Exceptional Stability against Water, UV Light, and Heat for CsPbBr3@Pb‐MOF Composites.

All‐inorganic lead halide perovskite nanocrystals (NCs) have been widely applied in optoelectronic devices owing to their excellent photoluminescence (PL) properties. However, poor stability upon exposure to water, UV light or heat strongly limits their practical application. Herein, CsPbBr3@Pb‐MOF composites with exceptional stability against water, UV light, and heat are synthesized by ultrasonic processing the precursors of lead‐based MOF (Pb‐MOF), oleylammonium bromide (OAmBr) and cesium oleate (Cs‐OA) solutions at room temperature. Pb‐MOF can not only provide the lead source for the in situ growth of CsPbBr3 NCs, but also the protective layer of perovskites NCs. The formed CsPbBr3@Pb‐MOF composites show a considerable PL quantum yield (PLQY) of 67.8%, and can maintain 90% of the initial PL intensity when immersed in water for 2 months. In addition, the outstanding PL stability against UV light and heat is demonstrated with CsPbBr3 NCs synthesized by the conventional method as a comparison. Finally, a green (light‐emitting diode) LED is fabricated using green‐emitting CsPbBr3@Pb‐MOF composites and exhibits excellent stability without packaging when immersed in water for 30 days. This study provides a practical approach to improve the stability in aqueous phase, which may pave the way for future applications for various optoelectronic devices. [ABSTRACT FROM AUTHOR]