Integrating Molecular Extrusion and Antisolvent Bathing: Methoxy Number as a Key Parameter for Self-Assembled Monolayers in Perovskite Solar Cells.

We directly incorporate self-assembled monolayers (SAM) into the perovskite precursor. Combined with antisolvent bathing, this approach enables one-step in situ molecular extrusion. By tuning the number of methoxy groups, we find that the mono-methoxy molecule 1MeO-4PACz exhibits optimal energy level alignment (HOMO = -5.36 eV), strong interfacial adhesion, and guides orderly perovskite crystallization, achieving an excellent balance between bulk and interfacial defects. The one-step device yields a power conversion efficiency of 22.35% and retains 90% of its initial efficiency after 1700 h in N2. In contrast, the tetra-methoxy molecule 4MeO-4PACz suffers from excessively strong coordination, becoming embedded in the bulk during crystallization and leading to increased defect density, resulting in a low efficiency of 6.87%. Two-step comparisons reveal the specific selectivity of the one-step process for molecular configuration. This work provides new insights into the design of SAM molecules toward scalable manufacturing.