The optimal synthesis of advanced nanomaterials with numerous reaction parameters, stages, and routes, poses one of the most complex challenges of modern colloidal science, and current strategies often fail to meet the demands of these combinatorially large systems. In response, we present an Artificial Chemist: the integration of machine learning-based experiment selection and high-efficiency autonomous flow chemistry. With the self-driving Artificial Chemist, we autonomously synthesize made-to-measure inorganic perovskite quantum dots (QDs) in flow, and simultaneously tune for their quantum yield and composition polydispersity at target bandgaps, spanning 1.9 eV to 2.9 eV. Utilizing the Artificial Chemist, eleven precision-tailored QD synthesis compositions are obtained without any prior knowledge, within 30 h, using less than 210 mL of total starting QD solutions, and without user selection of experiments. Using the knowledge generated from these studies, we then pre-train the Artificial Chemist to use a new batch of precursors and further accelerate the synthetic path discovery of QD compositions, by at least two-fold. The knowledge transfer strategy further enhances the optoelectronic properties of the in-flow synthesized QDs (within the same resources as the no-prior knowledge experiments) and mitigates the issues of batch-to-batch precursor variability, resulting in QDs averaging within 1 meV from their target bandgap.

Colloidal organic/inorganic metal-halide perovskite nanocrystals have recently emerged as a potential low-cost replacement for the semiconductor materials in commercial photovoltaics and light emitting diodes. However, unlike III-V and IV-VI semiconductor nanocrystals, studies of colloidal perovskite nanocrystals have yet to develop a fundamental and comprehensive understanding of nucleation and growth kinetics. Here, we introduce a modular and automated microfluidic platform for the systematic studies of room-temperature synthesized cesium-lead halide perovskite nanocrystals. With abundant data collection across the entirety of four orders of magnitude reaction time span, we comprehensively characterize nanocrystal growth within a modular microfluidic reactor. The developed high-throughput screening platform features a custom-designed three-port flow cell with translational capability for in situ spectral characterization of the in-flow synthesized perovskite nanocrystals along a tubular microreactor with an adjustable length, ranging from 3 cm to 196 cm. The translational flow cell allows for sampling of twenty unique residence times at a single equilibrated flow rate. The developed technique requires an average total liquid consumption of 20 μL per spectra and as little as 2 μL at the time of sampling. It may continuously sample up to 30 000 unique spectra per day in both single and multi-phase flow formats. Using the developed plug-and-play microfluidic platform, we study the growth of cesium lead trihalide perovskite nanocrystals through in situ monitoring of their absorption and emission band-gaps at residence times ranging from 100 ms to 17 min. The automated microfluidic platform enables a systematic study of the effect of mixing enhancement on the quality of the synthesized nanocrystals through a direct comparison between single- and multi-phase flow systems at similar reaction time scales. The improved mixing characteristics of the multi-phase flow format results in high-quality perovskite nanocrystals with kinetically tunable emission wavelength, ranging as much as 25 nm at equivalent residence times. Further application of this unique platform would allow rapid parameter optimization in the colloidal synthesis of a wide range of nanomaterials (e.g., metal or semiconductor), that is directly transferable to continuous manufacturing in a numbered-up platform with a similar characteristic length scale.

In an effort to produce the materials of next-generation photoelectronic devices, postsynthesis halide exchange reactions of perovskite quantum dots are explored to achieve enhanced bandgap tunability. However, comprehensive understanding of the multifaceted halide exchange reactions is inhibited by their vast relevant parameter space and complex reaction network. In this work, a facile room-temperature strategy is presented for rapid halide exchange of inorganic perovskite quantum dots. A comprehensive understanding of the halide exchange reactions is provided by isolating reaction kinetics from precursor mixing rates utilizing a modular microfluidic platform, Quantum Dot Exchanger (QDExer). The effects of ligand composition and halide salt source on the rate and extent of the halide exchange reactions are illustrated. This fluidic platform offers a unique time-and material-efficient approach for studies of solution phase-processed colloidal nanocrystals beyond those studied here and may accelerate the discovery and optimization of next-generation materials for energy technologies.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adfm.201900712.to outperform conventional and wellstudied II-VI, IV-VI, and III-V QDs (e.g., CdSe, [7] CdSe/ZnS, [8] PbS, [9] and InP [10] ) in QD-based solar cells [7] and light-emitting diodes (LEDs). [11,12] Perovskite QDs have enabled lower energy consumption and a wider reaching color gamut in QD-based LED displays and unparalleled improvements in photovoltaic power conversion efficiency of QD-based solar cells compared to other third-generation technologies. Recent work [13][14][15] has demonstrated that hybrid perovskite QDs, compared to their thin-film counterparts of equivalent composition, achieve higher open-circuit voltage. The outstanding performance of perovskite QDs can be attributed to their unique optical properties including inherently high charge carrier mobility, long diffusion lengths, high PLQY, and facile bandgap tunability. Moreover, postsynthesis halide exchange of perovskite QDs with halide salts offers an additional degree of control and tunability of the nanocrystal optical properties. [16] Over the last 3 years, various solid-solvent, [17] incompatible solvent-solvent, [18] and homogeneous solution-phase [16] anion exchange strategies have been developed for organic and inorganic perovskite QDs. Among these strategies, homogeneous solution-phase reactions are far more conducive toward continuous nanomanufacturing processes, enabling enhanced parameter control and multidimensional tunability. Further development and implementation of these materials could potentially result in more effective energy technologies toward addressing ever-growing global energy demands via low-cost, high-efficiency solar energy harnessing solutions.Conventionally, manual flask-based techniques have been the primary approach for the synthesis, characterization, and optimization of colloidal QDs. However, the time-and mate...

Solution-processed organic, [1-3] metallic, [4-6] and semiconductor [7,8] nanomaterials, possess unique size-related physicochemical, optical, magnetic, and electronic properties. These materials have enabled groundbreaking advancements in a variety of applications including catalysis, [9-11] drug delivery, [12,13] data storage, [14] and solar cells. [15] Different nucleation and growth models such as LaMer burst nucleation, [16] Ostwald ripening, [17] Finke-Watzky two-step mechanism, [18] orientated attachment, [19] and coalescence [20] have attempted to explain the mechanisms through which nanoparticles are formed in In recent years, microfluidic technologies have emerged as a powerful approach for the advanced synthesis and rapid optimization of various solution-processed nanomaterials, including semiconductor quantum dots and nanoplatelets, and metal plasmonic and reticular framework nanoparticles. These fluidic systems offer access to previously unattainable measurements and synthesis conditions at unparalleled efficiencies and sampling rates. Despite these advantages, microfluidic systems have yet to be extensively adopted by the colloidal nanomaterial community. To help bridge the gap, this progress report details the basic principles of microfluidic reactor design and performance, as well as the current state of online diagnostics and autonomous robotic experimentation strategies, toward the size, shape, and composition-controlled synthesis of various colloidal nanomaterials. By discussing the application of fluidic platforms in recent high-priority colloidal nanomaterial studies and their potential for integration with rapidly emerging artificial intelligence-based decision-making strategies, this report seeks to encourage interdisciplinary collaborations between microfluidic reactor engineers and colloidal nanomaterial chemists. Full convergence of these two research efforts offers significantly expedited and enhanced nanomaterial discovery, optimization, and manufacturing.

Inorganic lead halide perovskite (LHP) quantum dots (QDs) have recently emerged as a promising class of semiconducting materials for next-generation, solution-processed optoelectronic devices. [1] For example, inorganic LHPs have surpassed the performance of conventional IV-VI QDs in photovoltaic devices. [2] The prominence of LHPs among other semiconductor nanocrystals is mainly attributed to their high photoluminescence quantum yield (PLQY), high defect tolerance, facile bandgap tunability, and narrow emission linewidth. The ease of peak emission bandgap tuning (1.7-3.1 eV) makes inorganic LHP QDs a versatile material for widespread applications ranging from solar cells (1.77 eV), [3-6] light-emitting diodes (blue 2.7 eV, green 2.39 eV, and red 1.88 eV), [7-9] and various photocatalytic reactions. [10-12] The peak emission energy of cesium lead halide QDs (CsPbX 3 , X ¼ Cl, Br, I) can be readily tuned by varying i) QD size using the quantum confinement effect, [13-16] ii) ligand composition, [17-19] iii) the chemical composition of the QD through anion, [20-22] and/or cation exchange, [23] and iv) the precursor halide content. [1,24] Despite producing high-quality monodispersed CsPbX 3 QDs, [1] flask-based hot-injection synthetic routes impose major challenges from large-scale manufacturing and reproducibility perspectives. Hot-injection colloidal synthesis requires operating at high temperatures (>150 C), which increases the overall energy costs and necessitates specific reactor design modifications to ensure homogenous, uniform heat distribution across the reactor. Furthermore, manual, flask-based colloidal syntheses are notorious for their lack of reproducibility (batch-to-batch variation and operator error), and difficulty of integration with material diagnostic probes. [13,24,25] Room-temperature colloidal synthesis (e.g., ligand-assisted reprecipitation strategy) [7,26,27] and post-synthesis halide exchange reactions [20-22,28] of CsPbBr 3 QDs are considered attractive alternatives to the hot-injection synthesis strategy for facile and precise bandgap engineering of LHP QDs. QD purification normally involves washing steps that consist of antisolvent addition followed by centrifugation, aliquot disposal, and fresh solvent addition. Moreover, washing and the subsequent redispersal of LHP QDs in fresh solvent disrupts the surface ligands, leading to ligand detachment, [29,30] surface defects (lowering the PLQY), and reduced colloidal stability of the LHP QDs. [30] Removal of the intermediate washing step of halide exchange reactions can enable end-to-end continuous manufacturing of inorganic LHP QDs and accelerate their adoption by chemical and energy technologies.

Autonomous robotic experimentation strategies are rapidly rising in use because, without the need for user intervention, they can efficiently and precisely converge onto optimal intrinsic and extrinsic synthesis conditions for...

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