To achieve efficiency improvement of n-type oxide semiconductor/p-type Cu2O heterojunction solar cells fabricated using Cu2O sheets prepared by oxidizing thermally Cu sheets, the influence of heterojunction formation temperature on the obtainable conversion efficiency was investigated in different types of solar cells with Al-doped ZnO (AZO)/Cu2O and AZO/non-doped ZnO (ZO)/Cu2O structures. AZO/ZO/Cu2O p-n heterojunction and AZO/Cu2O Schottky barrier solar cells fabricated by forming AZO and ZO thin films at room temperature exhibited high efficiencies of 4.12 and 2.19%, respectively. Achieving higher efficiency solar cells requires that the surface of Cu2O sheets always be stabilized or treated using a low-damage deposition technique at a low deposition temperature. In addition to a surface condition improvement of Cu2O sheets, a significant improvement of obtained photovoltaic property in AZO/ZO/Cu2O heterojunction solar cells is attributable to enhanced potential barrier height and depletion layer width, resulting from the inserted buffer layer functioning as an n-type ZO layer as well as an active layer in the p-n heterojunction. (c) 2012 Published by Elsevier B.V.