Abstract
Perovskite solar cells (PSCs) based on formamidinium lead iodide (FAPbI₃) demonstrate near-ideal bandgaps approaching the Shockley-Queisser efficiency limit, yet residual MA⁺ from methylammonium chloride (MACl) additives compromises their operational stability under thermal/light stress. Therefore, we developed an α-phase-assisted antisolvent method employing MACl-free precursors to fabricate α-FAPbI(3) films. These films exhibit enhanced thermal stability and structural integrity, which were comprehensively characterized using multiple techniques. The optimized devices achieved a 26.1% power conversion efficiency (PCE), ranking among one of the highest reported values for FAPbI(3)-based inverted PSCs, and exhibit sustained stability under accelerated aging conditions. This strategy resolves the MA⁺-induced degradation bottleneck, paving the way for commercially viable high-performance PSCs.