Cu2-xS Surface Phases and Their Impact on the Electronic Structure of CuInS2 Thin Films – A Hidden Parameter in Solar Cell Optimization

Authors

  • Marcus Bär,

    Corresponding author
    1. Solar Energy Research, Helmholtz-Zentrum Berlin für, Materialien und Energie GmbH, Hahn-Meitner-Platz 1, D-14109 Berlin, Germany
    2. Institut für Physik und Chemie, Brandenburgische Technische Universität Cottbus, Konrad-Wachsmann-Allee 1, D-03046 Cottbus, Germany
    3. Department of Chemistry, University of Nevada, Las Vegas, Las Vegas, NV 89154, U.S.A.
    • Solar Energy Research, Helmholtz-Zentrum Berlin für, Materialien und Energie GmbH, Hahn-Meitner-Platz 1, D-14109 Berlin, Germany.
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  • Joachim Klaer,

    1. Solar Energy Research, Helmholtz-Zentrum Berlin für, Materialien und Energie GmbH, Hahn-Meitner-Platz 1, D-14109 Berlin, Germany
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  • Lothar Weinhardt,

    1. Department of Chemistry, University of Nevada, Las Vegas, Las Vegas, NV 89154, U.S.A.
    2. Institute for Photon Science and Synchrotron Radiation, Karlsruhe Institute of Technology, D-76344 Eggenstein-Leopoldshafen, Germany
    3. ANKA Synchrotron Radiation Facility, Karlsruhe Institute of Technology, D-76344 Eggenstein-Leopoldshafen, Germany
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  • Regan G. Wilks,

    1. Solar Energy Research, Helmholtz-Zentrum Berlin für, Materialien und Energie GmbH, Hahn-Meitner-Platz 1, D-14109 Berlin, Germany
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  • Stefan Krause,

    1. Department of Chemistry, University of Nevada, Las Vegas, Las Vegas, NV 89154, U.S.A.
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  • Monika Blum,

    1. Department of Chemistry, University of Nevada, Las Vegas, Las Vegas, NV 89154, U.S.A.
    2. Advanced Light Source (ALS), Lawrence Berkeley National Laboratory, Berkeley, CA 94720, U.S.A.
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  • Wanli Yang,

    1. Advanced Light Source (ALS), Lawrence Berkeley National Laboratory, Berkeley, CA 94720, U.S.A.
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  • Clemens Heske,

    1. Department of Chemistry, University of Nevada, Las Vegas, Las Vegas, NV 89154, U.S.A.
    2. Institute for Photon Science and Synchrotron Radiation, Karlsruhe Institute of Technology, D-76344 Eggenstein-Leopoldshafen, Germany
    3. ANKA Synchrotron Radiation Facility, Karlsruhe Institute of Technology, D-76344 Eggenstein-Leopoldshafen, Germany
    4. Institute for Chemical Technology and Polymer Chemistry, Karlsruhe Institute of Technology, D-76128 Karlsruhe, Germany
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  • Hans-Werner Schock

    1. Solar Energy Research, Helmholtz-Zentrum Berlin für, Materialien und Energie GmbH, Hahn-Meitner-Platz 1, D-14109 Berlin, Germany
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Abstract

The surface properties of CuInS2 (CIS) thin-film solar cell absorbers are investigated by a combination of electron and soft X-ray spectroscopies. Spatially separated regions of varying colors are observed and identified to be dominated by either CuS or Cu2S surface phases. After their removal by KCN etching, the samples cannot be distinguished by eye and the CIS surface is found to be Cu-deficient in both regions. However, a significantly more pronounced off-stoichiometry in the region initially covered by Cu2S can be identified. In this region, the resulting surface band gap is also significantly larger than the EgSurf of the initially CuS-terminated region. Such variations may represent a hidden parameter which, if overlooked, induces irreproducibility and thus prevents systematic optimization efforts.

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