Hydroxy Diphosphonic Acid‐Anchored Self‐Assembled Monolayers Enable Annealing‐Free High‐Efficiency Hole Transport Layers for Organic Solar Cells

Abstract This study presents a novel carbazole derivative functionalized with hydroxy diphosphonic acid groups (HDPACz) as an efficient annealing‐free hole transport layer (HTL) through strong bidentate anchoring to indium tin oxide (ITO). Compared to conventional mono‐phosphonic acid counterparts, HDPACz demonstrates superior ITO surface coverage and interfacial dipole, effectively modulating the work function of ITO. Theoretical calculations reveal enhanced adsorption energy (−3.95 vs −1.87 eV for 2PACz) and interfacial dipole strength in HDPACz. Organic solar cells (OSCs) employing 1‐HDPACz achieve a remarkable power conversion efficiency (PCE) of 19.38% with a high fill factor (77.22%). This work provides a new strategy for developing cost‐effective and scalable annealing‐free HTLs for high‐performance photovoltaics.