Solution processes in photoelectrochemical cells

The simplicity of construction of a photoelectrochemical cell (PEC) as compared with solid-state devices, combined with thin-film deposition technology, offers the potential for low-cost direct energy conversion. PEC’s utilizing cadmium chalcogenide photoanodes in alkali polysulfide solutions have shown sustained efficiency of solar-to-electric conversion over 12%. While the composition of the solution has been known for several years to have a remarkable effect on performance, the chemical and electrochemical processes involved remained obscure. We report here the result of a series of quantitative electrochemical experiments which show the species controlling the rate of hole-induced oxidation is disulfide, S2−2, whereas that controlling the reduction at the counterelectrode is the supersulfide ion, S−2, the product of the disulfide oxidation.