Thin-film photovoltaic cells composed of p-type Cu-doped US (CdS(Cu)) and n-type US layers (CdS(Cu)/CdS system) were fabricated by an all-vacuum deposition process. The cells showed a higher response in the longer-wavelength side than at the absorption edge of US with an increase in the thickness of the CdS(Cu) layer. High efficiency (over 8.5%) was obtained by improvement in CdS(Cu) layer fabrication. It is thought that the photovoltic effect of the cells is caused by a p-CdS(Cu)/n-CdS homojunction. (C) 2002 Published by Elsevier Science B.V.