This paper deals with homoepitaxial growth of Cu2O thin films using the electrochemical deposition (ECD) method. It also discusses the photovoltaic properties of solar cells that use the active layer of p-type Cu2O thin film prepared by epitaxial growth. Such a film was formed at 70 degrees C on a degenerated p-type Cu2O:Na (p(+) -type Cu2O: Na) substrate, and this film produced on a substrate with a (110) plane orientation was oriented only in the (110) plane. The crystallite size of the produced Cu2O thin film (58.8 nm) was larger than that of the film produced on FTO (SnO2: F) (14.6 nm). A photoelectric conversion efficiency of 236% was achieved for the AZO/p-type Cu2O thin film/p+-type Cu2O:Na heterojunction solar cell in which a degenerated Al-doped ZnO (AZO) thin film was prepared as the transparent electrode layer on the Cu2O thin film by pulse laser deposition. Furthermore, photoelectric conversion efficiency of 4.41% was achieved for the AZO/n-type Ga0.975Al0.025O/P-type Cu2O/p+-type Cu2O:Na heterojunction solar cell with n-type Ga0.975Al0.025O film inserted between the AZO and p-type Cu2O thin film. This clearly shows that the Cu2O thin film produced by epitaxial growth on a p(+)-type Cu2O:Na (p(+) - type Cu2O: Na) substrate is superior as an active layer. (C) 2016 Elsevier B.V. All rights reserved.