First‐Principles Calculations of the Structural, Electronic, and Optical Properties of Halide Perovskites γ‐CsPb(I1−xBrx)3

The structural, electronic, and optical properties of γ‐CsPb(Br x I 1− x ) 3 are explored using the first‐principles calculations. This study's findings reveal that the lattice parameters, the volume, the average Pb‐X ( X = I and Br) bond length, and the cohesive energy of γ‐CsPb(Br x I 1− x ) 3 decrease with increasing Br content. The standard bowing equation is adopted to do a fit for the bandgap with an increasing trend, yielding a bowing parameter of 0.29 eV. The bandgap enlargement is due to two factors. One is that the Br‐4 p orbital is lower than the I‐5 p orbital. It can cause a downward shift of the valence band maximum (VBM) when the Br content increases. The other is the enhancement of the total p–p coupling interaction because of the shortening of the average PbX bond length. It can shift the conduction band minimum upward and the VBM downward. Through analyzing the imaginary part of the dielectric function and the partial density of states, this study identifies four electron transitions ( E P1 , E P2 , E P3 , and E P4 ). The four electron transitions are also observed in the absorption coefficient spectra and the refractive index spectra. The results of the optical properties indicate that γ‐CsPb(Br x I 1− x ) 3 is a promising optoelectronic material with significant potential.