Synergistic Dual-Anchor Passivation at Buried Interfaces Enabling High-Efficiency and Stable Perovskite Solar Cells

The buried interfacial nonradiative recombination and carrier transport losses in perovskite solar cells, particularly caused by oxygen and iodide vacancy defects at the SnO 2 /perovskite interface, critically limit their efficiency and stability. Herein, we propose a bifunctional passivation strategy using guanidinium phosphate (GAP), which spatially separates phosphate and guanidine groups to synergistically anchor SnO 2 and perovskite interfaces. We systematically demonstrate the multifunctional synergistic roles of GAP molecules at the SnO 2 /perovskite buried interface, where phosphate groups establish robust coordination bonds with the SnO 2 surface to passivate oxygen vacancy defects while optimizing interfacial energy level alignment. At the same time, guanidinium cations suppress the formation of iodine vacancies in the perovskite through electrostatic interactions, induce oriented crystallization, and reduce grain boundary defect density. Additionally, GAP is a bridging molecule that fills interfacial voids, enhancing interfacial bonding strength and improving carrier transport efficiency across the interface. Based on this strategy, the champion device achieves a power conversion efficiency of 24.12% with negligible hysteresis. The unencapsulated devices retain more than 90% of their initial efficiency after 2000 h of aging under a 25% relative humidity. This work establishes a novel paradigm for designing multifunctional molecular passivators, advancing perovskite optoelectronics toward high efficiency and operational stability.