Understanding the Role of Intermolecular Interactions among Passivators in Surface Passivation for Tin–Lead Perovskite Solar Cells

Surface passivation is an effective strategy to address Sn 2+ oxidation and interfacial defects. However, current studies have primarily focused on the interaction between passivators and perovskites, while neglecting the influence of intermolecular interactions among passivators on their aggregation morphology and passivation efficacy. Herein, 6‐methylnicotinic acid hydrazide (MAH) and 6‐aminonicotinic acid hydrazide (AAH) were employed as passivators for a comparative study. Theoretically, the strong electron‐donating amino group (─NH 2 ) in AAH should endow it with stronger reducing and coordination abilities, yet the opposite phenomenon was observed in solid films, where AAH exhibited inferior passivation and antioxidant performance compared to MAH. It was found that the ─NH 2 group in AAH acted as a hydrogen‑bond donor and acceptor, inducing strong intermolecular hydrogen bonding and self‐aggregation, which led to disordered multilayer stacking on the perovskite surface and shielded the active functional groups. The methyl group with moderate steric hindrance in MAH effectively prevented self‑aggregation, allowing MAH to uniformly distribute on the perovskite surface and form bidentate coordination with Sn 2+ , thereby efficiently inhibiting Sn 2+ oxidation and passivating defects. The MAH‑treated Sn–Pb device achieved an efficiency of 23.92%, and when integrated into an all‑perovskite tandem cell, the device efficiency was further increased to 29.31%.