Intrinsic Point Defects in Inorganic Cesium Lead Iodide Perovskite CsPbI3

Cesium lead iodide (CsPbI3) has recently emerged as a promising solar photovoltaic absorber. However, the cubic perovskite (alpha-phase) remains stable only at high temperature and reverts to a photoinactive nonperovskite (gamma-phase) CsPbI3 at room temperature. In this work, the formation energies and transition energy levels of intrinsic point defects in gamma- (more stable than alpha-phase) and delta-phases have been studied systematically by first-principles calculations. It is found that CsPbI3 exhibits a unipolar self-doping behavior (p-type conductivity), which is in contrast to CH3NH3PbI3. Most of the intrinsic defects induce deeper transition energy levels in delta-phase than in y-phase. This is due to the small Pb-I-Pb bond angles in delta-phase that results in the weak antibonding character of valence band maximum (VBM). However, the strong antibonding character of VBM plays a critical role in keeping defect tolerance in semiconductors. Therefore, these results indicate the importance of the large metal halide metal bond angle for the performance of perovskite solar cells.