We describe significant improvements of the photovoltaic properties that were achieved in Al-doped ZnO(AZO)/n-type oxide semiconductor/p-type Cu_2O heterojunction solar cells fabricated using p-type Cu_2O sheets prepared by thermally oxidizing Cu sheets. The multicomponent oxide thin film used as the n-type semiconductor layer was prepared with various chemical compositions on non-intentionally heated Cu_2O sheets under various deposition conditions using a pulsed laser deposition method. In Cu_2O-based heterojunction solar cells fabricated using various ternary compounds as the n-type oxide thin-film layer, the best photovoltaic performance was obtained with an n-ZnGa_2O_4 thin-film layer. In most of the Cu_2O-based heterojunction solar cells using multicomponent oxides composed of combinations of various binary compounds, the obtained photovoltaic properties changed gradually as the chemical composition was varied. However, with the ZnO–MgO and Ga_2O_3–Al_2O_3systems, higher conversion efficiencies(á/ as well as a high open circuit voltage(Voc/ were obtained by using a relatively small amount of MgO or Al_2O_3, e.g.,(ZnO)0:91–(MgO)0:09 and(Ga_2O_3/0:975–(Al_2O_3/0:025, respectively. When Cu_2O-based heterojunction solar cells were fabricated using Al_2O_3–Ga_2O_3–MgO–ZnO(AGMZO)multicomponent oxide thin films deposited with metal atomic ratios of 10, 60, 10 and 20 at.% for the Al, Ga, Mg and Zn, respectively, a high Vocof 0.98 V and an á of 4.82% were obtained. In addition, an enhanced á and an improved fill factor could be achieved in AZO/n-type multicomponent oxide/p-type Cu_2O heterojunction solar cells fabricated using Na-doped Cu_2O(Cu_2O:Na) sheets that featured a resistivity controlled by optimizing the post-annealing temperature and duration. Consequently, an á of 6.25% and a Vocof 0.84 V were obtained in a Mg F2/AZO/n-(Ga_2O_3–Al_2O_3//p-Cu_2O:Na heterojunction solar cell fabricated using a Cu_2O:Na sheet with a resistivity of approximately 10 cm and a(Ga_(0:975)A_(l0:025)/2O3 thin film with a thickness of approximately 60 nm.In addition, a Vocof 0.96 V and an á of 5.4% were obtained in a Mg F_2/AZO/n-AGMZO/p-Cu_2O:Na heterojunction solar cell. We describe significant improvements in the photovoltaic properties that were achieved in Al-doped ZnO (AZO) / n-type oxide semiconductor / p-type Cu_2O heterojunction solar cells prepared using p-type Cu_2O sheets prepared by thermally oxidizing Cu sheets. The multicomponent oxide thin film used as the n-type semiconductor layer was prepared with various chemical compositions on non-intentionally heated Cu_2O sheets under various deposition conditions using a pulsed laser deposition method. In Cu_2O-based heterojunction solar cells fabricated using various ternary compounds as the n- type oxide thin-film layer, the most photovoltaic performance was obtained with an n-ZnGa 2 O 4 thin-film layer. as the chemical composition was varied. However, with the ZnO-MgO and Ga 2 O 3 -Al 2 O 3 systems, higher conv ersion efficiencies (á / as well as a high open circuit voltage (Voc / were obtained by using a relatively small amount of MgO or Al 2 O 3, eg, (ZnO) 0: 91- (MgO) 0: 09 and (Ga 2 O 3 / 975- (Al 2 O 3/0: 025, respectively. When Cu 2 O-based heterojunction solar cells were fabricated using Al 2 O 3 -Ga 2 O 3 -MgO-ZnO (AGMZO) multicomponent oxide thin films deposited with metal atomic ratios 10, 60, 10 and 20 at. % of the Al, Ga, Mg and Zn, respectively, a high Voc of 0.98 V and an a of 4.82% were obtained. In addition, an enhanced á and an improved fill factor could be achieved in AZO / n-type multicomponent oxide / p-type Cu_2O heterojunction solar cells fabricated using Na-doped Cu_2O (Cu_2O: Na) sheets that have a resistivity controlled by optimizing the post-annealing temperature and duration. Mg F2 / AZO / n- (Ga_2O_3-Al_2O_3 // p-Cu_2O: Na heterojunction solar cell fabricated using a Cu_2O: Na sheet with a resistivity of approxima tely 10 cm and a (Ga_(0: 975) A_ (10: 025) / 2O3 thin film with a thickness of approximately 60 nm. Addition, a Vocof 0.96 V and an á of 5.4% obtained in a Mg F_2 / AZO / n-AGMZO / p -Cu_2O: Na heterojunction solar cell.