All‐Inorganic Perovskite CsSnBr 3 as a Thermally Stable, Free‐Carrier Semiconductor

Hybrid organic-inorganic perovskites, especially methylammonium lead triiodide (MAPbI(3)), are intensely studied for their optoelectronic properties. The organic MA(+) cation is held responsible for the superior performance of MAPbI(3) but also its instability toward moisture and heat. To explore compositions beyond MAPbI(3), we performed experiments and calculations on two isomorphous perovskites CsSnBr3 and MASnBr(3). CsSnBr3 is slightly smaller than MASnBr(3) in cell dimension, but outperforms MASnBr(3) in band gap energy, charge-carrier reduced effective mass, and optical dielectric constant all by approximate to 19%. These merits accumulate to drastically cut the exciton binding energy from 33 meV for MASnBr(3) 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.