Chelating Dual Interface for Efficient and Stable Crystal Growth and Iodine Defect Management in Sn–Pb Perovskite Solar Cells

Suppressing Sn 2+ oxidation and rationally controlling the crystallization process of tin–lead perovskite (Sn–Pb PVK) films by suitable bonding methods have emerged as key approaches to achieving efficient and stable Sn–Pb perovskite solar cells (PSCs). Herein, the chelating coordination is performed at the top and bottom interfaces of Sn–Pb PVK films. The chelation strength is stronger toward Sn 2+ than Pb 2+ by introducing oligomeric proanthocyanidins (OPC) at the bottom interface. This difference in chelation strength resulted in a spontaneous gradient distribution of Sn/Pb within the perovskite layer during crystallization, particularly enhancing the enrichment of Sn 2+ at the bottom interface and facilitating the extraction and separation of photogenerated charge carriers in PSCs. Simultaneously, this top-down distribution of gradually increasing Sn content slowed down the crystallization rate of Sn–Pb PVK films, forming higher-quality films. On the top interface of the PVK, trifluoroacetamidine (TFA) was used to inhibit the generation of iodine vacancies (V I ) through chelating with surface-uncoordinated Pb 2+ /Sn 2+, further passivating defects while suppressing the oxidation of Sn 2+ . Ultimately, the PSCs with simultaneous chelation at both top and bottom interfaces achieved a power conversion efficiency (PCE) of 23.31% and an open-circuit voltage ( V OC ) exceeding 0.90 V. The stability of unencapsulated target devices in different environments also improved.