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.

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...

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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.

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Semiconductors are intriguing due to their unique electrical properties, particularly the behavior of their electrons in the presence of different stimuli (e.g., electric field, magnetic field, light irradiation), which differ greatly from conducting (i.e., metals) and insulating materials. In insulators and semiconductors, the available electronic states are discontinuous, with the existence of a gap between the lower energy states, commonly referred to as the valence band (VB), and the higher energy states, known as the conduction band (CB). The distinguishing factor between these materials is the size of the energy difference between the highest energy state in the VB and the lowest energy state in the CB, called the band gap. In insulators, the band gap is very large, making it difficult, if not impossible, to cause an electron to move from the VB to the CB. By comparison, semiconductors possess narrow to moderate band gaps, implying that it is possible to introduce enough energy to an electron to cause it to move from the VB to the CB, enabling electron transfer, the use of high energy electrons, or the emission of energy (i.e., photons) when the electron returns from the CB to the VB. The wide range of industrial application-specific requirements demands versatility in the target characteristics of semiconductor materials (e.g., size, morphology, composition, band gap, emission wavelength), which are vastly different from those commonly used in thin-film transistors. Typically, the semiconductor materials synthesized for use in the above applications are particulate materials produced across a range of sizes spanning five orders of magnitude (from just a few nm to hundreds of µm), and can be divided into two overarching categories, nano-and microsized particulate materials. Nanosized semiconductor materials, due in large part to their miniscule dimensions, present a variety of intriguing characteristics not observed in microsized semiconductor particles. First and foremost, if the dimensions of the semiconductor material decrease below a certain threshold known as the Bohr radius, the absorption and emission energies become highly dependent on the particle size, a phenomenon known as quantum confinement. [28-30] Moreover, nanosized structures have significantly larger surface-to-volume ratios which increases the surface contribution to the total free energy of the semiconductor materials, making them highly soluble [29] and therefore much easier to process and handle. Thus far, nanosized semiconductor particles have been effectively utilized in sensors, [7] LEDs, [9] Controlled synthesis of semiconductor nano/microparticles has attracted sub stantial attention for use in numerous applications from photovoltaics to photo catalysis and bioimaging due to the breadth of available physicochemical and optoelectronic properties. Microfluidic material synthesis strategies have recently been demonstrated as an effective technique for rapid development, controlled synthesis, and continuous manufacturing of solutionpr...

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We present a flow chemistry platform that decouples precursor mixing rates from reaction time using solely off-the-shelf components. We then utilize this platform towards material-efficient studies of mass transfer-controlled synthesis of inorganic perovskite quantum dots.