Stabilizing Precursor Solutions by Proton-Rich Additive for High-Performance Air-Processed Solar Cells

Storing perovskite precursor solutions under ambient conditions poses a significant challenge to commercialization, as humidity and oxidation accelerate ageing and introduce defects in devices. A major contributor to solution ageing and impurity perovskite phases is the deprotonation of hybrid organic cations, specifically methylammonium (MA⁺) and formamidinium (FA⁺). In this work, a proton-rich additive, 4-(aminomethyl)pyridine 2-iodide, is used to inhibit MA⁺ deprotonation in precursor solutions by generating free H⁺, thereby mitigating the degradation of organic cations under oxygen and humidity stress. The treated precursor stored under ambient conditions for several days exhibits no condensation reaction products. Due to the synergistic effect of H⁺ and I^-, the perovskite films exhibit a pure perovskite phase and inhibit the formation of abnormal "aggregate" perovskite crystals. Therefore, the additive reacts with FA⁺ to form new complexes, termed N-(4-methylpyridine)formamidinium), which efficiently passivate nonradiative defects. Consequently, this strategy enables the treated perovskite solar cells to achieve a power conversion efficiency (PCE) of 25.25%, demonstrating enhanced long-term stability under both light and thermal stress. Notably, the optimized device retains 95.5% of its initial PCE after 1200 h of continuous illumination and retains 91.61% of its initial PCE after 600 h at 85 ^°C and 85% relative humidity.