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

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.