Inorganic halide perovskite (IHP) quantum dots have been intensely investigated as fluorescent materials with narrow emission spectra and as building blocks for assembly of future photovoltaic and optoelectronic devices. Indeed, research on lead halide perovskites has begun to revolutionize solar energy research owing to their unique optoelectronic properties, such as ease of preparation and anion exchange, high photoluminescence quantum yield, long charge carrier diffusion lengths, and potential for advanced electronic properties through doping. Even with these prospects, the problem of instability still presents a major setback from its commercialization. For example, the ions within the crystals migrate more freely than in tetrahedral semiconductors due to their ionic nature thus making them more susceptible to ion exchange both in solution and in thin films. While post-synthetic anion exchange has emerged as a simple way to tune the bandgap energy and composition of this class of materials, ion migration can also cause undesired phase separation in mixed halide perovskite alloys, which contributes to instability and erosion of optoelectronic performance. Therefore, many researchers have devoted attention to understanding the process of this ion migration and exchanges. However, to date, the processes underlying anion exchange among IHP QDs remain under debate and largely unclear. Here, we elucidated the process of anion exchange in solution through the mixing of IHP QDs of different compositions and also by introduction of different halide sources, with in situ measurements of reaction progress. Our fundamental investigation of the extent and kinetics of these anion exchange processes aims to provide better-informed guidelines towards engineering IHP QDs and other halide perovskite materials for diverse applications such as tandem cells and white light-emitting diodes.

On the mechanism of anion exchange in halide perovskite quantum dot solutions

ACS Spring 2022

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