Fluoroacetate‐Mediated Dual‐Interface Ionic Stabilization in Perovskite Solar Cells

Crystallization kinetics and ionic dynamics jointly govern the efficiency and stability of perovskite solar cells (PSCs). Here, we report a fluoroacetate-mediated molecular strategy that regulates perovskite crystallization and ionic migration. Ethylammonium trifluoroacetate (EATFA) coordinates with lead and formamidinium ions, accelerating nucleation and moderating grain growth during the vacuum quenching process. Upon annealing, EATFA localizes at both top and bottom interfaces, where dual-sided enrichment passivates deep-level traps, enhances charge extraction, and suppresses light-induced halide accumulation. Deep-level transient spectroscopy (DLTS) and transient ion drift (TID) reveal that EATFA prevents the temperature-induced transition of iodide ions into an interstitial-mediated migration pathway observed in conventional films (activation energy decreased from 0.47 to 0.15 eV). Applied to 1.66-eV wide-bandgap PSCs, critical for silicon/perovskite tandems yet prone to ion-migration degradation, this strategy enhances both power-conversion efficiency (PCE) and operational stability under thermal, ultraviolet, and continuous stress, achieving 22.06% PCE in 1-square-centimeter blade-coated devices and retaining 95% of initial efficiency after 2000 h of maximum-power point tracking and 91% after 1000 h at 65°C. Similar improvements in 1.55-eV perovskites confirm the bandgap-independent nature of this approach, providing a unified route toward efficient and durable PSCs.