Multifunctional Additive Engineering Enables Controlled Crystallization for Scalable Perovskite Solar Cells

Scalable fabrication of high‐quality perovskite films is essential for the commercialization of perovskite solar cells (PSCs). However, the uncontrolled crystallization kinetics during slot‐die coating often result in large‐area perovskite film with high defect density and unfortunate spatial uniformity. Herein, we introduce but‐3‐yn‐1‐amine hydrochloride (BAH) as a multifunctional additive for slot‐die coated perovskite film. Through hydrogen bonding, electrostatic and coordination‐related interactions with organic cations and Pb‐halide species, BAH can homogenize the precursor colloidal distribution to delay perovskite crystallization. This controlled crystallization process produces compact perovskite film with enlarged grains, reduced buried interfacial voids, suppressed microstrain, low trap density and reduced energetic disorder. Consequently, non‐radiative recombination is effectively mitigated, leading to an efficiency of 26.17% for small‐area PSCs, and an efficiency of 21.42% for large‐area (164 cm 2 ) perovskite solar module. Moreover, the unencapsulated devices demonstrate excellent light stability, retaining 91.27% of the initial efficiency at maximum power point tracking test after 1300 h. This work establishes a comprehensive additive strategy for scalable slot‐die coated PSCs, addressing crystallization control, defect passivation and operational stability simultaneously.