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.