Coordination/π‐π Stacking Synergistic Strategy: Regulating Interface Defects and Charge Transport to Enhance the Performance of Tin‐Lead Perovskite Solar Cells

Abstract While mixed tin‐lead (Sn‐Pb) perovskites theoretically possess the potential to surpass the single‐junction Shockley‐Queisser efficiency limit, their practical performance remains constrained by significant carrier non‐radiative recombination at the perovskite/electron transport layer (ETL) interface. Although numerous interface modification strategies are reported for pure‐lead or select narrow‐bandgap systems, the deep‐level defects induced by Sn 2 ⁺ oxidation and the interfacial energy‐level misalignment in Sn‐Pb perovskites still lack molecular designs that synergistically combine efficient defect passivation with enhanced charge extraction. Here, an interfacial synergistic regulation strategy is proposed by introducing the bifunctional molecule 4,4′‐diaminodiphenyl ether (ODA) at the perovskite/PCBM interface. The ODA molecule facilitates efficient π‐π stacking between its aromatic backbone and PCBM, thereby enhancing interfacial contact and stability. Simultaneously, its amino functional groups effectively passivate undercoordinated defect sites on the perovskite surface, suppressing interfacial recombination. This approach enables the synergistic optimization of interfacial defect passivation and charge extraction capability, ultimately yielding a power conversion efficiency (PCE) of 23.7% for the resulting devices. Under unencapsulated conditions, the devices retain T 90 = 1200 h during maximum power point tracking. This work demonstrates a single‐molecule strategy for “passivation‐transport” dual functionality, offering a new design pathway for narrow‐bandgap perovskite photovoltaics.