Nucleation Regulation and Mesoscopic Dielectric Screening in α‐FAPbI₃

Abstract While significant advancements in power conversion efficiencies (PCEs) of α‐FAPbI₃perovskite solar cells (PSCs) have been made, attaining controllable perovskite crystallization is still a considerable hurdle. This challenge stems from the initial formation of δ‐FAPbI₃, a more energetically stable phase than the desired black α‐phase, during film deposition. This disrupts the heterogeneous nucleation of α‐FAPbI₃, causing the formation of mixed phases and defects. To this end, polarity engineering using molecular additives, specifically ((methyl‐sulfonyl)phenyl)ethylamines (MSPEs) are introduced. The findings reveal that the interaction of PbI₂‐MSPEs‐FAI intermediates is enhanced with the increased polarity of MSPEs, which in turn expedites the nucleation of α‐FAPbI₃. This leads to the development of high‐quality α‐FAPbI₃ films, characterized by vertical crystal orientation and reduced residual stresses. Additionally, the increased dipole moment of MSPE at perovskite grain boundaries attenuates Coulomb attractions among charged defects and screens carrier capture process, thereby diminishing non‐radiative recombination. Utilizing these mechanisms, PSCs treated with highly polar 2‐(4‐MSPE) achieve an impressive PCE of 25.2% in small‐area devices and 20.5% in large‐area perovskite solar modules (PSMs) with an active area of 70 cm². These results demonstrate the effectiveness of this strategy in achieving controllable crystallization of α‐FAPbI₃, paving the way for scalable‐production of high‐efficiency PSMs.