Tuning the Band Gap in the Halide Perovskite CsPbBr 3 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 CsPbBr 3 can be continuously widened through homovalent substitution of Sr 2+ for Pb 2+ using solid-state synthesis, creating a material with the formula CsPb 1- x Sr x Br 3 (0 ≤ x ≤ 1). Sr 2+ and Pb 2+ form a solid solution in CsPb 1- x Sr x Br 3 . Pure CsPbBr 3 has a band gap of 2.29(2) eV, which increases to 2.64(3) eV for CsPb 0.25 Sr 0.75 Br 3 . The increase in band gap is clearly visible in the color change of the materials and is also confirmed by a shift in the photoluminescence. 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 can be a viable method to tune the band gap of simple halide perovskites for absorptive and emissive applications such as color-tunable light-emitting diodes, tandem solar cells, and photodetectors.