Hybrid bulk heterojunction solar cells with vertically aligned ZnO/ZnO1-xSx nanorods in core-shell like nanostructure

Abstract

Hybrid inorganic-organic solar cells using vertically aligned ZnO nanorod array forming a core with nanocrystalline ZnO1-xSx shell integrated with polymeric P3HT+PCBM semiconductor blend are investigated. ZnO nanorod array over SnO2:F coated transparent conductor glass substrates are capped by sulfur chemiplating to create ZnO/ZnO1-xSx core-shell 3-dimensional electron transport electrode nanostructure. Dense array of vertically aligned nanorods help mitigate the short exciton diffusion length limitation in polymeric donor-acceptor blend by enhancing surface area and proximity with electron collector. The ZnO nanorod core via anion substitution at oxygen sites with sulfur increase p-type dopability of ZnO1-xSx shell and create a junction electric field. With low p-doped ZnO1-xSx shell in contact with P3HT+PCBM blend, this junction field is favorably directed to facilitate charge exciton dissociation, carrier separation and fast electron transport and minimize interface recombination. With large junction area, inclusive electric field and direct pathway through ZnO core for electron collection, the expected photocurrent enhancement is seen. Hybrid solar cells exhibit an overall conversion efficiency of 3.58% and strong dependence of photocurrent on the length of ZnO nanorods. The results indicate that the efficiency of such hybrid solar cells is significantly improved due to the unique morphology of the ZnO/ZnO1-xSx core-shell layer.