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A Neutral Barrier at CGS Grain Boundaries - Compositional and Structural Dependencies

Published online by Cambridge University Press:  01 February 2011

Michael Hafemeister ,
Susanne Siebentritt ,
Sascha Sadewasser ,
Christiane Frank-Rotsch  and
Martha Ch. Lux-Steiner
Michael Hafemeister
Affiliation:
michael.hafemeister@hmi.de, HMI Berlin, SE2, Glienicker Str.100, Berlin, 14109, Germany, +49 (030) 8062 2563 , +49 (030) 8062 3199
Susanne Siebentritt
Affiliation:
Siebentritt@hmi.de, Hahn-Meitner-Institut, Glienicker Str.100, Berlin, 14109, Germany
Sascha Sadewasser
Affiliation:
sadewasser@hmi.de, Hahn-Meitner-Institut, Glienicker Str.100, Berlin, 14109, Germany
Christiane Frank-Rotsch
Affiliation:
frank@ikz-berlin.de, Institut für Kristallzüchtung, Max-Born-Str. 2, Berlin, 12489, Germany
Martha Ch. Lux-Steiner
Affiliation:
lux-steiner@hmi.de, Hahn-Meitner-Institut, Glienicker Str.100, Berlin, 14109, Germany
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Abstract

Unlike other photoactive layers (e.g. Si) polycrystalline chalcopyrite layers achieve higher efficiency than monocrystalline ones. Although grain boundaries may play an important role for this phenomenon, there is currently no commonly accepted model for the electronic structure of grain boundaries. First experimental results on CuGaSe2 absorbers indicated a small neutral barrier for majority carriers (20-40meV) at sigma 3 grain boundaries, which is the predominant grain boundary in polycrystalline chalcopyrite absorbers [1]. These results are in discrepancy with theory, which predicts a 10 times higher barrier; we suspect that the copper excess might reduce the barrier height.

Here we present a study using Hall-effect and Kelvin Probe Force Microscopy (KPFM) measurements to investigate the composition dependence of the barrier height of epitaxially grown CuGaSe2 layers containing a sigma 3 grain boundary as a function of the Cu/Ga ratio. First results show that the barrier height is independent of the copper content. In addition, we present initial results on sigma 9 grain boundaries which are observed to occur in high efficiency absorbers.

Keywords

photovoltaicthin filmgrain boundaries
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1012: Symposium Y – Thin-Film Compound Semiconductor Photovoltaics-2007 , 2007 , 1012-Y09-04
Copyright
Copyright © Materials Research Society 2007

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