Hidden spontaneous polarisation in the chalcohalide photovoltaic Sn2SbS2I3

Enormous research efforts are currently devoted to the discovery of 'perovskite-inspired materials', aiming to replicate the astonishing optoelectronic performance of lead-halide perovskites (LHPs). Recently, chalco halides of group IV/V elements have attracted attention due to the stability provided by stronger metal-chalcogen bonds, alongside compositional flexibility and ns2 cations — a performance-defining feature of LHPs. Following the experimental report of stable, solution-grown tin-antimony sulfoiodide (Sn2SbS2I3) solar cells, with power conversion efficiencies above 4%, we comprehensively characterise the structural and electronic properties of this emerging material. We find that the experimentally-reported centrosymmetric Cmcm crystal structure represents an average over multiple polar Cmc2_1 configurations. This dynamic crystal structure and ferroelectric behaviour could benefit photovoltaic performance. Using state-of-the-art ab initio methods, we assess the efficiency limits of this material, finding maximal solar-conversion efficiencies η_max > 30 % with film thicknesses t > 0.5μm, at the radiative limit. Open-access Materials Horizons paper: https://doi.org/10.1039/D1MH00764E Talks on this and other works at: https://www.youtube.com/channel/UCoVGnBeZeWmKzv8_-PzCKCw