| Abstract Scope |
Metal halide perovskites are promising next-generation photovoltaic materials due to their tunable band gaps, low-cost solution processability, and high absorption coefficients. However, stability and efficiency remain limited by surface defects, undercoordinated lead sites, grain boundaries, and moisture sensitivity. Surface passivation can reduce non-radiative recombination and improve moisture protection, but conventional single-cation 2D passivation layers may introduce insulating behavior or phase impurities that limit charge-carrier extraction. Here, we propose a binary-cation passivation strategy using n-butylammonium iodide (BAI) and ethylenediamine diiodide (EDAI₂) to form a 2D/3D heterostructure on the perovskite surface. By tuning the cation ratio and fabrication conditions, we investigate the effects on morphology, crystallinity, optical properties, defect suppression, device performance, and stability. Our results demonstrate that rational material design enables a uniform, compact 2D surface layer, improving binary-cation effectiveness, device performance, and stability toward high-performance perovskite solar cells. |