Encapsulation of CsPbX 3 Perovskite Nanocrystals via Hydrogen‐Bonded Cocrystals Assisted by Pyr 14 BF 4 Ionic Liquid to Enhance Their Stability

ABSTRACT CsPbX 3 perovskite nanocrystals (NCs) have attracted considerable attention for their exceptional optoelectronic properties, yet their poor stability hinders practical applications. In this study, we developed a hydrogen‐bonded cocrystal‐coated composite (CsPbX 3 @CA‐M) by exploiting the rapid co‐crystallization of cyanuric acid (CA) and melamine (M) assisted by the ionic liquid Pyr 14 BF 4 (IL). The IL effectively coordinated with unbonded Pb atoms on the perovskite surface, suppressing surface defects and enhancing both quantum efficiency and stability. Simultaneously, the CA‐M cocrystal layer further reduced trap states through covalent bonding, improving structural robustness. The CsPbBr 3 @CA‐M composite retained its crystallinity and strong photoluminescence under UV irradiation and in 1 m NaOH or 1 m HNO 3 , demonstrating remarkable chemical durability. Even after 30 days of storage, its photoluminescence intensity remained nearly unchanged, whereas that of uncoated CsPbBr 3 NCs decayed rapidly. These findings confirm that CA‐M cocrystal encapsulation effectively shields perovskite NCs from environmental degradation, offering a simple and efficient strategy to simultaneously enhance their stability and optoelectronic performance.