Synergistic hydrophilic-hydrophobic polymers enable coordination engineering of MAPbBr₃ perovskite for waterproof luminescent fibers

Hydrophobic polymer encapsulation enhances the water stability of lead halide perovskites but often lacks precise control over the perovskite-polymer interfaces, limiting luminescence tunability. Herein, we propose a synergistic hydrophilic-hydrophobic polymer strategy to engineer the local coordination environment of MAPbBr₃ in luminescent fibers via electrospinning. Combining the hydrophobic polymer PMMA with the hydrophilic copolymer PMN, it is demonstrated that the PMN/PMMA weight ratio could modulate the Pb coordination environment (i.e. Pb-O vs Pb-Br bond), and subsequently tune the crystallinity of MAPbBr₃, by synchrotron radiation X-ray absorption fine structure spectroscopy (XAFS), small-angle X-ray scattering (SAXS), and wide-angle X-ray scattering (WAXS) characterization. This coordination engineering, coupled with crystallinity regulation, tailors the photoluminescence, resulting in a photoluminescence quantum yield (PLQY) enhancement of ∼48 % at the optimal weight ratio (PMN/PMMA = 0.08). Crucially, PMN endows the fibers with unique water-responsive behavior: moderate moisture could induce the increasing photoluminescence of MAPbBr₃ through recrystallization, whereas excessive water could result in degrading the unencapsulated MAPbBr₃ outside the fibers. This work establishes a polymer-mediated coordination control paradigm for developing waterproof, tunable perovskite luminescent materials.