This paper describes an improved CdS/CdTe polycrystalline thin-film solar-cell device structure that integrates a zinc stannate (Zn2SnO4or ZTO) buffer layer between the transparent conductive oxide (TCO) layer and the CdS window layer. Zinc stannate films have a high bandgap, high transmittance, low absorptance, and low surface roughness. In addition, these films are chemically stable and exhibit higher resistivities that are roughly matched to that of the CdS window layer in the device structure. Preliminary device results have demonstrated that by integrating a ZTO buffer layer in bothSnO2-based andCd2SnO4(CTO)-based CdS/CdTe devices, performance and reproducibility can be significantly enhanced. ©1999 American Institute of Physics.