Heterojunction solar cell with 2% efficiency based on a Cu2O substrate

We report on the fabrication of heterojunction solar cells made by deposition of transparent conducting oxide (TCO) films on ${\mathrm{Cu}}_2\mathrm{O}$ substrates. The TCO films have been grown by ion beam sputtering on good quality ${\mathrm{Cu}}_2\mathrm{O}$ sheets prepared by oxidizing copper at a high temperature. The best solar cell has reached an open-circuit voltage of $0.595\mathrm{V}$ , a short-circuit current density of $6.78\mathrm{mA}∕{\mathrm{cm}}^2$ , a fill factor of 50%, and a conversion efficiency of 2% under simulated AM1.5G illumination, which is the highest efficiency value reported for this kind of heterojunction devices. These devices represent a good starting point for the development of very low cost solar cells.