Strong Electron Localization in Tin Halide Perovskites.

Tin halide perovskites (THPs) have been established as a lower-toxicity alternative to lead halide perovskites. In spite of the increasing interest, the behavior of photoexcited charges has not been well understood in this class of materials. We here investigate the behavior of excess electrons in a series of tin halide perovskites by employing advanced electronic-structure calculations. We first focus on CsSnBr and show that electron localization is favorable in this compound and that bipolaronic states are the most stable form of self-trapped electrons. We then extend the analysis to CsSnI, CsSnCl, MASnBr, FASnBr, and DMASnBr and show that electron bipolarons are stable in all these compounds, thus indicating that strong electron localization is recurrent in THPs.