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 ¹H NMR, ¹H-¹H 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-cm² devices and a champion efficiency of 17.02% for 0.04-cm² 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 N₂ atmosphere.