Oriented Zinc Oxide Nanocrystalline Thin Films Grown from Sol-Gel Solution

Zinc oxide (ZnO) is a wide band gap (~3.37 eV) semiconductor. Thin film ZnO has many attractive applications in optoelectronics and sensors. Recently, nanostructured ZnO (e.g. ZnO quantum dot) has been demonstrated as a hyperbolic material; its dielectric function has opposite signs along different crystal axes within the mid-infrared, making it an interesting material for metamaterials and nanophotonics. Conventional sputtering deposition usually leads to the formation of polycrystalline ZnO films with randomly oriented grains and rough surface. This work demonstrated a solution-based process to grow ZnO thin films with highly oriented nanocrystals. Low-temperature plasmas were employed to modulate the microstructure and optical properties of the films. Such highly anisotropic nanostructured transparent semiconductor films may lead to interesting material properties in developing new optoelectronic devices

Electrochemical Innovations: Advancements in Lithium Metal Batteries & Supercapacitor For Energy Storage

Constructing an artificial solid electrolyte interphase (SEI) on lithium metal electrode is a promising approach to address the rampant growth of dangerous lithium morphologies (dendritic and dead Li0) and low Coulombic efficiency that plague development of lithium metal batteries. But it is not known how the Li+ transfer behavior in the SEI is coupled with mechanical properties. We demonstrate here a facile and scalable solution-processed approach to form a Li3N-rich SEI with a phase-pure crystalline structure that minimizes the diffusion energy barrier of Li+ across the SEI. Compared with a polycrystalline Li3N SEI obtained from conventional approaches, our phase-pure/single crystalline Li3N-rich SEI constitutes an interphase of high mechanical strength and a low Li+ diffusion barrier. We elucidate the correlation among Li+ transference number, diffusion behavior, concentration gradient, and the stability of the lithium metal electrode by integrating phase field simulations with experiments. We demonstrate extreme reversibility and ultra-stable charge/discharge cycling behaviors for both symmetric cells and full lithium-metal batteries constructed using this Li3N-rich SEI. These studies provide new insight into the designing and engineering of an ideal artificial SEI for stable and high-performance lithium metal batteries. The fast depletion of fossil fuel has brought severe energy crises. hindering social progress and threatens human development. The increasing global energy demand requires the development of renewable energy storage technologies. Supercapacitors, or electrical double layer capacitors (EDLCs), seem to be the most likely candidates for the next generation of energy storage devices. Supercapacitors possesses the advantage of the conventional capacitors and ionic batteries, and their properties include high power density, fast charge/discharge rate, long cycle life and environmental friendliness. Although EDLC holds great promises for fast-charging energy storage devices but suffers from a limited specific capacitance. The design and development of high performance EDLC-type carbon materials with the effective synergistic effect of high conductivity, tailored porous structure, and high surface area still remain challenging. Here, we report a novel hierarchical porous carbon with a combination of highly conductive electronic pathways and rich ionic storage units in three-dimensional network morphology, leading to high specific capacitance of EDLC. Specifically, by facile hydrothermal synthesis and carbonization, the carbon electrode derived from metal-organic framework and polymer fibers, exhibits extremely high specific capacitance of ~ 385 F g-1 at 0.1 A g-1 and can still maintain capacitance of 303 F g-1 at 10 A g-1. The high electrochemical performance can be attributed to the rich network of micro and mesoporous structures for electrolyte transport and ion adsorption as well as highly conductive electronic pathways inside the electrodes. The assembled EDLC thus delivers a high energy density of 10.53 Wh kg-1 and a power density of 5.454 kW kg-1 at the current density of 10 A g-1 in aqueous electrolyte. Hence, the present study is expected to open a promising route to developing porous materials for high-performance energy devices

Improving Conductivity of Solution Based Zinc Oxide Thin Film Electrode Using Plasma for Optoelectronic Devices

Transparent conductive oxides used in solar cells such as indium tin oxide are relatively expensive. Zinc oxide may be suitable alternative as it is inexpensive, nontoxic, and abundant with properties similar to indium tin oxide. High quality zinc oxide films are commonly prepared by high cost vacuum techniques. Solution processed solgels offer a simple, easy and low cost deposition technique for ZnO. However, ZnO films produced by these techniques have poor electrical properties. Plasma treatment has been used to improve these properties. However, these films still require vacuum deposition which results in higher manufacturing costs. The objective of this research was to determine if plasma treatment can enhance the conductivity of solution based zinc oxide thin films with transparency greater than 85% and resistivity less than 0.099 Ωcm. Pure zinc oxide films have high resistivity due to a low carrier concentration which can be increased by oxygen and/or zinc non‐stoichiometry, or doping with impurities. In this work, zinc oxide films were deposited by the sol-gel method, and treated with oxygen, hydrogen and nitrogen plasmas. Oxygen plasma treatment produced highly crystalline films with transmittance above 85% and a 30% reduction in resistivity. Hydrogen plasma treatment increased the electrical conductivity by 98% but decreased transmittance by xii 10%. This is the first report of improvement of conductivity of sol-gel zinc oxide film using oxygen and hydrogen plasma treatment

Realizing Rapid Kinetics of Na Ions in Tin‐Antimony Bimetallic Sulfide Anode with Engineered Porous Structure

Metallic sulfide anodes show great promise for sodium‐ion batteries due to their high theoretic capacities. However, their practical application is greatly hampered by poor electrochemical performance because of the large volume expansion of the sulfides and the sluggish kinetics of the Na+ ions. Herein, a porous bimetallic sulfide of the SnS/Sb2S3 heterostructure is constructed that is encapsulated in the sulfur and nitrogen codoped carbon matrix (SnS/Sb2S3@SNC) by a facile and scalable method. The porous structure can provide void space to alleviate the volume expansion upon cycling, guaranteeing excellent structural stability. The unique heterostructure and the S, N codoped carbon matrix together facilitate fast‐charge transport to improve reaction kinetics. Benefitting from these merits, the SnS/Sb2S3@SNC electrode exhibits high capacities of 425 mA h g−1 at 200 mA g−1 after 100 cycles, and 302 mA h g−1 at 500 mA g−1 after 400 cycles. Moreover, the SnS/Sb2S3@SNC anode shows an outstanding rate performance with a capacity of over 200 mA h g−1 at a high current density of 5000 mA g−1. This study provides a new strategy and insight into the design of electrode materials with the potential for the practical realization and applications of next‐generation batteries