Fabrication of Cu2SnS3 thin-film solar cells with power conversion efficiency of over 4%

Cu2SnS3 (CTS) thin films were produced by the co-evaporation of Cu, Sn, and cracked sulfur, followed by annealing. The as-deposited films were then annealed at 570 degrees C for 5 min in the presence of 100 mg of sulfur lumps in a rapid thermal processing furnace filled with N-2 gas at atmospheric pressure. Solar cells were then fabricated using the CTS films as absorber layers, and their efficiency was evaluated for different Cu/Sn compositional ratios. The largest grain size was found for films with a slightly Sn-rich composition. The highest performance was obtained for solar cells containing a CTS thin film with a Cu/Sn ratio of about 1.9. A cell with a Cu/Sn ratio of 1.87 exhibited an open-circuit voltage of 258 mV, a short-circuit current density of 35.6mA/cm(2), a fill factor of 0.467, and a power conversion efficiency of 4.29%. (C) 2015 The Japan Society of Applied Physics