First-principles study on the electronic and optical properties of the orthorhombic CsPbBr3 and CsPbI3 with Cmcm space group.

Cesium lead halide perovskites are regarded as effective candidates for light-absorbing materials in solar cells, which have shown excellent performances in experiments such as promising power conversion efficiency. In this article, we analyze the electronic and optical properties of the orthorhombic CsPbBr3 and CsPbI3 with Cmcm space group based on the first-principles calculations, which are rarely studied experimentally and theoretically. In addition, we also analyze the properties of the cubic and orthorhombic CsPbBr3 and CsPbI3 with Pm3¯m and Pnma space groups for comparison, respectively. The optimized lattice constants of all phases of CsPbBr3 and CsPbI3 are in good agreement with the available experimental results. The calculated bandgap values of the cubic CsPbBr3 and CsPbI3, and the orthorhombic (Pnma) CsPbBr3 are in good agreement with the experimental data. The results show that the orthorhombic (Cmcm) CsPbBr3 and CsPbI3 are direct bandgap semiconductors with bandgap values of 2.358 eV and 2.062 eV, respectively, which are close to the bandgap values of their orthorhombic (Pnma) counterparts. In addition, the optical properties in the photon energy range of 0–4 eV indicate that the potential of the orthorhombic (Cmcm) CsPbBr3 and CsPbI3 as light-absorbing materials is close to that of the orthorhombic (Pnma) CsPbBr3 and CsPbI3, respectively. [ABSTRACT FROM AUTHOR]