Aggregation‐Suppressed and Synergistically Anchored Co‐SAMs for High‐Efficiency Stable Perovskite Solar Cells

The interfacial properties of the hole transport layer (HTL) are absolutely critical for perovskite solar cells (PSCs) nowadays. [4‐(3,6‐Dimethyl‐9H‐carbazol‐9‐yl)butyl]phosphonic acid (Me‐4PACz) is widely used HTL within the class of self‐assembled materials. However, during its self‐assembly process, Me‐4PACz tends to form molecular clusters and micelles on indium tin oxide (ITO), leading to insufficient coverage. Therefore, we propose a co‐assembled monolayer (Co‐SAM) strategy via co‐depositing phenylphosphonic acid (PPA) or its derivatives as co‐dopants with Me‐4PACz, the intermolecular steric hindrance between phenyl and carbazole groups effectively suppresses Me‐4PACz aggregation. Simultaneously, the phosphonic acid groups of both molecules form a synergistic dual‐anchoring effect, significantly enhancing HTL uniformity and coverage. Furthermore, active substituents (‐OH, ‐NH 2 , ‐Br) in the dopants can passivate uncoordinated Pb 2+ ions and iodine vacancies at the perovskite interface, thereby optimizing the HTL/perovskite contact and improving carrier extraction ability. Results show that inverted devices based on Me‐4PACz+BrPPA Co‐SAM achieve a power conversion efficiency (PCE) of 23.73%, representing a substantial increase from 21.39% while maintaining excellent stability. This strategy provides a new direction for developing high‐performance Co‐SAM and advancing the industrialization of PSCs.