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

Abstract

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 CsPbI_3−xBr_x 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.