Mitigating deep-level defects through a self-healing process for highly efficient wide-bandgap inorganic CsPbI3-xBrx perovskite photovoltaics

Wide bandgap inorganic perovskites have attracted intensive attention owing to their potential applications in high-efficiency tandem solar cells and indoor photovoltaics. However, the performance of wide bandgap inorganic perovskite solar cells (PSCs) suffers from large energy loss due to a high degree of atom (or lattice) disorder and trap defects induced by phase transformation. Herein, the defect states of 1.82 eV inorganic CsPbI3-xBrx perovskite are investigated by thermal admittance spectroscopy, photoluminescence spectroscopy, transient photovoltage, and space-charge-limited current measurement. It is found that the deep-level interstitial defects with an activation energy of 321 meV can be reduced by two orders of magnitude under prolonged storage under low-humidity ambient conditions. Admittance spectroscopy in the low-frequency region also reveals the evolution of activation energy for ion migration. The self-healing process, which is assisted by the ion migration, is proposed to explain the mitigation of the deep-level interstitial defects. Device characterization and drift-diffusion model-based simulation further elucidate the reduction of nonradiative Shockley-Read-Hall recombination and the enhancement of carrier extraction, both attributed to the mitigation of the trap defects. This work highlights the critical roles of the self-healing process in diminishing the deep-level interstitial defects for high-performance inorganic perovskite optoelectronics.