A composition-tunable ZnxCd1-xSe/ZnO core-shell nanowire array: mechanisms for the enhanced charge separation and its photovoltaic applications

A composition-tunable ZnxCd1-xSe/ZnO (0 < x <= 1) core-shell nanowire array has been fabricated on a conductive glass substrate by the hydrothermal growth and the subsequent ion-exchange reaction. The band gap of the ZnxCd1-xSe shell can be readily tuned by adjusting the temperature of the cation exchange reaction. The charge separation and transport ability of the ZnxCd1-xSe@ZnO with different cation exchange temperatures were investigated. Based on the powerful surface photovoltaic spectrum, the mechanism for the enhanced charge separation was discussed and the charge transport model was established. Moreover, the catalytic activities of three different counter electrode materials such as Cu2S, PbS, and Cu2ZnSnS4 were also evaluated based on the ZnxCd1-xSe@ZnO photoanode. Benefitting from the efficient charge separation at the interface of the ZnxCd1-xSe@ZnO core-shell nanowire array and the novel Cu2S counter electrode with a nanowall structure, a maximum photoelectric conversion efficiency of 1.70% has been achieved. Despite the lower conversion efficiency, our findings provided a better understanding of the charge separation and transport properties in type II core-shell heterojunctions.