(63k) Autonomous Synthesis of Eco-Friendly Metal Halide Perovskite Nanocrystals

Metal halide perovskite (MHP) nanocrystals (NCs) have been of great interest in photonic and optoelectronic devices due to their size- and composition-tunable optical properties, high photoluminescence quantum yield (PLQY), large absorption cross section, and facile solution-phase synthesis and processing. Despite the intriguing properties of MHP NCs, their adoption by printed technologies is greatly hampered by the lead toxicity. Recently, copper (Cu)-based MHPs have emerged as a promising lead-free candidate with unique optical properties, such as a wide bandgap energy, a large stokes shift, narrow size distributions, and tunable self-trapped exciton (STE) emissions. Among Cu-based MHP NCs, cesium copper iodide (Cs₃Cu₂I₅) exhibits a high air stability and has a pure orthorhombic crystal structure, where tetrahedral [CuI₄] and trigonal [CuI₃] units are edge-shared to form [Cu₂I₅] clusters that are isolated by cesium cations.¹ While the synthesis and optical/morphology properties of cesium copper halide perovskites have been reported in literature,^1–4 the fast formation kinetics of these NCs could result in batch-to-batch variations, which complicates their fundamental and applied studies. Herein, we report a modular flow chemistry platform directed by machine learning (ML) to autonomously synthesize Cs₃Cu₂I₅ NCs with the desired optical and optoelectronic properties for photonic devices. Utilizing an active learning-guided experimentation mode of the developed self-driven flow chemistry strategy, we autonomously study the effects of precursor concentration, ligand population, reaction time, and temperature on the optical properties of Cs₃Cu₂I₅ NCs. Utilizing Bayesian optimization, we demonstrate the unique potential of miniaturized flow reactors equipped with an online monitoring probe for accelerated parameter space mapping and on-demand synthesis of high-performing lead-free MHP NCs while minimizing chemical consumption and waste generation.

References:

(1) Luo, Z.; Li, Q.; Zhang, L.; Wu, X.; Tan, L.; Zou, C.; Liu, Y.; Quan, Z. 0D Cs₃Cu₂X₅ (X = I, Br, and Cl) Nanocrystals: Colloidal Syntheses and Optical Properties. Small 2020, 16 (3), 1905226. https://doi.org/10.1002/smll.201905226.

(2) Li, Y.; Vashishtha, P.; Zhou, Z.; Li, Z.; Shivarudraiah, S. B.; Ma, C.; Liu, J.; Wong, K. S.; Su, H.; Halpert, J. E. Room Temperature Synthesis of Stable, Printable Cs₃Cu₂X₅ (X = I, Br/I, Br, Br/Cl, Cl) Colloidal Nanocrystals with Near-Unity Quantum Yield Green Emitters (X = Cl). Chem. Mater. 2020, 32 (13), 5515–5524. https://doi.org/10.1021/acs.chemmater.0c00280.

(3) Lu, Y.; Fang, S.; Li, G.; Li, L. Optimal Colloidal Synthesis and Quality Judgment of Low-Dimensional Cs₃Cu₂Cl₅ Nanocrystals with Efficient Green Emission. J. Alloys Compd. 2022, 903, 163924. https://doi.org/10.1016/j.jallcom.2022.163924.

(4) Li, C.-X.; Cho, S.-B.; Kim, D.-H.; Park, I.-K. Monodisperse Lead-Free Perovskite Cs₃Cu₂I₅ Nanocrystals: Role of the Metal Halide Additive. Chem. Mater. 2022, 34 (15), 6921–6932. https://doi.org/10.1021/acs.chemmater.2c01318.