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. Experiments and calculations were performed on two lead‐free, isomorphous perovskites CsSnBr3 and MASnBr3. The all‐inorganic perovskite CsSnBr3 features a suitable bandgap for making tandem solar cells, and an exciton binding energy below thermal energy. CsSnBr3 also exhibits distinctly higher stability toward moisture and heat than its organic analogs.