Electrodeposited cuprous oxide thin films on indium-doped tin oxide (ITO) substrates were sulphided by exposing them to a spray of aqueous solution of sodium sulphide or to a mixture of hydrogen sulphide and nitrogen gases. Both methods produced light darker and darker films having different photovoltaic characteristics in a solar cell structure. The photovoltages produced by the light darker films under AM 1.5 illumination was negative as compared to the positive photovoltages produced by the darker films. Spectral response measurements revealed that most of the light darker films produced positive photovoltages in the shorter wavelengths and negative photovoltages in the longer wavelengths. However, Some of the light darker films produced only the negative photovoltage for the entire spectral range and their photovoltaic properties were comparatively better. Darker films resulted in only the positive photovoltages in the entire spectral range. As a result of the sulphidation, the bulk crystal structure of the cuprous oxide thin films was not changed, however, the interfacial characteristics of the solar cell structure were modified. (C) 2000 Elsevier Science B.V. All rights reserved.