Investig Grup Mat FV

Investigaciones en el Grupo de Materiales Fotovoltaicos

Universidad Autónoma de Madrid (U.A.M.)

España

Presentación

Estudios Estructurales Calcopiritas ODC: CuInxSey

Estudios Ópticos

Láminas Delgadas

Contenido de la charla

Presentación: localización

Presentación: miembros

Departamento de Física Aplicada (U.A.M.):

Dr. Máximo León (Director del grupo) Dr. José Manuel Merino Dra. Ursula Fillat E. Josué Friedrich (PhD student)

External: Dr. Julio Ramiro (U. Rey Juan Carlos)

Presentación: colaboraciones Department of Semiconducting Materials Science (Institute of

Applied Physics, Chisinau, Moldova) Dr. Ernest Arushanov, Dr. Leonid Kulyuk, Dr. Sergei Levcenko

Department of Semiconductor Materials Technology (Tallinn Technical University, Tallinn, Estonia) Dr. Juri Krustov, Maarja Groossberg

Department of Radioelectronics (Belarusian State University of Informatics and Radioelectronics, Minsk, Belarus) Dr. I. V. Bodnar

Department of Solid State Physics (Physico-Technical Institut, Ioffe Institut, St. Petersburg, Russia) Dr. Y. V. Rud, Dr. B. Bairamov

Presentación: colaboraciones Photovoltaic Energy Unit (Department of Energy, C.I.E.M.A.T.

Madrid) Dr. M.T. Gutiérrez, Dr. J. Herrero, Dr. C. Guillén, J. Trigo

Departament of Physics, University of Zulia LUZ, Maracaibo, Ve. Dr. C. Durante-Rincón, E. Hernández

Institut of Polimers CSIC, Madrid Dr. J. Abajo

Department of Heterogeneous Material Systems (DAAD Exchange Programme, Hahn-Meitner Institut) Dr. T. Schedel-Niedrig, Dr. S. Schorr, Dr. S. Lehmann

Zinc Blenda

Estudios Estructurales: CalcopiritasCompuestos Compuestos

semiconductores semiconductores tipo I-III-VItipo I-III-VI22

Estudios Estructurales: Calcopiritas

Rietvel refinement of XRD diagrams for samples with different Cu contents

[J. Appl. Phys.80(10), 5610-6 (1996)]

ab

c

Cu

In

Se

La estructura requiere solo La estructura requiere solo tres parámetros: a, c , x. tres parámetros: a, c , x.

GE IGE I42d, 42d, con el Cu en con el Cu en posiciones de Wyckoff 4a posiciones de Wyckoff 4a (0,0,0), el In en 4b (0,0,1/2) (0,0,0), el In en 4b (0,0,1/2) y el Se en 8d (y el Se en 8d (xx,1/4,1/8),1/4,1/8)

La estructura requiere solo tres parámetros: a, c , x.

Rietvel refinement of XRD diagrams for samples with different Cu contents

[J. Appl. Phys.80(10), 5610-6 (1996)]

ab

c

Cu

In

Se

0.80 0.85 0.90 0.95 1.00

0.224

0.226

0.228

0.230

0.232

0.234

0.236

(b )

Cu-content (atom fraction)

x[S

e]

(Å)

x[Se] decreases with N(Cu): Cu-Se bond strengthened.

0.80 0.85 0.90 0.95 1.002.42

2.43

2.44

2.45

2.46

2.56

2.57

2.58

2.59

2.60

dIn-Se

dCu-Se

Inte

rato

mic

dis

tan

ces

(Å)

Cu-content (atom fraction)

dCu-Se decreases and dIn-Se increases with N(Cu)


Phillips & Van Vechten theory of solids

+ Jaffe & Zunger band structure calculations

+ available data on Cu-(Al,Ga,In)-(S,Se,Te) ternary chalcopyrites

new set of Cu-VI bond ionicities (fi,Cu-VI) derived

0.21 0.22 0.23 0.24 0.25 0.26 0.27 0.280.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65dCuGaS

2

eCuGaS2

dCuAlS2

eCuAlS2

cCuGaSe2

dCuAlSe2

fCuAlSe2

hC uAlTe2iC uAlTe

2

gC uAlTe2

dCuGaSe2

cCuGaSe2

aCuGaTe2gCuGaTe

2

bC uInSe2b,dC uInSe

2

d,eC uInS2

gCuInTe2

aCuInTe2

f i,Cu

-CV

I

x [anion]

Cu-VI bond more covalent than III-VI bond (more ionic)

fi,Cu-VI increases with x[VI]

x[VI] reasonable estimation of Cu-VI bond ionicity

º


XPS measurements in CuGaSe2, CuGaTe2, CuInSe2 and CuInTe2 samples

Auger parameter () for Cu, Ga, In, Se and Te, related to the free elements

Binding energies respect to Cu, for all the anion-cation bondings

Binding energies related to the free elements, Eb(Cu-VI) and Eb(III-VI)

From Eb and , the Chemical shift was deduced

0,25 0,30 0,35 0,40 0,45 0,50 0,55 0,60 0,65

0,05

0,10

0,15

0,20

0,25

0,30

0,35

0,40

0,45

No

rmal

ised

Ionicities


Phase transitions study in CuInSe2 and CuIn3Se5 ID15 (ESRF), High energy beamline

MAR imageplate detector

Primary X-ray beam(300m×300m)

E ~ 87 KeVCeramic oven(RT to ~1000oC)

Rotating ampoule withthe pre-sinthesised sample

(diffraction

cones)

(diffraction image)

Estudios Estructurales: ODC

High statistics Reducing preferred orientation effects

CuIn3Se5 at 600oC CuIn3Se5 at room temperature


Temperature

(oC)S. G. RB% Rwp% a (Å) c (Å)

x(Se)*/

y(Se)*/

z(Se)*

CuInSe2

R. T. I-42d 2.77 6.35 5.7876(1) 11.6296(4) 0.2254(3)

847 F-43m 6.85 11.07 5.8527(2) ----- -----

CuIn3Se5

R. T. P-42c 1.78 7.52 5.7592(3) 11.537(1)0.2566(4)/0.2223(5)/0.1305(5)

600 F-43m 3.53 11.70 5.7982(2) ----- -----

J. Phys. Chem. Solids 64, 1649-52 (2003)


Controversy in the local structure around Cu and In atoms in In-rich compounds, in the Cu-Se and In-Se bond lengths (XRD, EXAFS) [C.-H. Chang, S.-H. Wei, J.W. Jonson, S.B. Zang, N. Leyarovska, G. Bunker, T.J. Anderson, Phys. Rev. B 68, 54108 (2003).]

EXAFS measurements at Cu-K and In-K absorption edges in CuInSe2 (different Cu contents), Cu2In4Se7 and CuIn3Se5

Thin Solid Films 480-481, 295-300 (2005)

No apparent change in In-Se bond distance

Cu-Se bond distance tends to decrease

Higher Debbye-Waller factors for the Cu-Se bond


De las medidas de α con hν justo bajo el gap fundamental de diversos ODC (CuIn4Se6 and CuIn5Se8) se dedujo la energía de Urbach EU

EU se modela con un oscilador de Einstein:

CuIn5Se8 EU = 13.9 + 5.9(e222/T -1) -1

EU(X, T ) = EU(X) + EU(T)

X representa el desorden estructural

T refleja el desorden termicamente inducido


A Tamb el desorden estructural es el dominante debido a:

Inhomogeneidades estructurales Diferentes politipos

Si hubiera politipos (proposed by Wei) deberia darse una reducción en la intensidad de ciertas reflexiones; (103), (211) and (301) que no se observan.

Es más probable que haya microcristales con la misma estructura cristalina y diferente composición, aunque próxima.


Estudios ÓpticosOptical characterization of AgxCu1-xInSe2, CuIn1+2nSe2+3n and

CuGa1+2nSe2+3n (n=2.5, 3.0, 3.5) crystals by spectroscopic ellipsometry

Spectroscopic ellipsometry (SE) is an excellent technique for investigating the optical response of semiconductors, in particular, for determining the complex dielectric function ()=1()+i2(), related to the electronic band structure .

The analysis of the dielectric function has allowed us to identify and evaluate the energy of the electronic transitions E0 , E1(A) and E1(B).

Fig. shows experimental spectra of the real 1 () and

imaginary 2() components of the complex dielectric

function () of CuIn3Se5, CuGa3Se5 and CuGa5Se8

crystals.

Estudios Ópticos

Second numerical derivative spectra from the real (1) and imaginary (2)

part of the dielectric function for CuIn3Se5

Symbols display experimental data and lines the results of the fits. The arrows mark the obtained critical-point

energies.

The second-derivative spectra and theoretical fitting are shown on Figs. 4 to 6. The fits have been obtained considering:1. CPs of 3D type in the Eg region

2., CPs of the 2D type in the E1 region.

Table Fit parameters of the CP’s : A= amplitude,

E = energy threshold, = broadening and =phase angle

Transition Parameters CuIn3Se5

E0(4-1) A

E(eV)

(eV)

0.046(7)

1.160(5)

0.100 (5)

-86(8)

E1(A)

N1(V1)- N1(C1)

A

E(eV)

(eV)

2.1(4)

2.57(4)

0.34(4)

16(10 )

Band structure calculation not avalaible for OVC. Identification done using the CIS and CGS band structure calculations

The fundamental absorption edge E0=Eg can be related to an electronic transition of type. This threshold correspond to direct transition from VBM to CBM

Table Fit parameters of the CP’s .

Transitions Parame-ter CuGa3Se5 CuGa5Se8

E0(4-1)

A

E(eV)

(eV)

0.13(5)

1.87(4)

0.26(4)

-109(23)

0.10(1)

1.86(1)

0.22(1)

-169(8)

E1(A)

N1(V1)- N1(C1)

A

E(eV)

(eV)

1.8(3)

2.87(2)

0.35(3)

7*

1.0(1)

2.90(1)

0.28(2)

0*

E1(B)

N1(V2)- N1(C1)

A

E(eV)

(eV)

0.08(2)

4.01(3)

0.22(3)

172(12)

0.41(4)

3.88(3)

0.30(2)

78(11)

Estudios Opticos

The behaviour of Eg in CuInSe2 samples with different Cu/In ratios, 0.8 ≤ Cu/In ≤ 1.05, tends to decrease

Band gap values obtained from ellipsometry, reflectance and transmittance measurements in CuInSe2 and several ODC samples

In ternary compounds with compositions between Cu2In4Se7 and CuIn4Se6, it results in a very similar trend, i.e., a linear decrease with Cu/In

Explicación?

The stability of the Cu2Se-In2Se3 tie line results from the repetition of m units of the defect pair ( ) for every unit of CuInSe2

[S.B. Zhang, S. Wei & A. Zunger. Phys. Rev. Letters

78, 4059 (1997)]

The presence of a Cu vacant implies a shift of Se atom in the opposite direction x[Se] ↑Cu/In ratio decreases when increasing the number of such pairs.

Cu/In ↓ x[Se] ↑

22 CuCu InV

a

b

c

Cu

In

Se

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.00.220

0.225

0.230

0.235

0.240

0.245

0.250

0.255

0.260

0.265

X

(Se)

Cu/In

The upper valence band, in ternaries Cu chalcopyrite, is composed of Cu3d and Se4p electrons. The repulsive p-d interaction pushes the antibonding p-d state that constitutes the valence band maximum (VBM) to higher energies.

[S-H. Han, A. M. Hermann, F. S. Hasoon, H. A. Al-Thani and D. H. Levi. Appl. Phys. Lett. 85 576 (2004)] [S-H. Han, F. S. Hasoon, H. A. Al-Thani, A. M. Hermann and D. H. Levi. Appl. Phys. Lett. 86 021903 (2005)]

Due to the Cu-defect, the p-d repulsion should be lower than in stoichiometric compounds, inducing a lowering of the VBM and an increasing of the band gap energy.

The bigger slope in the case of the ODC compounds could be attributed to the formation of a higher number of ( ) pairs, lowering the VBM and then increasing the band gap energy as Cu/In diminishes

22 CuCu InV

Moldavian J. Appl. Phys. (to be published); 3rd MSCMP, Chisinau (Moldova)

Explicación?

Thin films

Flash evaporation: Useful for compounds with

different vapour pressures of the constituents

Relatively low substrate temperatures: 300oC – 350oC

C – crucible TP-S – substrates thermocoupleH – oven TP-C – crucible thermocoupleP – porta-substrates ME – thickness monitorSh – shutter Co – powder containerT – quartz tube

Thin films

Cu/In ratio controlled by deposition conditions: crucible temperature and deposition rate; Cu/Se by substrate temperatures

After optimisation of the conditions and annealings: single chalcopyrite phase, 1-2 µm grain size

As grown

After annealing

Thin films O.D.C. (~ CuIn3Se5) on the active layer, deposited by co-evaporation CdS by chemical bath method ZnO by sputtering. 1 cm2 area

0.0 0.1 0.2 0.3 0.40

5

10

15

20

25

30

CuInSe2

Idem + T.T . 200oC/2 min.

"as grown" After T.T.F.F. 39.87 44.48 2 .97 5 .07

JS

C (

mA

/cm

2)

Voltage (V)0.0 0.1 0.2 0.3 0.4

0

5

10

15

20

25

"as grown" After T.T.F.F. 61 .66 63 .40 5 .06 5 .93

CuG a0.2 5

In0.7 5

Se2

Idem + T.T . 200oC/2 min.

JS

C (

mA

/cm

2)

Voltage (V)

(CIS) = 5.1%; (CIGS) = 5.9% Thin Solid Films 361-362, 22-7 (2000)

Thin films

Oscillating porta-substrates to improve homogeneity in areas of 3×3 cm2 areas

“Flash” deposition and characterisation of several ODC: CuInxSey, CuGaxSey (as well as (CuGa,In)Se2)

Thin films

Tandem solar cells, in collaboration with the group of the CIEMAT

Profiting of two different parts of the solar spectrum because of two different gaps: 1.7 eV (upper absorber) 1.1 eV (down )

Different materials for the heterojunction

Glass

ITO

ITO

ITO

ITO

ODC (n)

Cu(Ga,In)(Se)2 (p)

Al

In2S3

Cu(In,Ga)S2

Single cells on flexible kapton/polymides substrates

Thin films Solar cells in mesoporous

templates: preliminary attempts

200 nm diameter pores

¡Muchas Gracias por su amable atención!

Documents

Investig Grup Mat FV