Eun Ho Song

Highly conformal SiO2/Al2O3 nanolaminate gas-diffusion barriers for large-area flexible electronics applications

The present study demonstrates a flexible gas-diffusion barrier film, containing an SiO(2)/Al(2)O(3) nanolaminate on a plastic substrate. Highly uniform and conformal coatings can be made by alternating the exposure of a flexible polyethersulfone surface to vapors of SiO(2) and Al(2)O(3), at nanoscale thickness cycles via RF-magnetron sputtering deposition. The calcium degradation test indicates that 24 cycles of a 10/10 nm inorganic bilayer, top-coated by UV-cured resin, greatly enhance the barrier performance, with a permeation rate of 3.79 × 10(-5) g m(-2) day(-1) based on the change in the ohmic behavior of the calcium sensor at 20 °C and 50% relative humidity. Also, the permeation rate for 30 cycles of an 8/8 nm inorganic bilayer coated with UV resin was beyond the limited measurable range of the Ca test at 60 °C and 95% relative humidity. It has been found that such laminate films can effectively suppress the void defects of a single inorganic layer, and are significantly less sensitive against moisture permeation. This nanostructure, fabricated by an RF-sputtering process at room temperature, is verified as being useful for highly water-sensitive organic electronics fabricated on plastic substrates.

Fuzzy Nanoassembly of Polyelectrolyte and Layered Clay Multicomposite toward a Reliable Gas Barrier

Flexible and transparent gas-diffusion barriers have played an important role in recent years. The present study describes a flexible barrier film with a tailored architecture of cationic polyelectrolytes and clay/polymer nanoassemblies. Highly oriented and well-aligned barrier films were achieved by the consecutive absorption of flexible cationic polymer and anionic montmorillonite platelets. The experimental results showed that the layer-by-layer deposition of oppositely charged thin films containing self-assembled poly(vinyl alcohol) and montmorillonites improved their gas barrier characteristics based on the Ca degradation test, enhancing their optical transparency. This nanostructure, fabricated using a solution process, is useful in many applications, for example, flexible and moisture-free organic electronics. This simple and fast method is suitable for the mass coating of large surface areas, as required in industry.

Highly Oriented Gold/Nanoclay–Polymer Nanocomposites for Flexible Gas Barrier Films

Layer-by-layer (LBL) assembly, which uses electronic and ionic intermolecular bonding under nonvacuum conditions, is a promising technology for fabricating gas barrier films owing to its simple processing and easy formation of a multilayer structure. In this research, nanoclay-polymer multilayers of Na(+)-montmorillonite (Na-MMT) were fabricated. Particularly, the addition of AuCl3 on fabricated MMT layers caused a reaction with the surface silanol functional groups (Si-O-H) of the MMT platelets, resulting in the formation of Au2O3 on the MMT-polymer multilayers. The Au2O3 filled the vacancies between the MMT platelets and linked the MMT platelets together, thus forming a gas barrier film that reduced the water vapor transmission rate (WVTR) to 3.2 × 10(-3) g m(-2) day(-1). AuCl3-treated MMT-polymer multilayers thus have the potential to be utilized for manufacturing gas barrier films for flexible electronics on a large scale.

Role of n-dopant based electron injection layer in n-doped organic light-emitting diodes and its simple alternative

We investigate the enhancement mechanism of the electroluminescence (EL) of alkali metal based n-doped organic light-emitting diodes (OLEDs). The dual role of the n-dopant (carrier transport and lowering of the injection barrier) induces a trade-off. When the electron transport layer (ETL) is optimally doped by the n-dopant for the highest conductivity, the amount of n-dopant at the ETL/cathode interface is insufficient to form enough chemical bonds with the cathode for efficient carrier injection. This insufficient amount of n-dopant limits the carrier injection properties. To solve this problem, we demonstrated that the addition of an electron injection layer (EIL) comprised of the n-dopant could increase its presence at the interface and, thereby, improve the carrier injection properties and, consequently, the EL efficiency. Moreover, simply using an alkali-metal alloy (rather than co-deposition) on the n-doped ETL as a cathode, instead of using the additional EIL, greatly improves the EL efficiency of...

The flexible Ca-test: An improved performance in a gas permeability measurement system

A flexible performance permeability measuring test for flexible organic light-emitting diodes is described in this paper. A single thin film layer of gas barriers is constructed on polyethersulfone (PES). The barrier coats the upper and lower surfaces of the PES layer. Two PES samples, one coated with Al(2)O(3) on both surfaces and the other coated on a single surface, were made for comparison. According to this test, the time-dependent transmission curve of the one sided barrier sample had a linear slope which measured 1.65 g∕m(2)∕day at room temperature at a 50% relative humidity. This result shows that the measurement time is about 182% faster than has been achieved with the conventional test structure that uses a glass substrate. In addition, this measurement structure not only reduces the inevitable electrical noise which occurs during measurement but also increases the water vapor permeation signal. These effects improve the sensing reliability of the test. In addition, this structure is flexible, so one can instantly detect barrier performance changes when applying external stress.

The Emission Properties of Integrated Organic Light Emitting Diodes With Organic Photo Sensor for Emotional Lighting Applications

This letter reports on a study of the emission properties of organic light-emitting diodes (OLEDs) controlled by an organic photo sensor (OPS) based on poly-3-hexylthiophene (P3HT) and [6, 6]-phenyl-C61 butyric acid methyl ester for emotional lighting applications. The emission characteristics exhibit the changes in the current and luminance of an OLED as a function of time when different illumination levels are exposed to the OPS. The luminance of the OLED increases from 283.4 to 1134 cd/m2 when the OPS is exposed to different illumination levels from full dark to 500 mW/cm2 using a xenon lamp.

Enhanced Power Efficiency of Organic Light-Emitting Diodes using Pentacene on

In this letter, we demonstrate high-performance organic light-emitting diodes (OLEDs) by matching various hole injection-transport layers (HITLs) with plasma surface treatments. The OLED device with pentacene HITL on CF4-plasma-treated indium tin oxide showed the highest performance due to relatively improved hole injection and the high-hole-mobility characteristics of the pentacene. Using a high-electron-mobility material as an electron transport layer to improve the carrier balance of electrons and holes, the electroluminescent efficiency was further improved. These methods are simple and promising for the enhancement of OLED performances. These findings will be applicable to mobile displays that feature low electric power consumption.

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We investigated the field emission characteristics of patterned carbon nanotubes (CNTs) on KOVAR substrates with different surface morphologies. The substrate with a micro-sized random pattern was fabricated through chemical wet etching, whereas the substrate with a nano-sized random pattern was formed by surface roughening process of polymer and chemical wet etching. The field emission characteristics of these substrates were the compared with those of non-treated substrates. It was clearly revealed that the field emission characteristics of CNTs were influenced by the surface morphology of the cathode substrate. When the surface of cathode was modified by random pattern, the modified substrate provided a large surface area and a wider print area. Also, the modified surface morphology of the cathode provided strong adhesion between the CNT paste and the cathode. Particularly, the substrate with the nano-sized random pattern showed that the turn-on field value decreases and the field enhancement factor value improves as compared with non-treated substrate.

-Plasma-Treated Indium Tin Oxide Anodes

This paper reports on a study of the electrical properties of integrated organic light emitting diode (OLED) with an organic photo sensor (OPS) based on poly-3-hexylthiophene (P3HT) and [6,6]-phenyl-C61 butyric acid methyl ester (PCBM) for emotional lighting applications. The emission characteristics exhibit the changes in the current and luminance of an OLED as a function of time when the OPS is exposed to different illumination levels from full dark to 500 m W/cm2 using a xenon lamp.

Carbon nanotube field emitters on KOVAR substrate modified by random pattern

The paper present transparent gas barrier technologies such as RF-sputtered inorganic nanolaminate, hydrophobic/hydrophilic surface modifications, and its measurements. Highly conformal and uniform deposition of Al2O3 and SiO2 barriers and hydrophilic dots on nano-imprinted hydrophobic surface structures successfully reduced water permeation rates according to the Ca degradation measurements.