Intermolecular Interaction Engineering for Efficient Large‐Area Tin‐based Perovskite Solar Cells

Poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) has been widely used as a hole transport layer (HTL) in environmentally friendly tin‐based perovskite solar cells (TPSCs). However, its intrinsic weak acidity and strong tendency toward molecular aggregates hinder its performance in TPSCs. Here, we develop a molecular engineering strategy by introducing a p‐type small molecule, 4,4'‐(5,6‐bis(2‐methoxyethoxy)benzo[c][1,2,5]thiadiazole‐4,7‐diyl)bis(2,5‐difluoro‐N,N‐bis(4‐methoxyphenyl)aniline) (FEG), to modify PEDOT:PSS and, crucially, employ a comprehensive set of solid‐state nuclear magnetic resonance (NMR) techniques to directly elucidate the intermolecular interactions governing this modification. Magic‐angle spinning 1 H NMR, 1 H‐ 1 H double‐quantum‐single‐quantum correlation spectroscopy, and variable spinning‐rate measurements reveal strong interactions between FEG and PSS that redistribute the PEDOT:PSS microstructure and promote greater charge delocalization within the conductive polymer network. This interaction improves PEDOT:PSS dispersion, neutralizes residual acidity and enhances interfacial wettability, enabling the growth of high‐quality Sn‐based perovskite films with enlarged grains, reduced defect density and relieved residual stress. As a result, trap‐assisted recombination is suppressed and hole extraction is improved. Consequently, FEG‐PEDOT:PSS‐based TPSCs achieve a record efficiency of 14.92% for 1‐cm 2 devices and a champion efficiency of 17.02% for 0.04‐cm 2 devices, substantially outperforming their pristine PEDOT counterparts. Furthermore, these devices exhibit excellent operational stability, maintaining over 85% of their initial efficiency after 1100 h of storage under a N 2 atmosphere.