Fused Triphenylamine‐Terminated Self‐Assembled Hole‐Transporting Monolayers for Perovskite Solar Cells

ABSTRACT Conventional self‐assembled hole‐transporting monolayers (SAMs) in perovskite solar cells (PSCs) suffer molecular aggregation, uneven coverage on rough FTO substrates, and insufficient interfacial defect passivation. The design and application of novel SAMs have become an important approach to enhancing device efficiency and stability. Herein, two asymmetric π‐extended SAMs, named T‐4PACz and FT‐4PACz, based on 4PACz skeleton with a triphenylamine terminal, were designed. FT‐4PACz, featuring a fused triphenylamine terminal, suppresses aggregation via moderate π–π stacking and adopts a parallel orientation on FTO, enhancing interfacial bonding and shortening carrier transport paths. Its exposed central nitrogen lone‐pair electrons strongly coordinate with Pb 2+ , passivating defects and regulating perovskite crystallization into dense, pinhole‐free films. Optimized HOMO alignment further reduces the hole‐injection barrier. Consequently, the champion inverted PSCs based on FT‐4PACz achieve a power conversion efficiency of 26.76%, significantly outperforming those based on T‐4PACz (25.09%) and 4PACz (24.28%). The devices retain >90% of their initial efficiency after 1020 h at 85 °C in N 2 . This work provides a rational molecular design strategy for high‐performance, stable SAMs for PSCs.