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Free keywords:
annealing; charge injection; copper compounds; II-VI semiconductors; indium compounds; nanorods; photoconductivity; photovoltaic effects; semiconductor-insulator-semiconductor structures; sulphur compounds; wide band gap semiconductors; zinc compounds
Abstract:
A ZnO-nanorod/In2S3/CuSCN radial heterostructure has recently shown promising photovoltaic conversion efficiencies. In this work, the charge separation and recombination in single ZnO/In2S3 and In2S3/CuSCN interfaces as well as the complete ZnO/In2S3/CuSCN structure were studied by time resolved microwave photoconductivity. Photoconductivity transients were measured for different thicknesses of the In2S3 light absorbing layer, under variation in the exciting light flux and before and after annealing of the ZnO nanorods at 450 °C. Upon excitation with 532 nm light, a long lived (millisecond) charge separation at the In2S3/ZnO interface was found, whereas no charge separation was present at the In2S3/CuSCN interface. The presence of the CuSCN hole conductor increased the initial amplitude of the time resolved microwave conductivity signal of the In2S3/ZnO interface by a factor of 8 for a 6 nm thick In2S3 layer, but the enhancement in amplitude dropped strongly for thicker films. The measurements show that the primary charge separation is located at the In2S3/ZnO interface but the charge injection yield into ZnO depends critically on the presence of CuSCN.
