Earth abundant thin film solar cells from co-evaporated Cu2SnS3 absorber layers

Cu2SnS3 (CTS) is starting to gain interest in the PV research community as an alternative earth abundant absorber for thin film photovoltaics. In this work, the structure, morphology and the composition of the CTS absorbers as well as their influence on the optoelectronic properties of the solar cells are analysed. The synthesis of Cu-Sn-S thin films by co-evaporation at a nominal temperature of 400 °C is presented. A combination of X-ray diffraction, Raman and UV-Vis spectroscopy suggests that the Cu2SnS3 is crystallising in a cubic structure with disorder in the Cu and Sn sites, leading to substantial band tailing. The best device was fabricated from absorbers exhibiting a Cu/Sn ratio of approximately 1.7 and had an efficiency of 1.8%, a short circuit current of 28 mA cm−2, and an open circuit voltage of 147 mV with a fill factor of 42.9%. From the quantum efficiency measurement, we estimate a band gap of 1.06 eV for the CTS absorber material. Capacitance-voltage measurements show charge carrier concentrations between 4 and 6 × 1016 cm−3.