Flexible chalcogenide perovskite Ba3Te2S7 with high electron mobility and strong optical absorption ability

Inorganic–organic hybrid halide perovskites exhibit outstanding optoelectronic characteristics, rendering them promising materials for photovoltaic applications. Despite achieving an impressive power conversion efficiency of up to 26.1%, their extensive use is hampered by the inherent instability of organic constituents and the toxicity associated with lead. With the motivation of searching for stable and non-toxic perovskite photovoltaic materials, we turned our attention to inorganic chalcogenide perovskites and performed extensive material screening excluding toxic elements. We found a stable and flexible chalcogenide perovskite Ba3Te2S7 with the distorted phase. This material boasts partial covalent bonds between Te4+ and S2− ions, enhancing both its structural stability and charge transfer capabilities. Furthermore, we observed a direct-to-indirect bandgap transition in Ba3Te2S7 with values of 0.39 eV and 0.37 eV from the monolayer to bulk, respectively. Notably, the electron mobility of Ba3Te2S7 can reach 104 cm2 V−1 s−1, surpassing hole mobility by two orders of magnitude. Moreover, the high optical absorption coefficient (105–106 cm−1) of bulk Ba3Te2S7 in the visible-light region, owing to the allowed band-edge optical transitions, combined with favorable conduction-band offsets for efficient electron injection from the absorber to the electron transporting layer (TiO2), positions Ba3Te2S7 as a promising material for photovoltaic applications.