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Among methods to synthesize perovskite nanocrystals, flow synthesis has demonstrated the possibility of overcoming batch-to-batch variability problems. This issue often occurs during synthesis using hot injection and ligand-assisted reprecipitation techniques. Microfluidic synthesis features high throughput, efficient heat transfer rates, as well as rapid and uniform mixing. In this work, we developed a portable fluorescence lifetime imager to study the physical and optical properties of perovskite nanocrystals during flow synthesis. The portable fluorescence lifetime imager was combined with a microfluidic synthesis platform. This setup acquired fluorescence lifetime in real-time during the synthesis process. Fluorescence lifetime provides PLQY of perovskite nanocrystals and their luminescence mechanism. In addition, the fluorescence lifetime of perovskite nanocrystals is determined by the spatial arrangement of the nanocrystals, synthesis parameters, fluorescence intermittency, etc. Perovskite is easily affected by environmental factors and then changes, so real-time measurement is essential. In order to control the size and shape of synthesized perovskite nanocrystals, we changed trace synthesis parameters (molar ratio of Cs, Pb, and halide precursors, reaction temperature, flow rate, and reaction time) of the microfluidic device. Meanwhile, direct fluorescence lifetime data from the microfluidic channel revealed synthesis results in real-time. As a comparison, all-inorganic cesium lead halide perovskite nanocrystals were synthesized in traditional batches and underwent post-processing, such as centrifugation, to obtain purified perovskite nanocrystals. We then used a custom-built frequency domain fluorescence lifetime system to measured and compared the purified perovskite nanocrystals and those from flow synthesis. It was shown that our microfluidic synthesis system mixed samples quickly and uniformly, and the real-time fluorescence lifetime data was a good indicator for uniformity of the synthesis results.
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