Potentiostatic deposition of Cu2O thin films on glass substrates coated with F-doped SnO2 from an alkaline electrolyte solution (pH 12.5) containing copper (II) sulfate and lactic acid was studied for fabrication of a Cu2O/Al-doped ZnO (AZO) heterojunction solar cell. The band gap of the electrodeposited Cu2O films was determined by photoelectrochemical measurements to be around 1.9 eV irrespective of the applied potentials. The solar cells with a glass/FTO/Cu2O/AZO structure were fabricated by sputtering an AZO film onto the Cu2O film followed by deposition of an Al contact by vacuum evaporation. The highest efficiency of 0.603% was obtained with a Cu2O film deposited at -0.6 V (vs. Ag/AgCl). This was attributed to better compactness and purity of the Cu2O film than those of the Cu2O films deposited at other potentials.