊙

Power Consumption times times ⊙

Image Sticking ⊙ ⊙

Best ⊙ Good Middle Bad x

OLED

LCD Thickness amp Weight Power Consumption

CRT Cost Color Viewing angle Response time=

+

12OLED 기초공정 이해와 실습

Organic Light Emitting Display

OLED

OLEDOLED의의 분류분류

PLEDPhOLED PMOLED AMOLED

FOLED 구동방식재료(저고분자)

형광성

저분자

발광재료

인광성

저분자

발광재료

형광성

고분자

발광재료

Flexible

기판

OLED

수동구동

OLED

능동구동

OLED

Emission Direction에 따라 Bottom Top amp Transparent OLED가 있음

13OLED 기초공정 이해와 실습

저분자 고분자

박막 성막 방식 진공 열증착 Ink-jet

순도 고순도 재료 용이 고순도 재료 어려움

열 안정성 낮다 높다

작동전압 7-15v 3-7v

NO

NON

OAl

2 Types

Small Molecule

Polymer

OLEDOLED의의 재료재료

n

14OLED 기초공정 이해와 실습

Early OLED (Small Molecule)Early OLED (Small Molecule)

EL emission spectrum is sensitive to thickness of organic layerDiamine layer transports holes and blocks electrons injected from MgAg electrode

bull MgAg ndash 101bull Luminescent film - 600Aringbull Diamine ndash 750Aring

CW Tang amp SA VanSlyke Kodak Research LaboratoriesCW Tang and S A VanSlyke in Kodak Appl Phys Letter 51 913 (1987)

15OLED 기초공정 이해와 실습

Light Emitting PolymersLight Emitting Polymers

First Polymer LED (PVK-polymer)- Partridge polymer 24 733 (1983)----

With conductive polymer anode tooWeak blue light

PPV-LED- The first observation of EL was in

1989 (Burroughs et al)- Friend et al U S Patent 5247190

(1990) Cambridge University andCDT work on polymers

- poly(14-phenylene vinylene) (PPV) poly[2-(2rsquo-ethylhexyloxy)-5-methoxy-

14-phenylene vinylene] (MEH-PPV)

n

PPV

Full colour spectrum

glass substrateITO

polymer layerAl Ca Mg

16OLED 기초공정 이해와 실습

Organic Molecular CrystalsOrganic Molecular Crystals

Inorganic semiconductors Organic semiconductors

2Bohr radius Rydberg

Band transport

Exciton Binding Energy ~25meV Exciton size ~ 50A

Strong Covalent Bond

Strong e-e screening( ~11)

Strong spin-orbit cou

ε ε

εminusprop prop

bull

bull

bull

gt

gt

gt

gt

J is a good quantum numberpling

gt

Hopping transport

Exciton Binding Energy ~ 05 - 1eV E

Exciton localized on singxciton size ~ 5 - 10A

le pol y

Weak Van der Waals interactions

Weak e-e screening( ~3)ε

bull

bull

gt

gt

gt

gt mer chain

Large exchange energy between the lowest singlet and triple

S is a good quantum number

t excitons

Weak spin-orbit couplingbullgt

gt

17OLED 기초공정 이해와 실습

Conjugated PolymerConjugated Polymer

bull sp2 bonding

poly-acetylene (1958)

bull π- electrons delocalized along the chain

bull Dimerization opens an energy gap 2-3 eV (Peierls instability)

18OLED 기초공정 이해와 실습

에너지에너지 밴드밴드 갭갭

Ionization energies of the HOMO levels and binding energies of the LUMO levels for different polyacenes in the gas phase (left solid lines) and in the crystalline state (right double lines) respectively

C C

H

H

nrarrinfin

Eg=14eV

19OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Hopping model

Small polaron model

Poole-Frenkel model

Multiple trapping amp release model

Etc (Exciton model Soliton model Ishiguro modelhellip)

20OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Hopping model

1

00

In most cases T-dep of mobility

exp where = 1 2 3 4TT

αμ μ α

⎡ ⎤⎛ ⎞⎢ ⎥= minus⎜ ⎟⎢ ⎥⎝ ⎠⎣ ⎦

Conventional semiconductor Organic semiconductorconduction band

valence band

LUMO level

HOMO level

delocalized states propagating

Phonon scattering (negative)rarr mobility increases as T darr

localized states hopping

Phonon scattering (positive)rarr mobility decreases as T darr

01 ~ 1 cm2V-1s-1

21OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Small polaron model

In a conjugated molecules a charge is self-trapped by the lattice deformationrarr creation of the localized mid gap states

Ex) A polaron in Polythiophene

32 22( ) exp

2 2

where polaron binding energy electron transfer energy lattice constant

T-dep of the mobility

bB

Bb

b

Eea J k Tk TE

EJa

πμminus ⎛ ⎞

= minus⎜ ⎟⎝ ⎠h

22OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Poole-Frenkel model

Field dependent mobility at high field (E gt 105 Vcm)

- Coulomb potential near localized states is modified by the applied field

( )120

( ) (0)exp

where (0) zero field mobility

Poole-Frenkel factor mag of electric field

T-dep amp field dep of the mobility

B

qF Fk T

eF

μ μ β

μ

β πεε

⎛ ⎞= ⎜ ⎟

⎝ ⎠

=

23OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Multiple trapping amp release model

Narrow delocalized band+ localized trap level (highly concenturated)

Process1) Carriers arrive at a trap and are trapped2) Thermally activated and released

0

0

exp

where mobility in the delocalized bandDensity of delocalized band edge

Concenturation of traps

T-dep of the mobility

tD

B

Ek T

μ μ α

μ

α

⎛ ⎞= minus⎜ ⎟

⎝ ⎠

=

24OLED 기초공정 이해와 실습

무기EL (p-n junction LED)

Light Emission

anode

cathodeETLEMLHTLHIL+

유기EL (polymers or small molecules)

전자수송층(ETL)

발광층(EML)정공

수송층(HTL)

양극(투명전극

ITO 유리 등)

음극(낮은 일함수 금속

Ca AlLi MgAg등)

-전자

정공

+

-+

두께 100 ~ 200 nm

Exciton

OLED OLED 작동원리작동원리

25OLED 기초공정 이해와 실습

Single-layer devices

Unbalanced carrier injection and lower efficiency

dArr

Heterostructures

ITOHILHTLEMLETLCathode(1) Lower the barrier at electrodes

Balanced carrier injection andimproved efficiency

(2) Band offsets between the layers andspace charges build up at hetero-junctionHigh carrier densitieseffective e-h capture

Multilayer StructureMultilayer Structure

Cathode

HILITO

GLASS

HTLEMLETL

-

+

26OLED 기초공정 이해와 실습

Cathode

HILITO

GLASS

HTLEMLETL

-

+

OLED Structure

N N

CH3

H3C

TPD m-MTDATA

N

N N

N

CH3

CH3

H3C

NO

NON

OAl

Alq3

Small Molecules (Fluorescence)

27OLED 기초공정 이해와 실습

OLED StructureSmall Molecules

(Phosphorescence)

NN

N

N

NN

N

N

CuN

N

NN

CuPc MTDATA

Cathode

HILITO

GLASS

HTLEML

ETL-

+

HBL

NNCH3H3C

BCP

28OLED 기초공정 이해와 실습

OLED Structure

Polymers

Cathode

ITO

GLASS

HTLEML

-

+

PEDOT

n

S O3- S O3

-S O3H S O3H S O3H S O3H

SS

SS

SS

O O

OO

O O

OO OO

n

n n

RR

PPV PF

29OLED 기초공정 이해와 실습

Cur

rent

den

sity Lum

inous Intensity

Voltage

ln V

ln J

J = qn0μVd

J = 98 εsμV2d3

Ligh

t

Current

slope = ηexte

Ex)

OLED OLED 특성특성

3 7

Diode Characteristics Rectification ratio 10 - 10 Power efficiency amp drive voltage

Light vs current

optconv ext

elec

opt opt elecext opt ext

elec elec

P hP eV

N s I IIN s I e e

νη η

η η

= =

= = rArr = times

30OLED 기초공정 이해와 실습

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

Vacuum Level

Anode

Cathode

HOMO

LUMO

Φa

Φc

EA

IP

CB

VB

Eg

에너지에너지 준위준위

31OLED 기초공정 이해와 실습

Current - Voltage Characteristics

2

16 17 3

0

0

1

diffusion voltage ~ 13 V

acceptor concentration ~ 10 - 10 cm

(~ 50 - 150 nm

2( )

Width of space charge layer 2 ( )

D

D

A

r DA

r D A

V VCV

N

C A q N V V

w V V qN

ε ε

ε ε

prop minus

= minus

= minus V = 0 )

OLED OLED 전기적전기적 특성특성

( ) Schottky equation

exp 1

ideality factor 1 1 ideal Schottky diodes B ext BJ J eV nk T V V IR

n n

⎡ ⎤= minus = minus⎣ ⎦ge =

Capacitance - Voltage Dependence

32OLED 기초공정 이해와 실습

I - V Characteristics C - V Characteristics

ITOPPVMetal Polymeric Schottky Diode

OLED OLED 전기적전기적 특성특성

33OLED 기초공정 이해와 실습

Injection Dominated Mechanisms

bull Thermionic emission

bull Tunneling

Bulk Dominated Mechanisms

bull Ohmic Conduction

bull Space Charge Limited Current Conduction

bull Space Charge Limited Current Conduction with Traps

Magnitude of Injection Barrier

전하전하 주입주입

34OLED 기초공정 이해와 실습

Thermionic Emission

Fowler-Nordheim Tunneling

2

2 2

3

exp 1 wehere exp

4 120( )

Richardson constant

bns s

B B

n B

eeVJ J J A Tk T k T

em kA m m A cm Kh

φ

π

⎡ ⎤⎛ ⎞ ⎛ ⎞minus= minus =⎢ ⎥⎜ ⎟ ⎜ ⎟

⎝ ⎠ ⎝ ⎠⎣ ⎦

= =

At low field thermionic emission at high field tunneling dominate

전하전하 주입주입

EF

Evac

-eFz(triangular shape)φ

Z=0 Z

Charge accumulationhigher the energy state `

Electron emission (F-N Tunneling)

Electron emission (Thermionic Emission)

2

3212

~ exp

( ) where 8 (2 )3

bJ EE

qb mqh

π

⎛ ⎞minus⎜ ⎟⎝ ⎠

Φ=

35OLED 기초공정 이해와 실습

Applied voltage

Lattice vibration

Localizedelectron

Hopping conductionBand-like conductionDelocalized electron

Lattice vibration(phonon)

Scattered electron

Low Mobility

bull holes μ ~10-4-10-8 Vs due to poor wave function overlap (large hopping distance)

bull electrons μ ~10-6-10-10Vs due to increased disorder and trapping at defect sites caused by impurities such as O2

rArr Build-up of space-charge density (bulk limited current)

전하전하 이동도이동도

36OLED 기초공정 이해와 실습

NoteMobility depends onElectric Field andTemperature

Mobilities of OrganicsMobilities of Organics

Alq3

37OLED 기초공정 이해와 실습

Ohmic conduction

OLEDOLED의의 전류전류

Current Dendity

current depends linearly on the bias voltageo nn qm VJd

=

2

3

0

1

2 1

(no traps)

(exponential trap distributions ( ) exp( )

one of electrodes(Ohmic contact) can supply more carriers per un

98

Current Density

SCLC condition

o

tt

r

m

m tN

VJd

T E N E kTV md T

ε ε μ

+

+ =

=

prop =

it time than can be transported through the dielectric (caused by low mobility)

Space charge limited (SCL) conduction

38OLED 기초공정 이해와 실습

2

2

3

Charge per unit area Q induced by a voltage V

Transit time across the semiconductor

9

Approximate SCLC densi

Child law (Mott- Gu

ty

Elec8

rney law)

o r

r

o rSCLC

r

VQ CVd

d dtE V

VQJt d

ε ε

μ μ

ε ε μ

= =

= =

asymp =

3 2

tric field distribution across the semiconductor

Majority space charges enhance the E field at the

3 3 ( ) at ( )2 2

enhance the injection of the cath

minority carrieode

rs (elect

V x VE x x d E dd d

= = =

rArr rons)

d

(+) (-)

x=0 x=d

Vd

15 Vd232

3)(d

xVxE =

++++

Virtual anode

-

Space Charge Limited CurrentSpace Charge Limited Current

39OLED 기초공정 이해와 실습

2

3

1

2 01

(no traps or discrete traps Mott-Gurney formula)

(exponential trap distributions ( ) exp( )

98

o rSCLC

mt

SCLC m t t

VJd

TVJ N E NmT

E kTd

ε ε μ

+

+

=

prop = =

ECB

EVB

Etrap

Discrete trapping center Exponential distributionof trapping centers

TrapTrap--Limited CurrentLimited Current

40OLED 기초공정 이해와 실습

Shen Burrows Bulovic McCarty Thompson Forrest Jpn J Appl Phys 35 L401 (1996)

ITOTPDAlq3MgAg

12

1

+

+

prop m

m

SCLC dVJ

TrapTrap--Limited CurrentLimited Current

41OLED 기초공정 이해와 실습

0

0

Activation energy at 0 Empirical parameter

Mobility at PF constant

PF

PF

E FT

T Tμβ

Δ =

=

PFPF

B eff

0

3

PFeff 0 0

( ) exp

exp( )

1 1 1with

E FFT μk T

F

qT T T

βμ

μ β

βπεε

⎛ ⎞Δ minus= minus⎜ ⎟⎜ ⎟

⎝ ⎠

equiv

= minus =

Poole Frenkel ModelPoole Frenkel Model

42OLED 기초공정 이해와 실습

1

22 2

0

0

(1)

(2)

EL F S e h

e ee he

T

h he hh

T

T rec rec e h

h eh e

h e

e hEL F S

h e

T rec

h e h e nh e EL F S EL

e h

n nJ n n nedJ n n ned

nJ

ne F

J J Je F

J Jn J J

ed n ed

η η γ

γτ

γτ

τ τ τ γ

μ

η η γμ μ

τ τ

η ηγ

minus

Φ =

minus minus =

minus minus =

lt =

=

Φ = prop

gt

= Φ = prop rArr Φ prop

EL Current RelationEL Current Relation

43OLED 기초공정 이해와 실습

Device Structure ITONPBAlq3Ca

22

21

ZZZ

fdVdQC

+minus

==πφieZiZZZ ||

))=+=

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

V0 independent of the NPB layer thickness

44OLED 기초공정 이해와 실습

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

Dashed line without interfacial charge

Wolfgang Brutting Stefan Berleb Anton G Muckl Organic Electronics 2 (2001)

Device Structure ITONPBAlq3Ca

45OLED 기초공정 이해와 실습

Langevin Recombination of carriers

bull Carriers are statistically independent therefore the e-h recombination is a random process and kinetically bimolecular

bull Total current attracted by a charge into the sphere of Coulombic capture radius rc

2

22

( ) ( )4

(4 ) 14 184

( ) (mean free path A)

n p c n pc

c cB

n p

qJ qp E qpr

qi r J Bqp r nmk T

qB a

μ μ μ μπε

ππε

μ μ λε

= + = +

= = cong asymp minus

there4 = + asympo

TkUd

BeP ~ minusProbability of dissociation

reUπε4

~2

e-

rc

Carrier RecombinationCarrier Recombination

P Langevin Ann Chem Phys 28 289 (1903)

46OLED 기초공정 이해와 실습

Electronic Processes in Organic Crystals and Polymers by MPope and C E Swenberg

ExcitonsExcitons

47OLED 기초공정 이해와 실습

C Adachi et al

Electrons and holesForm excitons

(bound e--h+ pairs)

Exciton Recombination ZoneExciton Recombination Zone

48OLED 기초공정 이해와 실습

MOLECULAR EXCITED STATESAFTER ELECTRICAL EXCITATION

Singletspin anti-symmetric

Tripletspin symmetric

25 75

MOLECULAR GROUND STATEspin anti-symmetric

Relaxation allowedfast efficientFluorescence

Relaxation disallowedslow inefficientPhosphorescence

|χ1χ2 gt = | gt

|χ1χ2 gt = | gt

|χ1χ2 gt

= | gt - | gt2

1

|χ1χ2 gt = | gt + | gt2

1ISC

Spin

OLEDOLED의의 형광형광인광인광

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 6: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

5OLED 기초공정 이해와 실습

삼성전자 (2005 5) 40rdquo WXGA (1280X800) AMOLED based on a-Si TFT

삼성SDI (2005 2) 17rdquo UXGA (1600X1200) AMOLED based on LTPS

LPL (2004 10) 201rdquo WXGA (1280X800) AMOLED based on LTPS

OLED OLED 디스플레이디스플레이

22rdquo QVGA (320X240) AMOLED based on a-Si TFT(20073)

6OLED 기초공정 이해와 실습

PMOLEDMobile Phone

Motorola(Pioneer)

Samsung(SNMD)

LG(Pioneer) Sanyo-Kodak

22rdquo AMOLED

AMOLED

OLED OLED 디스플레이디스플레이 상품상품

Sony PDA(65535Color 480ⅹ320 pixels) (2004)

7OLED 기초공정 이해와 실습

Sony Flexible Full Color Display 25rdquo(120X169 03mm 15g) (20075)

Delta Optoelectronics

(231X205) PLED

PLED PLED 디스플레이디스플레이 상품상품

CDT (1280X768 200511) PLED

8OLED 기초공정 이해와 실습

OLED AppplicationsOLED Appplications

9OLED 기초공정 이해와 실습

[J R Sheats et al Science 273 884 (1996)의 자료에 최근 발전을 추가함]

LEDLED의의 발전상황발전상황

10OLED 기초공정 이해와 실습

LCD와비교

자료 한국화학연구원 정보디스플레이 기술개발 사업단

OLED

LTPS TFT

AMOLED

LC

AMLCD

CF

BL a-Si TFT LTPS TFT

SelfSelf--emittingemittingFull color DisplayFull color Display

No Backlight Thin amp Light

Less Cell Process Simple Process

No Liquid Crystal Fast Response TimeWide Viewing Angle

mm 30g 50

(~1μs)

70~80

of LCD

170170

OLED OLED 특성특성

11OLED 기초공정 이해와 실습

Display ComparisonDisplay Comparison

CRT PDP LCD OLEDLarge Size ⊙

High Resolution ⊙ ⊙

ThicknessWeight times ⊙ ⊙

Response Time times ⊙

Viewing Angle ⊙ ⊙ times ⊙

Cost ⊙ times

Color ⊙ ⊙

Power Consumption times times ⊙

Image Sticking ⊙ ⊙

Best ⊙ Good Middle Bad x

OLED

LCD Thickness amp Weight Power Consumption

CRT Cost Color Viewing angle Response time=

+

12OLED 기초공정 이해와 실습

Organic Light Emitting Display

OLED

OLEDOLED의의 분류분류

PLEDPhOLED PMOLED AMOLED

FOLED 구동방식재료(저고분자)

형광성

저분자

발광재료

인광성

저분자

발광재료

형광성

고분자

발광재료

Flexible

기판

OLED

수동구동

OLED

능동구동

OLED

Emission Direction에 따라 Bottom Top amp Transparent OLED가 있음

13OLED 기초공정 이해와 실습

저분자 고분자

박막 성막 방식 진공 열증착 Ink-jet

순도 고순도 재료 용이 고순도 재료 어려움

열 안정성 낮다 높다

작동전압 7-15v 3-7v

NO

NON

OAl

2 Types

Small Molecule

Polymer

OLEDOLED의의 재료재료

n

14OLED 기초공정 이해와 실습

Early OLED (Small Molecule)Early OLED (Small Molecule)

EL emission spectrum is sensitive to thickness of organic layerDiamine layer transports holes and blocks electrons injected from MgAg electrode

bull MgAg ndash 101bull Luminescent film - 600Aringbull Diamine ndash 750Aring

CW Tang amp SA VanSlyke Kodak Research LaboratoriesCW Tang and S A VanSlyke in Kodak Appl Phys Letter 51 913 (1987)

15OLED 기초공정 이해와 실습

Light Emitting PolymersLight Emitting Polymers

First Polymer LED (PVK-polymer)- Partridge polymer 24 733 (1983)----

With conductive polymer anode tooWeak blue light

PPV-LED- The first observation of EL was in

1989 (Burroughs et al)- Friend et al U S Patent 5247190

(1990) Cambridge University andCDT work on polymers

- poly(14-phenylene vinylene) (PPV) poly[2-(2rsquo-ethylhexyloxy)-5-methoxy-

14-phenylene vinylene] (MEH-PPV)

n

PPV

Full colour spectrum

glass substrateITO

polymer layerAl Ca Mg

16OLED 기초공정 이해와 실습

Organic Molecular CrystalsOrganic Molecular Crystals

Inorganic semiconductors Organic semiconductors

2Bohr radius Rydberg

Band transport

Exciton Binding Energy ~25meV Exciton size ~ 50A

Strong Covalent Bond

Strong e-e screening( ~11)

Strong spin-orbit cou

ε ε

εminusprop prop

bull

bull

bull

gt

gt

gt

gt

J is a good quantum numberpling

gt

Hopping transport

Exciton Binding Energy ~ 05 - 1eV E

Exciton localized on singxciton size ~ 5 - 10A

le pol y

Weak Van der Waals interactions

Weak e-e screening( ~3)ε

bull

bull

gt

gt

gt

gt mer chain

Large exchange energy between the lowest singlet and triple

S is a good quantum number

t excitons

Weak spin-orbit couplingbullgt

gt

17OLED 기초공정 이해와 실습

Conjugated PolymerConjugated Polymer

bull sp2 bonding

poly-acetylene (1958)

bull π- electrons delocalized along the chain

bull Dimerization opens an energy gap 2-3 eV (Peierls instability)

18OLED 기초공정 이해와 실습

에너지에너지 밴드밴드 갭갭

Ionization energies of the HOMO levels and binding energies of the LUMO levels for different polyacenes in the gas phase (left solid lines) and in the crystalline state (right double lines) respectively

C C

H

H

nrarrinfin

Eg=14eV

19OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Hopping model

Small polaron model

Poole-Frenkel model

Multiple trapping amp release model

Etc (Exciton model Soliton model Ishiguro modelhellip)

20OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Hopping model

1

00

In most cases T-dep of mobility

exp where = 1 2 3 4TT

αμ μ α

⎡ ⎤⎛ ⎞⎢ ⎥= minus⎜ ⎟⎢ ⎥⎝ ⎠⎣ ⎦

Conventional semiconductor Organic semiconductorconduction band

valence band

LUMO level

HOMO level

delocalized states propagating

Phonon scattering (negative)rarr mobility increases as T darr

localized states hopping

Phonon scattering (positive)rarr mobility decreases as T darr

01 ~ 1 cm2V-1s-1

21OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Small polaron model

In a conjugated molecules a charge is self-trapped by the lattice deformationrarr creation of the localized mid gap states

Ex) A polaron in Polythiophene

32 22( ) exp

2 2

where polaron binding energy electron transfer energy lattice constant

T-dep of the mobility

bB

Bb

b

Eea J k Tk TE

EJa

πμminus ⎛ ⎞

= minus⎜ ⎟⎝ ⎠h

22OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Poole-Frenkel model

Field dependent mobility at high field (E gt 105 Vcm)

- Coulomb potential near localized states is modified by the applied field

( )120

( ) (0)exp

where (0) zero field mobility

Poole-Frenkel factor mag of electric field

T-dep amp field dep of the mobility

B

qF Fk T

eF

μ μ β

μ

β πεε

⎛ ⎞= ⎜ ⎟

⎝ ⎠

=

23OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Multiple trapping amp release model

Narrow delocalized band+ localized trap level (highly concenturated)

Process1) Carriers arrive at a trap and are trapped2) Thermally activated and released

0

0

exp

where mobility in the delocalized bandDensity of delocalized band edge

Concenturation of traps

T-dep of the mobility

tD

B

Ek T

μ μ α

μ

α

⎛ ⎞= minus⎜ ⎟

⎝ ⎠

=

24OLED 기초공정 이해와 실습

무기EL (p-n junction LED)

Light Emission

anode

cathodeETLEMLHTLHIL+

유기EL (polymers or small molecules)

전자수송층(ETL)

발광층(EML)정공

수송층(HTL)

양극(투명전극

ITO 유리 등)

음극(낮은 일함수 금속

Ca AlLi MgAg등)

-전자

정공

+

-+

두께 100 ~ 200 nm

Exciton

OLED OLED 작동원리작동원리

25OLED 기초공정 이해와 실습

Single-layer devices

Unbalanced carrier injection and lower efficiency

dArr

Heterostructures

ITOHILHTLEMLETLCathode(1) Lower the barrier at electrodes

Balanced carrier injection andimproved efficiency

(2) Band offsets between the layers andspace charges build up at hetero-junctionHigh carrier densitieseffective e-h capture

Multilayer StructureMultilayer Structure

Cathode

HILITO

GLASS

HTLEMLETL

-

+

26OLED 기초공정 이해와 실습

Cathode

HILITO

GLASS

HTLEMLETL

-

+

OLED Structure

N N

CH3

H3C

TPD m-MTDATA

N

N N

N

CH3

CH3

H3C

NO

NON

OAl

Alq3

Small Molecules (Fluorescence)

27OLED 기초공정 이해와 실습

OLED StructureSmall Molecules

(Phosphorescence)

NN

N

N

NN

N

N

CuN

N

NN

CuPc MTDATA

Cathode

HILITO

GLASS

HTLEML

ETL-

+

HBL

NNCH3H3C

BCP

28OLED 기초공정 이해와 실습

OLED Structure

Polymers

Cathode

ITO

GLASS

HTLEML

-

+

PEDOT

n

S O3- S O3

-S O3H S O3H S O3H S O3H

SS

SS

SS

O O

OO

O O

OO OO

n

n n

RR

PPV PF

29OLED 기초공정 이해와 실습

Cur

rent

den

sity Lum

inous Intensity

Voltage

ln V

ln J

J = qn0μVd

J = 98 εsμV2d3

Ligh

t

Current

slope = ηexte

Ex)

OLED OLED 특성특성

3 7

Diode Characteristics Rectification ratio 10 - 10 Power efficiency amp drive voltage

Light vs current

optconv ext

elec

opt opt elecext opt ext

elec elec

P hP eV

N s I IIN s I e e

νη η

η η

= =

= = rArr = times

30OLED 기초공정 이해와 실습

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

Vacuum Level

Anode

Cathode

HOMO

LUMO

Φa

Φc

EA

IP

CB

VB

Eg

에너지에너지 준위준위

31OLED 기초공정 이해와 실습

Current - Voltage Characteristics

2

16 17 3

0

0

1

diffusion voltage ~ 13 V

acceptor concentration ~ 10 - 10 cm

(~ 50 - 150 nm

2( )

Width of space charge layer 2 ( )

D

D

A

r DA

r D A

V VCV

N

C A q N V V

w V V qN

ε ε

ε ε

prop minus

= minus

= minus V = 0 )

OLED OLED 전기적전기적 특성특성

( ) Schottky equation

exp 1

ideality factor 1 1 ideal Schottky diodes B ext BJ J eV nk T V V IR

n n

⎡ ⎤= minus = minus⎣ ⎦ge =

Capacitance - Voltage Dependence

32OLED 기초공정 이해와 실습

I - V Characteristics C - V Characteristics

ITOPPVMetal Polymeric Schottky Diode

OLED OLED 전기적전기적 특성특성

33OLED 기초공정 이해와 실습

Injection Dominated Mechanisms

bull Thermionic emission

bull Tunneling

Bulk Dominated Mechanisms

bull Ohmic Conduction

bull Space Charge Limited Current Conduction

bull Space Charge Limited Current Conduction with Traps

Magnitude of Injection Barrier

전하전하 주입주입

34OLED 기초공정 이해와 실습

Thermionic Emission

Fowler-Nordheim Tunneling

2

2 2

3

exp 1 wehere exp

4 120( )

Richardson constant

bns s

B B

n B

eeVJ J J A Tk T k T

em kA m m A cm Kh

φ

π

⎡ ⎤⎛ ⎞ ⎛ ⎞minus= minus =⎢ ⎥⎜ ⎟ ⎜ ⎟

⎝ ⎠ ⎝ ⎠⎣ ⎦

= =

At low field thermionic emission at high field tunneling dominate

전하전하 주입주입

EF

Evac

-eFz(triangular shape)φ

Z=0 Z

Charge accumulationhigher the energy state `

Electron emission (F-N Tunneling)

Electron emission (Thermionic Emission)

2

3212

~ exp

( ) where 8 (2 )3

bJ EE

qb mqh

π

⎛ ⎞minus⎜ ⎟⎝ ⎠

Φ=

35OLED 기초공정 이해와 실습

Applied voltage

Lattice vibration

Localizedelectron

Hopping conductionBand-like conductionDelocalized electron

Lattice vibration(phonon)

Scattered electron

Low Mobility

bull holes μ ~10-4-10-8 Vs due to poor wave function overlap (large hopping distance)

bull electrons μ ~10-6-10-10Vs due to increased disorder and trapping at defect sites caused by impurities such as O2

rArr Build-up of space-charge density (bulk limited current)

전하전하 이동도이동도

36OLED 기초공정 이해와 실습

NoteMobility depends onElectric Field andTemperature

Mobilities of OrganicsMobilities of Organics

Alq3

37OLED 기초공정 이해와 실습

Ohmic conduction

OLEDOLED의의 전류전류

Current Dendity

current depends linearly on the bias voltageo nn qm VJd

=

2

3

0

1

2 1

(no traps)

(exponential trap distributions ( ) exp( )

one of electrodes(Ohmic contact) can supply more carriers per un

98

Current Density

SCLC condition

o

tt

r

m

m tN

VJd

T E N E kTV md T

ε ε μ

+

+ =

=

prop =

it time than can be transported through the dielectric (caused by low mobility)

Space charge limited (SCL) conduction

38OLED 기초공정 이해와 실습

2

2

3

Charge per unit area Q induced by a voltage V

Transit time across the semiconductor

9

Approximate SCLC densi

Child law (Mott- Gu

ty

Elec8

rney law)

o r

r

o rSCLC

r

VQ CVd

d dtE V

VQJt d

ε ε

μ μ

ε ε μ

= =

= =

asymp =

3 2

tric field distribution across the semiconductor

Majority space charges enhance the E field at the

3 3 ( ) at ( )2 2

enhance the injection of the cath

minority carrieode

rs (elect

V x VE x x d E dd d

= = =

rArr rons)

d

(+) (-)

x=0 x=d

Vd

15 Vd232

3)(d

xVxE =

++++

Virtual anode

-

Space Charge Limited CurrentSpace Charge Limited Current

39OLED 기초공정 이해와 실습

2

3

1

2 01

(no traps or discrete traps Mott-Gurney formula)

(exponential trap distributions ( ) exp( )

98

o rSCLC

mt

SCLC m t t

VJd

TVJ N E NmT

E kTd

ε ε μ

+

+

=

prop = =

ECB

EVB

Etrap

Discrete trapping center Exponential distributionof trapping centers

TrapTrap--Limited CurrentLimited Current

40OLED 기초공정 이해와 실습

Shen Burrows Bulovic McCarty Thompson Forrest Jpn J Appl Phys 35 L401 (1996)

ITOTPDAlq3MgAg

12

1

+

+

prop m

m

SCLC dVJ

TrapTrap--Limited CurrentLimited Current

41OLED 기초공정 이해와 실습

0

0

Activation energy at 0 Empirical parameter

Mobility at PF constant

PF

PF

E FT

T Tμβ

Δ =

=

PFPF

B eff

0

3

PFeff 0 0

( ) exp

exp( )

1 1 1with

E FFT μk T

F

qT T T

βμ

μ β

βπεε

⎛ ⎞Δ minus= minus⎜ ⎟⎜ ⎟

⎝ ⎠

equiv

= minus =

Poole Frenkel ModelPoole Frenkel Model

42OLED 기초공정 이해와 실습

1

22 2

0

0

(1)

(2)

EL F S e h

e ee he

T

h he hh

T

T rec rec e h

h eh e

h e

e hEL F S

h e

T rec

h e h e nh e EL F S EL

e h

n nJ n n nedJ n n ned

nJ

ne F

J J Je F

J Jn J J

ed n ed

η η γ

γτ

γτ

τ τ τ γ

μ

η η γμ μ

τ τ

η ηγ

minus

Φ =

minus minus =

minus minus =

lt =

=

Φ = prop

gt

= Φ = prop rArr Φ prop

EL Current RelationEL Current Relation

43OLED 기초공정 이해와 실습

Device Structure ITONPBAlq3Ca

22

21

ZZZ

fdVdQC

+minus

==πφieZiZZZ ||

))=+=

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

V0 independent of the NPB layer thickness

44OLED 기초공정 이해와 실습

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

Dashed line without interfacial charge

Wolfgang Brutting Stefan Berleb Anton G Muckl Organic Electronics 2 (2001)

Device Structure ITONPBAlq3Ca

45OLED 기초공정 이해와 실습

Langevin Recombination of carriers

bull Carriers are statistically independent therefore the e-h recombination is a random process and kinetically bimolecular

bull Total current attracted by a charge into the sphere of Coulombic capture radius rc

2

22

( ) ( )4

(4 ) 14 184

( ) (mean free path A)

n p c n pc

c cB

n p

qJ qp E qpr

qi r J Bqp r nmk T

qB a

μ μ μ μπε

ππε

μ μ λε

= + = +

= = cong asymp minus

there4 = + asympo

TkUd

BeP ~ minusProbability of dissociation

reUπε4

~2

e-

rc

Carrier RecombinationCarrier Recombination

P Langevin Ann Chem Phys 28 289 (1903)

46OLED 기초공정 이해와 실습

Electronic Processes in Organic Crystals and Polymers by MPope and C E Swenberg

ExcitonsExcitons

47OLED 기초공정 이해와 실습

C Adachi et al

Electrons and holesForm excitons

(bound e--h+ pairs)

Exciton Recombination ZoneExciton Recombination Zone

48OLED 기초공정 이해와 실습

MOLECULAR EXCITED STATESAFTER ELECTRICAL EXCITATION

Singletspin anti-symmetric

Tripletspin symmetric

25 75

MOLECULAR GROUND STATEspin anti-symmetric

Relaxation allowedfast efficientFluorescence

Relaxation disallowedslow inefficientPhosphorescence

|χ1χ2 gt = | gt

|χ1χ2 gt = | gt

|χ1χ2 gt

= | gt - | gt2

1

|χ1χ2 gt = | gt + | gt2

1ISC

Spin

OLEDOLED의의 형광형광인광인광

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 7: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

6OLED 기초공정 이해와 실습

PMOLEDMobile Phone

Motorola(Pioneer)

Samsung(SNMD)

LG(Pioneer) Sanyo-Kodak

22rdquo AMOLED

AMOLED

OLED OLED 디스플레이디스플레이 상품상품

Sony PDA(65535Color 480ⅹ320 pixels) (2004)

7OLED 기초공정 이해와 실습

Sony Flexible Full Color Display 25rdquo(120X169 03mm 15g) (20075)

Delta Optoelectronics

(231X205) PLED

PLED PLED 디스플레이디스플레이 상품상품

CDT (1280X768 200511) PLED

8OLED 기초공정 이해와 실습

OLED AppplicationsOLED Appplications

9OLED 기초공정 이해와 실습

[J R Sheats et al Science 273 884 (1996)의 자료에 최근 발전을 추가함]

LEDLED의의 발전상황발전상황

10OLED 기초공정 이해와 실습

LCD와비교

자료 한국화학연구원 정보디스플레이 기술개발 사업단

OLED

LTPS TFT

AMOLED

LC

AMLCD

CF

BL a-Si TFT LTPS TFT

SelfSelf--emittingemittingFull color DisplayFull color Display

No Backlight Thin amp Light

Less Cell Process Simple Process

No Liquid Crystal Fast Response TimeWide Viewing Angle

mm 30g 50

(~1μs)

70~80

of LCD

170170

OLED OLED 특성특성

11OLED 기초공정 이해와 실습

Display ComparisonDisplay Comparison

CRT PDP LCD OLEDLarge Size ⊙

High Resolution ⊙ ⊙

ThicknessWeight times ⊙ ⊙

Response Time times ⊙

Viewing Angle ⊙ ⊙ times ⊙

Cost ⊙ times

Color ⊙ ⊙

Power Consumption times times ⊙

Image Sticking ⊙ ⊙

Best ⊙ Good Middle Bad x

OLED

LCD Thickness amp Weight Power Consumption

CRT Cost Color Viewing angle Response time=

+

12OLED 기초공정 이해와 실습

Organic Light Emitting Display

OLED

OLEDOLED의의 분류분류

PLEDPhOLED PMOLED AMOLED

FOLED 구동방식재료(저고분자)

형광성

저분자

발광재료

인광성

저분자

발광재료

형광성

고분자

발광재료

Flexible

기판

OLED

수동구동

OLED

능동구동

OLED

Emission Direction에 따라 Bottom Top amp Transparent OLED가 있음

13OLED 기초공정 이해와 실습

저분자 고분자

박막 성막 방식 진공 열증착 Ink-jet

순도 고순도 재료 용이 고순도 재료 어려움

열 안정성 낮다 높다

작동전압 7-15v 3-7v

NO

NON

OAl

2 Types

Small Molecule

Polymer

OLEDOLED의의 재료재료

n

14OLED 기초공정 이해와 실습

Early OLED (Small Molecule)Early OLED (Small Molecule)

EL emission spectrum is sensitive to thickness of organic layerDiamine layer transports holes and blocks electrons injected from MgAg electrode

bull MgAg ndash 101bull Luminescent film - 600Aringbull Diamine ndash 750Aring

CW Tang amp SA VanSlyke Kodak Research LaboratoriesCW Tang and S A VanSlyke in Kodak Appl Phys Letter 51 913 (1987)

15OLED 기초공정 이해와 실습

Light Emitting PolymersLight Emitting Polymers

First Polymer LED (PVK-polymer)- Partridge polymer 24 733 (1983)----

With conductive polymer anode tooWeak blue light

PPV-LED- The first observation of EL was in

1989 (Burroughs et al)- Friend et al U S Patent 5247190

(1990) Cambridge University andCDT work on polymers

- poly(14-phenylene vinylene) (PPV) poly[2-(2rsquo-ethylhexyloxy)-5-methoxy-

14-phenylene vinylene] (MEH-PPV)

n

PPV

Full colour spectrum

glass substrateITO

polymer layerAl Ca Mg

16OLED 기초공정 이해와 실습

Organic Molecular CrystalsOrganic Molecular Crystals

Inorganic semiconductors Organic semiconductors

2Bohr radius Rydberg

Band transport

Exciton Binding Energy ~25meV Exciton size ~ 50A

Strong Covalent Bond

Strong e-e screening( ~11)

Strong spin-orbit cou

ε ε

εminusprop prop

bull

bull

bull

gt

gt

gt

gt

J is a good quantum numberpling

gt

Hopping transport

Exciton Binding Energy ~ 05 - 1eV E

Exciton localized on singxciton size ~ 5 - 10A

le pol y

Weak Van der Waals interactions

Weak e-e screening( ~3)ε

bull

bull

gt

gt

gt

gt mer chain

Large exchange energy between the lowest singlet and triple

S is a good quantum number

t excitons

Weak spin-orbit couplingbullgt

gt

17OLED 기초공정 이해와 실습

Conjugated PolymerConjugated Polymer

bull sp2 bonding

poly-acetylene (1958)

bull π- electrons delocalized along the chain

bull Dimerization opens an energy gap 2-3 eV (Peierls instability)

18OLED 기초공정 이해와 실습

에너지에너지 밴드밴드 갭갭

Ionization energies of the HOMO levels and binding energies of the LUMO levels for different polyacenes in the gas phase (left solid lines) and in the crystalline state (right double lines) respectively

C C

H

H

nrarrinfin

Eg=14eV

19OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Hopping model

Small polaron model

Poole-Frenkel model

Multiple trapping amp release model

Etc (Exciton model Soliton model Ishiguro modelhellip)

20OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Hopping model

1

00

In most cases T-dep of mobility

exp where = 1 2 3 4TT

αμ μ α

⎡ ⎤⎛ ⎞⎢ ⎥= minus⎜ ⎟⎢ ⎥⎝ ⎠⎣ ⎦

Conventional semiconductor Organic semiconductorconduction band

valence band

LUMO level

HOMO level

delocalized states propagating

Phonon scattering (negative)rarr mobility increases as T darr

localized states hopping

Phonon scattering (positive)rarr mobility decreases as T darr

01 ~ 1 cm2V-1s-1

21OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Small polaron model

In a conjugated molecules a charge is self-trapped by the lattice deformationrarr creation of the localized mid gap states

Ex) A polaron in Polythiophene

32 22( ) exp

2 2

where polaron binding energy electron transfer energy lattice constant

T-dep of the mobility

bB

Bb

b

Eea J k Tk TE

EJa

πμminus ⎛ ⎞

= minus⎜ ⎟⎝ ⎠h

22OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Poole-Frenkel model

Field dependent mobility at high field (E gt 105 Vcm)

- Coulomb potential near localized states is modified by the applied field

( )120

( ) (0)exp

where (0) zero field mobility

Poole-Frenkel factor mag of electric field

T-dep amp field dep of the mobility

B

qF Fk T

eF

μ μ β

μ

β πεε

⎛ ⎞= ⎜ ⎟

⎝ ⎠

=

23OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Multiple trapping amp release model

Narrow delocalized band+ localized trap level (highly concenturated)

Process1) Carriers arrive at a trap and are trapped2) Thermally activated and released

0

0

exp

where mobility in the delocalized bandDensity of delocalized band edge

Concenturation of traps

T-dep of the mobility

tD

B

Ek T

μ μ α

μ

α

⎛ ⎞= minus⎜ ⎟

⎝ ⎠

=

24OLED 기초공정 이해와 실습

무기EL (p-n junction LED)

Light Emission

anode

cathodeETLEMLHTLHIL+

유기EL (polymers or small molecules)

전자수송층(ETL)

발광층(EML)정공

수송층(HTL)

양극(투명전극

ITO 유리 등)

음극(낮은 일함수 금속

Ca AlLi MgAg등)

-전자

정공

+

-+

두께 100 ~ 200 nm

Exciton

OLED OLED 작동원리작동원리

25OLED 기초공정 이해와 실습

Single-layer devices

Unbalanced carrier injection and lower efficiency

dArr

Heterostructures

ITOHILHTLEMLETLCathode(1) Lower the barrier at electrodes

Balanced carrier injection andimproved efficiency

(2) Band offsets between the layers andspace charges build up at hetero-junctionHigh carrier densitieseffective e-h capture

Multilayer StructureMultilayer Structure

Cathode

HILITO

GLASS

HTLEMLETL

-

+

26OLED 기초공정 이해와 실습

Cathode

HILITO

GLASS

HTLEMLETL

-

+

OLED Structure

N N

CH3

H3C

TPD m-MTDATA

N

N N

N

CH3

CH3

H3C

NO

NON

OAl

Alq3

Small Molecules (Fluorescence)

27OLED 기초공정 이해와 실습

OLED StructureSmall Molecules

(Phosphorescence)

NN

N

N

NN

N

N

CuN

N

NN

CuPc MTDATA

Cathode

HILITO

GLASS

HTLEML

ETL-

+

HBL

NNCH3H3C

BCP

28OLED 기초공정 이해와 실습

OLED Structure

Polymers

Cathode

ITO

GLASS

HTLEML

-

+

PEDOT

n

S O3- S O3

-S O3H S O3H S O3H S O3H

SS

SS

SS

O O

OO

O O

OO OO

n

n n

RR

PPV PF

29OLED 기초공정 이해와 실습

Cur

rent

den

sity Lum

inous Intensity

Voltage

ln V

ln J

J = qn0μVd

J = 98 εsμV2d3

Ligh

t

Current

slope = ηexte

Ex)

OLED OLED 특성특성

3 7

Diode Characteristics Rectification ratio 10 - 10 Power efficiency amp drive voltage

Light vs current

optconv ext

elec

opt opt elecext opt ext

elec elec

P hP eV

N s I IIN s I e e

νη η

η η

= =

= = rArr = times

30OLED 기초공정 이해와 실습

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

Vacuum Level

Anode

Cathode

HOMO

LUMO

Φa

Φc

EA

IP

CB

VB

Eg

에너지에너지 준위준위

31OLED 기초공정 이해와 실습

Current - Voltage Characteristics

2

16 17 3

0

0

1

diffusion voltage ~ 13 V

acceptor concentration ~ 10 - 10 cm

(~ 50 - 150 nm

2( )

Width of space charge layer 2 ( )

D

D

A

r DA

r D A

V VCV

N

C A q N V V

w V V qN

ε ε

ε ε

prop minus

= minus

= minus V = 0 )

OLED OLED 전기적전기적 특성특성

( ) Schottky equation

exp 1

ideality factor 1 1 ideal Schottky diodes B ext BJ J eV nk T V V IR

n n

⎡ ⎤= minus = minus⎣ ⎦ge =

Capacitance - Voltage Dependence

32OLED 기초공정 이해와 실습

I - V Characteristics C - V Characteristics

ITOPPVMetal Polymeric Schottky Diode

OLED OLED 전기적전기적 특성특성

33OLED 기초공정 이해와 실습

Injection Dominated Mechanisms

bull Thermionic emission

bull Tunneling

Bulk Dominated Mechanisms

bull Ohmic Conduction

bull Space Charge Limited Current Conduction

bull Space Charge Limited Current Conduction with Traps

Magnitude of Injection Barrier

전하전하 주입주입

34OLED 기초공정 이해와 실습

Thermionic Emission

Fowler-Nordheim Tunneling

2

2 2

3

exp 1 wehere exp

4 120( )

Richardson constant

bns s

B B

n B

eeVJ J J A Tk T k T

em kA m m A cm Kh

φ

π

⎡ ⎤⎛ ⎞ ⎛ ⎞minus= minus =⎢ ⎥⎜ ⎟ ⎜ ⎟

⎝ ⎠ ⎝ ⎠⎣ ⎦

= =

At low field thermionic emission at high field tunneling dominate

전하전하 주입주입

EF

Evac

-eFz(triangular shape)φ

Z=0 Z

Charge accumulationhigher the energy state `

Electron emission (F-N Tunneling)

Electron emission (Thermionic Emission)

2

3212

~ exp

( ) where 8 (2 )3

bJ EE

qb mqh

π

⎛ ⎞minus⎜ ⎟⎝ ⎠

Φ=

35OLED 기초공정 이해와 실습

Applied voltage

Lattice vibration

Localizedelectron

Hopping conductionBand-like conductionDelocalized electron

Lattice vibration(phonon)

Scattered electron

Low Mobility

bull holes μ ~10-4-10-8 Vs due to poor wave function overlap (large hopping distance)

bull electrons μ ~10-6-10-10Vs due to increased disorder and trapping at defect sites caused by impurities such as O2

rArr Build-up of space-charge density (bulk limited current)

전하전하 이동도이동도

36OLED 기초공정 이해와 실습

NoteMobility depends onElectric Field andTemperature

Mobilities of OrganicsMobilities of Organics

Alq3

37OLED 기초공정 이해와 실습

Ohmic conduction

OLEDOLED의의 전류전류

Current Dendity

current depends linearly on the bias voltageo nn qm VJd

=

2

3

0

1

2 1

(no traps)

(exponential trap distributions ( ) exp( )

one of electrodes(Ohmic contact) can supply more carriers per un

98

Current Density

SCLC condition

o

tt

r

m

m tN

VJd

T E N E kTV md T

ε ε μ

+

+ =

=

prop =

it time than can be transported through the dielectric (caused by low mobility)

Space charge limited (SCL) conduction

38OLED 기초공정 이해와 실습

2

2

3

Charge per unit area Q induced by a voltage V

Transit time across the semiconductor

9

Approximate SCLC densi

Child law (Mott- Gu

ty

Elec8

rney law)

o r

r

o rSCLC

r

VQ CVd

d dtE V

VQJt d

ε ε

μ μ

ε ε μ

= =

= =

asymp =

3 2

tric field distribution across the semiconductor

Majority space charges enhance the E field at the

3 3 ( ) at ( )2 2

enhance the injection of the cath

minority carrieode

rs (elect

V x VE x x d E dd d

= = =

rArr rons)

d

(+) (-)

x=0 x=d

Vd

15 Vd232

3)(d

xVxE =

++++

Virtual anode

-

Space Charge Limited CurrentSpace Charge Limited Current

39OLED 기초공정 이해와 실습

2

3

1

2 01

(no traps or discrete traps Mott-Gurney formula)

(exponential trap distributions ( ) exp( )

98

o rSCLC

mt

SCLC m t t

VJd

TVJ N E NmT

E kTd

ε ε μ

+

+

=

prop = =

ECB

EVB

Etrap

Discrete trapping center Exponential distributionof trapping centers

TrapTrap--Limited CurrentLimited Current

40OLED 기초공정 이해와 실습

Shen Burrows Bulovic McCarty Thompson Forrest Jpn J Appl Phys 35 L401 (1996)

ITOTPDAlq3MgAg

12

1

+

+

prop m

m

SCLC dVJ

TrapTrap--Limited CurrentLimited Current

41OLED 기초공정 이해와 실습

0

0

Activation energy at 0 Empirical parameter

Mobility at PF constant

PF

PF

E FT

T Tμβ

Δ =

=

PFPF

B eff

0

3

PFeff 0 0

( ) exp

exp( )

1 1 1with

E FFT μk T

F

qT T T

βμ

μ β

βπεε

⎛ ⎞Δ minus= minus⎜ ⎟⎜ ⎟

⎝ ⎠

equiv

= minus =

Poole Frenkel ModelPoole Frenkel Model

42OLED 기초공정 이해와 실습

1

22 2

0

0

(1)

(2)

EL F S e h

e ee he

T

h he hh

T

T rec rec e h

h eh e

h e

e hEL F S

h e

T rec

h e h e nh e EL F S EL

e h

n nJ n n nedJ n n ned

nJ

ne F

J J Je F

J Jn J J

ed n ed

η η γ

γτ

γτ

τ τ τ γ

μ

η η γμ μ

τ τ

η ηγ

minus

Φ =

minus minus =

minus minus =

lt =

=

Φ = prop

gt

= Φ = prop rArr Φ prop

EL Current RelationEL Current Relation

43OLED 기초공정 이해와 실습

Device Structure ITONPBAlq3Ca

22

21

ZZZ

fdVdQC

+minus

==πφieZiZZZ ||

))=+=

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

V0 independent of the NPB layer thickness

44OLED 기초공정 이해와 실습

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

Dashed line without interfacial charge

Wolfgang Brutting Stefan Berleb Anton G Muckl Organic Electronics 2 (2001)

Device Structure ITONPBAlq3Ca

45OLED 기초공정 이해와 실습

Langevin Recombination of carriers

bull Carriers are statistically independent therefore the e-h recombination is a random process and kinetically bimolecular

bull Total current attracted by a charge into the sphere of Coulombic capture radius rc

2

22

( ) ( )4

(4 ) 14 184

( ) (mean free path A)

n p c n pc

c cB

n p

qJ qp E qpr

qi r J Bqp r nmk T

qB a

μ μ μ μπε

ππε

μ μ λε

= + = +

= = cong asymp minus

there4 = + asympo

TkUd

BeP ~ minusProbability of dissociation

reUπε4

~2

e-

rc

Carrier RecombinationCarrier Recombination

P Langevin Ann Chem Phys 28 289 (1903)

46OLED 기초공정 이해와 실습

Electronic Processes in Organic Crystals and Polymers by MPope and C E Swenberg

ExcitonsExcitons

47OLED 기초공정 이해와 실습

C Adachi et al

Electrons and holesForm excitons

(bound e--h+ pairs)

Exciton Recombination ZoneExciton Recombination Zone

48OLED 기초공정 이해와 실습

MOLECULAR EXCITED STATESAFTER ELECTRICAL EXCITATION

Singletspin anti-symmetric

Tripletspin symmetric

25 75

MOLECULAR GROUND STATEspin anti-symmetric

Relaxation allowedfast efficientFluorescence

Relaxation disallowedslow inefficientPhosphorescence

|χ1χ2 gt = | gt

|χ1χ2 gt = | gt

|χ1χ2 gt

= | gt - | gt2

1

|χ1χ2 gt = | gt + | gt2

1ISC

Spin

OLEDOLED의의 형광형광인광인광

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 8: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

7OLED 기초공정 이해와 실습

Sony Flexible Full Color Display 25rdquo(120X169 03mm 15g) (20075)

Delta Optoelectronics

(231X205) PLED

PLED PLED 디스플레이디스플레이 상품상품

CDT (1280X768 200511) PLED

8OLED 기초공정 이해와 실습

OLED AppplicationsOLED Appplications

9OLED 기초공정 이해와 실습

[J R Sheats et al Science 273 884 (1996)의 자료에 최근 발전을 추가함]

LEDLED의의 발전상황발전상황

10OLED 기초공정 이해와 실습

LCD와비교

자료 한국화학연구원 정보디스플레이 기술개발 사업단

OLED

LTPS TFT

AMOLED

LC

AMLCD

CF

BL a-Si TFT LTPS TFT

SelfSelf--emittingemittingFull color DisplayFull color Display

No Backlight Thin amp Light

Less Cell Process Simple Process

No Liquid Crystal Fast Response TimeWide Viewing Angle

mm 30g 50

(~1μs)

70~80

of LCD

170170

OLED OLED 특성특성

11OLED 기초공정 이해와 실습

Display ComparisonDisplay Comparison

CRT PDP LCD OLEDLarge Size ⊙

High Resolution ⊙ ⊙

ThicknessWeight times ⊙ ⊙

Response Time times ⊙

Viewing Angle ⊙ ⊙ times ⊙

Cost ⊙ times

Color ⊙ ⊙

Power Consumption times times ⊙

Image Sticking ⊙ ⊙

Best ⊙ Good Middle Bad x

OLED

LCD Thickness amp Weight Power Consumption

CRT Cost Color Viewing angle Response time=

+

12OLED 기초공정 이해와 실습

Organic Light Emitting Display

OLED

OLEDOLED의의 분류분류

PLEDPhOLED PMOLED AMOLED

FOLED 구동방식재료(저고분자)

형광성

저분자

발광재료

인광성

저분자

발광재료

형광성

고분자

발광재료

Flexible

기판

OLED

수동구동

OLED

능동구동

OLED

Emission Direction에 따라 Bottom Top amp Transparent OLED가 있음

13OLED 기초공정 이해와 실습

저분자 고분자

박막 성막 방식 진공 열증착 Ink-jet

순도 고순도 재료 용이 고순도 재료 어려움

열 안정성 낮다 높다

작동전압 7-15v 3-7v

NO

NON

OAl

2 Types

Small Molecule

Polymer

OLEDOLED의의 재료재료

n

14OLED 기초공정 이해와 실습

Early OLED (Small Molecule)Early OLED (Small Molecule)

EL emission spectrum is sensitive to thickness of organic layerDiamine layer transports holes and blocks electrons injected from MgAg electrode

bull MgAg ndash 101bull Luminescent film - 600Aringbull Diamine ndash 750Aring

CW Tang amp SA VanSlyke Kodak Research LaboratoriesCW Tang and S A VanSlyke in Kodak Appl Phys Letter 51 913 (1987)

15OLED 기초공정 이해와 실습

Light Emitting PolymersLight Emitting Polymers

First Polymer LED (PVK-polymer)- Partridge polymer 24 733 (1983)----

With conductive polymer anode tooWeak blue light

PPV-LED- The first observation of EL was in

1989 (Burroughs et al)- Friend et al U S Patent 5247190

(1990) Cambridge University andCDT work on polymers

- poly(14-phenylene vinylene) (PPV) poly[2-(2rsquo-ethylhexyloxy)-5-methoxy-

14-phenylene vinylene] (MEH-PPV)

n

PPV

Full colour spectrum

glass substrateITO

polymer layerAl Ca Mg

16OLED 기초공정 이해와 실습

Organic Molecular CrystalsOrganic Molecular Crystals

Inorganic semiconductors Organic semiconductors

2Bohr radius Rydberg

Band transport

Exciton Binding Energy ~25meV Exciton size ~ 50A

Strong Covalent Bond

Strong e-e screening( ~11)

Strong spin-orbit cou

ε ε

εminusprop prop

bull

bull

bull

gt

gt

gt

gt

J is a good quantum numberpling

gt

Hopping transport

Exciton Binding Energy ~ 05 - 1eV E

Exciton localized on singxciton size ~ 5 - 10A

le pol y

Weak Van der Waals interactions

Weak e-e screening( ~3)ε

bull

bull

gt

gt

gt

gt mer chain

Large exchange energy between the lowest singlet and triple

S is a good quantum number

t excitons

Weak spin-orbit couplingbullgt

gt

17OLED 기초공정 이해와 실습

Conjugated PolymerConjugated Polymer

bull sp2 bonding

poly-acetylene (1958)

bull π- electrons delocalized along the chain

bull Dimerization opens an energy gap 2-3 eV (Peierls instability)

18OLED 기초공정 이해와 실습

에너지에너지 밴드밴드 갭갭

Ionization energies of the HOMO levels and binding energies of the LUMO levels for different polyacenes in the gas phase (left solid lines) and in the crystalline state (right double lines) respectively

C C

H

H

nrarrinfin

Eg=14eV

19OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Hopping model

Small polaron model

Poole-Frenkel model

Multiple trapping amp release model

Etc (Exciton model Soliton model Ishiguro modelhellip)

20OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Hopping model

1

00

In most cases T-dep of mobility

exp where = 1 2 3 4TT

αμ μ α

⎡ ⎤⎛ ⎞⎢ ⎥= minus⎜ ⎟⎢ ⎥⎝ ⎠⎣ ⎦

Conventional semiconductor Organic semiconductorconduction band

valence band

LUMO level

HOMO level

delocalized states propagating

Phonon scattering (negative)rarr mobility increases as T darr

localized states hopping

Phonon scattering (positive)rarr mobility decreases as T darr

01 ~ 1 cm2V-1s-1

21OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Small polaron model

In a conjugated molecules a charge is self-trapped by the lattice deformationrarr creation of the localized mid gap states

Ex) A polaron in Polythiophene

32 22( ) exp

2 2

where polaron binding energy electron transfer energy lattice constant

T-dep of the mobility

bB

Bb

b

Eea J k Tk TE

EJa

πμminus ⎛ ⎞

= minus⎜ ⎟⎝ ⎠h

22OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Poole-Frenkel model

Field dependent mobility at high field (E gt 105 Vcm)

- Coulomb potential near localized states is modified by the applied field

( )120

( ) (0)exp

where (0) zero field mobility

Poole-Frenkel factor mag of electric field

T-dep amp field dep of the mobility

B

qF Fk T

eF

μ μ β

μ

β πεε

⎛ ⎞= ⎜ ⎟

⎝ ⎠

=

23OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Multiple trapping amp release model

Narrow delocalized band+ localized trap level (highly concenturated)

Process1) Carriers arrive at a trap and are trapped2) Thermally activated and released

0

0

exp

where mobility in the delocalized bandDensity of delocalized band edge

Concenturation of traps

T-dep of the mobility

tD

B

Ek T

μ μ α

μ

α

⎛ ⎞= minus⎜ ⎟

⎝ ⎠

=

24OLED 기초공정 이해와 실습

무기EL (p-n junction LED)

Light Emission

anode

cathodeETLEMLHTLHIL+

유기EL (polymers or small molecules)

전자수송층(ETL)

발광층(EML)정공

수송층(HTL)

양극(투명전극

ITO 유리 등)

음극(낮은 일함수 금속

Ca AlLi MgAg등)

-전자

정공

+

-+

두께 100 ~ 200 nm

Exciton

OLED OLED 작동원리작동원리

25OLED 기초공정 이해와 실습

Single-layer devices

Unbalanced carrier injection and lower efficiency

dArr

Heterostructures

ITOHILHTLEMLETLCathode(1) Lower the barrier at electrodes

Balanced carrier injection andimproved efficiency

(2) Band offsets between the layers andspace charges build up at hetero-junctionHigh carrier densitieseffective e-h capture

Multilayer StructureMultilayer Structure

Cathode

HILITO

GLASS

HTLEMLETL

-

+

26OLED 기초공정 이해와 실습

Cathode

HILITO

GLASS

HTLEMLETL

-

+

OLED Structure

N N

CH3

H3C

TPD m-MTDATA

N

N N

N

CH3

CH3

H3C

NO

NON

OAl

Alq3

Small Molecules (Fluorescence)

27OLED 기초공정 이해와 실습

OLED StructureSmall Molecules

(Phosphorescence)

NN

N

N

NN

N

N

CuN

N

NN

CuPc MTDATA

Cathode

HILITO

GLASS

HTLEML

ETL-

+

HBL

NNCH3H3C

BCP

28OLED 기초공정 이해와 실습

OLED Structure

Polymers

Cathode

ITO

GLASS

HTLEML

-

+

PEDOT

n

S O3- S O3

-S O3H S O3H S O3H S O3H

SS

SS

SS

O O

OO

O O

OO OO

n

n n

RR

PPV PF

29OLED 기초공정 이해와 실습

Cur

rent

den

sity Lum

inous Intensity

Voltage

ln V

ln J

J = qn0μVd

J = 98 εsμV2d3

Ligh

t

Current

slope = ηexte

Ex)

OLED OLED 특성특성

3 7

Diode Characteristics Rectification ratio 10 - 10 Power efficiency amp drive voltage

Light vs current

optconv ext

elec

opt opt elecext opt ext

elec elec

P hP eV

N s I IIN s I e e

νη η

η η

= =

= = rArr = times

30OLED 기초공정 이해와 실습

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

Vacuum Level

Anode

Cathode

HOMO

LUMO

Φa

Φc

EA

IP

CB

VB

Eg

에너지에너지 준위준위

31OLED 기초공정 이해와 실습

Current - Voltage Characteristics

2

16 17 3

0

0

1

diffusion voltage ~ 13 V

acceptor concentration ~ 10 - 10 cm

(~ 50 - 150 nm

2( )

Width of space charge layer 2 ( )

D

D

A

r DA

r D A

V VCV

N

C A q N V V

w V V qN

ε ε

ε ε

prop minus

= minus

= minus V = 0 )

OLED OLED 전기적전기적 특성특성

( ) Schottky equation

exp 1

ideality factor 1 1 ideal Schottky diodes B ext BJ J eV nk T V V IR

n n

⎡ ⎤= minus = minus⎣ ⎦ge =

Capacitance - Voltage Dependence

32OLED 기초공정 이해와 실습

I - V Characteristics C - V Characteristics

ITOPPVMetal Polymeric Schottky Diode

OLED OLED 전기적전기적 특성특성

33OLED 기초공정 이해와 실습

Injection Dominated Mechanisms

bull Thermionic emission

bull Tunneling

Bulk Dominated Mechanisms

bull Ohmic Conduction

bull Space Charge Limited Current Conduction

bull Space Charge Limited Current Conduction with Traps

Magnitude of Injection Barrier

전하전하 주입주입

34OLED 기초공정 이해와 실습

Thermionic Emission

Fowler-Nordheim Tunneling

2

2 2

3

exp 1 wehere exp

4 120( )

Richardson constant

bns s

B B

n B

eeVJ J J A Tk T k T

em kA m m A cm Kh

φ

π

⎡ ⎤⎛ ⎞ ⎛ ⎞minus= minus =⎢ ⎥⎜ ⎟ ⎜ ⎟

⎝ ⎠ ⎝ ⎠⎣ ⎦

= =

At low field thermionic emission at high field tunneling dominate

전하전하 주입주입

EF

Evac

-eFz(triangular shape)φ

Z=0 Z

Charge accumulationhigher the energy state `

Electron emission (F-N Tunneling)

Electron emission (Thermionic Emission)

2

3212

~ exp

( ) where 8 (2 )3

bJ EE

qb mqh

π

⎛ ⎞minus⎜ ⎟⎝ ⎠

Φ=

35OLED 기초공정 이해와 실습

Applied voltage

Lattice vibration

Localizedelectron

Hopping conductionBand-like conductionDelocalized electron

Lattice vibration(phonon)

Scattered electron

Low Mobility

bull holes μ ~10-4-10-8 Vs due to poor wave function overlap (large hopping distance)

bull electrons μ ~10-6-10-10Vs due to increased disorder and trapping at defect sites caused by impurities such as O2

rArr Build-up of space-charge density (bulk limited current)

전하전하 이동도이동도

36OLED 기초공정 이해와 실습

NoteMobility depends onElectric Field andTemperature

Mobilities of OrganicsMobilities of Organics

Alq3

37OLED 기초공정 이해와 실습

Ohmic conduction

OLEDOLED의의 전류전류

Current Dendity

current depends linearly on the bias voltageo nn qm VJd

=

2

3

0

1

2 1

(no traps)

(exponential trap distributions ( ) exp( )

one of electrodes(Ohmic contact) can supply more carriers per un

98

Current Density

SCLC condition

o

tt

r

m

m tN

VJd

T E N E kTV md T

ε ε μ

+

+ =

=

prop =

it time than can be transported through the dielectric (caused by low mobility)

Space charge limited (SCL) conduction

38OLED 기초공정 이해와 실습

2

2

3

Charge per unit area Q induced by a voltage V

Transit time across the semiconductor

9

Approximate SCLC densi

Child law (Mott- Gu

ty

Elec8

rney law)

o r

r

o rSCLC

r

VQ CVd

d dtE V

VQJt d

ε ε

μ μ

ε ε μ

= =

= =

asymp =

3 2

tric field distribution across the semiconductor

Majority space charges enhance the E field at the

3 3 ( ) at ( )2 2

enhance the injection of the cath

minority carrieode

rs (elect

V x VE x x d E dd d

= = =

rArr rons)

d

(+) (-)

x=0 x=d

Vd

15 Vd232

3)(d

xVxE =

++++

Virtual anode

-

Space Charge Limited CurrentSpace Charge Limited Current

39OLED 기초공정 이해와 실습

2

3

1

2 01

(no traps or discrete traps Mott-Gurney formula)

(exponential trap distributions ( ) exp( )

98

o rSCLC

mt

SCLC m t t

VJd

TVJ N E NmT

E kTd

ε ε μ

+

+

=

prop = =

ECB

EVB

Etrap

Discrete trapping center Exponential distributionof trapping centers

TrapTrap--Limited CurrentLimited Current

40OLED 기초공정 이해와 실습

Shen Burrows Bulovic McCarty Thompson Forrest Jpn J Appl Phys 35 L401 (1996)

ITOTPDAlq3MgAg

12

1

+

+

prop m

m

SCLC dVJ

TrapTrap--Limited CurrentLimited Current

41OLED 기초공정 이해와 실습

0

0

Activation energy at 0 Empirical parameter

Mobility at PF constant

PF

PF

E FT

T Tμβ

Δ =

=

PFPF

B eff

0

3

PFeff 0 0

( ) exp

exp( )

1 1 1with

E FFT μk T

F

qT T T

βμ

μ β

βπεε

⎛ ⎞Δ minus= minus⎜ ⎟⎜ ⎟

⎝ ⎠

equiv

= minus =

Poole Frenkel ModelPoole Frenkel Model

42OLED 기초공정 이해와 실습

1

22 2

0

0

(1)

(2)

EL F S e h

e ee he

T

h he hh

T

T rec rec e h

h eh e

h e

e hEL F S

h e

T rec

h e h e nh e EL F S EL

e h

n nJ n n nedJ n n ned

nJ

ne F

J J Je F

J Jn J J

ed n ed

η η γ

γτ

γτ

τ τ τ γ

μ

η η γμ μ

τ τ

η ηγ

minus

Φ =

minus minus =

minus minus =

lt =

=

Φ = prop

gt

= Φ = prop rArr Φ prop

EL Current RelationEL Current Relation

43OLED 기초공정 이해와 실습

Device Structure ITONPBAlq3Ca

22

21

ZZZ

fdVdQC

+minus

==πφieZiZZZ ||

))=+=

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

V0 independent of the NPB layer thickness

44OLED 기초공정 이해와 실습

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

Dashed line without interfacial charge

Wolfgang Brutting Stefan Berleb Anton G Muckl Organic Electronics 2 (2001)

Device Structure ITONPBAlq3Ca

45OLED 기초공정 이해와 실습

Langevin Recombination of carriers

bull Carriers are statistically independent therefore the e-h recombination is a random process and kinetically bimolecular

bull Total current attracted by a charge into the sphere of Coulombic capture radius rc

2

22

( ) ( )4

(4 ) 14 184

( ) (mean free path A)

n p c n pc

c cB

n p

qJ qp E qpr

qi r J Bqp r nmk T

qB a

μ μ μ μπε

ππε

μ μ λε

= + = +

= = cong asymp minus

there4 = + asympo

TkUd

BeP ~ minusProbability of dissociation

reUπε4

~2

e-

rc

Carrier RecombinationCarrier Recombination

P Langevin Ann Chem Phys 28 289 (1903)

46OLED 기초공정 이해와 실습

Electronic Processes in Organic Crystals and Polymers by MPope and C E Swenberg

ExcitonsExcitons

47OLED 기초공정 이해와 실습

C Adachi et al

Electrons and holesForm excitons

(bound e--h+ pairs)

Exciton Recombination ZoneExciton Recombination Zone

48OLED 기초공정 이해와 실습

MOLECULAR EXCITED STATESAFTER ELECTRICAL EXCITATION

Singletspin anti-symmetric

Tripletspin symmetric

25 75

MOLECULAR GROUND STATEspin anti-symmetric

Relaxation allowedfast efficientFluorescence

Relaxation disallowedslow inefficientPhosphorescence

|χ1χ2 gt = | gt

|χ1χ2 gt = | gt

|χ1χ2 gt

= | gt - | gt2

1

|χ1χ2 gt = | gt + | gt2

1ISC

Spin

OLEDOLED의의 형광형광인광인광

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 9: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

8OLED 기초공정 이해와 실습

OLED AppplicationsOLED Appplications

9OLED 기초공정 이해와 실습

[J R Sheats et al Science 273 884 (1996)의 자료에 최근 발전을 추가함]

LEDLED의의 발전상황발전상황

10OLED 기초공정 이해와 실습

LCD와비교

자료 한국화학연구원 정보디스플레이 기술개발 사업단

OLED

LTPS TFT

AMOLED

LC

AMLCD

CF

BL a-Si TFT LTPS TFT

SelfSelf--emittingemittingFull color DisplayFull color Display

No Backlight Thin amp Light

Less Cell Process Simple Process

No Liquid Crystal Fast Response TimeWide Viewing Angle

mm 30g 50

(~1μs)

70~80

of LCD

170170

OLED OLED 특성특성

11OLED 기초공정 이해와 실습

Display ComparisonDisplay Comparison

CRT PDP LCD OLEDLarge Size ⊙

High Resolution ⊙ ⊙

ThicknessWeight times ⊙ ⊙

Response Time times ⊙

Viewing Angle ⊙ ⊙ times ⊙

Cost ⊙ times

Color ⊙ ⊙

Power Consumption times times ⊙

Image Sticking ⊙ ⊙

Best ⊙ Good Middle Bad x

OLED

LCD Thickness amp Weight Power Consumption

CRT Cost Color Viewing angle Response time=

+

12OLED 기초공정 이해와 실습

Organic Light Emitting Display

OLED

OLEDOLED의의 분류분류

PLEDPhOLED PMOLED AMOLED

FOLED 구동방식재료(저고분자)

형광성

저분자

발광재료

인광성

저분자

발광재료

형광성

고분자

발광재료

Flexible

기판

OLED

수동구동

OLED

능동구동

OLED

Emission Direction에 따라 Bottom Top amp Transparent OLED가 있음

13OLED 기초공정 이해와 실습

저분자 고분자

박막 성막 방식 진공 열증착 Ink-jet

순도 고순도 재료 용이 고순도 재료 어려움

열 안정성 낮다 높다

작동전압 7-15v 3-7v

NO

NON

OAl

2 Types

Small Molecule

Polymer

OLEDOLED의의 재료재료

n

14OLED 기초공정 이해와 실습

Early OLED (Small Molecule)Early OLED (Small Molecule)

EL emission spectrum is sensitive to thickness of organic layerDiamine layer transports holes and blocks electrons injected from MgAg electrode

bull MgAg ndash 101bull Luminescent film - 600Aringbull Diamine ndash 750Aring

CW Tang amp SA VanSlyke Kodak Research LaboratoriesCW Tang and S A VanSlyke in Kodak Appl Phys Letter 51 913 (1987)

15OLED 기초공정 이해와 실습

Light Emitting PolymersLight Emitting Polymers

First Polymer LED (PVK-polymer)- Partridge polymer 24 733 (1983)----

With conductive polymer anode tooWeak blue light

PPV-LED- The first observation of EL was in

1989 (Burroughs et al)- Friend et al U S Patent 5247190

(1990) Cambridge University andCDT work on polymers

- poly(14-phenylene vinylene) (PPV) poly[2-(2rsquo-ethylhexyloxy)-5-methoxy-

14-phenylene vinylene] (MEH-PPV)

n

PPV

Full colour spectrum

glass substrateITO

polymer layerAl Ca Mg

16OLED 기초공정 이해와 실습

Organic Molecular CrystalsOrganic Molecular Crystals

Inorganic semiconductors Organic semiconductors

2Bohr radius Rydberg

Band transport

Exciton Binding Energy ~25meV Exciton size ~ 50A

Strong Covalent Bond

Strong e-e screening( ~11)

Strong spin-orbit cou

ε ε

εminusprop prop

bull

bull

bull

gt

gt

gt

gt

J is a good quantum numberpling

gt

Hopping transport

Exciton Binding Energy ~ 05 - 1eV E

Exciton localized on singxciton size ~ 5 - 10A

le pol y

Weak Van der Waals interactions

Weak e-e screening( ~3)ε

bull

bull

gt

gt

gt

gt mer chain

Large exchange energy between the lowest singlet and triple

S is a good quantum number

t excitons

Weak spin-orbit couplingbullgt

gt

17OLED 기초공정 이해와 실습

Conjugated PolymerConjugated Polymer

bull sp2 bonding

poly-acetylene (1958)

bull π- electrons delocalized along the chain

bull Dimerization opens an energy gap 2-3 eV (Peierls instability)

18OLED 기초공정 이해와 실습

에너지에너지 밴드밴드 갭갭

Ionization energies of the HOMO levels and binding energies of the LUMO levels for different polyacenes in the gas phase (left solid lines) and in the crystalline state (right double lines) respectively

C C

H

H

nrarrinfin

Eg=14eV

19OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Hopping model

Small polaron model

Poole-Frenkel model

Multiple trapping amp release model

Etc (Exciton model Soliton model Ishiguro modelhellip)

20OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Hopping model

1

00

In most cases T-dep of mobility

exp where = 1 2 3 4TT

αμ μ α

⎡ ⎤⎛ ⎞⎢ ⎥= minus⎜ ⎟⎢ ⎥⎝ ⎠⎣ ⎦

Conventional semiconductor Organic semiconductorconduction band

valence band

LUMO level

HOMO level

delocalized states propagating

Phonon scattering (negative)rarr mobility increases as T darr

localized states hopping

Phonon scattering (positive)rarr mobility decreases as T darr

01 ~ 1 cm2V-1s-1

21OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Small polaron model

In a conjugated molecules a charge is self-trapped by the lattice deformationrarr creation of the localized mid gap states

Ex) A polaron in Polythiophene

32 22( ) exp

2 2

where polaron binding energy electron transfer energy lattice constant

T-dep of the mobility

bB

Bb

b

Eea J k Tk TE

EJa

πμminus ⎛ ⎞

= minus⎜ ⎟⎝ ⎠h

22OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Poole-Frenkel model

Field dependent mobility at high field (E gt 105 Vcm)

- Coulomb potential near localized states is modified by the applied field

( )120

( ) (0)exp

where (0) zero field mobility

Poole-Frenkel factor mag of electric field

T-dep amp field dep of the mobility

B

qF Fk T

eF

μ μ β

μ

β πεε

⎛ ⎞= ⎜ ⎟

⎝ ⎠

=

23OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Multiple trapping amp release model

Narrow delocalized band+ localized trap level (highly concenturated)

Process1) Carriers arrive at a trap and are trapped2) Thermally activated and released

0

0

exp

where mobility in the delocalized bandDensity of delocalized band edge

Concenturation of traps

T-dep of the mobility

tD

B

Ek T

μ μ α

μ

α

⎛ ⎞= minus⎜ ⎟

⎝ ⎠

=

24OLED 기초공정 이해와 실습

무기EL (p-n junction LED)

Light Emission

anode

cathodeETLEMLHTLHIL+

유기EL (polymers or small molecules)

전자수송층(ETL)

발광층(EML)정공

수송층(HTL)

양극(투명전극

ITO 유리 등)

음극(낮은 일함수 금속

Ca AlLi MgAg등)

-전자

정공

+

-+

두께 100 ~ 200 nm

Exciton

OLED OLED 작동원리작동원리

25OLED 기초공정 이해와 실습

Single-layer devices

Unbalanced carrier injection and lower efficiency

dArr

Heterostructures

ITOHILHTLEMLETLCathode(1) Lower the barrier at electrodes

Balanced carrier injection andimproved efficiency

(2) Band offsets between the layers andspace charges build up at hetero-junctionHigh carrier densitieseffective e-h capture

Multilayer StructureMultilayer Structure

Cathode

HILITO

GLASS

HTLEMLETL

-

+

26OLED 기초공정 이해와 실습

Cathode

HILITO

GLASS

HTLEMLETL

-

+

OLED Structure

N N

CH3

H3C

TPD m-MTDATA

N

N N

N

CH3

CH3

H3C

NO

NON

OAl

Alq3

Small Molecules (Fluorescence)

27OLED 기초공정 이해와 실습

OLED StructureSmall Molecules

(Phosphorescence)

NN

N

N

NN

N

N

CuN

N

NN

CuPc MTDATA

Cathode

HILITO

GLASS

HTLEML

ETL-

+

HBL

NNCH3H3C

BCP

28OLED 기초공정 이해와 실습

OLED Structure

Polymers

Cathode

ITO

GLASS

HTLEML

-

+

PEDOT

n

S O3- S O3

-S O3H S O3H S O3H S O3H

SS

SS

SS

O O

OO

O O

OO OO

n

n n

RR

PPV PF

29OLED 기초공정 이해와 실습

Cur

rent

den

sity Lum

inous Intensity

Voltage

ln V

ln J

J = qn0μVd

J = 98 εsμV2d3

Ligh

t

Current

slope = ηexte

Ex)

OLED OLED 특성특성

3 7

Diode Characteristics Rectification ratio 10 - 10 Power efficiency amp drive voltage

Light vs current

optconv ext

elec

opt opt elecext opt ext

elec elec

P hP eV

N s I IIN s I e e

νη η

η η

= =

= = rArr = times

30OLED 기초공정 이해와 실습

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

Vacuum Level

Anode

Cathode

HOMO

LUMO

Φa

Φc

EA

IP

CB

VB

Eg

에너지에너지 준위준위

31OLED 기초공정 이해와 실습

Current - Voltage Characteristics

2

16 17 3

0

0

1

diffusion voltage ~ 13 V

acceptor concentration ~ 10 - 10 cm

(~ 50 - 150 nm

2( )

Width of space charge layer 2 ( )

D

D

A

r DA

r D A

V VCV

N

C A q N V V

w V V qN

ε ε

ε ε

prop minus

= minus

= minus V = 0 )

OLED OLED 전기적전기적 특성특성

( ) Schottky equation

exp 1

ideality factor 1 1 ideal Schottky diodes B ext BJ J eV nk T V V IR

n n

⎡ ⎤= minus = minus⎣ ⎦ge =

Capacitance - Voltage Dependence

32OLED 기초공정 이해와 실습

I - V Characteristics C - V Characteristics

ITOPPVMetal Polymeric Schottky Diode

OLED OLED 전기적전기적 특성특성

33OLED 기초공정 이해와 실습

Injection Dominated Mechanisms

bull Thermionic emission

bull Tunneling

Bulk Dominated Mechanisms

bull Ohmic Conduction

bull Space Charge Limited Current Conduction

bull Space Charge Limited Current Conduction with Traps

Magnitude of Injection Barrier

전하전하 주입주입

34OLED 기초공정 이해와 실습

Thermionic Emission

Fowler-Nordheim Tunneling

2

2 2

3

exp 1 wehere exp

4 120( )

Richardson constant

bns s

B B

n B

eeVJ J J A Tk T k T

em kA m m A cm Kh

φ

π

⎡ ⎤⎛ ⎞ ⎛ ⎞minus= minus =⎢ ⎥⎜ ⎟ ⎜ ⎟

⎝ ⎠ ⎝ ⎠⎣ ⎦

= =

At low field thermionic emission at high field tunneling dominate

전하전하 주입주입

EF

Evac

-eFz(triangular shape)φ

Z=0 Z

Charge accumulationhigher the energy state `

Electron emission (F-N Tunneling)

Electron emission (Thermionic Emission)

2

3212

~ exp

( ) where 8 (2 )3

bJ EE

qb mqh

π

⎛ ⎞minus⎜ ⎟⎝ ⎠

Φ=

35OLED 기초공정 이해와 실습

Applied voltage

Lattice vibration

Localizedelectron

Hopping conductionBand-like conductionDelocalized electron

Lattice vibration(phonon)

Scattered electron

Low Mobility

bull holes μ ~10-4-10-8 Vs due to poor wave function overlap (large hopping distance)

bull electrons μ ~10-6-10-10Vs due to increased disorder and trapping at defect sites caused by impurities such as O2

rArr Build-up of space-charge density (bulk limited current)

전하전하 이동도이동도

36OLED 기초공정 이해와 실습

NoteMobility depends onElectric Field andTemperature

Mobilities of OrganicsMobilities of Organics

Alq3

37OLED 기초공정 이해와 실습

Ohmic conduction

OLEDOLED의의 전류전류

Current Dendity

current depends linearly on the bias voltageo nn qm VJd

=

2

3

0

1

2 1

(no traps)

(exponential trap distributions ( ) exp( )

one of electrodes(Ohmic contact) can supply more carriers per un

98

Current Density

SCLC condition

o

tt

r

m

m tN

VJd

T E N E kTV md T

ε ε μ

+

+ =

=

prop =

it time than can be transported through the dielectric (caused by low mobility)

Space charge limited (SCL) conduction

38OLED 기초공정 이해와 실습

2

2

3

Charge per unit area Q induced by a voltage V

Transit time across the semiconductor

9

Approximate SCLC densi

Child law (Mott- Gu

ty

Elec8

rney law)

o r

r

o rSCLC

r

VQ CVd

d dtE V

VQJt d

ε ε

μ μ

ε ε μ

= =

= =

asymp =

3 2

tric field distribution across the semiconductor

Majority space charges enhance the E field at the

3 3 ( ) at ( )2 2

enhance the injection of the cath

minority carrieode

rs (elect

V x VE x x d E dd d

= = =

rArr rons)

d

(+) (-)

x=0 x=d

Vd

15 Vd232

3)(d

xVxE =

++++

Virtual anode

-

Space Charge Limited CurrentSpace Charge Limited Current

39OLED 기초공정 이해와 실습

2

3

1

2 01

(no traps or discrete traps Mott-Gurney formula)

(exponential trap distributions ( ) exp( )

98

o rSCLC

mt

SCLC m t t

VJd

TVJ N E NmT

E kTd

ε ε μ

+

+

=

prop = =

ECB

EVB

Etrap

Discrete trapping center Exponential distributionof trapping centers

TrapTrap--Limited CurrentLimited Current

40OLED 기초공정 이해와 실습

Shen Burrows Bulovic McCarty Thompson Forrest Jpn J Appl Phys 35 L401 (1996)

ITOTPDAlq3MgAg

12

1

+

+

prop m

m

SCLC dVJ

TrapTrap--Limited CurrentLimited Current

41OLED 기초공정 이해와 실습

0

0

Activation energy at 0 Empirical parameter

Mobility at PF constant

PF

PF

E FT

T Tμβ

Δ =

=

PFPF

B eff

0

3

PFeff 0 0

( ) exp

exp( )

1 1 1with

E FFT μk T

F

qT T T

βμ

μ β

βπεε

⎛ ⎞Δ minus= minus⎜ ⎟⎜ ⎟

⎝ ⎠

equiv

= minus =

Poole Frenkel ModelPoole Frenkel Model

42OLED 기초공정 이해와 실습

1

22 2

0

0

(1)

(2)

EL F S e h

e ee he

T

h he hh

T

T rec rec e h

h eh e

h e

e hEL F S

h e

T rec

h e h e nh e EL F S EL

e h

n nJ n n nedJ n n ned

nJ

ne F

J J Je F

J Jn J J

ed n ed

η η γ

γτ

γτ

τ τ τ γ

μ

η η γμ μ

τ τ

η ηγ

minus

Φ =

minus minus =

minus minus =

lt =

=

Φ = prop

gt

= Φ = prop rArr Φ prop

EL Current RelationEL Current Relation

43OLED 기초공정 이해와 실습

Device Structure ITONPBAlq3Ca

22

21

ZZZ

fdVdQC

+minus

==πφieZiZZZ ||

))=+=

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

V0 independent of the NPB layer thickness

44OLED 기초공정 이해와 실습

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

Dashed line without interfacial charge

Wolfgang Brutting Stefan Berleb Anton G Muckl Organic Electronics 2 (2001)

Device Structure ITONPBAlq3Ca

45OLED 기초공정 이해와 실습

Langevin Recombination of carriers

bull Carriers are statistically independent therefore the e-h recombination is a random process and kinetically bimolecular

bull Total current attracted by a charge into the sphere of Coulombic capture radius rc

2

22

( ) ( )4

(4 ) 14 184

( ) (mean free path A)

n p c n pc

c cB

n p

qJ qp E qpr

qi r J Bqp r nmk T

qB a

μ μ μ μπε

ππε

μ μ λε

= + = +

= = cong asymp minus

there4 = + asympo

TkUd

BeP ~ minusProbability of dissociation

reUπε4

~2

e-

rc

Carrier RecombinationCarrier Recombination

P Langevin Ann Chem Phys 28 289 (1903)

46OLED 기초공정 이해와 실습

Electronic Processes in Organic Crystals and Polymers by MPope and C E Swenberg

ExcitonsExcitons

47OLED 기초공정 이해와 실습

C Adachi et al

Electrons and holesForm excitons

(bound e--h+ pairs)

Exciton Recombination ZoneExciton Recombination Zone

48OLED 기초공정 이해와 실습

MOLECULAR EXCITED STATESAFTER ELECTRICAL EXCITATION

Singletspin anti-symmetric

Tripletspin symmetric

25 75

MOLECULAR GROUND STATEspin anti-symmetric

Relaxation allowedfast efficientFluorescence

Relaxation disallowedslow inefficientPhosphorescence

|χ1χ2 gt = | gt

|χ1χ2 gt = | gt

|χ1χ2 gt

= | gt - | gt2

1

|χ1χ2 gt = | gt + | gt2

1ISC

Spin

OLEDOLED의의 형광형광인광인광

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 10: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

9OLED 기초공정 이해와 실습

[J R Sheats et al Science 273 884 (1996)의 자료에 최근 발전을 추가함]

LEDLED의의 발전상황발전상황

10OLED 기초공정 이해와 실습

LCD와비교

자료 한국화학연구원 정보디스플레이 기술개발 사업단

OLED

LTPS TFT

AMOLED

LC

AMLCD

CF

BL a-Si TFT LTPS TFT

SelfSelf--emittingemittingFull color DisplayFull color Display

No Backlight Thin amp Light

Less Cell Process Simple Process

No Liquid Crystal Fast Response TimeWide Viewing Angle

mm 30g 50

(~1μs)

70~80

of LCD

170170

OLED OLED 특성특성

11OLED 기초공정 이해와 실습

Display ComparisonDisplay Comparison

CRT PDP LCD OLEDLarge Size ⊙

High Resolution ⊙ ⊙

ThicknessWeight times ⊙ ⊙

Response Time times ⊙

Viewing Angle ⊙ ⊙ times ⊙

Cost ⊙ times

Color ⊙ ⊙

Power Consumption times times ⊙

Image Sticking ⊙ ⊙

Best ⊙ Good Middle Bad x

OLED

LCD Thickness amp Weight Power Consumption

CRT Cost Color Viewing angle Response time=

+

12OLED 기초공정 이해와 실습

Organic Light Emitting Display

OLED

OLEDOLED의의 분류분류

PLEDPhOLED PMOLED AMOLED

FOLED 구동방식재료(저고분자)

형광성

저분자

발광재료

인광성

저분자

발광재료

형광성

고분자

발광재료

Flexible

기판

OLED

수동구동

OLED

능동구동

OLED

Emission Direction에 따라 Bottom Top amp Transparent OLED가 있음

13OLED 기초공정 이해와 실습

저분자 고분자

박막 성막 방식 진공 열증착 Ink-jet

순도 고순도 재료 용이 고순도 재료 어려움

열 안정성 낮다 높다

작동전압 7-15v 3-7v

NO

NON

OAl

2 Types

Small Molecule

Polymer

OLEDOLED의의 재료재료

n

14OLED 기초공정 이해와 실습

Early OLED (Small Molecule)Early OLED (Small Molecule)

EL emission spectrum is sensitive to thickness of organic layerDiamine layer transports holes and blocks electrons injected from MgAg electrode

bull MgAg ndash 101bull Luminescent film - 600Aringbull Diamine ndash 750Aring

CW Tang amp SA VanSlyke Kodak Research LaboratoriesCW Tang and S A VanSlyke in Kodak Appl Phys Letter 51 913 (1987)

15OLED 기초공정 이해와 실습

Light Emitting PolymersLight Emitting Polymers

First Polymer LED (PVK-polymer)- Partridge polymer 24 733 (1983)----

With conductive polymer anode tooWeak blue light

PPV-LED- The first observation of EL was in

1989 (Burroughs et al)- Friend et al U S Patent 5247190

(1990) Cambridge University andCDT work on polymers

- poly(14-phenylene vinylene) (PPV) poly[2-(2rsquo-ethylhexyloxy)-5-methoxy-

14-phenylene vinylene] (MEH-PPV)

n

PPV

Full colour spectrum

glass substrateITO

polymer layerAl Ca Mg

16OLED 기초공정 이해와 실습

Organic Molecular CrystalsOrganic Molecular Crystals

Inorganic semiconductors Organic semiconductors

2Bohr radius Rydberg

Band transport

Exciton Binding Energy ~25meV Exciton size ~ 50A

Strong Covalent Bond

Strong e-e screening( ~11)

Strong spin-orbit cou

ε ε

εminusprop prop

bull

bull

bull

gt

gt

gt

gt

J is a good quantum numberpling

gt

Hopping transport

Exciton Binding Energy ~ 05 - 1eV E

Exciton localized on singxciton size ~ 5 - 10A

le pol y

Weak Van der Waals interactions

Weak e-e screening( ~3)ε

bull

bull

gt

gt

gt

gt mer chain

Large exchange energy between the lowest singlet and triple

S is a good quantum number

t excitons

Weak spin-orbit couplingbullgt

gt

17OLED 기초공정 이해와 실습

Conjugated PolymerConjugated Polymer

bull sp2 bonding

poly-acetylene (1958)

bull π- electrons delocalized along the chain

bull Dimerization opens an energy gap 2-3 eV (Peierls instability)

18OLED 기초공정 이해와 실습

에너지에너지 밴드밴드 갭갭

Ionization energies of the HOMO levels and binding energies of the LUMO levels for different polyacenes in the gas phase (left solid lines) and in the crystalline state (right double lines) respectively

C C

H

H

nrarrinfin

Eg=14eV

19OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Hopping model

Small polaron model

Poole-Frenkel model

Multiple trapping amp release model

Etc (Exciton model Soliton model Ishiguro modelhellip)

20OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Hopping model

1

00

In most cases T-dep of mobility

exp where = 1 2 3 4TT

αμ μ α

⎡ ⎤⎛ ⎞⎢ ⎥= minus⎜ ⎟⎢ ⎥⎝ ⎠⎣ ⎦

Conventional semiconductor Organic semiconductorconduction band

valence band

LUMO level

HOMO level

delocalized states propagating

Phonon scattering (negative)rarr mobility increases as T darr

localized states hopping

Phonon scattering (positive)rarr mobility decreases as T darr

01 ~ 1 cm2V-1s-1

21OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Small polaron model

In a conjugated molecules a charge is self-trapped by the lattice deformationrarr creation of the localized mid gap states

Ex) A polaron in Polythiophene

32 22( ) exp

2 2

where polaron binding energy electron transfer energy lattice constant

T-dep of the mobility

bB

Bb

b

Eea J k Tk TE

EJa

πμminus ⎛ ⎞

= minus⎜ ⎟⎝ ⎠h

22OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Poole-Frenkel model

Field dependent mobility at high field (E gt 105 Vcm)

- Coulomb potential near localized states is modified by the applied field

( )120

( ) (0)exp

where (0) zero field mobility

Poole-Frenkel factor mag of electric field

T-dep amp field dep of the mobility

B

qF Fk T

eF

μ μ β

μ

β πεε

⎛ ⎞= ⎜ ⎟

⎝ ⎠

=

23OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Multiple trapping amp release model

Narrow delocalized band+ localized trap level (highly concenturated)

Process1) Carriers arrive at a trap and are trapped2) Thermally activated and released

0

0

exp

where mobility in the delocalized bandDensity of delocalized band edge

Concenturation of traps

T-dep of the mobility

tD

B

Ek T

μ μ α

μ

α

⎛ ⎞= minus⎜ ⎟

⎝ ⎠

=

24OLED 기초공정 이해와 실습

무기EL (p-n junction LED)

Light Emission

anode

cathodeETLEMLHTLHIL+

유기EL (polymers or small molecules)

전자수송층(ETL)

발광층(EML)정공

수송층(HTL)

양극(투명전극

ITO 유리 등)

음극(낮은 일함수 금속

Ca AlLi MgAg등)

-전자

정공

+

-+

두께 100 ~ 200 nm

Exciton

OLED OLED 작동원리작동원리

25OLED 기초공정 이해와 실습

Single-layer devices

Unbalanced carrier injection and lower efficiency

dArr

Heterostructures

ITOHILHTLEMLETLCathode(1) Lower the barrier at electrodes

Balanced carrier injection andimproved efficiency

(2) Band offsets between the layers andspace charges build up at hetero-junctionHigh carrier densitieseffective e-h capture

Multilayer StructureMultilayer Structure

Cathode

HILITO

GLASS

HTLEMLETL

-

+

26OLED 기초공정 이해와 실습

Cathode

HILITO

GLASS

HTLEMLETL

-

+

OLED Structure

N N

CH3

H3C

TPD m-MTDATA

N

N N

N

CH3

CH3

H3C

NO

NON

OAl

Alq3

Small Molecules (Fluorescence)

27OLED 기초공정 이해와 실습

OLED StructureSmall Molecules

(Phosphorescence)

NN

N

N

NN

N

N

CuN

N

NN

CuPc MTDATA

Cathode

HILITO

GLASS

HTLEML

ETL-

+

HBL

NNCH3H3C

BCP

28OLED 기초공정 이해와 실습

OLED Structure

Polymers

Cathode

ITO

GLASS

HTLEML

-

+

PEDOT

n

S O3- S O3

-S O3H S O3H S O3H S O3H

SS

SS

SS

O O

OO

O O

OO OO

n

n n

RR

PPV PF

29OLED 기초공정 이해와 실습

Cur

rent

den

sity Lum

inous Intensity

Voltage

ln V

ln J

J = qn0μVd

J = 98 εsμV2d3

Ligh

t

Current

slope = ηexte

Ex)

OLED OLED 특성특성

3 7

Diode Characteristics Rectification ratio 10 - 10 Power efficiency amp drive voltage

Light vs current

optconv ext

elec

opt opt elecext opt ext

elec elec

P hP eV

N s I IIN s I e e

νη η

η η

= =

= = rArr = times

30OLED 기초공정 이해와 실습

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

Vacuum Level

Anode

Cathode

HOMO

LUMO

Φa

Φc

EA

IP

CB

VB

Eg

에너지에너지 준위준위

31OLED 기초공정 이해와 실습

Current - Voltage Characteristics

2

16 17 3

0

0

1

diffusion voltage ~ 13 V

acceptor concentration ~ 10 - 10 cm

(~ 50 - 150 nm

2( )

Width of space charge layer 2 ( )

D

D

A

r DA

r D A

V VCV

N

C A q N V V

w V V qN

ε ε

ε ε

prop minus

= minus

= minus V = 0 )

OLED OLED 전기적전기적 특성특성

( ) Schottky equation

exp 1

ideality factor 1 1 ideal Schottky diodes B ext BJ J eV nk T V V IR

n n

⎡ ⎤= minus = minus⎣ ⎦ge =

Capacitance - Voltage Dependence

32OLED 기초공정 이해와 실습

I - V Characteristics C - V Characteristics

ITOPPVMetal Polymeric Schottky Diode

OLED OLED 전기적전기적 특성특성

33OLED 기초공정 이해와 실습

Injection Dominated Mechanisms

bull Thermionic emission

bull Tunneling

Bulk Dominated Mechanisms

bull Ohmic Conduction

bull Space Charge Limited Current Conduction

bull Space Charge Limited Current Conduction with Traps

Magnitude of Injection Barrier

전하전하 주입주입

34OLED 기초공정 이해와 실습

Thermionic Emission

Fowler-Nordheim Tunneling

2

2 2

3

exp 1 wehere exp

4 120( )

Richardson constant

bns s

B B

n B

eeVJ J J A Tk T k T

em kA m m A cm Kh

φ

π

⎡ ⎤⎛ ⎞ ⎛ ⎞minus= minus =⎢ ⎥⎜ ⎟ ⎜ ⎟

⎝ ⎠ ⎝ ⎠⎣ ⎦

= =

At low field thermionic emission at high field tunneling dominate

전하전하 주입주입

EF

Evac

-eFz(triangular shape)φ

Z=0 Z

Charge accumulationhigher the energy state `

Electron emission (F-N Tunneling)

Electron emission (Thermionic Emission)

2

3212

~ exp

( ) where 8 (2 )3

bJ EE

qb mqh

π

⎛ ⎞minus⎜ ⎟⎝ ⎠

Φ=

35OLED 기초공정 이해와 실습

Applied voltage

Lattice vibration

Localizedelectron

Hopping conductionBand-like conductionDelocalized electron

Lattice vibration(phonon)

Scattered electron

Low Mobility

bull holes μ ~10-4-10-8 Vs due to poor wave function overlap (large hopping distance)

bull electrons μ ~10-6-10-10Vs due to increased disorder and trapping at defect sites caused by impurities such as O2

rArr Build-up of space-charge density (bulk limited current)

전하전하 이동도이동도

36OLED 기초공정 이해와 실습

NoteMobility depends onElectric Field andTemperature

Mobilities of OrganicsMobilities of Organics

Alq3

37OLED 기초공정 이해와 실습

Ohmic conduction

OLEDOLED의의 전류전류

Current Dendity

current depends linearly on the bias voltageo nn qm VJd

=

2

3

0

1

2 1

(no traps)

(exponential trap distributions ( ) exp( )

one of electrodes(Ohmic contact) can supply more carriers per un

98

Current Density

SCLC condition

o

tt

r

m

m tN

VJd

T E N E kTV md T

ε ε μ

+

+ =

=

prop =

it time than can be transported through the dielectric (caused by low mobility)

Space charge limited (SCL) conduction

38OLED 기초공정 이해와 실습

2

2

3

Charge per unit area Q induced by a voltage V

Transit time across the semiconductor

9

Approximate SCLC densi

Child law (Mott- Gu

ty

Elec8

rney law)

o r

r

o rSCLC

r

VQ CVd

d dtE V

VQJt d

ε ε

μ μ

ε ε μ

= =

= =

asymp =

3 2

tric field distribution across the semiconductor

Majority space charges enhance the E field at the

3 3 ( ) at ( )2 2

enhance the injection of the cath

minority carrieode

rs (elect

V x VE x x d E dd d

= = =

rArr rons)

d

(+) (-)

x=0 x=d

Vd

15 Vd232

3)(d

xVxE =

++++

Virtual anode

-

Space Charge Limited CurrentSpace Charge Limited Current

39OLED 기초공정 이해와 실습

2

3

1

2 01

(no traps or discrete traps Mott-Gurney formula)

(exponential trap distributions ( ) exp( )

98

o rSCLC

mt

SCLC m t t

VJd

TVJ N E NmT

E kTd

ε ε μ

+

+

=

prop = =

ECB

EVB

Etrap

Discrete trapping center Exponential distributionof trapping centers

TrapTrap--Limited CurrentLimited Current

40OLED 기초공정 이해와 실습

Shen Burrows Bulovic McCarty Thompson Forrest Jpn J Appl Phys 35 L401 (1996)

ITOTPDAlq3MgAg

12

1

+

+

prop m

m

SCLC dVJ

TrapTrap--Limited CurrentLimited Current

41OLED 기초공정 이해와 실습

0

0

Activation energy at 0 Empirical parameter

Mobility at PF constant

PF

PF

E FT

T Tμβ

Δ =

=

PFPF

B eff

0

3

PFeff 0 0

( ) exp

exp( )

1 1 1with

E FFT μk T

F

qT T T

βμ

μ β

βπεε

⎛ ⎞Δ minus= minus⎜ ⎟⎜ ⎟

⎝ ⎠

equiv

= minus =

Poole Frenkel ModelPoole Frenkel Model

42OLED 기초공정 이해와 실습

1

22 2

0

0

(1)

(2)

EL F S e h

e ee he

T

h he hh

T

T rec rec e h

h eh e

h e

e hEL F S

h e

T rec

h e h e nh e EL F S EL

e h

n nJ n n nedJ n n ned

nJ

ne F

J J Je F

J Jn J J

ed n ed

η η γ

γτ

γτ

τ τ τ γ

μ

η η γμ μ

τ τ

η ηγ

minus

Φ =

minus minus =

minus minus =

lt =

=

Φ = prop

gt

= Φ = prop rArr Φ prop

EL Current RelationEL Current Relation

43OLED 기초공정 이해와 실습

Device Structure ITONPBAlq3Ca

22

21

ZZZ

fdVdQC

+minus

==πφieZiZZZ ||

))=+=

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

V0 independent of the NPB layer thickness

44OLED 기초공정 이해와 실습

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

Dashed line without interfacial charge

Wolfgang Brutting Stefan Berleb Anton G Muckl Organic Electronics 2 (2001)

Device Structure ITONPBAlq3Ca

45OLED 기초공정 이해와 실습

Langevin Recombination of carriers

bull Carriers are statistically independent therefore the e-h recombination is a random process and kinetically bimolecular

bull Total current attracted by a charge into the sphere of Coulombic capture radius rc

2

22

( ) ( )4

(4 ) 14 184

( ) (mean free path A)

n p c n pc

c cB

n p

qJ qp E qpr

qi r J Bqp r nmk T

qB a

μ μ μ μπε

ππε

μ μ λε

= + = +

= = cong asymp minus

there4 = + asympo

TkUd

BeP ~ minusProbability of dissociation

reUπε4

~2

e-

rc

Carrier RecombinationCarrier Recombination

P Langevin Ann Chem Phys 28 289 (1903)

46OLED 기초공정 이해와 실습

Electronic Processes in Organic Crystals and Polymers by MPope and C E Swenberg

ExcitonsExcitons

47OLED 기초공정 이해와 실습

C Adachi et al

Electrons and holesForm excitons

(bound e--h+ pairs)

Exciton Recombination ZoneExciton Recombination Zone

48OLED 기초공정 이해와 실습

MOLECULAR EXCITED STATESAFTER ELECTRICAL EXCITATION

Singletspin anti-symmetric

Tripletspin symmetric

25 75

MOLECULAR GROUND STATEspin anti-symmetric

Relaxation allowedfast efficientFluorescence

Relaxation disallowedslow inefficientPhosphorescence

|χ1χ2 gt = | gt

|χ1χ2 gt = | gt

|χ1χ2 gt

= | gt - | gt2

1

|χ1χ2 gt = | gt + | gt2

1ISC

Spin

OLEDOLED의의 형광형광인광인광

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 11: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

10OLED 기초공정 이해와 실습

LCD와비교

자료 한국화학연구원 정보디스플레이 기술개발 사업단

OLED

LTPS TFT

AMOLED

LC

AMLCD

CF

BL a-Si TFT LTPS TFT

SelfSelf--emittingemittingFull color DisplayFull color Display

No Backlight Thin amp Light

Less Cell Process Simple Process

No Liquid Crystal Fast Response TimeWide Viewing Angle

mm 30g 50

(~1μs)

70~80

of LCD

170170

OLED OLED 특성특성

11OLED 기초공정 이해와 실습

Display ComparisonDisplay Comparison

CRT PDP LCD OLEDLarge Size ⊙

High Resolution ⊙ ⊙

ThicknessWeight times ⊙ ⊙

Response Time times ⊙

Viewing Angle ⊙ ⊙ times ⊙

Cost ⊙ times

Color ⊙ ⊙

Power Consumption times times ⊙

Image Sticking ⊙ ⊙

Best ⊙ Good Middle Bad x

OLED

LCD Thickness amp Weight Power Consumption

CRT Cost Color Viewing angle Response time=

+

12OLED 기초공정 이해와 실습

Organic Light Emitting Display

OLED

OLEDOLED의의 분류분류

PLEDPhOLED PMOLED AMOLED

FOLED 구동방식재료(저고분자)

형광성

저분자

발광재료

인광성

저분자

발광재료

형광성

고분자

발광재료

Flexible

기판

OLED

수동구동

OLED

능동구동

OLED

Emission Direction에 따라 Bottom Top amp Transparent OLED가 있음

13OLED 기초공정 이해와 실습

저분자 고분자

박막 성막 방식 진공 열증착 Ink-jet

순도 고순도 재료 용이 고순도 재료 어려움

열 안정성 낮다 높다

작동전압 7-15v 3-7v

NO

NON

OAl

2 Types

Small Molecule

Polymer

OLEDOLED의의 재료재료

n

14OLED 기초공정 이해와 실습

Early OLED (Small Molecule)Early OLED (Small Molecule)

EL emission spectrum is sensitive to thickness of organic layerDiamine layer transports holes and blocks electrons injected from MgAg electrode

bull MgAg ndash 101bull Luminescent film - 600Aringbull Diamine ndash 750Aring

CW Tang amp SA VanSlyke Kodak Research LaboratoriesCW Tang and S A VanSlyke in Kodak Appl Phys Letter 51 913 (1987)

15OLED 기초공정 이해와 실습

Light Emitting PolymersLight Emitting Polymers

First Polymer LED (PVK-polymer)- Partridge polymer 24 733 (1983)----

With conductive polymer anode tooWeak blue light

PPV-LED- The first observation of EL was in

1989 (Burroughs et al)- Friend et al U S Patent 5247190

(1990) Cambridge University andCDT work on polymers

- poly(14-phenylene vinylene) (PPV) poly[2-(2rsquo-ethylhexyloxy)-5-methoxy-

14-phenylene vinylene] (MEH-PPV)

n

PPV

Full colour spectrum

glass substrateITO

polymer layerAl Ca Mg

16OLED 기초공정 이해와 실습

Organic Molecular CrystalsOrganic Molecular Crystals

Inorganic semiconductors Organic semiconductors

2Bohr radius Rydberg

Band transport

Exciton Binding Energy ~25meV Exciton size ~ 50A

Strong Covalent Bond

Strong e-e screening( ~11)

Strong spin-orbit cou

ε ε

εminusprop prop

bull

bull

bull

gt

gt

gt

gt

J is a good quantum numberpling

gt

Hopping transport

Exciton Binding Energy ~ 05 - 1eV E

Exciton localized on singxciton size ~ 5 - 10A

le pol y

Weak Van der Waals interactions

Weak e-e screening( ~3)ε

bull

bull

gt

gt

gt

gt mer chain

Large exchange energy between the lowest singlet and triple

S is a good quantum number

t excitons

Weak spin-orbit couplingbullgt

gt

17OLED 기초공정 이해와 실습

Conjugated PolymerConjugated Polymer

bull sp2 bonding

poly-acetylene (1958)

bull π- electrons delocalized along the chain

bull Dimerization opens an energy gap 2-3 eV (Peierls instability)

18OLED 기초공정 이해와 실습

에너지에너지 밴드밴드 갭갭

Ionization energies of the HOMO levels and binding energies of the LUMO levels for different polyacenes in the gas phase (left solid lines) and in the crystalline state (right double lines) respectively

C C

H

H

nrarrinfin

Eg=14eV

19OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Hopping model

Small polaron model

Poole-Frenkel model

Multiple trapping amp release model

Etc (Exciton model Soliton model Ishiguro modelhellip)

20OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Hopping model

1

00

In most cases T-dep of mobility

exp where = 1 2 3 4TT

αμ μ α

⎡ ⎤⎛ ⎞⎢ ⎥= minus⎜ ⎟⎢ ⎥⎝ ⎠⎣ ⎦

Conventional semiconductor Organic semiconductorconduction band

valence band

LUMO level

HOMO level

delocalized states propagating

Phonon scattering (negative)rarr mobility increases as T darr

localized states hopping

Phonon scattering (positive)rarr mobility decreases as T darr

01 ~ 1 cm2V-1s-1

21OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Small polaron model

In a conjugated molecules a charge is self-trapped by the lattice deformationrarr creation of the localized mid gap states

Ex) A polaron in Polythiophene

32 22( ) exp

2 2

where polaron binding energy electron transfer energy lattice constant

T-dep of the mobility

bB

Bb

b

Eea J k Tk TE

EJa

πμminus ⎛ ⎞

= minus⎜ ⎟⎝ ⎠h

22OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Poole-Frenkel model

Field dependent mobility at high field (E gt 105 Vcm)

- Coulomb potential near localized states is modified by the applied field

( )120

( ) (0)exp

where (0) zero field mobility

Poole-Frenkel factor mag of electric field

T-dep amp field dep of the mobility

B

qF Fk T

eF

μ μ β

μ

β πεε

⎛ ⎞= ⎜ ⎟

⎝ ⎠

=

23OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Multiple trapping amp release model

Narrow delocalized band+ localized trap level (highly concenturated)

Process1) Carriers arrive at a trap and are trapped2) Thermally activated and released

0

0

exp

where mobility in the delocalized bandDensity of delocalized band edge

Concenturation of traps

T-dep of the mobility

tD

B

Ek T

μ μ α

μ

α

⎛ ⎞= minus⎜ ⎟

⎝ ⎠

=

24OLED 기초공정 이해와 실습

무기EL (p-n junction LED)

Light Emission

anode

cathodeETLEMLHTLHIL+

유기EL (polymers or small molecules)

전자수송층(ETL)

발광층(EML)정공

수송층(HTL)

양극(투명전극

ITO 유리 등)

음극(낮은 일함수 금속

Ca AlLi MgAg등)

-전자

정공

+

-+

두께 100 ~ 200 nm

Exciton

OLED OLED 작동원리작동원리

25OLED 기초공정 이해와 실습

Single-layer devices

Unbalanced carrier injection and lower efficiency

dArr

Heterostructures

ITOHILHTLEMLETLCathode(1) Lower the barrier at electrodes

Balanced carrier injection andimproved efficiency

(2) Band offsets between the layers andspace charges build up at hetero-junctionHigh carrier densitieseffective e-h capture

Multilayer StructureMultilayer Structure

Cathode

HILITO

GLASS

HTLEMLETL

-

+

26OLED 기초공정 이해와 실습

Cathode

HILITO

GLASS

HTLEMLETL

-

+

OLED Structure

N N

CH3

H3C

TPD m-MTDATA

N

N N

N

CH3

CH3

H3C

NO

NON

OAl

Alq3

Small Molecules (Fluorescence)

27OLED 기초공정 이해와 실습

OLED StructureSmall Molecules

(Phosphorescence)

NN

N

N

NN

N

N

CuN

N

NN

CuPc MTDATA

Cathode

HILITO

GLASS

HTLEML

ETL-

+

HBL

NNCH3H3C

BCP

28OLED 기초공정 이해와 실습

OLED Structure

Polymers

Cathode

ITO

GLASS

HTLEML

-

+

PEDOT

n

S O3- S O3

-S O3H S O3H S O3H S O3H

SS

SS

SS

O O

OO

O O

OO OO

n

n n

RR

PPV PF

29OLED 기초공정 이해와 실습

Cur

rent

den

sity Lum

inous Intensity

Voltage

ln V

ln J

J = qn0μVd

J = 98 εsμV2d3

Ligh

t

Current

slope = ηexte

Ex)

OLED OLED 특성특성

3 7

Diode Characteristics Rectification ratio 10 - 10 Power efficiency amp drive voltage

Light vs current

optconv ext

elec

opt opt elecext opt ext

elec elec

P hP eV

N s I IIN s I e e

νη η

η η

= =

= = rArr = times

30OLED 기초공정 이해와 실습

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

Vacuum Level

Anode

Cathode

HOMO

LUMO

Φa

Φc

EA

IP

CB

VB

Eg

에너지에너지 준위준위

31OLED 기초공정 이해와 실습

Current - Voltage Characteristics

2

16 17 3

0

0

1

diffusion voltage ~ 13 V

acceptor concentration ~ 10 - 10 cm

(~ 50 - 150 nm

2( )

Width of space charge layer 2 ( )

D

D

A

r DA

r D A

V VCV

N

C A q N V V

w V V qN

ε ε

ε ε

prop minus

= minus

= minus V = 0 )

OLED OLED 전기적전기적 특성특성

( ) Schottky equation

exp 1

ideality factor 1 1 ideal Schottky diodes B ext BJ J eV nk T V V IR

n n

⎡ ⎤= minus = minus⎣ ⎦ge =

Capacitance - Voltage Dependence

32OLED 기초공정 이해와 실습

I - V Characteristics C - V Characteristics

ITOPPVMetal Polymeric Schottky Diode

OLED OLED 전기적전기적 특성특성

33OLED 기초공정 이해와 실습

Injection Dominated Mechanisms

bull Thermionic emission

bull Tunneling

Bulk Dominated Mechanisms

bull Ohmic Conduction

bull Space Charge Limited Current Conduction

bull Space Charge Limited Current Conduction with Traps

Magnitude of Injection Barrier

전하전하 주입주입

34OLED 기초공정 이해와 실습

Thermionic Emission

Fowler-Nordheim Tunneling

2

2 2

3

exp 1 wehere exp

4 120( )

Richardson constant

bns s

B B

n B

eeVJ J J A Tk T k T

em kA m m A cm Kh

φ

π

⎡ ⎤⎛ ⎞ ⎛ ⎞minus= minus =⎢ ⎥⎜ ⎟ ⎜ ⎟

⎝ ⎠ ⎝ ⎠⎣ ⎦

= =

At low field thermionic emission at high field tunneling dominate

전하전하 주입주입

EF

Evac

-eFz(triangular shape)φ

Z=0 Z

Charge accumulationhigher the energy state `

Electron emission (F-N Tunneling)

Electron emission (Thermionic Emission)

2

3212

~ exp

( ) where 8 (2 )3

bJ EE

qb mqh

π

⎛ ⎞minus⎜ ⎟⎝ ⎠

Φ=

35OLED 기초공정 이해와 실습

Applied voltage

Lattice vibration

Localizedelectron

Hopping conductionBand-like conductionDelocalized electron

Lattice vibration(phonon)

Scattered electron

Low Mobility

bull holes μ ~10-4-10-8 Vs due to poor wave function overlap (large hopping distance)

bull electrons μ ~10-6-10-10Vs due to increased disorder and trapping at defect sites caused by impurities such as O2

rArr Build-up of space-charge density (bulk limited current)

전하전하 이동도이동도

36OLED 기초공정 이해와 실습

NoteMobility depends onElectric Field andTemperature

Mobilities of OrganicsMobilities of Organics

Alq3

37OLED 기초공정 이해와 실습

Ohmic conduction

OLEDOLED의의 전류전류

Current Dendity

current depends linearly on the bias voltageo nn qm VJd

=

2

3

0

1

2 1

(no traps)

(exponential trap distributions ( ) exp( )

one of electrodes(Ohmic contact) can supply more carriers per un

98

Current Density

SCLC condition

o

tt

r

m

m tN

VJd

T E N E kTV md T

ε ε μ

+

+ =

=

prop =

it time than can be transported through the dielectric (caused by low mobility)

Space charge limited (SCL) conduction

38OLED 기초공정 이해와 실습

2

2

3

Charge per unit area Q induced by a voltage V

Transit time across the semiconductor

9

Approximate SCLC densi

Child law (Mott- Gu

ty

Elec8

rney law)

o r

r

o rSCLC

r

VQ CVd

d dtE V

VQJt d

ε ε

μ μ

ε ε μ

= =

= =

asymp =

3 2

tric field distribution across the semiconductor

Majority space charges enhance the E field at the

3 3 ( ) at ( )2 2

enhance the injection of the cath

minority carrieode

rs (elect

V x VE x x d E dd d

= = =

rArr rons)

d

(+) (-)

x=0 x=d

Vd

15 Vd232

3)(d

xVxE =

++++

Virtual anode

-

Space Charge Limited CurrentSpace Charge Limited Current

39OLED 기초공정 이해와 실습

2

3

1

2 01

(no traps or discrete traps Mott-Gurney formula)

(exponential trap distributions ( ) exp( )

98

o rSCLC

mt

SCLC m t t

VJd

TVJ N E NmT

E kTd

ε ε μ

+

+

=

prop = =

ECB

EVB

Etrap

Discrete trapping center Exponential distributionof trapping centers

TrapTrap--Limited CurrentLimited Current

40OLED 기초공정 이해와 실습

Shen Burrows Bulovic McCarty Thompson Forrest Jpn J Appl Phys 35 L401 (1996)

ITOTPDAlq3MgAg

12

1

+

+

prop m

m

SCLC dVJ

TrapTrap--Limited CurrentLimited Current

41OLED 기초공정 이해와 실습

0

0

Activation energy at 0 Empirical parameter

Mobility at PF constant

PF

PF

E FT

T Tμβ

Δ =

=

PFPF

B eff

0

3

PFeff 0 0

( ) exp

exp( )

1 1 1with

E FFT μk T

F

qT T T

βμ

μ β

βπεε

⎛ ⎞Δ minus= minus⎜ ⎟⎜ ⎟

⎝ ⎠

equiv

= minus =

Poole Frenkel ModelPoole Frenkel Model

42OLED 기초공정 이해와 실습

1

22 2

0

0

(1)

(2)

EL F S e h

e ee he

T

h he hh

T

T rec rec e h

h eh e

h e

e hEL F S

h e

T rec

h e h e nh e EL F S EL

e h

n nJ n n nedJ n n ned

nJ

ne F

J J Je F

J Jn J J

ed n ed

η η γ

γτ

γτ

τ τ τ γ

μ

η η γμ μ

τ τ

η ηγ

minus

Φ =

minus minus =

minus minus =

lt =

=

Φ = prop

gt

= Φ = prop rArr Φ prop

EL Current RelationEL Current Relation

43OLED 기초공정 이해와 실습

Device Structure ITONPBAlq3Ca

22

21

ZZZ

fdVdQC

+minus

==πφieZiZZZ ||

))=+=

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

V0 independent of the NPB layer thickness

44OLED 기초공정 이해와 실습

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

Dashed line without interfacial charge

Wolfgang Brutting Stefan Berleb Anton G Muckl Organic Electronics 2 (2001)

Device Structure ITONPBAlq3Ca

45OLED 기초공정 이해와 실습

Langevin Recombination of carriers

bull Carriers are statistically independent therefore the e-h recombination is a random process and kinetically bimolecular

bull Total current attracted by a charge into the sphere of Coulombic capture radius rc

2

22

( ) ( )4

(4 ) 14 184

( ) (mean free path A)

n p c n pc

c cB

n p

qJ qp E qpr

qi r J Bqp r nmk T

qB a

μ μ μ μπε

ππε

μ μ λε

= + = +

= = cong asymp minus

there4 = + asympo

TkUd

BeP ~ minusProbability of dissociation

reUπε4

~2

e-

rc

Carrier RecombinationCarrier Recombination

P Langevin Ann Chem Phys 28 289 (1903)

46OLED 기초공정 이해와 실습

Electronic Processes in Organic Crystals and Polymers by MPope and C E Swenberg

ExcitonsExcitons

47OLED 기초공정 이해와 실습

C Adachi et al

Electrons and holesForm excitons

(bound e--h+ pairs)

Exciton Recombination ZoneExciton Recombination Zone

48OLED 기초공정 이해와 실습

MOLECULAR EXCITED STATESAFTER ELECTRICAL EXCITATION

Singletspin anti-symmetric

Tripletspin symmetric

25 75

MOLECULAR GROUND STATEspin anti-symmetric

Relaxation allowedfast efficientFluorescence

Relaxation disallowedslow inefficientPhosphorescence

|χ1χ2 gt = | gt

|χ1χ2 gt = | gt

|χ1χ2 gt

= | gt - | gt2

1

|χ1χ2 gt = | gt + | gt2

1ISC

Spin

OLEDOLED의의 형광형광인광인광

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 12: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

11OLED 기초공정 이해와 실습

Display ComparisonDisplay Comparison

CRT PDP LCD OLEDLarge Size ⊙

High Resolution ⊙ ⊙

ThicknessWeight times ⊙ ⊙

Response Time times ⊙

Viewing Angle ⊙ ⊙ times ⊙

Cost ⊙ times

Color ⊙ ⊙

Power Consumption times times ⊙

Image Sticking ⊙ ⊙

Best ⊙ Good Middle Bad x

OLED

LCD Thickness amp Weight Power Consumption

CRT Cost Color Viewing angle Response time=

+

12OLED 기초공정 이해와 실습

Organic Light Emitting Display

OLED

OLEDOLED의의 분류분류

PLEDPhOLED PMOLED AMOLED

FOLED 구동방식재료(저고분자)

형광성

저분자

발광재료

인광성

저분자

발광재료

형광성

고분자

발광재료

Flexible

기판

OLED

수동구동

OLED

능동구동

OLED

Emission Direction에 따라 Bottom Top amp Transparent OLED가 있음

13OLED 기초공정 이해와 실습

저분자 고분자

박막 성막 방식 진공 열증착 Ink-jet

순도 고순도 재료 용이 고순도 재료 어려움

열 안정성 낮다 높다

작동전압 7-15v 3-7v

NO

NON

OAl

2 Types

Small Molecule

Polymer

OLEDOLED의의 재료재료

n

14OLED 기초공정 이해와 실습

Early OLED (Small Molecule)Early OLED (Small Molecule)

EL emission spectrum is sensitive to thickness of organic layerDiamine layer transports holes and blocks electrons injected from MgAg electrode

bull MgAg ndash 101bull Luminescent film - 600Aringbull Diamine ndash 750Aring

CW Tang amp SA VanSlyke Kodak Research LaboratoriesCW Tang and S A VanSlyke in Kodak Appl Phys Letter 51 913 (1987)

15OLED 기초공정 이해와 실습

Light Emitting PolymersLight Emitting Polymers

First Polymer LED (PVK-polymer)- Partridge polymer 24 733 (1983)----

With conductive polymer anode tooWeak blue light

PPV-LED- The first observation of EL was in

1989 (Burroughs et al)- Friend et al U S Patent 5247190

(1990) Cambridge University andCDT work on polymers

- poly(14-phenylene vinylene) (PPV) poly[2-(2rsquo-ethylhexyloxy)-5-methoxy-

14-phenylene vinylene] (MEH-PPV)

n

PPV

Full colour spectrum

glass substrateITO

polymer layerAl Ca Mg

16OLED 기초공정 이해와 실습

Organic Molecular CrystalsOrganic Molecular Crystals

Inorganic semiconductors Organic semiconductors

2Bohr radius Rydberg

Band transport

Exciton Binding Energy ~25meV Exciton size ~ 50A

Strong Covalent Bond

Strong e-e screening( ~11)

Strong spin-orbit cou

ε ε

εminusprop prop

bull

bull

bull

gt

gt

gt

gt

J is a good quantum numberpling

gt

Hopping transport

Exciton Binding Energy ~ 05 - 1eV E

Exciton localized on singxciton size ~ 5 - 10A

le pol y

Weak Van der Waals interactions

Weak e-e screening( ~3)ε

bull

bull

gt

gt

gt

gt mer chain

Large exchange energy between the lowest singlet and triple

S is a good quantum number

t excitons

Weak spin-orbit couplingbullgt

gt

17OLED 기초공정 이해와 실습

Conjugated PolymerConjugated Polymer

bull sp2 bonding

poly-acetylene (1958)

bull π- electrons delocalized along the chain

bull Dimerization opens an energy gap 2-3 eV (Peierls instability)

18OLED 기초공정 이해와 실습

에너지에너지 밴드밴드 갭갭

Ionization energies of the HOMO levels and binding energies of the LUMO levels for different polyacenes in the gas phase (left solid lines) and in the crystalline state (right double lines) respectively

C C

H

H

nrarrinfin

Eg=14eV

19OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Hopping model

Small polaron model

Poole-Frenkel model

Multiple trapping amp release model

Etc (Exciton model Soliton model Ishiguro modelhellip)

20OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Hopping model

1

00

In most cases T-dep of mobility

exp where = 1 2 3 4TT

αμ μ α

⎡ ⎤⎛ ⎞⎢ ⎥= minus⎜ ⎟⎢ ⎥⎝ ⎠⎣ ⎦

Conventional semiconductor Organic semiconductorconduction band

valence band

LUMO level

HOMO level

delocalized states propagating

Phonon scattering (negative)rarr mobility increases as T darr

localized states hopping

Phonon scattering (positive)rarr mobility decreases as T darr

01 ~ 1 cm2V-1s-1

21OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Small polaron model

In a conjugated molecules a charge is self-trapped by the lattice deformationrarr creation of the localized mid gap states

Ex) A polaron in Polythiophene

32 22( ) exp

2 2

where polaron binding energy electron transfer energy lattice constant

T-dep of the mobility

bB

Bb

b

Eea J k Tk TE

EJa

πμminus ⎛ ⎞

= minus⎜ ⎟⎝ ⎠h

22OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Poole-Frenkel model

Field dependent mobility at high field (E gt 105 Vcm)

- Coulomb potential near localized states is modified by the applied field

( )120

( ) (0)exp

where (0) zero field mobility

Poole-Frenkel factor mag of electric field

T-dep amp field dep of the mobility

B

qF Fk T

eF

μ μ β

μ

β πεε

⎛ ⎞= ⎜ ⎟

⎝ ⎠

=

23OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Multiple trapping amp release model

Narrow delocalized band+ localized trap level (highly concenturated)

Process1) Carriers arrive at a trap and are trapped2) Thermally activated and released

0

0

exp

where mobility in the delocalized bandDensity of delocalized band edge

Concenturation of traps

T-dep of the mobility

tD

B

Ek T

μ μ α

μ

α

⎛ ⎞= minus⎜ ⎟

⎝ ⎠

=

24OLED 기초공정 이해와 실습

무기EL (p-n junction LED)

Light Emission

anode

cathodeETLEMLHTLHIL+

유기EL (polymers or small molecules)

전자수송층(ETL)

발광층(EML)정공

수송층(HTL)

양극(투명전극

ITO 유리 등)

음극(낮은 일함수 금속

Ca AlLi MgAg등)

-전자

정공

+

-+

두께 100 ~ 200 nm

Exciton

OLED OLED 작동원리작동원리

25OLED 기초공정 이해와 실습

Single-layer devices

Unbalanced carrier injection and lower efficiency

dArr

Heterostructures

ITOHILHTLEMLETLCathode(1) Lower the barrier at electrodes

Balanced carrier injection andimproved efficiency

(2) Band offsets between the layers andspace charges build up at hetero-junctionHigh carrier densitieseffective e-h capture

Multilayer StructureMultilayer Structure

Cathode

HILITO

GLASS

HTLEMLETL

-

+

26OLED 기초공정 이해와 실습

Cathode

HILITO

GLASS

HTLEMLETL

-

+

OLED Structure

N N

CH3

H3C

TPD m-MTDATA

N

N N

N

CH3

CH3

H3C

NO

NON

OAl

Alq3

Small Molecules (Fluorescence)

27OLED 기초공정 이해와 실습

OLED StructureSmall Molecules

(Phosphorescence)

NN

N

N

NN

N

N

CuN

N

NN

CuPc MTDATA

Cathode

HILITO

GLASS

HTLEML

ETL-

+

HBL

NNCH3H3C

BCP

28OLED 기초공정 이해와 실습

OLED Structure

Polymers

Cathode

ITO

GLASS

HTLEML

-

+

PEDOT

n

S O3- S O3

-S O3H S O3H S O3H S O3H

SS

SS

SS

O O

OO

O O

OO OO

n

n n

RR

PPV PF

29OLED 기초공정 이해와 실습

Cur

rent

den

sity Lum

inous Intensity

Voltage

ln V

ln J

J = qn0μVd

J = 98 εsμV2d3

Ligh

t

Current

slope = ηexte

Ex)

OLED OLED 특성특성

3 7

Diode Characteristics Rectification ratio 10 - 10 Power efficiency amp drive voltage

Light vs current

optconv ext

elec

opt opt elecext opt ext

elec elec

P hP eV

N s I IIN s I e e

νη η

η η

= =

= = rArr = times

30OLED 기초공정 이해와 실습

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

Vacuum Level

Anode

Cathode

HOMO

LUMO

Φa

Φc

EA

IP

CB

VB

Eg

에너지에너지 준위준위

31OLED 기초공정 이해와 실습

Current - Voltage Characteristics

2

16 17 3

0

0

1

diffusion voltage ~ 13 V

acceptor concentration ~ 10 - 10 cm

(~ 50 - 150 nm

2( )

Width of space charge layer 2 ( )

D

D

A

r DA

r D A

V VCV

N

C A q N V V

w V V qN

ε ε

ε ε

prop minus

= minus

= minus V = 0 )

OLED OLED 전기적전기적 특성특성

( ) Schottky equation

exp 1

ideality factor 1 1 ideal Schottky diodes B ext BJ J eV nk T V V IR

n n

⎡ ⎤= minus = minus⎣ ⎦ge =

Capacitance - Voltage Dependence

32OLED 기초공정 이해와 실습

I - V Characteristics C - V Characteristics

ITOPPVMetal Polymeric Schottky Diode

OLED OLED 전기적전기적 특성특성

33OLED 기초공정 이해와 실습

Injection Dominated Mechanisms

bull Thermionic emission

bull Tunneling

Bulk Dominated Mechanisms

bull Ohmic Conduction

bull Space Charge Limited Current Conduction

bull Space Charge Limited Current Conduction with Traps

Magnitude of Injection Barrier

전하전하 주입주입

34OLED 기초공정 이해와 실습

Thermionic Emission

Fowler-Nordheim Tunneling

2

2 2

3

exp 1 wehere exp

4 120( )

Richardson constant

bns s

B B

n B

eeVJ J J A Tk T k T

em kA m m A cm Kh

φ

π

⎡ ⎤⎛ ⎞ ⎛ ⎞minus= minus =⎢ ⎥⎜ ⎟ ⎜ ⎟

⎝ ⎠ ⎝ ⎠⎣ ⎦

= =

At low field thermionic emission at high field tunneling dominate

전하전하 주입주입

EF

Evac

-eFz(triangular shape)φ

Z=0 Z

Charge accumulationhigher the energy state `

Electron emission (F-N Tunneling)

Electron emission (Thermionic Emission)

2

3212

~ exp

( ) where 8 (2 )3

bJ EE

qb mqh

π

⎛ ⎞minus⎜ ⎟⎝ ⎠

Φ=

35OLED 기초공정 이해와 실습

Applied voltage

Lattice vibration

Localizedelectron

Hopping conductionBand-like conductionDelocalized electron

Lattice vibration(phonon)

Scattered electron

Low Mobility

bull holes μ ~10-4-10-8 Vs due to poor wave function overlap (large hopping distance)

bull electrons μ ~10-6-10-10Vs due to increased disorder and trapping at defect sites caused by impurities such as O2

rArr Build-up of space-charge density (bulk limited current)

전하전하 이동도이동도

36OLED 기초공정 이해와 실습

NoteMobility depends onElectric Field andTemperature

Mobilities of OrganicsMobilities of Organics

Alq3

37OLED 기초공정 이해와 실습

Ohmic conduction

OLEDOLED의의 전류전류

Current Dendity

current depends linearly on the bias voltageo nn qm VJd

=

2

3

0

1

2 1

(no traps)

(exponential trap distributions ( ) exp( )

one of electrodes(Ohmic contact) can supply more carriers per un

98

Current Density

SCLC condition

o

tt

r

m

m tN

VJd

T E N E kTV md T

ε ε μ

+

+ =

=

prop =

it time than can be transported through the dielectric (caused by low mobility)

Space charge limited (SCL) conduction

38OLED 기초공정 이해와 실습

2

2

3

Charge per unit area Q induced by a voltage V

Transit time across the semiconductor

9

Approximate SCLC densi

Child law (Mott- Gu

ty

Elec8

rney law)

o r

r

o rSCLC

r

VQ CVd

d dtE V

VQJt d

ε ε

μ μ

ε ε μ

= =

= =

asymp =

3 2

tric field distribution across the semiconductor

Majority space charges enhance the E field at the

3 3 ( ) at ( )2 2

enhance the injection of the cath

minority carrieode

rs (elect

V x VE x x d E dd d

= = =

rArr rons)

d

(+) (-)

x=0 x=d

Vd

15 Vd232

3)(d

xVxE =

++++

Virtual anode

-

Space Charge Limited CurrentSpace Charge Limited Current

39OLED 기초공정 이해와 실습

2

3

1

2 01

(no traps or discrete traps Mott-Gurney formula)

(exponential trap distributions ( ) exp( )

98

o rSCLC

mt

SCLC m t t

VJd

TVJ N E NmT

E kTd

ε ε μ

+

+

=

prop = =

ECB

EVB

Etrap

Discrete trapping center Exponential distributionof trapping centers

TrapTrap--Limited CurrentLimited Current

40OLED 기초공정 이해와 실습

Shen Burrows Bulovic McCarty Thompson Forrest Jpn J Appl Phys 35 L401 (1996)

ITOTPDAlq3MgAg

12

1

+

+

prop m

m

SCLC dVJ

TrapTrap--Limited CurrentLimited Current

41OLED 기초공정 이해와 실습

0

0

Activation energy at 0 Empirical parameter

Mobility at PF constant

PF

PF

E FT

T Tμβ

Δ =

=

PFPF

B eff

0

3

PFeff 0 0

( ) exp

exp( )

1 1 1with

E FFT μk T

F

qT T T

βμ

μ β

βπεε

⎛ ⎞Δ minus= minus⎜ ⎟⎜ ⎟

⎝ ⎠

equiv

= minus =

Poole Frenkel ModelPoole Frenkel Model

42OLED 기초공정 이해와 실습

1

22 2

0

0

(1)

(2)

EL F S e h

e ee he

T

h he hh

T

T rec rec e h

h eh e

h e

e hEL F S

h e

T rec

h e h e nh e EL F S EL

e h

n nJ n n nedJ n n ned

nJ

ne F

J J Je F

J Jn J J

ed n ed

η η γ

γτ

γτ

τ τ τ γ

μ

η η γμ μ

τ τ

η ηγ

minus

Φ =

minus minus =

minus minus =

lt =

=

Φ = prop

gt

= Φ = prop rArr Φ prop

EL Current RelationEL Current Relation

43OLED 기초공정 이해와 실습

Device Structure ITONPBAlq3Ca

22

21

ZZZ

fdVdQC

+minus

==πφieZiZZZ ||

))=+=

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

V0 independent of the NPB layer thickness

44OLED 기초공정 이해와 실습

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

Dashed line without interfacial charge

Wolfgang Brutting Stefan Berleb Anton G Muckl Organic Electronics 2 (2001)

Device Structure ITONPBAlq3Ca

45OLED 기초공정 이해와 실습

Langevin Recombination of carriers

bull Carriers are statistically independent therefore the e-h recombination is a random process and kinetically bimolecular

bull Total current attracted by a charge into the sphere of Coulombic capture radius rc

2

22

( ) ( )4

(4 ) 14 184

( ) (mean free path A)

n p c n pc

c cB

n p

qJ qp E qpr

qi r J Bqp r nmk T

qB a

μ μ μ μπε

ππε

μ μ λε

= + = +

= = cong asymp minus

there4 = + asympo

TkUd

BeP ~ minusProbability of dissociation

reUπε4

~2

e-

rc

Carrier RecombinationCarrier Recombination

P Langevin Ann Chem Phys 28 289 (1903)

46OLED 기초공정 이해와 실습

Electronic Processes in Organic Crystals and Polymers by MPope and C E Swenberg

ExcitonsExcitons

47OLED 기초공정 이해와 실습

C Adachi et al

Electrons and holesForm excitons

(bound e--h+ pairs)

Exciton Recombination ZoneExciton Recombination Zone

48OLED 기초공정 이해와 실습

MOLECULAR EXCITED STATESAFTER ELECTRICAL EXCITATION

Singletspin anti-symmetric

Tripletspin symmetric

25 75

MOLECULAR GROUND STATEspin anti-symmetric

Relaxation allowedfast efficientFluorescence

Relaxation disallowedslow inefficientPhosphorescence

|χ1χ2 gt = | gt

|χ1χ2 gt = | gt

|χ1χ2 gt

= | gt - | gt2

1

|χ1χ2 gt = | gt + | gt2

1ISC

Spin

OLEDOLED의의 형광형광인광인광

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 13: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

12OLED 기초공정 이해와 실습

Organic Light Emitting Display

OLED

OLEDOLED의의 분류분류

PLEDPhOLED PMOLED AMOLED

FOLED 구동방식재료(저고분자)

형광성

저분자

발광재료

인광성

저분자

발광재료

형광성

고분자

발광재료

Flexible

기판

OLED

수동구동

OLED

능동구동

OLED

Emission Direction에 따라 Bottom Top amp Transparent OLED가 있음

13OLED 기초공정 이해와 실습

저분자 고분자

박막 성막 방식 진공 열증착 Ink-jet

순도 고순도 재료 용이 고순도 재료 어려움

열 안정성 낮다 높다

작동전압 7-15v 3-7v

NO

NON

OAl

2 Types

Small Molecule

Polymer

OLEDOLED의의 재료재료

n

14OLED 기초공정 이해와 실습

Early OLED (Small Molecule)Early OLED (Small Molecule)

EL emission spectrum is sensitive to thickness of organic layerDiamine layer transports holes and blocks electrons injected from MgAg electrode

bull MgAg ndash 101bull Luminescent film - 600Aringbull Diamine ndash 750Aring

CW Tang amp SA VanSlyke Kodak Research LaboratoriesCW Tang and S A VanSlyke in Kodak Appl Phys Letter 51 913 (1987)

15OLED 기초공정 이해와 실습

Light Emitting PolymersLight Emitting Polymers

First Polymer LED (PVK-polymer)- Partridge polymer 24 733 (1983)----

With conductive polymer anode tooWeak blue light

PPV-LED- The first observation of EL was in

1989 (Burroughs et al)- Friend et al U S Patent 5247190

(1990) Cambridge University andCDT work on polymers

- poly(14-phenylene vinylene) (PPV) poly[2-(2rsquo-ethylhexyloxy)-5-methoxy-

14-phenylene vinylene] (MEH-PPV)

n

PPV

Full colour spectrum

glass substrateITO

polymer layerAl Ca Mg

16OLED 기초공정 이해와 실습

Organic Molecular CrystalsOrganic Molecular Crystals

Inorganic semiconductors Organic semiconductors

2Bohr radius Rydberg

Band transport

Exciton Binding Energy ~25meV Exciton size ~ 50A

Strong Covalent Bond

Strong e-e screening( ~11)

Strong spin-orbit cou

ε ε

εminusprop prop

bull

bull

bull

gt

gt

gt

gt

J is a good quantum numberpling

gt

Hopping transport

Exciton Binding Energy ~ 05 - 1eV E

Exciton localized on singxciton size ~ 5 - 10A

le pol y

Weak Van der Waals interactions

Weak e-e screening( ~3)ε

bull

bull

gt

gt

gt

gt mer chain

Large exchange energy between the lowest singlet and triple

S is a good quantum number

t excitons

Weak spin-orbit couplingbullgt

gt

17OLED 기초공정 이해와 실습

Conjugated PolymerConjugated Polymer

bull sp2 bonding

poly-acetylene (1958)

bull π- electrons delocalized along the chain

bull Dimerization opens an energy gap 2-3 eV (Peierls instability)

18OLED 기초공정 이해와 실습

에너지에너지 밴드밴드 갭갭

Ionization energies of the HOMO levels and binding energies of the LUMO levels for different polyacenes in the gas phase (left solid lines) and in the crystalline state (right double lines) respectively

C C

H

H

nrarrinfin

Eg=14eV

19OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Hopping model

Small polaron model

Poole-Frenkel model

Multiple trapping amp release model

Etc (Exciton model Soliton model Ishiguro modelhellip)

20OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Hopping model

1

00

In most cases T-dep of mobility

exp where = 1 2 3 4TT

αμ μ α

⎡ ⎤⎛ ⎞⎢ ⎥= minus⎜ ⎟⎢ ⎥⎝ ⎠⎣ ⎦

Conventional semiconductor Organic semiconductorconduction band

valence band

LUMO level

HOMO level

delocalized states propagating

Phonon scattering (negative)rarr mobility increases as T darr

localized states hopping

Phonon scattering (positive)rarr mobility decreases as T darr

01 ~ 1 cm2V-1s-1

21OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Small polaron model

In a conjugated molecules a charge is self-trapped by the lattice deformationrarr creation of the localized mid gap states

Ex) A polaron in Polythiophene

32 22( ) exp

2 2

where polaron binding energy electron transfer energy lattice constant

T-dep of the mobility

bB

Bb

b

Eea J k Tk TE

EJa

πμminus ⎛ ⎞

= minus⎜ ⎟⎝ ⎠h

22OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Poole-Frenkel model

Field dependent mobility at high field (E gt 105 Vcm)

- Coulomb potential near localized states is modified by the applied field

( )120

( ) (0)exp

where (0) zero field mobility

Poole-Frenkel factor mag of electric field

T-dep amp field dep of the mobility

B

qF Fk T

eF

μ μ β

μ

β πεε

⎛ ⎞= ⎜ ⎟

⎝ ⎠

=

23OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Multiple trapping amp release model

Narrow delocalized band+ localized trap level (highly concenturated)

Process1) Carriers arrive at a trap and are trapped2) Thermally activated and released

0

0

exp

where mobility in the delocalized bandDensity of delocalized band edge

Concenturation of traps

T-dep of the mobility

tD

B

Ek T

μ μ α

μ

α

⎛ ⎞= minus⎜ ⎟

⎝ ⎠

=

24OLED 기초공정 이해와 실습

무기EL (p-n junction LED)

Light Emission

anode

cathodeETLEMLHTLHIL+

유기EL (polymers or small molecules)

전자수송층(ETL)

발광층(EML)정공

수송층(HTL)

양극(투명전극

ITO 유리 등)

음극(낮은 일함수 금속

Ca AlLi MgAg등)

-전자

정공

+

-+

두께 100 ~ 200 nm

Exciton

OLED OLED 작동원리작동원리

25OLED 기초공정 이해와 실습

Single-layer devices

Unbalanced carrier injection and lower efficiency

dArr

Heterostructures

ITOHILHTLEMLETLCathode(1) Lower the barrier at electrodes

Balanced carrier injection andimproved efficiency

(2) Band offsets between the layers andspace charges build up at hetero-junctionHigh carrier densitieseffective e-h capture

Multilayer StructureMultilayer Structure

Cathode

HILITO

GLASS

HTLEMLETL

-

+

26OLED 기초공정 이해와 실습

Cathode

HILITO

GLASS

HTLEMLETL

-

+

OLED Structure

N N

CH3

H3C

TPD m-MTDATA

N

N N

N

CH3

CH3

H3C

NO

NON

OAl

Alq3

Small Molecules (Fluorescence)

27OLED 기초공정 이해와 실습

OLED StructureSmall Molecules

(Phosphorescence)

NN

N

N

NN

N

N

CuN

N

NN

CuPc MTDATA

Cathode

HILITO

GLASS

HTLEML

ETL-

+

HBL

NNCH3H3C

BCP

28OLED 기초공정 이해와 실습

OLED Structure

Polymers

Cathode

ITO

GLASS

HTLEML

-

+

PEDOT

n

S O3- S O3

-S O3H S O3H S O3H S O3H

SS

SS

SS

O O

OO

O O

OO OO

n

n n

RR

PPV PF

29OLED 기초공정 이해와 실습

Cur

rent

den

sity Lum

inous Intensity

Voltage

ln V

ln J

J = qn0μVd

J = 98 εsμV2d3

Ligh

t

Current

slope = ηexte

Ex)

OLED OLED 특성특성

3 7

Diode Characteristics Rectification ratio 10 - 10 Power efficiency amp drive voltage

Light vs current

optconv ext

elec

opt opt elecext opt ext

elec elec

P hP eV

N s I IIN s I e e

νη η

η η

= =

= = rArr = times

30OLED 기초공정 이해와 실습

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

Vacuum Level

Anode

Cathode

HOMO

LUMO

Φa

Φc

EA

IP

CB

VB

Eg

에너지에너지 준위준위

31OLED 기초공정 이해와 실습

Current - Voltage Characteristics

2

16 17 3

0

0

1

diffusion voltage ~ 13 V

acceptor concentration ~ 10 - 10 cm

(~ 50 - 150 nm

2( )

Width of space charge layer 2 ( )

D

D

A

r DA

r D A

V VCV

N

C A q N V V

w V V qN

ε ε

ε ε

prop minus

= minus

= minus V = 0 )

OLED OLED 전기적전기적 특성특성

( ) Schottky equation

exp 1

ideality factor 1 1 ideal Schottky diodes B ext BJ J eV nk T V V IR

n n

⎡ ⎤= minus = minus⎣ ⎦ge =

Capacitance - Voltage Dependence

32OLED 기초공정 이해와 실습

I - V Characteristics C - V Characteristics

ITOPPVMetal Polymeric Schottky Diode

OLED OLED 전기적전기적 특성특성

33OLED 기초공정 이해와 실습

Injection Dominated Mechanisms

bull Thermionic emission

bull Tunneling

Bulk Dominated Mechanisms

bull Ohmic Conduction

bull Space Charge Limited Current Conduction

bull Space Charge Limited Current Conduction with Traps

Magnitude of Injection Barrier

전하전하 주입주입

34OLED 기초공정 이해와 실습

Thermionic Emission

Fowler-Nordheim Tunneling

2

2 2

3

exp 1 wehere exp

4 120( )

Richardson constant

bns s

B B

n B

eeVJ J J A Tk T k T

em kA m m A cm Kh

φ

π

⎡ ⎤⎛ ⎞ ⎛ ⎞minus= minus =⎢ ⎥⎜ ⎟ ⎜ ⎟

⎝ ⎠ ⎝ ⎠⎣ ⎦

= =

At low field thermionic emission at high field tunneling dominate

전하전하 주입주입

EF

Evac

-eFz(triangular shape)φ

Z=0 Z

Charge accumulationhigher the energy state `

Electron emission (F-N Tunneling)

Electron emission (Thermionic Emission)

2

3212

~ exp

( ) where 8 (2 )3

bJ EE

qb mqh

π

⎛ ⎞minus⎜ ⎟⎝ ⎠

Φ=

35OLED 기초공정 이해와 실습

Applied voltage

Lattice vibration

Localizedelectron

Hopping conductionBand-like conductionDelocalized electron

Lattice vibration(phonon)

Scattered electron

Low Mobility

bull holes μ ~10-4-10-8 Vs due to poor wave function overlap (large hopping distance)

bull electrons μ ~10-6-10-10Vs due to increased disorder and trapping at defect sites caused by impurities such as O2

rArr Build-up of space-charge density (bulk limited current)

전하전하 이동도이동도

36OLED 기초공정 이해와 실습

NoteMobility depends onElectric Field andTemperature

Mobilities of OrganicsMobilities of Organics

Alq3

37OLED 기초공정 이해와 실습

Ohmic conduction

OLEDOLED의의 전류전류

Current Dendity

current depends linearly on the bias voltageo nn qm VJd

=

2

3

0

1

2 1

(no traps)

(exponential trap distributions ( ) exp( )

one of electrodes(Ohmic contact) can supply more carriers per un

98

Current Density

SCLC condition

o

tt

r

m

m tN

VJd

T E N E kTV md T

ε ε μ

+

+ =

=

prop =

it time than can be transported through the dielectric (caused by low mobility)

Space charge limited (SCL) conduction

38OLED 기초공정 이해와 실습

2

2

3

Charge per unit area Q induced by a voltage V

Transit time across the semiconductor

9

Approximate SCLC densi

Child law (Mott- Gu

ty

Elec8

rney law)

o r

r

o rSCLC

r

VQ CVd

d dtE V

VQJt d

ε ε

μ μ

ε ε μ

= =

= =

asymp =

3 2

tric field distribution across the semiconductor

Majority space charges enhance the E field at the

3 3 ( ) at ( )2 2

enhance the injection of the cath

minority carrieode

rs (elect

V x VE x x d E dd d

= = =

rArr rons)

d

(+) (-)

x=0 x=d

Vd

15 Vd232

3)(d

xVxE =

++++

Virtual anode

-

Space Charge Limited CurrentSpace Charge Limited Current

39OLED 기초공정 이해와 실습

2

3

1

2 01

(no traps or discrete traps Mott-Gurney formula)

(exponential trap distributions ( ) exp( )

98

o rSCLC

mt

SCLC m t t

VJd

TVJ N E NmT

E kTd

ε ε μ

+

+

=

prop = =

ECB

EVB

Etrap

Discrete trapping center Exponential distributionof trapping centers

TrapTrap--Limited CurrentLimited Current

40OLED 기초공정 이해와 실습

Shen Burrows Bulovic McCarty Thompson Forrest Jpn J Appl Phys 35 L401 (1996)

ITOTPDAlq3MgAg

12

1

+

+

prop m

m

SCLC dVJ

TrapTrap--Limited CurrentLimited Current

41OLED 기초공정 이해와 실습

0

0

Activation energy at 0 Empirical parameter

Mobility at PF constant

PF

PF

E FT

T Tμβ

Δ =

=

PFPF

B eff

0

3

PFeff 0 0

( ) exp

exp( )

1 1 1with

E FFT μk T

F

qT T T

βμ

μ β

βπεε

⎛ ⎞Δ minus= minus⎜ ⎟⎜ ⎟

⎝ ⎠

equiv

= minus =

Poole Frenkel ModelPoole Frenkel Model

42OLED 기초공정 이해와 실습

1

22 2

0

0

(1)

(2)

EL F S e h

e ee he

T

h he hh

T

T rec rec e h

h eh e

h e

e hEL F S

h e

T rec

h e h e nh e EL F S EL

e h

n nJ n n nedJ n n ned

nJ

ne F

J J Je F

J Jn J J

ed n ed

η η γ

γτ

γτ

τ τ τ γ

μ

η η γμ μ

τ τ

η ηγ

minus

Φ =

minus minus =

minus minus =

lt =

=

Φ = prop

gt

= Φ = prop rArr Φ prop

EL Current RelationEL Current Relation

43OLED 기초공정 이해와 실습

Device Structure ITONPBAlq3Ca

22

21

ZZZ

fdVdQC

+minus

==πφieZiZZZ ||

))=+=

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

V0 independent of the NPB layer thickness

44OLED 기초공정 이해와 실습

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

Dashed line without interfacial charge

Wolfgang Brutting Stefan Berleb Anton G Muckl Organic Electronics 2 (2001)

Device Structure ITONPBAlq3Ca

45OLED 기초공정 이해와 실습

Langevin Recombination of carriers

bull Carriers are statistically independent therefore the e-h recombination is a random process and kinetically bimolecular

bull Total current attracted by a charge into the sphere of Coulombic capture radius rc

2

22

( ) ( )4

(4 ) 14 184

( ) (mean free path A)

n p c n pc

c cB

n p

qJ qp E qpr

qi r J Bqp r nmk T

qB a

μ μ μ μπε

ππε

μ μ λε

= + = +

= = cong asymp minus

there4 = + asympo

TkUd

BeP ~ minusProbability of dissociation

reUπε4

~2

e-

rc

Carrier RecombinationCarrier Recombination

P Langevin Ann Chem Phys 28 289 (1903)

46OLED 기초공정 이해와 실습

Electronic Processes in Organic Crystals and Polymers by MPope and C E Swenberg

ExcitonsExcitons

47OLED 기초공정 이해와 실습

C Adachi et al

Electrons and holesForm excitons

(bound e--h+ pairs)

Exciton Recombination ZoneExciton Recombination Zone

48OLED 기초공정 이해와 실습

MOLECULAR EXCITED STATESAFTER ELECTRICAL EXCITATION

Singletspin anti-symmetric

Tripletspin symmetric

25 75

MOLECULAR GROUND STATEspin anti-symmetric

Relaxation allowedfast efficientFluorescence

Relaxation disallowedslow inefficientPhosphorescence

|χ1χ2 gt = | gt

|χ1χ2 gt = | gt

|χ1χ2 gt

= | gt - | gt2

1

|χ1χ2 gt = | gt + | gt2

1ISC

Spin

OLEDOLED의의 형광형광인광인광

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 14: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

13OLED 기초공정 이해와 실습

저분자 고분자

박막 성막 방식 진공 열증착 Ink-jet

순도 고순도 재료 용이 고순도 재료 어려움

열 안정성 낮다 높다

작동전압 7-15v 3-7v

NO

NON

OAl

2 Types

Small Molecule

Polymer

OLEDOLED의의 재료재료

n

14OLED 기초공정 이해와 실습

Early OLED (Small Molecule)Early OLED (Small Molecule)

EL emission spectrum is sensitive to thickness of organic layerDiamine layer transports holes and blocks electrons injected from MgAg electrode

bull MgAg ndash 101bull Luminescent film - 600Aringbull Diamine ndash 750Aring

CW Tang amp SA VanSlyke Kodak Research LaboratoriesCW Tang and S A VanSlyke in Kodak Appl Phys Letter 51 913 (1987)

15OLED 기초공정 이해와 실습

Light Emitting PolymersLight Emitting Polymers

First Polymer LED (PVK-polymer)- Partridge polymer 24 733 (1983)----

With conductive polymer anode tooWeak blue light

PPV-LED- The first observation of EL was in

1989 (Burroughs et al)- Friend et al U S Patent 5247190

(1990) Cambridge University andCDT work on polymers

- poly(14-phenylene vinylene) (PPV) poly[2-(2rsquo-ethylhexyloxy)-5-methoxy-

14-phenylene vinylene] (MEH-PPV)

n

PPV

Full colour spectrum

glass substrateITO

polymer layerAl Ca Mg

16OLED 기초공정 이해와 실습

Organic Molecular CrystalsOrganic Molecular Crystals

Inorganic semiconductors Organic semiconductors

2Bohr radius Rydberg

Band transport

Exciton Binding Energy ~25meV Exciton size ~ 50A

Strong Covalent Bond

Strong e-e screening( ~11)

Strong spin-orbit cou

ε ε

εminusprop prop

bull

bull

bull

gt

gt

gt

gt

J is a good quantum numberpling

gt

Hopping transport

Exciton Binding Energy ~ 05 - 1eV E

Exciton localized on singxciton size ~ 5 - 10A

le pol y

Weak Van der Waals interactions

Weak e-e screening( ~3)ε

bull

bull

gt

gt

gt

gt mer chain

Large exchange energy between the lowest singlet and triple

S is a good quantum number

t excitons

Weak spin-orbit couplingbullgt

gt

17OLED 기초공정 이해와 실습

Conjugated PolymerConjugated Polymer

bull sp2 bonding

poly-acetylene (1958)

bull π- electrons delocalized along the chain

bull Dimerization opens an energy gap 2-3 eV (Peierls instability)

18OLED 기초공정 이해와 실습

에너지에너지 밴드밴드 갭갭

Ionization energies of the HOMO levels and binding energies of the LUMO levels for different polyacenes in the gas phase (left solid lines) and in the crystalline state (right double lines) respectively

C C

H

H

nrarrinfin

Eg=14eV

19OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Hopping model

Small polaron model

Poole-Frenkel model

Multiple trapping amp release model

Etc (Exciton model Soliton model Ishiguro modelhellip)

20OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Hopping model

1

00

In most cases T-dep of mobility

exp where = 1 2 3 4TT

αμ μ α

⎡ ⎤⎛ ⎞⎢ ⎥= minus⎜ ⎟⎢ ⎥⎝ ⎠⎣ ⎦

Conventional semiconductor Organic semiconductorconduction band

valence band

LUMO level

HOMO level

delocalized states propagating

Phonon scattering (negative)rarr mobility increases as T darr

localized states hopping

Phonon scattering (positive)rarr mobility decreases as T darr

01 ~ 1 cm2V-1s-1

21OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Small polaron model

In a conjugated molecules a charge is self-trapped by the lattice deformationrarr creation of the localized mid gap states

Ex) A polaron in Polythiophene

32 22( ) exp

2 2

where polaron binding energy electron transfer energy lattice constant

T-dep of the mobility

bB

Bb

b

Eea J k Tk TE

EJa

πμminus ⎛ ⎞

= minus⎜ ⎟⎝ ⎠h

22OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Poole-Frenkel model

Field dependent mobility at high field (E gt 105 Vcm)

- Coulomb potential near localized states is modified by the applied field

( )120

( ) (0)exp

where (0) zero field mobility

Poole-Frenkel factor mag of electric field

T-dep amp field dep of the mobility

B

qF Fk T

eF

μ μ β

μ

β πεε

⎛ ⎞= ⎜ ⎟

⎝ ⎠

=

23OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Multiple trapping amp release model

Narrow delocalized band+ localized trap level (highly concenturated)

Process1) Carriers arrive at a trap and are trapped2) Thermally activated and released

0

0

exp

where mobility in the delocalized bandDensity of delocalized band edge

Concenturation of traps

T-dep of the mobility

tD

B

Ek T

μ μ α

μ

α

⎛ ⎞= minus⎜ ⎟

⎝ ⎠

=

24OLED 기초공정 이해와 실습

무기EL (p-n junction LED)

Light Emission

anode

cathodeETLEMLHTLHIL+

유기EL (polymers or small molecules)

전자수송층(ETL)

발광층(EML)정공

수송층(HTL)

양극(투명전극

ITO 유리 등)

음극(낮은 일함수 금속

Ca AlLi MgAg등)

-전자

정공

+

-+

두께 100 ~ 200 nm

Exciton

OLED OLED 작동원리작동원리

25OLED 기초공정 이해와 실습

Single-layer devices

Unbalanced carrier injection and lower efficiency

dArr

Heterostructures

ITOHILHTLEMLETLCathode(1) Lower the barrier at electrodes

Balanced carrier injection andimproved efficiency

(2) Band offsets between the layers andspace charges build up at hetero-junctionHigh carrier densitieseffective e-h capture

Multilayer StructureMultilayer Structure

Cathode

HILITO

GLASS

HTLEMLETL

-

+

26OLED 기초공정 이해와 실습

Cathode

HILITO

GLASS

HTLEMLETL

-

+

OLED Structure

N N

CH3

H3C

TPD m-MTDATA

N

N N

N

CH3

CH3

H3C

NO

NON

OAl

Alq3

Small Molecules (Fluorescence)

27OLED 기초공정 이해와 실습

OLED StructureSmall Molecules

(Phosphorescence)

NN

N

N

NN

N

N

CuN

N

NN

CuPc MTDATA

Cathode

HILITO

GLASS

HTLEML

ETL-

+

HBL

NNCH3H3C

BCP

28OLED 기초공정 이해와 실습

OLED Structure

Polymers

Cathode

ITO

GLASS

HTLEML

-

+

PEDOT

n

S O3- S O3

-S O3H S O3H S O3H S O3H

SS

SS

SS

O O

OO

O O

OO OO

n

n n

RR

PPV PF

29OLED 기초공정 이해와 실습

Cur

rent

den

sity Lum

inous Intensity

Voltage

ln V

ln J

J = qn0μVd

J = 98 εsμV2d3

Ligh

t

Current

slope = ηexte

Ex)

OLED OLED 특성특성

3 7

Diode Characteristics Rectification ratio 10 - 10 Power efficiency amp drive voltage

Light vs current

optconv ext

elec

opt opt elecext opt ext

elec elec

P hP eV

N s I IIN s I e e

νη η

η η

= =

= = rArr = times

30OLED 기초공정 이해와 실습

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

Vacuum Level

Anode

Cathode

HOMO

LUMO

Φa

Φc

EA

IP

CB

VB

Eg

에너지에너지 준위준위

31OLED 기초공정 이해와 실습

Current - Voltage Characteristics

2

16 17 3

0

0

1

diffusion voltage ~ 13 V

acceptor concentration ~ 10 - 10 cm

(~ 50 - 150 nm

2( )

Width of space charge layer 2 ( )

D

D

A

r DA

r D A

V VCV

N

C A q N V V

w V V qN

ε ε

ε ε

prop minus

= minus

= minus V = 0 )

OLED OLED 전기적전기적 특성특성

( ) Schottky equation

exp 1

ideality factor 1 1 ideal Schottky diodes B ext BJ J eV nk T V V IR

n n

⎡ ⎤= minus = minus⎣ ⎦ge =

Capacitance - Voltage Dependence

32OLED 기초공정 이해와 실습

I - V Characteristics C - V Characteristics

ITOPPVMetal Polymeric Schottky Diode

OLED OLED 전기적전기적 특성특성

33OLED 기초공정 이해와 실습

Injection Dominated Mechanisms

bull Thermionic emission

bull Tunneling

Bulk Dominated Mechanisms

bull Ohmic Conduction

bull Space Charge Limited Current Conduction

bull Space Charge Limited Current Conduction with Traps

Magnitude of Injection Barrier

전하전하 주입주입

34OLED 기초공정 이해와 실습

Thermionic Emission

Fowler-Nordheim Tunneling

2

2 2

3

exp 1 wehere exp

4 120( )

Richardson constant

bns s

B B

n B

eeVJ J J A Tk T k T

em kA m m A cm Kh

φ

π

⎡ ⎤⎛ ⎞ ⎛ ⎞minus= minus =⎢ ⎥⎜ ⎟ ⎜ ⎟

⎝ ⎠ ⎝ ⎠⎣ ⎦

= =

At low field thermionic emission at high field tunneling dominate

전하전하 주입주입

EF

Evac

-eFz(triangular shape)φ

Z=0 Z

Charge accumulationhigher the energy state `

Electron emission (F-N Tunneling)

Electron emission (Thermionic Emission)

2

3212

~ exp

( ) where 8 (2 )3

bJ EE

qb mqh

π

⎛ ⎞minus⎜ ⎟⎝ ⎠

Φ=

35OLED 기초공정 이해와 실습

Applied voltage

Lattice vibration

Localizedelectron

Hopping conductionBand-like conductionDelocalized electron

Lattice vibration(phonon)

Scattered electron

Low Mobility

bull holes μ ~10-4-10-8 Vs due to poor wave function overlap (large hopping distance)

bull electrons μ ~10-6-10-10Vs due to increased disorder and trapping at defect sites caused by impurities such as O2

rArr Build-up of space-charge density (bulk limited current)

전하전하 이동도이동도

36OLED 기초공정 이해와 실습

NoteMobility depends onElectric Field andTemperature

Mobilities of OrganicsMobilities of Organics

Alq3

37OLED 기초공정 이해와 실습

Ohmic conduction

OLEDOLED의의 전류전류

Current Dendity

current depends linearly on the bias voltageo nn qm VJd

=

2

3

0

1

2 1

(no traps)

(exponential trap distributions ( ) exp( )

one of electrodes(Ohmic contact) can supply more carriers per un

98

Current Density

SCLC condition

o

tt

r

m

m tN

VJd

T E N E kTV md T

ε ε μ

+

+ =

=

prop =

it time than can be transported through the dielectric (caused by low mobility)

Space charge limited (SCL) conduction

38OLED 기초공정 이해와 실습

2

2

3

Charge per unit area Q induced by a voltage V

Transit time across the semiconductor

9

Approximate SCLC densi

Child law (Mott- Gu

ty

Elec8

rney law)

o r

r

o rSCLC

r

VQ CVd

d dtE V

VQJt d

ε ε

μ μ

ε ε μ

= =

= =

asymp =

3 2

tric field distribution across the semiconductor

Majority space charges enhance the E field at the

3 3 ( ) at ( )2 2

enhance the injection of the cath

minority carrieode

rs (elect

V x VE x x d E dd d

= = =

rArr rons)

d

(+) (-)

x=0 x=d

Vd

15 Vd232

3)(d

xVxE =

++++

Virtual anode

-

Space Charge Limited CurrentSpace Charge Limited Current

39OLED 기초공정 이해와 실습

2

3

1

2 01

(no traps or discrete traps Mott-Gurney formula)

(exponential trap distributions ( ) exp( )

98

o rSCLC

mt

SCLC m t t

VJd

TVJ N E NmT

E kTd

ε ε μ

+

+

=

prop = =

ECB

EVB

Etrap

Discrete trapping center Exponential distributionof trapping centers

TrapTrap--Limited CurrentLimited Current

40OLED 기초공정 이해와 실습

Shen Burrows Bulovic McCarty Thompson Forrest Jpn J Appl Phys 35 L401 (1996)

ITOTPDAlq3MgAg

12

1

+

+

prop m

m

SCLC dVJ

TrapTrap--Limited CurrentLimited Current

41OLED 기초공정 이해와 실습

0

0

Activation energy at 0 Empirical parameter

Mobility at PF constant

PF

PF

E FT

T Tμβ

Δ =

=

PFPF

B eff

0

3

PFeff 0 0

( ) exp

exp( )

1 1 1with

E FFT μk T

F

qT T T

βμ

μ β

βπεε

⎛ ⎞Δ minus= minus⎜ ⎟⎜ ⎟

⎝ ⎠

equiv

= minus =

Poole Frenkel ModelPoole Frenkel Model

42OLED 기초공정 이해와 실습

1

22 2

0

0

(1)

(2)

EL F S e h

e ee he

T

h he hh

T

T rec rec e h

h eh e

h e

e hEL F S

h e

T rec

h e h e nh e EL F S EL

e h

n nJ n n nedJ n n ned

nJ

ne F

J J Je F

J Jn J J

ed n ed

η η γ

γτ

γτ

τ τ τ γ

μ

η η γμ μ

τ τ

η ηγ

minus

Φ =

minus minus =

minus minus =

lt =

=

Φ = prop

gt

= Φ = prop rArr Φ prop

EL Current RelationEL Current Relation

43OLED 기초공정 이해와 실습

Device Structure ITONPBAlq3Ca

22

21

ZZZ

fdVdQC

+minus

==πφieZiZZZ ||

))=+=

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

V0 independent of the NPB layer thickness

44OLED 기초공정 이해와 실습

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

Dashed line without interfacial charge

Wolfgang Brutting Stefan Berleb Anton G Muckl Organic Electronics 2 (2001)

Device Structure ITONPBAlq3Ca

45OLED 기초공정 이해와 실습

Langevin Recombination of carriers

bull Carriers are statistically independent therefore the e-h recombination is a random process and kinetically bimolecular

bull Total current attracted by a charge into the sphere of Coulombic capture radius rc

2

22

( ) ( )4

(4 ) 14 184

( ) (mean free path A)

n p c n pc

c cB

n p

qJ qp E qpr

qi r J Bqp r nmk T

qB a

μ μ μ μπε

ππε

μ μ λε

= + = +

= = cong asymp minus

there4 = + asympo

TkUd

BeP ~ minusProbability of dissociation

reUπε4

~2

e-

rc

Carrier RecombinationCarrier Recombination

P Langevin Ann Chem Phys 28 289 (1903)

46OLED 기초공정 이해와 실습

Electronic Processes in Organic Crystals and Polymers by MPope and C E Swenberg

ExcitonsExcitons

47OLED 기초공정 이해와 실습

C Adachi et al

Electrons and holesForm excitons

(bound e--h+ pairs)

Exciton Recombination ZoneExciton Recombination Zone

48OLED 기초공정 이해와 실습

MOLECULAR EXCITED STATESAFTER ELECTRICAL EXCITATION

Singletspin anti-symmetric

Tripletspin symmetric

25 75

MOLECULAR GROUND STATEspin anti-symmetric

Relaxation allowedfast efficientFluorescence

Relaxation disallowedslow inefficientPhosphorescence

|χ1χ2 gt = | gt

|χ1χ2 gt = | gt

|χ1χ2 gt

= | gt - | gt2

1

|χ1χ2 gt = | gt + | gt2

1ISC

Spin

OLEDOLED의의 형광형광인광인광

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 15: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

14OLED 기초공정 이해와 실습

Early OLED (Small Molecule)Early OLED (Small Molecule)

EL emission spectrum is sensitive to thickness of organic layerDiamine layer transports holes and blocks electrons injected from MgAg electrode

bull MgAg ndash 101bull Luminescent film - 600Aringbull Diamine ndash 750Aring

CW Tang amp SA VanSlyke Kodak Research LaboratoriesCW Tang and S A VanSlyke in Kodak Appl Phys Letter 51 913 (1987)

15OLED 기초공정 이해와 실습

Light Emitting PolymersLight Emitting Polymers

First Polymer LED (PVK-polymer)- Partridge polymer 24 733 (1983)----

With conductive polymer anode tooWeak blue light

PPV-LED- The first observation of EL was in

1989 (Burroughs et al)- Friend et al U S Patent 5247190

(1990) Cambridge University andCDT work on polymers

- poly(14-phenylene vinylene) (PPV) poly[2-(2rsquo-ethylhexyloxy)-5-methoxy-

14-phenylene vinylene] (MEH-PPV)

n

PPV

Full colour spectrum

glass substrateITO

polymer layerAl Ca Mg

16OLED 기초공정 이해와 실습

Organic Molecular CrystalsOrganic Molecular Crystals

Inorganic semiconductors Organic semiconductors

2Bohr radius Rydberg

Band transport

Exciton Binding Energy ~25meV Exciton size ~ 50A

Strong Covalent Bond

Strong e-e screening( ~11)

Strong spin-orbit cou

ε ε

εminusprop prop

bull

bull

bull

gt

gt

gt

gt

J is a good quantum numberpling

gt

Hopping transport

Exciton Binding Energy ~ 05 - 1eV E

Exciton localized on singxciton size ~ 5 - 10A

le pol y

Weak Van der Waals interactions

Weak e-e screening( ~3)ε

bull

bull

gt

gt

gt

gt mer chain

Large exchange energy between the lowest singlet and triple

S is a good quantum number

t excitons

Weak spin-orbit couplingbullgt

gt

17OLED 기초공정 이해와 실습

Conjugated PolymerConjugated Polymer

bull sp2 bonding

poly-acetylene (1958)

bull π- electrons delocalized along the chain

bull Dimerization opens an energy gap 2-3 eV (Peierls instability)

18OLED 기초공정 이해와 실습

에너지에너지 밴드밴드 갭갭

Ionization energies of the HOMO levels and binding energies of the LUMO levels for different polyacenes in the gas phase (left solid lines) and in the crystalline state (right double lines) respectively

C C

H

H

nrarrinfin

Eg=14eV

19OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Hopping model

Small polaron model

Poole-Frenkel model

Multiple trapping amp release model

Etc (Exciton model Soliton model Ishiguro modelhellip)

20OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Hopping model

1

00

In most cases T-dep of mobility

exp where = 1 2 3 4TT

αμ μ α

⎡ ⎤⎛ ⎞⎢ ⎥= minus⎜ ⎟⎢ ⎥⎝ ⎠⎣ ⎦

Conventional semiconductor Organic semiconductorconduction band

valence band

LUMO level

HOMO level

delocalized states propagating

Phonon scattering (negative)rarr mobility increases as T darr

localized states hopping

Phonon scattering (positive)rarr mobility decreases as T darr

01 ~ 1 cm2V-1s-1

21OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Small polaron model

In a conjugated molecules a charge is self-trapped by the lattice deformationrarr creation of the localized mid gap states

Ex) A polaron in Polythiophene

32 22( ) exp

2 2

where polaron binding energy electron transfer energy lattice constant

T-dep of the mobility

bB

Bb

b

Eea J k Tk TE

EJa

πμminus ⎛ ⎞

= minus⎜ ⎟⎝ ⎠h

22OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Poole-Frenkel model

Field dependent mobility at high field (E gt 105 Vcm)

- Coulomb potential near localized states is modified by the applied field

( )120

( ) (0)exp

where (0) zero field mobility

Poole-Frenkel factor mag of electric field

T-dep amp field dep of the mobility

B

qF Fk T

eF

μ μ β

μ

β πεε

⎛ ⎞= ⎜ ⎟

⎝ ⎠

=

23OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Multiple trapping amp release model

Narrow delocalized band+ localized trap level (highly concenturated)

Process1) Carriers arrive at a trap and are trapped2) Thermally activated and released

0

0

exp

where mobility in the delocalized bandDensity of delocalized band edge

Concenturation of traps

T-dep of the mobility

tD

B

Ek T

μ μ α

μ

α

⎛ ⎞= minus⎜ ⎟

⎝ ⎠

=

24OLED 기초공정 이해와 실습

무기EL (p-n junction LED)

Light Emission

anode

cathodeETLEMLHTLHIL+

유기EL (polymers or small molecules)

전자수송층(ETL)

발광층(EML)정공

수송층(HTL)

양극(투명전극

ITO 유리 등)

음극(낮은 일함수 금속

Ca AlLi MgAg등)

-전자

정공

+

-+

두께 100 ~ 200 nm

Exciton

OLED OLED 작동원리작동원리

25OLED 기초공정 이해와 실습

Single-layer devices

Unbalanced carrier injection and lower efficiency

dArr

Heterostructures

ITOHILHTLEMLETLCathode(1) Lower the barrier at electrodes

Balanced carrier injection andimproved efficiency

(2) Band offsets between the layers andspace charges build up at hetero-junctionHigh carrier densitieseffective e-h capture

Multilayer StructureMultilayer Structure

Cathode

HILITO

GLASS

HTLEMLETL

-

+

26OLED 기초공정 이해와 실습

Cathode

HILITO

GLASS

HTLEMLETL

-

+

OLED Structure

N N

CH3

H3C

TPD m-MTDATA

N

N N

N

CH3

CH3

H3C

NO

NON

OAl

Alq3

Small Molecules (Fluorescence)

27OLED 기초공정 이해와 실습

OLED StructureSmall Molecules

(Phosphorescence)

NN

N

N

NN

N

N

CuN

N

NN

CuPc MTDATA

Cathode

HILITO

GLASS

HTLEML

ETL-

+

HBL

NNCH3H3C

BCP

28OLED 기초공정 이해와 실습

OLED Structure

Polymers

Cathode

ITO

GLASS

HTLEML

-

+

PEDOT

n

S O3- S O3

-S O3H S O3H S O3H S O3H

SS

SS

SS

O O

OO

O O

OO OO

n

n n

RR

PPV PF

29OLED 기초공정 이해와 실습

Cur

rent

den

sity Lum

inous Intensity

Voltage

ln V

ln J

J = qn0μVd

J = 98 εsμV2d3

Ligh

t

Current

slope = ηexte

Ex)

OLED OLED 특성특성

3 7

Diode Characteristics Rectification ratio 10 - 10 Power efficiency amp drive voltage

Light vs current

optconv ext

elec

opt opt elecext opt ext

elec elec

P hP eV

N s I IIN s I e e

νη η

η η

= =

= = rArr = times

30OLED 기초공정 이해와 실습

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

Vacuum Level

Anode

Cathode

HOMO

LUMO

Φa

Φc

EA

IP

CB

VB

Eg

에너지에너지 준위준위

31OLED 기초공정 이해와 실습

Current - Voltage Characteristics

2

16 17 3

0

0

1

diffusion voltage ~ 13 V

acceptor concentration ~ 10 - 10 cm

(~ 50 - 150 nm

2( )

Width of space charge layer 2 ( )

D

D

A

r DA

r D A

V VCV

N

C A q N V V

w V V qN

ε ε

ε ε

prop minus

= minus

= minus V = 0 )

OLED OLED 전기적전기적 특성특성

( ) Schottky equation

exp 1

ideality factor 1 1 ideal Schottky diodes B ext BJ J eV nk T V V IR

n n

⎡ ⎤= minus = minus⎣ ⎦ge =

Capacitance - Voltage Dependence

32OLED 기초공정 이해와 실습

I - V Characteristics C - V Characteristics

ITOPPVMetal Polymeric Schottky Diode

OLED OLED 전기적전기적 특성특성

33OLED 기초공정 이해와 실습

Injection Dominated Mechanisms

bull Thermionic emission

bull Tunneling

Bulk Dominated Mechanisms

bull Ohmic Conduction

bull Space Charge Limited Current Conduction

bull Space Charge Limited Current Conduction with Traps

Magnitude of Injection Barrier

전하전하 주입주입

34OLED 기초공정 이해와 실습

Thermionic Emission

Fowler-Nordheim Tunneling

2

2 2

3

exp 1 wehere exp

4 120( )

Richardson constant

bns s

B B

n B

eeVJ J J A Tk T k T

em kA m m A cm Kh

φ

π

⎡ ⎤⎛ ⎞ ⎛ ⎞minus= minus =⎢ ⎥⎜ ⎟ ⎜ ⎟

⎝ ⎠ ⎝ ⎠⎣ ⎦

= =

At low field thermionic emission at high field tunneling dominate

전하전하 주입주입

EF

Evac

-eFz(triangular shape)φ

Z=0 Z

Charge accumulationhigher the energy state `

Electron emission (F-N Tunneling)

Electron emission (Thermionic Emission)

2

3212

~ exp

( ) where 8 (2 )3

bJ EE

qb mqh

π

⎛ ⎞minus⎜ ⎟⎝ ⎠

Φ=

35OLED 기초공정 이해와 실습

Applied voltage

Lattice vibration

Localizedelectron

Hopping conductionBand-like conductionDelocalized electron

Lattice vibration(phonon)

Scattered electron

Low Mobility

bull holes μ ~10-4-10-8 Vs due to poor wave function overlap (large hopping distance)

bull electrons μ ~10-6-10-10Vs due to increased disorder and trapping at defect sites caused by impurities such as O2

rArr Build-up of space-charge density (bulk limited current)

전하전하 이동도이동도

36OLED 기초공정 이해와 실습

NoteMobility depends onElectric Field andTemperature

Mobilities of OrganicsMobilities of Organics

Alq3

37OLED 기초공정 이해와 실습

Ohmic conduction

OLEDOLED의의 전류전류

Current Dendity

current depends linearly on the bias voltageo nn qm VJd

=

2

3

0

1

2 1

(no traps)

(exponential trap distributions ( ) exp( )

one of electrodes(Ohmic contact) can supply more carriers per un

98

Current Density

SCLC condition

o

tt

r

m

m tN

VJd

T E N E kTV md T

ε ε μ

+

+ =

=

prop =

it time than can be transported through the dielectric (caused by low mobility)

Space charge limited (SCL) conduction

38OLED 기초공정 이해와 실습

2

2

3

Charge per unit area Q induced by a voltage V

Transit time across the semiconductor

9

Approximate SCLC densi

Child law (Mott- Gu

ty

Elec8

rney law)

o r

r

o rSCLC

r

VQ CVd

d dtE V

VQJt d

ε ε

μ μ

ε ε μ

= =

= =

asymp =

3 2

tric field distribution across the semiconductor

Majority space charges enhance the E field at the

3 3 ( ) at ( )2 2

enhance the injection of the cath

minority carrieode

rs (elect

V x VE x x d E dd d

= = =

rArr rons)

d

(+) (-)

x=0 x=d

Vd

15 Vd232

3)(d

xVxE =

++++

Virtual anode

-

Space Charge Limited CurrentSpace Charge Limited Current

39OLED 기초공정 이해와 실습

2

3

1

2 01

(no traps or discrete traps Mott-Gurney formula)

(exponential trap distributions ( ) exp( )

98

o rSCLC

mt

SCLC m t t

VJd

TVJ N E NmT

E kTd

ε ε μ

+

+

=

prop = =

ECB

EVB

Etrap

Discrete trapping center Exponential distributionof trapping centers

TrapTrap--Limited CurrentLimited Current

40OLED 기초공정 이해와 실습

Shen Burrows Bulovic McCarty Thompson Forrest Jpn J Appl Phys 35 L401 (1996)

ITOTPDAlq3MgAg

12

1

+

+

prop m

m

SCLC dVJ

TrapTrap--Limited CurrentLimited Current

41OLED 기초공정 이해와 실습

0

0

Activation energy at 0 Empirical parameter

Mobility at PF constant

PF

PF

E FT

T Tμβ

Δ =

=

PFPF

B eff

0

3

PFeff 0 0

( ) exp

exp( )

1 1 1with

E FFT μk T

F

qT T T

βμ

μ β

βπεε

⎛ ⎞Δ minus= minus⎜ ⎟⎜ ⎟

⎝ ⎠

equiv

= minus =

Poole Frenkel ModelPoole Frenkel Model

42OLED 기초공정 이해와 실습

1

22 2

0

0

(1)

(2)

EL F S e h

e ee he

T

h he hh

T

T rec rec e h

h eh e

h e

e hEL F S

h e

T rec

h e h e nh e EL F S EL

e h

n nJ n n nedJ n n ned

nJ

ne F

J J Je F

J Jn J J

ed n ed

η η γ

γτ

γτ

τ τ τ γ

μ

η η γμ μ

τ τ

η ηγ

minus

Φ =

minus minus =

minus minus =

lt =

=

Φ = prop

gt

= Φ = prop rArr Φ prop

EL Current RelationEL Current Relation

43OLED 기초공정 이해와 실습

Device Structure ITONPBAlq3Ca

22

21

ZZZ

fdVdQC

+minus

==πφieZiZZZ ||

))=+=

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

V0 independent of the NPB layer thickness

44OLED 기초공정 이해와 실습

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

Dashed line without interfacial charge

Wolfgang Brutting Stefan Berleb Anton G Muckl Organic Electronics 2 (2001)

Device Structure ITONPBAlq3Ca

45OLED 기초공정 이해와 실습

Langevin Recombination of carriers

bull Carriers are statistically independent therefore the e-h recombination is a random process and kinetically bimolecular

bull Total current attracted by a charge into the sphere of Coulombic capture radius rc

2

22

( ) ( )4

(4 ) 14 184

( ) (mean free path A)

n p c n pc

c cB

n p

qJ qp E qpr

qi r J Bqp r nmk T

qB a

μ μ μ μπε

ππε

μ μ λε

= + = +

= = cong asymp minus

there4 = + asympo

TkUd

BeP ~ minusProbability of dissociation

reUπε4

~2

e-

rc

Carrier RecombinationCarrier Recombination

P Langevin Ann Chem Phys 28 289 (1903)

46OLED 기초공정 이해와 실습

Electronic Processes in Organic Crystals and Polymers by MPope and C E Swenberg

ExcitonsExcitons

47OLED 기초공정 이해와 실습

C Adachi et al

Electrons and holesForm excitons

(bound e--h+ pairs)

Exciton Recombination ZoneExciton Recombination Zone

48OLED 기초공정 이해와 실습

MOLECULAR EXCITED STATESAFTER ELECTRICAL EXCITATION

Singletspin anti-symmetric

Tripletspin symmetric

25 75

MOLECULAR GROUND STATEspin anti-symmetric

Relaxation allowedfast efficientFluorescence

Relaxation disallowedslow inefficientPhosphorescence

|χ1χ2 gt = | gt

|χ1χ2 gt = | gt

|χ1χ2 gt

= | gt - | gt2

1

|χ1χ2 gt = | gt + | gt2

1ISC

Spin

OLEDOLED의의 형광형광인광인광

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 16: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

15OLED 기초공정 이해와 실습

Light Emitting PolymersLight Emitting Polymers

First Polymer LED (PVK-polymer)- Partridge polymer 24 733 (1983)----

With conductive polymer anode tooWeak blue light

PPV-LED- The first observation of EL was in

1989 (Burroughs et al)- Friend et al U S Patent 5247190

(1990) Cambridge University andCDT work on polymers

- poly(14-phenylene vinylene) (PPV) poly[2-(2rsquo-ethylhexyloxy)-5-methoxy-

14-phenylene vinylene] (MEH-PPV)

n

PPV

Full colour spectrum

glass substrateITO

polymer layerAl Ca Mg

16OLED 기초공정 이해와 실습

Organic Molecular CrystalsOrganic Molecular Crystals

Inorganic semiconductors Organic semiconductors

2Bohr radius Rydberg

Band transport

Exciton Binding Energy ~25meV Exciton size ~ 50A

Strong Covalent Bond

Strong e-e screening( ~11)

Strong spin-orbit cou

ε ε

εminusprop prop

bull

bull

bull

gt

gt

gt

gt

J is a good quantum numberpling

gt

Hopping transport

Exciton Binding Energy ~ 05 - 1eV E

Exciton localized on singxciton size ~ 5 - 10A

le pol y

Weak Van der Waals interactions

Weak e-e screening( ~3)ε

bull

bull

gt

gt

gt

gt mer chain

Large exchange energy between the lowest singlet and triple

S is a good quantum number

t excitons

Weak spin-orbit couplingbullgt

gt

17OLED 기초공정 이해와 실습

Conjugated PolymerConjugated Polymer

bull sp2 bonding

poly-acetylene (1958)

bull π- electrons delocalized along the chain

bull Dimerization opens an energy gap 2-3 eV (Peierls instability)

18OLED 기초공정 이해와 실습

에너지에너지 밴드밴드 갭갭

Ionization energies of the HOMO levels and binding energies of the LUMO levels for different polyacenes in the gas phase (left solid lines) and in the crystalline state (right double lines) respectively

C C

H

H

nrarrinfin

Eg=14eV

19OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Hopping model

Small polaron model

Poole-Frenkel model

Multiple trapping amp release model

Etc (Exciton model Soliton model Ishiguro modelhellip)

20OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Hopping model

1

00

In most cases T-dep of mobility

exp where = 1 2 3 4TT

αμ μ α

⎡ ⎤⎛ ⎞⎢ ⎥= minus⎜ ⎟⎢ ⎥⎝ ⎠⎣ ⎦

Conventional semiconductor Organic semiconductorconduction band

valence band

LUMO level

HOMO level

delocalized states propagating

Phonon scattering (negative)rarr mobility increases as T darr

localized states hopping

Phonon scattering (positive)rarr mobility decreases as T darr

01 ~ 1 cm2V-1s-1

21OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Small polaron model

In a conjugated molecules a charge is self-trapped by the lattice deformationrarr creation of the localized mid gap states

Ex) A polaron in Polythiophene

32 22( ) exp

2 2

where polaron binding energy electron transfer energy lattice constant

T-dep of the mobility

bB

Bb

b

Eea J k Tk TE

EJa

πμminus ⎛ ⎞

= minus⎜ ⎟⎝ ⎠h

22OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Poole-Frenkel model

Field dependent mobility at high field (E gt 105 Vcm)

- Coulomb potential near localized states is modified by the applied field

( )120

( ) (0)exp

where (0) zero field mobility

Poole-Frenkel factor mag of electric field

T-dep amp field dep of the mobility

B

qF Fk T

eF

μ μ β

μ

β πεε

⎛ ⎞= ⎜ ⎟

⎝ ⎠

=

23OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Multiple trapping amp release model

Narrow delocalized band+ localized trap level (highly concenturated)

Process1) Carriers arrive at a trap and are trapped2) Thermally activated and released

0

0

exp

where mobility in the delocalized bandDensity of delocalized band edge

Concenturation of traps

T-dep of the mobility

tD

B

Ek T

μ μ α

μ

α

⎛ ⎞= minus⎜ ⎟

⎝ ⎠

=

24OLED 기초공정 이해와 실습

무기EL (p-n junction LED)

Light Emission

anode

cathodeETLEMLHTLHIL+

유기EL (polymers or small molecules)

전자수송층(ETL)

발광층(EML)정공

수송층(HTL)

양극(투명전극

ITO 유리 등)

음극(낮은 일함수 금속

Ca AlLi MgAg등)

-전자

정공

+

-+

두께 100 ~ 200 nm

Exciton

OLED OLED 작동원리작동원리

25OLED 기초공정 이해와 실습

Single-layer devices

Unbalanced carrier injection and lower efficiency

dArr

Heterostructures

ITOHILHTLEMLETLCathode(1) Lower the barrier at electrodes

Balanced carrier injection andimproved efficiency

(2) Band offsets between the layers andspace charges build up at hetero-junctionHigh carrier densitieseffective e-h capture

Multilayer StructureMultilayer Structure

Cathode

HILITO

GLASS

HTLEMLETL

-

+

26OLED 기초공정 이해와 실습

Cathode

HILITO

GLASS

HTLEMLETL

-

+

OLED Structure

N N

CH3

H3C

TPD m-MTDATA

N

N N

N

CH3

CH3

H3C

NO

NON

OAl

Alq3

Small Molecules (Fluorescence)

27OLED 기초공정 이해와 실습

OLED StructureSmall Molecules

(Phosphorescence)

NN

N

N

NN

N

N

CuN

N

NN

CuPc MTDATA

Cathode

HILITO

GLASS

HTLEML

ETL-

+

HBL

NNCH3H3C

BCP

28OLED 기초공정 이해와 실습

OLED Structure

Polymers

Cathode

ITO

GLASS

HTLEML

-

+

PEDOT

n

S O3- S O3

-S O3H S O3H S O3H S O3H

SS

SS

SS

O O

OO

O O

OO OO

n

n n

RR

PPV PF

29OLED 기초공정 이해와 실습

Cur

rent

den

sity Lum

inous Intensity

Voltage

ln V

ln J

J = qn0μVd

J = 98 εsμV2d3

Ligh

t

Current

slope = ηexte

Ex)

OLED OLED 특성특성

3 7

Diode Characteristics Rectification ratio 10 - 10 Power efficiency amp drive voltage

Light vs current

optconv ext

elec

opt opt elecext opt ext

elec elec

P hP eV

N s I IIN s I e e

νη η

η η

= =

= = rArr = times

30OLED 기초공정 이해와 실습

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

Vacuum Level

Anode

Cathode

HOMO

LUMO

Φa

Φc

EA

IP

CB

VB

Eg

에너지에너지 준위준위

31OLED 기초공정 이해와 실습

Current - Voltage Characteristics

2

16 17 3

0

0

1

diffusion voltage ~ 13 V

acceptor concentration ~ 10 - 10 cm

(~ 50 - 150 nm

2( )

Width of space charge layer 2 ( )

D

D

A

r DA

r D A

V VCV

N

C A q N V V

w V V qN

ε ε

ε ε

prop minus

= minus

= minus V = 0 )

OLED OLED 전기적전기적 특성특성

( ) Schottky equation

exp 1

ideality factor 1 1 ideal Schottky diodes B ext BJ J eV nk T V V IR

n n

⎡ ⎤= minus = minus⎣ ⎦ge =

Capacitance - Voltage Dependence

32OLED 기초공정 이해와 실습

I - V Characteristics C - V Characteristics

ITOPPVMetal Polymeric Schottky Diode

OLED OLED 전기적전기적 특성특성

33OLED 기초공정 이해와 실습

Injection Dominated Mechanisms

bull Thermionic emission

bull Tunneling

Bulk Dominated Mechanisms

bull Ohmic Conduction

bull Space Charge Limited Current Conduction

bull Space Charge Limited Current Conduction with Traps

Magnitude of Injection Barrier

전하전하 주입주입

34OLED 기초공정 이해와 실습

Thermionic Emission

Fowler-Nordheim Tunneling

2

2 2

3

exp 1 wehere exp

4 120( )

Richardson constant

bns s

B B

n B

eeVJ J J A Tk T k T

em kA m m A cm Kh

φ

π

⎡ ⎤⎛ ⎞ ⎛ ⎞minus= minus =⎢ ⎥⎜ ⎟ ⎜ ⎟

⎝ ⎠ ⎝ ⎠⎣ ⎦

= =

At low field thermionic emission at high field tunneling dominate

전하전하 주입주입

EF

Evac

-eFz(triangular shape)φ

Z=0 Z

Charge accumulationhigher the energy state `

Electron emission (F-N Tunneling)

Electron emission (Thermionic Emission)

2

3212

~ exp

( ) where 8 (2 )3

bJ EE

qb mqh

π

⎛ ⎞minus⎜ ⎟⎝ ⎠

Φ=

35OLED 기초공정 이해와 실습

Applied voltage

Lattice vibration

Localizedelectron

Hopping conductionBand-like conductionDelocalized electron

Lattice vibration(phonon)

Scattered electron

Low Mobility

bull holes μ ~10-4-10-8 Vs due to poor wave function overlap (large hopping distance)

bull electrons μ ~10-6-10-10Vs due to increased disorder and trapping at defect sites caused by impurities such as O2

rArr Build-up of space-charge density (bulk limited current)

전하전하 이동도이동도

36OLED 기초공정 이해와 실습

NoteMobility depends onElectric Field andTemperature

Mobilities of OrganicsMobilities of Organics

Alq3

37OLED 기초공정 이해와 실습

Ohmic conduction

OLEDOLED의의 전류전류

Current Dendity

current depends linearly on the bias voltageo nn qm VJd

=

2

3

0

1

2 1

(no traps)

(exponential trap distributions ( ) exp( )

one of electrodes(Ohmic contact) can supply more carriers per un

98

Current Density

SCLC condition

o

tt

r

m

m tN

VJd

T E N E kTV md T

ε ε μ

+

+ =

=

prop =

it time than can be transported through the dielectric (caused by low mobility)

Space charge limited (SCL) conduction

38OLED 기초공정 이해와 실습

2

2

3

Charge per unit area Q induced by a voltage V

Transit time across the semiconductor

9

Approximate SCLC densi

Child law (Mott- Gu

ty

Elec8

rney law)

o r

r

o rSCLC

r

VQ CVd

d dtE V

VQJt d

ε ε

μ μ

ε ε μ

= =

= =

asymp =

3 2

tric field distribution across the semiconductor

Majority space charges enhance the E field at the

3 3 ( ) at ( )2 2

enhance the injection of the cath

minority carrieode

rs (elect

V x VE x x d E dd d

= = =

rArr rons)

d

(+) (-)

x=0 x=d

Vd

15 Vd232

3)(d

xVxE =

++++

Virtual anode

-

Space Charge Limited CurrentSpace Charge Limited Current

39OLED 기초공정 이해와 실습

2

3

1

2 01

(no traps or discrete traps Mott-Gurney formula)

(exponential trap distributions ( ) exp( )

98

o rSCLC

mt

SCLC m t t

VJd

TVJ N E NmT

E kTd

ε ε μ

+

+

=

prop = =

ECB

EVB

Etrap

Discrete trapping center Exponential distributionof trapping centers

TrapTrap--Limited CurrentLimited Current

40OLED 기초공정 이해와 실습

Shen Burrows Bulovic McCarty Thompson Forrest Jpn J Appl Phys 35 L401 (1996)

ITOTPDAlq3MgAg

12

1

+

+

prop m

m

SCLC dVJ

TrapTrap--Limited CurrentLimited Current

41OLED 기초공정 이해와 실습

0

0

Activation energy at 0 Empirical parameter

Mobility at PF constant

PF

PF

E FT

T Tμβ

Δ =

=

PFPF

B eff

0

3

PFeff 0 0

( ) exp

exp( )

1 1 1with

E FFT μk T

F

qT T T

βμ

μ β

βπεε

⎛ ⎞Δ minus= minus⎜ ⎟⎜ ⎟

⎝ ⎠

equiv

= minus =

Poole Frenkel ModelPoole Frenkel Model

42OLED 기초공정 이해와 실습

1

22 2

0

0

(1)

(2)

EL F S e h

e ee he

T

h he hh

T

T rec rec e h

h eh e

h e

e hEL F S

h e

T rec

h e h e nh e EL F S EL

e h

n nJ n n nedJ n n ned

nJ

ne F

J J Je F

J Jn J J

ed n ed

η η γ

γτ

γτ

τ τ τ γ

μ

η η γμ μ

τ τ

η ηγ

minus

Φ =

minus minus =

minus minus =

lt =

=

Φ = prop

gt

= Φ = prop rArr Φ prop

EL Current RelationEL Current Relation

43OLED 기초공정 이해와 실습

Device Structure ITONPBAlq3Ca

22

21

ZZZ

fdVdQC

+minus

==πφieZiZZZ ||

))=+=

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

V0 independent of the NPB layer thickness

44OLED 기초공정 이해와 실습

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

Dashed line without interfacial charge

Wolfgang Brutting Stefan Berleb Anton G Muckl Organic Electronics 2 (2001)

Device Structure ITONPBAlq3Ca

45OLED 기초공정 이해와 실습

Langevin Recombination of carriers

bull Carriers are statistically independent therefore the e-h recombination is a random process and kinetically bimolecular

bull Total current attracted by a charge into the sphere of Coulombic capture radius rc

2

22

( ) ( )4

(4 ) 14 184

( ) (mean free path A)

n p c n pc

c cB

n p

qJ qp E qpr

qi r J Bqp r nmk T

qB a

μ μ μ μπε

ππε

μ μ λε

= + = +

= = cong asymp minus

there4 = + asympo

TkUd

BeP ~ minusProbability of dissociation

reUπε4

~2

e-

rc

Carrier RecombinationCarrier Recombination

P Langevin Ann Chem Phys 28 289 (1903)

46OLED 기초공정 이해와 실습

Electronic Processes in Organic Crystals and Polymers by MPope and C E Swenberg

ExcitonsExcitons

47OLED 기초공정 이해와 실습

C Adachi et al

Electrons and holesForm excitons

(bound e--h+ pairs)

Exciton Recombination ZoneExciton Recombination Zone

48OLED 기초공정 이해와 실습

MOLECULAR EXCITED STATESAFTER ELECTRICAL EXCITATION

Singletspin anti-symmetric

Tripletspin symmetric

25 75

MOLECULAR GROUND STATEspin anti-symmetric

Relaxation allowedfast efficientFluorescence

Relaxation disallowedslow inefficientPhosphorescence

|χ1χ2 gt = | gt

|χ1χ2 gt = | gt

|χ1χ2 gt

= | gt - | gt2

1

|χ1χ2 gt = | gt + | gt2

1ISC

Spin

OLEDOLED의의 형광형광인광인광

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 17: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

16OLED 기초공정 이해와 실습

Organic Molecular CrystalsOrganic Molecular Crystals

Inorganic semiconductors Organic semiconductors

2Bohr radius Rydberg

Band transport

Exciton Binding Energy ~25meV Exciton size ~ 50A

Strong Covalent Bond

Strong e-e screening( ~11)

Strong spin-orbit cou

ε ε

εminusprop prop

bull

bull

bull

gt

gt

gt

gt

J is a good quantum numberpling

gt

Hopping transport

Exciton Binding Energy ~ 05 - 1eV E

Exciton localized on singxciton size ~ 5 - 10A

le pol y

Weak Van der Waals interactions

Weak e-e screening( ~3)ε

bull

bull

gt

gt

gt

gt mer chain

Large exchange energy between the lowest singlet and triple

S is a good quantum number

t excitons

Weak spin-orbit couplingbullgt

gt

17OLED 기초공정 이해와 실습

Conjugated PolymerConjugated Polymer

bull sp2 bonding

poly-acetylene (1958)

bull π- electrons delocalized along the chain

bull Dimerization opens an energy gap 2-3 eV (Peierls instability)

18OLED 기초공정 이해와 실습

에너지에너지 밴드밴드 갭갭

Ionization energies of the HOMO levels and binding energies of the LUMO levels for different polyacenes in the gas phase (left solid lines) and in the crystalline state (right double lines) respectively

C C

H

H

nrarrinfin

Eg=14eV

19OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Hopping model

Small polaron model

Poole-Frenkel model

Multiple trapping amp release model

Etc (Exciton model Soliton model Ishiguro modelhellip)

20OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Hopping model

1

00

In most cases T-dep of mobility

exp where = 1 2 3 4TT

αμ μ α

⎡ ⎤⎛ ⎞⎢ ⎥= minus⎜ ⎟⎢ ⎥⎝ ⎠⎣ ⎦

Conventional semiconductor Organic semiconductorconduction band

valence band

LUMO level

HOMO level

delocalized states propagating

Phonon scattering (negative)rarr mobility increases as T darr

localized states hopping

Phonon scattering (positive)rarr mobility decreases as T darr

01 ~ 1 cm2V-1s-1

21OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Small polaron model

In a conjugated molecules a charge is self-trapped by the lattice deformationrarr creation of the localized mid gap states

Ex) A polaron in Polythiophene

32 22( ) exp

2 2

where polaron binding energy electron transfer energy lattice constant

T-dep of the mobility

bB

Bb

b

Eea J k Tk TE

EJa

πμminus ⎛ ⎞

= minus⎜ ⎟⎝ ⎠h

22OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Poole-Frenkel model

Field dependent mobility at high field (E gt 105 Vcm)

- Coulomb potential near localized states is modified by the applied field

( )120

( ) (0)exp

where (0) zero field mobility

Poole-Frenkel factor mag of electric field

T-dep amp field dep of the mobility

B

qF Fk T

eF

μ μ β

μ

β πεε

⎛ ⎞= ⎜ ⎟

⎝ ⎠

=

23OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Multiple trapping amp release model

Narrow delocalized band+ localized trap level (highly concenturated)

Process1) Carriers arrive at a trap and are trapped2) Thermally activated and released

0

0

exp

where mobility in the delocalized bandDensity of delocalized band edge

Concenturation of traps

T-dep of the mobility

tD

B

Ek T

μ μ α

μ

α

⎛ ⎞= minus⎜ ⎟

⎝ ⎠

=

24OLED 기초공정 이해와 실습

무기EL (p-n junction LED)

Light Emission

anode

cathodeETLEMLHTLHIL+

유기EL (polymers or small molecules)

전자수송층(ETL)

발광층(EML)정공

수송층(HTL)

양극(투명전극

ITO 유리 등)

음극(낮은 일함수 금속

Ca AlLi MgAg등)

-전자

정공

+

-+

두께 100 ~ 200 nm

Exciton

OLED OLED 작동원리작동원리

25OLED 기초공정 이해와 실습

Single-layer devices

Unbalanced carrier injection and lower efficiency

dArr

Heterostructures

ITOHILHTLEMLETLCathode(1) Lower the barrier at electrodes

Balanced carrier injection andimproved efficiency

(2) Band offsets between the layers andspace charges build up at hetero-junctionHigh carrier densitieseffective e-h capture

Multilayer StructureMultilayer Structure

Cathode

HILITO

GLASS

HTLEMLETL

-

+

26OLED 기초공정 이해와 실습

Cathode

HILITO

GLASS

HTLEMLETL

-

+

OLED Structure

N N

CH3

H3C

TPD m-MTDATA

N

N N

N

CH3

CH3

H3C

NO

NON

OAl

Alq3

Small Molecules (Fluorescence)

27OLED 기초공정 이해와 실습

OLED StructureSmall Molecules

(Phosphorescence)

NN

N

N

NN

N

N

CuN

N

NN

CuPc MTDATA

Cathode

HILITO

GLASS

HTLEML

ETL-

+

HBL

NNCH3H3C

BCP

28OLED 기초공정 이해와 실습

OLED Structure

Polymers

Cathode

ITO

GLASS

HTLEML

-

+

PEDOT

n

S O3- S O3

-S O3H S O3H S O3H S O3H

SS

SS

SS

O O

OO

O O

OO OO

n

n n

RR

PPV PF

29OLED 기초공정 이해와 실습

Cur

rent

den

sity Lum

inous Intensity

Voltage

ln V

ln J

J = qn0μVd

J = 98 εsμV2d3

Ligh

t

Current

slope = ηexte

Ex)

OLED OLED 특성특성

3 7

Diode Characteristics Rectification ratio 10 - 10 Power efficiency amp drive voltage

Light vs current

optconv ext

elec

opt opt elecext opt ext

elec elec

P hP eV

N s I IIN s I e e

νη η

η η

= =

= = rArr = times

30OLED 기초공정 이해와 실습

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

Vacuum Level

Anode

Cathode

HOMO

LUMO

Φa

Φc

EA

IP

CB

VB

Eg

에너지에너지 준위준위

31OLED 기초공정 이해와 실습

Current - Voltage Characteristics

2

16 17 3

0

0

1

diffusion voltage ~ 13 V

acceptor concentration ~ 10 - 10 cm

(~ 50 - 150 nm

2( )

Width of space charge layer 2 ( )

D

D

A

r DA

r D A

V VCV

N

C A q N V V

w V V qN

ε ε

ε ε

prop minus

= minus

= minus V = 0 )

OLED OLED 전기적전기적 특성특성

( ) Schottky equation

exp 1

ideality factor 1 1 ideal Schottky diodes B ext BJ J eV nk T V V IR

n n

⎡ ⎤= minus = minus⎣ ⎦ge =

Capacitance - Voltage Dependence

32OLED 기초공정 이해와 실습

I - V Characteristics C - V Characteristics

ITOPPVMetal Polymeric Schottky Diode

OLED OLED 전기적전기적 특성특성

33OLED 기초공정 이해와 실습

Injection Dominated Mechanisms

bull Thermionic emission

bull Tunneling

Bulk Dominated Mechanisms

bull Ohmic Conduction

bull Space Charge Limited Current Conduction

bull Space Charge Limited Current Conduction with Traps

Magnitude of Injection Barrier

전하전하 주입주입

34OLED 기초공정 이해와 실습

Thermionic Emission

Fowler-Nordheim Tunneling

2

2 2

3

exp 1 wehere exp

4 120( )

Richardson constant

bns s

B B

n B

eeVJ J J A Tk T k T

em kA m m A cm Kh

φ

π

⎡ ⎤⎛ ⎞ ⎛ ⎞minus= minus =⎢ ⎥⎜ ⎟ ⎜ ⎟

⎝ ⎠ ⎝ ⎠⎣ ⎦

= =

At low field thermionic emission at high field tunneling dominate

전하전하 주입주입

EF

Evac

-eFz(triangular shape)φ

Z=0 Z

Charge accumulationhigher the energy state `

Electron emission (F-N Tunneling)

Electron emission (Thermionic Emission)

2

3212

~ exp

( ) where 8 (2 )3

bJ EE

qb mqh

π

⎛ ⎞minus⎜ ⎟⎝ ⎠

Φ=

35OLED 기초공정 이해와 실습

Applied voltage

Lattice vibration

Localizedelectron

Hopping conductionBand-like conductionDelocalized electron

Lattice vibration(phonon)

Scattered electron

Low Mobility

bull holes μ ~10-4-10-8 Vs due to poor wave function overlap (large hopping distance)

bull electrons μ ~10-6-10-10Vs due to increased disorder and trapping at defect sites caused by impurities such as O2

rArr Build-up of space-charge density (bulk limited current)

전하전하 이동도이동도

36OLED 기초공정 이해와 실습

NoteMobility depends onElectric Field andTemperature

Mobilities of OrganicsMobilities of Organics

Alq3

37OLED 기초공정 이해와 실습

Ohmic conduction

OLEDOLED의의 전류전류

Current Dendity

current depends linearly on the bias voltageo nn qm VJd

=

2

3

0

1

2 1

(no traps)

(exponential trap distributions ( ) exp( )

one of electrodes(Ohmic contact) can supply more carriers per un

98

Current Density

SCLC condition

o

tt

r

m

m tN

VJd

T E N E kTV md T

ε ε μ

+

+ =

=

prop =

it time than can be transported through the dielectric (caused by low mobility)

Space charge limited (SCL) conduction

38OLED 기초공정 이해와 실습

2

2

3

Charge per unit area Q induced by a voltage V

Transit time across the semiconductor

9

Approximate SCLC densi

Child law (Mott- Gu

ty

Elec8

rney law)

o r

r

o rSCLC

r

VQ CVd

d dtE V

VQJt d

ε ε

μ μ

ε ε μ

= =

= =

asymp =

3 2

tric field distribution across the semiconductor

Majority space charges enhance the E field at the

3 3 ( ) at ( )2 2

enhance the injection of the cath

minority carrieode

rs (elect

V x VE x x d E dd d

= = =

rArr rons)

d

(+) (-)

x=0 x=d

Vd

15 Vd232

3)(d

xVxE =

++++

Virtual anode

-

Space Charge Limited CurrentSpace Charge Limited Current

39OLED 기초공정 이해와 실습

2

3

1

2 01

(no traps or discrete traps Mott-Gurney formula)

(exponential trap distributions ( ) exp( )

98

o rSCLC

mt

SCLC m t t

VJd

TVJ N E NmT

E kTd

ε ε μ

+

+

=

prop = =

ECB

EVB

Etrap

Discrete trapping center Exponential distributionof trapping centers

TrapTrap--Limited CurrentLimited Current

40OLED 기초공정 이해와 실습

Shen Burrows Bulovic McCarty Thompson Forrest Jpn J Appl Phys 35 L401 (1996)

ITOTPDAlq3MgAg

12

1

+

+

prop m

m

SCLC dVJ

TrapTrap--Limited CurrentLimited Current

41OLED 기초공정 이해와 실습

0

0

Activation energy at 0 Empirical parameter

Mobility at PF constant

PF

PF

E FT

T Tμβ

Δ =

=

PFPF

B eff

0

3

PFeff 0 0

( ) exp

exp( )

1 1 1with

E FFT μk T

F

qT T T

βμ

μ β

βπεε

⎛ ⎞Δ minus= minus⎜ ⎟⎜ ⎟

⎝ ⎠

equiv

= minus =

Poole Frenkel ModelPoole Frenkel Model

42OLED 기초공정 이해와 실습

1

22 2

0

0

(1)

(2)

EL F S e h

e ee he

T

h he hh

T

T rec rec e h

h eh e

h e

e hEL F S

h e

T rec

h e h e nh e EL F S EL

e h

n nJ n n nedJ n n ned

nJ

ne F

J J Je F

J Jn J J

ed n ed

η η γ

γτ

γτ

τ τ τ γ

μ

η η γμ μ

τ τ

η ηγ

minus

Φ =

minus minus =

minus minus =

lt =

=

Φ = prop

gt

= Φ = prop rArr Φ prop

EL Current RelationEL Current Relation

43OLED 기초공정 이해와 실습

Device Structure ITONPBAlq3Ca

22

21

ZZZ

fdVdQC

+minus

==πφieZiZZZ ||

))=+=

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

V0 independent of the NPB layer thickness

44OLED 기초공정 이해와 실습

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

Dashed line without interfacial charge

Wolfgang Brutting Stefan Berleb Anton G Muckl Organic Electronics 2 (2001)

Device Structure ITONPBAlq3Ca

45OLED 기초공정 이해와 실습

Langevin Recombination of carriers

bull Carriers are statistically independent therefore the e-h recombination is a random process and kinetically bimolecular

bull Total current attracted by a charge into the sphere of Coulombic capture radius rc

2

22

( ) ( )4

(4 ) 14 184

( ) (mean free path A)

n p c n pc

c cB

n p

qJ qp E qpr

qi r J Bqp r nmk T

qB a

μ μ μ μπε

ππε

μ μ λε

= + = +

= = cong asymp minus

there4 = + asympo

TkUd

BeP ~ minusProbability of dissociation

reUπε4

~2

e-

rc

Carrier RecombinationCarrier Recombination

P Langevin Ann Chem Phys 28 289 (1903)

46OLED 기초공정 이해와 실습

Electronic Processes in Organic Crystals and Polymers by MPope and C E Swenberg

ExcitonsExcitons

47OLED 기초공정 이해와 실습

C Adachi et al

Electrons and holesForm excitons

(bound e--h+ pairs)

Exciton Recombination ZoneExciton Recombination Zone

48OLED 기초공정 이해와 실습

MOLECULAR EXCITED STATESAFTER ELECTRICAL EXCITATION

Singletspin anti-symmetric

Tripletspin symmetric

25 75

MOLECULAR GROUND STATEspin anti-symmetric

Relaxation allowedfast efficientFluorescence

Relaxation disallowedslow inefficientPhosphorescence

|χ1χ2 gt = | gt

|χ1χ2 gt = | gt

|χ1χ2 gt

= | gt - | gt2

1

|χ1χ2 gt = | gt + | gt2

1ISC

Spin

OLEDOLED의의 형광형광인광인광

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 18: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

17OLED 기초공정 이해와 실습

Conjugated PolymerConjugated Polymer

bull sp2 bonding

poly-acetylene (1958)

bull π- electrons delocalized along the chain

bull Dimerization opens an energy gap 2-3 eV (Peierls instability)

18OLED 기초공정 이해와 실습

에너지에너지 밴드밴드 갭갭

Ionization energies of the HOMO levels and binding energies of the LUMO levels for different polyacenes in the gas phase (left solid lines) and in the crystalline state (right double lines) respectively

C C

H

H

nrarrinfin

Eg=14eV

19OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Hopping model

Small polaron model

Poole-Frenkel model

Multiple trapping amp release model

Etc (Exciton model Soliton model Ishiguro modelhellip)

20OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Hopping model

1

00

In most cases T-dep of mobility

exp where = 1 2 3 4TT

αμ μ α

⎡ ⎤⎛ ⎞⎢ ⎥= minus⎜ ⎟⎢ ⎥⎝ ⎠⎣ ⎦

Conventional semiconductor Organic semiconductorconduction band

valence band

LUMO level

HOMO level

delocalized states propagating

Phonon scattering (negative)rarr mobility increases as T darr

localized states hopping

Phonon scattering (positive)rarr mobility decreases as T darr

01 ~ 1 cm2V-1s-1

21OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Small polaron model

In a conjugated molecules a charge is self-trapped by the lattice deformationrarr creation of the localized mid gap states

Ex) A polaron in Polythiophene

32 22( ) exp

2 2

where polaron binding energy electron transfer energy lattice constant

T-dep of the mobility

bB

Bb

b

Eea J k Tk TE

EJa

πμminus ⎛ ⎞

= minus⎜ ⎟⎝ ⎠h

22OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Poole-Frenkel model

Field dependent mobility at high field (E gt 105 Vcm)

- Coulomb potential near localized states is modified by the applied field

( )120

( ) (0)exp

where (0) zero field mobility

Poole-Frenkel factor mag of electric field

T-dep amp field dep of the mobility

B

qF Fk T

eF

μ μ β

μ

β πεε

⎛ ⎞= ⎜ ⎟

⎝ ⎠

=

23OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Multiple trapping amp release model

Narrow delocalized band+ localized trap level (highly concenturated)

Process1) Carriers arrive at a trap and are trapped2) Thermally activated and released

0

0

exp

where mobility in the delocalized bandDensity of delocalized band edge

Concenturation of traps

T-dep of the mobility

tD

B

Ek T

μ μ α

μ

α

⎛ ⎞= minus⎜ ⎟

⎝ ⎠

=

24OLED 기초공정 이해와 실습

무기EL (p-n junction LED)

Light Emission

anode

cathodeETLEMLHTLHIL+

유기EL (polymers or small molecules)

전자수송층(ETL)

발광층(EML)정공

수송층(HTL)

양극(투명전극

ITO 유리 등)

음극(낮은 일함수 금속

Ca AlLi MgAg등)

-전자

정공

+

-+

두께 100 ~ 200 nm

Exciton

OLED OLED 작동원리작동원리

25OLED 기초공정 이해와 실습

Single-layer devices

Unbalanced carrier injection and lower efficiency

dArr

Heterostructures

ITOHILHTLEMLETLCathode(1) Lower the barrier at electrodes

Balanced carrier injection andimproved efficiency

(2) Band offsets between the layers andspace charges build up at hetero-junctionHigh carrier densitieseffective e-h capture

Multilayer StructureMultilayer Structure

Cathode

HILITO

GLASS

HTLEMLETL

-

+

26OLED 기초공정 이해와 실습

Cathode

HILITO

GLASS

HTLEMLETL

-

+

OLED Structure

N N

CH3

H3C

TPD m-MTDATA

N

N N

N

CH3

CH3

H3C

NO

NON

OAl

Alq3

Small Molecules (Fluorescence)

27OLED 기초공정 이해와 실습

OLED StructureSmall Molecules

(Phosphorescence)

NN

N

N

NN

N

N

CuN

N

NN

CuPc MTDATA

Cathode

HILITO

GLASS

HTLEML

ETL-

+

HBL

NNCH3H3C

BCP

28OLED 기초공정 이해와 실습

OLED Structure

Polymers

Cathode

ITO

GLASS

HTLEML

-

+

PEDOT

n

S O3- S O3

-S O3H S O3H S O3H S O3H

SS

SS

SS

O O

OO

O O

OO OO

n

n n

RR

PPV PF

29OLED 기초공정 이해와 실습

Cur

rent

den

sity Lum

inous Intensity

Voltage

ln V

ln J

J = qn0μVd

J = 98 εsμV2d3

Ligh

t

Current

slope = ηexte

Ex)

OLED OLED 특성특성

3 7

Diode Characteristics Rectification ratio 10 - 10 Power efficiency amp drive voltage

Light vs current

optconv ext

elec

opt opt elecext opt ext

elec elec

P hP eV

N s I IIN s I e e

νη η

η η

= =

= = rArr = times

30OLED 기초공정 이해와 실습

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

Vacuum Level

Anode

Cathode

HOMO

LUMO

Φa

Φc

EA

IP

CB

VB

Eg

에너지에너지 준위준위

31OLED 기초공정 이해와 실습

Current - Voltage Characteristics

2

16 17 3

0

0

1

diffusion voltage ~ 13 V

acceptor concentration ~ 10 - 10 cm

(~ 50 - 150 nm

2( )

Width of space charge layer 2 ( )

D

D

A

r DA

r D A

V VCV

N

C A q N V V

w V V qN

ε ε

ε ε

prop minus

= minus

= minus V = 0 )

OLED OLED 전기적전기적 특성특성

( ) Schottky equation

exp 1

ideality factor 1 1 ideal Schottky diodes B ext BJ J eV nk T V V IR

n n

⎡ ⎤= minus = minus⎣ ⎦ge =

Capacitance - Voltage Dependence

32OLED 기초공정 이해와 실습

I - V Characteristics C - V Characteristics

ITOPPVMetal Polymeric Schottky Diode

OLED OLED 전기적전기적 특성특성

33OLED 기초공정 이해와 실습

Injection Dominated Mechanisms

bull Thermionic emission

bull Tunneling

Bulk Dominated Mechanisms

bull Ohmic Conduction

bull Space Charge Limited Current Conduction

bull Space Charge Limited Current Conduction with Traps

Magnitude of Injection Barrier

전하전하 주입주입

34OLED 기초공정 이해와 실습

Thermionic Emission

Fowler-Nordheim Tunneling

2

2 2

3

exp 1 wehere exp

4 120( )

Richardson constant

bns s

B B

n B

eeVJ J J A Tk T k T

em kA m m A cm Kh

φ

π

⎡ ⎤⎛ ⎞ ⎛ ⎞minus= minus =⎢ ⎥⎜ ⎟ ⎜ ⎟

⎝ ⎠ ⎝ ⎠⎣ ⎦

= =

At low field thermionic emission at high field tunneling dominate

전하전하 주입주입

EF

Evac

-eFz(triangular shape)φ

Z=0 Z

Charge accumulationhigher the energy state `

Electron emission (F-N Tunneling)

Electron emission (Thermionic Emission)

2

3212

~ exp

( ) where 8 (2 )3

bJ EE

qb mqh

π

⎛ ⎞minus⎜ ⎟⎝ ⎠

Φ=

35OLED 기초공정 이해와 실습

Applied voltage

Lattice vibration

Localizedelectron

Hopping conductionBand-like conductionDelocalized electron

Lattice vibration(phonon)

Scattered electron

Low Mobility

bull holes μ ~10-4-10-8 Vs due to poor wave function overlap (large hopping distance)

bull electrons μ ~10-6-10-10Vs due to increased disorder and trapping at defect sites caused by impurities such as O2

rArr Build-up of space-charge density (bulk limited current)

전하전하 이동도이동도

36OLED 기초공정 이해와 실습

NoteMobility depends onElectric Field andTemperature

Mobilities of OrganicsMobilities of Organics

Alq3

37OLED 기초공정 이해와 실습

Ohmic conduction

OLEDOLED의의 전류전류

Current Dendity

current depends linearly on the bias voltageo nn qm VJd

=

2

3

0

1

2 1

(no traps)

(exponential trap distributions ( ) exp( )

one of electrodes(Ohmic contact) can supply more carriers per un

98

Current Density

SCLC condition

o

tt

r

m

m tN

VJd

T E N E kTV md T

ε ε μ

+

+ =

=

prop =

it time than can be transported through the dielectric (caused by low mobility)

Space charge limited (SCL) conduction

38OLED 기초공정 이해와 실습

2

2

3

Charge per unit area Q induced by a voltage V

Transit time across the semiconductor

9

Approximate SCLC densi

Child law (Mott- Gu

ty

Elec8

rney law)

o r

r

o rSCLC

r

VQ CVd

d dtE V

VQJt d

ε ε

μ μ

ε ε μ

= =

= =

asymp =

3 2

tric field distribution across the semiconductor

Majority space charges enhance the E field at the

3 3 ( ) at ( )2 2

enhance the injection of the cath

minority carrieode

rs (elect

V x VE x x d E dd d

= = =

rArr rons)

d

(+) (-)

x=0 x=d

Vd

15 Vd232

3)(d

xVxE =

++++

Virtual anode

-

Space Charge Limited CurrentSpace Charge Limited Current

39OLED 기초공정 이해와 실습

2

3

1

2 01

(no traps or discrete traps Mott-Gurney formula)

(exponential trap distributions ( ) exp( )

98

o rSCLC

mt

SCLC m t t

VJd

TVJ N E NmT

E kTd

ε ε μ

+

+

=

prop = =

ECB

EVB

Etrap

Discrete trapping center Exponential distributionof trapping centers

TrapTrap--Limited CurrentLimited Current

40OLED 기초공정 이해와 실습

Shen Burrows Bulovic McCarty Thompson Forrest Jpn J Appl Phys 35 L401 (1996)

ITOTPDAlq3MgAg

12

1

+

+

prop m

m

SCLC dVJ

TrapTrap--Limited CurrentLimited Current

41OLED 기초공정 이해와 실습

0

0

Activation energy at 0 Empirical parameter

Mobility at PF constant

PF

PF

E FT

T Tμβ

Δ =

=

PFPF

B eff

0

3

PFeff 0 0

( ) exp

exp( )

1 1 1with

E FFT μk T

F

qT T T

βμ

μ β

βπεε

⎛ ⎞Δ minus= minus⎜ ⎟⎜ ⎟

⎝ ⎠

equiv

= minus =

Poole Frenkel ModelPoole Frenkel Model

42OLED 기초공정 이해와 실습

1

22 2

0

0

(1)

(2)

EL F S e h

e ee he

T

h he hh

T

T rec rec e h

h eh e

h e

e hEL F S

h e

T rec

h e h e nh e EL F S EL

e h

n nJ n n nedJ n n ned

nJ

ne F

J J Je F

J Jn J J

ed n ed

η η γ

γτ

γτ

τ τ τ γ

μ

η η γμ μ

τ τ

η ηγ

minus

Φ =

minus minus =

minus minus =

lt =

=

Φ = prop

gt

= Φ = prop rArr Φ prop

EL Current RelationEL Current Relation

43OLED 기초공정 이해와 실습

Device Structure ITONPBAlq3Ca

22

21

ZZZ

fdVdQC

+minus

==πφieZiZZZ ||

))=+=

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

V0 independent of the NPB layer thickness

44OLED 기초공정 이해와 실습

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

Dashed line without interfacial charge

Wolfgang Brutting Stefan Berleb Anton G Muckl Organic Electronics 2 (2001)

Device Structure ITONPBAlq3Ca

45OLED 기초공정 이해와 실습

Langevin Recombination of carriers

bull Carriers are statistically independent therefore the e-h recombination is a random process and kinetically bimolecular

bull Total current attracted by a charge into the sphere of Coulombic capture radius rc

2

22

( ) ( )4

(4 ) 14 184

( ) (mean free path A)

n p c n pc

c cB

n p

qJ qp E qpr

qi r J Bqp r nmk T

qB a

μ μ μ μπε

ππε

μ μ λε

= + = +

= = cong asymp minus

there4 = + asympo

TkUd

BeP ~ minusProbability of dissociation

reUπε4

~2

e-

rc

Carrier RecombinationCarrier Recombination

P Langevin Ann Chem Phys 28 289 (1903)

46OLED 기초공정 이해와 실습

Electronic Processes in Organic Crystals and Polymers by MPope and C E Swenberg

ExcitonsExcitons

47OLED 기초공정 이해와 실습

C Adachi et al

Electrons and holesForm excitons

(bound e--h+ pairs)

Exciton Recombination ZoneExciton Recombination Zone

48OLED 기초공정 이해와 실습

MOLECULAR EXCITED STATESAFTER ELECTRICAL EXCITATION

Singletspin anti-symmetric

Tripletspin symmetric

25 75

MOLECULAR GROUND STATEspin anti-symmetric

Relaxation allowedfast efficientFluorescence

Relaxation disallowedslow inefficientPhosphorescence

|χ1χ2 gt = | gt

|χ1χ2 gt = | gt

|χ1χ2 gt

= | gt - | gt2

1

|χ1χ2 gt = | gt + | gt2

1ISC

Spin

OLEDOLED의의 형광형광인광인광

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 19: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

18OLED 기초공정 이해와 실습

에너지에너지 밴드밴드 갭갭

Ionization energies of the HOMO levels and binding energies of the LUMO levels for different polyacenes in the gas phase (left solid lines) and in the crystalline state (right double lines) respectively

C C

H

H

nrarrinfin

Eg=14eV

19OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Hopping model

Small polaron model

Poole-Frenkel model

Multiple trapping amp release model

Etc (Exciton model Soliton model Ishiguro modelhellip)

20OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Hopping model

1

00

In most cases T-dep of mobility

exp where = 1 2 3 4TT

αμ μ α

⎡ ⎤⎛ ⎞⎢ ⎥= minus⎜ ⎟⎢ ⎥⎝ ⎠⎣ ⎦

Conventional semiconductor Organic semiconductorconduction band

valence band

LUMO level

HOMO level

delocalized states propagating

Phonon scattering (negative)rarr mobility increases as T darr

localized states hopping

Phonon scattering (positive)rarr mobility decreases as T darr

01 ~ 1 cm2V-1s-1

21OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Small polaron model

In a conjugated molecules a charge is self-trapped by the lattice deformationrarr creation of the localized mid gap states

Ex) A polaron in Polythiophene

32 22( ) exp

2 2

where polaron binding energy electron transfer energy lattice constant

T-dep of the mobility

bB

Bb

b

Eea J k Tk TE

EJa

πμminus ⎛ ⎞

= minus⎜ ⎟⎝ ⎠h

22OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Poole-Frenkel model

Field dependent mobility at high field (E gt 105 Vcm)

- Coulomb potential near localized states is modified by the applied field

( )120

( ) (0)exp

where (0) zero field mobility

Poole-Frenkel factor mag of electric field

T-dep amp field dep of the mobility

B

qF Fk T

eF

μ μ β

μ

β πεε

⎛ ⎞= ⎜ ⎟

⎝ ⎠

=

23OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Multiple trapping amp release model

Narrow delocalized band+ localized trap level (highly concenturated)

Process1) Carriers arrive at a trap and are trapped2) Thermally activated and released

0

0

exp

where mobility in the delocalized bandDensity of delocalized band edge

Concenturation of traps

T-dep of the mobility

tD

B

Ek T

μ μ α

μ

α

⎛ ⎞= minus⎜ ⎟

⎝ ⎠

=

24OLED 기초공정 이해와 실습

무기EL (p-n junction LED)

Light Emission

anode

cathodeETLEMLHTLHIL+

유기EL (polymers or small molecules)

전자수송층(ETL)

발광층(EML)정공

수송층(HTL)

양극(투명전극

ITO 유리 등)

음극(낮은 일함수 금속

Ca AlLi MgAg등)

-전자

정공

+

-+

두께 100 ~ 200 nm

Exciton

OLED OLED 작동원리작동원리

25OLED 기초공정 이해와 실습

Single-layer devices

Unbalanced carrier injection and lower efficiency

dArr

Heterostructures

ITOHILHTLEMLETLCathode(1) Lower the barrier at electrodes

Balanced carrier injection andimproved efficiency

(2) Band offsets between the layers andspace charges build up at hetero-junctionHigh carrier densitieseffective e-h capture

Multilayer StructureMultilayer Structure

Cathode

HILITO

GLASS

HTLEMLETL

-

+

26OLED 기초공정 이해와 실습

Cathode

HILITO

GLASS

HTLEMLETL

-

+

OLED Structure

N N

CH3

H3C

TPD m-MTDATA

N

N N

N

CH3

CH3

H3C

NO

NON

OAl

Alq3

Small Molecules (Fluorescence)

27OLED 기초공정 이해와 실습

OLED StructureSmall Molecules

(Phosphorescence)

NN

N

N

NN

N

N

CuN

N

NN

CuPc MTDATA

Cathode

HILITO

GLASS

HTLEML

ETL-

+

HBL

NNCH3H3C

BCP

28OLED 기초공정 이해와 실습

OLED Structure

Polymers

Cathode

ITO

GLASS

HTLEML

-

+

PEDOT

n

S O3- S O3

-S O3H S O3H S O3H S O3H

SS

SS

SS

O O

OO

O O

OO OO

n

n n

RR

PPV PF

29OLED 기초공정 이해와 실습

Cur

rent

den

sity Lum

inous Intensity

Voltage

ln V

ln J

J = qn0μVd

J = 98 εsμV2d3

Ligh

t

Current

slope = ηexte

Ex)

OLED OLED 특성특성

3 7

Diode Characteristics Rectification ratio 10 - 10 Power efficiency amp drive voltage

Light vs current

optconv ext

elec

opt opt elecext opt ext

elec elec

P hP eV

N s I IIN s I e e

νη η

η η

= =

= = rArr = times

30OLED 기초공정 이해와 실습

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

Vacuum Level

Anode

Cathode

HOMO

LUMO

Φa

Φc

EA

IP

CB

VB

Eg

에너지에너지 준위준위

31OLED 기초공정 이해와 실습

Current - Voltage Characteristics

2

16 17 3

0

0

1

diffusion voltage ~ 13 V

acceptor concentration ~ 10 - 10 cm

(~ 50 - 150 nm

2( )

Width of space charge layer 2 ( )

D

D

A

r DA

r D A

V VCV

N

C A q N V V

w V V qN

ε ε

ε ε

prop minus

= minus

= minus V = 0 )

OLED OLED 전기적전기적 특성특성

( ) Schottky equation

exp 1

ideality factor 1 1 ideal Schottky diodes B ext BJ J eV nk T V V IR

n n

⎡ ⎤= minus = minus⎣ ⎦ge =

Capacitance - Voltage Dependence

32OLED 기초공정 이해와 실습

I - V Characteristics C - V Characteristics

ITOPPVMetal Polymeric Schottky Diode

OLED OLED 전기적전기적 특성특성

33OLED 기초공정 이해와 실습

Injection Dominated Mechanisms

bull Thermionic emission

bull Tunneling

Bulk Dominated Mechanisms

bull Ohmic Conduction

bull Space Charge Limited Current Conduction

bull Space Charge Limited Current Conduction with Traps

Magnitude of Injection Barrier

전하전하 주입주입

34OLED 기초공정 이해와 실습

Thermionic Emission

Fowler-Nordheim Tunneling

2

2 2

3

exp 1 wehere exp

4 120( )

Richardson constant

bns s

B B

n B

eeVJ J J A Tk T k T

em kA m m A cm Kh

φ

π

⎡ ⎤⎛ ⎞ ⎛ ⎞minus= minus =⎢ ⎥⎜ ⎟ ⎜ ⎟

⎝ ⎠ ⎝ ⎠⎣ ⎦

= =

At low field thermionic emission at high field tunneling dominate

전하전하 주입주입

EF

Evac

-eFz(triangular shape)φ

Z=0 Z

Charge accumulationhigher the energy state `

Electron emission (F-N Tunneling)

Electron emission (Thermionic Emission)

2

3212

~ exp

( ) where 8 (2 )3

bJ EE

qb mqh

π

⎛ ⎞minus⎜ ⎟⎝ ⎠

Φ=

35OLED 기초공정 이해와 실습

Applied voltage

Lattice vibration

Localizedelectron

Hopping conductionBand-like conductionDelocalized electron

Lattice vibration(phonon)

Scattered electron

Low Mobility

bull holes μ ~10-4-10-8 Vs due to poor wave function overlap (large hopping distance)

bull electrons μ ~10-6-10-10Vs due to increased disorder and trapping at defect sites caused by impurities such as O2

rArr Build-up of space-charge density (bulk limited current)

전하전하 이동도이동도

36OLED 기초공정 이해와 실습

NoteMobility depends onElectric Field andTemperature

Mobilities of OrganicsMobilities of Organics

Alq3

37OLED 기초공정 이해와 실습

Ohmic conduction

OLEDOLED의의 전류전류

Current Dendity

current depends linearly on the bias voltageo nn qm VJd

=

2

3

0

1

2 1

(no traps)

(exponential trap distributions ( ) exp( )

one of electrodes(Ohmic contact) can supply more carriers per un

98

Current Density

SCLC condition

o

tt

r

m

m tN

VJd

T E N E kTV md T

ε ε μ

+

+ =

=

prop =

it time than can be transported through the dielectric (caused by low mobility)

Space charge limited (SCL) conduction

38OLED 기초공정 이해와 실습

2

2

3

Charge per unit area Q induced by a voltage V

Transit time across the semiconductor

9

Approximate SCLC densi

Child law (Mott- Gu

ty

Elec8

rney law)

o r

r

o rSCLC

r

VQ CVd

d dtE V

VQJt d

ε ε

μ μ

ε ε μ

= =

= =

asymp =

3 2

tric field distribution across the semiconductor

Majority space charges enhance the E field at the

3 3 ( ) at ( )2 2

enhance the injection of the cath

minority carrieode

rs (elect

V x VE x x d E dd d

= = =

rArr rons)

d

(+) (-)

x=0 x=d

Vd

15 Vd232

3)(d

xVxE =

++++

Virtual anode

-

Space Charge Limited CurrentSpace Charge Limited Current

39OLED 기초공정 이해와 실습

2

3

1

2 01

(no traps or discrete traps Mott-Gurney formula)

(exponential trap distributions ( ) exp( )

98

o rSCLC

mt

SCLC m t t

VJd

TVJ N E NmT

E kTd

ε ε μ

+

+

=

prop = =

ECB

EVB

Etrap

Discrete trapping center Exponential distributionof trapping centers

TrapTrap--Limited CurrentLimited Current

40OLED 기초공정 이해와 실습

Shen Burrows Bulovic McCarty Thompson Forrest Jpn J Appl Phys 35 L401 (1996)

ITOTPDAlq3MgAg

12

1

+

+

prop m

m

SCLC dVJ

TrapTrap--Limited CurrentLimited Current

41OLED 기초공정 이해와 실습

0

0

Activation energy at 0 Empirical parameter

Mobility at PF constant

PF

PF

E FT

T Tμβ

Δ =

=

PFPF

B eff

0

3

PFeff 0 0

( ) exp

exp( )

1 1 1with

E FFT μk T

F

qT T T

βμ

μ β

βπεε

⎛ ⎞Δ minus= minus⎜ ⎟⎜ ⎟

⎝ ⎠

equiv

= minus =

Poole Frenkel ModelPoole Frenkel Model

42OLED 기초공정 이해와 실습

1

22 2

0

0

(1)

(2)

EL F S e h

e ee he

T

h he hh

T

T rec rec e h

h eh e

h e

e hEL F S

h e

T rec

h e h e nh e EL F S EL

e h

n nJ n n nedJ n n ned

nJ

ne F

J J Je F

J Jn J J

ed n ed

η η γ

γτ

γτ

τ τ τ γ

μ

η η γμ μ

τ τ

η ηγ

minus

Φ =

minus minus =

minus minus =

lt =

=

Φ = prop

gt

= Φ = prop rArr Φ prop

EL Current RelationEL Current Relation

43OLED 기초공정 이해와 실습

Device Structure ITONPBAlq3Ca

22

21

ZZZ

fdVdQC

+minus

==πφieZiZZZ ||

))=+=

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

V0 independent of the NPB layer thickness

44OLED 기초공정 이해와 실습

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

Dashed line without interfacial charge

Wolfgang Brutting Stefan Berleb Anton G Muckl Organic Electronics 2 (2001)

Device Structure ITONPBAlq3Ca

45OLED 기초공정 이해와 실습

Langevin Recombination of carriers

bull Carriers are statistically independent therefore the e-h recombination is a random process and kinetically bimolecular

bull Total current attracted by a charge into the sphere of Coulombic capture radius rc

2

22

( ) ( )4

(4 ) 14 184

( ) (mean free path A)

n p c n pc

c cB

n p

qJ qp E qpr

qi r J Bqp r nmk T

qB a

μ μ μ μπε

ππε

μ μ λε

= + = +

= = cong asymp minus

there4 = + asympo

TkUd

BeP ~ minusProbability of dissociation

reUπε4

~2

e-

rc

Carrier RecombinationCarrier Recombination

P Langevin Ann Chem Phys 28 289 (1903)

46OLED 기초공정 이해와 실습

Electronic Processes in Organic Crystals and Polymers by MPope and C E Swenberg

ExcitonsExcitons

47OLED 기초공정 이해와 실습

C Adachi et al

Electrons and holesForm excitons

(bound e--h+ pairs)

Exciton Recombination ZoneExciton Recombination Zone

48OLED 기초공정 이해와 실습

MOLECULAR EXCITED STATESAFTER ELECTRICAL EXCITATION

Singletspin anti-symmetric

Tripletspin symmetric

25 75

MOLECULAR GROUND STATEspin anti-symmetric

Relaxation allowedfast efficientFluorescence

Relaxation disallowedslow inefficientPhosphorescence

|χ1χ2 gt = | gt

|χ1χ2 gt = | gt

|χ1χ2 gt

= | gt - | gt2

1

|χ1χ2 gt = | gt + | gt2

1ISC

Spin

OLEDOLED의의 형광형광인광인광

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 20: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

19OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Hopping model

Small polaron model

Poole-Frenkel model

Multiple trapping amp release model

Etc (Exciton model Soliton model Ishiguro modelhellip)

20OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Hopping model

1

00

In most cases T-dep of mobility

exp where = 1 2 3 4TT

αμ μ α

⎡ ⎤⎛ ⎞⎢ ⎥= minus⎜ ⎟⎢ ⎥⎝ ⎠⎣ ⎦

Conventional semiconductor Organic semiconductorconduction band

valence band

LUMO level

HOMO level

delocalized states propagating

Phonon scattering (negative)rarr mobility increases as T darr

localized states hopping

Phonon scattering (positive)rarr mobility decreases as T darr

01 ~ 1 cm2V-1s-1

21OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Small polaron model

In a conjugated molecules a charge is self-trapped by the lattice deformationrarr creation of the localized mid gap states

Ex) A polaron in Polythiophene

32 22( ) exp

2 2

where polaron binding energy electron transfer energy lattice constant

T-dep of the mobility

bB

Bb

b

Eea J k Tk TE

EJa

πμminus ⎛ ⎞

= minus⎜ ⎟⎝ ⎠h

22OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Poole-Frenkel model

Field dependent mobility at high field (E gt 105 Vcm)

- Coulomb potential near localized states is modified by the applied field

( )120

( ) (0)exp

where (0) zero field mobility

Poole-Frenkel factor mag of electric field

T-dep amp field dep of the mobility

B

qF Fk T

eF

μ μ β

μ

β πεε

⎛ ⎞= ⎜ ⎟

⎝ ⎠

=

23OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Multiple trapping amp release model

Narrow delocalized band+ localized trap level (highly concenturated)

Process1) Carriers arrive at a trap and are trapped2) Thermally activated and released

0

0

exp

where mobility in the delocalized bandDensity of delocalized band edge

Concenturation of traps

T-dep of the mobility

tD

B

Ek T

μ μ α

μ

α

⎛ ⎞= minus⎜ ⎟

⎝ ⎠

=

24OLED 기초공정 이해와 실습

무기EL (p-n junction LED)

Light Emission

anode

cathodeETLEMLHTLHIL+

유기EL (polymers or small molecules)

전자수송층(ETL)

발광층(EML)정공

수송층(HTL)

양극(투명전극

ITO 유리 등)

음극(낮은 일함수 금속

Ca AlLi MgAg등)

-전자

정공

+

-+

두께 100 ~ 200 nm

Exciton

OLED OLED 작동원리작동원리

25OLED 기초공정 이해와 실습

Single-layer devices

Unbalanced carrier injection and lower efficiency

dArr

Heterostructures

ITOHILHTLEMLETLCathode(1) Lower the barrier at electrodes

Balanced carrier injection andimproved efficiency

(2) Band offsets between the layers andspace charges build up at hetero-junctionHigh carrier densitieseffective e-h capture

Multilayer StructureMultilayer Structure

Cathode

HILITO

GLASS

HTLEMLETL

-

+

26OLED 기초공정 이해와 실습

Cathode

HILITO

GLASS

HTLEMLETL

-

+

OLED Structure

N N

CH3

H3C

TPD m-MTDATA

N

N N

N

CH3

CH3

H3C

NO

NON

OAl

Alq3

Small Molecules (Fluorescence)

27OLED 기초공정 이해와 실습

OLED StructureSmall Molecules

(Phosphorescence)

NN

N

N

NN

N

N

CuN

N

NN

CuPc MTDATA

Cathode

HILITO

GLASS

HTLEML

ETL-

+

HBL

NNCH3H3C

BCP

28OLED 기초공정 이해와 실습

OLED Structure

Polymers

Cathode

ITO

GLASS

HTLEML

-

+

PEDOT

n

S O3- S O3

-S O3H S O3H S O3H S O3H

SS

SS

SS

O O

OO

O O

OO OO

n

n n

RR

PPV PF

29OLED 기초공정 이해와 실습

Cur

rent

den

sity Lum

inous Intensity

Voltage

ln V

ln J

J = qn0μVd

J = 98 εsμV2d3

Ligh

t

Current

slope = ηexte

Ex)

OLED OLED 특성특성

3 7

Diode Characteristics Rectification ratio 10 - 10 Power efficiency amp drive voltage

Light vs current

optconv ext

elec

opt opt elecext opt ext

elec elec

P hP eV

N s I IIN s I e e

νη η

η η

= =

= = rArr = times

30OLED 기초공정 이해와 실습

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

Vacuum Level

Anode

Cathode

HOMO

LUMO

Φa

Φc

EA

IP

CB

VB

Eg

에너지에너지 준위준위

31OLED 기초공정 이해와 실습

Current - Voltage Characteristics

2

16 17 3

0

0

1

diffusion voltage ~ 13 V

acceptor concentration ~ 10 - 10 cm

(~ 50 - 150 nm

2( )

Width of space charge layer 2 ( )

D

D

A

r DA

r D A

V VCV

N

C A q N V V

w V V qN

ε ε

ε ε

prop minus

= minus

= minus V = 0 )

OLED OLED 전기적전기적 특성특성

( ) Schottky equation

exp 1

ideality factor 1 1 ideal Schottky diodes B ext BJ J eV nk T V V IR

n n

⎡ ⎤= minus = minus⎣ ⎦ge =

Capacitance - Voltage Dependence

32OLED 기초공정 이해와 실습

I - V Characteristics C - V Characteristics

ITOPPVMetal Polymeric Schottky Diode

OLED OLED 전기적전기적 특성특성

33OLED 기초공정 이해와 실습

Injection Dominated Mechanisms

bull Thermionic emission

bull Tunneling

Bulk Dominated Mechanisms

bull Ohmic Conduction

bull Space Charge Limited Current Conduction

bull Space Charge Limited Current Conduction with Traps

Magnitude of Injection Barrier

전하전하 주입주입

34OLED 기초공정 이해와 실습

Thermionic Emission

Fowler-Nordheim Tunneling

2

2 2

3

exp 1 wehere exp

4 120( )

Richardson constant

bns s

B B

n B

eeVJ J J A Tk T k T

em kA m m A cm Kh

φ

π

⎡ ⎤⎛ ⎞ ⎛ ⎞minus= minus =⎢ ⎥⎜ ⎟ ⎜ ⎟

⎝ ⎠ ⎝ ⎠⎣ ⎦

= =

At low field thermionic emission at high field tunneling dominate

전하전하 주입주입

EF

Evac

-eFz(triangular shape)φ

Z=0 Z

Charge accumulationhigher the energy state `

Electron emission (F-N Tunneling)

Electron emission (Thermionic Emission)

2

3212

~ exp

( ) where 8 (2 )3

bJ EE

qb mqh

π

⎛ ⎞minus⎜ ⎟⎝ ⎠

Φ=

35OLED 기초공정 이해와 실습

Applied voltage

Lattice vibration

Localizedelectron

Hopping conductionBand-like conductionDelocalized electron

Lattice vibration(phonon)

Scattered electron

Low Mobility

bull holes μ ~10-4-10-8 Vs due to poor wave function overlap (large hopping distance)

bull electrons μ ~10-6-10-10Vs due to increased disorder and trapping at defect sites caused by impurities such as O2

rArr Build-up of space-charge density (bulk limited current)

전하전하 이동도이동도

36OLED 기초공정 이해와 실습

NoteMobility depends onElectric Field andTemperature

Mobilities of OrganicsMobilities of Organics

Alq3

37OLED 기초공정 이해와 실습

Ohmic conduction

OLEDOLED의의 전류전류

Current Dendity

current depends linearly on the bias voltageo nn qm VJd

=

2

3

0

1

2 1

(no traps)

(exponential trap distributions ( ) exp( )

one of electrodes(Ohmic contact) can supply more carriers per un

98

Current Density

SCLC condition

o

tt

r

m

m tN

VJd

T E N E kTV md T

ε ε μ

+

+ =

=

prop =

it time than can be transported through the dielectric (caused by low mobility)

Space charge limited (SCL) conduction

38OLED 기초공정 이해와 실습

2

2

3

Charge per unit area Q induced by a voltage V

Transit time across the semiconductor

9

Approximate SCLC densi

Child law (Mott- Gu

ty

Elec8

rney law)

o r

r

o rSCLC

r

VQ CVd

d dtE V

VQJt d

ε ε

μ μ

ε ε μ

= =

= =

asymp =

3 2

tric field distribution across the semiconductor

Majority space charges enhance the E field at the

3 3 ( ) at ( )2 2

enhance the injection of the cath

minority carrieode

rs (elect

V x VE x x d E dd d

= = =

rArr rons)

d

(+) (-)

x=0 x=d

Vd

15 Vd232

3)(d

xVxE =

++++

Virtual anode

-

Space Charge Limited CurrentSpace Charge Limited Current

39OLED 기초공정 이해와 실습

2

3

1

2 01

(no traps or discrete traps Mott-Gurney formula)

(exponential trap distributions ( ) exp( )

98

o rSCLC

mt

SCLC m t t

VJd

TVJ N E NmT

E kTd

ε ε μ

+

+

=

prop = =

ECB

EVB

Etrap

Discrete trapping center Exponential distributionof trapping centers

TrapTrap--Limited CurrentLimited Current

40OLED 기초공정 이해와 실습

Shen Burrows Bulovic McCarty Thompson Forrest Jpn J Appl Phys 35 L401 (1996)

ITOTPDAlq3MgAg

12

1

+

+

prop m

m

SCLC dVJ

TrapTrap--Limited CurrentLimited Current

41OLED 기초공정 이해와 실습

0

0

Activation energy at 0 Empirical parameter

Mobility at PF constant

PF

PF

E FT

T Tμβ

Δ =

=

PFPF

B eff

0

3

PFeff 0 0

( ) exp

exp( )

1 1 1with

E FFT μk T

F

qT T T

βμ

μ β

βπεε

⎛ ⎞Δ minus= minus⎜ ⎟⎜ ⎟

⎝ ⎠

equiv

= minus =

Poole Frenkel ModelPoole Frenkel Model

42OLED 기초공정 이해와 실습

1

22 2

0

0

(1)

(2)

EL F S e h

e ee he

T

h he hh

T

T rec rec e h

h eh e

h e

e hEL F S

h e

T rec

h e h e nh e EL F S EL

e h

n nJ n n nedJ n n ned

nJ

ne F

J J Je F

J Jn J J

ed n ed

η η γ

γτ

γτ

τ τ τ γ

μ

η η γμ μ

τ τ

η ηγ

minus

Φ =

minus minus =

minus minus =

lt =

=

Φ = prop

gt

= Φ = prop rArr Φ prop

EL Current RelationEL Current Relation

43OLED 기초공정 이해와 실습

Device Structure ITONPBAlq3Ca

22

21

ZZZ

fdVdQC

+minus

==πφieZiZZZ ||

))=+=

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

V0 independent of the NPB layer thickness

44OLED 기초공정 이해와 실습

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

Dashed line without interfacial charge

Wolfgang Brutting Stefan Berleb Anton G Muckl Organic Electronics 2 (2001)

Device Structure ITONPBAlq3Ca

45OLED 기초공정 이해와 실습

Langevin Recombination of carriers

bull Carriers are statistically independent therefore the e-h recombination is a random process and kinetically bimolecular

bull Total current attracted by a charge into the sphere of Coulombic capture radius rc

2

22

( ) ( )4

(4 ) 14 184

( ) (mean free path A)

n p c n pc

c cB

n p

qJ qp E qpr

qi r J Bqp r nmk T

qB a

μ μ μ μπε

ππε

μ μ λε

= + = +

= = cong asymp minus

there4 = + asympo

TkUd

BeP ~ minusProbability of dissociation

reUπε4

~2

e-

rc

Carrier RecombinationCarrier Recombination

P Langevin Ann Chem Phys 28 289 (1903)

46OLED 기초공정 이해와 실습

Electronic Processes in Organic Crystals and Polymers by MPope and C E Swenberg

ExcitonsExcitons

47OLED 기초공정 이해와 실습

C Adachi et al

Electrons and holesForm excitons

(bound e--h+ pairs)

Exciton Recombination ZoneExciton Recombination Zone

48OLED 기초공정 이해와 실습

MOLECULAR EXCITED STATESAFTER ELECTRICAL EXCITATION

Singletspin anti-symmetric

Tripletspin symmetric

25 75

MOLECULAR GROUND STATEspin anti-symmetric

Relaxation allowedfast efficientFluorescence

Relaxation disallowedslow inefficientPhosphorescence

|χ1χ2 gt = | gt

|χ1χ2 gt = | gt

|χ1χ2 gt

= | gt - | gt2

1

|χ1χ2 gt = | gt + | gt2

1ISC

Spin

OLEDOLED의의 형광형광인광인광

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 21: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

20OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Hopping model

1

00

In most cases T-dep of mobility

exp where = 1 2 3 4TT

αμ μ α

⎡ ⎤⎛ ⎞⎢ ⎥= minus⎜ ⎟⎢ ⎥⎝ ⎠⎣ ⎦

Conventional semiconductor Organic semiconductorconduction band

valence band

LUMO level

HOMO level

delocalized states propagating

Phonon scattering (negative)rarr mobility increases as T darr

localized states hopping

Phonon scattering (positive)rarr mobility decreases as T darr

01 ~ 1 cm2V-1s-1

21OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Small polaron model

In a conjugated molecules a charge is self-trapped by the lattice deformationrarr creation of the localized mid gap states

Ex) A polaron in Polythiophene

32 22( ) exp

2 2

where polaron binding energy electron transfer energy lattice constant

T-dep of the mobility

bB

Bb

b

Eea J k Tk TE

EJa

πμminus ⎛ ⎞

= minus⎜ ⎟⎝ ⎠h

22OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Poole-Frenkel model

Field dependent mobility at high field (E gt 105 Vcm)

- Coulomb potential near localized states is modified by the applied field

( )120

( ) (0)exp

where (0) zero field mobility

Poole-Frenkel factor mag of electric field

T-dep amp field dep of the mobility

B

qF Fk T

eF

μ μ β

μ

β πεε

⎛ ⎞= ⎜ ⎟

⎝ ⎠

=

23OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Multiple trapping amp release model

Narrow delocalized band+ localized trap level (highly concenturated)

Process1) Carriers arrive at a trap and are trapped2) Thermally activated and released

0

0

exp

where mobility in the delocalized bandDensity of delocalized band edge

Concenturation of traps

T-dep of the mobility

tD

B

Ek T

μ μ α

μ

α

⎛ ⎞= minus⎜ ⎟

⎝ ⎠

=

24OLED 기초공정 이해와 실습

무기EL (p-n junction LED)

Light Emission

anode

cathodeETLEMLHTLHIL+

유기EL (polymers or small molecules)

전자수송층(ETL)

발광층(EML)정공

수송층(HTL)

양극(투명전극

ITO 유리 등)

음극(낮은 일함수 금속

Ca AlLi MgAg등)

-전자

정공

+

-+

두께 100 ~ 200 nm

Exciton

OLED OLED 작동원리작동원리

25OLED 기초공정 이해와 실습

Single-layer devices

Unbalanced carrier injection and lower efficiency

dArr

Heterostructures

ITOHILHTLEMLETLCathode(1) Lower the barrier at electrodes

Balanced carrier injection andimproved efficiency

(2) Band offsets between the layers andspace charges build up at hetero-junctionHigh carrier densitieseffective e-h capture

Multilayer StructureMultilayer Structure

Cathode

HILITO

GLASS

HTLEMLETL

-

+

26OLED 기초공정 이해와 실습

Cathode

HILITO

GLASS

HTLEMLETL

-

+

OLED Structure

N N

CH3

H3C

TPD m-MTDATA

N

N N

N

CH3

CH3

H3C

NO

NON

OAl

Alq3

Small Molecules (Fluorescence)

27OLED 기초공정 이해와 실습

OLED StructureSmall Molecules

(Phosphorescence)

NN

N

N

NN

N

N

CuN

N

NN

CuPc MTDATA

Cathode

HILITO

GLASS

HTLEML

ETL-

+

HBL

NNCH3H3C

BCP

28OLED 기초공정 이해와 실습

OLED Structure

Polymers

Cathode

ITO

GLASS

HTLEML

-

+

PEDOT

n

S O3- S O3

-S O3H S O3H S O3H S O3H

SS

SS

SS

O O

OO

O O

OO OO

n

n n

RR

PPV PF

29OLED 기초공정 이해와 실습

Cur

rent

den

sity Lum

inous Intensity

Voltage

ln V

ln J

J = qn0μVd

J = 98 εsμV2d3

Ligh

t

Current

slope = ηexte

Ex)

OLED OLED 특성특성

3 7

Diode Characteristics Rectification ratio 10 - 10 Power efficiency amp drive voltage

Light vs current

optconv ext

elec

opt opt elecext opt ext

elec elec

P hP eV

N s I IIN s I e e

νη η

η η

= =

= = rArr = times

30OLED 기초공정 이해와 실습

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

Vacuum Level

Anode

Cathode

HOMO

LUMO

Φa

Φc

EA

IP

CB

VB

Eg

에너지에너지 준위준위

31OLED 기초공정 이해와 실습

Current - Voltage Characteristics

2

16 17 3

0

0

1

diffusion voltage ~ 13 V

acceptor concentration ~ 10 - 10 cm

(~ 50 - 150 nm

2( )

Width of space charge layer 2 ( )

D

D

A

r DA

r D A

V VCV

N

C A q N V V

w V V qN

ε ε

ε ε

prop minus

= minus

= minus V = 0 )

OLED OLED 전기적전기적 특성특성

( ) Schottky equation

exp 1

ideality factor 1 1 ideal Schottky diodes B ext BJ J eV nk T V V IR

n n

⎡ ⎤= minus = minus⎣ ⎦ge =

Capacitance - Voltage Dependence

32OLED 기초공정 이해와 실습

I - V Characteristics C - V Characteristics

ITOPPVMetal Polymeric Schottky Diode

OLED OLED 전기적전기적 특성특성

33OLED 기초공정 이해와 실습

Injection Dominated Mechanisms

bull Thermionic emission

bull Tunneling

Bulk Dominated Mechanisms

bull Ohmic Conduction

bull Space Charge Limited Current Conduction

bull Space Charge Limited Current Conduction with Traps

Magnitude of Injection Barrier

전하전하 주입주입

34OLED 기초공정 이해와 실습

Thermionic Emission

Fowler-Nordheim Tunneling

2

2 2

3

exp 1 wehere exp

4 120( )

Richardson constant

bns s

B B

n B

eeVJ J J A Tk T k T

em kA m m A cm Kh

φ

π

⎡ ⎤⎛ ⎞ ⎛ ⎞minus= minus =⎢ ⎥⎜ ⎟ ⎜ ⎟

⎝ ⎠ ⎝ ⎠⎣ ⎦

= =

At low field thermionic emission at high field tunneling dominate

전하전하 주입주입

EF

Evac

-eFz(triangular shape)φ

Z=0 Z

Charge accumulationhigher the energy state `

Electron emission (F-N Tunneling)

Electron emission (Thermionic Emission)

2

3212

~ exp

( ) where 8 (2 )3

bJ EE

qb mqh

π

⎛ ⎞minus⎜ ⎟⎝ ⎠

Φ=

35OLED 기초공정 이해와 실습

Applied voltage

Lattice vibration

Localizedelectron

Hopping conductionBand-like conductionDelocalized electron

Lattice vibration(phonon)

Scattered electron

Low Mobility

bull holes μ ~10-4-10-8 Vs due to poor wave function overlap (large hopping distance)

bull electrons μ ~10-6-10-10Vs due to increased disorder and trapping at defect sites caused by impurities such as O2

rArr Build-up of space-charge density (bulk limited current)

전하전하 이동도이동도

36OLED 기초공정 이해와 실습

NoteMobility depends onElectric Field andTemperature

Mobilities of OrganicsMobilities of Organics

Alq3

37OLED 기초공정 이해와 실습

Ohmic conduction

OLEDOLED의의 전류전류

Current Dendity

current depends linearly on the bias voltageo nn qm VJd

=

2

3

0

1

2 1

(no traps)

(exponential trap distributions ( ) exp( )

one of electrodes(Ohmic contact) can supply more carriers per un

98

Current Density

SCLC condition

o

tt

r

m

m tN

VJd

T E N E kTV md T

ε ε μ

+

+ =

=

prop =

it time than can be transported through the dielectric (caused by low mobility)

Space charge limited (SCL) conduction

38OLED 기초공정 이해와 실습

2

2

3

Charge per unit area Q induced by a voltage V

Transit time across the semiconductor

9

Approximate SCLC densi

Child law (Mott- Gu

ty

Elec8

rney law)

o r

r

o rSCLC

r

VQ CVd

d dtE V

VQJt d

ε ε

μ μ

ε ε μ

= =

= =

asymp =

3 2

tric field distribution across the semiconductor

Majority space charges enhance the E field at the

3 3 ( ) at ( )2 2

enhance the injection of the cath

minority carrieode

rs (elect

V x VE x x d E dd d

= = =

rArr rons)

d

(+) (-)

x=0 x=d

Vd

15 Vd232

3)(d

xVxE =

++++

Virtual anode

-

Space Charge Limited CurrentSpace Charge Limited Current

39OLED 기초공정 이해와 실습

2

3

1

2 01

(no traps or discrete traps Mott-Gurney formula)

(exponential trap distributions ( ) exp( )

98

o rSCLC

mt

SCLC m t t

VJd

TVJ N E NmT

E kTd

ε ε μ

+

+

=

prop = =

ECB

EVB

Etrap

Discrete trapping center Exponential distributionof trapping centers

TrapTrap--Limited CurrentLimited Current

40OLED 기초공정 이해와 실습

Shen Burrows Bulovic McCarty Thompson Forrest Jpn J Appl Phys 35 L401 (1996)

ITOTPDAlq3MgAg

12

1

+

+

prop m

m

SCLC dVJ

TrapTrap--Limited CurrentLimited Current

41OLED 기초공정 이해와 실습

0

0

Activation energy at 0 Empirical parameter

Mobility at PF constant

PF

PF

E FT

T Tμβ

Δ =

=

PFPF

B eff

0

3

PFeff 0 0

( ) exp

exp( )

1 1 1with

E FFT μk T

F

qT T T

βμ

μ β

βπεε

⎛ ⎞Δ minus= minus⎜ ⎟⎜ ⎟

⎝ ⎠

equiv

= minus =

Poole Frenkel ModelPoole Frenkel Model

42OLED 기초공정 이해와 실습

1

22 2

0

0

(1)

(2)

EL F S e h

e ee he

T

h he hh

T

T rec rec e h

h eh e

h e

e hEL F S

h e

T rec

h e h e nh e EL F S EL

e h

n nJ n n nedJ n n ned

nJ

ne F

J J Je F

J Jn J J

ed n ed

η η γ

γτ

γτ

τ τ τ γ

μ

η η γμ μ

τ τ

η ηγ

minus

Φ =

minus minus =

minus minus =

lt =

=

Φ = prop

gt

= Φ = prop rArr Φ prop

EL Current RelationEL Current Relation

43OLED 기초공정 이해와 실습

Device Structure ITONPBAlq3Ca

22

21

ZZZ

fdVdQC

+minus

==πφieZiZZZ ||

))=+=

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

V0 independent of the NPB layer thickness

44OLED 기초공정 이해와 실습

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

Dashed line without interfacial charge

Wolfgang Brutting Stefan Berleb Anton G Muckl Organic Electronics 2 (2001)

Device Structure ITONPBAlq3Ca

45OLED 기초공정 이해와 실습

Langevin Recombination of carriers

bull Carriers are statistically independent therefore the e-h recombination is a random process and kinetically bimolecular

bull Total current attracted by a charge into the sphere of Coulombic capture radius rc

2

22

( ) ( )4

(4 ) 14 184

( ) (mean free path A)

n p c n pc

c cB

n p

qJ qp E qpr

qi r J Bqp r nmk T

qB a

μ μ μ μπε

ππε

μ μ λε

= + = +

= = cong asymp minus

there4 = + asympo

TkUd

BeP ~ minusProbability of dissociation

reUπε4

~2

e-

rc

Carrier RecombinationCarrier Recombination

P Langevin Ann Chem Phys 28 289 (1903)

46OLED 기초공정 이해와 실습

Electronic Processes in Organic Crystals and Polymers by MPope and C E Swenberg

ExcitonsExcitons

47OLED 기초공정 이해와 실습

C Adachi et al

Electrons and holesForm excitons

(bound e--h+ pairs)

Exciton Recombination ZoneExciton Recombination Zone

48OLED 기초공정 이해와 실습

MOLECULAR EXCITED STATESAFTER ELECTRICAL EXCITATION

Singletspin anti-symmetric

Tripletspin symmetric

25 75

MOLECULAR GROUND STATEspin anti-symmetric

Relaxation allowedfast efficientFluorescence

Relaxation disallowedslow inefficientPhosphorescence

|χ1χ2 gt = | gt

|χ1χ2 gt = | gt

|χ1χ2 gt

= | gt - | gt2

1

|χ1χ2 gt = | gt + | gt2

1ISC

Spin

OLEDOLED의의 형광형광인광인광

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 22: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

21OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Small polaron model

In a conjugated molecules a charge is self-trapped by the lattice deformationrarr creation of the localized mid gap states

Ex) A polaron in Polythiophene

32 22( ) exp

2 2

where polaron binding energy electron transfer energy lattice constant

T-dep of the mobility

bB

Bb

b

Eea J k Tk TE

EJa

πμminus ⎛ ⎞

= minus⎜ ⎟⎝ ⎠h

22OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Poole-Frenkel model

Field dependent mobility at high field (E gt 105 Vcm)

- Coulomb potential near localized states is modified by the applied field

( )120

( ) (0)exp

where (0) zero field mobility

Poole-Frenkel factor mag of electric field

T-dep amp field dep of the mobility

B

qF Fk T

eF

μ μ β

μ

β πεε

⎛ ⎞= ⎜ ⎟

⎝ ⎠

=

23OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Multiple trapping amp release model

Narrow delocalized band+ localized trap level (highly concenturated)

Process1) Carriers arrive at a trap and are trapped2) Thermally activated and released

0

0

exp

where mobility in the delocalized bandDensity of delocalized band edge

Concenturation of traps

T-dep of the mobility

tD

B

Ek T

μ μ α

μ

α

⎛ ⎞= minus⎜ ⎟

⎝ ⎠

=

24OLED 기초공정 이해와 실습

무기EL (p-n junction LED)

Light Emission

anode

cathodeETLEMLHTLHIL+

유기EL (polymers or small molecules)

전자수송층(ETL)

발광층(EML)정공

수송층(HTL)

양극(투명전극

ITO 유리 등)

음극(낮은 일함수 금속

Ca AlLi MgAg등)

-전자

정공

+

-+

두께 100 ~ 200 nm

Exciton

OLED OLED 작동원리작동원리

25OLED 기초공정 이해와 실습

Single-layer devices

Unbalanced carrier injection and lower efficiency

dArr

Heterostructures

ITOHILHTLEMLETLCathode(1) Lower the barrier at electrodes

Balanced carrier injection andimproved efficiency

(2) Band offsets between the layers andspace charges build up at hetero-junctionHigh carrier densitieseffective e-h capture

Multilayer StructureMultilayer Structure

Cathode

HILITO

GLASS

HTLEMLETL

-

+

26OLED 기초공정 이해와 실습

Cathode

HILITO

GLASS

HTLEMLETL

-

+

OLED Structure

N N

CH3

H3C

TPD m-MTDATA

N

N N

N

CH3

CH3

H3C

NO

NON

OAl

Alq3

Small Molecules (Fluorescence)

27OLED 기초공정 이해와 실습

OLED StructureSmall Molecules

(Phosphorescence)

NN

N

N

NN

N

N

CuN

N

NN

CuPc MTDATA

Cathode

HILITO

GLASS

HTLEML

ETL-

+

HBL

NNCH3H3C

BCP

28OLED 기초공정 이해와 실습

OLED Structure

Polymers

Cathode

ITO

GLASS

HTLEML

-

+

PEDOT

n

S O3- S O3

-S O3H S O3H S O3H S O3H

SS

SS

SS

O O

OO

O O

OO OO

n

n n

RR

PPV PF

29OLED 기초공정 이해와 실습

Cur

rent

den

sity Lum

inous Intensity

Voltage

ln V

ln J

J = qn0μVd

J = 98 εsμV2d3

Ligh

t

Current

slope = ηexte

Ex)

OLED OLED 특성특성

3 7

Diode Characteristics Rectification ratio 10 - 10 Power efficiency amp drive voltage

Light vs current

optconv ext

elec

opt opt elecext opt ext

elec elec

P hP eV

N s I IIN s I e e

νη η

η η

= =

= = rArr = times

30OLED 기초공정 이해와 실습

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

Vacuum Level

Anode

Cathode

HOMO

LUMO

Φa

Φc

EA

IP

CB

VB

Eg

에너지에너지 준위준위

31OLED 기초공정 이해와 실습

Current - Voltage Characteristics

2

16 17 3

0

0

1

diffusion voltage ~ 13 V

acceptor concentration ~ 10 - 10 cm

(~ 50 - 150 nm

2( )

Width of space charge layer 2 ( )

D

D

A

r DA

r D A

V VCV

N

C A q N V V

w V V qN

ε ε

ε ε

prop minus

= minus

= minus V = 0 )

OLED OLED 전기적전기적 특성특성

( ) Schottky equation

exp 1

ideality factor 1 1 ideal Schottky diodes B ext BJ J eV nk T V V IR

n n

⎡ ⎤= minus = minus⎣ ⎦ge =

Capacitance - Voltage Dependence

32OLED 기초공정 이해와 실습

I - V Characteristics C - V Characteristics

ITOPPVMetal Polymeric Schottky Diode

OLED OLED 전기적전기적 특성특성

33OLED 기초공정 이해와 실습

Injection Dominated Mechanisms

bull Thermionic emission

bull Tunneling

Bulk Dominated Mechanisms

bull Ohmic Conduction

bull Space Charge Limited Current Conduction

bull Space Charge Limited Current Conduction with Traps

Magnitude of Injection Barrier

전하전하 주입주입

34OLED 기초공정 이해와 실습

Thermionic Emission

Fowler-Nordheim Tunneling

2

2 2

3

exp 1 wehere exp

4 120( )

Richardson constant

bns s

B B

n B

eeVJ J J A Tk T k T

em kA m m A cm Kh

φ

π

⎡ ⎤⎛ ⎞ ⎛ ⎞minus= minus =⎢ ⎥⎜ ⎟ ⎜ ⎟

⎝ ⎠ ⎝ ⎠⎣ ⎦

= =

At low field thermionic emission at high field tunneling dominate

전하전하 주입주입

EF

Evac

-eFz(triangular shape)φ

Z=0 Z

Charge accumulationhigher the energy state `

Electron emission (F-N Tunneling)

Electron emission (Thermionic Emission)

2

3212

~ exp

( ) where 8 (2 )3

bJ EE

qb mqh

π

⎛ ⎞minus⎜ ⎟⎝ ⎠

Φ=

35OLED 기초공정 이해와 실습

Applied voltage

Lattice vibration

Localizedelectron

Hopping conductionBand-like conductionDelocalized electron

Lattice vibration(phonon)

Scattered electron

Low Mobility

bull holes μ ~10-4-10-8 Vs due to poor wave function overlap (large hopping distance)

bull electrons μ ~10-6-10-10Vs due to increased disorder and trapping at defect sites caused by impurities such as O2

rArr Build-up of space-charge density (bulk limited current)

전하전하 이동도이동도

36OLED 기초공정 이해와 실습

NoteMobility depends onElectric Field andTemperature

Mobilities of OrganicsMobilities of Organics

Alq3

37OLED 기초공정 이해와 실습

Ohmic conduction

OLEDOLED의의 전류전류

Current Dendity

current depends linearly on the bias voltageo nn qm VJd

=

2

3

0

1

2 1

(no traps)

(exponential trap distributions ( ) exp( )

one of electrodes(Ohmic contact) can supply more carriers per un

98

Current Density

SCLC condition

o

tt

r

m

m tN

VJd

T E N E kTV md T

ε ε μ

+

+ =

=

prop =

it time than can be transported through the dielectric (caused by low mobility)

Space charge limited (SCL) conduction

38OLED 기초공정 이해와 실습

2

2

3

Charge per unit area Q induced by a voltage V

Transit time across the semiconductor

9

Approximate SCLC densi

Child law (Mott- Gu

ty

Elec8

rney law)

o r

r

o rSCLC

r

VQ CVd

d dtE V

VQJt d

ε ε

μ μ

ε ε μ

= =

= =

asymp =

3 2

tric field distribution across the semiconductor

Majority space charges enhance the E field at the

3 3 ( ) at ( )2 2

enhance the injection of the cath

minority carrieode

rs (elect

V x VE x x d E dd d

= = =

rArr rons)

d

(+) (-)

x=0 x=d

Vd

15 Vd232

3)(d

xVxE =

++++

Virtual anode

-

Space Charge Limited CurrentSpace Charge Limited Current

39OLED 기초공정 이해와 실습

2

3

1

2 01

(no traps or discrete traps Mott-Gurney formula)

(exponential trap distributions ( ) exp( )

98

o rSCLC

mt

SCLC m t t

VJd

TVJ N E NmT

E kTd

ε ε μ

+

+

=

prop = =

ECB

EVB

Etrap

Discrete trapping center Exponential distributionof trapping centers

TrapTrap--Limited CurrentLimited Current

40OLED 기초공정 이해와 실습

Shen Burrows Bulovic McCarty Thompson Forrest Jpn J Appl Phys 35 L401 (1996)

ITOTPDAlq3MgAg

12

1

+

+

prop m

m

SCLC dVJ

TrapTrap--Limited CurrentLimited Current

41OLED 기초공정 이해와 실습

0

0

Activation energy at 0 Empirical parameter

Mobility at PF constant

PF

PF

E FT

T Tμβ

Δ =

=

PFPF

B eff

0

3

PFeff 0 0

( ) exp

exp( )

1 1 1with

E FFT μk T

F

qT T T

βμ

μ β

βπεε

⎛ ⎞Δ minus= minus⎜ ⎟⎜ ⎟

⎝ ⎠

equiv

= minus =

Poole Frenkel ModelPoole Frenkel Model

42OLED 기초공정 이해와 실습

1

22 2

0

0

(1)

(2)

EL F S e h

e ee he

T

h he hh

T

T rec rec e h

h eh e

h e

e hEL F S

h e

T rec

h e h e nh e EL F S EL

e h

n nJ n n nedJ n n ned

nJ

ne F

J J Je F

J Jn J J

ed n ed

η η γ

γτ

γτ

τ τ τ γ

μ

η η γμ μ

τ τ

η ηγ

minus

Φ =

minus minus =

minus minus =

lt =

=

Φ = prop

gt

= Φ = prop rArr Φ prop

EL Current RelationEL Current Relation

43OLED 기초공정 이해와 실습

Device Structure ITONPBAlq3Ca

22

21

ZZZ

fdVdQC

+minus

==πφieZiZZZ ||

))=+=

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

V0 independent of the NPB layer thickness

44OLED 기초공정 이해와 실습

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

Dashed line without interfacial charge

Wolfgang Brutting Stefan Berleb Anton G Muckl Organic Electronics 2 (2001)

Device Structure ITONPBAlq3Ca

45OLED 기초공정 이해와 실습

Langevin Recombination of carriers

bull Carriers are statistically independent therefore the e-h recombination is a random process and kinetically bimolecular

bull Total current attracted by a charge into the sphere of Coulombic capture radius rc

2

22

( ) ( )4

(4 ) 14 184

( ) (mean free path A)

n p c n pc

c cB

n p

qJ qp E qpr

qi r J Bqp r nmk T

qB a

μ μ μ μπε

ππε

μ μ λε

= + = +

= = cong asymp minus

there4 = + asympo

TkUd

BeP ~ minusProbability of dissociation

reUπε4

~2

e-

rc

Carrier RecombinationCarrier Recombination

P Langevin Ann Chem Phys 28 289 (1903)

46OLED 기초공정 이해와 실습

Electronic Processes in Organic Crystals and Polymers by MPope and C E Swenberg

ExcitonsExcitons

47OLED 기초공정 이해와 실습

C Adachi et al

Electrons and holesForm excitons

(bound e--h+ pairs)

Exciton Recombination ZoneExciton Recombination Zone

48OLED 기초공정 이해와 실습

MOLECULAR EXCITED STATESAFTER ELECTRICAL EXCITATION

Singletspin anti-symmetric

Tripletspin symmetric

25 75

MOLECULAR GROUND STATEspin anti-symmetric

Relaxation allowedfast efficientFluorescence

Relaxation disallowedslow inefficientPhosphorescence

|χ1χ2 gt = | gt

|χ1χ2 gt = | gt

|χ1χ2 gt

= | gt - | gt2

1

|χ1χ2 gt = | gt + | gt2

1ISC

Spin

OLEDOLED의의 형광형광인광인광

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 23: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

22OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Poole-Frenkel model

Field dependent mobility at high field (E gt 105 Vcm)

- Coulomb potential near localized states is modified by the applied field

( )120

( ) (0)exp

where (0) zero field mobility

Poole-Frenkel factor mag of electric field

T-dep amp field dep of the mobility

B

qF Fk T

eF

μ μ β

μ

β πεε

⎛ ⎞= ⎜ ⎟

⎝ ⎠

=

23OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Multiple trapping amp release model

Narrow delocalized band+ localized trap level (highly concenturated)

Process1) Carriers arrive at a trap and are trapped2) Thermally activated and released

0

0

exp

where mobility in the delocalized bandDensity of delocalized band edge

Concenturation of traps

T-dep of the mobility

tD

B

Ek T

μ μ α

μ

α

⎛ ⎞= minus⎜ ⎟

⎝ ⎠

=

24OLED 기초공정 이해와 실습

무기EL (p-n junction LED)

Light Emission

anode

cathodeETLEMLHTLHIL+

유기EL (polymers or small molecules)

전자수송층(ETL)

발광층(EML)정공

수송층(HTL)

양극(투명전극

ITO 유리 등)

음극(낮은 일함수 금속

Ca AlLi MgAg등)

-전자

정공

+

-+

두께 100 ~ 200 nm

Exciton

OLED OLED 작동원리작동원리

25OLED 기초공정 이해와 실습

Single-layer devices

Unbalanced carrier injection and lower efficiency

dArr

Heterostructures

ITOHILHTLEMLETLCathode(1) Lower the barrier at electrodes

Balanced carrier injection andimproved efficiency

(2) Band offsets between the layers andspace charges build up at hetero-junctionHigh carrier densitieseffective e-h capture

Multilayer StructureMultilayer Structure

Cathode

HILITO

GLASS

HTLEMLETL

-

+

26OLED 기초공정 이해와 실습

Cathode

HILITO

GLASS

HTLEMLETL

-

+

OLED Structure

N N

CH3

H3C

TPD m-MTDATA

N

N N

N

CH3

CH3

H3C

NO

NON

OAl

Alq3

Small Molecules (Fluorescence)

27OLED 기초공정 이해와 실습

OLED StructureSmall Molecules

(Phosphorescence)

NN

N

N

NN

N

N

CuN

N

NN

CuPc MTDATA

Cathode

HILITO

GLASS

HTLEML

ETL-

+

HBL

NNCH3H3C

BCP

28OLED 기초공정 이해와 실습

OLED Structure

Polymers

Cathode

ITO

GLASS

HTLEML

-

+

PEDOT

n

S O3- S O3

-S O3H S O3H S O3H S O3H

SS

SS

SS

O O

OO

O O

OO OO

n

n n

RR

PPV PF

29OLED 기초공정 이해와 실습

Cur

rent

den

sity Lum

inous Intensity

Voltage

ln V

ln J

J = qn0μVd

J = 98 εsμV2d3

Ligh

t

Current

slope = ηexte

Ex)

OLED OLED 특성특성

3 7

Diode Characteristics Rectification ratio 10 - 10 Power efficiency amp drive voltage

Light vs current

optconv ext

elec

opt opt elecext opt ext

elec elec

P hP eV

N s I IIN s I e e

νη η

η η

= =

= = rArr = times

30OLED 기초공정 이해와 실습

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

Vacuum Level

Anode

Cathode

HOMO

LUMO

Φa

Φc

EA

IP

CB

VB

Eg

에너지에너지 준위준위

31OLED 기초공정 이해와 실습

Current - Voltage Characteristics

2

16 17 3

0

0

1

diffusion voltage ~ 13 V

acceptor concentration ~ 10 - 10 cm

(~ 50 - 150 nm

2( )

Width of space charge layer 2 ( )

D

D

A

r DA

r D A

V VCV

N

C A q N V V

w V V qN

ε ε

ε ε

prop minus

= minus

= minus V = 0 )

OLED OLED 전기적전기적 특성특성

( ) Schottky equation

exp 1

ideality factor 1 1 ideal Schottky diodes B ext BJ J eV nk T V V IR

n n

⎡ ⎤= minus = minus⎣ ⎦ge =

Capacitance - Voltage Dependence

32OLED 기초공정 이해와 실습

I - V Characteristics C - V Characteristics

ITOPPVMetal Polymeric Schottky Diode

OLED OLED 전기적전기적 특성특성

33OLED 기초공정 이해와 실습

Injection Dominated Mechanisms

bull Thermionic emission

bull Tunneling

Bulk Dominated Mechanisms

bull Ohmic Conduction

bull Space Charge Limited Current Conduction

bull Space Charge Limited Current Conduction with Traps

Magnitude of Injection Barrier

전하전하 주입주입

34OLED 기초공정 이해와 실습

Thermionic Emission

Fowler-Nordheim Tunneling

2

2 2

3

exp 1 wehere exp

4 120( )

Richardson constant

bns s

B B

n B

eeVJ J J A Tk T k T

em kA m m A cm Kh

φ

π

⎡ ⎤⎛ ⎞ ⎛ ⎞minus= minus =⎢ ⎥⎜ ⎟ ⎜ ⎟

⎝ ⎠ ⎝ ⎠⎣ ⎦

= =

At low field thermionic emission at high field tunneling dominate

전하전하 주입주입

EF

Evac

-eFz(triangular shape)φ

Z=0 Z

Charge accumulationhigher the energy state `

Electron emission (F-N Tunneling)

Electron emission (Thermionic Emission)

2

3212

~ exp

( ) where 8 (2 )3

bJ EE

qb mqh

π

⎛ ⎞minus⎜ ⎟⎝ ⎠

Φ=

35OLED 기초공정 이해와 실습

Applied voltage

Lattice vibration

Localizedelectron

Hopping conductionBand-like conductionDelocalized electron

Lattice vibration(phonon)

Scattered electron

Low Mobility

bull holes μ ~10-4-10-8 Vs due to poor wave function overlap (large hopping distance)

bull electrons μ ~10-6-10-10Vs due to increased disorder and trapping at defect sites caused by impurities such as O2

rArr Build-up of space-charge density (bulk limited current)

전하전하 이동도이동도

36OLED 기초공정 이해와 실습

NoteMobility depends onElectric Field andTemperature

Mobilities of OrganicsMobilities of Organics

Alq3

37OLED 기초공정 이해와 실습

Ohmic conduction

OLEDOLED의의 전류전류

Current Dendity

current depends linearly on the bias voltageo nn qm VJd

=

2

3

0

1

2 1

(no traps)

(exponential trap distributions ( ) exp( )

one of electrodes(Ohmic contact) can supply more carriers per un

98

Current Density

SCLC condition

o

tt

r

m

m tN

VJd

T E N E kTV md T

ε ε μ

+

+ =

=

prop =

it time than can be transported through the dielectric (caused by low mobility)

Space charge limited (SCL) conduction

38OLED 기초공정 이해와 실습

2

2

3

Charge per unit area Q induced by a voltage V

Transit time across the semiconductor

9

Approximate SCLC densi

Child law (Mott- Gu

ty

Elec8

rney law)

o r

r

o rSCLC

r

VQ CVd

d dtE V

VQJt d

ε ε

μ μ

ε ε μ

= =

= =

asymp =

3 2

tric field distribution across the semiconductor

Majority space charges enhance the E field at the

3 3 ( ) at ( )2 2

enhance the injection of the cath

minority carrieode

rs (elect

V x VE x x d E dd d

= = =

rArr rons)

d

(+) (-)

x=0 x=d

Vd

15 Vd232

3)(d

xVxE =

++++

Virtual anode

-

Space Charge Limited CurrentSpace Charge Limited Current

39OLED 기초공정 이해와 실습

2

3

1

2 01

(no traps or discrete traps Mott-Gurney formula)

(exponential trap distributions ( ) exp( )

98

o rSCLC

mt

SCLC m t t

VJd

TVJ N E NmT

E kTd

ε ε μ

+

+

=

prop = =

ECB

EVB

Etrap

Discrete trapping center Exponential distributionof trapping centers

TrapTrap--Limited CurrentLimited Current

40OLED 기초공정 이해와 실습

Shen Burrows Bulovic McCarty Thompson Forrest Jpn J Appl Phys 35 L401 (1996)

ITOTPDAlq3MgAg

12

1

+

+

prop m

m

SCLC dVJ

TrapTrap--Limited CurrentLimited Current

41OLED 기초공정 이해와 실습

0

0

Activation energy at 0 Empirical parameter

Mobility at PF constant

PF

PF

E FT

T Tμβ

Δ =

=

PFPF

B eff

0

3

PFeff 0 0

( ) exp

exp( )

1 1 1with

E FFT μk T

F

qT T T

βμ

μ β

βπεε

⎛ ⎞Δ minus= minus⎜ ⎟⎜ ⎟

⎝ ⎠

equiv

= minus =

Poole Frenkel ModelPoole Frenkel Model

42OLED 기초공정 이해와 실습

1

22 2

0

0

(1)

(2)

EL F S e h

e ee he

T

h he hh

T

T rec rec e h

h eh e

h e

e hEL F S

h e

T rec

h e h e nh e EL F S EL

e h

n nJ n n nedJ n n ned

nJ

ne F

J J Je F

J Jn J J

ed n ed

η η γ

γτ

γτ

τ τ τ γ

μ

η η γμ μ

τ τ

η ηγ

minus

Φ =

minus minus =

minus minus =

lt =

=

Φ = prop

gt

= Φ = prop rArr Φ prop

EL Current RelationEL Current Relation

43OLED 기초공정 이해와 실습

Device Structure ITONPBAlq3Ca

22

21

ZZZ

fdVdQC

+minus

==πφieZiZZZ ||

))=+=

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

V0 independent of the NPB layer thickness

44OLED 기초공정 이해와 실습

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

Dashed line without interfacial charge

Wolfgang Brutting Stefan Berleb Anton G Muckl Organic Electronics 2 (2001)

Device Structure ITONPBAlq3Ca

45OLED 기초공정 이해와 실습

Langevin Recombination of carriers

bull Carriers are statistically independent therefore the e-h recombination is a random process and kinetically bimolecular

bull Total current attracted by a charge into the sphere of Coulombic capture radius rc

2

22

( ) ( )4

(4 ) 14 184

( ) (mean free path A)

n p c n pc

c cB

n p

qJ qp E qpr

qi r J Bqp r nmk T

qB a

μ μ μ μπε

ππε

μ μ λε

= + = +

= = cong asymp minus

there4 = + asympo

TkUd

BeP ~ minusProbability of dissociation

reUπε4

~2

e-

rc

Carrier RecombinationCarrier Recombination

P Langevin Ann Chem Phys 28 289 (1903)

46OLED 기초공정 이해와 실습

Electronic Processes in Organic Crystals and Polymers by MPope and C E Swenberg

ExcitonsExcitons

47OLED 기초공정 이해와 실습

C Adachi et al

Electrons and holesForm excitons

(bound e--h+ pairs)

Exciton Recombination ZoneExciton Recombination Zone

48OLED 기초공정 이해와 실습

MOLECULAR EXCITED STATESAFTER ELECTRICAL EXCITATION

Singletspin anti-symmetric

Tripletspin symmetric

25 75

MOLECULAR GROUND STATEspin anti-symmetric

Relaxation allowedfast efficientFluorescence

Relaxation disallowedslow inefficientPhosphorescence

|χ1χ2 gt = | gt

|χ1χ2 gt = | gt

|χ1χ2 gt

= | gt - | gt2

1

|χ1χ2 gt = | gt + | gt2

1ISC

Spin

OLEDOLED의의 형광형광인광인광

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 24: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

23OLED 기초공정 이해와 실습

Transport in Organic Molecular CrystalsTransport in Organic Molecular Crystals

Multiple trapping amp release model

Narrow delocalized band+ localized trap level (highly concenturated)

Process1) Carriers arrive at a trap and are trapped2) Thermally activated and released

0

0

exp

where mobility in the delocalized bandDensity of delocalized band edge

Concenturation of traps

T-dep of the mobility

tD

B

Ek T

μ μ α

μ

α

⎛ ⎞= minus⎜ ⎟

⎝ ⎠

=

24OLED 기초공정 이해와 실습

무기EL (p-n junction LED)

Light Emission

anode

cathodeETLEMLHTLHIL+

유기EL (polymers or small molecules)

전자수송층(ETL)

발광층(EML)정공

수송층(HTL)

양극(투명전극

ITO 유리 등)

음극(낮은 일함수 금속

Ca AlLi MgAg등)

-전자

정공

+

-+

두께 100 ~ 200 nm

Exciton

OLED OLED 작동원리작동원리

25OLED 기초공정 이해와 실습

Single-layer devices

Unbalanced carrier injection and lower efficiency

dArr

Heterostructures

ITOHILHTLEMLETLCathode(1) Lower the barrier at electrodes

Balanced carrier injection andimproved efficiency

(2) Band offsets between the layers andspace charges build up at hetero-junctionHigh carrier densitieseffective e-h capture

Multilayer StructureMultilayer Structure

Cathode

HILITO

GLASS

HTLEMLETL

-

+

26OLED 기초공정 이해와 실습

Cathode

HILITO

GLASS

HTLEMLETL

-

+

OLED Structure

N N

CH3

H3C

TPD m-MTDATA

N

N N

N

CH3

CH3

H3C

NO

NON

OAl

Alq3

Small Molecules (Fluorescence)

27OLED 기초공정 이해와 실습

OLED StructureSmall Molecules

(Phosphorescence)

NN

N

N

NN

N

N

CuN

N

NN

CuPc MTDATA

Cathode

HILITO

GLASS

HTLEML

ETL-

+

HBL

NNCH3H3C

BCP

28OLED 기초공정 이해와 실습

OLED Structure

Polymers

Cathode

ITO

GLASS

HTLEML

-

+

PEDOT

n

S O3- S O3

-S O3H S O3H S O3H S O3H

SS

SS

SS

O O

OO

O O

OO OO

n

n n

RR

PPV PF

29OLED 기초공정 이해와 실습

Cur

rent

den

sity Lum

inous Intensity

Voltage

ln V

ln J

J = qn0μVd

J = 98 εsμV2d3

Ligh

t

Current

slope = ηexte

Ex)

OLED OLED 특성특성

3 7

Diode Characteristics Rectification ratio 10 - 10 Power efficiency amp drive voltage

Light vs current

optconv ext

elec

opt opt elecext opt ext

elec elec

P hP eV

N s I IIN s I e e

νη η

η η

= =

= = rArr = times

30OLED 기초공정 이해와 실습

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

Vacuum Level

Anode

Cathode

HOMO

LUMO

Φa

Φc

EA

IP

CB

VB

Eg

에너지에너지 준위준위

31OLED 기초공정 이해와 실습

Current - Voltage Characteristics

2

16 17 3

0

0

1

diffusion voltage ~ 13 V

acceptor concentration ~ 10 - 10 cm

(~ 50 - 150 nm

2( )

Width of space charge layer 2 ( )

D

D

A

r DA

r D A

V VCV

N

C A q N V V

w V V qN

ε ε

ε ε

prop minus

= minus

= minus V = 0 )

OLED OLED 전기적전기적 특성특성

( ) Schottky equation

exp 1

ideality factor 1 1 ideal Schottky diodes B ext BJ J eV nk T V V IR

n n

⎡ ⎤= minus = minus⎣ ⎦ge =

Capacitance - Voltage Dependence

32OLED 기초공정 이해와 실습

I - V Characteristics C - V Characteristics

ITOPPVMetal Polymeric Schottky Diode

OLED OLED 전기적전기적 특성특성

33OLED 기초공정 이해와 실습

Injection Dominated Mechanisms

bull Thermionic emission

bull Tunneling

Bulk Dominated Mechanisms

bull Ohmic Conduction

bull Space Charge Limited Current Conduction

bull Space Charge Limited Current Conduction with Traps

Magnitude of Injection Barrier

전하전하 주입주입

34OLED 기초공정 이해와 실습

Thermionic Emission

Fowler-Nordheim Tunneling

2

2 2

3

exp 1 wehere exp

4 120( )

Richardson constant

bns s

B B

n B

eeVJ J J A Tk T k T

em kA m m A cm Kh

φ

π

⎡ ⎤⎛ ⎞ ⎛ ⎞minus= minus =⎢ ⎥⎜ ⎟ ⎜ ⎟

⎝ ⎠ ⎝ ⎠⎣ ⎦

= =

At low field thermionic emission at high field tunneling dominate

전하전하 주입주입

EF

Evac

-eFz(triangular shape)φ

Z=0 Z

Charge accumulationhigher the energy state `

Electron emission (F-N Tunneling)

Electron emission (Thermionic Emission)

2

3212

~ exp

( ) where 8 (2 )3

bJ EE

qb mqh

π

⎛ ⎞minus⎜ ⎟⎝ ⎠

Φ=

35OLED 기초공정 이해와 실습

Applied voltage

Lattice vibration

Localizedelectron

Hopping conductionBand-like conductionDelocalized electron

Lattice vibration(phonon)

Scattered electron

Low Mobility

bull holes μ ~10-4-10-8 Vs due to poor wave function overlap (large hopping distance)

bull electrons μ ~10-6-10-10Vs due to increased disorder and trapping at defect sites caused by impurities such as O2

rArr Build-up of space-charge density (bulk limited current)

전하전하 이동도이동도

36OLED 기초공정 이해와 실습

NoteMobility depends onElectric Field andTemperature

Mobilities of OrganicsMobilities of Organics

Alq3

37OLED 기초공정 이해와 실습

Ohmic conduction

OLEDOLED의의 전류전류

Current Dendity

current depends linearly on the bias voltageo nn qm VJd

=

2

3

0

1

2 1

(no traps)

(exponential trap distributions ( ) exp( )

one of electrodes(Ohmic contact) can supply more carriers per un

98

Current Density

SCLC condition

o

tt

r

m

m tN

VJd

T E N E kTV md T

ε ε μ

+

+ =

=

prop =

it time than can be transported through the dielectric (caused by low mobility)

Space charge limited (SCL) conduction

38OLED 기초공정 이해와 실습

2

2

3

Charge per unit area Q induced by a voltage V

Transit time across the semiconductor

9

Approximate SCLC densi

Child law (Mott- Gu

ty

Elec8

rney law)

o r

r

o rSCLC

r

VQ CVd

d dtE V

VQJt d

ε ε

μ μ

ε ε μ

= =

= =

asymp =

3 2

tric field distribution across the semiconductor

Majority space charges enhance the E field at the

3 3 ( ) at ( )2 2

enhance the injection of the cath

minority carrieode

rs (elect

V x VE x x d E dd d

= = =

rArr rons)

d

(+) (-)

x=0 x=d

Vd

15 Vd232

3)(d

xVxE =

++++

Virtual anode

-

Space Charge Limited CurrentSpace Charge Limited Current

39OLED 기초공정 이해와 실습

2

3

1

2 01

(no traps or discrete traps Mott-Gurney formula)

(exponential trap distributions ( ) exp( )

98

o rSCLC

mt

SCLC m t t

VJd

TVJ N E NmT

E kTd

ε ε μ

+

+

=

prop = =

ECB

EVB

Etrap

Discrete trapping center Exponential distributionof trapping centers

TrapTrap--Limited CurrentLimited Current

40OLED 기초공정 이해와 실습

Shen Burrows Bulovic McCarty Thompson Forrest Jpn J Appl Phys 35 L401 (1996)

ITOTPDAlq3MgAg

12

1

+

+

prop m

m

SCLC dVJ

TrapTrap--Limited CurrentLimited Current

41OLED 기초공정 이해와 실습

0

0

Activation energy at 0 Empirical parameter

Mobility at PF constant

PF

PF

E FT

T Tμβ

Δ =

=

PFPF

B eff

0

3

PFeff 0 0

( ) exp

exp( )

1 1 1with

E FFT μk T

F

qT T T

βμ

μ β

βπεε

⎛ ⎞Δ minus= minus⎜ ⎟⎜ ⎟

⎝ ⎠

equiv

= minus =

Poole Frenkel ModelPoole Frenkel Model

42OLED 기초공정 이해와 실습

1

22 2

0

0

(1)

(2)

EL F S e h

e ee he

T

h he hh

T

T rec rec e h

h eh e

h e

e hEL F S

h e

T rec

h e h e nh e EL F S EL

e h

n nJ n n nedJ n n ned

nJ

ne F

J J Je F

J Jn J J

ed n ed

η η γ

γτ

γτ

τ τ τ γ

μ

η η γμ μ

τ τ

η ηγ

minus

Φ =

minus minus =

minus minus =

lt =

=

Φ = prop

gt

= Φ = prop rArr Φ prop

EL Current RelationEL Current Relation

43OLED 기초공정 이해와 실습

Device Structure ITONPBAlq3Ca

22

21

ZZZ

fdVdQC

+minus

==πφieZiZZZ ||

))=+=

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

V0 independent of the NPB layer thickness

44OLED 기초공정 이해와 실습

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

Dashed line without interfacial charge

Wolfgang Brutting Stefan Berleb Anton G Muckl Organic Electronics 2 (2001)

Device Structure ITONPBAlq3Ca

45OLED 기초공정 이해와 실습

Langevin Recombination of carriers

bull Carriers are statistically independent therefore the e-h recombination is a random process and kinetically bimolecular

bull Total current attracted by a charge into the sphere of Coulombic capture radius rc

2

22

( ) ( )4

(4 ) 14 184

( ) (mean free path A)

n p c n pc

c cB

n p

qJ qp E qpr

qi r J Bqp r nmk T

qB a

μ μ μ μπε

ππε

μ μ λε

= + = +

= = cong asymp minus

there4 = + asympo

TkUd

BeP ~ minusProbability of dissociation

reUπε4

~2

e-

rc

Carrier RecombinationCarrier Recombination

P Langevin Ann Chem Phys 28 289 (1903)

46OLED 기초공정 이해와 실습

Electronic Processes in Organic Crystals and Polymers by MPope and C E Swenberg

ExcitonsExcitons

47OLED 기초공정 이해와 실습

C Adachi et al

Electrons and holesForm excitons

(bound e--h+ pairs)

Exciton Recombination ZoneExciton Recombination Zone

48OLED 기초공정 이해와 실습

MOLECULAR EXCITED STATESAFTER ELECTRICAL EXCITATION

Singletspin anti-symmetric

Tripletspin symmetric

25 75

MOLECULAR GROUND STATEspin anti-symmetric

Relaxation allowedfast efficientFluorescence

Relaxation disallowedslow inefficientPhosphorescence

|χ1χ2 gt = | gt

|χ1χ2 gt = | gt

|χ1χ2 gt

= | gt - | gt2

1

|χ1χ2 gt = | gt + | gt2

1ISC

Spin

OLEDOLED의의 형광형광인광인광

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 25: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

24OLED 기초공정 이해와 실습

무기EL (p-n junction LED)

Light Emission

anode

cathodeETLEMLHTLHIL+

유기EL (polymers or small molecules)

전자수송층(ETL)

발광층(EML)정공

수송층(HTL)

양극(투명전극

ITO 유리 등)

음극(낮은 일함수 금속

Ca AlLi MgAg등)

-전자

정공

+

-+

두께 100 ~ 200 nm

Exciton

OLED OLED 작동원리작동원리

25OLED 기초공정 이해와 실습

Single-layer devices

Unbalanced carrier injection and lower efficiency

dArr

Heterostructures

ITOHILHTLEMLETLCathode(1) Lower the barrier at electrodes

Balanced carrier injection andimproved efficiency

(2) Band offsets between the layers andspace charges build up at hetero-junctionHigh carrier densitieseffective e-h capture

Multilayer StructureMultilayer Structure

Cathode

HILITO

GLASS

HTLEMLETL

-

+

26OLED 기초공정 이해와 실습

Cathode

HILITO

GLASS

HTLEMLETL

-

+

OLED Structure

N N

CH3

H3C

TPD m-MTDATA

N

N N

N

CH3

CH3

H3C

NO

NON

OAl

Alq3

Small Molecules (Fluorescence)

27OLED 기초공정 이해와 실습

OLED StructureSmall Molecules

(Phosphorescence)

NN

N

N

NN

N

N

CuN

N

NN

CuPc MTDATA

Cathode

HILITO

GLASS

HTLEML

ETL-

+

HBL

NNCH3H3C

BCP

28OLED 기초공정 이해와 실습

OLED Structure

Polymers

Cathode

ITO

GLASS

HTLEML

-

+

PEDOT

n

S O3- S O3

-S O3H S O3H S O3H S O3H

SS

SS

SS

O O

OO

O O

OO OO

n

n n

RR

PPV PF

29OLED 기초공정 이해와 실습

Cur

rent

den

sity Lum

inous Intensity

Voltage

ln V

ln J

J = qn0μVd

J = 98 εsμV2d3

Ligh

t

Current

slope = ηexte

Ex)

OLED OLED 특성특성

3 7

Diode Characteristics Rectification ratio 10 - 10 Power efficiency amp drive voltage

Light vs current

optconv ext

elec

opt opt elecext opt ext

elec elec

P hP eV

N s I IIN s I e e

νη η

η η

= =

= = rArr = times

30OLED 기초공정 이해와 실습

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

Vacuum Level

Anode

Cathode

HOMO

LUMO

Φa

Φc

EA

IP

CB

VB

Eg

에너지에너지 준위준위

31OLED 기초공정 이해와 실습

Current - Voltage Characteristics

2

16 17 3

0

0

1

diffusion voltage ~ 13 V

acceptor concentration ~ 10 - 10 cm

(~ 50 - 150 nm

2( )

Width of space charge layer 2 ( )

D

D

A

r DA

r D A

V VCV

N

C A q N V V

w V V qN

ε ε

ε ε

prop minus

= minus

= minus V = 0 )

OLED OLED 전기적전기적 특성특성

( ) Schottky equation

exp 1

ideality factor 1 1 ideal Schottky diodes B ext BJ J eV nk T V V IR

n n

⎡ ⎤= minus = minus⎣ ⎦ge =

Capacitance - Voltage Dependence

32OLED 기초공정 이해와 실습

I - V Characteristics C - V Characteristics

ITOPPVMetal Polymeric Schottky Diode

OLED OLED 전기적전기적 특성특성

33OLED 기초공정 이해와 실습

Injection Dominated Mechanisms

bull Thermionic emission

bull Tunneling

Bulk Dominated Mechanisms

bull Ohmic Conduction

bull Space Charge Limited Current Conduction

bull Space Charge Limited Current Conduction with Traps

Magnitude of Injection Barrier

전하전하 주입주입

34OLED 기초공정 이해와 실습

Thermionic Emission

Fowler-Nordheim Tunneling

2

2 2

3

exp 1 wehere exp

4 120( )

Richardson constant

bns s

B B

n B

eeVJ J J A Tk T k T

em kA m m A cm Kh

φ

π

⎡ ⎤⎛ ⎞ ⎛ ⎞minus= minus =⎢ ⎥⎜ ⎟ ⎜ ⎟

⎝ ⎠ ⎝ ⎠⎣ ⎦

= =

At low field thermionic emission at high field tunneling dominate

전하전하 주입주입

EF

Evac

-eFz(triangular shape)φ

Z=0 Z

Charge accumulationhigher the energy state `

Electron emission (F-N Tunneling)

Electron emission (Thermionic Emission)

2

3212

~ exp

( ) where 8 (2 )3

bJ EE

qb mqh

π

⎛ ⎞minus⎜ ⎟⎝ ⎠

Φ=

35OLED 기초공정 이해와 실습

Applied voltage

Lattice vibration

Localizedelectron

Hopping conductionBand-like conductionDelocalized electron

Lattice vibration(phonon)

Scattered electron

Low Mobility

bull holes μ ~10-4-10-8 Vs due to poor wave function overlap (large hopping distance)

bull electrons μ ~10-6-10-10Vs due to increased disorder and trapping at defect sites caused by impurities such as O2

rArr Build-up of space-charge density (bulk limited current)

전하전하 이동도이동도

36OLED 기초공정 이해와 실습

NoteMobility depends onElectric Field andTemperature

Mobilities of OrganicsMobilities of Organics

Alq3

37OLED 기초공정 이해와 실습

Ohmic conduction

OLEDOLED의의 전류전류

Current Dendity

current depends linearly on the bias voltageo nn qm VJd

=

2

3

0

1

2 1

(no traps)

(exponential trap distributions ( ) exp( )

one of electrodes(Ohmic contact) can supply more carriers per un

98

Current Density

SCLC condition

o

tt

r

m

m tN

VJd

T E N E kTV md T

ε ε μ

+

+ =

=

prop =

it time than can be transported through the dielectric (caused by low mobility)

Space charge limited (SCL) conduction

38OLED 기초공정 이해와 실습

2

2

3

Charge per unit area Q induced by a voltage V

Transit time across the semiconductor

9

Approximate SCLC densi

Child law (Mott- Gu

ty

Elec8

rney law)

o r

r

o rSCLC

r

VQ CVd

d dtE V

VQJt d

ε ε

μ μ

ε ε μ

= =

= =

asymp =

3 2

tric field distribution across the semiconductor

Majority space charges enhance the E field at the

3 3 ( ) at ( )2 2

enhance the injection of the cath

minority carrieode

rs (elect

V x VE x x d E dd d

= = =

rArr rons)

d

(+) (-)

x=0 x=d

Vd

15 Vd232

3)(d

xVxE =

++++

Virtual anode

-

Space Charge Limited CurrentSpace Charge Limited Current

39OLED 기초공정 이해와 실습

2

3

1

2 01

(no traps or discrete traps Mott-Gurney formula)

(exponential trap distributions ( ) exp( )

98

o rSCLC

mt

SCLC m t t

VJd

TVJ N E NmT

E kTd

ε ε μ

+

+

=

prop = =

ECB

EVB

Etrap

Discrete trapping center Exponential distributionof trapping centers

TrapTrap--Limited CurrentLimited Current

40OLED 기초공정 이해와 실습

Shen Burrows Bulovic McCarty Thompson Forrest Jpn J Appl Phys 35 L401 (1996)

ITOTPDAlq3MgAg

12

1

+

+

prop m

m

SCLC dVJ

TrapTrap--Limited CurrentLimited Current

41OLED 기초공정 이해와 실습

0

0

Activation energy at 0 Empirical parameter

Mobility at PF constant

PF

PF

E FT

T Tμβ

Δ =

=

PFPF

B eff

0

3

PFeff 0 0

( ) exp

exp( )

1 1 1with

E FFT μk T

F

qT T T

βμ

μ β

βπεε

⎛ ⎞Δ minus= minus⎜ ⎟⎜ ⎟

⎝ ⎠

equiv

= minus =

Poole Frenkel ModelPoole Frenkel Model

42OLED 기초공정 이해와 실습

1

22 2

0

0

(1)

(2)

EL F S e h

e ee he

T

h he hh

T

T rec rec e h

h eh e

h e

e hEL F S

h e

T rec

h e h e nh e EL F S EL

e h

n nJ n n nedJ n n ned

nJ

ne F

J J Je F

J Jn J J

ed n ed

η η γ

γτ

γτ

τ τ τ γ

μ

η η γμ μ

τ τ

η ηγ

minus

Φ =

minus minus =

minus minus =

lt =

=

Φ = prop

gt

= Φ = prop rArr Φ prop

EL Current RelationEL Current Relation

43OLED 기초공정 이해와 실습

Device Structure ITONPBAlq3Ca

22

21

ZZZ

fdVdQC

+minus

==πφieZiZZZ ||

))=+=

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

V0 independent of the NPB layer thickness

44OLED 기초공정 이해와 실습

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

Dashed line without interfacial charge

Wolfgang Brutting Stefan Berleb Anton G Muckl Organic Electronics 2 (2001)

Device Structure ITONPBAlq3Ca

45OLED 기초공정 이해와 실습

Langevin Recombination of carriers

bull Carriers are statistically independent therefore the e-h recombination is a random process and kinetically bimolecular

bull Total current attracted by a charge into the sphere of Coulombic capture radius rc

2

22

( ) ( )4

(4 ) 14 184

( ) (mean free path A)

n p c n pc

c cB

n p

qJ qp E qpr

qi r J Bqp r nmk T

qB a

μ μ μ μπε

ππε

μ μ λε

= + = +

= = cong asymp minus

there4 = + asympo

TkUd

BeP ~ minusProbability of dissociation

reUπε4

~2

e-

rc

Carrier RecombinationCarrier Recombination

P Langevin Ann Chem Phys 28 289 (1903)

46OLED 기초공정 이해와 실습

Electronic Processes in Organic Crystals and Polymers by MPope and C E Swenberg

ExcitonsExcitons

47OLED 기초공정 이해와 실습

C Adachi et al

Electrons and holesForm excitons

(bound e--h+ pairs)

Exciton Recombination ZoneExciton Recombination Zone

48OLED 기초공정 이해와 실습

MOLECULAR EXCITED STATESAFTER ELECTRICAL EXCITATION

Singletspin anti-symmetric

Tripletspin symmetric

25 75

MOLECULAR GROUND STATEspin anti-symmetric

Relaxation allowedfast efficientFluorescence

Relaxation disallowedslow inefficientPhosphorescence

|χ1χ2 gt = | gt

|χ1χ2 gt = | gt

|χ1χ2 gt

= | gt - | gt2

1

|χ1χ2 gt = | gt + | gt2

1ISC

Spin

OLEDOLED의의 형광형광인광인광

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 26: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

25OLED 기초공정 이해와 실습

Single-layer devices

Unbalanced carrier injection and lower efficiency

dArr

Heterostructures

ITOHILHTLEMLETLCathode(1) Lower the barrier at electrodes

Balanced carrier injection andimproved efficiency

(2) Band offsets between the layers andspace charges build up at hetero-junctionHigh carrier densitieseffective e-h capture

Multilayer StructureMultilayer Structure

Cathode

HILITO

GLASS

HTLEMLETL

-

+

26OLED 기초공정 이해와 실습

Cathode

HILITO

GLASS

HTLEMLETL

-

+

OLED Structure

N N

CH3

H3C

TPD m-MTDATA

N

N N

N

CH3

CH3

H3C

NO

NON

OAl

Alq3

Small Molecules (Fluorescence)

27OLED 기초공정 이해와 실습

OLED StructureSmall Molecules

(Phosphorescence)

NN

N

N

NN

N

N

CuN

N

NN

CuPc MTDATA

Cathode

HILITO

GLASS

HTLEML

ETL-

+

HBL

NNCH3H3C

BCP

28OLED 기초공정 이해와 실습

OLED Structure

Polymers

Cathode

ITO

GLASS

HTLEML

-

+

PEDOT

n

S O3- S O3

-S O3H S O3H S O3H S O3H

SS

SS

SS

O O

OO

O O

OO OO

n

n n

RR

PPV PF

29OLED 기초공정 이해와 실습

Cur

rent

den

sity Lum

inous Intensity

Voltage

ln V

ln J

J = qn0μVd

J = 98 εsμV2d3

Ligh

t

Current

slope = ηexte

Ex)

OLED OLED 특성특성

3 7

Diode Characteristics Rectification ratio 10 - 10 Power efficiency amp drive voltage

Light vs current

optconv ext

elec

opt opt elecext opt ext

elec elec

P hP eV

N s I IIN s I e e

νη η

η η

= =

= = rArr = times

30OLED 기초공정 이해와 실습

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

Vacuum Level

Anode

Cathode

HOMO

LUMO

Φa

Φc

EA

IP

CB

VB

Eg

에너지에너지 준위준위

31OLED 기초공정 이해와 실습

Current - Voltage Characteristics

2

16 17 3

0

0

1

diffusion voltage ~ 13 V

acceptor concentration ~ 10 - 10 cm

(~ 50 - 150 nm

2( )

Width of space charge layer 2 ( )

D

D

A

r DA

r D A

V VCV

N

C A q N V V

w V V qN

ε ε

ε ε

prop minus

= minus

= minus V = 0 )

OLED OLED 전기적전기적 특성특성

( ) Schottky equation

exp 1

ideality factor 1 1 ideal Schottky diodes B ext BJ J eV nk T V V IR

n n

⎡ ⎤= minus = minus⎣ ⎦ge =

Capacitance - Voltage Dependence

32OLED 기초공정 이해와 실습

I - V Characteristics C - V Characteristics

ITOPPVMetal Polymeric Schottky Diode

OLED OLED 전기적전기적 특성특성

33OLED 기초공정 이해와 실습

Injection Dominated Mechanisms

bull Thermionic emission

bull Tunneling

Bulk Dominated Mechanisms

bull Ohmic Conduction

bull Space Charge Limited Current Conduction

bull Space Charge Limited Current Conduction with Traps

Magnitude of Injection Barrier

전하전하 주입주입

34OLED 기초공정 이해와 실습

Thermionic Emission

Fowler-Nordheim Tunneling

2

2 2

3

exp 1 wehere exp

4 120( )

Richardson constant

bns s

B B

n B

eeVJ J J A Tk T k T

em kA m m A cm Kh

φ

π

⎡ ⎤⎛ ⎞ ⎛ ⎞minus= minus =⎢ ⎥⎜ ⎟ ⎜ ⎟

⎝ ⎠ ⎝ ⎠⎣ ⎦

= =

At low field thermionic emission at high field tunneling dominate

전하전하 주입주입

EF

Evac

-eFz(triangular shape)φ

Z=0 Z

Charge accumulationhigher the energy state `

Electron emission (F-N Tunneling)

Electron emission (Thermionic Emission)

2

3212

~ exp

( ) where 8 (2 )3

bJ EE

qb mqh

π

⎛ ⎞minus⎜ ⎟⎝ ⎠

Φ=

35OLED 기초공정 이해와 실습

Applied voltage

Lattice vibration

Localizedelectron

Hopping conductionBand-like conductionDelocalized electron

Lattice vibration(phonon)

Scattered electron

Low Mobility

bull holes μ ~10-4-10-8 Vs due to poor wave function overlap (large hopping distance)

bull electrons μ ~10-6-10-10Vs due to increased disorder and trapping at defect sites caused by impurities such as O2

rArr Build-up of space-charge density (bulk limited current)

전하전하 이동도이동도

36OLED 기초공정 이해와 실습

NoteMobility depends onElectric Field andTemperature

Mobilities of OrganicsMobilities of Organics

Alq3

37OLED 기초공정 이해와 실습

Ohmic conduction

OLEDOLED의의 전류전류

Current Dendity

current depends linearly on the bias voltageo nn qm VJd

=

2

3

0

1

2 1

(no traps)

(exponential trap distributions ( ) exp( )

one of electrodes(Ohmic contact) can supply more carriers per un

98

Current Density

SCLC condition

o

tt

r

m

m tN

VJd

T E N E kTV md T

ε ε μ

+

+ =

=

prop =

it time than can be transported through the dielectric (caused by low mobility)

Space charge limited (SCL) conduction

38OLED 기초공정 이해와 실습

2

2

3

Charge per unit area Q induced by a voltage V

Transit time across the semiconductor

9

Approximate SCLC densi

Child law (Mott- Gu

ty

Elec8

rney law)

o r

r

o rSCLC

r

VQ CVd

d dtE V

VQJt d

ε ε

μ μ

ε ε μ

= =

= =

asymp =

3 2

tric field distribution across the semiconductor

Majority space charges enhance the E field at the

3 3 ( ) at ( )2 2

enhance the injection of the cath

minority carrieode

rs (elect

V x VE x x d E dd d

= = =

rArr rons)

d

(+) (-)

x=0 x=d

Vd

15 Vd232

3)(d

xVxE =

++++

Virtual anode

-

Space Charge Limited CurrentSpace Charge Limited Current

39OLED 기초공정 이해와 실습

2

3

1

2 01

(no traps or discrete traps Mott-Gurney formula)

(exponential trap distributions ( ) exp( )

98

o rSCLC

mt

SCLC m t t

VJd

TVJ N E NmT

E kTd

ε ε μ

+

+

=

prop = =

ECB

EVB

Etrap

Discrete trapping center Exponential distributionof trapping centers

TrapTrap--Limited CurrentLimited Current

40OLED 기초공정 이해와 실습

Shen Burrows Bulovic McCarty Thompson Forrest Jpn J Appl Phys 35 L401 (1996)

ITOTPDAlq3MgAg

12

1

+

+

prop m

m

SCLC dVJ

TrapTrap--Limited CurrentLimited Current

41OLED 기초공정 이해와 실습

0

0

Activation energy at 0 Empirical parameter

Mobility at PF constant

PF

PF

E FT

T Tμβ

Δ =

=

PFPF

B eff

0

3

PFeff 0 0

( ) exp

exp( )

1 1 1with

E FFT μk T

F

qT T T

βμ

μ β

βπεε

⎛ ⎞Δ minus= minus⎜ ⎟⎜ ⎟

⎝ ⎠

equiv

= minus =

Poole Frenkel ModelPoole Frenkel Model

42OLED 기초공정 이해와 실습

1

22 2

0

0

(1)

(2)

EL F S e h

e ee he

T

h he hh

T

T rec rec e h

h eh e

h e

e hEL F S

h e

T rec

h e h e nh e EL F S EL

e h

n nJ n n nedJ n n ned

nJ

ne F

J J Je F

J Jn J J

ed n ed

η η γ

γτ

γτ

τ τ τ γ

μ

η η γμ μ

τ τ

η ηγ

minus

Φ =

minus minus =

minus minus =

lt =

=

Φ = prop

gt

= Φ = prop rArr Φ prop

EL Current RelationEL Current Relation

43OLED 기초공정 이해와 실습

Device Structure ITONPBAlq3Ca

22

21

ZZZ

fdVdQC

+minus

==πφieZiZZZ ||

))=+=

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

V0 independent of the NPB layer thickness

44OLED 기초공정 이해와 실습

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

Dashed line without interfacial charge

Wolfgang Brutting Stefan Berleb Anton G Muckl Organic Electronics 2 (2001)

Device Structure ITONPBAlq3Ca

45OLED 기초공정 이해와 실습

Langevin Recombination of carriers

bull Carriers are statistically independent therefore the e-h recombination is a random process and kinetically bimolecular

bull Total current attracted by a charge into the sphere of Coulombic capture radius rc

2

22

( ) ( )4

(4 ) 14 184

( ) (mean free path A)

n p c n pc

c cB

n p

qJ qp E qpr

qi r J Bqp r nmk T

qB a

μ μ μ μπε

ππε

μ μ λε

= + = +

= = cong asymp minus

there4 = + asympo

TkUd

BeP ~ minusProbability of dissociation

reUπε4

~2

e-

rc

Carrier RecombinationCarrier Recombination

P Langevin Ann Chem Phys 28 289 (1903)

46OLED 기초공정 이해와 실습

Electronic Processes in Organic Crystals and Polymers by MPope and C E Swenberg

ExcitonsExcitons

47OLED 기초공정 이해와 실습

C Adachi et al

Electrons and holesForm excitons

(bound e--h+ pairs)

Exciton Recombination ZoneExciton Recombination Zone

48OLED 기초공정 이해와 실습

MOLECULAR EXCITED STATESAFTER ELECTRICAL EXCITATION

Singletspin anti-symmetric

Tripletspin symmetric

25 75

MOLECULAR GROUND STATEspin anti-symmetric

Relaxation allowedfast efficientFluorescence

Relaxation disallowedslow inefficientPhosphorescence

|χ1χ2 gt = | gt

|χ1χ2 gt = | gt

|χ1χ2 gt

= | gt - | gt2

1

|χ1χ2 gt = | gt + | gt2

1ISC

Spin

OLEDOLED의의 형광형광인광인광

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 27: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

26OLED 기초공정 이해와 실습

Cathode

HILITO

GLASS

HTLEMLETL

-

+

OLED Structure

N N

CH3

H3C

TPD m-MTDATA

N

N N

N

CH3

CH3

H3C

NO

NON

OAl

Alq3

Small Molecules (Fluorescence)

27OLED 기초공정 이해와 실습

OLED StructureSmall Molecules

(Phosphorescence)

NN

N

N

NN

N

N

CuN

N

NN

CuPc MTDATA

Cathode

HILITO

GLASS

HTLEML

ETL-

+

HBL

NNCH3H3C

BCP

28OLED 기초공정 이해와 실습

OLED Structure

Polymers

Cathode

ITO

GLASS

HTLEML

-

+

PEDOT

n

S O3- S O3

-S O3H S O3H S O3H S O3H

SS

SS

SS

O O

OO

O O

OO OO

n

n n

RR

PPV PF

29OLED 기초공정 이해와 실습

Cur

rent

den

sity Lum

inous Intensity

Voltage

ln V

ln J

J = qn0μVd

J = 98 εsμV2d3

Ligh

t

Current

slope = ηexte

Ex)

OLED OLED 특성특성

3 7

Diode Characteristics Rectification ratio 10 - 10 Power efficiency amp drive voltage

Light vs current

optconv ext

elec

opt opt elecext opt ext

elec elec

P hP eV

N s I IIN s I e e

νη η

η η

= =

= = rArr = times

30OLED 기초공정 이해와 실습

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

Vacuum Level

Anode

Cathode

HOMO

LUMO

Φa

Φc

EA

IP

CB

VB

Eg

에너지에너지 준위준위

31OLED 기초공정 이해와 실습

Current - Voltage Characteristics

2

16 17 3

0

0

1

diffusion voltage ~ 13 V

acceptor concentration ~ 10 - 10 cm

(~ 50 - 150 nm

2( )

Width of space charge layer 2 ( )

D

D

A

r DA

r D A

V VCV

N

C A q N V V

w V V qN

ε ε

ε ε

prop minus

= minus

= minus V = 0 )

OLED OLED 전기적전기적 특성특성

( ) Schottky equation

exp 1

ideality factor 1 1 ideal Schottky diodes B ext BJ J eV nk T V V IR

n n

⎡ ⎤= minus = minus⎣ ⎦ge =

Capacitance - Voltage Dependence

32OLED 기초공정 이해와 실습

I - V Characteristics C - V Characteristics

ITOPPVMetal Polymeric Schottky Diode

OLED OLED 전기적전기적 특성특성

33OLED 기초공정 이해와 실습

Injection Dominated Mechanisms

bull Thermionic emission

bull Tunneling

Bulk Dominated Mechanisms

bull Ohmic Conduction

bull Space Charge Limited Current Conduction

bull Space Charge Limited Current Conduction with Traps

Magnitude of Injection Barrier

전하전하 주입주입

34OLED 기초공정 이해와 실습

Thermionic Emission

Fowler-Nordheim Tunneling

2

2 2

3

exp 1 wehere exp

4 120( )

Richardson constant

bns s

B B

n B

eeVJ J J A Tk T k T

em kA m m A cm Kh

φ

π

⎡ ⎤⎛ ⎞ ⎛ ⎞minus= minus =⎢ ⎥⎜ ⎟ ⎜ ⎟

⎝ ⎠ ⎝ ⎠⎣ ⎦

= =

At low field thermionic emission at high field tunneling dominate

전하전하 주입주입

EF

Evac

-eFz(triangular shape)φ

Z=0 Z

Charge accumulationhigher the energy state `

Electron emission (F-N Tunneling)

Electron emission (Thermionic Emission)

2

3212

~ exp

( ) where 8 (2 )3

bJ EE

qb mqh

π

⎛ ⎞minus⎜ ⎟⎝ ⎠

Φ=

35OLED 기초공정 이해와 실습

Applied voltage

Lattice vibration

Localizedelectron

Hopping conductionBand-like conductionDelocalized electron

Lattice vibration(phonon)

Scattered electron

Low Mobility

bull holes μ ~10-4-10-8 Vs due to poor wave function overlap (large hopping distance)

bull electrons μ ~10-6-10-10Vs due to increased disorder and trapping at defect sites caused by impurities such as O2

rArr Build-up of space-charge density (bulk limited current)

전하전하 이동도이동도

36OLED 기초공정 이해와 실습

NoteMobility depends onElectric Field andTemperature

Mobilities of OrganicsMobilities of Organics

Alq3

37OLED 기초공정 이해와 실습

Ohmic conduction

OLEDOLED의의 전류전류

Current Dendity

current depends linearly on the bias voltageo nn qm VJd

=

2

3

0

1

2 1

(no traps)

(exponential trap distributions ( ) exp( )

one of electrodes(Ohmic contact) can supply more carriers per un

98

Current Density

SCLC condition

o

tt

r

m

m tN

VJd

T E N E kTV md T

ε ε μ

+

+ =

=

prop =

it time than can be transported through the dielectric (caused by low mobility)

Space charge limited (SCL) conduction

38OLED 기초공정 이해와 실습

2

2

3

Charge per unit area Q induced by a voltage V

Transit time across the semiconductor

9

Approximate SCLC densi

Child law (Mott- Gu

ty

Elec8

rney law)

o r

r

o rSCLC

r

VQ CVd

d dtE V

VQJt d

ε ε

μ μ

ε ε μ

= =

= =

asymp =

3 2

tric field distribution across the semiconductor

Majority space charges enhance the E field at the

3 3 ( ) at ( )2 2

enhance the injection of the cath

minority carrieode

rs (elect

V x VE x x d E dd d

= = =

rArr rons)

d

(+) (-)

x=0 x=d

Vd

15 Vd232

3)(d

xVxE =

++++

Virtual anode

-

Space Charge Limited CurrentSpace Charge Limited Current

39OLED 기초공정 이해와 실습

2

3

1

2 01

(no traps or discrete traps Mott-Gurney formula)

(exponential trap distributions ( ) exp( )

98

o rSCLC

mt

SCLC m t t

VJd

TVJ N E NmT

E kTd

ε ε μ

+

+

=

prop = =

ECB

EVB

Etrap

Discrete trapping center Exponential distributionof trapping centers

TrapTrap--Limited CurrentLimited Current

40OLED 기초공정 이해와 실습

Shen Burrows Bulovic McCarty Thompson Forrest Jpn J Appl Phys 35 L401 (1996)

ITOTPDAlq3MgAg

12

1

+

+

prop m

m

SCLC dVJ

TrapTrap--Limited CurrentLimited Current

41OLED 기초공정 이해와 실습

0

0

Activation energy at 0 Empirical parameter

Mobility at PF constant

PF

PF

E FT

T Tμβ

Δ =

=

PFPF

B eff

0

3

PFeff 0 0

( ) exp

exp( )

1 1 1with

E FFT μk T

F

qT T T

βμ

μ β

βπεε

⎛ ⎞Δ minus= minus⎜ ⎟⎜ ⎟

⎝ ⎠

equiv

= minus =

Poole Frenkel ModelPoole Frenkel Model

42OLED 기초공정 이해와 실습

1

22 2

0

0

(1)

(2)

EL F S e h

e ee he

T

h he hh

T

T rec rec e h

h eh e

h e

e hEL F S

h e

T rec

h e h e nh e EL F S EL

e h

n nJ n n nedJ n n ned

nJ

ne F

J J Je F

J Jn J J

ed n ed

η η γ

γτ

γτ

τ τ τ γ

μ

η η γμ μ

τ τ

η ηγ

minus

Φ =

minus minus =

minus minus =

lt =

=

Φ = prop

gt

= Φ = prop rArr Φ prop

EL Current RelationEL Current Relation

43OLED 기초공정 이해와 실습

Device Structure ITONPBAlq3Ca

22

21

ZZZ

fdVdQC

+minus

==πφieZiZZZ ||

))=+=

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

V0 independent of the NPB layer thickness

44OLED 기초공정 이해와 실습

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

Dashed line without interfacial charge

Wolfgang Brutting Stefan Berleb Anton G Muckl Organic Electronics 2 (2001)

Device Structure ITONPBAlq3Ca

45OLED 기초공정 이해와 실습

Langevin Recombination of carriers

bull Carriers are statistically independent therefore the e-h recombination is a random process and kinetically bimolecular

bull Total current attracted by a charge into the sphere of Coulombic capture radius rc

2

22

( ) ( )4

(4 ) 14 184

( ) (mean free path A)

n p c n pc

c cB

n p

qJ qp E qpr

qi r J Bqp r nmk T

qB a

μ μ μ μπε

ππε

μ μ λε

= + = +

= = cong asymp minus

there4 = + asympo

TkUd

BeP ~ minusProbability of dissociation

reUπε4

~2

e-

rc

Carrier RecombinationCarrier Recombination

P Langevin Ann Chem Phys 28 289 (1903)

46OLED 기초공정 이해와 실습

Electronic Processes in Organic Crystals and Polymers by MPope and C E Swenberg

ExcitonsExcitons

47OLED 기초공정 이해와 실습

C Adachi et al

Electrons and holesForm excitons

(bound e--h+ pairs)

Exciton Recombination ZoneExciton Recombination Zone

48OLED 기초공정 이해와 실습

MOLECULAR EXCITED STATESAFTER ELECTRICAL EXCITATION

Singletspin anti-symmetric

Tripletspin symmetric

25 75

MOLECULAR GROUND STATEspin anti-symmetric

Relaxation allowedfast efficientFluorescence

Relaxation disallowedslow inefficientPhosphorescence

|χ1χ2 gt = | gt

|χ1χ2 gt = | gt

|χ1χ2 gt

= | gt - | gt2

1

|χ1χ2 gt = | gt + | gt2

1ISC

Spin

OLEDOLED의의 형광형광인광인광

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 28: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

27OLED 기초공정 이해와 실습

OLED StructureSmall Molecules

(Phosphorescence)

NN

N

N

NN

N

N

CuN

N

NN

CuPc MTDATA

Cathode

HILITO

GLASS

HTLEML

ETL-

+

HBL

NNCH3H3C

BCP

28OLED 기초공정 이해와 실습

OLED Structure

Polymers

Cathode

ITO

GLASS

HTLEML

-

+

PEDOT

n

S O3- S O3

-S O3H S O3H S O3H S O3H

SS

SS

SS

O O

OO

O O

OO OO

n

n n

RR

PPV PF

29OLED 기초공정 이해와 실습

Cur

rent

den

sity Lum

inous Intensity

Voltage

ln V

ln J

J = qn0μVd

J = 98 εsμV2d3

Ligh

t

Current

slope = ηexte

Ex)

OLED OLED 특성특성

3 7

Diode Characteristics Rectification ratio 10 - 10 Power efficiency amp drive voltage

Light vs current

optconv ext

elec

opt opt elecext opt ext

elec elec

P hP eV

N s I IIN s I e e

νη η

η η

= =

= = rArr = times

30OLED 기초공정 이해와 실습

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

Vacuum Level

Anode

Cathode

HOMO

LUMO

Φa

Φc

EA

IP

CB

VB

Eg

에너지에너지 준위준위

31OLED 기초공정 이해와 실습

Current - Voltage Characteristics

2

16 17 3

0

0

1

diffusion voltage ~ 13 V

acceptor concentration ~ 10 - 10 cm

(~ 50 - 150 nm

2( )

Width of space charge layer 2 ( )

D

D

A

r DA

r D A

V VCV

N

C A q N V V

w V V qN

ε ε

ε ε

prop minus

= minus

= minus V = 0 )

OLED OLED 전기적전기적 특성특성

( ) Schottky equation

exp 1

ideality factor 1 1 ideal Schottky diodes B ext BJ J eV nk T V V IR

n n

⎡ ⎤= minus = minus⎣ ⎦ge =

Capacitance - Voltage Dependence

32OLED 기초공정 이해와 실습

I - V Characteristics C - V Characteristics

ITOPPVMetal Polymeric Schottky Diode

OLED OLED 전기적전기적 특성특성

33OLED 기초공정 이해와 실습

Injection Dominated Mechanisms

bull Thermionic emission

bull Tunneling

Bulk Dominated Mechanisms

bull Ohmic Conduction

bull Space Charge Limited Current Conduction

bull Space Charge Limited Current Conduction with Traps

Magnitude of Injection Barrier

전하전하 주입주입

34OLED 기초공정 이해와 실습

Thermionic Emission

Fowler-Nordheim Tunneling

2

2 2

3

exp 1 wehere exp

4 120( )

Richardson constant

bns s

B B

n B

eeVJ J J A Tk T k T

em kA m m A cm Kh

φ

π

⎡ ⎤⎛ ⎞ ⎛ ⎞minus= minus =⎢ ⎥⎜ ⎟ ⎜ ⎟

⎝ ⎠ ⎝ ⎠⎣ ⎦

= =

At low field thermionic emission at high field tunneling dominate

전하전하 주입주입

EF

Evac

-eFz(triangular shape)φ

Z=0 Z

Charge accumulationhigher the energy state `

Electron emission (F-N Tunneling)

Electron emission (Thermionic Emission)

2

3212

~ exp

( ) where 8 (2 )3

bJ EE

qb mqh

π

⎛ ⎞minus⎜ ⎟⎝ ⎠

Φ=

35OLED 기초공정 이해와 실습

Applied voltage

Lattice vibration

Localizedelectron

Hopping conductionBand-like conductionDelocalized electron

Lattice vibration(phonon)

Scattered electron

Low Mobility

bull holes μ ~10-4-10-8 Vs due to poor wave function overlap (large hopping distance)

bull electrons μ ~10-6-10-10Vs due to increased disorder and trapping at defect sites caused by impurities such as O2

rArr Build-up of space-charge density (bulk limited current)

전하전하 이동도이동도

36OLED 기초공정 이해와 실습

NoteMobility depends onElectric Field andTemperature

Mobilities of OrganicsMobilities of Organics

Alq3

37OLED 기초공정 이해와 실습

Ohmic conduction

OLEDOLED의의 전류전류

Current Dendity

current depends linearly on the bias voltageo nn qm VJd

=

2

3

0

1

2 1

(no traps)

(exponential trap distributions ( ) exp( )

one of electrodes(Ohmic contact) can supply more carriers per un

98

Current Density

SCLC condition

o

tt

r

m

m tN

VJd

T E N E kTV md T

ε ε μ

+

+ =

=

prop =

it time than can be transported through the dielectric (caused by low mobility)

Space charge limited (SCL) conduction

38OLED 기초공정 이해와 실습

2

2

3

Charge per unit area Q induced by a voltage V

Transit time across the semiconductor

9

Approximate SCLC densi

Child law (Mott- Gu

ty

Elec8

rney law)

o r

r

o rSCLC

r

VQ CVd

d dtE V

VQJt d

ε ε

μ μ

ε ε μ

= =

= =

asymp =

3 2

tric field distribution across the semiconductor

Majority space charges enhance the E field at the

3 3 ( ) at ( )2 2

enhance the injection of the cath

minority carrieode

rs (elect

V x VE x x d E dd d

= = =

rArr rons)

d

(+) (-)

x=0 x=d

Vd

15 Vd232

3)(d

xVxE =

++++

Virtual anode

-

Space Charge Limited CurrentSpace Charge Limited Current

39OLED 기초공정 이해와 실습

2

3

1

2 01

(no traps or discrete traps Mott-Gurney formula)

(exponential trap distributions ( ) exp( )

98

o rSCLC

mt

SCLC m t t

VJd

TVJ N E NmT

E kTd

ε ε μ

+

+

=

prop = =

ECB

EVB

Etrap

Discrete trapping center Exponential distributionof trapping centers

TrapTrap--Limited CurrentLimited Current

40OLED 기초공정 이해와 실습

Shen Burrows Bulovic McCarty Thompson Forrest Jpn J Appl Phys 35 L401 (1996)

ITOTPDAlq3MgAg

12

1

+

+

prop m

m

SCLC dVJ

TrapTrap--Limited CurrentLimited Current

41OLED 기초공정 이해와 실습

0

0

Activation energy at 0 Empirical parameter

Mobility at PF constant

PF

PF

E FT

T Tμβ

Δ =

=

PFPF

B eff

0

3

PFeff 0 0

( ) exp

exp( )

1 1 1with

E FFT μk T

F

qT T T

βμ

μ β

βπεε

⎛ ⎞Δ minus= minus⎜ ⎟⎜ ⎟

⎝ ⎠

equiv

= minus =

Poole Frenkel ModelPoole Frenkel Model

42OLED 기초공정 이해와 실습

1

22 2

0

0

(1)

(2)

EL F S e h

e ee he

T

h he hh

T

T rec rec e h

h eh e

h e

e hEL F S

h e

T rec

h e h e nh e EL F S EL

e h

n nJ n n nedJ n n ned

nJ

ne F

J J Je F

J Jn J J

ed n ed

η η γ

γτ

γτ

τ τ τ γ

μ

η η γμ μ

τ τ

η ηγ

minus

Φ =

minus minus =

minus minus =

lt =

=

Φ = prop

gt

= Φ = prop rArr Φ prop

EL Current RelationEL Current Relation

43OLED 기초공정 이해와 실습

Device Structure ITONPBAlq3Ca

22

21

ZZZ

fdVdQC

+minus

==πφieZiZZZ ||

))=+=

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

V0 independent of the NPB layer thickness

44OLED 기초공정 이해와 실습

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

Dashed line without interfacial charge

Wolfgang Brutting Stefan Berleb Anton G Muckl Organic Electronics 2 (2001)

Device Structure ITONPBAlq3Ca

45OLED 기초공정 이해와 실습

Langevin Recombination of carriers

bull Carriers are statistically independent therefore the e-h recombination is a random process and kinetically bimolecular

bull Total current attracted by a charge into the sphere of Coulombic capture radius rc

2

22

( ) ( )4

(4 ) 14 184

( ) (mean free path A)

n p c n pc

c cB

n p

qJ qp E qpr

qi r J Bqp r nmk T

qB a

μ μ μ μπε

ππε

μ μ λε

= + = +

= = cong asymp minus

there4 = + asympo

TkUd

BeP ~ minusProbability of dissociation

reUπε4

~2

e-

rc

Carrier RecombinationCarrier Recombination

P Langevin Ann Chem Phys 28 289 (1903)

46OLED 기초공정 이해와 실습

Electronic Processes in Organic Crystals and Polymers by MPope and C E Swenberg

ExcitonsExcitons

47OLED 기초공정 이해와 실습

C Adachi et al

Electrons and holesForm excitons

(bound e--h+ pairs)

Exciton Recombination ZoneExciton Recombination Zone

48OLED 기초공정 이해와 실습

MOLECULAR EXCITED STATESAFTER ELECTRICAL EXCITATION

Singletspin anti-symmetric

Tripletspin symmetric

25 75

MOLECULAR GROUND STATEspin anti-symmetric

Relaxation allowedfast efficientFluorescence

Relaxation disallowedslow inefficientPhosphorescence

|χ1χ2 gt = | gt

|χ1χ2 gt = | gt

|χ1χ2 gt

= | gt - | gt2

1

|χ1χ2 gt = | gt + | gt2

1ISC

Spin

OLEDOLED의의 형광형광인광인광

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 29: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

28OLED 기초공정 이해와 실습

OLED Structure

Polymers

Cathode

ITO

GLASS

HTLEML

-

+

PEDOT

n

S O3- S O3

-S O3H S O3H S O3H S O3H

SS

SS

SS

O O

OO

O O

OO OO

n

n n

RR

PPV PF

29OLED 기초공정 이해와 실습

Cur

rent

den

sity Lum

inous Intensity

Voltage

ln V

ln J

J = qn0μVd

J = 98 εsμV2d3

Ligh

t

Current

slope = ηexte

Ex)

OLED OLED 특성특성

3 7

Diode Characteristics Rectification ratio 10 - 10 Power efficiency amp drive voltage

Light vs current

optconv ext

elec

opt opt elecext opt ext

elec elec

P hP eV

N s I IIN s I e e

νη η

η η

= =

= = rArr = times

30OLED 기초공정 이해와 실습

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

Vacuum Level

Anode

Cathode

HOMO

LUMO

Φa

Φc

EA

IP

CB

VB

Eg

에너지에너지 준위준위

31OLED 기초공정 이해와 실습

Current - Voltage Characteristics

2

16 17 3

0

0

1

diffusion voltage ~ 13 V

acceptor concentration ~ 10 - 10 cm

(~ 50 - 150 nm

2( )

Width of space charge layer 2 ( )

D

D

A

r DA

r D A

V VCV

N

C A q N V V

w V V qN

ε ε

ε ε

prop minus

= minus

= minus V = 0 )

OLED OLED 전기적전기적 특성특성

( ) Schottky equation

exp 1

ideality factor 1 1 ideal Schottky diodes B ext BJ J eV nk T V V IR

n n

⎡ ⎤= minus = minus⎣ ⎦ge =

Capacitance - Voltage Dependence

32OLED 기초공정 이해와 실습

I - V Characteristics C - V Characteristics

ITOPPVMetal Polymeric Schottky Diode

OLED OLED 전기적전기적 특성특성

33OLED 기초공정 이해와 실습

Injection Dominated Mechanisms

bull Thermionic emission

bull Tunneling

Bulk Dominated Mechanisms

bull Ohmic Conduction

bull Space Charge Limited Current Conduction

bull Space Charge Limited Current Conduction with Traps

Magnitude of Injection Barrier

전하전하 주입주입

34OLED 기초공정 이해와 실습

Thermionic Emission

Fowler-Nordheim Tunneling

2

2 2

3

exp 1 wehere exp

4 120( )

Richardson constant

bns s

B B

n B

eeVJ J J A Tk T k T

em kA m m A cm Kh

φ

π

⎡ ⎤⎛ ⎞ ⎛ ⎞minus= minus =⎢ ⎥⎜ ⎟ ⎜ ⎟

⎝ ⎠ ⎝ ⎠⎣ ⎦

= =

At low field thermionic emission at high field tunneling dominate

전하전하 주입주입

EF

Evac

-eFz(triangular shape)φ

Z=0 Z

Charge accumulationhigher the energy state `

Electron emission (F-N Tunneling)

Electron emission (Thermionic Emission)

2

3212

~ exp

( ) where 8 (2 )3

bJ EE

qb mqh

π

⎛ ⎞minus⎜ ⎟⎝ ⎠

Φ=

35OLED 기초공정 이해와 실습

Applied voltage

Lattice vibration

Localizedelectron

Hopping conductionBand-like conductionDelocalized electron

Lattice vibration(phonon)

Scattered electron

Low Mobility

bull holes μ ~10-4-10-8 Vs due to poor wave function overlap (large hopping distance)

bull electrons μ ~10-6-10-10Vs due to increased disorder and trapping at defect sites caused by impurities such as O2

rArr Build-up of space-charge density (bulk limited current)

전하전하 이동도이동도

36OLED 기초공정 이해와 실습

NoteMobility depends onElectric Field andTemperature

Mobilities of OrganicsMobilities of Organics

Alq3

37OLED 기초공정 이해와 실습

Ohmic conduction

OLEDOLED의의 전류전류

Current Dendity

current depends linearly on the bias voltageo nn qm VJd

=

2

3

0

1

2 1

(no traps)

(exponential trap distributions ( ) exp( )

one of electrodes(Ohmic contact) can supply more carriers per un

98

Current Density

SCLC condition

o

tt

r

m

m tN

VJd

T E N E kTV md T

ε ε μ

+

+ =

=

prop =

it time than can be transported through the dielectric (caused by low mobility)

Space charge limited (SCL) conduction

38OLED 기초공정 이해와 실습

2

2

3

Charge per unit area Q induced by a voltage V

Transit time across the semiconductor

9

Approximate SCLC densi

Child law (Mott- Gu

ty

Elec8

rney law)

o r

r

o rSCLC

r

VQ CVd

d dtE V

VQJt d

ε ε

μ μ

ε ε μ

= =

= =

asymp =

3 2

tric field distribution across the semiconductor

Majority space charges enhance the E field at the

3 3 ( ) at ( )2 2

enhance the injection of the cath

minority carrieode

rs (elect

V x VE x x d E dd d

= = =

rArr rons)

d

(+) (-)

x=0 x=d

Vd

15 Vd232

3)(d

xVxE =

++++

Virtual anode

-

Space Charge Limited CurrentSpace Charge Limited Current

39OLED 기초공정 이해와 실습

2

3

1

2 01

(no traps or discrete traps Mott-Gurney formula)

(exponential trap distributions ( ) exp( )

98

o rSCLC

mt

SCLC m t t

VJd

TVJ N E NmT

E kTd

ε ε μ

+

+

=

prop = =

ECB

EVB

Etrap

Discrete trapping center Exponential distributionof trapping centers

TrapTrap--Limited CurrentLimited Current

40OLED 기초공정 이해와 실습

Shen Burrows Bulovic McCarty Thompson Forrest Jpn J Appl Phys 35 L401 (1996)

ITOTPDAlq3MgAg

12

1

+

+

prop m

m

SCLC dVJ

TrapTrap--Limited CurrentLimited Current

41OLED 기초공정 이해와 실습

0

0

Activation energy at 0 Empirical parameter

Mobility at PF constant

PF

PF

E FT

T Tμβ

Δ =

=

PFPF

B eff

0

3

PFeff 0 0

( ) exp

exp( )

1 1 1with

E FFT μk T

F

qT T T

βμ

μ β

βπεε

⎛ ⎞Δ minus= minus⎜ ⎟⎜ ⎟

⎝ ⎠

equiv

= minus =

Poole Frenkel ModelPoole Frenkel Model

42OLED 기초공정 이해와 실습

1

22 2

0

0

(1)

(2)

EL F S e h

e ee he

T

h he hh

T

T rec rec e h

h eh e

h e

e hEL F S

h e

T rec

h e h e nh e EL F S EL

e h

n nJ n n nedJ n n ned

nJ

ne F

J J Je F

J Jn J J

ed n ed

η η γ

γτ

γτ

τ τ τ γ

μ

η η γμ μ

τ τ

η ηγ

minus

Φ =

minus minus =

minus minus =

lt =

=

Φ = prop

gt

= Φ = prop rArr Φ prop

EL Current RelationEL Current Relation

43OLED 기초공정 이해와 실습

Device Structure ITONPBAlq3Ca

22

21

ZZZ

fdVdQC

+minus

==πφieZiZZZ ||

))=+=

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

V0 independent of the NPB layer thickness

44OLED 기초공정 이해와 실습

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

Dashed line without interfacial charge

Wolfgang Brutting Stefan Berleb Anton G Muckl Organic Electronics 2 (2001)

Device Structure ITONPBAlq3Ca

45OLED 기초공정 이해와 실습

Langevin Recombination of carriers

bull Carriers are statistically independent therefore the e-h recombination is a random process and kinetically bimolecular

bull Total current attracted by a charge into the sphere of Coulombic capture radius rc

2

22

( ) ( )4

(4 ) 14 184

( ) (mean free path A)

n p c n pc

c cB

n p

qJ qp E qpr

qi r J Bqp r nmk T

qB a

μ μ μ μπε

ππε

μ μ λε

= + = +

= = cong asymp minus

there4 = + asympo

TkUd

BeP ~ minusProbability of dissociation

reUπε4

~2

e-

rc

Carrier RecombinationCarrier Recombination

P Langevin Ann Chem Phys 28 289 (1903)

46OLED 기초공정 이해와 실습

Electronic Processes in Organic Crystals and Polymers by MPope and C E Swenberg

ExcitonsExcitons

47OLED 기초공정 이해와 실습

C Adachi et al

Electrons and holesForm excitons

(bound e--h+ pairs)

Exciton Recombination ZoneExciton Recombination Zone

48OLED 기초공정 이해와 실습

MOLECULAR EXCITED STATESAFTER ELECTRICAL EXCITATION

Singletspin anti-symmetric

Tripletspin symmetric

25 75

MOLECULAR GROUND STATEspin anti-symmetric

Relaxation allowedfast efficientFluorescence

Relaxation disallowedslow inefficientPhosphorescence

|χ1χ2 gt = | gt

|χ1χ2 gt = | gt

|χ1χ2 gt

= | gt - | gt2

1

|χ1χ2 gt = | gt + | gt2

1ISC

Spin

OLEDOLED의의 형광형광인광인광

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 30: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

29OLED 기초공정 이해와 실습

Cur

rent

den

sity Lum

inous Intensity

Voltage

ln V

ln J

J = qn0μVd

J = 98 εsμV2d3

Ligh

t

Current

slope = ηexte

Ex)

OLED OLED 특성특성

3 7

Diode Characteristics Rectification ratio 10 - 10 Power efficiency amp drive voltage

Light vs current

optconv ext

elec

opt opt elecext opt ext

elec elec

P hP eV

N s I IIN s I e e

νη η

η η

= =

= = rArr = times

30OLED 기초공정 이해와 실습

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

Vacuum Level

Anode

Cathode

HOMO

LUMO

Φa

Φc

EA

IP

CB

VB

Eg

에너지에너지 준위준위

31OLED 기초공정 이해와 실습

Current - Voltage Characteristics

2

16 17 3

0

0

1

diffusion voltage ~ 13 V

acceptor concentration ~ 10 - 10 cm

(~ 50 - 150 nm

2( )

Width of space charge layer 2 ( )

D

D

A

r DA

r D A

V VCV

N

C A q N V V

w V V qN

ε ε

ε ε

prop minus

= minus

= minus V = 0 )

OLED OLED 전기적전기적 특성특성

( ) Schottky equation

exp 1

ideality factor 1 1 ideal Schottky diodes B ext BJ J eV nk T V V IR

n n

⎡ ⎤= minus = minus⎣ ⎦ge =

Capacitance - Voltage Dependence

32OLED 기초공정 이해와 실습

I - V Characteristics C - V Characteristics

ITOPPVMetal Polymeric Schottky Diode

OLED OLED 전기적전기적 특성특성

33OLED 기초공정 이해와 실습

Injection Dominated Mechanisms

bull Thermionic emission

bull Tunneling

Bulk Dominated Mechanisms

bull Ohmic Conduction

bull Space Charge Limited Current Conduction

bull Space Charge Limited Current Conduction with Traps

Magnitude of Injection Barrier

전하전하 주입주입

34OLED 기초공정 이해와 실습

Thermionic Emission

Fowler-Nordheim Tunneling

2

2 2

3

exp 1 wehere exp

4 120( )

Richardson constant

bns s

B B

n B

eeVJ J J A Tk T k T

em kA m m A cm Kh

φ

π

⎡ ⎤⎛ ⎞ ⎛ ⎞minus= minus =⎢ ⎥⎜ ⎟ ⎜ ⎟

⎝ ⎠ ⎝ ⎠⎣ ⎦

= =

At low field thermionic emission at high field tunneling dominate

전하전하 주입주입

EF

Evac

-eFz(triangular shape)φ

Z=0 Z

Charge accumulationhigher the energy state `

Electron emission (F-N Tunneling)

Electron emission (Thermionic Emission)

2

3212

~ exp

( ) where 8 (2 )3

bJ EE

qb mqh

π

⎛ ⎞minus⎜ ⎟⎝ ⎠

Φ=

35OLED 기초공정 이해와 실습

Applied voltage

Lattice vibration

Localizedelectron

Hopping conductionBand-like conductionDelocalized electron

Lattice vibration(phonon)

Scattered electron

Low Mobility

bull holes μ ~10-4-10-8 Vs due to poor wave function overlap (large hopping distance)

bull electrons μ ~10-6-10-10Vs due to increased disorder and trapping at defect sites caused by impurities such as O2

rArr Build-up of space-charge density (bulk limited current)

전하전하 이동도이동도

36OLED 기초공정 이해와 실습

NoteMobility depends onElectric Field andTemperature

Mobilities of OrganicsMobilities of Organics

Alq3

37OLED 기초공정 이해와 실습

Ohmic conduction

OLEDOLED의의 전류전류

Current Dendity

current depends linearly on the bias voltageo nn qm VJd

=

2

3

0

1

2 1

(no traps)

(exponential trap distributions ( ) exp( )

one of electrodes(Ohmic contact) can supply more carriers per un

98

Current Density

SCLC condition

o

tt

r

m

m tN

VJd

T E N E kTV md T

ε ε μ

+

+ =

=

prop =

it time than can be transported through the dielectric (caused by low mobility)

Space charge limited (SCL) conduction

38OLED 기초공정 이해와 실습

2

2

3

Charge per unit area Q induced by a voltage V

Transit time across the semiconductor

9

Approximate SCLC densi

Child law (Mott- Gu

ty

Elec8

rney law)

o r

r

o rSCLC

r

VQ CVd

d dtE V

VQJt d

ε ε

μ μ

ε ε μ

= =

= =

asymp =

3 2

tric field distribution across the semiconductor

Majority space charges enhance the E field at the

3 3 ( ) at ( )2 2

enhance the injection of the cath

minority carrieode

rs (elect

V x VE x x d E dd d

= = =

rArr rons)

d

(+) (-)

x=0 x=d

Vd

15 Vd232

3)(d

xVxE =

++++

Virtual anode

-

Space Charge Limited CurrentSpace Charge Limited Current

39OLED 기초공정 이해와 실습

2

3

1

2 01

(no traps or discrete traps Mott-Gurney formula)

(exponential trap distributions ( ) exp( )

98

o rSCLC

mt

SCLC m t t

VJd

TVJ N E NmT

E kTd

ε ε μ

+

+

=

prop = =

ECB

EVB

Etrap

Discrete trapping center Exponential distributionof trapping centers

TrapTrap--Limited CurrentLimited Current

40OLED 기초공정 이해와 실습

Shen Burrows Bulovic McCarty Thompson Forrest Jpn J Appl Phys 35 L401 (1996)

ITOTPDAlq3MgAg

12

1

+

+

prop m

m

SCLC dVJ

TrapTrap--Limited CurrentLimited Current

41OLED 기초공정 이해와 실습

0

0

Activation energy at 0 Empirical parameter

Mobility at PF constant

PF

PF

E FT

T Tμβ

Δ =

=

PFPF

B eff

0

3

PFeff 0 0

( ) exp

exp( )

1 1 1with

E FFT μk T

F

qT T T

βμ

μ β

βπεε

⎛ ⎞Δ minus= minus⎜ ⎟⎜ ⎟

⎝ ⎠

equiv

= minus =

Poole Frenkel ModelPoole Frenkel Model

42OLED 기초공정 이해와 실습

1

22 2

0

0

(1)

(2)

EL F S e h

e ee he

T

h he hh

T

T rec rec e h

h eh e

h e

e hEL F S

h e

T rec

h e h e nh e EL F S EL

e h

n nJ n n nedJ n n ned

nJ

ne F

J J Je F

J Jn J J

ed n ed

η η γ

γτ

γτ

τ τ τ γ

μ

η η γμ μ

τ τ

η ηγ

minus

Φ =

minus minus =

minus minus =

lt =

=

Φ = prop

gt

= Φ = prop rArr Φ prop

EL Current RelationEL Current Relation

43OLED 기초공정 이해와 실습

Device Structure ITONPBAlq3Ca

22

21

ZZZ

fdVdQC

+minus

==πφieZiZZZ ||

))=+=

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

V0 independent of the NPB layer thickness

44OLED 기초공정 이해와 실습

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

Dashed line without interfacial charge

Wolfgang Brutting Stefan Berleb Anton G Muckl Organic Electronics 2 (2001)

Device Structure ITONPBAlq3Ca

45OLED 기초공정 이해와 실습

Langevin Recombination of carriers

bull Carriers are statistically independent therefore the e-h recombination is a random process and kinetically bimolecular

bull Total current attracted by a charge into the sphere of Coulombic capture radius rc

2

22

( ) ( )4

(4 ) 14 184

( ) (mean free path A)

n p c n pc

c cB

n p

qJ qp E qpr

qi r J Bqp r nmk T

qB a

μ μ μ μπε

ππε

μ μ λε

= + = +

= = cong asymp minus

there4 = + asympo

TkUd

BeP ~ minusProbability of dissociation

reUπε4

~2

e-

rc

Carrier RecombinationCarrier Recombination

P Langevin Ann Chem Phys 28 289 (1903)

46OLED 기초공정 이해와 실습

Electronic Processes in Organic Crystals and Polymers by MPope and C E Swenberg

ExcitonsExcitons

47OLED 기초공정 이해와 실습

C Adachi et al

Electrons and holesForm excitons

(bound e--h+ pairs)

Exciton Recombination ZoneExciton Recombination Zone

48OLED 기초공정 이해와 실습

MOLECULAR EXCITED STATESAFTER ELECTRICAL EXCITATION

Singletspin anti-symmetric

Tripletspin symmetric

25 75

MOLECULAR GROUND STATEspin anti-symmetric

Relaxation allowedfast efficientFluorescence

Relaxation disallowedslow inefficientPhosphorescence

|χ1χ2 gt = | gt

|χ1χ2 gt = | gt

|χ1χ2 gt

= | gt - | gt2

1

|χ1χ2 gt = | gt + | gt2

1ISC

Spin

OLEDOLED의의 형광형광인광인광

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 31: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

30OLED 기초공정 이해와 실습

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

bull HOMO Highest Occupied Molecular

Orbital

bull LUMO Lowest Unoccupied Molecular

Orbital

bull IP Ionization Potential(from UPS CV)

bull Eg Band Gap Energy(from UV Abs

Spectrum)

bull EA Electron Affinity (= IP-Eg)

bull CB Conduction Band

bull VB Valence Band

bull Φa Work Function(Anode)

bull Φc Work Function(Cathode)

Vacuum Level

Anode

Cathode

HOMO

LUMO

Φa

Φc

EA

IP

CB

VB

Eg

에너지에너지 준위준위

31OLED 기초공정 이해와 실습

Current - Voltage Characteristics

2

16 17 3

0

0

1

diffusion voltage ~ 13 V

acceptor concentration ~ 10 - 10 cm

(~ 50 - 150 nm

2( )

Width of space charge layer 2 ( )

D

D

A

r DA

r D A

V VCV

N

C A q N V V

w V V qN

ε ε

ε ε

prop minus

= minus

= minus V = 0 )

OLED OLED 전기적전기적 특성특성

( ) Schottky equation

exp 1

ideality factor 1 1 ideal Schottky diodes B ext BJ J eV nk T V V IR

n n

⎡ ⎤= minus = minus⎣ ⎦ge =

Capacitance - Voltage Dependence

32OLED 기초공정 이해와 실습

I - V Characteristics C - V Characteristics

ITOPPVMetal Polymeric Schottky Diode

OLED OLED 전기적전기적 특성특성

33OLED 기초공정 이해와 실습

Injection Dominated Mechanisms

bull Thermionic emission

bull Tunneling

Bulk Dominated Mechanisms

bull Ohmic Conduction

bull Space Charge Limited Current Conduction

bull Space Charge Limited Current Conduction with Traps

Magnitude of Injection Barrier

전하전하 주입주입

34OLED 기초공정 이해와 실습

Thermionic Emission

Fowler-Nordheim Tunneling

2

2 2

3

exp 1 wehere exp

4 120( )

Richardson constant

bns s

B B

n B

eeVJ J J A Tk T k T

em kA m m A cm Kh

φ

π

⎡ ⎤⎛ ⎞ ⎛ ⎞minus= minus =⎢ ⎥⎜ ⎟ ⎜ ⎟

⎝ ⎠ ⎝ ⎠⎣ ⎦

= =

At low field thermionic emission at high field tunneling dominate

전하전하 주입주입

EF

Evac

-eFz(triangular shape)φ

Z=0 Z

Charge accumulationhigher the energy state `

Electron emission (F-N Tunneling)

Electron emission (Thermionic Emission)

2

3212

~ exp

( ) where 8 (2 )3

bJ EE

qb mqh

π

⎛ ⎞minus⎜ ⎟⎝ ⎠

Φ=

35OLED 기초공정 이해와 실습

Applied voltage

Lattice vibration

Localizedelectron

Hopping conductionBand-like conductionDelocalized electron

Lattice vibration(phonon)

Scattered electron

Low Mobility

bull holes μ ~10-4-10-8 Vs due to poor wave function overlap (large hopping distance)

bull electrons μ ~10-6-10-10Vs due to increased disorder and trapping at defect sites caused by impurities such as O2

rArr Build-up of space-charge density (bulk limited current)

전하전하 이동도이동도

36OLED 기초공정 이해와 실습

NoteMobility depends onElectric Field andTemperature

Mobilities of OrganicsMobilities of Organics

Alq3

37OLED 기초공정 이해와 실습

Ohmic conduction

OLEDOLED의의 전류전류

Current Dendity

current depends linearly on the bias voltageo nn qm VJd

=

2

3

0

1

2 1

(no traps)

(exponential trap distributions ( ) exp( )

one of electrodes(Ohmic contact) can supply more carriers per un

98

Current Density

SCLC condition

o

tt

r

m

m tN

VJd

T E N E kTV md T

ε ε μ

+

+ =

=

prop =

it time than can be transported through the dielectric (caused by low mobility)

Space charge limited (SCL) conduction

38OLED 기초공정 이해와 실습

2

2

3

Charge per unit area Q induced by a voltage V

Transit time across the semiconductor

9

Approximate SCLC densi

Child law (Mott- Gu

ty

Elec8

rney law)

o r

r

o rSCLC

r

VQ CVd

d dtE V

VQJt d

ε ε

μ μ

ε ε μ

= =

= =

asymp =

3 2

tric field distribution across the semiconductor

Majority space charges enhance the E field at the

3 3 ( ) at ( )2 2

enhance the injection of the cath

minority carrieode

rs (elect

V x VE x x d E dd d

= = =

rArr rons)

d

(+) (-)

x=0 x=d

Vd

15 Vd232

3)(d

xVxE =

++++

Virtual anode

-

Space Charge Limited CurrentSpace Charge Limited Current

39OLED 기초공정 이해와 실습

2

3

1

2 01

(no traps or discrete traps Mott-Gurney formula)

(exponential trap distributions ( ) exp( )

98

o rSCLC

mt

SCLC m t t

VJd

TVJ N E NmT

E kTd

ε ε μ

+

+

=

prop = =

ECB

EVB

Etrap

Discrete trapping center Exponential distributionof trapping centers

TrapTrap--Limited CurrentLimited Current

40OLED 기초공정 이해와 실습

Shen Burrows Bulovic McCarty Thompson Forrest Jpn J Appl Phys 35 L401 (1996)

ITOTPDAlq3MgAg

12

1

+

+

prop m

m

SCLC dVJ

TrapTrap--Limited CurrentLimited Current

41OLED 기초공정 이해와 실습

0

0

Activation energy at 0 Empirical parameter

Mobility at PF constant

PF

PF

E FT

T Tμβ

Δ =

=

PFPF

B eff

0

3

PFeff 0 0

( ) exp

exp( )

1 1 1with

E FFT μk T

F

qT T T

βμ

μ β

βπεε

⎛ ⎞Δ minus= minus⎜ ⎟⎜ ⎟

⎝ ⎠

equiv

= minus =

Poole Frenkel ModelPoole Frenkel Model

42OLED 기초공정 이해와 실습

1

22 2

0

0

(1)

(2)

EL F S e h

e ee he

T

h he hh

T

T rec rec e h

h eh e

h e

e hEL F S

h e

T rec

h e h e nh e EL F S EL

e h

n nJ n n nedJ n n ned

nJ

ne F

J J Je F

J Jn J J

ed n ed

η η γ

γτ

γτ

τ τ τ γ

μ

η η γμ μ

τ τ

η ηγ

minus

Φ =

minus minus =

minus minus =

lt =

=

Φ = prop

gt

= Φ = prop rArr Φ prop

EL Current RelationEL Current Relation

43OLED 기초공정 이해와 실습

Device Structure ITONPBAlq3Ca

22

21

ZZZ

fdVdQC

+minus

==πφieZiZZZ ||

))=+=

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

V0 independent of the NPB layer thickness

44OLED 기초공정 이해와 실습

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

Dashed line without interfacial charge

Wolfgang Brutting Stefan Berleb Anton G Muckl Organic Electronics 2 (2001)

Device Structure ITONPBAlq3Ca

45OLED 기초공정 이해와 실습

Langevin Recombination of carriers

bull Carriers are statistically independent therefore the e-h recombination is a random process and kinetically bimolecular

bull Total current attracted by a charge into the sphere of Coulombic capture radius rc

2

22

( ) ( )4

(4 ) 14 184

( ) (mean free path A)

n p c n pc

c cB

n p

qJ qp E qpr

qi r J Bqp r nmk T

qB a

μ μ μ μπε

ππε

μ μ λε

= + = +

= = cong asymp minus

there4 = + asympo

TkUd

BeP ~ minusProbability of dissociation

reUπε4

~2

e-

rc

Carrier RecombinationCarrier Recombination

P Langevin Ann Chem Phys 28 289 (1903)

46OLED 기초공정 이해와 실습

Electronic Processes in Organic Crystals and Polymers by MPope and C E Swenberg

ExcitonsExcitons

47OLED 기초공정 이해와 실습

C Adachi et al

Electrons and holesForm excitons

(bound e--h+ pairs)

Exciton Recombination ZoneExciton Recombination Zone

48OLED 기초공정 이해와 실습

MOLECULAR EXCITED STATESAFTER ELECTRICAL EXCITATION

Singletspin anti-symmetric

Tripletspin symmetric

25 75

MOLECULAR GROUND STATEspin anti-symmetric

Relaxation allowedfast efficientFluorescence

Relaxation disallowedslow inefficientPhosphorescence

|χ1χ2 gt = | gt

|χ1χ2 gt = | gt

|χ1χ2 gt

= | gt - | gt2

1

|χ1χ2 gt = | gt + | gt2

1ISC

Spin

OLEDOLED의의 형광형광인광인광

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 32: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

31OLED 기초공정 이해와 실습

Current - Voltage Characteristics

2

16 17 3

0

0

1

diffusion voltage ~ 13 V

acceptor concentration ~ 10 - 10 cm

(~ 50 - 150 nm

2( )

Width of space charge layer 2 ( )

D

D

A

r DA

r D A

V VCV

N

C A q N V V

w V V qN

ε ε

ε ε

prop minus

= minus

= minus V = 0 )

OLED OLED 전기적전기적 특성특성

( ) Schottky equation

exp 1

ideality factor 1 1 ideal Schottky diodes B ext BJ J eV nk T V V IR

n n

⎡ ⎤= minus = minus⎣ ⎦ge =

Capacitance - Voltage Dependence

32OLED 기초공정 이해와 실습

I - V Characteristics C - V Characteristics

ITOPPVMetal Polymeric Schottky Diode

OLED OLED 전기적전기적 특성특성

33OLED 기초공정 이해와 실습

Injection Dominated Mechanisms

bull Thermionic emission

bull Tunneling

Bulk Dominated Mechanisms

bull Ohmic Conduction

bull Space Charge Limited Current Conduction

bull Space Charge Limited Current Conduction with Traps

Magnitude of Injection Barrier

전하전하 주입주입

34OLED 기초공정 이해와 실습

Thermionic Emission

Fowler-Nordheim Tunneling

2

2 2

3

exp 1 wehere exp

4 120( )

Richardson constant

bns s

B B

n B

eeVJ J J A Tk T k T

em kA m m A cm Kh

φ

π

⎡ ⎤⎛ ⎞ ⎛ ⎞minus= minus =⎢ ⎥⎜ ⎟ ⎜ ⎟

⎝ ⎠ ⎝ ⎠⎣ ⎦

= =

At low field thermionic emission at high field tunneling dominate

전하전하 주입주입

EF

Evac

-eFz(triangular shape)φ

Z=0 Z

Charge accumulationhigher the energy state `

Electron emission (F-N Tunneling)

Electron emission (Thermionic Emission)

2

3212

~ exp

( ) where 8 (2 )3

bJ EE

qb mqh

π

⎛ ⎞minus⎜ ⎟⎝ ⎠

Φ=

35OLED 기초공정 이해와 실습

Applied voltage

Lattice vibration

Localizedelectron

Hopping conductionBand-like conductionDelocalized electron

Lattice vibration(phonon)

Scattered electron

Low Mobility

bull holes μ ~10-4-10-8 Vs due to poor wave function overlap (large hopping distance)

bull electrons μ ~10-6-10-10Vs due to increased disorder and trapping at defect sites caused by impurities such as O2

rArr Build-up of space-charge density (bulk limited current)

전하전하 이동도이동도

36OLED 기초공정 이해와 실습

NoteMobility depends onElectric Field andTemperature

Mobilities of OrganicsMobilities of Organics

Alq3

37OLED 기초공정 이해와 실습

Ohmic conduction

OLEDOLED의의 전류전류

Current Dendity

current depends linearly on the bias voltageo nn qm VJd

=

2

3

0

1

2 1

(no traps)

(exponential trap distributions ( ) exp( )

one of electrodes(Ohmic contact) can supply more carriers per un

98

Current Density

SCLC condition

o

tt

r

m

m tN

VJd

T E N E kTV md T

ε ε μ

+

+ =

=

prop =

it time than can be transported through the dielectric (caused by low mobility)

Space charge limited (SCL) conduction

38OLED 기초공정 이해와 실습

2

2

3

Charge per unit area Q induced by a voltage V

Transit time across the semiconductor

9

Approximate SCLC densi

Child law (Mott- Gu

ty

Elec8

rney law)

o r

r

o rSCLC

r

VQ CVd

d dtE V

VQJt d

ε ε

μ μ

ε ε μ

= =

= =

asymp =

3 2

tric field distribution across the semiconductor

Majority space charges enhance the E field at the

3 3 ( ) at ( )2 2

enhance the injection of the cath

minority carrieode

rs (elect

V x VE x x d E dd d

= = =

rArr rons)

d

(+) (-)

x=0 x=d

Vd

15 Vd232

3)(d

xVxE =

++++

Virtual anode

-

Space Charge Limited CurrentSpace Charge Limited Current

39OLED 기초공정 이해와 실습

2

3

1

2 01

(no traps or discrete traps Mott-Gurney formula)

(exponential trap distributions ( ) exp( )

98

o rSCLC

mt

SCLC m t t

VJd

TVJ N E NmT

E kTd

ε ε μ

+

+

=

prop = =

ECB

EVB

Etrap

Discrete trapping center Exponential distributionof trapping centers

TrapTrap--Limited CurrentLimited Current

40OLED 기초공정 이해와 실습

Shen Burrows Bulovic McCarty Thompson Forrest Jpn J Appl Phys 35 L401 (1996)

ITOTPDAlq3MgAg

12

1

+

+

prop m

m

SCLC dVJ

TrapTrap--Limited CurrentLimited Current

41OLED 기초공정 이해와 실습

0

0

Activation energy at 0 Empirical parameter

Mobility at PF constant

PF

PF

E FT

T Tμβ

Δ =

=

PFPF

B eff

0

3

PFeff 0 0

( ) exp

exp( )

1 1 1with

E FFT μk T

F

qT T T

βμ

μ β

βπεε

⎛ ⎞Δ minus= minus⎜ ⎟⎜ ⎟

⎝ ⎠

equiv

= minus =

Poole Frenkel ModelPoole Frenkel Model

42OLED 기초공정 이해와 실습

1

22 2

0

0

(1)

(2)

EL F S e h

e ee he

T

h he hh

T

T rec rec e h

h eh e

h e

e hEL F S

h e

T rec

h e h e nh e EL F S EL

e h

n nJ n n nedJ n n ned

nJ

ne F

J J Je F

J Jn J J

ed n ed

η η γ

γτ

γτ

τ τ τ γ

μ

η η γμ μ

τ τ

η ηγ

minus

Φ =

minus minus =

minus minus =

lt =

=

Φ = prop

gt

= Φ = prop rArr Φ prop

EL Current RelationEL Current Relation

43OLED 기초공정 이해와 실습

Device Structure ITONPBAlq3Ca

22

21

ZZZ

fdVdQC

+minus

==πφieZiZZZ ||

))=+=

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

V0 independent of the NPB layer thickness

44OLED 기초공정 이해와 실습

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

Dashed line without interfacial charge

Wolfgang Brutting Stefan Berleb Anton G Muckl Organic Electronics 2 (2001)

Device Structure ITONPBAlq3Ca

45OLED 기초공정 이해와 실습

Langevin Recombination of carriers

bull Carriers are statistically independent therefore the e-h recombination is a random process and kinetically bimolecular

bull Total current attracted by a charge into the sphere of Coulombic capture radius rc

2

22

( ) ( )4

(4 ) 14 184

( ) (mean free path A)

n p c n pc

c cB

n p

qJ qp E qpr

qi r J Bqp r nmk T

qB a

μ μ μ μπε

ππε

μ μ λε

= + = +

= = cong asymp minus

there4 = + asympo

TkUd

BeP ~ minusProbability of dissociation

reUπε4

~2

e-

rc

Carrier RecombinationCarrier Recombination

P Langevin Ann Chem Phys 28 289 (1903)

46OLED 기초공정 이해와 실습

Electronic Processes in Organic Crystals and Polymers by MPope and C E Swenberg

ExcitonsExcitons

47OLED 기초공정 이해와 실습

C Adachi et al

Electrons and holesForm excitons

(bound e--h+ pairs)

Exciton Recombination ZoneExciton Recombination Zone

48OLED 기초공정 이해와 실습

MOLECULAR EXCITED STATESAFTER ELECTRICAL EXCITATION

Singletspin anti-symmetric

Tripletspin symmetric

25 75

MOLECULAR GROUND STATEspin anti-symmetric

Relaxation allowedfast efficientFluorescence

Relaxation disallowedslow inefficientPhosphorescence

|χ1χ2 gt = | gt

|χ1χ2 gt = | gt

|χ1χ2 gt

= | gt - | gt2

1

|χ1χ2 gt = | gt + | gt2

1ISC

Spin

OLEDOLED의의 형광형광인광인광

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 33: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

32OLED 기초공정 이해와 실습

I - V Characteristics C - V Characteristics

ITOPPVMetal Polymeric Schottky Diode

OLED OLED 전기적전기적 특성특성

33OLED 기초공정 이해와 실습

Injection Dominated Mechanisms

bull Thermionic emission

bull Tunneling

Bulk Dominated Mechanisms

bull Ohmic Conduction

bull Space Charge Limited Current Conduction

bull Space Charge Limited Current Conduction with Traps

Magnitude of Injection Barrier

전하전하 주입주입

34OLED 기초공정 이해와 실습

Thermionic Emission

Fowler-Nordheim Tunneling

2

2 2

3

exp 1 wehere exp

4 120( )

Richardson constant

bns s

B B

n B

eeVJ J J A Tk T k T

em kA m m A cm Kh

φ

π

⎡ ⎤⎛ ⎞ ⎛ ⎞minus= minus =⎢ ⎥⎜ ⎟ ⎜ ⎟

⎝ ⎠ ⎝ ⎠⎣ ⎦

= =

At low field thermionic emission at high field tunneling dominate

전하전하 주입주입

EF

Evac

-eFz(triangular shape)φ

Z=0 Z

Charge accumulationhigher the energy state `

Electron emission (F-N Tunneling)

Electron emission (Thermionic Emission)

2

3212

~ exp

( ) where 8 (2 )3

bJ EE

qb mqh

π

⎛ ⎞minus⎜ ⎟⎝ ⎠

Φ=

35OLED 기초공정 이해와 실습

Applied voltage

Lattice vibration

Localizedelectron

Hopping conductionBand-like conductionDelocalized electron

Lattice vibration(phonon)

Scattered electron

Low Mobility

bull holes μ ~10-4-10-8 Vs due to poor wave function overlap (large hopping distance)

bull electrons μ ~10-6-10-10Vs due to increased disorder and trapping at defect sites caused by impurities such as O2

rArr Build-up of space-charge density (bulk limited current)

전하전하 이동도이동도

36OLED 기초공정 이해와 실습

NoteMobility depends onElectric Field andTemperature

Mobilities of OrganicsMobilities of Organics

Alq3

37OLED 기초공정 이해와 실습

Ohmic conduction

OLEDOLED의의 전류전류

Current Dendity

current depends linearly on the bias voltageo nn qm VJd

=

2

3

0

1

2 1

(no traps)

(exponential trap distributions ( ) exp( )

one of electrodes(Ohmic contact) can supply more carriers per un

98

Current Density

SCLC condition

o

tt

r

m

m tN

VJd

T E N E kTV md T

ε ε μ

+

+ =

=

prop =

it time than can be transported through the dielectric (caused by low mobility)

Space charge limited (SCL) conduction

38OLED 기초공정 이해와 실습

2

2

3

Charge per unit area Q induced by a voltage V

Transit time across the semiconductor

9

Approximate SCLC densi

Child law (Mott- Gu

ty

Elec8

rney law)

o r

r

o rSCLC

r

VQ CVd

d dtE V

VQJt d

ε ε

μ μ

ε ε μ

= =

= =

asymp =

3 2

tric field distribution across the semiconductor

Majority space charges enhance the E field at the

3 3 ( ) at ( )2 2

enhance the injection of the cath

minority carrieode

rs (elect

V x VE x x d E dd d

= = =

rArr rons)

d

(+) (-)

x=0 x=d

Vd

15 Vd232

3)(d

xVxE =

++++

Virtual anode

-

Space Charge Limited CurrentSpace Charge Limited Current

39OLED 기초공정 이해와 실습

2

3

1

2 01

(no traps or discrete traps Mott-Gurney formula)

(exponential trap distributions ( ) exp( )

98

o rSCLC

mt

SCLC m t t

VJd

TVJ N E NmT

E kTd

ε ε μ

+

+

=

prop = =

ECB

EVB

Etrap

Discrete trapping center Exponential distributionof trapping centers

TrapTrap--Limited CurrentLimited Current

40OLED 기초공정 이해와 실습

Shen Burrows Bulovic McCarty Thompson Forrest Jpn J Appl Phys 35 L401 (1996)

ITOTPDAlq3MgAg

12

1

+

+

prop m

m

SCLC dVJ

TrapTrap--Limited CurrentLimited Current

41OLED 기초공정 이해와 실습

0

0

Activation energy at 0 Empirical parameter

Mobility at PF constant

PF

PF

E FT

T Tμβ

Δ =

=

PFPF

B eff

0

3

PFeff 0 0

( ) exp

exp( )

1 1 1with

E FFT μk T

F

qT T T

βμ

μ β

βπεε

⎛ ⎞Δ minus= minus⎜ ⎟⎜ ⎟

⎝ ⎠

equiv

= minus =

Poole Frenkel ModelPoole Frenkel Model

42OLED 기초공정 이해와 실습

1

22 2

0

0

(1)

(2)

EL F S e h

e ee he

T

h he hh

T

T rec rec e h

h eh e

h e

e hEL F S

h e

T rec

h e h e nh e EL F S EL

e h

n nJ n n nedJ n n ned

nJ

ne F

J J Je F

J Jn J J

ed n ed

η η γ

γτ

γτ

τ τ τ γ

μ

η η γμ μ

τ τ

η ηγ

minus

Φ =

minus minus =

minus minus =

lt =

=

Φ = prop

gt

= Φ = prop rArr Φ prop

EL Current RelationEL Current Relation

43OLED 기초공정 이해와 실습

Device Structure ITONPBAlq3Ca

22

21

ZZZ

fdVdQC

+minus

==πφieZiZZZ ||

))=+=

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

V0 independent of the NPB layer thickness

44OLED 기초공정 이해와 실습

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

Dashed line without interfacial charge

Wolfgang Brutting Stefan Berleb Anton G Muckl Organic Electronics 2 (2001)

Device Structure ITONPBAlq3Ca

45OLED 기초공정 이해와 실습

Langevin Recombination of carriers

bull Carriers are statistically independent therefore the e-h recombination is a random process and kinetically bimolecular

bull Total current attracted by a charge into the sphere of Coulombic capture radius rc

2

22

( ) ( )4

(4 ) 14 184

( ) (mean free path A)

n p c n pc

c cB

n p

qJ qp E qpr

qi r J Bqp r nmk T

qB a

μ μ μ μπε

ππε

μ μ λε

= + = +

= = cong asymp minus

there4 = + asympo

TkUd

BeP ~ minusProbability of dissociation

reUπε4

~2

e-

rc

Carrier RecombinationCarrier Recombination

P Langevin Ann Chem Phys 28 289 (1903)

46OLED 기초공정 이해와 실습

Electronic Processes in Organic Crystals and Polymers by MPope and C E Swenberg

ExcitonsExcitons

47OLED 기초공정 이해와 실습

C Adachi et al

Electrons and holesForm excitons

(bound e--h+ pairs)

Exciton Recombination ZoneExciton Recombination Zone

48OLED 기초공정 이해와 실습

MOLECULAR EXCITED STATESAFTER ELECTRICAL EXCITATION

Singletspin anti-symmetric

Tripletspin symmetric

25 75

MOLECULAR GROUND STATEspin anti-symmetric

Relaxation allowedfast efficientFluorescence

Relaxation disallowedslow inefficientPhosphorescence

|χ1χ2 gt = | gt

|χ1χ2 gt = | gt

|χ1χ2 gt

= | gt - | gt2

1

|χ1χ2 gt = | gt + | gt2

1ISC

Spin

OLEDOLED의의 형광형광인광인광

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 34: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

33OLED 기초공정 이해와 실습

Injection Dominated Mechanisms

bull Thermionic emission

bull Tunneling

Bulk Dominated Mechanisms

bull Ohmic Conduction

bull Space Charge Limited Current Conduction

bull Space Charge Limited Current Conduction with Traps

Magnitude of Injection Barrier

전하전하 주입주입

34OLED 기초공정 이해와 실습

Thermionic Emission

Fowler-Nordheim Tunneling

2

2 2

3

exp 1 wehere exp

4 120( )

Richardson constant

bns s

B B

n B

eeVJ J J A Tk T k T

em kA m m A cm Kh

φ

π

⎡ ⎤⎛ ⎞ ⎛ ⎞minus= minus =⎢ ⎥⎜ ⎟ ⎜ ⎟

⎝ ⎠ ⎝ ⎠⎣ ⎦

= =

At low field thermionic emission at high field tunneling dominate

전하전하 주입주입

EF

Evac

-eFz(triangular shape)φ

Z=0 Z

Charge accumulationhigher the energy state `

Electron emission (F-N Tunneling)

Electron emission (Thermionic Emission)

2

3212

~ exp

( ) where 8 (2 )3

bJ EE

qb mqh

π

⎛ ⎞minus⎜ ⎟⎝ ⎠

Φ=

35OLED 기초공정 이해와 실습

Applied voltage

Lattice vibration

Localizedelectron

Hopping conductionBand-like conductionDelocalized electron

Lattice vibration(phonon)

Scattered electron

Low Mobility

bull holes μ ~10-4-10-8 Vs due to poor wave function overlap (large hopping distance)

bull electrons μ ~10-6-10-10Vs due to increased disorder and trapping at defect sites caused by impurities such as O2

rArr Build-up of space-charge density (bulk limited current)

전하전하 이동도이동도

36OLED 기초공정 이해와 실습

NoteMobility depends onElectric Field andTemperature

Mobilities of OrganicsMobilities of Organics

Alq3

37OLED 기초공정 이해와 실습

Ohmic conduction

OLEDOLED의의 전류전류

Current Dendity

current depends linearly on the bias voltageo nn qm VJd

=

2

3

0

1

2 1

(no traps)

(exponential trap distributions ( ) exp( )

one of electrodes(Ohmic contact) can supply more carriers per un

98

Current Density

SCLC condition

o

tt

r

m

m tN

VJd

T E N E kTV md T

ε ε μ

+

+ =

=

prop =

it time than can be transported through the dielectric (caused by low mobility)

Space charge limited (SCL) conduction

38OLED 기초공정 이해와 실습

2

2

3

Charge per unit area Q induced by a voltage V

Transit time across the semiconductor

9

Approximate SCLC densi

Child law (Mott- Gu

ty

Elec8

rney law)

o r

r

o rSCLC

r

VQ CVd

d dtE V

VQJt d

ε ε

μ μ

ε ε μ

= =

= =

asymp =

3 2

tric field distribution across the semiconductor

Majority space charges enhance the E field at the

3 3 ( ) at ( )2 2

enhance the injection of the cath

minority carrieode

rs (elect

V x VE x x d E dd d

= = =

rArr rons)

d

(+) (-)

x=0 x=d

Vd

15 Vd232

3)(d

xVxE =

++++

Virtual anode

-

Space Charge Limited CurrentSpace Charge Limited Current

39OLED 기초공정 이해와 실습

2

3

1

2 01

(no traps or discrete traps Mott-Gurney formula)

(exponential trap distributions ( ) exp( )

98

o rSCLC

mt

SCLC m t t

VJd

TVJ N E NmT

E kTd

ε ε μ

+

+

=

prop = =

ECB

EVB

Etrap

Discrete trapping center Exponential distributionof trapping centers

TrapTrap--Limited CurrentLimited Current

40OLED 기초공정 이해와 실습

Shen Burrows Bulovic McCarty Thompson Forrest Jpn J Appl Phys 35 L401 (1996)

ITOTPDAlq3MgAg

12

1

+

+

prop m

m

SCLC dVJ

TrapTrap--Limited CurrentLimited Current

41OLED 기초공정 이해와 실습

0

0

Activation energy at 0 Empirical parameter

Mobility at PF constant

PF

PF

E FT

T Tμβ

Δ =

=

PFPF

B eff

0

3

PFeff 0 0

( ) exp

exp( )

1 1 1with

E FFT μk T

F

qT T T

βμ

μ β

βπεε

⎛ ⎞Δ minus= minus⎜ ⎟⎜ ⎟

⎝ ⎠

equiv

= minus =

Poole Frenkel ModelPoole Frenkel Model

42OLED 기초공정 이해와 실습

1

22 2

0

0

(1)

(2)

EL F S e h

e ee he

T

h he hh

T

T rec rec e h

h eh e

h e

e hEL F S

h e

T rec

h e h e nh e EL F S EL

e h

n nJ n n nedJ n n ned

nJ

ne F

J J Je F

J Jn J J

ed n ed

η η γ

γτ

γτ

τ τ τ γ

μ

η η γμ μ

τ τ

η ηγ

minus

Φ =

minus minus =

minus minus =

lt =

=

Φ = prop

gt

= Φ = prop rArr Φ prop

EL Current RelationEL Current Relation

43OLED 기초공정 이해와 실습

Device Structure ITONPBAlq3Ca

22

21

ZZZ

fdVdQC

+minus

==πφieZiZZZ ||

))=+=

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

V0 independent of the NPB layer thickness

44OLED 기초공정 이해와 실습

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

Dashed line without interfacial charge

Wolfgang Brutting Stefan Berleb Anton G Muckl Organic Electronics 2 (2001)

Device Structure ITONPBAlq3Ca

45OLED 기초공정 이해와 실습

Langevin Recombination of carriers

bull Carriers are statistically independent therefore the e-h recombination is a random process and kinetically bimolecular

bull Total current attracted by a charge into the sphere of Coulombic capture radius rc

2

22

( ) ( )4

(4 ) 14 184

( ) (mean free path A)

n p c n pc

c cB

n p

qJ qp E qpr

qi r J Bqp r nmk T

qB a

μ μ μ μπε

ππε

μ μ λε

= + = +

= = cong asymp minus

there4 = + asympo

TkUd

BeP ~ minusProbability of dissociation

reUπε4

~2

e-

rc

Carrier RecombinationCarrier Recombination

P Langevin Ann Chem Phys 28 289 (1903)

46OLED 기초공정 이해와 실습

Electronic Processes in Organic Crystals and Polymers by MPope and C E Swenberg

ExcitonsExcitons

47OLED 기초공정 이해와 실습

C Adachi et al

Electrons and holesForm excitons

(bound e--h+ pairs)

Exciton Recombination ZoneExciton Recombination Zone

48OLED 기초공정 이해와 실습

MOLECULAR EXCITED STATESAFTER ELECTRICAL EXCITATION

Singletspin anti-symmetric

Tripletspin symmetric

25 75

MOLECULAR GROUND STATEspin anti-symmetric

Relaxation allowedfast efficientFluorescence

Relaxation disallowedslow inefficientPhosphorescence

|χ1χ2 gt = | gt

|χ1χ2 gt = | gt

|χ1χ2 gt

= | gt - | gt2

1

|χ1χ2 gt = | gt + | gt2

1ISC

Spin

OLEDOLED의의 형광형광인광인광

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 35: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

34OLED 기초공정 이해와 실습

Thermionic Emission

Fowler-Nordheim Tunneling

2

2 2

3

exp 1 wehere exp

4 120( )

Richardson constant

bns s

B B

n B

eeVJ J J A Tk T k T

em kA m m A cm Kh

φ

π

⎡ ⎤⎛ ⎞ ⎛ ⎞minus= minus =⎢ ⎥⎜ ⎟ ⎜ ⎟

⎝ ⎠ ⎝ ⎠⎣ ⎦

= =

At low field thermionic emission at high field tunneling dominate

전하전하 주입주입

EF

Evac

-eFz(triangular shape)φ

Z=0 Z

Charge accumulationhigher the energy state `

Electron emission (F-N Tunneling)

Electron emission (Thermionic Emission)

2

3212

~ exp

( ) where 8 (2 )3

bJ EE

qb mqh

π

⎛ ⎞minus⎜ ⎟⎝ ⎠

Φ=

35OLED 기초공정 이해와 실습

Applied voltage

Lattice vibration

Localizedelectron

Hopping conductionBand-like conductionDelocalized electron

Lattice vibration(phonon)

Scattered electron

Low Mobility

bull holes μ ~10-4-10-8 Vs due to poor wave function overlap (large hopping distance)

bull electrons μ ~10-6-10-10Vs due to increased disorder and trapping at defect sites caused by impurities such as O2

rArr Build-up of space-charge density (bulk limited current)

전하전하 이동도이동도

36OLED 기초공정 이해와 실습

NoteMobility depends onElectric Field andTemperature

Mobilities of OrganicsMobilities of Organics

Alq3

37OLED 기초공정 이해와 실습

Ohmic conduction

OLEDOLED의의 전류전류

Current Dendity

current depends linearly on the bias voltageo nn qm VJd

=

2

3

0

1

2 1

(no traps)

(exponential trap distributions ( ) exp( )

one of electrodes(Ohmic contact) can supply more carriers per un

98

Current Density

SCLC condition

o

tt

r

m

m tN

VJd

T E N E kTV md T

ε ε μ

+

+ =

=

prop =

it time than can be transported through the dielectric (caused by low mobility)

Space charge limited (SCL) conduction

38OLED 기초공정 이해와 실습

2

2

3

Charge per unit area Q induced by a voltage V

Transit time across the semiconductor

9

Approximate SCLC densi

Child law (Mott- Gu

ty

Elec8

rney law)

o r

r

o rSCLC

r

VQ CVd

d dtE V

VQJt d

ε ε

μ μ

ε ε μ

= =

= =

asymp =

3 2

tric field distribution across the semiconductor

Majority space charges enhance the E field at the

3 3 ( ) at ( )2 2

enhance the injection of the cath

minority carrieode

rs (elect

V x VE x x d E dd d

= = =

rArr rons)

d

(+) (-)

x=0 x=d

Vd

15 Vd232

3)(d

xVxE =

++++

Virtual anode

-

Space Charge Limited CurrentSpace Charge Limited Current

39OLED 기초공정 이해와 실습

2

3

1

2 01

(no traps or discrete traps Mott-Gurney formula)

(exponential trap distributions ( ) exp( )

98

o rSCLC

mt

SCLC m t t

VJd

TVJ N E NmT

E kTd

ε ε μ

+

+

=

prop = =

ECB

EVB

Etrap

Discrete trapping center Exponential distributionof trapping centers

TrapTrap--Limited CurrentLimited Current

40OLED 기초공정 이해와 실습

Shen Burrows Bulovic McCarty Thompson Forrest Jpn J Appl Phys 35 L401 (1996)

ITOTPDAlq3MgAg

12

1

+

+

prop m

m

SCLC dVJ

TrapTrap--Limited CurrentLimited Current

41OLED 기초공정 이해와 실습

0

0

Activation energy at 0 Empirical parameter

Mobility at PF constant

PF

PF

E FT

T Tμβ

Δ =

=

PFPF

B eff

0

3

PFeff 0 0

( ) exp

exp( )

1 1 1with

E FFT μk T

F

qT T T

βμ

μ β

βπεε

⎛ ⎞Δ minus= minus⎜ ⎟⎜ ⎟

⎝ ⎠

equiv

= minus =

Poole Frenkel ModelPoole Frenkel Model

42OLED 기초공정 이해와 실습

1

22 2

0

0

(1)

(2)

EL F S e h

e ee he

T

h he hh

T

T rec rec e h

h eh e

h e

e hEL F S

h e

T rec

h e h e nh e EL F S EL

e h

n nJ n n nedJ n n ned

nJ

ne F

J J Je F

J Jn J J

ed n ed

η η γ

γτ

γτ

τ τ τ γ

μ

η η γμ μ

τ τ

η ηγ

minus

Φ =

minus minus =

minus minus =

lt =

=

Φ = prop

gt

= Φ = prop rArr Φ prop

EL Current RelationEL Current Relation

43OLED 기초공정 이해와 실습

Device Structure ITONPBAlq3Ca

22

21

ZZZ

fdVdQC

+minus

==πφieZiZZZ ||

))=+=

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

V0 independent of the NPB layer thickness

44OLED 기초공정 이해와 실습

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

Dashed line without interfacial charge

Wolfgang Brutting Stefan Berleb Anton G Muckl Organic Electronics 2 (2001)

Device Structure ITONPBAlq3Ca

45OLED 기초공정 이해와 실습

Langevin Recombination of carriers

bull Carriers are statistically independent therefore the e-h recombination is a random process and kinetically bimolecular

bull Total current attracted by a charge into the sphere of Coulombic capture radius rc

2

22

( ) ( )4

(4 ) 14 184

( ) (mean free path A)

n p c n pc

c cB

n p

qJ qp E qpr

qi r J Bqp r nmk T

qB a

μ μ μ μπε

ππε

μ μ λε

= + = +

= = cong asymp minus

there4 = + asympo

TkUd

BeP ~ minusProbability of dissociation

reUπε4

~2

e-

rc

Carrier RecombinationCarrier Recombination

P Langevin Ann Chem Phys 28 289 (1903)

46OLED 기초공정 이해와 실습

Electronic Processes in Organic Crystals and Polymers by MPope and C E Swenberg

ExcitonsExcitons

47OLED 기초공정 이해와 실습

C Adachi et al

Electrons and holesForm excitons

(bound e--h+ pairs)

Exciton Recombination ZoneExciton Recombination Zone

48OLED 기초공정 이해와 실습

MOLECULAR EXCITED STATESAFTER ELECTRICAL EXCITATION

Singletspin anti-symmetric

Tripletspin symmetric

25 75

MOLECULAR GROUND STATEspin anti-symmetric

Relaxation allowedfast efficientFluorescence

Relaxation disallowedslow inefficientPhosphorescence

|χ1χ2 gt = | gt

|χ1χ2 gt = | gt

|χ1χ2 gt

= | gt - | gt2

1

|χ1χ2 gt = | gt + | gt2

1ISC

Spin

OLEDOLED의의 형광형광인광인광

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 36: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

35OLED 기초공정 이해와 실습

Applied voltage

Lattice vibration

Localizedelectron

Hopping conductionBand-like conductionDelocalized electron

Lattice vibration(phonon)

Scattered electron

Low Mobility

bull holes μ ~10-4-10-8 Vs due to poor wave function overlap (large hopping distance)

bull electrons μ ~10-6-10-10Vs due to increased disorder and trapping at defect sites caused by impurities such as O2

rArr Build-up of space-charge density (bulk limited current)

전하전하 이동도이동도

36OLED 기초공정 이해와 실습

NoteMobility depends onElectric Field andTemperature

Mobilities of OrganicsMobilities of Organics

Alq3

37OLED 기초공정 이해와 실습

Ohmic conduction

OLEDOLED의의 전류전류

Current Dendity

current depends linearly on the bias voltageo nn qm VJd

=

2

3

0

1

2 1

(no traps)

(exponential trap distributions ( ) exp( )

one of electrodes(Ohmic contact) can supply more carriers per un

98

Current Density

SCLC condition

o

tt

r

m

m tN

VJd

T E N E kTV md T

ε ε μ

+

+ =

=

prop =

it time than can be transported through the dielectric (caused by low mobility)

Space charge limited (SCL) conduction

38OLED 기초공정 이해와 실습

2

2

3

Charge per unit area Q induced by a voltage V

Transit time across the semiconductor

9

Approximate SCLC densi

Child law (Mott- Gu

ty

Elec8

rney law)

o r

r

o rSCLC

r

VQ CVd

d dtE V

VQJt d

ε ε

μ μ

ε ε μ

= =

= =

asymp =

3 2

tric field distribution across the semiconductor

Majority space charges enhance the E field at the

3 3 ( ) at ( )2 2

enhance the injection of the cath

minority carrieode

rs (elect

V x VE x x d E dd d

= = =

rArr rons)

d

(+) (-)

x=0 x=d

Vd

15 Vd232

3)(d

xVxE =

++++

Virtual anode

-

Space Charge Limited CurrentSpace Charge Limited Current

39OLED 기초공정 이해와 실습

2

3

1

2 01

(no traps or discrete traps Mott-Gurney formula)

(exponential trap distributions ( ) exp( )

98

o rSCLC

mt

SCLC m t t

VJd

TVJ N E NmT

E kTd

ε ε μ

+

+

=

prop = =

ECB

EVB

Etrap

Discrete trapping center Exponential distributionof trapping centers

TrapTrap--Limited CurrentLimited Current

40OLED 기초공정 이해와 실습

Shen Burrows Bulovic McCarty Thompson Forrest Jpn J Appl Phys 35 L401 (1996)

ITOTPDAlq3MgAg

12

1

+

+

prop m

m

SCLC dVJ

TrapTrap--Limited CurrentLimited Current

41OLED 기초공정 이해와 실습

0

0

Activation energy at 0 Empirical parameter

Mobility at PF constant

PF

PF

E FT

T Tμβ

Δ =

=

PFPF

B eff

0

3

PFeff 0 0

( ) exp

exp( )

1 1 1with

E FFT μk T

F

qT T T

βμ

μ β

βπεε

⎛ ⎞Δ minus= minus⎜ ⎟⎜ ⎟

⎝ ⎠

equiv

= minus =

Poole Frenkel ModelPoole Frenkel Model

42OLED 기초공정 이해와 실습

1

22 2

0

0

(1)

(2)

EL F S e h

e ee he

T

h he hh

T

T rec rec e h

h eh e

h e

e hEL F S

h e

T rec

h e h e nh e EL F S EL

e h

n nJ n n nedJ n n ned

nJ

ne F

J J Je F

J Jn J J

ed n ed

η η γ

γτ

γτ

τ τ τ γ

μ

η η γμ μ

τ τ

η ηγ

minus

Φ =

minus minus =

minus minus =

lt =

=

Φ = prop

gt

= Φ = prop rArr Φ prop

EL Current RelationEL Current Relation

43OLED 기초공정 이해와 실습

Device Structure ITONPBAlq3Ca

22

21

ZZZ

fdVdQC

+minus

==πφieZiZZZ ||

))=+=

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

V0 independent of the NPB layer thickness

44OLED 기초공정 이해와 실습

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

Dashed line without interfacial charge

Wolfgang Brutting Stefan Berleb Anton G Muckl Organic Electronics 2 (2001)

Device Structure ITONPBAlq3Ca

45OLED 기초공정 이해와 실습

Langevin Recombination of carriers

bull Carriers are statistically independent therefore the e-h recombination is a random process and kinetically bimolecular

bull Total current attracted by a charge into the sphere of Coulombic capture radius rc

2

22

( ) ( )4

(4 ) 14 184

( ) (mean free path A)

n p c n pc

c cB

n p

qJ qp E qpr

qi r J Bqp r nmk T

qB a

μ μ μ μπε

ππε

μ μ λε

= + = +

= = cong asymp minus

there4 = + asympo

TkUd

BeP ~ minusProbability of dissociation

reUπε4

~2

e-

rc

Carrier RecombinationCarrier Recombination

P Langevin Ann Chem Phys 28 289 (1903)

46OLED 기초공정 이해와 실습

Electronic Processes in Organic Crystals and Polymers by MPope and C E Swenberg

ExcitonsExcitons

47OLED 기초공정 이해와 실습

C Adachi et al

Electrons and holesForm excitons

(bound e--h+ pairs)

Exciton Recombination ZoneExciton Recombination Zone

48OLED 기초공정 이해와 실습

MOLECULAR EXCITED STATESAFTER ELECTRICAL EXCITATION

Singletspin anti-symmetric

Tripletspin symmetric

25 75

MOLECULAR GROUND STATEspin anti-symmetric

Relaxation allowedfast efficientFluorescence

Relaxation disallowedslow inefficientPhosphorescence

|χ1χ2 gt = | gt

|χ1χ2 gt = | gt

|χ1χ2 gt

= | gt - | gt2

1

|χ1χ2 gt = | gt + | gt2

1ISC

Spin

OLEDOLED의의 형광형광인광인광

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 37: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

36OLED 기초공정 이해와 실습

NoteMobility depends onElectric Field andTemperature

Mobilities of OrganicsMobilities of Organics

Alq3

37OLED 기초공정 이해와 실습

Ohmic conduction

OLEDOLED의의 전류전류

Current Dendity

current depends linearly on the bias voltageo nn qm VJd

=

2

3

0

1

2 1

(no traps)

(exponential trap distributions ( ) exp( )

one of electrodes(Ohmic contact) can supply more carriers per un

98

Current Density

SCLC condition

o

tt

r

m

m tN

VJd

T E N E kTV md T

ε ε μ

+

+ =

=

prop =

it time than can be transported through the dielectric (caused by low mobility)

Space charge limited (SCL) conduction

38OLED 기초공정 이해와 실습

2

2

3

Charge per unit area Q induced by a voltage V

Transit time across the semiconductor

9

Approximate SCLC densi

Child law (Mott- Gu

ty

Elec8

rney law)

o r

r

o rSCLC

r

VQ CVd

d dtE V

VQJt d

ε ε

μ μ

ε ε μ

= =

= =

asymp =

3 2

tric field distribution across the semiconductor

Majority space charges enhance the E field at the

3 3 ( ) at ( )2 2

enhance the injection of the cath

minority carrieode

rs (elect

V x VE x x d E dd d

= = =

rArr rons)

d

(+) (-)

x=0 x=d

Vd

15 Vd232

3)(d

xVxE =

++++

Virtual anode

-

Space Charge Limited CurrentSpace Charge Limited Current

39OLED 기초공정 이해와 실습

2

3

1

2 01

(no traps or discrete traps Mott-Gurney formula)

(exponential trap distributions ( ) exp( )

98

o rSCLC

mt

SCLC m t t

VJd

TVJ N E NmT

E kTd

ε ε μ

+

+

=

prop = =

ECB

EVB

Etrap

Discrete trapping center Exponential distributionof trapping centers

TrapTrap--Limited CurrentLimited Current

40OLED 기초공정 이해와 실습

Shen Burrows Bulovic McCarty Thompson Forrest Jpn J Appl Phys 35 L401 (1996)

ITOTPDAlq3MgAg

12

1

+

+

prop m

m

SCLC dVJ

TrapTrap--Limited CurrentLimited Current

41OLED 기초공정 이해와 실습

0

0

Activation energy at 0 Empirical parameter

Mobility at PF constant

PF

PF

E FT

T Tμβ

Δ =

=

PFPF

B eff

0

3

PFeff 0 0

( ) exp

exp( )

1 1 1with

E FFT μk T

F

qT T T

βμ

μ β

βπεε

⎛ ⎞Δ minus= minus⎜ ⎟⎜ ⎟

⎝ ⎠

equiv

= minus =

Poole Frenkel ModelPoole Frenkel Model

42OLED 기초공정 이해와 실습

1

22 2

0

0

(1)

(2)

EL F S e h

e ee he

T

h he hh

T

T rec rec e h

h eh e

h e

e hEL F S

h e

T rec

h e h e nh e EL F S EL

e h

n nJ n n nedJ n n ned

nJ

ne F

J J Je F

J Jn J J

ed n ed

η η γ

γτ

γτ

τ τ τ γ

μ

η η γμ μ

τ τ

η ηγ

minus

Φ =

minus minus =

minus minus =

lt =

=

Φ = prop

gt

= Φ = prop rArr Φ prop

EL Current RelationEL Current Relation

43OLED 기초공정 이해와 실습

Device Structure ITONPBAlq3Ca

22

21

ZZZ

fdVdQC

+minus

==πφieZiZZZ ||

))=+=

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

V0 independent of the NPB layer thickness

44OLED 기초공정 이해와 실습

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

Dashed line without interfacial charge

Wolfgang Brutting Stefan Berleb Anton G Muckl Organic Electronics 2 (2001)

Device Structure ITONPBAlq3Ca

45OLED 기초공정 이해와 실습

Langevin Recombination of carriers

bull Carriers are statistically independent therefore the e-h recombination is a random process and kinetically bimolecular

bull Total current attracted by a charge into the sphere of Coulombic capture radius rc

2

22

( ) ( )4

(4 ) 14 184

( ) (mean free path A)

n p c n pc

c cB

n p

qJ qp E qpr

qi r J Bqp r nmk T

qB a

μ μ μ μπε

ππε

μ μ λε

= + = +

= = cong asymp minus

there4 = + asympo

TkUd

BeP ~ minusProbability of dissociation

reUπε4

~2

e-

rc

Carrier RecombinationCarrier Recombination

P Langevin Ann Chem Phys 28 289 (1903)

46OLED 기초공정 이해와 실습

Electronic Processes in Organic Crystals and Polymers by MPope and C E Swenberg

ExcitonsExcitons

47OLED 기초공정 이해와 실습

C Adachi et al

Electrons and holesForm excitons

(bound e--h+ pairs)

Exciton Recombination ZoneExciton Recombination Zone

48OLED 기초공정 이해와 실습

MOLECULAR EXCITED STATESAFTER ELECTRICAL EXCITATION

Singletspin anti-symmetric

Tripletspin symmetric

25 75

MOLECULAR GROUND STATEspin anti-symmetric

Relaxation allowedfast efficientFluorescence

Relaxation disallowedslow inefficientPhosphorescence

|χ1χ2 gt = | gt

|χ1χ2 gt = | gt

|χ1χ2 gt

= | gt - | gt2

1

|χ1χ2 gt = | gt + | gt2

1ISC

Spin

OLEDOLED의의 형광형광인광인광

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 38: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

37OLED 기초공정 이해와 실습

Ohmic conduction

OLEDOLED의의 전류전류

Current Dendity

current depends linearly on the bias voltageo nn qm VJd

=

2

3

0

1

2 1

(no traps)

(exponential trap distributions ( ) exp( )

one of electrodes(Ohmic contact) can supply more carriers per un

98

Current Density

SCLC condition

o

tt

r

m

m tN

VJd

T E N E kTV md T

ε ε μ

+

+ =

=

prop =

it time than can be transported through the dielectric (caused by low mobility)

Space charge limited (SCL) conduction

38OLED 기초공정 이해와 실습

2

2

3

Charge per unit area Q induced by a voltage V

Transit time across the semiconductor

9

Approximate SCLC densi

Child law (Mott- Gu

ty

Elec8

rney law)

o r

r

o rSCLC

r

VQ CVd

d dtE V

VQJt d

ε ε

μ μ

ε ε μ

= =

= =

asymp =

3 2

tric field distribution across the semiconductor

Majority space charges enhance the E field at the

3 3 ( ) at ( )2 2

enhance the injection of the cath

minority carrieode

rs (elect

V x VE x x d E dd d

= = =

rArr rons)

d

(+) (-)

x=0 x=d

Vd

15 Vd232

3)(d

xVxE =

++++

Virtual anode

-

Space Charge Limited CurrentSpace Charge Limited Current

39OLED 기초공정 이해와 실습

2

3

1

2 01

(no traps or discrete traps Mott-Gurney formula)

(exponential trap distributions ( ) exp( )

98

o rSCLC

mt

SCLC m t t

VJd

TVJ N E NmT

E kTd

ε ε μ

+

+

=

prop = =

ECB

EVB

Etrap

Discrete trapping center Exponential distributionof trapping centers

TrapTrap--Limited CurrentLimited Current

40OLED 기초공정 이해와 실습

Shen Burrows Bulovic McCarty Thompson Forrest Jpn J Appl Phys 35 L401 (1996)

ITOTPDAlq3MgAg

12

1

+

+

prop m

m

SCLC dVJ

TrapTrap--Limited CurrentLimited Current

41OLED 기초공정 이해와 실습

0

0

Activation energy at 0 Empirical parameter

Mobility at PF constant

PF

PF

E FT

T Tμβ

Δ =

=

PFPF

B eff

0

3

PFeff 0 0

( ) exp

exp( )

1 1 1with

E FFT μk T

F

qT T T

βμ

μ β

βπεε

⎛ ⎞Δ minus= minus⎜ ⎟⎜ ⎟

⎝ ⎠

equiv

= minus =

Poole Frenkel ModelPoole Frenkel Model

42OLED 기초공정 이해와 실습

1

22 2

0

0

(1)

(2)

EL F S e h

e ee he

T

h he hh

T

T rec rec e h

h eh e

h e

e hEL F S

h e

T rec

h e h e nh e EL F S EL

e h

n nJ n n nedJ n n ned

nJ

ne F

J J Je F

J Jn J J

ed n ed

η η γ

γτ

γτ

τ τ τ γ

μ

η η γμ μ

τ τ

η ηγ

minus

Φ =

minus minus =

minus minus =

lt =

=

Φ = prop

gt

= Φ = prop rArr Φ prop

EL Current RelationEL Current Relation

43OLED 기초공정 이해와 실습

Device Structure ITONPBAlq3Ca

22

21

ZZZ

fdVdQC

+minus

==πφieZiZZZ ||

))=+=

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

V0 independent of the NPB layer thickness

44OLED 기초공정 이해와 실습

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

Dashed line without interfacial charge

Wolfgang Brutting Stefan Berleb Anton G Muckl Organic Electronics 2 (2001)

Device Structure ITONPBAlq3Ca

45OLED 기초공정 이해와 실습

Langevin Recombination of carriers

bull Carriers are statistically independent therefore the e-h recombination is a random process and kinetically bimolecular

bull Total current attracted by a charge into the sphere of Coulombic capture radius rc

2

22

( ) ( )4

(4 ) 14 184

( ) (mean free path A)

n p c n pc

c cB

n p

qJ qp E qpr

qi r J Bqp r nmk T

qB a

μ μ μ μπε

ππε

μ μ λε

= + = +

= = cong asymp minus

there4 = + asympo

TkUd

BeP ~ minusProbability of dissociation

reUπε4

~2

e-

rc

Carrier RecombinationCarrier Recombination

P Langevin Ann Chem Phys 28 289 (1903)

46OLED 기초공정 이해와 실습

Electronic Processes in Organic Crystals and Polymers by MPope and C E Swenberg

ExcitonsExcitons

47OLED 기초공정 이해와 실습

C Adachi et al

Electrons and holesForm excitons

(bound e--h+ pairs)

Exciton Recombination ZoneExciton Recombination Zone

48OLED 기초공정 이해와 실습

MOLECULAR EXCITED STATESAFTER ELECTRICAL EXCITATION

Singletspin anti-symmetric

Tripletspin symmetric

25 75

MOLECULAR GROUND STATEspin anti-symmetric

Relaxation allowedfast efficientFluorescence

Relaxation disallowedslow inefficientPhosphorescence

|χ1χ2 gt = | gt

|χ1χ2 gt = | gt

|χ1χ2 gt

= | gt - | gt2

1

|χ1χ2 gt = | gt + | gt2

1ISC

Spin

OLEDOLED의의 형광형광인광인광

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 39: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

38OLED 기초공정 이해와 실습

2

2

3

Charge per unit area Q induced by a voltage V

Transit time across the semiconductor

9

Approximate SCLC densi

Child law (Mott- Gu

ty

Elec8

rney law)

o r

r

o rSCLC

r

VQ CVd

d dtE V

VQJt d

ε ε

μ μ

ε ε μ

= =

= =

asymp =

3 2

tric field distribution across the semiconductor

Majority space charges enhance the E field at the

3 3 ( ) at ( )2 2

enhance the injection of the cath

minority carrieode

rs (elect

V x VE x x d E dd d

= = =

rArr rons)

d

(+) (-)

x=0 x=d

Vd

15 Vd232

3)(d

xVxE =

++++

Virtual anode

-

Space Charge Limited CurrentSpace Charge Limited Current

39OLED 기초공정 이해와 실습

2

3

1

2 01

(no traps or discrete traps Mott-Gurney formula)

(exponential trap distributions ( ) exp( )

98

o rSCLC

mt

SCLC m t t

VJd

TVJ N E NmT

E kTd

ε ε μ

+

+

=

prop = =

ECB

EVB

Etrap

Discrete trapping center Exponential distributionof trapping centers

TrapTrap--Limited CurrentLimited Current

40OLED 기초공정 이해와 실습

Shen Burrows Bulovic McCarty Thompson Forrest Jpn J Appl Phys 35 L401 (1996)

ITOTPDAlq3MgAg

12

1

+

+

prop m

m

SCLC dVJ

TrapTrap--Limited CurrentLimited Current

41OLED 기초공정 이해와 실습

0

0

Activation energy at 0 Empirical parameter

Mobility at PF constant

PF

PF

E FT

T Tμβ

Δ =

=

PFPF

B eff

0

3

PFeff 0 0

( ) exp

exp( )

1 1 1with

E FFT μk T

F

qT T T

βμ

μ β

βπεε

⎛ ⎞Δ minus= minus⎜ ⎟⎜ ⎟

⎝ ⎠

equiv

= minus =

Poole Frenkel ModelPoole Frenkel Model

42OLED 기초공정 이해와 실습

1

22 2

0

0

(1)

(2)

EL F S e h

e ee he

T

h he hh

T

T rec rec e h

h eh e

h e

e hEL F S

h e

T rec

h e h e nh e EL F S EL

e h

n nJ n n nedJ n n ned

nJ

ne F

J J Je F

J Jn J J

ed n ed

η η γ

γτ

γτ

τ τ τ γ

μ

η η γμ μ

τ τ

η ηγ

minus

Φ =

minus minus =

minus minus =

lt =

=

Φ = prop

gt

= Φ = prop rArr Φ prop

EL Current RelationEL Current Relation

43OLED 기초공정 이해와 실습

Device Structure ITONPBAlq3Ca

22

21

ZZZ

fdVdQC

+minus

==πφieZiZZZ ||

))=+=

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

V0 independent of the NPB layer thickness

44OLED 기초공정 이해와 실습

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

Dashed line without interfacial charge

Wolfgang Brutting Stefan Berleb Anton G Muckl Organic Electronics 2 (2001)

Device Structure ITONPBAlq3Ca

45OLED 기초공정 이해와 실습

Langevin Recombination of carriers

bull Carriers are statistically independent therefore the e-h recombination is a random process and kinetically bimolecular

bull Total current attracted by a charge into the sphere of Coulombic capture radius rc

2

22

( ) ( )4

(4 ) 14 184

( ) (mean free path A)

n p c n pc

c cB

n p

qJ qp E qpr

qi r J Bqp r nmk T

qB a

μ μ μ μπε

ππε

μ μ λε

= + = +

= = cong asymp minus

there4 = + asympo

TkUd

BeP ~ minusProbability of dissociation

reUπε4

~2

e-

rc

Carrier RecombinationCarrier Recombination

P Langevin Ann Chem Phys 28 289 (1903)

46OLED 기초공정 이해와 실습

Electronic Processes in Organic Crystals and Polymers by MPope and C E Swenberg

ExcitonsExcitons

47OLED 기초공정 이해와 실습

C Adachi et al

Electrons and holesForm excitons

(bound e--h+ pairs)

Exciton Recombination ZoneExciton Recombination Zone

48OLED 기초공정 이해와 실습

MOLECULAR EXCITED STATESAFTER ELECTRICAL EXCITATION

Singletspin anti-symmetric

Tripletspin symmetric

25 75

MOLECULAR GROUND STATEspin anti-symmetric

Relaxation allowedfast efficientFluorescence

Relaxation disallowedslow inefficientPhosphorescence

|χ1χ2 gt = | gt

|χ1χ2 gt = | gt

|χ1χ2 gt

= | gt - | gt2

1

|χ1χ2 gt = | gt + | gt2

1ISC

Spin

OLEDOLED의의 형광형광인광인광

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 40: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

39OLED 기초공정 이해와 실습

2

3

1

2 01

(no traps or discrete traps Mott-Gurney formula)

(exponential trap distributions ( ) exp( )

98

o rSCLC

mt

SCLC m t t

VJd

TVJ N E NmT

E kTd

ε ε μ

+

+

=

prop = =

ECB

EVB

Etrap

Discrete trapping center Exponential distributionof trapping centers

TrapTrap--Limited CurrentLimited Current

40OLED 기초공정 이해와 실습

Shen Burrows Bulovic McCarty Thompson Forrest Jpn J Appl Phys 35 L401 (1996)

ITOTPDAlq3MgAg

12

1

+

+

prop m

m

SCLC dVJ

TrapTrap--Limited CurrentLimited Current

41OLED 기초공정 이해와 실습

0

0

Activation energy at 0 Empirical parameter

Mobility at PF constant

PF

PF

E FT

T Tμβ

Δ =

=

PFPF

B eff

0

3

PFeff 0 0

( ) exp

exp( )

1 1 1with

E FFT μk T

F

qT T T

βμ

μ β

βπεε

⎛ ⎞Δ minus= minus⎜ ⎟⎜ ⎟

⎝ ⎠

equiv

= minus =

Poole Frenkel ModelPoole Frenkel Model

42OLED 기초공정 이해와 실습

1

22 2

0

0

(1)

(2)

EL F S e h

e ee he

T

h he hh

T

T rec rec e h

h eh e

h e

e hEL F S

h e

T rec

h e h e nh e EL F S EL

e h

n nJ n n nedJ n n ned

nJ

ne F

J J Je F

J Jn J J

ed n ed

η η γ

γτ

γτ

τ τ τ γ

μ

η η γμ μ

τ τ

η ηγ

minus

Φ =

minus minus =

minus minus =

lt =

=

Φ = prop

gt

= Φ = prop rArr Φ prop

EL Current RelationEL Current Relation

43OLED 기초공정 이해와 실습

Device Structure ITONPBAlq3Ca

22

21

ZZZ

fdVdQC

+minus

==πφieZiZZZ ||

))=+=

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

V0 independent of the NPB layer thickness

44OLED 기초공정 이해와 실습

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

Dashed line without interfacial charge

Wolfgang Brutting Stefan Berleb Anton G Muckl Organic Electronics 2 (2001)

Device Structure ITONPBAlq3Ca

45OLED 기초공정 이해와 실습

Langevin Recombination of carriers

bull Carriers are statistically independent therefore the e-h recombination is a random process and kinetically bimolecular

bull Total current attracted by a charge into the sphere of Coulombic capture radius rc

2

22

( ) ( )4

(4 ) 14 184

( ) (mean free path A)

n p c n pc

c cB

n p

qJ qp E qpr

qi r J Bqp r nmk T

qB a

μ μ μ μπε

ππε

μ μ λε

= + = +

= = cong asymp minus

there4 = + asympo

TkUd

BeP ~ minusProbability of dissociation

reUπε4

~2

e-

rc

Carrier RecombinationCarrier Recombination

P Langevin Ann Chem Phys 28 289 (1903)

46OLED 기초공정 이해와 실습

Electronic Processes in Organic Crystals and Polymers by MPope and C E Swenberg

ExcitonsExcitons

47OLED 기초공정 이해와 실습

C Adachi et al

Electrons and holesForm excitons

(bound e--h+ pairs)

Exciton Recombination ZoneExciton Recombination Zone

48OLED 기초공정 이해와 실습

MOLECULAR EXCITED STATESAFTER ELECTRICAL EXCITATION

Singletspin anti-symmetric

Tripletspin symmetric

25 75

MOLECULAR GROUND STATEspin anti-symmetric

Relaxation allowedfast efficientFluorescence

Relaxation disallowedslow inefficientPhosphorescence

|χ1χ2 gt = | gt

|χ1χ2 gt = | gt

|χ1χ2 gt

= | gt - | gt2

1

|χ1χ2 gt = | gt + | gt2

1ISC

Spin

OLEDOLED의의 형광형광인광인광

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 41: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

40OLED 기초공정 이해와 실습

Shen Burrows Bulovic McCarty Thompson Forrest Jpn J Appl Phys 35 L401 (1996)

ITOTPDAlq3MgAg

12

1

+

+

prop m

m

SCLC dVJ

TrapTrap--Limited CurrentLimited Current

41OLED 기초공정 이해와 실습

0

0

Activation energy at 0 Empirical parameter

Mobility at PF constant

PF

PF

E FT

T Tμβ

Δ =

=

PFPF

B eff

0

3

PFeff 0 0

( ) exp

exp( )

1 1 1with

E FFT μk T

F

qT T T

βμ

μ β

βπεε

⎛ ⎞Δ minus= minus⎜ ⎟⎜ ⎟

⎝ ⎠

equiv

= minus =

Poole Frenkel ModelPoole Frenkel Model

42OLED 기초공정 이해와 실습

1

22 2

0

0

(1)

(2)

EL F S e h

e ee he

T

h he hh

T

T rec rec e h

h eh e

h e

e hEL F S

h e

T rec

h e h e nh e EL F S EL

e h

n nJ n n nedJ n n ned

nJ

ne F

J J Je F

J Jn J J

ed n ed

η η γ

γτ

γτ

τ τ τ γ

μ

η η γμ μ

τ τ

η ηγ

minus

Φ =

minus minus =

minus minus =

lt =

=

Φ = prop

gt

= Φ = prop rArr Φ prop

EL Current RelationEL Current Relation

43OLED 기초공정 이해와 실습

Device Structure ITONPBAlq3Ca

22

21

ZZZ

fdVdQC

+minus

==πφieZiZZZ ||

))=+=

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

V0 independent of the NPB layer thickness

44OLED 기초공정 이해와 실습

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

Dashed line without interfacial charge

Wolfgang Brutting Stefan Berleb Anton G Muckl Organic Electronics 2 (2001)

Device Structure ITONPBAlq3Ca

45OLED 기초공정 이해와 실습

Langevin Recombination of carriers

bull Carriers are statistically independent therefore the e-h recombination is a random process and kinetically bimolecular

bull Total current attracted by a charge into the sphere of Coulombic capture radius rc

2

22

( ) ( )4

(4 ) 14 184

( ) (mean free path A)

n p c n pc

c cB

n p

qJ qp E qpr

qi r J Bqp r nmk T

qB a

μ μ μ μπε

ππε

μ μ λε

= + = +

= = cong asymp minus

there4 = + asympo

TkUd

BeP ~ minusProbability of dissociation

reUπε4

~2

e-

rc

Carrier RecombinationCarrier Recombination

P Langevin Ann Chem Phys 28 289 (1903)

46OLED 기초공정 이해와 실습

Electronic Processes in Organic Crystals and Polymers by MPope and C E Swenberg

ExcitonsExcitons

47OLED 기초공정 이해와 실습

C Adachi et al

Electrons and holesForm excitons

(bound e--h+ pairs)

Exciton Recombination ZoneExciton Recombination Zone

48OLED 기초공정 이해와 실습

MOLECULAR EXCITED STATESAFTER ELECTRICAL EXCITATION

Singletspin anti-symmetric

Tripletspin symmetric

25 75

MOLECULAR GROUND STATEspin anti-symmetric

Relaxation allowedfast efficientFluorescence

Relaxation disallowedslow inefficientPhosphorescence

|χ1χ2 gt = | gt

|χ1χ2 gt = | gt

|χ1χ2 gt

= | gt - | gt2

1

|χ1χ2 gt = | gt + | gt2

1ISC

Spin

OLEDOLED의의 형광형광인광인광

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 42: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

41OLED 기초공정 이해와 실습

0

0

Activation energy at 0 Empirical parameter

Mobility at PF constant

PF

PF

E FT

T Tμβ

Δ =

=

PFPF

B eff

0

3

PFeff 0 0

( ) exp

exp( )

1 1 1with

E FFT μk T

F

qT T T

βμ

μ β

βπεε

⎛ ⎞Δ minus= minus⎜ ⎟⎜ ⎟

⎝ ⎠

equiv

= minus =

Poole Frenkel ModelPoole Frenkel Model

42OLED 기초공정 이해와 실습

1

22 2

0

0

(1)

(2)

EL F S e h

e ee he

T

h he hh

T

T rec rec e h

h eh e

h e

e hEL F S

h e

T rec

h e h e nh e EL F S EL

e h

n nJ n n nedJ n n ned

nJ

ne F

J J Je F

J Jn J J

ed n ed

η η γ

γτ

γτ

τ τ τ γ

μ

η η γμ μ

τ τ

η ηγ

minus

Φ =

minus minus =

minus minus =

lt =

=

Φ = prop

gt

= Φ = prop rArr Φ prop

EL Current RelationEL Current Relation

43OLED 기초공정 이해와 실습

Device Structure ITONPBAlq3Ca

22

21

ZZZ

fdVdQC

+minus

==πφieZiZZZ ||

))=+=

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

V0 independent of the NPB layer thickness

44OLED 기초공정 이해와 실습

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

Dashed line without interfacial charge

Wolfgang Brutting Stefan Berleb Anton G Muckl Organic Electronics 2 (2001)

Device Structure ITONPBAlq3Ca

45OLED 기초공정 이해와 실습

Langevin Recombination of carriers

bull Carriers are statistically independent therefore the e-h recombination is a random process and kinetically bimolecular

bull Total current attracted by a charge into the sphere of Coulombic capture radius rc

2

22

( ) ( )4

(4 ) 14 184

( ) (mean free path A)

n p c n pc

c cB

n p

qJ qp E qpr

qi r J Bqp r nmk T

qB a

μ μ μ μπε

ππε

μ μ λε

= + = +

= = cong asymp minus

there4 = + asympo

TkUd

BeP ~ minusProbability of dissociation

reUπε4

~2

e-

rc

Carrier RecombinationCarrier Recombination

P Langevin Ann Chem Phys 28 289 (1903)

46OLED 기초공정 이해와 실습

Electronic Processes in Organic Crystals and Polymers by MPope and C E Swenberg

ExcitonsExcitons

47OLED 기초공정 이해와 실습

C Adachi et al

Electrons and holesForm excitons

(bound e--h+ pairs)

Exciton Recombination ZoneExciton Recombination Zone

48OLED 기초공정 이해와 실습

MOLECULAR EXCITED STATESAFTER ELECTRICAL EXCITATION

Singletspin anti-symmetric

Tripletspin symmetric

25 75

MOLECULAR GROUND STATEspin anti-symmetric

Relaxation allowedfast efficientFluorescence

Relaxation disallowedslow inefficientPhosphorescence

|χ1χ2 gt = | gt

|χ1χ2 gt = | gt

|χ1χ2 gt

= | gt - | gt2

1

|χ1χ2 gt = | gt + | gt2

1ISC

Spin

OLEDOLED의의 형광형광인광인광

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 43: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

42OLED 기초공정 이해와 실습

1

22 2

0

0

(1)

(2)

EL F S e h

e ee he

T

h he hh

T

T rec rec e h

h eh e

h e

e hEL F S

h e

T rec

h e h e nh e EL F S EL

e h

n nJ n n nedJ n n ned

nJ

ne F

J J Je F

J Jn J J

ed n ed

η η γ

γτ

γτ

τ τ τ γ

μ

η η γμ μ

τ τ

η ηγ

minus

Φ =

minus minus =

minus minus =

lt =

=

Φ = prop

gt

= Φ = prop rArr Φ prop

EL Current RelationEL Current Relation

43OLED 기초공정 이해와 실습

Device Structure ITONPBAlq3Ca

22

21

ZZZ

fdVdQC

+minus

==πφieZiZZZ ||

))=+=

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

V0 independent of the NPB layer thickness

44OLED 기초공정 이해와 실습

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

Dashed line without interfacial charge

Wolfgang Brutting Stefan Berleb Anton G Muckl Organic Electronics 2 (2001)

Device Structure ITONPBAlq3Ca

45OLED 기초공정 이해와 실습

Langevin Recombination of carriers

bull Carriers are statistically independent therefore the e-h recombination is a random process and kinetically bimolecular

bull Total current attracted by a charge into the sphere of Coulombic capture radius rc

2

22

( ) ( )4

(4 ) 14 184

( ) (mean free path A)

n p c n pc

c cB

n p

qJ qp E qpr

qi r J Bqp r nmk T

qB a

μ μ μ μπε

ππε

μ μ λε

= + = +

= = cong asymp minus

there4 = + asympo

TkUd

BeP ~ minusProbability of dissociation

reUπε4

~2

e-

rc

Carrier RecombinationCarrier Recombination

P Langevin Ann Chem Phys 28 289 (1903)

46OLED 기초공정 이해와 실습

Electronic Processes in Organic Crystals and Polymers by MPope and C E Swenberg

ExcitonsExcitons

47OLED 기초공정 이해와 실습

C Adachi et al

Electrons and holesForm excitons

(bound e--h+ pairs)

Exciton Recombination ZoneExciton Recombination Zone

48OLED 기초공정 이해와 실습

MOLECULAR EXCITED STATESAFTER ELECTRICAL EXCITATION

Singletspin anti-symmetric

Tripletspin symmetric

25 75

MOLECULAR GROUND STATEspin anti-symmetric

Relaxation allowedfast efficientFluorescence

Relaxation disallowedslow inefficientPhosphorescence

|χ1χ2 gt = | gt

|χ1χ2 gt = | gt

|χ1χ2 gt

= | gt - | gt2

1

|χ1χ2 gt = | gt + | gt2

1ISC

Spin

OLEDOLED의의 형광형광인광인광

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 44: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

43OLED 기초공정 이해와 실습

Device Structure ITONPBAlq3Ca

22

21

ZZZ

fdVdQC

+minus

==πφieZiZZZ ||

))=+=

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

V0 independent of the NPB layer thickness

44OLED 기초공정 이해와 실습

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

Dashed line without interfacial charge

Wolfgang Brutting Stefan Berleb Anton G Muckl Organic Electronics 2 (2001)

Device Structure ITONPBAlq3Ca

45OLED 기초공정 이해와 실습

Langevin Recombination of carriers

bull Carriers are statistically independent therefore the e-h recombination is a random process and kinetically bimolecular

bull Total current attracted by a charge into the sphere of Coulombic capture radius rc

2

22

( ) ( )4

(4 ) 14 184

( ) (mean free path A)

n p c n pc

c cB

n p

qJ qp E qpr

qi r J Bqp r nmk T

qB a

μ μ μ μπε

ππε

μ μ λε

= + = +

= = cong asymp minus

there4 = + asympo

TkUd

BeP ~ minusProbability of dissociation

reUπε4

~2

e-

rc

Carrier RecombinationCarrier Recombination

P Langevin Ann Chem Phys 28 289 (1903)

46OLED 기초공정 이해와 실습

Electronic Processes in Organic Crystals and Polymers by MPope and C E Swenberg

ExcitonsExcitons

47OLED 기초공정 이해와 실습

C Adachi et al

Electrons and holesForm excitons

(bound e--h+ pairs)

Exciton Recombination ZoneExciton Recombination Zone

48OLED 기초공정 이해와 실습

MOLECULAR EXCITED STATESAFTER ELECTRICAL EXCITATION

Singletspin anti-symmetric

Tripletspin symmetric

25 75

MOLECULAR GROUND STATEspin anti-symmetric

Relaxation allowedfast efficientFluorescence

Relaxation disallowedslow inefficientPhosphorescence

|χ1χ2 gt = | gt

|χ1χ2 gt = | gt

|χ1χ2 gt

= | gt - | gt2

1

|χ1χ2 gt = | gt + | gt2

1ISC

Spin

OLEDOLED의의 형광형광인광인광

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 45: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

44OLED 기초공정 이해와 실습

Interfacial Charge and Electrical FieldInterfacial Charge and Electrical Field

Dashed line without interfacial charge

Wolfgang Brutting Stefan Berleb Anton G Muckl Organic Electronics 2 (2001)

Device Structure ITONPBAlq3Ca

45OLED 기초공정 이해와 실습

Langevin Recombination of carriers

bull Carriers are statistically independent therefore the e-h recombination is a random process and kinetically bimolecular

bull Total current attracted by a charge into the sphere of Coulombic capture radius rc

2

22

( ) ( )4

(4 ) 14 184

( ) (mean free path A)

n p c n pc

c cB

n p

qJ qp E qpr

qi r J Bqp r nmk T

qB a

μ μ μ μπε

ππε

μ μ λε

= + = +

= = cong asymp minus

there4 = + asympo

TkUd

BeP ~ minusProbability of dissociation

reUπε4

~2

e-

rc

Carrier RecombinationCarrier Recombination

P Langevin Ann Chem Phys 28 289 (1903)

46OLED 기초공정 이해와 실습

Electronic Processes in Organic Crystals and Polymers by MPope and C E Swenberg

ExcitonsExcitons

47OLED 기초공정 이해와 실습

C Adachi et al

Electrons and holesForm excitons

(bound e--h+ pairs)

Exciton Recombination ZoneExciton Recombination Zone

48OLED 기초공정 이해와 실습

MOLECULAR EXCITED STATESAFTER ELECTRICAL EXCITATION

Singletspin anti-symmetric

Tripletspin symmetric

25 75

MOLECULAR GROUND STATEspin anti-symmetric

Relaxation allowedfast efficientFluorescence

Relaxation disallowedslow inefficientPhosphorescence

|χ1χ2 gt = | gt

|χ1χ2 gt = | gt

|χ1χ2 gt

= | gt - | gt2

1

|χ1χ2 gt = | gt + | gt2

1ISC

Spin

OLEDOLED의의 형광형광인광인광

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 46: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

45OLED 기초공정 이해와 실습

Langevin Recombination of carriers

bull Carriers are statistically independent therefore the e-h recombination is a random process and kinetically bimolecular

bull Total current attracted by a charge into the sphere of Coulombic capture radius rc

2

22

( ) ( )4

(4 ) 14 184

( ) (mean free path A)

n p c n pc

c cB

n p

qJ qp E qpr

qi r J Bqp r nmk T

qB a

μ μ μ μπε

ππε

μ μ λε

= + = +

= = cong asymp minus

there4 = + asympo

TkUd

BeP ~ minusProbability of dissociation

reUπε4

~2

e-

rc

Carrier RecombinationCarrier Recombination

P Langevin Ann Chem Phys 28 289 (1903)

46OLED 기초공정 이해와 실습

Electronic Processes in Organic Crystals and Polymers by MPope and C E Swenberg

ExcitonsExcitons

47OLED 기초공정 이해와 실습

C Adachi et al

Electrons and holesForm excitons

(bound e--h+ pairs)

Exciton Recombination ZoneExciton Recombination Zone

48OLED 기초공정 이해와 실습

MOLECULAR EXCITED STATESAFTER ELECTRICAL EXCITATION

Singletspin anti-symmetric

Tripletspin symmetric

25 75

MOLECULAR GROUND STATEspin anti-symmetric

Relaxation allowedfast efficientFluorescence

Relaxation disallowedslow inefficientPhosphorescence

|χ1χ2 gt = | gt

|χ1χ2 gt = | gt

|χ1χ2 gt

= | gt - | gt2

1

|χ1χ2 gt = | gt + | gt2

1ISC

Spin

OLEDOLED의의 형광형광인광인광

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 47: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

46OLED 기초공정 이해와 실습

Electronic Processes in Organic Crystals and Polymers by MPope and C E Swenberg

ExcitonsExcitons

47OLED 기초공정 이해와 실습

C Adachi et al

Electrons and holesForm excitons

(bound e--h+ pairs)

Exciton Recombination ZoneExciton Recombination Zone

48OLED 기초공정 이해와 실습

MOLECULAR EXCITED STATESAFTER ELECTRICAL EXCITATION

Singletspin anti-symmetric

Tripletspin symmetric

25 75

MOLECULAR GROUND STATEspin anti-symmetric

Relaxation allowedfast efficientFluorescence

Relaxation disallowedslow inefficientPhosphorescence

|χ1χ2 gt = | gt

|χ1χ2 gt = | gt

|χ1χ2 gt

= | gt - | gt2

1

|χ1χ2 gt = | gt + | gt2

1ISC

Spin

OLEDOLED의의 형광형광인광인광

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 48: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

47OLED 기초공정 이해와 실습

C Adachi et al

Electrons and holesForm excitons

(bound e--h+ pairs)

Exciton Recombination ZoneExciton Recombination Zone

48OLED 기초공정 이해와 실습

MOLECULAR EXCITED STATESAFTER ELECTRICAL EXCITATION

Singletspin anti-symmetric

Tripletspin symmetric

25 75

MOLECULAR GROUND STATEspin anti-symmetric

Relaxation allowedfast efficientFluorescence

Relaxation disallowedslow inefficientPhosphorescence

|χ1χ2 gt = | gt

|χ1χ2 gt = | gt

|χ1χ2 gt

= | gt - | gt2

1

|χ1χ2 gt = | gt + | gt2

1ISC

Spin

OLEDOLED의의 형광형광인광인광

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 49: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

48OLED 기초공정 이해와 실습

MOLECULAR EXCITED STATESAFTER ELECTRICAL EXCITATION

Singletspin anti-symmetric

Tripletspin symmetric

25 75

MOLECULAR GROUND STATEspin anti-symmetric

Relaxation allowedfast efficientFluorescence

Relaxation disallowedslow inefficientPhosphorescence

|χ1χ2 gt = | gt

|χ1χ2 gt = | gt

|χ1χ2 gt

= | gt - | gt2

1

|χ1χ2 gt = | gt + | gt2

1ISC

Spin

OLEDOLED의의 형광형광인광인광

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 50: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

49OLED 기초공정 이해와 실습

Electronic Process in MoleculesElectronic Process in Molecules

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 51: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

50OLED 기초공정 이해와 실습

In OLEDs with Small Molecules

Experimentally determined fraction = 22plusmn3 singletsMA Baldo etal Phys Rev B (1999)

From the comparison of the PL of DCM2Alq3 and PtOEPAlq3

SingletTriplet FormationSingletTriplet Formation

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 52: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

51OLED 기초공정 이해와 실습

For a random injection of electron-hole pairs and spin independentrecombination ηs = 25 as there are three spin triplets to every one spin singlet

Experimentally 8020 lele Sη

⎟⎟⎠

⎞⎜⎜⎝

⎛photons emitted photons detected

20le1~

⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜

=

pairs hole -electron injected

excitons

fraction exciton singlet =Sη

⎟⎠⎞

⎜⎝⎛

excitons excitonssinglet

1~

⎟⎟⎠

⎞⎜⎜⎝

⎛excitonssinglet photons emitted

⎟⎟⎠

⎞⎜⎜⎝

⎛=

pairs hole-electron injected photons detected

ELη

EL Quantum EfficiencyEL Quantum Efficiency

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 53: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

52OLED 기초공정 이해와 실습

Carrier RecombinationCarrier Recombination

4 Singlet exciton decays radiatively

νh

1 Unbound electron-hole pair on neighbouring chains

+

_

2 Electron-hole pair is captured to form a weakly bound CT exciton

+

_

3 Inter-conversion to a strongly bound exciton

+ _

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 54: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

53OLED 기초공정 이해와 실습

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

RH Friend et al Nature 413 828(2001)

TEL

SEL

SPL

TPL

S NN

NN

bullgeη18geSη

39geSη

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 55: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

54OLED 기초공정 이해와 실습

ηmax = σs(σs +3 σT)

ZV Vardeny et al Nature 409494(2001) ZV Vardeny et al PRL 88197401(2002)

Conjugation Length Dependent ExcitonConjugation Length Dependent Exciton

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 56: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

55OLED 기초공정 이해와 실습

Diffusion Length of Singlet ExcitonDiffusion Length of Singlet Exciton

Cathode

ITO

GLASS

Alq3doped Alq3

Diamine

Alq3

( ) 2

4 2

( ) (0)exp

( ) ( ) 1 ( )

20 16 76 10

q L q LEL Alq DCM

xxL

I e e

L nm nsD cm s

ρ ρ

λ φ λ φ λ

τ

minus minus

minus

⎛ ⎞= minus⎜ ⎟⎝ ⎠

prop minus +

asymp asymp

rArr = times

C W Tang et al J Appl Phys 65 3610 (1989)

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 57: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

56OLED 기초공정 이해와 실습

M A Baldo D F OrsquoBrien M E Thompson and S R Forrest Phys Rev B 60 14422 (1999)

Diffusion Length of Triplet ExcitonDiffusion Length of Triplet Exciton

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 58: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

57OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

Bulovic et al Chem Phys Lett 287 455 (1998) 308 317 (1999)

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 59: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

58OLED 기초공정 이해와 실습

Inte

nsity

Wavelength

Host absorption

Host emittigDopant absorption

Dopant emitting

Stokersquos shift Stokersquos shift

HostHost--Dopant SystemDopant System

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 60: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

59OLED 기초공정 이해와 실습

Foumlrster Resonant dipole-dipole coupling very fast lt 10-9 s

Dexter Diffusion of excitons from doner to acceptor

Host and dopant(guest)

D Doner(Host)A Acceptor(Dopant) Excited State

Energy TransferEnergy Transfer

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 61: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

60OLED 기초공정 이해와 실습

M

LigandLigandLigand

Ligand

LigandLigand

LigandLigand

LigandLigand

M

LigandLigand

Ligand-centeredExciton (LC)

Metal-Ligand Charge TransferExciton (MLCT)

bull The emissive state is a mixture of a LC exciton and a MLCT excitonbull The MLCT state has stronger singlet - triplet mixing due to the overlap with

the heavy - metal atombull For strong spin-orbit coupling the IC and ISC rates are very fast

IC

IC

ISC

1LC

3LC1MLCT

3MLCTPhosphorescence

Ground state S0

Heavy MetalHeavy Metal--Organic ComplexesOrganic Complexes

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 62: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

61OLED 기초공정 이해와 실습

N

O

NC CN

TDK

Alq3Red shift

modifided

Gaq3

Perylene

distyrylbiphenylIdemitsu

Pioneerquinacridone

DPTDPT

rubrenerubrene BTXBTX

ABTX

DCJTBKodak

Kodak

Kodak

B G Y Or R

Host

Dopant

SN

O

OH

S

O

OCH3

NH

HN

O

O

NO

NON

O Al

CH3

H3CCH3

L

(Rj)m

(Ri)n

2

Alq-familyN

ON

NON

O Al NO

N

NON

O Ga

Mitsubishi

Mitsubishi Mitsubishi

Mitsubishi

MADN

ArN

N

Chen

Representative HostDopant System

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 63: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

62OLED 기초공정 이해와 실습

Blue Green Red

Phosphor-escence

Materials

Host Materials

Hole Blocking Materials

N

IrO

2

ON

F

F

IrN

O O

2

NIr

N

O O

2

CF3F3C

n

O

CN

CH CH2 nN

N N

NNH3C CH3

NN

N

N N

N N

N N

Pt

N

IrO

2

O

S

F

F

F

F

F

F F

FF

F F

FF

F F

FF

F

F

F

F

F

F

FF

F

F

F

F

F

FF

F

F

F

F

FF

F

F

F

F

N

Ir

2

Si CH3H3C

BCP

C60F42

CN-PPV

CBPmCP

UGH2 TAZ

PVK

FIrpic(CF3ppy)2Ir(pic)

Ir(ppy)3

Ir(ppy)2acac

Ir(mpp)3 PtOEP

Btp2Ir(acac)

NIr

2

H3C

NO Al O

O

BAlq

Representative HostDopant System

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 64: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

63OLED 기초공정 이해와 실습

Exciton Blocking LayerExciton confinement

low nonradiative recombHigh quantum efficiency

Material Triplet energyPtOEP 19 eVIr(ppy)3 24 eVCBP 26 eVBCP 25 eVAlq3 20 eV

M A Baldo et al Appl Phys Lett 75 4 (1999)

BCPDopantHTL ETL

TripletTripletrarrrarrSinglet EL EmissionSinglet EL Emission

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 65: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

64OLED 기초공정 이해와 실습

HostHost--Dopant SystemDopant System

ηext ~ 22 100 cdm2

PtOEP doped in CBPAlq3

N N

N NPt

EL from triplet excitons

Ref M A Baldo C Adachi and S R Forrest Phys Rev B 62 10967 (2000)

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 66: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

65OLED 기초공정 이해와 실습

M A Baldo M E Thompson amp S R Forrest Nature 403 750 (2000 2 17)

Phosphorescent SensitizerPhosphorescent Sensitizer

Foumlrster energy transfer

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 67: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

66OLED 기초공정 이해와 실습

ITOHMTPD(60 nm)12 (ppy)2Ir(acac)TAZ (25 nm)Alq3 (50 nm)MgAgAg

Adachi et al J Appl Phys Vol 90 No 10 5048 (2001)

High Efficiency ~ 100 internal QEHigh Efficiency ~ 100 internal QE

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 68: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

67OLED 기초공정 이해와 실습

Monomer and DimerMonomer and Dimer

A class of compound that exhibits the optical absorption characteristic of a monomer but their luminescence is characteristic of a physical dimer

Excimer M+MExciplex D+A or D+AGround state dissociative

Red shiftBroad peak with no vibronic structure

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 69: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

68OLED 기초공정 이해와 실습

Cathode

Electron Transport Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

Anode

Cathode

Emission Layer

Hole Transport Layer

Anode

Cathode

Electron Transport Layer

Blocking Layer

Emission Layer

Hole Transport Layer

Hole Injection Layer

AnodeGlass substrate

Glass substrate

Glass substrate

Small Molecule Fluorescence OLED

Small Molecule Phosphorescence

OLED

Polymer OLED (PLED)

OLEDOLED의의 적층구조적층구조

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 70: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

69OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Eg

Φm

χ

I

Metal Semiconductor

eBΦhBΦ

Φs

EF

EAce minusΦ=Φah IP Φminus=Φ

Band Alignment ModelBand Alignment Model

Mott-Schottky Model

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 71: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

70OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

After contact Mott-Schottky model

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

EF

Band Alignment ModelBand Alignment Model

Vacuum Level Alignment

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 72: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

71OLED 기초공정 이해와 실습

Before contact

Impurity level

VL VL

CB

VB

EF

EF

Eg

Φm

χ

I

Metal Semiconductor

VL

CB

VB

EF

Vbi

Eg

Φm

χ

I

Metal Semiconductor

eBΦ

hBΦ

Φs

++ +

---

Δ

EF

After contact Vacuum level shift

Band Alignment ModelBand Alignment Model

Interface Dipole Model

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 73: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

72OLED 기초공정 이해와 실습

bull Charge exchangebull Chemistrybull Interface electronic effectsbull Adsorbate induced metal work function modificationbull Abrupt shift in vacuum level between materials rarr 05 ~ 10eV

bull Boundary region between weakly interacting bull No surface or interface active bondsbull Near vacuum level alignment le 01eVbull Exception

PTCDAharrAlq3 05eV

Metal-Organic Heterojunction

Organic-Organic Heterojunction

HeterojunctionHeterojunction

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 74: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

73OLED 기초공정 이해와 실습

Work Function and Energy GapWork Function and Energy Gap

Metal Work Function Energy Gap

2

E(eV)

3

4

5

6

7

8

F4-TCNQNTCDA

TCNQ

PTCDA

BCP CBP

α-NPD

F16-CuPc

PTCBI

Alq3

CuPcZnPc

Pentacene

Al (428)Mg(366)

Ag (447)Sn (442)

Au (510)PEDOTPSS (515)

Ti Zn (433)In (412)

W (455) Mo (460) Cu (465)

Ni (515)

Pt (565)

Si (517)

Si (405)Ta (419)

Ir (527)Re (510)

Pb (498)Co (497) Rh (497)Ru (471)Cr (460)

V (430)

Energy LevelLumoHomo

α-6T

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 75: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

74OLED 기초공정 이해와 실습

Carrier injection by Fowler-Nordheim tunneling

Barrier Height of CathodeBarrier Height of Cathode

Band diagram (in forward bias) for various electrode material

I D Parker J Appl Phys 75 1656 (1994)

Device efficiency for various cathode material with ITOMEH-PPVdevices

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 76: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

75OLED 기초공정 이해와 실습

MetalMetal--Organic heterojunctionOrganic heterojunction

Tang Lee et al Chem PhysLett 39692(2004)

Hole injection barrier as a function of metal work function

Schematic energy diagram of the organicmetal interface

μminusgtΦltminusΦ=Φ ][ smb

sΦminusΦ=Δ infin0

0Δ+Φ=Φ mbm

1Δ+Φ=+Φ=Φ mbeorg EA

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 77: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

76OLED 기초공정 이해와 실습

Buffer Layer Enhanced InjectionBuffer Layer Enhanced Injection

Buffer Layerpoly(methylmethacrylate) LB filmsCsF LiF Al2O3 SiO2 Si3N4 Cs2CO3NaCl MgO

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 78: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

77OLED 기초공정 이해와 실습

bull The stable Al2O3 improves the electron tunneling and removes the exciton-quenching gap states that are intrinsic to the Alq3Al interface

bull Interposing Al2O3 buffer layer between Alq3 and Al can reduce the electron injection barrier

Buffer Layer (AlBuffer Layer (Al22OO33) for EIL) for EIL

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 79: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

78OLED 기초공정 이해와 실습

Buffer Layer (LiF) for EILBuffer Layer (LiF) for EIL

Device structure ITONPB(50nm)Alq3(100nm)LiF(0~5nm)Ag

X J Wang et al J A P 95 3828(2004)

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 80: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

79OLED 기초공정 이해와 실습

Buffer Layer (MgFBuffer Layer (MgF22) for EIL) for EIL

Device A ITOTPDAlq3MgAg

Device BITOTPDAlq3MgF2MgAg

Device C ITOMgF2TPDAlq3MgAg

Device D ITOMgF2TPDAlq3MgF2MgAg

Device A and Device B with different MgF2 layer thickness B J Chen and X W Sun Semicond Sci Technol 20 801(2005)

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 81: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

80OLED 기초공정 이해와 실습

LUMO

HOMO

Anode HTL EL ETL Cathodeh+

EF

Фm1

h+EF

Фm2

EV

Anode with low ФmAnode with high Фm

Hole InjectionHole Injection

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 82: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

81OLED 기초공정 이해와 실습

High Work Function

ITO

Spike

1500~2000Å

Al

Organic

ITO

Spike 존재 부분에서Cathode-AnodeShort의 가능성 큼

불량발생

Vacuum LevelConduction Band(CB)

Valence Band(VB)

HIL

HTL

ETL

EILEMLExciton

ITO

Cathode

Organic

ITO

Low Surface Roughness

(HIL과의 Energy Barrier 최소화 Plasma amp UVO Treatment) Others Low Resistivity amp High optical transmittance

ITO ITO 전극의전극의 균일성균일성

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 83: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

82OLED 기초공정 이해와 실습

Platinum has the largest work function of 57 eV among metals A dramatic increase in the injected current was achieved by interposing a 05 nm thick Pt layer between ITO and TPD

The improvement with the carbon layer was explained in terms of high ionization potentials and effectiveness in adhesion

Large Work Function MaterialLarge Work Function Material

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 84: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

83OLED 기초공정 이해와 실습

The increase in the work function is attributed to the presence of an interfacial dipole resulting from a surface rich in negatively charged oxygen

Plasma Treatment (ITO)Plasma Treatment (ITO)

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 85: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

84OLED 기초공정 이해와 실습

phosphoric acid (H3PO4)

Thin dipole layers can be built at the surface which induce work-function shifts of the order of 1 eV

Dipole Layer Between ITO and HTLDipole Layer Between ITO and HTL

tetrabutylammonium hydroxideN(C4H9)4OH

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 86: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

85OLED 기초공정 이해와 실습

NPB(65nm)Alq3(75nm)MgAg(100nm)

(a) UV-ozone treated ITO anode(b) Untreated ITO overlaid by a

03nm thick CFx film

NPB(65nm)Alq3(75nm)MgAg(100nm) after exposure to air for 24 hrs

(a)UV-ozone treated ITO anode(b)Untreated ITO overlaid by a 03nm

thick CFx film

Note ФITO = 450eV for cleaned ITO

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 87: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

86OLED 기초공정 이해와 실습

J-V Characteristics

NPB(65nm)Alq3(75nm)MgAg(100nm)(a) Untreated ITO anode(Closed circles)(b) UV-ozone treated ITO anode(cross symbols)(c) Untreated ITO overlaid by a 03nm thick CFx film (open circle)

Operational Stability

Buffer Layer (CFx Films)Buffer Layer (CFx Films)

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 88: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

87OLED 기초공정 이해와 실습

Buffer Layer (C60)Buffer Layer (C60)

J Y Lee APL 88 073512(2006)I-V curves of the devices

The schematic diagram for the interfacial energy barrier shift

L-V curves of the devices

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 89: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

88OLED 기초공정 이해와 실습

ITOAlq3(x nm)NPBAlq3CaAg

The increase in device efficiency induced by inserting a Alq3 layer is correlated with a decrease in hole-injection efficiency which leads to an improved balance between hole and electron currents arriving at the recombination zone

Carrier BalanceCarrier Balance

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 90: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

89OLED 기초공정 이해와 실습

Buffer Layer (CuPc)Buffer Layer (CuPc)

S C Kim et al APL 78 1445(2001)

Thin (14nm) CuPc layer interposed between an ITO anode and a HTL improve hole-injection if the CuPcTPD barrier is smaller than the ITOTPD barrier

Thick (102nm) CuPc layer reduces the hole injection and balances the number of hole and electron which results in high device efficiency

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 91: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

90OLED 기초공정 이해와 실습

Buffer Layer (ZnPc)Buffer Layer (ZnPc)

J Blochwitz et al Org Elec 2 97(2001)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Energetic structure for undoped case (left) and doped with F4-TCNQ(right)

Fermi level shift and space charge layer width changes due to the doping

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 92: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

91OLED 기초공정 이해와 실습

Note Energy Barrier DE does not only depend on F but also on the dipole-layer formed at the Interface

PEDOTMetal HeterojunctionPEDOTMetal Heterojunction

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 93: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

92OLED 기초공정 이해와 실습

Organic Material p-doped(a) Both materials undoped(b) Molecular level bending in the doped

layer(c) Interface dipole barrier formation

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 94: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

93OLED 기초공정 이해와 실습

Organic-Organic Interface (a) Undoped α-NPD(HTL)BCP(ETL) interface on Au(b) α-NPD05F4TCNQBCP interface on Au(c) Undoped α-NPDBCP interface on Mg

Note ФAu = 514eV ФMg = 365eV

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 95: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

94OLED 기초공정 이해와 실습

Molecular level diagrams for organic-organic Interface

OrganicOrganic--Organic HeterojunctionOrganic Heterojunction

I G Hill et al JAP 86 4515(1999)

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 96: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

95OLED 기초공정 이해와 실습

Injection to Doped LevelInjection to Doped Level

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 97: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

96OLED 기초공정 이해와 실습

Injection to Doped Level (pin)Injection to Doped Level (pin)

Jingsong Huang et al Appl Phys Lett 80 139 (2002)

bull n-doped transport layerbull p-doped transport layerbull Intrinsic emitting layerbull Blocking layers

Low operating voltage andhigh efficient device

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 98: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

97OLED 기초공정 이해와 실습

-

+

HTLETL

-

p n

Metal

CB

VB

EFe

EFh

+

--

Inorganic LED (eg GaAsAlGaAs) Organic LED

bull Exponential current-voltage relationbull Flat-band under operationbull Low work-function contacts not needed

bull space charge limited currentsbull low work function metals needed IT

O-preparation necessary

Injection to Doped Level (pin)Injection to Doped Level (pin)

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 99: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

98OLED 기초공정 이해와 실습

Electron injection

Blocking BarrierHole Injection

ITO α-NPD PtOEP BCP Alq3 MgAgin Alq3

Recombination Zone

EVAC

EF

EVAC

EF

025eV 06eV

015eV

065eV+++++

- - - --

Hole Blocking LayerHole Blocking Layer

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 100: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

99OLED 기초공정 이해와 실습

Tandem(Stacked) OLEDTandem(Stacked) OLED

Z Shen et al Science 276 2009(1997)

(A) Cross-section of the layers SOLED (B) Top view of a SOLED device

(A)Emission intensity with separate element of SOLED

(B)Emission intensity for two simultaneously illuminated SOLED elements under various operating voltages

B

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 101: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

100OLED 기초공정 이해와 실습

Full Color Display Fabrication

B G RBlue EL

+Color Changing Material

BlueGreen Red EL

Emitting Layer

ColorTechnology

Company Pioneer NEC

Merits

Demerits

High efficiency

Mask alignment

White EL+

Color Filter

B G R

Reduced steps

White balance

B G R

Idemitsu Kosan

Reduced steps

High efficiency Blue amp CCM

TDK Sanyo

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 102: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

101OLED 기초공정 이해와 실습

Fabrication for Small Molecules

Vacuum Deposition

Shadow Mask

Substrate

Source Organic layer

deposition (RGB)

Mask shift Shadow mask 123

Glass Substrate

Pattern accuracy ~ plusmn20 mm

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 103: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

102OLED 기초공정 이해와 실습

Fabrication Methods for Polymers

Ink-jet Printing

Red emitterRhodamin

e 101PPV)

Ink-jet

Green emitter (PPV)

Inkjet Printing

Polyimid Bank

Blue emitter (PF)

Substrate

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 104: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

103OLED 기초공정 이해와 실습

Multilayer Formation of PLEDMultilayer Formation of PLED

Orthogonal solvents for individual layersbull PEDOT (Aqueous Suspension) rArr EML (Organic Solvents

Toluene)

Change the polarity (or solubility) of the deposited material

bull Polar Sulphonium (Precursor PPV) rArr non-polar polymer (insoluble in all organic solvents) (uarr by Heating )

Introduce reactive molecular groups bull Semiconductor materials polymerized rArr insoluble cross-

linked layers

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 105: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

104OLED 기초공정 이해와 실습

Multilayer Formation with Solution MethodMultilayer Formation with Solution Method

Cross section through the multilayer PLED

Klaus Meerholz Nature 437 327(2005)

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 106: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

105OLED 기초공정 이해와 실습

C D Muumlller et al Nature 421 829(2003)

Synthesis of the three oxetane-functionalized spirobifluorene-co-fluorene polymers emitting blue green and red light P1~P4 and Photoacid

Pixel Formation with CrossPixel Formation with Cross--linked PLEDlinked PLED

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 107: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

106OLED 기초공정 이해와 실습

White LightWhite Light

Simultaneous excitation Coevaporation of different emitting Componds

bull Multilayer devices by consecutive evaporation of different emitting compounds (Small Molecules)

bull Co-evaporation of different emitting compounds (Small Molecules)

bull Blend of different soluable emitters in a single layer (Polymer)

Exciplex Emissionbull Two blue emitting organic molecules of different electron

affinities Purity of color emission

Single Active Molecular Materialsbull Solid state emission

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 108: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

107OLED 기초공정 이해와 실습

10

05

00

Ligh

t (ar

b u

nits)

800700600500400Wavelength (nm)

08

06

04

02

CIE

y

06040200CIE x

ηext ~ 24 1000 cdm2 CIE (033 036)

White OLEDWhite OLED

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 109: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

108OLED 기초공정 이해와 실습

Structure of organic layers for a two-element white organic lightemitting device or 2-WSOLED

Forward-viewing external and luminous power efficiencies of1- 2- and 3-SOLEDs as functions of J

White Light (Stacked OLED)White Light (Stacked OLED)

H Kanno et al Appl Phys Lett 89 023503(2006)

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 110: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

109OLED 기초공정 이해와 실습

Color coordinates of OLED

Color CIE(xy)Red (064 036)

Green (038 063)Blue (014 014)

White (030 034)

Small Molecule (Phosphorescence)

Color CIE(xy)Red (067 032)

Green (038 061)Blue (015 017)

White (030 034)

Polymer (Phosphorescence)

NTSC

OLED

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 111: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

110OLED 기초공정 이해와 실습

ηint = ηinjection x ηrecombination x ηfluorescence

Extraction loss (total internal reflection amp waveguiding)

71for 2021)11(1 efficiencyout -Couple 2

212 asymp=asympasympminusminus= εχ n

nnEL

Optical Out-Coupling Efficiency Improvement Eliminate Internal ReflectionEliminate Internal Reflection

Micro-lens Array

Shaped Glass

OLEDOLED의의 양자효율양자효율

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 112: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

111OLED 기초공정 이해와 실습

ITOTPDAlq3+QuinacridoneMg 소자의수분 존재(3 ) 하에서

시간에 따른 발광 상태 변화

Degradation amp EncapsulationDegradation amp Encapsulation

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 113: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

112OLED 기초공정 이해와 실습

DegradationDegradation

Long Term ldquoIntrinsicrdquo Decrease in ELbull Instability of organic materials (under electrical stress) rArr

Degradation of Devices

bull Challenging particularly for Blue

Dark Spots Growth of Non-emissive Areasbull Ambient induced growth of dark spots

bull Metal diffusion into polymers

Catastrophic Failure

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 114: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

113OLED 기초공정 이해와 실습

DegradationDegradation

Mixed emitting layer (squares) OLED and standard bilayer (triangles) OLED with I = 25mAcm2 L0= 1050 710 cdm2 V0 = 75 80V

(A) J-V (B) L-J for ITONPBAlq3Mg-Ag(open circles) ITOrubrene-doped NPBAlq3Mg-Ag (solid circles) IT0CuPc(15nm)NPBAlq3Mg-Ag (triangles)

Injection of Holes into Alq3 rArr Long Term Degradation of Device

Hany Aziz et al Science 283 1900(1999)

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 115: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

114OLED 기초공정 이해와 실습

DegradationDegradation

The area of circular features as a function of time measured forNPBCaAg and Alq3CaAg stacks deposited on both ITO and glass substrates

Circular features (left column) and dark spots of EL (right column) taken for the same OLED at different time intervals after it was fabricated (a) and (b) 7 h (c) and (d) 24 h

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 116: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

115OLED 기초공정 이해와 실습

DegradationDegradation

SIMS profiles for device structure of ITOHTLELCaAg

Dark non-emissive area in the devices after they were electrically stressed for 20 min (a) without parylene layer (b) with parylene layer

Metal diffusion into the polymers rArr Dark non-emissive areas in the Devices

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 117: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

116OLED 기초공정 이해와 실습

water vapor and oxygen less than 10-6 gm2day (at 38degC and 90 RH)

Vitex Systems (Sunnyvale CA)

박막박막 EncapsulationEncapsulation

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 118: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

117OLED 기초공정 이해와 실습

Degradation amp EncapsulationDegradation amp Encapsulation

Metal Can TypeMetal Can Type

Glass Cap TypeGlass Cap Type

Thin Film PackageThin Film Package

118OLED 기초공정 이해와 실습

감사합니다

Page 119: OLED기술 및 발광원리pds14.egloos.com/pds/200901/24/89/a0107989_497a6a… ·  · 2009-01-24Kyung-pook National University Display Technology Education Center 경북대학교디스플레이기술교육센터

118OLED 기초공정 이해와 실습

감사합니다