Enhanced Efficiency of Inorganic CsPbI3−xBrx Perovskite Solar Cell via Self‐Regulation of Antisite Defects

Abstract Deep defects often act as Shockley–Read–Hall recombination centers in semiconductor materials, degrading the photoelectric performance and long‐term stability of assembled photovoltaic devices. In this report, deep level transient spectroscopy is probed to determine defect concentrations and defect energy levels in all‐inorganic CsPbI 3− x Br x perovskite solar cells. Combining that data with the density functional theory calculation, the dominant deep defect states are assigned to antisite defect pairs (Pb I and I Pb ) and interstitial defects (Pb i ) in freshly prepared CsPbI 3− x Br x films. Astonishingly, all these defects are reduced by approximately one or two orders of magnitude after resting the films overnight, in excellent agreement with the defect‐reduced trends from the fluorescence spectra, transient photovoltage, and space‐charge‐limited current measurements. The reduced defect concentrations are proposed to be connected with their self‐regulation during the storage. To assess the thermodynamics possibilities, two reaction procedures are designed to calculate their formation enthalpies and negative Gibbs energy change revealed their spontaneous processes. Then, strain relief is the direct driving force for ion migration, thus defect‐regulation by tracing the X‐ray diffraction patterns. Furthermore, the power conversion efficiency is improved and the J–V hysteresis is suppressed due to reduced ion migration via relaxed strain.