(200f) Modular Fluidic Microreactor for Fully Decoupled Precursor Mixing and Reaction Times in Mechanistic Studies of Metal Halide Perovskite Quantum Dot Synthesis

Metal halide perovskite quantum dots are a rapidly growing class of nanomaterials which have sparked significant interest for their broad reaching applications spanning from photocatalysis to optoelectronic devices.^[1] Despite the high value of metal halide perovskite QDs, their synthesis optimization and control have been mostly limited to inefficient and inconsistent flask-based processes. Such batch synthesis reactors consume a large volume of often high-cost materials, require extensive manual labor, and possess inconsistent heat and mass transfer properties when moving between experiments and from flask to flask. These issues impair the accuracy and reduce the effectiveness of existing research efforts. In response, recently microscale flow synthesis strategies have been developed towards more efficient and systematic studies of perovskite quantum dots.^[2–4] Among these flow synthesis platforms, fluoropolymer tubing-based microreactors are another quickly rising area of research, as they offer low-cost, fully modular, and commercially available microreactor components with quick assembly time as compared to conventional chip-based systems. These fluidic platforms offer micro-liter scale reactions volumes with automated, high-throughput, and non-invasive measurement strategies.^[5]

However, as a property inherent to continuous flow processes, reaction time and mixing rates are strongly coupled to the total fluid velocity moving along the flow direction. In this work, we have developed a microscale fluidic microprocessor strategy which can independently control mixing times from 53 ms to 7.3 s with an arbitrarily long residence (i.e., reaction) time. This microscale flow synthesis approach was accomplished by first developing and analyzing a fluoropolymer-based passive micromixer developed using commercially available tubing. We then integrate the passive micromixer module with an automated, material-efficient fluidic sampling module, which allows for two independent flow rates to run simultaneously within the platform. Utilizing the developed modular fluidic platform, “samples” with a specific chemical formulation are pulled from the mixing line and passed to the reaction/analysis line where they continue to react after forming homogenous reactive phase plugs. These plugs move through the flow reactor channel towards a spectral monitoring module for in-situ UV-Vis absorption and photoluminescence measurements.

In the next step, we applied the developed modular flow synthesis platform towards the room-temperature synthesis of cesium-lead-bromide perovskite quantum dots ^[6] and unveiled a mechanistic understanding of the quantum dot growth process through time-resolved spectral sampling. We then conducted a full compositional analysis coupled with variations in the precursor mixing time to attain highly tunable emission colors as well as quantum dot size distributions, quantum yields, reaction yields, and numbers of quantum dots formed. These experiments were coupled with a first principle mesoscopic kinetic Monte Carlo simulation to provide further insights into the mechanism behind the ligand-assisted reprecipitation process at early time scales. The strategies and models developed in this work offer a greater understanding of controlled synthesis of perovskite quantum dots with fast formation kinetics.

References

[1] Q. A. Akkerman, G. Rainò, M. V. Kovalenko, L. Manna, Nat. Mater. 2018, 17, 394.

[2] K. Abdel‐Latif, R. W. Epps, C. B. Kerr, C. M. Papa, F. N. Castellano, M. Abolhasani, Adv. Funct. Mater. 2019, 29, 1900712.

[3] R. W. Epps, K. C. Felton, C. W. Coley, M. Abolhasani, Lab Chip 2017, 17, 4040.

[4] L. Bezinge, R. M. Maceiczyk, I. Lignos, M. V. Kovalenko, A. J. deMello, ACS Appl. Mater. Interfaces 2018, 10, 18869.

[5] S. Marre, K. F. Jensen, Chem. Soc. Rev. 2010, 39, 1183.

[6] S. Wei, Y. Yang, X. Kang, L. Wang, L. Huang, D. Pan, Chem. Comm. 2016, 52, 7265.