Nghiên cứu

Trang chủ / Nghiên cứu

Năm công bố

Enhanced endurance organolead halide perovskite resistive switching memories operable under an extremely low bending radius

It was demonstrated that organolead halide perovskites (OHPs) show a resistive switching behavior with an ultralow electric field of a few kilovolts per centimeter. However, a slow switching time and relatively short endurance remain major obstacles for the realization of the next-generation memory. Here, we report a performance-enhanced OHP resistive switching device. To fabricate topologically and electronically improved OHP thin films, we added hydroiodic acid solution (for an additive) in the precursor solution of the OHP. With drastically improved morphology such as small grain size, low peak-to-valley depth, and precise thickness, the OHP thin films showed an excellent performance as insulating layers in Ag/CH3NH3PbI3/Pt cells, with an endurance of over 103 cycles, a high on/off ratio of 106, and an operation speed of 640 μs and without electroforming. We suggest plausible resistive switching and …

Đọc thêm

Polarized Light‐Emitting Diodes Based on Patterned MoS2 Nanosheet Hole Transport Layer

Here, this study successfully fabricates few‐layer MoS2 nanosheets from (NH4)2MoS4 and applies them as the hole transport layer as well as the template for highly polarized organic light‐emitting diodes (OLEDs). The obtained material consists of polycrystalline MoS2 nanosheets with thicknesses of 2 nm. The MoS2 nanosheets are patterned by rubbing/ion‐beam treatment. The Raman spectra shows that {poly(9,9‐dioctylfluorene‐alt‐benzothiadiazole), poly[(9,9‐di‐n‐octylfluorenyl‐2,7‐diyl)‐alt‐(benzo[2,1,3]thiadiazol‐4,8‐diyl)]} (F8BT) on patterned MoS2 exhibits distinctive polarization behavior. It is discovered that patterned MoS2 not only improves the device efficiency but also changes the polarization behavior of the devices owing to the alignment of F8BT. This work demonstrates a highly efficient polarized OLED with a polarization ratio of 62.5:1 in the emission spectrum (166.7:1 at the peak intensity of 540 …

Đọc thêm

Facile solution synthesis of tungsten trioxide doped with

A facile, highly efficient approach to obtain molybdenum trioxide (MoO 3)-doped tungsten trioxide (WO 3) is reported. An annealing process was used to transform ammonium tetrathiotungstate [(NH 4) 2 WS 4] to WO 3 in the presence of oxygen. Ammonium tetrathiomolybdate [(NH 4) 2 MoS 4] was used as a dopant to improve the film for use in an electrochromic (EC) cell.(NH 4) 2 MoS 4 at different concentrations (10, 20, 30, and 40 mM) was added to the (NH 4) 2 WS 4 precursor by sonication and the samples were annealed at 500 C in air. Raman, X-ray diffraction, and X-ray photoelectron spectroscopy measurements confirmed that the (NH 4) 2 WS 4 precursor decomposed to WO 3 and the (NH 4) 2 MoS 4–(NH 4) 2 WS 4 precursor was transformed to MoO 3-doped WO 3 after annealing at 500 C. It is shown that the MoO 3-doped WO 3 film is more uniform and porous than pure WO 3, confirming the doping quality …

Đọc thêm

Control of the Crystal Growth Shape in CH3NH3PbBr3 Perovskite Materials

CH3NH3PbBr3 (MAPbBr3) materials with perovskite structure were grown by a two-step process using Pb(CH3COO)2·3H2O and methyl amine bromide (MABr). By changing the concentration of MABr in isopropyl alcohol (IPA) solvent and the annealing temperature, the shape of CH3NH3PbBr3 materials can be controlled to afford nanocubes, nanowires, nanorods, and wrinkled structures. MAPbBr3 with single cubic structure was obtained at a MABr concentration of 3 mg/mL in IPA, and a nanorod array of MAPbBr3 was realized at a MABr concentration of 9 mg/mL in IPA at room temperature. Uniformly wrinkled shapes were formed after the synthesis temperature was increased to 60 and 90 °C. The X-ray diffraction patterns, Fourier transform infrared spectra, and X-ray photoelectron spectra of CH3NH3PbBr3 nanorods confirmed that the pure perovskite phase was obtained by dipping Pb(CH3COO)2·3H2O in …

Đọc thêm

Air‐Stable Cesium Lead Iodide Perovskite for Ultra‐Low Operating Voltage Resistive Switching

CsPbX3 (X = halide, Cl, Br, or I) all‐inorganic halide perovskites (IHPs) are regarded as promising functional materials because of their tunable optoelectronic characteristics and superior stability to organic–inorganic hybrid halide perovskites. Herein, nonvolatile resistive switching (RS) memory devices based on all‐inorganic CsPbI3 perovskite are reported. An air‐stable CsPbI3 perovskite film with a thickness of only 200 nm is successfully synthesized on a platinum‐coated silicon substrate using low temperature all‐solution process. The RS memory devices of Ag/polymethylmethacrylate (PMMA)/CsPbI3/Pt/Ti/SiO2/Si structure exhibit reproducible and reliable bipolar switching characteristics with an ultralow operating voltage (<+0.2 V), high on/off ratio (>106), reversible RS by pulse voltage operation (pulse duration < 1 ms), and multilevel data storage. The mechanical flexibility of the CsPbI3 perovskite RS …

Đọc thêm

Low-dimensional halide perovskites: review and issues

Halide perovskites are emerging materials for future optoelectronics and electronics due to their remarkable advantages such as a high light absorption coefficient, long charge carrier diffusion length, facile synthesis method, and low cost. As polycrystalline halide perovskite thin films, which have been studied so far, have crucial limitations, low-dimensional halide perovskites have attracted attention due to their unique optical properties and charge transport properties, which have not been observed before. This review highlights the limitations of polycrystalline halide perovskites thin films and the unique characteristics of low-dimensional halide perovskite nanostructures including their electrical, optical, and chemical properties. After introducing the recent developments of various low-dimensional halide perovskite nanostructures including the synthesis methods, their properties, and applications, a brief overview of …

Đọc thêm

Data Storage: Air‐Stable Cesium Lead Iodide Perovskite for Ultra‐Low Operating Voltage Resistive Switching (Adv. Funct. Mater. 5/2018)

Cesium lead iodide (CsPbI3) perovskite, an all‐inorganic halide perovskite, is synthesized on a platinum‐coated silicon substrate for an ultra‐low operating voltage resistive switching memory device by Soo Young Kim, Ho Won Jang, and co‐workers in article number 1705783. An electrochemical metallization mechanism involving metal conducting filaments is proposed to explain the resistive switching behavior which can be applied to next‐generation synaptic devices.

Đọc thêm

Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals for Light Conversion

In this report, we present a new approach for the fabrication and application of Cs4PbBr6 microcrystals (Cs4PbBr6 MCs). The Cs4PbBr6 MCs are synthesized via an anti-solvent induced crystallization of PbBr2:CsBr directly in dimethylsulfoxide (DMSO) by introducing HBr (HBr, 48% aqueous solution). The ratio of HBr and DMSO plays a vital role in the formation of Cs4PbBr6. By controlling the HBr/DMSO ratio, pure Cs4PbBr6 or the CsPbBr3 phase can be obtained. The Cs4PbBr6 MCs were initially obtained by adding HBr to CsBr:PbBr2/DMSO. However, on increasing the amount of the added HBr, Cs4PbBr6 MCs were converted to CsPbBr3 MCs and the photoluminescence (PL) disappeared. It was also found that CsPbBr3 MCs can be transformed to Cs4PbBr6 MCs by simply adding DMSO to the dried CsPbBr3 MCs. The Cs4PbBr6 MCs exhibit a strong PL at 516 nm with a full width at half-maximum of 25 nm …

Đọc thêm

A thorough study on electrochromic properties of metal doped tungsten trioxide film prepared by a facile solution process

In this research, we investigate the effect of metal doping on the electrochromic (EC) performance of tungsten trioxide (WO3) films. These films were prepared by a novel method involving solution processing and thermal annealing. In this procedure, ammonium tetrathiotungstate ((NH4)2WS4) was dissolved in dimethylformamide at a high concentration ratio (200 mg mL−1) to obtain a homogeneous solution and then spin-coated onto the indium thin oxide (ITO) substrate for use as a working electrode. Subsequently, the film was annealed at the different temperatures (200, 300, 400, and 500 °C) to form a crystal structure of WO3. X-ray diffraction, Raman, and X-ray photoelectron spectroscopic results confirm the crystal formation of WO3. Moreover, in order to improve the electrochromic performance, different concentrations (10, 20, 30, and 40 mM) of different metal chlorides such as PtCl4, PdCl2, AuCl3, AgCl …

Đọc thêm

Recent Advances toward High‐Efficiency Halide Perovskite Light‐Emitting Diodes: Review and Perspective

Organic–inorganic halide perovskite materials have attracted significant attention during the last few years because of their superior properties for electronic and optoelectronic devices, such as their long charge‐carrier diffusion lengths and high photoluminescence quantum yields of up to 100% with tunable bandgaps over the entire visible spectral range. In addition to solar cells, light‐emitting diodes represent a fascinating application for halide perovskite materials. Here, the recent progress relating to halide perovskite LEDs is reviewed. The current strategies for improving the performance of halide LEDs, focusing on morphological engineering, dimensional engineering, compositional engineering, surface passivation, interfacial engineering, and the plasmonic effect are discussed. The challenges and perspectives for the future development of halide perovskite LEDs are also considered.

Đọc thêm

The role of metal dopants in WS2 nanoflowers in enhancing the hydrogen evolution reaction

We demonstrate a facile and efficient method for the synthesis of a metal-doped WS2nanoflower (NF) catalyst. We also report its application for the electrocatalytic hydrogen evolution reaction (HER). The flower-like WS2 particles were produced by a hydrothermal reaction, and, subsequently, the WS2 was doped with metal chlorides such as AuCl3, AgCl, PtCl2, and PdCl2, followed by reduction with sodium borohydride to form metal-doped WS2 NFs. The Pd-doped WS2 NF catalyst showed a high HER performance, having a Tafel slope of 54 mV/dec and an overpotential of -175 mV at −10 mA cm−2. The improvement is attributed to the energy band alignment near the H+/H2reduction potential and the large surface area of the WS2 NFs.

Đọc thêm

Tungsten trioxide doped with CdSe quantum dots for smart windows

Nanocrystal quantum dots (QDs) provide tunable optoelectronic properties on the basis of their dimension. CdSe QDs, which are size-dependent colloidal nanocrystals, are used for efficient electrochromic devices owing to their unique properties in modulating quantum confinement, resulting in enhanced electron insertion during the electrochromic process. Incorporating a well-known metal oxide electrochromic material such as WO3 into CdSe QDs enhances the redox process. Herein, we propose a facile method for producing and optimizing CdSe QDs doped in WO3. The fabrication of the electrochromic film involves a solution and annealing process. Moreover, the effect of the QD size to optimize the electrochromic layer is studied. As a result, the coloration efficiency of WO3 and optimized CdSe QD–WO3 are obtained as 68.6 and 112.3 cm2/C, respectively. Thus, size-tunable nanocrystal QDs combined with a …

Đọc thêm

Halide Perovskite Quantum Dots for Light‐Emitting Diodes: Properties, Synthesis, Applications, and Outlooks

Recently, quantum dot light‐emitting devices have drawn significant attention in the field of display technologies due to their low power consumption, high color purity, and solution processability. Among these, halide perovskite quantum dots (HPQDs) have emerged as the most efficient quantum dots for light‐emitting applications, with photoluminescence quantum yields (PLQYs) approaching 100%. In this Review, the current progress of HPQDs, including their synthesis, properties, and applications in light‐emitting devices, are summarized and discussed. First, the optical and physical properties of HPQDs and their advantages as emissive layers in light‐emitting devices are discussed. Next, synthetic strategies for the synthesis of high‐quality and high‐PLQY HPQDs are introduced. Subsequently, critical parameters affecting the properties and structures of HPQDs, such as the role of surface passivation, fast anion …

Đọc thêm

Surface extension of MeS2 (Me= Mo or W) nanosheets by embedding MeSx for hydrogen evolution reaction

Description Two-dimensional transition metal dichalcogenides (2D-TMDs), such as MoS2 and WS2 nanosheets (MeS2-NS), are reported as efficient catalysts for hydrogen evolution reaction (HER), which can potentially replace the expensive platinum catalyst. In this report, 1T phase MeS2 (1T-MeS2) NS are synthesized by lithium-intercalation exfoliation method, subsequently being modified by amorphous MoSx and WSx (MeSx@MeS2-NS) through a solvothermal method. Interestingly, MeSx@MeS2-NS significantly improves the HER performance compared with bare MeS2-NS as catalysts. Among these, MoSx@MoS2 is observed to be the best combination for HER, with an onset potential and Tafel slope of 114 mV and 45.1 mV decade−1, respectively. The enhancement in the HER device using MeSx@MeS2-NS as the catalyst originates from vertically grown MeSx, which provides additional active sulfur sites for the …

Đọc thêm

MoSe2-GO/rGO Composite Catalyst for Hydrogen Evolution Reaction

There has been considerable research to engineer composites of transition metal dichalcogenides with other materials to improve their catalytic performance. In this work, we present a modified solution-processed method for the formation of molybdenum selenide (MoSe 2) nanosheets and a facile method of structuring composites with graphene oxide (GO) or reduced graphene oxide (rGO) at different ratios to prevent aggregation of the MoSe 2 nanosheets and hence improve their electrocatalytic hydrogen evolution reaction performance. The prepared GO, rGO, and MoSe 2 nanosheets were characterized by X-ray powder diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and scanning electron microscopy. The electrocatalytic performance results showed that the pure MoSe 2 nanosheets exhibited a somewhat high Tafel slope of 80 mV/dec, whereas the MoSe 2-GO and MoSe 2-rGO composites showed lower Tafel slopes of 57 and 67 mV/dec at ratios of 6: 4 and 4: 6, respectively. We attribute the improved catalytic effects to the better contact and faster carrier transfer between the edge of MoSe 2 and the electrode due to the addition of GO or rGO. View Full-Text

Đọc thêm