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The postsynthetic anion exchange of CsPbI3 nanocrystals for photoluminescence tuning and enhanced quantum efficiency

CsPbI3 perovskite nanocrystals (NCs) are generally unstable, with low photoluminescence quantum yield (PLQY) and show deep red emission not suitable for optoelectronic applications. Herein, we propose a facile postsynthetic anion exchange method to enhance PLQY and stability via the controlled addition of ZnBr2 solution, in which the emission peak is adjusted from 690 nm to 550 nm and the PLQY was enhanced from about 50% to near unity (98%). We further unveiled the ion exchange kinetics of the rapid transitions between two phases (CsPbI3 and CsPbBrI2) within 40 minutes, and also demonstrated that the electron trap and hole trap transformed mutually with the increase of halogen enabling the variable PLQYs. Moreover, the as-prepared CsPbBrI2 NCs exhibit enhanced stability under UV irradiation and in water compared with that of pristine CsPbI3 NCs. The good stability and highly efficient narrow-band emission centered at 630 nm for CsPbBrI2 NCs show its potential application-possibility in liquid-crystal display backlight. It is suggested that the postsynthetic ZnBr2 halogen ion exchange method demonstrated here opens a new door for the synthesis of high-performance halide perovskite nanocrystals and the development of illumination and display applications.