Understanding the Principles of Co-deposition of Mixed-SAMs in MAPbI ₃ -Based p-i-n Structure Perovskite Solar Cells

The integration of self-assembled monolayers (SAMs) in perovskite (PVK) solar cells often presents processing challenges that can hinder their industrial uptake. To address these limitations and enhance the manufacturability of the SAMs/PVK interface, a co-deposition strategy was recently developed, wherein both SAMs and PVK films are formed simultaneously in a single step. As the fundamental principles governing the SAM/PVK co-deposition process remain insufficiently explored, here we selected four commercially available SAMs molecules─MeO-4PACz, Me-4PACz, Me-2PACz, and 2PACz─and we mixed them based on their molecular size, polarity, and hydrophobicity, forming pairs. The co-deposition process of mixed-SAMs with MAPbI₃ precursor solutions was studied, and corresponding solar cell devices were fabricated. Among the three combinations tested, the MeO-4PACz + Me-4PACz one yields the most promising results, and a power conversion efficiency of approximately 19% was achieved without any additional passivation strategies. Our findings reveal that the co-deposition process of mixed-SAMs is primarily influenced by the interplay between molecular size and polarity. The binding strength of co-deposited mixed SAMs to the In₂O₃:Sn (ITO) substrate is largely dictated by their solvation behavior in the PVK precursor-DMF:DMSO solvent system. This conclusion is supported by quantum chemistry calculations and further corroborated by surface, structural, and compositional analysis.