PHOTOELECTROCHEMICAL EVIDENCE FOR SATURATED OPTICAL-ABSORPTION IN ELECTROLYTIC CUPROUS-OXIDE

An illuminated cuprous oxide-covered electrode immersed in alkaline media exhibits a nonlinear dependence of photocurrent on the intensity of 488 nm laser illumination. Results from intensity modulation experiments show that the differential efficiency for converting photons to photocurrent in the p-type cuprous oxide thin film is inversely proportional to the square root of illumination intensity. A charge transfer model that includes intensity dependent optical absorption in the cuprous oxide layer is found to be consistent with the observed photocurrent response. Analysis of the experimental results using the charge transfer model shows that the saturation intensity for cuprous oxide is approximately 100 mW/cm2. Photoelectrochemical charge transfer is found to be efficient in the potential region where the nonlinear photocurrent response is observed, with nearly all photoinjected minority carriers being consumed by the interfacial charge transfer reaction rather than by recombination.