Self‐Adaptive Anhydrous Passivation Mitigates Open‐Circuit Voltage Loss in Pb‐Sn Mixed Perovskite Solar Cells

Lead (Pb)‐Tin (Sn) mixed perovskite solar cells (LTPSCs) attract considerable attention due to their potential application as rear subcells in tandem solar cells. However, the LTPSCs suffer from low fill factor (FF) and lower open‐circuit voltage ( V OC ) due to a large energy mismatch between the perovskite and charge‐transport materials, as well as inadequate crystallization. Here, based on the self‐adaptive anhydrous passivation strategy, a multifunctional anhydrous molecule, Trimellitic Anhydride (TMAH), is introduced into the perovskite precursor. Owing to the self‐adaptive property of TMAH, it generates its in situ hydrolysis product, Trimellitic Acid (TMA). The ‐C═O and ‐COO − functional groups in TMAH, together with TMA, form stable chelate complexes with metal cations (Pb 2+ /Sn 2+ ), thereby regulating the nucleation and crystallization. In addition, TMA facilitates secondary defect passivation and improves resistance to moisture and oxygen infiltration, thereby protecting the perovskite from harsh environmental conditions. As a result, TMAH together with TMA promotes (100)‐oriented crystal formation, lowers the perovskite work function, and provides better energy‐level alignment with the carrier transport layer, thereby reducing the V OC and FF deficiencies. Ultimately, a power conversion efficiency of 24.05% is achieved for LTPSCs with the highest V OC value of 0.905 V and exhibited robust operational stability.