Photovoltaic properties of single-crystal CdS-Cu2S cells

Photovoltaic cells have been prepared by plating a variety of undoped and doped single-crystal slices of CdS with Cu 2 S. The dopants investigated included copper, indium and chlorine. It is shown that the optimum starting material for maximum photovoltaic efficiency is copper doped with CdS with a dark resistivity of the order 10 2 Ω cm. Devices prepared on copper-doped crystals have such desirable features as fast speed of response, good temperature stability and saturation of the open-circuit voltage at low light intensities. Good efficiency is only obtained in cells formed on undoped CdS after a period of baking in air at 200 °C, which reduces their speed of response and introduces some other undesirable features. These effects are thought to originate with optical absorption processes in a high-resistivity, photoconductive region of CdS which is produced by copper diffusion at the interface.