Jin Wook Jeong

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.

The vertically stacked organic sensor-transistor on a flexible substrate

The authors report on the photo-response characteristics of flexible sensor-transistor circuits (ST-circuits) made with (poly(3-hexylethiophene)/phenyl-C61-butryic acid methyl ester) (P3HT/PCBM) bulk heterojunction polymer and pentacene-based organic field-effect transistors, which are stacked via poly(dimethylsiloxane) (PDMS) on the plastic substrate. The results indicate that the anode-source current is variable because of both the charge separation of the photogenerated excitons and the accumulated charges at the OFET channel layer. The light dependent photo response (ΔI/I0) is modulated from 0.47 to 1.9 by the gate-source voltage at the fixed anode-source voltage of the ST-circuits.

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.

Carbon nanotube and conducting polymer dual-layered films fabricated by microcontact printing

We report carbon nanotube/conducting polymer dual-layered film (CPDF) electrodes fabricated by microcontact printing for flexible transparent electrodes of organic thin film transistors (OTFTs). The CPDFs show ∼1000 Ω/sq surface resistivity and ∼93% transmittance at an extremely low loading of single-walled carbon nanotubes, and can be self-aligned with a precision of 20 μm. The CPDFs are applied as the source and drain electrodes in OTFTs without any supplementary alignment process, which leads to a mobility and a current on/off ratio of approximately 0.02 cm2 V−1 s−1 and ∼104, respectively.

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.

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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A self-assembled microarray (SAMA) of organic light-emitting diodes (OLEDs) has been fabricated using self-assembled monolayers (SAMs) by microcontact printing (μCP). The hydrophobic methyl-terminated SAMs modify the surface properties of the substrates to become hydrophobic, i.e., with low surface energy. Thus, the hydrophobic SAMs pattern, by the μCP, can be applied to form SAMAs on the patterned SAMs since the difference of the local surface energy modifies the patterns on the substrates. In this study, octadecyltrichlorosilane based hydrophobic methyl-terminated SAMs have been used and the fabricated OLEDs, with the SAMAs show local light emissions on the micron scale with efficient performances.

-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.

Self-assembled microarray of organic light-emitting diodes using a self- assembled monolayer by microcontact printing

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.