Air-Processed n -Butylpyridinium Bromide-Doped CsPbI ₂ Br Perovskite Solar Cells: Stress Relief, Energy Level Modulation, and 14.51% Efficiency

to suppress defect-mediated ion migration. Additionally, the hydrophobic structure of the cations retards moisture intrusion, thereby enhancing the environmental stability. The synergistic effect of N-BuPyBr alleviates structural stress, reduces lattice distortion, downshifts the conduction band minimum, and enhances energy level alignment with the electron transport layer (ETL). Consequently, the treated PSCs achieved a power conversion efficiency (PCE) of 14.51% and exhibited superior stability under 25% relative humidity (RH) in ambient conditions, maintaining high performance over an extended period.