Dual-Functional Amino Acid Mediated Buried SAM Interfaces for Efficient Inverted Perovskite Solar Cells

Self-assembled monolayers (SAMs) are pivotal in inverted perovskite solar cells (PSCs) for their transparency, tunability, selective charge transport, and structural adaptability, yet challenges like molecular aggregation and incomplete coverage persist despite advances in charge extraction. Hole transport layer (HTL) engineering is thus vital for efficient carrier collection, hole selectivity, and optimal perovskite quality through interfacial chemistry. Here, we introduce a coadsorption (CA) strategy that harnesses the dual functionality of l -Histidine with [2-(3,6-dimethoxy-9 H -carbazol-9-yl)ethyl]phosphonic acid (MeO-2PACz) at the buried interface via a facile one-step process. l -Histidine first mitigates MeO-2PACz aggregation via intermolecular interactions in the precursor solution, yielding smoother films, a higher work function, and enhanced hydrophilicity, thereby enabling uniform perovskite deposition. Concurrently, its imidazole moiety acts as a Lewis base, coordinating undercoordinated Pb 2+ sites through Pb–N bonds to passivate defects, promoting films with superior crystallinity, reduced trap-state density, suppressed nonradiative recombination, and accelerated hole extraction. These attributes also enhance interfacial stability by limiting ion migration and moisture degradation. The synergistic effects of l -Histidine's dual role, antiaggregation and defect passivation, result in a power conversion efficiency (PCE) of 19.18%, outperforming pristine MeO-2PACz devices, and provide valuable insights into the rational design of small-molecule additives for coadsorption strategies.