Band alignment at sputtered ZnSx O1–x/Cu(In,Ga)(Se,S)2 heterojunctions

Valence band offsets ΔEVBM at ZnSx O1–x/Cu(In,Ga)(Se,S)2 (CIGSSe) heterojunctions have been studied by photoemission spectroscopy (XPS, UPS) as a function of composition x in sputtered ZnSx O1–x films. In the composition range from ZnO to ZnS we found ΔEVBM between –(2.1 ± 0.3) eV and –(0.8 ± 0.4) eV, respectively. Considering the optical band gaps, the conduction band offsets ΔECBM range from –(0.1 ± 0.3) eV to +(1.4 ± 0.4) eV. These results suggest that sputtered ZnSx O1–x is suitable as substitution for the CdS buffer and ZnO window layers in standard chalcopyrite-based solar cells. Current–voltage characteristics of the solar cells have been investigated as a function of the composition x. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)