Enhancing Long-TermOperational Stability of Pseudohalide-BasedWide-Bandgap Perovskite Solar Cells

The instability of wide-bandgap perovskite solar cells (PSCs) impedes their practical applications. Here, ammonium formate is incorporated into perovskite precursors to optimize composition, enhancing film quality, optoelectronic properties, and stability. Time-resolved photoluminescence reveals prolonged carrier lifetimes (reduced nonradiative recombination), while morphological analysis demonstrates enlarged grain sizes, enabling efficient charge transport and defect mitigation. Optimized devices achieve a power conversion efficiency of 20.37% (vs 17.47% for the control device) under AM 1.5G 1-sun illumination, with improved open-circuit voltage (1.14 V (with ammonium formate) vs 1.11 V (without ammonium formate)) and fill factor (81.10% (with ammonium formate) vs 74.14% (without ammonium formate)). Unencapsulated devices retain >80% of their initial efficiency after 300 h under light/dark cycling and 230 h under continuous 1-sun illumination (55 ± 5% humidity), outperforming control cells (<50% retention). Ammonium formate suppresses PbI₂ formation and surface recombination, enhancing the operational durability. This work provides a facile compositional engineering strategy to advance long-term stability in wide-bandgap PSCs.