A “Guest‐Solvent” Additive Strategy for Ambient‐Printed Films with Enhanced Efficiency in <scp>FAPbI₃</scp> Perovskite Solar Cells and Modules^†

Comprehensive Summary Achieving high‐performance perovskite solar modules (pero‐SMs) over large areas under ambient conditions remains a significant barrier to the commercialization of perovskite photovoltaics. This challenge arises from the strong solvent‐perovskite coordination interactions in the hygroscopic perovskite precursor ink, which complicate the control of nucleation‐growth kinetics and phase evolution during film formation in the presence of moisture, thereby hindering the formation of high‐quality perovskite films. In this work, a “guest‐solvent” additive strategy was developed by incorporating N , N ‐dimethylthioformamide (DMT) into the perovskite precursor ink to effectively modulate the coordination between the solvent and perovskite. It is demonstrated that DMT, structurally similar to the “main‐solvent” system (DMF and DMSO), possesses lower coordination ability with Pb 2+ and forms non‐covalent interactions with the primary solvents. These interactions weaken the solvent‐perovskite coordination without sacrificing solubility, thereby stabilizing homogeneous nucleation and promoting direct crystallization from the sol‐gel phase to α‐FAPbI 3 . As a result, the ambient‐printed FAPbI 3 films exhibited high quality, with more compact grain stacking, smoother morphology, higher phase purity, and fewer defects. Consequently, the resulting perovskite solar cells (0.062 cm 2 ) and pero‐SMs (15.64 cm 2 ) fabricated via blade coating under ambient conditions achieved remarkable power conversion efficiencies (PCEs) of 24.46% and 22.54%, respectively.