Tuning the Band Gap in CsPbBr3 Through Sr Substitution

The ability to continuously tune the band gap of a semiconductor allows its optical properties to be precisely tailored for specific applications. We demonstrate that the band gap of the halide perovskite CsPbBr3 can be continuously widened through homovalent substitution of Sr2+ for Pb2+ using solid-state synthesis, creating a material with the formula CsPb1-xSrxBr3 (0 ≤ x ≤ 1). Sr2+ and Pb2+ form a solid solution in CsPb1-xSrxBr3. Pure CsPbBr3 has a band gap of 2.29(2) eV, which increases to 2.64(3) eV for CsPb0.25Sr0.75Br3. Density-functional theory calculations support the hypothesis that Sr incorporation widens the band gap without introducing mid-gap defect states. These results demonstrate that homovalent B-site alloying is a viable method to tune the band gap of halide perovskites without introducing compensating defects that form when B-site cations of a different charge are introduced.