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Kameel Abdel-Latif1 Robert Epps1 Corwin Kerr1 Christopher Papa1 Felix Castellano1 Milad Abolhasani1

1, North Carolina State University, Raleigh, North Carolina, United States

Inorganic perovskite quantum dots (IPQDs) have demonstrated remarkable success as a more energy-efficient alternative to well-studied metal chalcogenide QDs, and are attracting attention from the energy and chemical industries for a wide range of applications including photovoltaic devices, LED displays, and solar-enabled organic synthesis (photocatalysis). The facile bandgap tunability at room temperature through anion exchange reactions, high photoluminescence quantum yield, and relatively high defect tolerance, differentiate IPQDs from the other colloidal semiconductor nanocrystals. Despite the groundbreaking advancements of IPQDs in the field, their unique ionic nature (different than metal chalcogenide QDs) require new colloidal synthesis routes and surface chemistries. Conventionally, batch synthesis methods are utilized to synthesize, screen, and optimize solution-processed QDs. However, the massive reaction parameter space associated with IPQDs, in combination with the inherent mass and heat transfer challenges of batch methods, necessitate the utilization of material- and time-efficient synthesis methods for fundamental and applied studies of IQPDs. In this work, we develop and utilize a modular microfluidic platform for accelerated in-situ studies of IPQDs anion exchange reactions with minimum reagent consumption. The developed flow synthesis platform enables precise process control of halide exchange reactions, isolating reaction kinetics from precursor mixing rates in a gas-liquid segmented flow system. Utilizing the modular microfluidic strategy, we study in detail the effects of halide composition, ligand ratios, and halide salt source across reaction (residence) times ranging from 0.5 to 90 s. Capitalizing on the wealth of the systematic studies of anion exchange reaction, enabled by the developed time- and material-efficient strategy, we postulate a three-stage reaction mechanism for the homogeneous IPQDs halide exchange reaction. We complement our in situ findings of IPQDs anion exchange reactions with off-line material characterization techniques, gleaning new insights on the overall understanding of the anion exchange reaction network. The results of our kinetic studies of IPQDs halide exchange reactions in combination with the versatility and performance efficiency of the developed modular microfluidic platform, enable on-demand synthesis of IPQDs with a desired bandgap (composition) for targeted applications in optoelectronics and energy technologies.

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