Tae Hyun Park

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.

Hydrophilic dots on hydrophobic nanopatterned surfaces as a flexible gas barrier.

The present study demonstrates a transparent polymeric gas barrier film mimicking the Namib Desert beetles back. SiO(2) hydrophilic dots have been deposited on a nanopatterned hydrophobic surface. A nanopatterned surface was fabricated by UV-curable nanoimprinting techniques. The surface energies of the hydrophobic and hydrophilic domains were 7.29 and >73.12 mN/m, respectively. The characteristics of water vapor transfer from hydrophobic to hydrophilic regions due to difference of the attractive force at interfaces are shown to yield the enhanced barrier performance according to the Ca degradation measurements. This strategy is suitable for organic electronics, solar cells, and plastic optics applications requiring moisture-free properties with high transmission.

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.

Highly efficient tris(8-hydroxyquinoline) aluminum-based organic light-emitting diodes utilized by balanced energy transfer with cosensitizing fluorescent dyes

We report on the development of highly efficient organic light-emitting diodes (OLEDs) utilized by balancing the energy transfer between multiple dopants, that is, multiple emissions from the multiple dopants were realized by balanced distributed energy transfer. From the cosensitizing fluorescent OLEDs, the peak external quantum efficiency (EQE) of 4.8% at 130 cd/m2 is demonstrated, which realized theoretical limits of ∼5.0% and means that nearly 100% of the singlet excitons are radiative. Also, the optimized device accompanying thickness-modulated electron transport layer for the enhanced light outcoupling demonstrated the highly improved peak EQE and current efficiency of 6.7%, and 23.4 cd/A.

Hydrophobic nanopatterning on a flexible gas barrier film by using a poly(dimethylsiloxane)elastomer

In this work, we fabricated a hydrophobic and transparent gas barrier film via a nanopatterned poly(dimethylsiloxane) elastomer imprinting on an ultraviolet-curable polymer resin. A Ca degradation method (water permeation rate) and surface energy measurements were used to determine the level of modification of the surface characteristics. As a result, the decreased surface energy from 25.8 to 7.29 mN m(-1) led to a lower water vapor transmission rate from 3.06 x 10(-1) to 6.24 x 10(-2) g m(-2) day(-1) according to the degree of decreased Ca height from 100 nm. A tunable wettability is beneficial for application where controlling the direction of moisture flow is important, such as in flexible organic electronics.

Low-haze light extraction from organic light-emitting diode lighting with auxiliary electrode by selective microlens arrays.

Improved out-coupling efficiency and low haze of organic light-emitting diode (OLED) lighting with an auxiliary electrode are demonstrated by selective microlens arrays (SMLAs). The microlens arrays, aligned with the auxiliary electrode, were selectively fabricated, since the fully packed microlens arrays lead to OLED lighting with high haze. The external quantum efficiency and power efficiency of the devices with the SMLAs increased by 32% when compared with the devices without these arrays. Using the SMLAs, dark grid lines in the emission region became brighter, with a low haze, and the spectra of the emitted light had no shift.

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.

Micro-pixel array of organic light-emitting diodes applying imprinting technique with a polymer replica

Efficient micro-pixel array of small molecule organic light-emitting diodes (OLEDs) has been fabricated by an imprinting technique which uses a polymer replica. To confirm the effect of the oxygen plasma for removing the residual layer, the performance of two kinds of OLEDs with varying thicknesses of resin as the micro-pixel array, have been compared. The measured results of the OLEDs have shown comparable device performances that are significantly characterized depending on the residues on the substrate. The performance of enhanced device has achieved efficiencies of 3.6 cd/A and 1.9 lm/W at 20 mA/cm2.