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

Abstract

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.