A Droplet-Reactor System Capable of Automation for the Continuous and Scalable Production of Noble-Metal Nanocrystals

Noble-metal nanocrystals with well-controlled shapes or morphologies are of great interest for a variety of applications. To utilize these nanomaterials in consumer products, one has to produce the colloidal nanocrystals in large quantities while maintaining good control over their physical parameters and properties. Droplet reactors have shown great potential for the continuous and scalable production of colloidal nanocrystals with controlled shapes. However, the efficiencies of most previously reported systems are still limited because of the complex post-treatment procedures. For example, the mixture of silicone oil and an aqueous suspension of solid products has to be separated by leveraging their miscibility and difference in density, while the solid products often need to be purified and concentrated by centrifugation. Herein, we report the design and construction of a droplet-reactor system that include new features such as a homemade unit for the automatic separation of silicone oil from the aqueous phase as well as a cross-flow filtration unit for the effective purification and concentration of the nanocrystals. Using various types of Pd nanocrystals as examples, we have demonstrated the feasibility of using this system to automatically produce and collect samples with uniform sizes and well-controlled shapes

A Droplet-Reactor System Capable of Automation for the Continuous and Scalable Production of Noble-Metal Nanocrystals

Noble-metal nanocrystals with well-controlled shapes or morphologies are of great interest for a variety of applications. To utilize these nanomaterials in consumer products, one has to produce the colloidal nanocrystals in large quantities while maintaining good control over their physical parameters and properties. Droplet reactors have shown great potential for the continuous and scalable production of colloidal nanocrystals with controlled shapes. However, the efficiencies of most previously reported systems are still limited because of the complex post-treatment procedures. For example, the mixture of silicone oil and an aqueous suspension of solid products has to be separated by leveraging their miscibility and difference in density, while the solid products often need to be purified and concentrated by centrifugation. Herein, we report the design and construction of a droplet-reactor system that include new features such as a homemade unit for the automatic separation of silicone oil from the aqueous phase as well as a cross-flow filtration unit for the effective purification and concentration of the nanocrystals. Using various types of Pd nanocrystals as examples, we have demonstrated the feasibility of using this system to automatically produce and collect samples with uniform sizes and well-controlled shapes

High Performance of Perovskite Solar Cells via Catalytic Treatment in Two-Step Process: The Case of Solvent Engineering

Currently, the potential mechanism of the solvent-assisted crystallization for mixed cations perovskite thin film (FA_<i>x</i>MA_1–<i>x</i>PbI₃) prepared via two-step solution-process still remains obscure. Here, we clarified the molecular-competing-reacted process of NH₂CHNH₂I (FAI) and CH₃NH₃I (MAI) with PbI₂(DMSO)_<i>x</i> complex in dimethyl sulfoxide (DMSO) and diethyl ether (DE) catalytic solvent system in the sequential two-step solution-process. The microscopic dynamics was characterized via the characterizations of in situ photoluminescence spectra. In addition, we found that the thermal stability of the perovskite films suffered from the residual solvent with high boiling point, for example, DMSO. The further DE treatment could promote the volatility process of DMSO and accelerate the crystallization process of perovskite films. The highest PCE over 19% with slight hysteresis effect was eventually obtained with a reproducible FA_0.88MA_0.12PbI₃ solar cell, which displayed a constant power output within 100 s upon light soaking and stable PCE output within 30 d in the thermal stability test

Supplementary document for Event-based X-ray imager by ghosting-free scintillator film - 6902951.pdf

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Facile Synthesis of Iridium Nanocrystals with Well-Controlled Facets Using Seed-Mediated Growth

Iridium nanoparticles have only been reported with roughly spherical shapes and sizes of 1–5 nm, making it impossible to investigate their facet-dependent catalytic properties. Here we report for the first time a simple method based on seed-mediated growth for the facile synthesis of Ir nanocrystals with well-controlled facets. The essence of this approach is to coat an ultrathin conformal shell of Ir on a Pd seed with a well-defined shape at a relatively high temperature to ensure fast surface diffusion. In this way, the facets on the initial Pd seed are faithfully replicated in the resultant Pd@Ir core–shell nanocrystal. With 6 nm Pd cubes and octahedra encased by {100} and {111} facets, respectively, as the seeds, we have successfully generated Pd@Ir cubes and octahedra covered by Ir{100} and Ir{111} facets. The Pd@Ir cubes showed higher H₂ selectivity (31.8% vs 8.9%) toward the decomposition of hydrazine compared with Pd@Ir octahedra with roughly the same size

Continuous and Scalable Production of Well-Controlled Noble-Metal Nanocrystals in Milliliter-Sized Droplet Reactors

Noble-metal nanocrystals are essential to applications in a variety of areas, including catalysis, electronics, and photonics. Despite the large number of reports, there still exists a gap between academic studies and industrial applications due to the lack of ability to produce the nanocrystals in large quantities while still maintaining the good uniformity and precise controls. Because the nucleation and growth of colloidal nanocrystals are highly sensitive to experimental conditions, it is impractical to scale up their production by simply increasing the reaction volume. Here we report a new and practical approach based on milliliter-sized droplet reactors to the scalable production of nanocrystals. The droplets of 0.25 mL in volume were produced as a continuous flow in a fluidic device assembled from commercially available components. As a proof of concept, we have synthesized Pd, Au, and Pd-M (M = Au, Pt, and Ag) nanocrystals with controlled sizes, shapes, compositions, and structures on a scale of 1–10 g per hour (e.g., 3.6 g per hour for Pd cubes of 10 nm in edge length)

Double Perovskite Single Crystals with High Laser Irradiation Stability for Solid-State Laser Lighting and Anti-counterfeiting

Laser lighting devices, comprising an ultraviolet (UV) laser chip and a phosphor material, have emerged as a highly efficient approach for generating high-brightness light sources. However, the high power density of laser excitation may exacerbate thermal quenching in conventional polycrystalline or amorphous phosphors, leading to luminous saturation and the eventual failure of the device. Here, for the first time, we raise a single-crystal (SCs) material for laser lighting considering the absence of grain boundaries that scatter electrons and phonons, achieving high thermal conductivity (0.81 W m–1 K–1) and heat-resistance (575 °C). The SCs products exhibit a high photoluminescence quantum yield (89%) as well as excellent stability toward high-power lasers (>12.41 kW/cm2), superior to all previously reported amorphous or polycrystalline matrices. Finally, the laser lighting device was fabricated by assembling the SC with a UV laser chip (50 mW), and the device can maintain its performance even after continuous operation for 4 h. Double perovskite single crystals doped with Yb3+/Er3+ demonstrated multimodal luminescence with the irradiation of 355 and 980 nm lasers, respectively. This characteristic holds significant promise for applications in spectrally tunable laser lighting and multimodal anticounterfeiting

Synthesis of Pt–Ni Octahedra in Continuous-Flow Droplet Reactors for the Scalable Production of Highly Active Catalysts toward Oxygen Reduction

A number of groups have reported the syntheses of nanosized Pt–Ni octahedra with remarkable activities toward the oxygen reduction reaction (ORR), a process key to the operation of proton-exchange membrane fuel cells. However, the throughputs of those batch-based syntheses are typically limited to a scale of 5–25 mg Pt per batch, which is far below the amount needed for commercial evaluation. Here we report the use of droplet reactors for the continuous and scalable production of Pt–Ni octahedra with high activities toward ORR. In a typical synthesis, Pt­(acac)₂, Ni­(acac)₂, and W­(CO)₆ were dissolved in a mixture of oleylamine, oleic acid, and benzyl ether, and then pumped into a polytetrafluoroethylene tube. When the solution entered the reaction zone at a temperature held in the range of 170–230 °C, W­(CO)₆ quickly decomposed to generate CO gas, naturally separating the reaction solution into discrete, uniform droplets. Each droplet then served as a reactor for the nucleation and growth of Pt–Ni octahedra whose size and composition could be controlled by changing the composition of the solvent and/or adjusting the amount of Ni­(acac)₂ added into the reaction solution. For a catalyst based on Pt_2.4Ni octahedra of 9 nm in edge length, it showed an ORR mass activity of 2.67 A mg_Pt^–1 at 0.9 V, representing an 11-fold improvement over a state-of-the-art commercial Pt/C catalyst (0.24 A mg_Pt^–1)

Low-Temperature-Processed Amorphous Bi₂S₃ Film as an Inorganic Electron Transport Layer for Perovskite Solar Cells

Organic–inorganic hybrid perovskite solar cells have attracted great attention due to their unique properties and rapid increased power conversion efficiency. Currently, PC₆₁BM is widely used as the electron transport layer (ETL) for inverted hybrid perovksite solar cells. Here we propose and demonstrate that Bi₂S₃, a ribboned compound with intrinsic high mobility and stability, could be used as the ETL for perovksite solar cells. Through a simple thermal evaporation with the substrate kept at room temperature, we successfully produced a compact and smooth amorphous Bi₂S₃ ETL with high conductivity. Our NiO/CH₃NH₃PbI₃/Bi₂S₃ solar cell achieved a device efficiency of 13%, which is comparable with our counterpart device using PC₆₁BM as the ETL. Moreover, our device showed much improved ambient storage stability due to the hydrophobic and hermetic encapsulation of the perovskite layer by the Bi₂S₃ ETL. We believe thermally evaporated Bi₂S₃ is a promising ETL for inverted hybrid perovskite solar cells and worthy of further exploration

Cs₂AgInCl₆ Double Perovskite Single Crystals: Parity Forbidden Transitions and Their Application For Sensitive and Fast UV Photodetectors

Double perovskite Cs₂AgInCl₆ is newly reported as a stable and environmentally friendly alternative to lead halide perovskites. However, the fundamental properties of this material remain unexplored. Here, we first produced high-quality Cs₂AgInCl₆ single crystals (SCs) with a low trap density of 8.6 × 10⁸ cm^–3, even lower than the value reported in the best lead halide perovskite SCs. Through systematical optical and electronic characterization, we experimentally verified the existence of the proposed parity-forbidden transition in Cs₂AgInCl₆ and identified the role of oxygen in controlling its optical properties. Furthermore, sensitive (dectivity of ∼10¹² Jones), fast (3 dB bandwidth of 1035 Hz), and stable UV photodetectors were fabricated based on our Cs₂AgInCl₆ SCs, showcasing their advantages for optoelectronic applications