Gun Woo Hyung

Highly efficient white organic light-emitting diodes using two emitting materials for three primary colors (red, green, and blue)

The authors have demonstrated highly efficient white organic light-emitting diodes (WOLEDs) by using two emissive materials as a dopant, 1,4-bis[2-(7-N-diphenyamino-2-(9,9-diethyl-9H-fluoren-2-yl)) vinyl] benzene (DAF-ph) and iridium(III) bis(5-acetyl-2-phenylpyridinato-N,C2′) acetylacetonate ((acppy)2Ir(acac)). It was found that the OLED fabricated in this study emitted a white color consisting of three primary colors (red, green, and blue). The luminance-voltage (L-V) characteristics of the WOLEDs showed the maximum luminance of 30500cd∕m2 at 14V and the maximum luminous efficiency of 38.0cd∕A, respectively. The CIEx,y coordinates of the WOLED also showed (x=0.33, y=0.40) at 10V.

Enhanced life time and suppressed efficiency roll-off in phosphorescent organic light-emitting diodes with multiple quantum well structures

We demonstrate red phosphorescent organic light-emitting diodes (OLEDs) with multiple quantum well structures which confine triplet exciton inside an emitting layer (EML) region. Five types of OLEDs, from a single to five quantum wells, are fabricated with charge control layers to produce high efficiencies, and the performance of the devices is investigated. The improved quantum efficiency and lifetime of the OLED with four quantum wells, and its suppressed quantum efficiency roll-off of 17.6%, can be described by the increased electron–hole charge balance owing to the bipolar property as well as the efficient triplet exciton confinement within each EML, and by prevention of serious triplet–triplet and/or triplet–polaron annihilation as well as the Forster self-quenching due to charge control layers.

Colloidal ZnO quantum dot-based, solution-processed transparent field-effect transistors

ZnO-based transistors were solution-processed using ~3.6 nm sized ZnO quantum dots (QDs). Spin-deposited ZnO QD layer was annealed to remove QD capping organic molecules and to increase the connectivity of adjacent QDs. The resulting QD layer was highly transparent and crack free without any noticeable pores. 600 °C annealing of QD channel layer resulted in the highest electrical performances of bottom-gate QD-based transistors. A small quantity of Sn doping into the QD channel layer was found to be effective in further improving the electrical characteristics of the QD-based transistor, in particular exhibiting a higher field-effect mobility (0.282 cm2 V−1 s−1) by more than 4 factors than that of an undoped QD-based one. Finally, a fully transparent Sn-doped QD-based device was demonstrated by sputter deposition of Ga-doped ZnO as source–drain transparent electrodes and its electrical properties were evaluated.

Amorphous Indium Gallium Zinc Oxide Thin-Film Transistors with a Low-Temperature Polymeric Gate Dielectric on a Flexible Substrate

Amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs) with a solution-processed polymeric gate dielectric of cross-linked poly(4-vinylphenol) (c-PVP) film were fabricated on a poly(ethylene terephthalate) (PET) substrate on which an a-IGZO film, as the active channel layer, was deposited by radio frequency (RF) sputtering. The entire TFT fabrication process was carried out at a temperature below 110 °C. The device exhibited an on/off ratio of 1.5×106 and a high field-effect mobility of 10.2 cm2 V-1 s-1, which is, to our knowledge, the best result ever achieved among a-IGZO TFTs with polymeric gate dielectrics on a plastic substrate.

Improved Performance of Pentacene Thin-Film Transistors with Al2O3 Gate Dielectric: Annealing Effect on the Surface Properties

We have fabricated pentacene thin-film transistors (TFTs) with modified Al2O3 layers as gate dielectrics. The effects of thermal treatments on the E-beam-processed Al2O3 layers in the TFTs were investigated by using various analytical tools such as X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), atomic force microscope (AFM), and a contact angle method. From the results of the analyses, it was confirmed that the performance of thermally treated Al2O3 gate dielectrics is much better than that of non-treated ones. Finally, pentacene TFTs were fabricated with optimum conditions and improved electrical properties were obtained for low-voltage (below -3 V) TFTs as follows: a mobility of 0.9 cm2 V-1 s-1, a threshold voltage of -1.3 V, a sub-threshold slope of 0.12 V/decade, and an on/off current ratio of 2.2 ×105.

P-164: Highly Efficient White Organic Light-Emitting Diodes Using Two Emitting Materials for Three Primary Colors (Red, Green and Blue)

These results have demonstrated the highly efficient white organic light-emitting diodes (WOLEDs) with two separated emissive materials for the three primary colors, red, green, and blue, using blue fluorescent and red phosphorescent dopants. The two devices with the optimum structure showed a maximum luminance of 30500 and 20400 cd/m2 and a luminous efficiency of 38.0 and 32.7 cd/A. Furthermore, device B showed better CIEx,y coordinates of (x=0.36, y=0.35) at 10V. We expect that the WOLEDs fabricated using device structures and materials described here may be applicable for backlights in liquid crystal displays.

Fabrication of ZnO-Based Flexible Thin-Film Transistors by a Low-Temperature Process

In this paper we have studied a low-temperature process of fabricating zinc oxide (ZnO) thin-film transistors (TFTs) on polyethylene terephthlate (PET) substrate. PET film has a lower glass transition temperature (Tg = 120°C) than costly Polyethersulphone (PES) film (Tg = 230°C). Therefore we applied a low-temperature cross-linked poly-vinylphenol (c-PVP) process to annealing at 110°C instead of the conventional c-PVP process (annealing at 165°C). The resulting TFTs based on oxide fabricated by the low-temperature process were similar in electrical characteristics to conventional TFTs. In addition, the ZnO TFTs fabricated by the low-temperature process exhibited a field-effect mobility of 0.075 cm2/Vs, a threshold voltage of 15 V and an on/off ratio of 1.7 × 105 respectively.

Fabrication of Atomic Layer Deposited Zinc Oxide Thin Film Transistors with Organic Gate Insulator on Flexible Substrate

In the fabrication of transparent conductive oxide thin film transistor (TFT), an atomic layer deposited (ALD) zinc oxide (ZnO) and a cross-linked poly-vinyl-alcohol (c-PVA) were each used as active layer and gate insulating layer on poly-ethylene (PET) substrate respectively. Considering the transmittance and the deposition rate of the ALD ZnO at a low temperature without any damage on PET substrate, the ZnO layer was deposited at a temperature of 120°C on a spin-coated c-PVA layer. From the atomic force microscope (AFM) images, it was possible to conclude that the surface morphologies of ZnO deposited on a c-PVA layer was not inferior to those of ZnO deposited on bare-Si and that the c-PVA can be used as a gate insulator at 120°C. The fabricated ZnO TFT showed good electrical characteristics such as the mobility of 0.1 cm2/V · s, on-off current ratio of 4.5 × 104.

P-160: Ultra Simple White Organic Light-Emitting Diodes Using only Three Organic Materials

The authors have demonstrated ultra simple white organic light-emitting diodes using only three organic materials, 2-methyl-9,10- di(2-naphthyl)anthracene (MADN), new blue fluorescent emitter (NBFE), and new red fluorescent emitter (NRFE). The fluorescent white organic light-emitting diode fabricated in this study showed the high external quantum efficiency of 6.48%, the luminous efficiency of 13.10 cd/A, and CIEx,y coordinates of (0.33, 0.42) at 100 cd/m2, respectively.

Efficient Hole Injection for Top-Emitting Organic Light-Emitting Diodes Using Nickel Oxide by Oxygen Plasma Treatment

To improve the performance of top-emitting organic light-emitting diodes (TEOLEDs), the effect of oxygen plasma treatment duration on the electrical properties of multi metal Ni/Ag/Ni thin film anodes was investigated. The results revealed that a Ni/Ag/Ni thin-film layer formed upon oxygen plasma treatment for 180 s effectively increased electron-hole recombination probability by improving their charge balance.