Site-Selective Passivation of Lead-Free Perovskites via Polymer Phase Transition

While lead-free double perovskites show potential for eco-friendly optoelectronics, their practical application is hindered by inherent instability and surface defect states. Herein, the synergistic chemical bonding mechanisms at the perovskite-polymer interface are systematically elucidated by comparing four representative polymers: poly(methyl methacrylate) (PMMA), polystyrene (PS), poly(ethylene oxide) (PEO), and poly(vinylidene fluoride) (PVDF). Rather than conventional one-way physical encapsulation, the primary novelty of this study lies in the mechanistic identification of a mutual structural synergism where the strong chemical interactions at the perovskite surface are likely to facilitate a structural rearrangement of the surrounding PVDF chains, triggering a substantial phase transition into their electroactive phases. Driven by this structural rearrangement, the preferentially oriented dipoles at the perovskite-polymer interface are expected to passivate vulnerable cationic and anionic surface defects, thereby suppressing nonradiative recombination. Furthermore, overcoming the limitations of mere macroscopic hydrophobicity, this robust chemical dipole anchoring establishes an effective interfacial barrier against moisture permeation. Consequently, the optimized PVDF composite exhibits preservation of its intrinsic luminescent properties, maintaining stable luminescence after 1600 h in water and 7 days of thermal stress at 150 °C. This fundamental mechanistic understanding facilitates the successful integration of these composites as a stable color conversion layer for white light-emitting diodes (WLEDs) and secure optical encryption labels. Ultimately, the physicochemical insights from this work offer promising chemical design guidelines for the development of stable and lead-free optoelectronic materials.