A single-molecular bridge for simultaneously passivating dual-interface defects to fabricate high-efficiency and stable perovskite solar cells

Buried interface defects exist between the electron transport layer (ETL) and the perovskite (PVK) active layer, which severely limit the efficiency, hysteresis, and stability of SnO₂-based perovskite solar cells (PSCs). In this study, we introduced L-2-amino-5-ureidovaleric acid (LAUA) between SnO₂ and the perovskite film, which is a bidirectional modifier with carboxyl (-COOH), amino (-NH₂), and urea (-NH-CO-NH₂) groups at its two ends. The -COOH groups can effectively bind to the uncoordinated Sn⁴⁺ and dangling hydroxyl groups (-OH) on the SnO₂ surface, thereby optimizing the interface morphology and energy level alignment. On the other end, the -NH₂ groups can undergo specific interactions with Pb²⁺ in MAPbI₃, which delay the crystallization rate and passivate Pb-related defects at the buried interface. Additionally, the urea groups are capable of interacting with uncoordinated Pb²⁺ and I^-. These synergistic effects promote the efficient extraction of interfacial carriers, reduce interface-induced energy loss, suppress the residual of excess PbI₂ at grain boundaries, optimize film surface flatness, and ultimately achieve the balanced transport of charge carriers. Consequently, the LAUA-modified device exhibited a champion PCE of 26.21%, featuring enhanced long-term stability.