The ternary compound semiconductor Cu2SnS3 (CTS) is formed from non‐toxic materials that are abundant in Earth's crust and other low‐cost elements. CTS has also been reported to a band gap energy range of 0.93–1.77 eV and an absorption coefficient of 1.0×104 cm–1. Consequently, CTS is a potential material for the p‐type absorber layer of thin film solar cells. In this study, we examined the dependence of the optical, electrical and photovoltaic properties of CTS thin films on the Cu/Sn composition ratio. CTS thin films were fabricated by sulfurizing evaporated Cu‐Sn precursors with different Cu/Sn composition ratios at 560 °C for 2 h in a N2 atmosphere and sulfur vapor. The Cu/Sn composition ratios of the sulfurized films were determined to be 1.6–2.5 by X‐ray fluorescence. The solar cell comprising a CTS thin film with a Cu/Sn composition ratio of 1.77 exhibited the best performance among the cells examined, an open‐circuit voltage of 242 mV, a short‐circuit current density of 28.9 mA/cm2, a fill factor of 41.7% and a conversion efficiency of 2.92% were obtained. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

We report on the sulfurization of metal-alloyed precursors in Cu 2 SnS 3 (CTS)-based thin-film solar cells. CTS thin films were prepared through the sulfurization of Cu-Sn alloy precursors at sulfurization temperatures of 500-580 °C for 2 h in a N 2 atmosphere with sulfur vapor. The Cu/Sn composition ratios of the sulfurized films were determined by X-ray fluorescence analysis to be in the range of 1.77-1.89. The photovoltaic properties of CTS-based solar cells improved with increasing sulfurization temperature owing to the higher external quantum efficiency at long wavelengths. The solar cell comprising a CTS thin film with a sulfurization temperature of 580 °C exhibited the optimum performance among the cells examined: an open-circuit voltage of 244 mV, a short-circuit current density of 29 mA/cm 2 , a fill factor of 0.385, and a conversion efficiency of 2.7% were obtained.

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%.

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The optical properties of Cu2SnS3 (CTS) bulk crystals grown by chemical vapor transport were studied by photoluminescence (PL) spectroscopy. The PL spectra from the CTS bulk crystals were analyzed as a function of excitation power and temperature. The main phase of the as-grown samples was determined to be monoclinic CTS by Raman spectroscopy. The observed PL spectra from the CTS bulk crystals were composed of peaks corresponding to free-exciton, two bound-excitons, and donor-acceptor pair recombination luminescence. The peak energies for the free-exciton and two bound-exciton emissions were 0.9317, 0.9291, and 0.9260 eV, respectively, at temperature of 4.2 K. The bound-exciton luminescence was not observed above 30 K. The thermal activation energies for the free-exciton and two bound-exciton emissions were 6.5, 4.8, and 5.2 meV, respectively. The fundamental band gap in the CTS bulk crystals was expected to be ca. 0.94 eV.