Rationally Designed Self‐Assembled Monolayer for Dual‐Site Passivation Enables Efficient and Stable Perovskite Solar Cells

ABSTRACT Self‐assembled monolayers (SAMs) have emerged as promising hole transport layers in inverted perovskite solar cells (PSCs), yet their practical application is hindered by molecular aggregation, imperfect surface coverage, and weak interfacial interactions with the perovskite layer. These issues induce considerable interfacial energy losses, constraining further improvements in power conversion efficiency (PCE) and device stability. Here, we present a rational site‐specific halogenation strategy that strengthens SAM‐perovskite interactions through lattice‐matched, dual‐site passivation. Using (4‐(3,6‐diphenyl‐9H‐carbazol‐9‐yl) butyl) phosphonic acid (Ph‐4PACz) as a twisted carbazole‐based scaffold with intrinsically improved dispersibility, we synthesize three dichlorinated positional isomers (o‐Cl‐, m‐Cl‐, and p‐Cl‐Ph‐4PACz) by selectively introducing chlorine atoms at designated positions on the peripheral phenyl ring. This structural tuning modulates the molecular dipole moment and spatial configuration, effectively suppresses molecular aggregation and promotes strong coordination with neighboring Pb 2+ defect sites in the perovskite lattice. Among them, p‐Cl‐Ph‐4PACz exhibits ideal spatial matching, enabling robust dual‐site coordination, improved crystallinity, reduced interfacial defects, and suppressed nonradiative recombination. As a result, inverted PSCs based on p‐Cl‐Ph‐4PACz achieve a PCE of 26.58% (certified at 26.13%) and exhibit excellent operational stability, retaining 95.9% of their initial efficiency after 1000 h of continuous illumination under the ISOS‐L‐2 protocol.