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Built-in Potential and Open Circuit Voltage of Heterojunction CuIn1-xGaxSe2 Solar Cells

Published online by Cambridge University Press:  01 February 2011

Akimasa Yamada
Affiliation:
National Institute of Advanced Industrial Science and Technology AIST Central 2, Umezono, Tsukuba 305-8568Japan
Koji Matsubara
Affiliation:
National Institute of Advanced Industrial Science and Technology AIST Central 2, Umezono, Tsukuba 305-8568Japan
Keiichiro Sakurai
Affiliation:
National Institute of Advanced Industrial Science and Technology AIST Central 2, Umezono, Tsukuba 305-8568Japan
Shogo Ishizuka
Affiliation:
National Institute of Advanced Industrial Science and Technology AIST Central 2, Umezono, Tsukuba 305-8568Japan
Hitoshi Tampo Hajime
Affiliation:
National Institute of Advanced Industrial Science and Technology AIST Central 2, Umezono, Tsukuba 305-8568Japan
Shibata Tomoyuki Baba
Affiliation:
Tokyo University of Science 2641 Yamazaki, Noda, Chiba 278-8510Japan
Yasuyuki Kimura
Affiliation:
Tokyo University of Science 2641 Yamazaki, Noda, Chiba 278-8510Japan
Satoshi Nakamura
Affiliation:
Tokyo University of Science 2641 Yamazaki, Noda, Chiba 278-8510Japan
Hisayuki Nakanishi
Affiliation:
Tokyo University of Science 2641 Yamazaki, Noda, Chiba 278-8510Japan
Shigeru Niki
Affiliation:
National Institute of Advanced Industrial Science and Technology AIST Central 2, Umezono, Tsukuba 305-8568Japan
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Abstract

The reasons why the open circuit voltage (Voc) of high-x CuIn1-xGaxSe2 (CIGS)/ZnO solar cells remain low are discussed. Here it is shown that the Voc ceiling can be interpreted simply on the basis of a model that the valence-band energy (Ev) of CIGS is almost immovable irrespective of x. When the conduction-band energy (Ec) of ZnO is lower than that of high-x CIGS (DEc<0), the built-in potential (Vbi) of a CIGS/ZnO junction is equivalent to the flat-band potential (Vbi) that arises from the separation between the Fermi energies of the two materials. If the Ev (and therefore the Fermi energy) of p-type CIGS is constant with increasing x, the Vbi and Voc that follows the Vbi remain unchanged since the Fermi energy of ZnO is constant. This unchangeable Voc reduces the conversion efficiency of high-x CIGS cells in cooperation with reduced photocurrents due to a larger bandgap. A positive offset, ΔEc>o gives rise to a photoelectrons barrier in the conduction-band that partially cancels Voc, thus the Voc of a low-x CIGS cell is governed by the Ec of CIGS. Based upon this concept, a material selection guideline is given for the windows and transparent electrodes appropriate for high-x CIGS absorbers-based solar cells.

Type
Research Article
Copyright
Copyright © Materials Research Society 2005

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References

1 , Landolt-Börnstein New Series, Semiconductors, III/17a, 17b, 17h ed. Madelung, O., Schulz, M. and Weiss, H. (Springer-Verlag, Berlin-Heidelberg, 1982, 1985).Google Scholar
2Measured at CART site (Oklahoma) using the FieldSpec Pro FR manufactured by Spectral Devices, Inc. of Boulder in collaboration with DOE's ARM Program (1996).Google Scholar
3 Ramanathan, K., Contreras, M. A., Perkins, C. L., Asher, S., Hasoon, F. S., Keane, J., Young, D., Romero, M., Metzger, W., Noufi, R., Ward, J. and Duda, A., Prog. Photovolt.: Res. Appl. 11, 225 (2003).Google Scholar
4 Shafarman, W.N., R. Klenk and McCandless, B.E., J. Appl. Phys. 79, 7324 (1996).Google Scholar
5 Herberholz, R., Nadenau, V., Rühle, U., Köble, C., Schock, H.W. and Dimmler, B., Solar Energ. Mater. Solar Cells 49, 227 (1997).Google Scholar
6 Zhang, S.B., Wei, S.H. and Zunger, A., J. Appl. Phys. 83, 3192 (1998).Google Scholar
7 Sugiyama, M., Nakanishi, H. and Chichibu, S.F., Jpn. J. Appl. Phys. 40, L428 (2001).Google Scholar
8 Turcu, M., K, I.M.ötschau and Rau, U., Appl. Phys. A 73, 769 (2001).Google Scholar
9 Schroeder, D.J., Hernandez, J.L., Berry, G.D. and Rockett, A.A., J. Appl. Phys. 83, 1519 (1998).Google Scholar
10 Swank, R.K., Phys.Rev. 53, 844 (1967).Google Scholar
11 Zhang, X.J., Ji, W. and Tang, S. H., J. Opt. Soc. Am. B 14, 1951 (1997).Google Scholar
12 Look, D.C., Mater. Sci. Eng. B 80, 383 (2001).Google Scholar
13 Yu, P.W., Faile, S.P. and Park, Y.S., Appl. Phys. Lett. 26, 384 (1975).Google Scholar
14 Matson, R.J., Noufi, R., Bachmann, K. J. and Cahen, C., Appl. Phys. Lett. 50, 158 (1987).Google Scholar
15 Minami, T., Miyata, T. and Yamamoto, T., Surf. Coat. Technol. 108-109, 583 (1998).Google Scholar
16 Tjeng, L.H., Vos, A.R. and Sawatzky, G.A., Surf. Sci. 235, 269 (1990).Google Scholar
17 Minemoto, T., Hashimoto, Y., Satoh, T., Negami, T., Takakura, H. and Hamakawa, Y., J. Appl. Phys. 89, 8327 (2001).Google Scholar
18 Ohtomo, A., Kawasaki, M., Koida, T., Masubuchi, K., Koinuma, H., Sakurai, Y., Yoshida, Y., Yasuda, T. and Segawa, Y., Appl. Phys. Lett. 72, 2466 (1998).Google Scholar
19 Matsubara, K., Tampo, H., Shibata, H., Yamada, A., Fons, P., Iwata, K., and Niki, S., Appl. Phys. Lett. 85, 1374 (2004).Google Scholar
20 Wilke, W., CMaierhofer, h. and Horn, K., J. Vac. Sci. Technol. B 8, 760 (1990).Google Scholar