Constructing Robust Buried Interfaces of Inverted Perovskite Solar Cells by Bridge‐Anchored Co‐SAMs

ABSTRACT

Self‐assembled monolayers (SAMs) have become key hole‐selective contacts in inverted perovskite solar cells, enabling high efficiencies and low optical losses. However, the ultrathin SAM remains prone to incomplete coverage and weak anchoring, which limits further improvement in performance. Here we introduce a bridge‐anchored co‐SAM concept in which [2‐(3,6‐dimethoxy‐9H‐carbazol‐9‐yl)ethyl]phosphonic acid (MeO‐2PACz) is co‐assembled with 3‐(hydroxy(phenyl)phosphoryl)propanoic acid (3‐HPP), a bifunctional phosphonic–carboxylic acid that simultaneously reinforces the ITO/SAM and SAM/perovskite interfaces. Density functional theory (DFT) and spectroscopy reveal that 3‐HPP possesses a larger molecular dipole and highly localized phosphonic/carboxylic that coordinate to ITO –M–OH sites and chelate under‐coordinated Pb ²⁺ at the perovskite surface, while also hydrogen‐bonding to FA ⁺ . Excess 3‐HPP therefore partitions vertically: part of the molecules densify and strengthen the MeO‐2PACz monolayer on ITO, whereas the rest form a soft, Pb‐selective passivation layer at the buried perovskite interface. Inverted PSCs achieve a champion efficiency of 26.0% with a fill factor of 85.28%, improved built‐in potential and reduced non‐radiative and transport losses, together with significantly enhanced operational and UV/thermal stability. By simultaneously reinforcing substrate and perovskite contacts, the bridge‐anchored co‐SAM offers a scalable route to defect‐tolerant buried interfaces that underpin long‐term, high‐efficiency inverted devices.