Homogenizing interfacial assembly via indole-mediated binary monolayers for perovskite solar cells

Self-assembled monolayers (SAMs) have emerged as efficient hole-transport layers for inverted perovskite solar cells (PSCs), yet molecular self-aggregation during assembly limits interfacial homogeneity and device performance. Here we report an indole-carbazole co-adsorption strategy by incorporating N-indoleacetic acid (Nd) into (4-(3,6-diphenyl-9H-carbazol-9-yl)butyl)phosphonic acid (Ph-4PACz) to construct phase-homogeneous monolayers. Nd interacts with Ph-4PACz via synergistic π-π stacking and hydrogen bonding, resulting in a uniform alternating Ph-4PACz/Nd molecular arrangement. This co-adsorbed structure enables optimized interfacial energy alignment, enhances perovskite film uniformity, and suppresses trap-assisted non-radiative recombination. As a result, devices achieve an efficiency of 26.95% (certified 26.57%) on 0.0717 cm² and 25.61% on 1 cm², retaining 93.36% of their initial efficiency after 1500 h of maximum power point tracking under continuous illumination and 91.10% after 1200 h at 85 °C. The strategy is broadly applicable to carbazole-based SAMs and wide-bandgap PSCs, offering a general co-adsorption route toward efficient and stable devices.