Large‐Scale In Situ Formation Perovskite Quantum Dots/Elastomer Composite for High‐Performance White Light‐Emitting Diodes

ABSTRACT Metal halide perovskite quantum dots (PQDs) are promising emitters for light conversion but suffer from poor compatibility and scalability in polymer composites. Herein, we report a one‐step, solvent‐free mechanochemical strategy for the in situ synthesis of CsPbX 3 (Br/Cl) QDs within halogenated butyl rubber (HIIR) via open‐mill shear, yielding monodisperse 2.6 nm CsPbBr 3 QDs uniformly embedded in a topological entanglement network. The CsPbX 3 /HIIR composite exhibited a narrow emission at 515 nm (FWHM 17 nm), photoluminescence quantum yield of 91%, and ultra‐long lifetime of 1189 ns. Spectroscopic and mechanistic studies revealed that the in situ‐generated IIR‐OOCC 17 H 35 chains create an interfacial allyl ester passivation layer that suppresses surface traps and blocks H 2 O/O 2 ingress. Consequently, films retained > 90% initial intensity after 30‐day ambient storage, 99.8% after 30‐day water immersion, and 44% after 500 h blue‐light irradiation (5000 nit). Flexible white LEDs achieved standard white emission (0.333, 0.338), color‐rendering index of 55.7, and wide color gamut of 132% NTSC. The low‐cost and high‐efficiency manufacturing process can be readily scaled to 17 × 17 cm 2 films, offering an industrially viable route for stretchable displays, X‐ray scintillators, and wearable photonics.