Minyang Yang

Nanorecycling: Monolithic Integration of Copper and Copper Oxide Nanowire Network Electrode through Selective Reversible Photothermochemical Reduction

Laser induced selective photothermochemical reduction is demonstrated to locally and reversibly control the oxidation state of Cu and Cu oxide nanowires in ambient conditions without any inert gas environment. This new concept of nanorecycling can monolithically integrate Cu and Cu oxide nanowires by restoring oxidized Cu, considered unusable for the electrode, back to a metallic state for repetitive reuse.

Microelectrode fabrication by laser direct curing of tiny nanoparticle self-generated from organometallic ink

In this paper, we present a new laser direct patterning method that selectively cures nanoparticles self-generated from organometallic ink by proper thermal decomposition. This approach has several advantages in the curing rate, resolution and pattern quality compared with the conventional nanoparticle ink based direct laser curing method. It was found that a laser wavelength which is more weakly absorbed by the nanoparticles could produce a more stable and homogeneous curing condition. Finally, arbitrary shaped silver electrodes with narrow width and uniform profile could be achieved on a polymer substrate at a high curing rate of 25 mm/s. This process can be applied for flexible electronics fabrications on heat sensitive polymer substrates.

Fabrication and characterization of WO3/Ag/WO3 multilayer transparent anode with solution-processed WO3 for polymer light-emitting diodes

The dielectric/metal/dielectric multilayer is suitable for a transparent electrode because of its high-optical and high-electrical properties; however, it is fabricated by an expensive and inefficient multistep vacuum process. We present a WO3/Ag/WO3 (WAW) multilayer transparent anode with solution-processed WO3 for polymer light-emitting diodes (PLEDs). This WAW multilayer not only has high transmittance and low resistance but also can be easily and rapidly fabricated. We devised a novel method to deposit a thin WO3 layer by a solution process in an air environment. A tungstic acid solution was prepared from an aqueous solution of Na2WO4 and then converted to WO3 nanoparticles (NPs) by a thermal treatment. Thin WO3 NP layers form WAW multilayer with a thermal-evaporated Ag layer, and they improve the transmittance of the WAW multilayer because of its high transmittance and refractive index. Moreover, the surface of the WO3 layer is homogeneous and flat with low roughness because of the WO3 NP generation from the tungstic acid solution without aggregation. We performed optical simulation and experiments, and the optimized WAW multilayer had a high transmittance of 85% with a sheet resistance of 4 Ω/sq. Finally, PLEDs based on the WAW multilayer anode achieved a maximum luminance of 35,550 cd/m2 at 8 V, and this result implies that the solution-processed WAW multilayer is appropriate for use as a transparent anode in PLEDs.

Solution processed polymer light-emitting diodes utilizing a ZnO/organic ionic interlayer with Al cathode

This letter reports polymer light-emitting diodes that employ a soluble zinc oxide (ZnO) nanoparticle (NP) and organic ionic interlayer as an electron-injection layer exhibits remarkable enhancement of device performance despite aluminum cathode. The ionic solution infiltrated into ZnO NP layer, which contains poly(ethylene oxide) and tetra-n-butylammonium tetrafluoborate, significantly lowers the large electron-injection barrier by forming a permanent interfacial dipole. The polymer, phenyl substituted poly(para-phenylene vinylene) known as “Super Yellow,” yellow light-emitting diodes employing the ZnO NP and ionic interlayer show a maximum efficiency of 6.3 cd/A at a 1209u2002cd/m2 and 5.4 V. The maximum brightness of the device reached 24u2002000u2002cd/m2 at 9 V.

Simultaneously Enhancing the Cohesion and Electrical Conductivity of PEDOT:PSS Conductive Polymer Films using DMSO Additives

UNLABELLEDnConductive polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (nnnPEDOTnPSS) has attracted significant attention as a hole transport and electrode layer that substitutes metal electrodes in flexible organic devices. However, its weak cohesion critically limits the reliable integration ofnnnPEDOTnPSS in flexible electronics, which highlights the importance of further investigation of the cohesion ofnnnPEDOTnPSS. Furthermore, the electrical conductivity ofnnnPEDOTnPSS is insufficient for high current-carrying devices such as organic photovoltaics (OPVs) and organic light emitting diodes (OLEDs). In this study, we improve the cohesion and electrical conductivity through adding dimethyl sulfoxide (DMSO), and we demonstrate the significant changes in the properties that are dependent on the wt % of DMSO. In particular, with the addition of 3 wt % DMSO, the maximum enhancements for cohesion and electrical conductivity are observed where the values increase by 470% and 6050%, respectively, due to the inter-PEDOT bridging mechanism. Furthermore, when OLED devices using thennnPEDOTnPSS films are fabricated using the 3 wt % DMSO, the display exhibits 18% increased current efficiency.

Enhanced antifungal activity of Ni-doped ZnO nanostructures under dark conditions

In this work, we report the antifungal activity of undoped and Ni-doped ZnO nanoparticles (NPs) synthesized using a reflux method in the absence of structure-directing agents under mild reaction conditions. The Ni-doped ZnO NPs were prepared with different molar concentrations of Ni (0–6%) in the starting solution, and the effect of Ni-doping on the structural, morphological and optical properties was assessed, along with their antifungal activity and cytotoxicity. X-ray diffraction confirmed the formation of the single phase hexagonal wurtzite structure of ZnO, and the successful incorporation of Ni ions into the ZnO host matrix without the formation of secondary phases. Fourier transform infrared spectroscopy showed a frequency shift in the Zn–O vibration bands due to the incorporation of Ni ions into the ZnO lattice. Scanning electron microscopy images revealed the variation in the morphology of the ZnO NPs with Ni-doping. With an increase in Ni-doping, the absorption edge and the near band edge emissions exhibited a red-shift in the UV-vis absorption and photoluminescence (PL) spectra, respectively, while the defect related visible emission in the PL spectra was quenched. The antifungal effectiveness of the undoped and Ni-doped ZnO NPs was studied using Candida albicans fungi in vitro in the dark, while their cytotoxicity was assessed using HEK293T and HEp2 cells. The experimental results showed that the incorporation of Ni into the ZnO matrix has a beneficial influence on the bioactivity, since the ability of the ZnO NPs to kill the fungi and their cytocompatibility were significantly enhanced due to Ni-doping. By combining the experimental results with FESEM analysis, it was hypothesized that (i) the direct interaction of NPs with the cell membrane, and (ii) the generation of reactive oxygen species from the surface of ZnO are the two possible mechanisms responsible for the enhanced antifungal activity of the Ni-doped ZnO NPs.

Laser-assisted fabrication of single-layer flexible touch sensor

Single-layer flexible touch sensor that is designed for the indium-tin-oxide (ITO)-free, bendable, durable, multi-sensible, and single layer transparent touch sensor was developed via a low-cost and one-step laser-induced fabrication technology. To this end, an entirely novel approach involving material, device structure, and even fabrication method was adopted. Conventional metal oxides based multilayer touch structure was substituted by the single layer structure composed of integrated silver wire networks of sensors and bezel interconnections. This structure is concurrently fabricated on a glass substitutive plastic film via the laser-induced fabrication method using the low-cost organometallic/nanoparticle hybrid complex. In addition, this study addresses practical solutions to heterochromia and interference problem with a color display unit. As a result, a practical touch sensor is successfully demonstrated through resolving the heterochromia and interference problems with color display unit. This study could provide the breakthrough for early realization of wearable device.

High-energy, flexible micro-supercapacitors by one-step laser fabrication of a self-generated nanoporous metal/oxide electrode

A high-performance and flexible micro-supercapacitor based on a self-generated nanoporous silver layer was fabricated by a one-step laser-induced growth-sintering process of a particle-free organometallic solution. The porous structures self-generated on a polymer film and were freely adjustable by controlling the rate of laser input dose. By changing the patterning mode, the nanoporous electrodes with extremely high surface area and highly conductive current collectors were formed in a single processing domain. Electrodeposition of hetero metal oxides (manganese and iron oxides) as the active materials followed, and a flexible micro-supercapacitor with high volumetric energy density of 16.3 mW h cm−3 and power density of 3.54 W cm−3 was formed. This was achieved through the large surface area and high electrical conductivity of the nanoporous silver layer, and high operating voltage due to the asymmetrical electrode configuration. This method resulted in a faster and more cost-effective manufacturing process than conventional MSCs fabrication. It also achieved the highest volumetric energy density in metal/oxide-based MSCs as a state-of-the-art performance.

Highly Controlled Nanoporous Ag Electrode by Vaporization Control of 2-Ethoxyethanol for a Flexible Supercapacitor Application

Controlling the surface morphology of the electrode on the nanoscale has been studied extensively because the surface morphology of a material directly leads to the functionalization in various fields of studies. In this study, we designed a simple and cost-effective method to fine-tune the surface morphology and create controlled nanopores on the silver electrode by utilizing 2-ethoxyethanol and two successive heat treatments. High electrical conductivity and mechanical robustness of nanoporous silver corroborate its prospect to be employed in various applications requiring a certain degree of flexibility. As a proof-of-concept, a high-performance supercapacitor was fabricated by electrodepositing MnO2. This method is expected to be useful in various electronic applications as well as energy storage devices.

Nanowires: Nanorecycling: Monolithic Integration of Copper and Copper Oxide Nanowire Network Electrode through Selective Reversible Photothermochemical Reduction (Adv. Mater. 41/2015)

On page 6397 B. Kang, M.-Y. Yang, S. H. Ko, and co-workers demonstrate laser-induced selective photothermo-chemical reduction to locally and reversibly control the oxidation state of Cu and Cu oxide nanowires in ambient conditions without an inert gas environment. This new concept of nano-recycling can monolithically integrate Cu and Cu oxide nanowires by restoring oxidized Cu, considered unusable for the electrode, back to the metallic state for repetitive reuse.