Alkylammonium Salt as Additives to Expand the Processing Window of Wide‐Bandgap Perovskite Solar Cells Made in Ambient Air

Abstract Wide‐bandgap (WBG) perovskites are critical for advancing tandem solar cell technology, yet their fabrication remains constrained by narrow processing windows and environmental instability. A synergistic alkylammonium salt additive strategy coupled with a mild gas‐flow‐assisted crystallization method is presented to produce ambient‐air‐processed WBG perovskite solar cells (PSCs) with improved reproducibility and scalability. Co‐utilizing long‐chain alkylammonium chlorides (xACls) and methylammonium chloride (MACl) reduced gas‐flow speed requirements while expanding the crystallization kinetics window, suppressing non‐radiative recombination and defects, which are verified by fluorescence lifetime imaging microscopy (FLIM), in situ UV–vis spectroscopy, and XRD. High‐quality Cs 0.2 FA 0.8 PbI 2.3 Br 0.7 films are successfully prepared under a low gas flow speed (≈2.7 m s −1 ), which is much lower than the traditional gas quenching method (>26 m s −1 ). Cs 0.2 FA 0.8 PbI 2.3 Br 0.7 solar cells made by using 12ACl/MACl additives yielded a champion power conversion efficiency (PCE) of 19.72% ( V oc : 1.238 V), which is among the highest efficiency for WBG PSCs made in ambient air. This method has the advantages of high humidity tolerance (PCE >19% for cells made under 20–65% RH), compatibility with cost‐effective fan drying, elimination of anti‐solvents, and >70% inert gas‐flow intensity reduction, establishing an eco‐friendly scalable protocol that bridges lab‐to‐industry translation for high‐performance WBG PSCs.