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Investigation of the Sub-Bandgap Photoresponse in CuGaS2 : Fe for Intermediate Band Solar Cells

Authors


Thomas Unold, Helmholtz-Zentrum Berlin für Materialien und Energie, Solar Energy – Institute of Technology, Hahn-Meitner-Platz 1, 14109 Berlin, Germany.

E-mail: unold@helmholtz-berlin.de

ABSTRACT

Transition-metal doped chalcopyrite thin films have been proposed as a suitable absorber material for intermediate band solar cells. In this work, CuGa1−xFexS2 thin films were grown by vacuum co-evaporation at a substrate temperature of 400 °C with various amounts of incorporated Fe. The optical response of thin films grown on soda-lime glass was evaluated by transmittance/reflectance measurements. Photovoltaic devices were fabricated from CuGa1−xFexS2 thin films concurrently deposited on Mo-coated glass substrates using the standard chalcopyrite glass/Mo/absorber/CdS/ZnO device structure. The device characteristics of these solar cells were evaluated by current–voltage and quantum efficiency measurements. For Fe-containing CuGaS2 films, distinct sub-gap absorption bands at 1·2 eV and 1·9 eV are detected, which increase in prominence with increasing Fe content. On the other hand, the solar cell parameters were found to deteriorate with increasing iron content, indicating an increase in non-radiative recombination when high levels of iron are incorporated. However, for the lowest iron content (x = 0·003), an increase in the sub-gap photoresponse at about 1·9 eV is observed, which is attributed to a combination of sufficient intermediate band absorption and carrier collection at this dilution level. Copyright © 2011 John Wiley & Sons, Ltd.

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