Fabrication of Cu2GeS3-based thin film solar cells by sulfurization of Cu/Ge stacked precursors

In- and Se-free Cu 2 GeS 3 thin films were prepared by thermal evaporation followed by sulfurization, and photovoltaic cells with a glass/Mo/Cu 2 GeS 3 /CdS/ZnO:Al/Al structure were fabricated. The composition ratios of the obtained films were Cu/Ge = 1.96 and S/metal = 0.92 on glass, and Cu/Ge = 2.08 and S/metal = 0.94 on a Mo-coated glass substrate. By X-ray diffraction measurement, the sulfurized films were identified to be Cu 2 GeS 3 . By optical measurement, the band gap energy was estimated to be 1.5–1.6 eV. In the visible region, a Cu 2 GeS 3 film has an optical absorption coefficient that is on the order of 10 4 cm −1 . A solar cell fabricated using the Cu 2 GeS 3 thin film exhibited an open-circuit voltage of 380 mV and a conversion efficiency of 1.70%.