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, -NH₂, -Br) in the dopants can passivate uncoordinated Pb²⁺ 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.