Effects of Bromine Substitution and Vacancy Defects on the Structural and Electronic Properties of Black Orthorhombic CsPbI₃ Perovskite

The structural and electronic properties of both Br substitution and vacancy structures of black orthorhombic CsPbI₃ (γ‐CsPbI₃) perovskite are investigated by carrying out first‐principle calculations in density functional theory (DFT). For mixed perovskites CsPb(I_1−x Br _x )₃, x is 0.0, 0.25, 0.5, 0.75, and 1.0, respectively. The studies suggest that the I_II site should be preferentially substituted by Br atom rather than the I_I site and the structure becomes more stable with increasing Br content. These compounds are direct‐bandgap semiconductors in the range of 1.887−2.137 eV. Moreover, the vacancy changes the electroconductibility of γ‐CsPbI₃. γ‐CsPbI₃:V_Pb and γ‐CsPbI₃:V_I exhibit p‐type and n‐type conductivity, respectively. γ‐CsPbI₃:V_Cs still is a semiconductor with a direct bandgap, which presents a slight decrease in electroconductibility due to the increase in bandgap. The calculated structural parameters show that both substitution and vacancy can induce structural distortion. Partial density of states (PDOS) suggests that the top of the valence band arises from hybridization of Pb s‐ and halogen p‐orbitals, whereas the bottom of the conduction band has predominantly Pb p‐orbitals for two kinds of crystal structures. These results provide strong support for developing high‐performance perovskite photovoltaic materials in optoelectronic devices.