The distinctive phase stability and defect physics in CsPbI₂Br perovskite

In this work, the structural, optoelectronic, and defect properties of both the α-phase and β-phase CsPbI₂Br are investigated based on first-principles calculations. First, we calculate the bandgap of α-CsPbI₂Br using the standard HSE06 method which is in accordance with the experimental bandgap value of 1.9 eV. We also find that α-CsPbI₂Br shows comparable optoelectronic properties to CsPbI₃. More intriguingly, our calculated results show that both α-phase and β-phase CsPbI₂Br possess better thermal and phase stability than CsPbI₃ due to the mixture of halide elements, and the optical absorption coefficient of CsPbI₂Br also resembles that of CsPbI₃ and MAPbI₃ due to the lone pair electrons of Pb. Furthermore, the formation energies and transition energy levels of intrinsic point defects indicate that CsPbI₂Br exhibits unipolar self-doping behavior (p-type conductivity) and similarly good defect tolerance while the dominant defect changes. Therefore, our present work provides fundamental understanding of the great performance of CsPbI₂Br thin films and offers strategies for designing more superior CsPbI₂Br-based devices.