Scalable Fabrication of High‐Efficiency Thin‐Film Perovskite Solar Cells in Air via Polymer‐Mediated Synthesis of α‐FAPbI 3 Microcrystals

ABSTRACT Formamidinium lead triiodide (FAPbI 3 ) perovskite solar cells (PSCs) demonstrate exceptional photovoltaic performance but face critical stability challenges impeding commercialization. Herein, we integrate polypropylene glycol (PPG) into an inverse temperature crystallization process to synthesize highly stable α‐FAPbI 3 microcrystals, which retain phase purity for over six months in air. Our approach enables large‐scale production (nearly 50 g) of PPG‐coated α‐FAPbI 3 (target) microcrystals from low‐cost PbI 2 , with over 95% yield—sufficient to manufacture 23 m 2 of perovskite solar modules. Redissolving the target α‐FAPbI 3 microcrystals, followed by spin‐coating and annealing, yields target perovskite films with reduced defect density, minimized residual strain, and enhanced carrier transport. Mechanistic investigations reveal that colloidal species form upon the redissolution of target microcrystals which modulate the film crystallization kinetics, i.e. accelerating (100)‐oriented nucleation and growth. Employing this integrated strategy, a champion PSC with a power conversion efficiency (PCE) of 26.50% (certified 26.22%) was obtained at a laboratory scale (0.06 cm 2 ) and 22.66% for a module with an aperture area of 28.99 cm 2 , together with prolonged operational stability. This work opens new avenues for the industrial‐scale fabrication of efficient and stable large‐area perovskite photovoltaics.