Crystallization Control Based on the Regulation of Solvent–Perovskite Coordination for High‐Performance Ambient Printable FAPbI₃ Perovskite Solar Cells

Abstract The critical requirement for ambient‐printed formamidinium lead iodide (FAPbI₃) lies in the control of nucleation–growth kinetics and defect formation behavior, which are extensively influenced by interactions between the solvent and perovskite. Here, a strategy is developed that combines a cosolvent and an additive to efficiently tailor the coordination between the solvent and perovskite. Through in situ characterizations, the direct crystallization from the sol–gel phase to α‐FAPbI₃ is illustrated. When the solvent exhibits strong interactions with the perovskite, the sol–gel phases cannot effectively transform into α‐FAPbI₃, resulting in a lower nucleation rate and confined crystal growth directions. Consequently, it becomes challenging to fabricate high‐quality void‐free perovskite films. Conversely, weaker solvent–perovskite coordination promotes direct crystallization from sol–gel phases to α‐FAPbI₃. This process exhibits more balanced nucleation–growth kinetics and restrains the formation of defects and microstrains in situ. This strategy leads to improved structural and optoelectronic properties within the FAPbI₃ films, characterized by more compact grain stacking, smoother surface morphology, released lattice strain, and fewer defects. The ambient‐printed FAPbI₃ perovskite solar cells fabricated using this strategy exhibit a remarkable power conversion efficiency of 24%, with significantly reduced efficiency deviation and negligible decreases in the stabilized output.