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

Abstract

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.