Identifying Short-Range Disorder in Crystalline Bulk Cu2SnS3 Phases: A Solid-State Nuclear Magnetic Resonance Spectroscopic Investigation

Cu2SnS3 has recently attracted attention as a low-cost, earth-abundant absorber material for thin-film solar cells. Unfortunately, multiple Cu2SnS3 structures exist and the conditions under which different structures form are poorly defined. The structures of tetragonal and monoclinic Cu2SnS3 phases are clarified by use of solid-state nuclear magnetic resonance spectroscopy (ssNMR). The monoclinic Cu2SnS3 phase is shown to form under Sn-rich, Cu-poor conditions and the tetragonal Cu2SnS3 phase forms under Cu-rich, Sn-poor conditions, indicating that there is a composition difference between the structures that has not previously been reported. Furthermore, the monoclinic phase is destabilized at temperatures between 200 and 345 °C, when the material becomes tetragonal.