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Valence band offsets at Cu(In,Ga)Se2/Zn(O,S) interfaces

Adler, Tobias and Botros, Miriam and Witte, Wolfram and Hariskos, Dimitrios and Menner, Richard and Powalla, Michael and Klein, Andreas (2014):
Valence band offsets at Cu(In,Ga)Se2/Zn(O,S) interfaces.
In: physica status solidi (a), 211 (9), WILEY-VCH Verlag GmbH & Co. KGaA, pp. 1972-1980, ISSN 18626300,
[Online-Edition: http://dx.doi.org/10.1002/pssa.201330353],
[Article]

Abstract

The energy band alignment at interfaces between Cu-chalcopyrites and Zn(O,S) buffer layers, which are important for thin-film solar cells, are considered. Valence band offsets derived from X-ray photoelectron spectroscopy for Cu(In,Ga)Se2 absorber layers with CdS and Zn(O,S) compounds are compared to theoretical predictions. It is shown that the valence band offsets at Cu(In,Ga)Se2/Zn(O,S) interfaces approximately follow the theoretical prediction and vary significantly from sample to sample. The integral sulfide content of chemical bath deposited Zn(O,S) is reproducibly found to be 50–70%, fortuitously resulting in a conduction band offset suitable for solar cell applications with Cu(In,Ga)Se2 absorber materials. The observed variation in offset can neither be explained by variation of the Cu content in the Cu(In,Ga)Se2 near the interface nor by local variation of the chemical composition. Fermi level pinning induced by high defect concentrations is a possible origin of the variation of band offset.

Item Type: Article
Erschienen: 2014
Creators: Adler, Tobias and Botros, Miriam and Witte, Wolfram and Hariskos, Dimitrios and Menner, Richard and Powalla, Michael and Klein, Andreas
Title: Valence band offsets at Cu(In,Ga)Se2/Zn(O,S) interfaces
Language: English
Abstract:

The energy band alignment at interfaces between Cu-chalcopyrites and Zn(O,S) buffer layers, which are important for thin-film solar cells, are considered. Valence band offsets derived from X-ray photoelectron spectroscopy for Cu(In,Ga)Se2 absorber layers with CdS and Zn(O,S) compounds are compared to theoretical predictions. It is shown that the valence band offsets at Cu(In,Ga)Se2/Zn(O,S) interfaces approximately follow the theoretical prediction and vary significantly from sample to sample. The integral sulfide content of chemical bath deposited Zn(O,S) is reproducibly found to be 50–70%, fortuitously resulting in a conduction band offset suitable for solar cell applications with Cu(In,Ga)Se2 absorber materials. The observed variation in offset can neither be explained by variation of the Cu content in the Cu(In,Ga)Se2 near the interface nor by local variation of the chemical composition. Fermi level pinning induced by high defect concentrations is a possible origin of the variation of band offset.

Journal or Publication Title: physica status solidi (a)
Volume: 211
Number: 9
Publisher: WILEY-VCH Verlag GmbH & Co. KGaA
Uncontrolled Keywords: buffer layers, Cu(In,Ga)Se2, photoemission, valence band offset, ZnO, ZnS
Divisions: 11 Department of Materials and Earth Sciences > Material Science > Surface Science
11 Department of Materials and Earth Sciences > Material Science
11 Department of Materials and Earth Sciences
Date Deposited: 27 Feb 2015 13:11
Official URL: http://dx.doi.org/10.1002/pssa.201330353
Identification Number: doi:10.1002/pssa.201330353
Funders: Funded by the German Bundesministerium für Bildung und Forschung (BMBF). Grant Number: 03SF0359
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