This paper introduces the present status and prospects for further efficiency improvement of Cu2O-based p-n heterojunction solar cells that feature an n-type oxide semiconductor thin film/p-Cu2O sheet structure. This structure was achieved by both stabilizing the surface of polycrystalline p-Cu2O sheets that had been prepared by thermal oxidization of Cu sheets and also developing low-temperature and low-damage deposition technology for applying thin films as an n-oxide semiconductor layer. The highest efficiency of 5.38% and open circuit voltage of 0.8 V were obtained in an AZO/n-Ga2O3/p-Cu2O heterojunction solar cell fabricated with a non-doped Ga2O3 thin film prepared on a Cu2O sheet at room temperature with a thickness of 75 nm under an O-2 gas pressure of 1.7 Pa by a pulsed laser deposition. It should be noted that the obtainable photovoltaic properties in AZO/n-oxide semiconductor/p-Cu2O heterojunction solar cells are considerably more affected by the surface condition of the p-Cu2O layer, i.e., the interface at the heterojunction, than the diffusion potential resulting from the difference of work functions between the p-Cu2O and n-semiconductor layers. To achieve a higher efficiency in AZO/n-oxide semiconductor/p-Cu2O heterojunction solar cells, it is necessary to improve the interface at the heterojunction as well as reduce the series resistance and increase the parallel resistance of the heterojunction solar cells. (C) 2013 Elsevier B.V. All rights reserved.