All-Inorganic Perovskite CsSnBr₃ as a Thermally Stable, Free-Carrier Semiconductor

Hybrid organic-inorganic perovskites, especially methylammonium lead triiodide (MAPbI₃ ), are intensely studied for their optoelectronic properties. The organic MA⁺ cation is held responsible for the superior performance of MAPbI₃ but also its instability toward moisture and heat. To explore compositions beyond MAPbI₃ , we performed experiments and calculations on two isomorphous perovskites CsSnBr₃ and MASnBr₃ . CsSnBr₃ is slightly smaller than MASnBr₃ in cell dimension, but outperforms MASnBr₃ in band gap energy, charge-carrier reduced effective mass, and optical dielectric constant all by ≈19 %. These merits accumulate to drastically cut the exciton binding energy from 33 meV for MASnBr₃ to 19.6 meV for CsSnBr₃ , making CsSnBr₃ a black, free-carrier semiconductor. CsSnBr₃ also exhibits distinctly higher stability toward moisture and heat than its organic counterparts. These advantages suggest ecofriendly applications for CsSnBr₃ , such as tandem solar cells and direct X-ray detectors.