Photocorrosion of coupled CdS/CdSe photoelectrodes coated with ZnO - Atomic force microscopy and X-ray diffraction studies

The stability of photoelectrochemical cells based on chemically deposited CdS/CdSe coupled films has been examined. Changes in surface structure and composition of coated and uncoated CdS(250)/CdSe coupled films as well as CdSe films have been examined by atomic force microscopy and X-ray diffraction. The superior stability at short times of the coupled system, compared to CdSe, is related to the increase in the hexagonal character (stronger bonding) and the smaller recombination rate of the photogenerated carriers. At large operation times, the lower stability of the coupled system is related to band opening, which increases the oxidation rates of the passivating Se/S layer. The recrystallization illuminated CdSe photoanodes, and coupled films working in the dark can be explained by the presence of surface states and back reactions. Stable short-circuit currents were obtained with coupled films coated with a thin layer (350 Angstrom) of ZnO. It is likely that oxidation and redeposition of the protective ZnO film competes for hole consumption. The rough morphology of the coated photoelectrodes correlates to a substantial increase in surface area that resembles ZnO particulate film electrodes sensitized by CdSe and CdS.