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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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
118OLED 기초공정 이해와 실습
감사합니다