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Study of Band Alignment at the Interface between CBD-CdS and CIGS grown by H2O-introduced co-evaporation

Published online by Cambridge University Press:  01 February 2011

Norio Terada ,
Hirotake Kashiwabara ,
Kazuya Kikunaga ,
Shimpei Teshima ,
Tetsuji Okuda ,
Shigeru Niki ,
Keiichiro Sakurai ,
Akimasa Yamada ,
Koji Matsubara  and
Shogo Ishizuka
Norio Terada
Affiliation:
terada@eee.kagoshima-u.ac.jp, Kagoshima University, Nano Structure and Advanced Materials, 1-21-40 Korimoto, Kagoshima, 890-0065, Japan, +81-99-285-7782, +81-99-285-7782
Hirotake Kashiwabara
Affiliation:
ee01016@h13.eee.kagoshima-u.ac.jp, Kagoshima University, 1-21-40 Korimoto, Kagoshima, 890-0065, Japan
Kazuya Kikunaga
Affiliation:
ee01023@h13.eee.kagoshima-u.ac.jp, Kagoshima University, 1-21-40 Korimoto, Kagoshima, 890-0065, Japan
Shimpei Teshima
Affiliation:
bt202029@ms.kagoshima-u.ac.jp, Kagoshima University, 1-21-40 Korimoto, Kagoshima, 890-0065, Japan
Tetsuji Okuda
Affiliation:
okuda@eee.kagoshima-u.ac.jp, Kagoshima University, 1-21-40 Korimoto, Kagoshima, 890-0065, Japan
Shigeru Niki
Affiliation:
shigeru-niki@aist.go.jp, Research Center for Photovoltaics, National Institute of Advanced Industrial Science and Technology, 1-1-1 Umezono, Tsukuba, 305-8568, Japan
Keiichiro Sakurai
Affiliation:
k-sakurai@aist.go.jp, Research Center for Photovoltaics, National Institute of Advanced Industrial Science and Technology, 1-1-1 Umezono, Tsukuba, 305-8568, Japan
Akimasa Yamada
Affiliation:
a.yamada@aist.go.jp, Research Center for Photovoltaics, National Institute of Advanced Industrial Science and Technology, 1-1-1 Umezono, Tsukuba, 305-8568, Japan
Koji Matsubara
Affiliation:
koji.matsubara@aist.go.jp, Research Center for Photovoltaics, National Institute of Advanced Industrial Science and Technology, 1-1-1 Umezono, Tsukuba, 305-8568, Japan
Shogo Ishizuka
Affiliation:
shogo-ishizuka@aist.go.jp, Research Center for Photovoltaics, National Institute of Advanced Industrial Science and Technology, 1-1-1 Umezono, Tsukuba, 305-8568, Japan
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Abstract

For understanding the origin of the improvements of properties in the CIGS-based cells, of which the CIGS absorber has been fabricated by H2O-introduced co-evaporation [CIGS-H2O], band alignment at the interfaces between chemical bath deposited CdS and CIGS-H2O with Ga substitution ratio ~ 40 % has been studied by photoemission and inverse photoemission spectroscopy. The CdS layer over the CIGS-H2O showed an identical electronic structure with that of CdS on the conventionally grown CIGS; band gap energy of 2.3 ~ 2.4 and a location of conduction band minimum (CBM) and valence band maximum (VBM) relative to Fermi level were + 0.75 eV and -1.6 ~ -1.7 eV, respectively. In the interface region, decreases of CBM and a rise of VBM were observed. Total amount of the decrease of CBM over the interface was 0.2 ~ 0.3 eV. XPS measurements of the core-level signals over the interface showed a small upward bend bending of 0.1 ~ 0.2 eV. Consequently, the conduction band offset (CBO) and valence bad offset (VBO) at the CBD-interface over the CIGS-H2O (Ga~40%) are about +0.1, and 0.9 ~ 1.1 eV, respectively. This positive CBO is contrast with a slightly negative CBO at the interface between CBD-CdS/conventionally grown CIGS with Ga ~ 40 % measured previously. These results indicate that the H2O introduction is effective to extend the upper limit of the Ga substitution ratio where the Type-I conduction band alignment is maintained. The observed band alignments are consistent with the rise of Voc and efficiency in the CIGS-H2O based cells.

Keywords

photovoltaicelectronic structurethin film
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1012: Symposium Y – Thin-Film Compound Semiconductor Photovoltaics-2007 , 2007 , 1012-Y07-04
Copyright
Copyright © Materials Research Society 2007

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