Anion exchange in cesium lead halide perovskite nanocrystals (CsPbX3 where X= Cl, Br or I) takes place rapidly and reversibly, making it a facile method to tune the band gap energy of these materials. In this work, we studied the reversible transformation between individual CsPbCl3 nanocrystals and CsPbBr3 using fluorescence microscopy. The variation in emission wavelength and intensity provide a signature for when individual nanocrystals undergo this transformation. We observed that both waiting times for individual nanocrystals to begin transforming and switching times for changes in fluorescence intensity to occur depended on the concentration of substitutional halide ions. The concentration dependence of switching time, has not been seen in other systems, and is attributed to the high solid-state miscibility of CsPbCl3 and CsPbBr3. We develop a physical model, consistent with all experimental observations, in which the activation energy for anion exchange events in a nanocrystal depends on the density of exchanged ions. The heterogeneity in reaction kinetics observed among individual nanocrystals provides new insights into the complex behavior that has been previously observed for this reaction at the ensemble level.

Role of solid-state miscibility during anion exchange in cesium lead halide nanocrystals probed by single-particle fluorescence

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.