Design of highly transparent ohmic contact to N face n-GaN for enhancing light extraction in GaN-based micro LED display.

In GaN-based vertical micro LEDs, conventional metal n-contacts on the N face n-GaN suffer from a low aperture ratio due to the high reflection of metals, resulting in low-light extraction efficiencies. Great efforts have been devoted to enhancing transparency by employing transparent conducting oxides for n-contacts, but they exhibited poor Ohmic behavior due to their large work functions. Herein, we introduce an InN/ITO n-contact to achieve both superior contact property and high transparency. At the initial stage, the ITO with thin In interlayer was utilized, and the change in contact properties was observed with different annealing temperatures in the N2 atmosphere. After annealing at 200 °C, the In/ITO n-contact exhibited Ohmic behavior with high a transparency of 74% in the blue wavelength region. The metallic In transformed into InN during the annealing process, as confirmed by transmission electron microscopy. The formation of InN caused polarization-induced band bending at the InN/GaN interface, providing evidence of enhanced Ohmic properties. In the application of vertical GaN µLED, the EQE increased from 6.59% to 11.5% while operating at 50 A/cm2 after the annealing process.

LEGO-like Assembly of Fibrous Modules for Display Textiles.

Due to their promising advantages over classical rigid devices, the development of display textiles has exciting potential for various fields, including sensor technology, healthcare, and communication. To realize display textiles, it is necessary to prepare light-emitting building blocks at the fiber level and then weave or knit them to form the desired textile structures. However, from a practical viewpoint, it is difficult to continuously weave functional fibers containing light-emitting devices using conventional textile technologies. To address this issue, we introduced fibrous modules that can be assembled like LEGO blocks to realize textile displays. A unique feature of this work is that the light-emitting pixels are generated through a simple contact between modular electrochemiluminescent (ECL) fibers. Each fiber is composed of a single metallic wire coated with a gel-type ECL electrolyte that is formed by using a simple dip-coating method in ambient air. The sticky nature of the gel electrolyte enables the construction of light-emitting pixels through the simple physical contact of two or more fiber modules without the need for external pressure or heating. The diversity of this technology offers in terms of fibrous module arrangements and assembly can provide various options for designing the geometries of light-emitting pixels. We have implemented this technique to demonstrate not only a 1 × 1 pixel but also 3 × 3 pixels with an irregular shape. These results demonstrate that the unique strategy for display devices developed in this work provides a feasible approach for various electronic and optical textile applications.

Water Washable and Flexible Light-Emitting Fibers Based on Electrochemiluminescent Gels.

Herein, a new concept of device architecture to fabricate fibrous light-emitting devices is demonstrated based on an electrochemiluminescence (ECL) material for an electronic textile system. A unique feature of this work is that instead of conventional semiconductor materials, such as organics, perovskites, and quantum dots for fibrous light emitting devices, a solid-state ECL electrolyte gel is employed as a light-emitting layer. The solid-state ECL gel is prepared from a precursor solution composed of matrix polymer, ionic liquid, and ECL luminophore. From this, we successfully realize light-emitting fibers through a simple and cost-effective single-step dip-coating method in ambient air, without complicated multistep vacuum processes. The resulting fiber devices reliably operated under applied AC bias of ±2.5 V and showed luminance of 47 cd m-2. More importantly, the light-emitting fibers exhibited outstanding water resistance without any passivation layers, owing to the water immiscible and hydrophobic nature of the ECL gel. In addition, because of their simple structure, the fiber devices can be easily deformed and woven together with commercial knitwear by hand. Therefore, these results suggest a promising strategy for the development of practical fiber displays and contribute to progress in electronic textile technology.

Completely Hazy and Transparent Films by Embedding Air Gaps for Elimination of Angular Color Shift in Organic Light-Emitting Diodes.

Red, green, and blue top-emission organic light-emitting diodes (RGB TOLEDs) suffer from white color change with viewing angle due to the microcavity effect, called white angular dependence (WAD). Great efforts are devoted by applying various kinds of hazy films, but they suffer from poor mechanical stability and optical transmittance. Herein, we introduce an air-gap-embedded hazy film (AEHF) to solve these problems and suppress WAD in RGB TOLEDs. The AEHF is designed with optical simulation to realize high haze with transparency. By tuning geometries of the air gap inside the polymer, the AEHF realizes high haze of more than 90% in all RGB colors while maintaining high transparency. To experimentally demonstrate the AEHF, the O2 plasma is treated on a polymer film with AgCl as an etching mask to fabricate microstructures with high aspect ratios. Afterward, PDMS is coated on the patterned surface; air gaps develop spontaneously in the valleys between microstructures during the coating process. Using these processes, an air gap with 1.2 µm size and 400 nm period is formed inside the film and ∼100% haze is achieved while maintaining a high transmittance of 88%; these results agree well with rigorous coupled wave analysis results. By utilizing the AEHF into TOLEDs, the WAD can be drastically suppressed by 95.2% compared with that of a device without AEHF.

Indium Tin Oxide Branched Nanowire and Poly(3-hexylthiophene) Hybrid Structure for a Photorechargeable Supercapacitor.

We report a photorechargeable supercapacitor that can convert solar energy to chemical energy and store it. The supercapacitor is composed of indium tin oxide branched nanowires (ITO BRs) and poly(3-hexylthiophene) (P3HT) semiconducting polymers. ITO BRs showed electrical double layer capacitive characteristics that originated from the unique porous and self-connected network structure. The hybrid structure of ITO BR/P3HT exhibited spontaneous light harvesting, energy conversion, and charge storage. As a result, photocharging/discharging of ITO BR/P3HT showed an areal capacitance of 2.44 mF/cm2 at a current density of 0.02 mA/cm2. The proof-of-concept photorechargeable device, composed of ITO BRs, ITO BR/P3HT, and Na2SO4/polyvinyl acetate gel electrolyte, generated a photovoltage as high as 0.28 V and stored charge effectively for tens of seconds. The combination of dual functions in a single hybrid material may achieve breakthrough advances.

Grain Boundary Engineering of Cu-Ag Thin-Film Catalysts for Selective (Photo)Electrochemical CO2 Reduction to CO and CH4.

We investigated the relationship between grain boundary (GB) oxidation of Cu-Ag thin-film catalysts and selectivity of the (photo)electrochemical CO2 reduction reaction (CO2 RR). The change in the thickness of the Cu thin film accompanies the variation of GB density, and the Ag layer (3 nm) has an island-like morphology on the Cu thin film. Therefore, oxygen from ambient air penetrates into the Cu thin film through the GB of Cu and binds with it because the uncoordinated Cu atoms at the GBs are unstable. It was found that the Cu thin film with a small grain size was susceptible to spontaneous oxidation and degraded the faradaic efficiency (FE) of CO and CH4. However, a relatively thick (≥80 nm) Cu layer was effective in preventing the GB oxidation and realized catalytic properties similar to those of bulk Cu-Ag catalysts. The optimized Cu (100 nm)-Ag (3 nm) thin film exhibited a unique bifunctional characteristic, which enables selective production of both CO (FECO = 79.8%) and CH4 (FECH4 = 59.3%) at a reductive potential of -1.0 and -1.4 VRHE, respectively. Moreover, the Cu-Ag thin film was used as a cocatalyst for photo-electrochemical CO2 reduction by patterning the Cu-Ag thin film and a SiO2 passivation layer on a p-type Si photocathode. This novel architecture improved the selectivity of CO and CH4 under light illumination (100 mW/cm2).

Air-gap-embedded robust hazy films to reduce the screen-door effect in virtual reality displays.

We report a way to make an air-gap-embedded flexible film to reduce the screen-door effect (SDE) in virtual reality (VR) displays. Oxygen plasma was treated with a polyethylene terephthalate substrate to produce wavelength-scale micropatterns. These micropatterns induce an effective haze, but it is easily destroyed by a very small external scratch. Such a problem could be solved by coating the patterns with poly(dimethylsiloxane) (PDMS). The viscosity of PDMS, controlled by the ratio of the base and curing agents, plays a key role in determining the size of air-gaps at the valleys of micropatterns. As the ratio of base agent increases to 40, the average haze abruptly increased from 0.9% to 88.6% in visible wavelengths, while the average total transmittance maintained was between 89.8 and 91.7%. The origin of air-gap-induced haze is confirmed by numerical simulations. The hazy film remarkably reduced the SDE of the VR display from 30.27% to 4.83% for red color, from 21.82% to 2.58% for green, and from 26.02% to 3.38% for blue, as the size of air-gaps increases from 0 to 406 ± 91 nm. No defects were found after 10 000 bending cycles with a bending radius of 3 mm.

Nano-imprinting of refractive-index-matched indium tin oxide sol-gel in light-emitting diodes for eliminating total internal reflection.

Refractive-index (RI)-matched nanostructures are implemented in GaN-based light-emitting diodes (LEDs) for enhancing light output efficiency. The RI-matched indium tin oxide (ITO) nanostructures are successfully implemented in GaN-based lateral LEDs by using ITO sol-gel and nanoimprint lithography. The ITO sol-gel nanostructures annealed at 300 °C have RI of 1.95, showing high transparency of 90% and high diffused transmittance of 34%. Consequently, the light output power in LEDs with the RI-matched nanostructures increases by 8% in comparison with that in LEDs containing flat ITO. Ray tracing and finite-difference time-domain (FDTD) simulations show that the RI-matched nanostructures on the transparent current spreading layer dramatically reduce Fresnel reflection loss at the interface of the current spreading layer with the nanostructure and extract confined waveguide lights in LEDs.

[Trend in the Eradication Rates of Helicobacter pylori Infection Over the Last 10 Years in West Gyeonggi-do, Korea: A Single Center Experience].

Background/Aims: The eradication rate of Helicobacter pylori (H. pylori) has been decreasing recently in Korea due to antibiotics resistance. The aim of this study was to investigate the trend of eradication rate and clinical factors affecting the eradication rate of H. pylori in the last 10 years in west Gyeonggi-do, Korea. Methods: The trends of eradication rate of H. pylori, gender, age, concomitant mediations, and clinical factors were retrospectively evaluated in patients with H. pylori infection between 2006 and 2015 (n=2,485). Results: The overall H. pylori eradication rate for the standard triple therapy was 82.5%. The annual eradication rates from 2006 to 2015 were 90%, 77.9%, 75.8%, 83.2%, 85.6%, 90.1%, 81.3%, 81.1%, 78.7%, and 78.8%, respectively, showing a significant decrement during the last five years (p<0.001). Higher eradication rate was observed in males than in females (p<0.001). Esomeprazole showed a higher eradication rate compared with pantoprazole between 2006 and 2010 (p<0.022). Age and the use of probiotics and mucosal protective agents played no significant role in the H. pylori eradication rate. The overall eradication rate for bismuth-based quadruple therapy was 94.4%. Conclusions: The eradication rate of H. pylori over the last 10 years for first-line therapy ranged from 75.8 to 90.1%; the eradication rate for triple therapy has declined. However, the eradication rate for quadruple therapy has remained unchanged over the last 10 years.