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)
Estudios Estructurales: Calcopiritas
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
Estudios Estructurales: Calcopiritas
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
Estudios Estructurales: Calcopiritas
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
Estudios Estructurales: ODC
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)
Estudios Estructurales: ODC
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
Estudios Estructurales: ODC
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
Estudios Estructurales: ODC
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 Estructurales: ODC
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!
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