Regulating the Crystallization‐Defect‐Strain Improves the Stability and Scalability of FACs Perovskite Photovoltaics

ABSTRACT Formamidinium–cesium (FACs) perovskite is thermally stable, but the rapid crystallization process generates bulk defects and residual strains. We introduce a multifunctional additive, 3‐(Trifluoromethyl)aniline hydrochloride (3TFACl), to effectively regulate the crystallization process to improve stability and scalability of perovskite solar cells (PSCs) through multiple interactions with perovskite components. Crystallization‐defect‐strain engineering is synergistically integrated during film deposition. The champion power conversion efficiency (PCE) of p–i–n PSCs and 12 cm 2 module reach 26.76% (certified 26.12%) and 22.77%, respectively. The unencapsulated devices still maintain more than 94.36% of the initial efficiency after 1500 h maximum power point tracking (MPPT) (ISOS‐L‐1I protocol) and 80.5% initial efficiency after 1000 h under 85°C (ISOS‐D‐2I protocol). This work proposes a molecular design strategy with a simple structure but high synergy to achieve efficient, stable, and scalable perovskite photovoltaic devices.