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 deposi ted CdS/CdSe coupled films has been examined. Changes in surface struc ture and composition of coated and uncoated CdS250/CdSe coupled films as well as CdSe films have been examined by atomic force microscopy an d X-ray diffraction. The superior stability at short times of the coup led system, compared to CdSe, is related to the increase in the hexago nal character (stronger bonding) and the smaller recombination rate of the photogenerated carriers. At large operation times, the lower stab ility of the coupled system is related to band opening, which increase s the oxidation rates of the passivating Se/S layer. The recrystalliza tion illuminated CdSe photoanodes, and coupled films working in the da rk can be explained by the presence of surface states and back reactio ns. Stable short-circuit currents were obtained with coupled films coa ted with a thin layer (350 Angstrom) of ZnO. It is likely that oxidati on and redeposition of the protective ZnO film competes for hole consu mption. The rough morphology of the coated photoelectrodes correlates to a substantial increase in surface area that resembles ZnO particula te film electrodes sensitized by CdSe and CdS.