Integrative Enhancement of Energy-Level Alignment and Defect Passivation for High-Performance Lead-Free Perovskite Solar Cells

CsGeI₂Br-based perovskites with a favorable bandgap and high absorption coefficient, show great promise as candidates for efficient lead-free perovskite solar cells (PSCs). However, the significant defect recombination and energy alignment mismatch at the perovskite-transport layer interface limit both the device's performance and long-term stability. To overcome these challenges, the photovoltaic potential of the device is unlocked by optimizing the optical and electronic parameters through a rigorous numerical simulation, including the transport layer materials, doping density, bulk/interface defect density, and carrier mobility. As a result, the optimized device achieved a champion power conversion efficiency of 28.00%. To further elucidate the inherent physical behavior, the activator energy of carrier recombination, along with the conduction and valence band offsets, are also investigated. Additionally, different types of device structures, including p-i-n and HTL-free structures, are briefly examined. Finally, a detailed roadmap for enhancing the efficiency of the device is proposed, offering valuable insights for improving inorganic lead-free CsGeI₂Br perovskite solar cells in optoelectronic applications.