Here, a simplified synthesis of graphitic carbon nitride quantum dots (g‐C3N4‐QDs) with improved solution and electroluminescent properties using a one‐pot methylamine intercalation–stripping method (OMIM) to hydrothermally exfoliate QDs from bulk graphitic carbon nitride (g‐C3N4) is presented. The quantum dots synthesized by this method retain the blue photoluminescence with extremely high fluorescent quantum yield (47.0%). As compared to previously reported quantum dots, the g‐C3N4‐QDs synthesized herein have lower polydispersity and improved solution stability due to high absolute zeta‐potential (−41.23 mV), which combine to create a much more tractable material for solution processed thin film fabrication. Spin coating of these QDs yields uniform films with full coverage and low surface roughness ideal for quantum dot light‐emitting diode (QLED) fabrication. When incorporated into a functional QLED with OMIM g‐C3N4‐QDs as the emitting layer, the LED demonstrates ≈60× higher luminance (605 vs 11 Cd m−2) at lower operating voltage (9 vs 21 V), as compared to the previously reported first generation g‐C3N4 QLEDs, though further work is needed to improve device stability.
Pseudocapacitance holds great promise for energy density improvement of supercapacitors, but electrode materials show practical capacity far below theoretical values due to limited ion diffusion accessibility and/or low electron transferability. Herein, inducing two kinds of straight ion-movement channels and fast charge storage/delivery for enhanced reaction kinetics is proposed. Very thick electrodes consisting of vertically aligned and ordered arrays of NiCo2S4-nanoflake-covered slender nickel columns (NCs) are achieved via a scalable route. The vertical standing ∼5 nm ultrathin NiCo2S4 flakes build a porous covering with straight ion channels without the “dead volume”, leading to thickness-independent capacity. Benefiting from the architecture acting as a “superhighway” for ultrafast ion/electron transport and providing a large surface area, high electrical conductivity, and abundant availability of electrochemical active sites, the NiCo2S4@NC-array electrode achieves a specific capacity up to 486.9 mAh g–1. The electrode even can work with a high specific capacity of 150 mAh g–1 at a very high current density of 100 A g–1. In particular, due to the advanced structure features, the electrode exhibits excellent flexibility with a unexpected improvement of capacity when being largely bent and excellent cycling stability with an obvious resistance decrease after the cycles. An asymmetric pseudocapacitor applying the NiCo2S4@NC-array as a positive electrode achieves an energy density of 66.5 Wh kg–1 at a power density of 400 W kg–1, superior to the most reported values for asymmetric devices with NiCo2S4 electrodes. This work provides a scalable approach with mold-replication-like simplicity toward achieving thickness-independent electrodes with ultrafast ion/electron transport for energy storage.
Although perovskite wafers with a scalable size and thickness are suitable for direct X‐ray detection, polycrystalline perovskite wafers have drawbacks such as the high defect density, defective grain boundaries, and low crystallinity. Herein, PbI2‐DMSO powders are introduced into the MAPbI3 wafer to facilitate crystal growth. The PbI2 powders absorb a certain amount of DMSO to form the PbI2‐DMSO powders and PbI2‐DMSO is converted back into PbI2 under heating while releasing DMSO vapor. During isostatic pressing of the MAPbI3 wafer with the PbI2‐DMSO solid additive, the released DMSO vapor facilitates in situ growth in the MAPbI3 wafer with enhanced crystallinity and reduced defect density. A dense and compact MAPbI3 wafer with a high mobility‐lifetime (µτ) product of 8.70 × 10−4 cm2 V−1 is produced. The MAPbI3‐based direct X‐ray detector fabricated for demonstration shows a high sensitivity of 1.58 × 104 µC Gyair−1 cm−2 and a low detection limit of 410 nGyair s−1.
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