High Performance Multilayer MoS₂ Transistors with Scandium Contacts

While there has been growing interest in two-dimensional (2-D) crystals other than graphene, evaluating their potential usefulness for electronic applications is still in its infancy due to the lack of a complete picture of their performance potential. The focus of this article is on contacts. We demonstrate that through a proper understanding and design of source/drain contacts and the right choice of number of MoS₂ layers the excellent intrinsic properties of this 2-D material can be harvested. Using scandium contacts on 10-nm-thick exfoliated MoS₂ flakes that are covered by a 15 nm Al₂O₃ film, high effective mobilities of 700 cm²/(V s) are achieved at room temperature. This breakthrough is largely attributed to the fact that we succeeded in eliminating contact resistance effects that limited the device performance in the past unrecognized. In fact, the apparent linear dependence of current on drain voltage had mislead researchers to believe that a truly Ohmic contact had already been achieved, a misconception that we also elucidate in the present article

Electrospun Hierarchical TiO₂ Nanorods with High Porosity for Efficient Dye-Sensitized Solar Cells

Ultraporous anatase TiO₂ nanorods with a composite structure of mesopores and macropores fabricated via a simple microemulsion electrospinning approach were first used as photoanode materials for high-efficiency dye-sensitized solar cells (DSSCs). The special multiscale porous structure was formed by using low-cost paraffin oil microemulsion droplets as the soft template, which can not only provide enhanced adsorption sites for dye molecules but also facilitate the electrolyte diffusion. The morphology, porosity, and photovoltaic and electron dynamic characteristics of the porous TiO₂ nanorod based DSSCs were investigated in detail by scanning electron microscopy (SEM), N₂ sorption measurements, current density–voltage (<i>J</i>–<i>V</i>) curves, UV–vis diffuse reflectance spectra, electrochemical impedance spectroscopy (EIS), intensity modulated photocurrent/photovoltage spectroscopy (IMPS/IMVS), and open-circuit voltage decay (OCVD) measurements. The results revealed that, although fewer amounts of dyes were anchored on the porous TiO₂ nanorod films, they exhibited stronger light scattering ability, fast electrolyte diffusion, and extended electron lifetime compared to the commercial P25 nanoparticles. A power conversion efficiency of 6.07% was obtained for the porous TiO₂ nanorod based DSSCs. Moreover, this value can be further improved to 8.53% when bilayer structured photoanode with porous TiO₂ nanorods acting as the light scattering layer was constructed. This study demonstrated that the porous TiO₂ nanorods can work as promising photoanode materials for DSSCs

Large-Area Synthesis of a Ni₂P Honeycomb Electrode for Highly Efficient Water Splitting

Transition metal phosphides have recently been regarded as robust, inexpensive electrocatalysts for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). Thus far, tremendous scientific efforts have been applied to improve the catalytic activity of the catalyst, whereas the scale-up fabrication of morphology-controlled catalysts while maintaining their desired performance remains a great challenge. Herein, we present a facile and scalable approach to fabricate the macroporous Ni₂P/nickel foam electrode. The obtained electrocatalyst exhibits superior bifunctional catalytic activity and durability, as evidenced by a low overpotential of 205 and 300 mV required to achieve a high current density of 100 mA cm^–2 for HER and OER, respectively. Such a spray-based strategy is believed to widely adapt for the preparation of electrodes with uniform macroporous structures over a large area (e.g., 100 cm²), which provides a universal strategy for the mass fabrication of high performance water-splitting electrodes

A CsPbBr₃ Perovskite Quantum Dot/Graphene Oxide Composite for Photocatalytic CO₂ Reduction

Halide perovskite quantum dots (QDs), primarily regarded as optoelectronic materials for LED and photovoltaic devices, have not been applied for photochemical conversion (e.g., water splitting or CO₂ reduction) applications because of their insufficient stability in the presence of moisture or polar solvents. Herein, we report the use of CsPbBr₃ QDs as novel photocatalysts to convert CO₂ into solar fuels in nonaqueous media. Under AM 1.5G simulated illumination, the CsPbBr₃ QDs steadily generated and injected electrons into CO₂, catalyzing CO₂ reduction at a rate of 23.7 μmol/g h with a selectivity over 99.3%. Additionally, through the construction of a CsPbBr₃ QD/graphene oxide (CsPbBr₃ QD/GO) composite, the rate of electron consumption increased 25.5% because of improved electron extraction and transport. This study is anticipated to provide new opportunities to utilize halide perovskite QD materials in photocatalytic applications