ABSTRACT Regulating buried interfaces is pivotal for suppressing interfacial defects and facilitating crystallization toward compact, high‐quality perovskite films. Here, we propose a thermally activated lithium formate (LiHCOO) buried interface strategy that triggers in situ pseudo‐halide diffusion, thereby simultaneously reconstructing the SnO 2 /perovskite interface and regulating perovskite nucleation and growth. High‐temperature treatment transforms LiHCOO from its low‐temperature hexagonal polymorph to a metastable monoclinic phase with a more open molecular packing structure, thereby enabling deeper HCOO − diffusion into the buried perovskite. Diffused HCOO − strongly interacts with undercoordinated Pb 2+ sites, inhibiting pinhole formation, reducing trap density, compensating for halide vacancy related defects, and releasing residual tensile strain. Meanwhile, LiHCOO modification passivates the SnO 2 surface by reducing oxygen vacancies and hydroxyl defects, improving interfacial electrical properties. This enhances the built‐in potential of perovskite devices from 0.91 to 1.00 V while optimizing energy level alignment. Ultimately, the optimized perovskite solar cell achieved a champion efficiency of 25.48%, with an open‐circuit voltage of 1.213 V and a fill factor of 82.57%, while also demonstrating outstanding long‐term stability. This work reveals polymorph‐mediated pseudo‐halide diffusion as a novel approach to low‐loss and robust perovskite photovoltaics.
Gao et al. (Fri,) studied this question.
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