Stable CdTe Photoanodes with Energetics Matching Those of a Coating Intermediate Band

A TiO2 coating was grown on a CdTe absorber by atomic layer deposition for stabilization against its photocorrosion during photoelectrochemical water splitting. Under simulated sunlight (AM 1.5G, 100 mW cm-2), this multilayer CdS/CdTe/TiO2/Ni/NiOx photoanode produced a light-limited photocurrent density of 24.5 ± 0.5 mA cm-2 and a photovoltage of 780 ± 20 mV. This record energy-conversion performance was comparable to those of baseline CdS/CdTe solar cells and was achieved only after the development of proper CdTe surface treatments prior to coating the stabilization layer. The TiO2 coating, with its in-gap charge-transport intermediate band, facilitates hole transport as light exits the CdTe/TiO2 interface. With proper interfacial chemistry, the electrochemical potential energy of the coating intermediate band matched that of the CdTe valence band. Moreover, the stabilized CdS/CdTe/TiO2/Ni/NiOx photoanodes showed 100 h stability for water oxidation under light-on/light-off cycles. This study provides insightful guidance for designing stabilization contacts for efficient and stable light-driven water oxidation.