Guang Sup Cho

Enhanced out-coupling factor of microcavity organic light-emitting devices with irregular microlens array

We studied microcavity organic light-emitting devices with a microlens system. A microcavity for organic light-emitting devices (OLED) was fabricated by stacks of SiO(2) and SiN(x) layers and a metal cathode together with the microlens array. Electroluminescence of the devices showed that color variation under the viewing angle due to the microcavity is suppressed remarkably by microlens arrays, which makes the use of devices acceptable in many applications. It was also demonstrated that the external out-coupling factor of the devise increases by a factor of ~1.8 with wide viewing angles compared to conventional OLEDs.

Enhanced light emission from one-layered organic light-emitting devices doped with organic salt by simultaneous thermal and electrical annealing

The authors studied the effect of thermal and electrical annealing on light emission of fluorescent one-layered organic light-emitting devices (OLEDs) doped with organic salts. From the annealed OLEDs, we clearly observed homogeneous and enhanced electroluminescent (EL) emission over the whole active area with fast responses. Moreover, improved efficiency was also observed from annealed phosphorescent OLEDs. These improved EL characteristics indicate that simultaneous annealing can induce proper adsorption of charged salt ions at the electrode surfaces, leading to enhanced electroluminescence of one-layered OLEDs due to increased and balanced injection of carriers.

Double interfacial layers for highly efficient organic light-emitting devices

The authors report on a highly efficient phosphorescent organic light-emitting device (PHOLED) achieved by introducing nanoscale double interfacial layers, made by ultrathin surfactant and low work-function metal layers. It is shown that double interfacial layers play multiple roles in the enhancement of device performance: increasing electron injection, hole blocking, and reducing surface roughness of electroluminescent layer. With double interfacial layers, a PHOLED has shown efficiency as high as ∼60cd∕A with a current density of 1.6mA∕cm2 and a luminance of 1000cd∕m2 at 6.5V, which is higher than that of a control device with a single CsF interfacial layer.

Highly efficient green phosphorescent single-layered organic light-emitting devices

The authors studied the highly efficient green electrophosphorescent light-emission from single-layered organic light-emitting devices made by a simple wet process with a composite solution. The solution was prepared by predissolving organic charge transport, host compounds with green phosphorescent guest iridium complex, and a copolymer of oxadiazole units. The fabricated devices show excellent performances, i.e., operation at relatively low voltages, resulting in a high peak current efficiency (ηc) of 48cd∕A and power efficiency (ηp) of 45lm∕W at a current density of 0.02mA∕cm2. Even at 1000cd∕m2 (2mA∕cm2), high ηc of 50cd∕A and ηp of 22lm∕W were obtained.

Electron temperature and plasma density in surface-discharged alternating-current plasma display panels

The electron temperature and plasma density at the lateral distance of 125 /spl mu/m from the center of sustaining electrode gap have been investigated by a Langmuir probe along with the high-speed discharge image in coplanar alternating current plasma display panels. The plasma density at the lateral distance of 125 /spl mu/m from the center of sustaining electrode gap is shown to be maximum value of 3.7/spl times/10/sup 11/ cm/sup -3/, whereas the electron temperature is measured to be decreased from 1.8 to 0.8 eV as the gas pressure increases from 150 to 400 torr in this experiment. It is noted that the electron temperatures measured by the Langmuir probe and high-speed image camera are in good agreement with each other within 5% error limit.

Production of nitric oxide using a microwave plasma torch and its application to fungal cell differentiation

The generation of nitric oxide by a microwave plasma torch is proposed for its application to cell differentiation. A microwave plasma torch was developed based on basic kinetic theory. The analytical theory indicates that nitric oxide density is nearly proportional to oxygen molecular density and that the high-temperature flame is an effective means of generating nitric oxide. Experimental data pertaining to nitric oxide production are presented in terms of the oxygen input in units of cubic centimeters per minute. The apparent length of the torch flame increases as the oxygen input increases. The various levels of nitric oxide are observed depending on the flow rate of nitrogen gas, the mole fraction of oxygen gas, and the microwave power. In order to evaluate the potential of nitric oxide as an activator of cell differentiation, we applied nitric oxide generated from the microwave plasma torch to a model microbial cell (Neurospora crassa: non-pathogenic fungus). Germination and hyphal differentiation of fungal cells were not dramatically changed but there was a significant increase in spore formation after treatment with nitric oxide. In addition, the expression level of a sporulation related gene acon-3 was significantly elevated after 24 h upon nitric oxide treatment. Increase in the level of nitric oxide, nitrite and nitrate in water after nitric oxide treatment seems to be responsible for activation of fungal sporulation. Our results suggest that nitric oxide generated by plasma can be used as a possible activator of cell differentiation and development.

One-dimensional birefringent photonic crystal laser

We studied the polarized laser emission from an anisotropic one-dimensional (1D) birefringent photonic crystal (PC) laser. An active medium layer, which consisted of an epoxy resin doped with fluorescent dye, was sandwiched between two anisotropic 1D PC films. It was shown that efficient laser emissions were generated by optical pumping at relatively low lasing thresholds. The wavelengths of the emitted lasers were 611 and 618 nm, which correspond to the two split eigenmodes at the low-energy band edges that are due to the anisotropy of the PCs. We also demonstrated that the polarization of the lasing emission can be controlled by adjusting the birefringence of the anisotropic PCs.

Research on Changes in Short Circuit Current of C-Si Solar Cell by Charge Density Waves

We measure solar currents transformed from quantum efficiency as a function of incident angles of solar lights. According to conventional models for solar cells, solar currents can be induced when electrons are separated into electrons and holes in the presence of incident solar lights. On the contrary, solar currents can be possible at the time when pinned charge density waves go beyond the pinning potential barrier under the influence of incident solar beams suggested by some authors. In this experiment, measured solar currents and our theory are in good correspondence to confirm the angle dependence of solar lights.

Microwave plasma sources by using pulse mode SSPA

Summary form only given. For the various plasma applications, the microwave source has been developed in recent years. High efficiency solid-state power amplifiers(SSPA) using GaN HEMT and MOSFET have been designed for the generation of stable low temperature plasma. We measured temperature of plasma by using heat paper in various conditions and found condition of low temperature plasma generation. When the peak power is 40 W and the base power is 15.8 W, the temperature of the plasma is measured to be below 40 degrees Celsius in Ar gas flow rate 3.5~5.0 lpm. When the peak power is 200 W and the base power is 14.5 W, the temperature of the plasma is also found to be below 40 degrees Celsius in Ar gas flow rate 3.0~3.5 lpm. Design and experimental results of pulse mode SSPA and microwave plasma structure are presented.

P‐166: Highly Efficient Organic Light‐Emitting Devices with Double Interfacial Layers

We report on a highly efficient phosphorescent organic light-emitting devices achieved by introducing nanoscale double interfacial layers. The double interfacial layers play multiple roles in the enhancement of devices performance: increasing electron injection, hole-blocking, and preventing luminescence quenching at the electrode surface. As an experimental result, current efficiency was improved to 240%, yielding a peak brightness over 40,000 cd/m2 and peak efficiency over 60 cd/A.