Charge-transfer processes in coupled semiconductor systems. Photochemistry and photoelectrochemistry of the colloidal cadmium sulfide-zinc oxide system

Picosecond laser flash photolysis and photoelectrochemical studies have been carried out to elucidate the charge-transfer processes in CdS-ZnO coupled semiconductor systems. Charge injection from excited CdS into ZnO occurs within the laser pulse duration of 18 ps. Long-lived trapped charge carriers demonstrate the improved charge separation in CdS-ZnO coupled semiconductor systems. The feasibility of employing a colloidal CdS-ZnO system in a photoelectrochemical cell has been demonstrated by modifying the surface of an optically transparent electrode with ZnO and CdS colloids. Charge injection from excited CdS into ZnO particle on the electrode with ZnO and CdS colloids. Charge injection from excited CdS into ZnO particle on the electrode surface is confirmed by recording the photocurrent action spectra. An incident photon-to-photocurrent conversion efficiency of 15% has been observed for OTE/ZnO/CdS at 420 nm. 26 refs., 11 figs.