• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.537-538
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• 2005

A way of measuring an efficiency of organic light-emitting diodes are studied. The efficiency is obtained from the current-voltage-luminance characteristics of the devices. Basically, number of charge carriers are obtained from the current-voltage characteristics, and the number of photons are obtained from the current of Si-photodetector. The organic light-emitting diodes are assumed as a lambertian light source and a program is made for calculating the efficiency. A device structure of ITO/TPD/$Alq_3$/Al is manufactured using thermal-vapor evaporation. This device is set into a measuring system and measured the efficiency. The efficiencies are measured using the lab-made program and commercially available equipments. The obtained values are similar to each other within 10% uncertainty.

• 한국정보디스플레이학회:학술대회논문집
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• 2009.10a
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• pp.1511-1514
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• 2009

Organic light emitting layer in OLED device was formed by gravure printing process in this work. Organic surface coated by gravure printing typically showed relatively bad uniformity. Thickness and roughness control was characterized by applying various mixed solvents in this work. Poly (N-vinyl carbazole) (PVK) and fact-tris(2-phenylpyridine)iridium($Ir(ppy)_3$) are host dopant system materials. PVK was used as a host and Ir(ppy)3 as green-emitting dopant. To luminance efficiency of the plasma treatment on etched ITO glass and then PEDOT:PSS spin coated. The device layer structure of OLED devices is as follow Glass/ITO/PEDOT:PSS/PVK+Ir(ppy)3-Active layer /LiF/Al. It was printed by gravure printing technology for polymer light emitting diode (PLED). To control the thickness multi-printing technique was applied. As the number of the printing was increased the thickness enhancement was increased. To control the roughness of organic layer film, thermal annealing process was applied. The annealing temperature was varied from room temperature, $40^{\circ}C$, $80^{\circ}C$, to $120^{\circ}C$.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.22 no.12
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• pp.1045-1057
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• 2009

The authors investigated the InGaN/GaN multi-quantum well blue light emitting devices with the implementation of the photonic crystals fabricated at the top surface of p-GaN layer and the bottom interface of n-GaN layer. The top photonic crystals result in the lattice-dependent photoluminescence spectra at the wavelength of 450 nm and however, the bottom photonic crystal shows a big shift of the photoluminescence peak from 444 nm to 394 nm. The sample with the bottom photonic crystal structure also shows the lasing effect at the wavelength of 468 nm. Furthermore, the quality enhancement for the crystal growth of GaN thin film on the bottom photonic crystal comes from the modulated compressive stress which was measured by the micro-Raman spectroscopy.

• 한국정보디스플레이학회:학술대회논문집
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• 2007.08a
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• pp.683-686
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• 2007

We have developed the transparent passivation layer for transparent organic light-emitting devices (TOLEDs) using CsCl layer. The CsCl passivation layer improves the optical transmittance of Ca/Ag double layer which have used as a semitransparent cathode, resulting in substantial increase of the luminance by the enhanced light extraction out of the cathode surface of the TOLEDs.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.4
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• pp.379-385
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• 2006

A stacked white organic light-emitting diode (OLED) having a blue/orange emitting layer was fabricated by synthesizing nitro-DPVT, a new derivative of the blue-emitting material DPVBi on the market. The white-emission of the two-wavelength type was successfully obtained by using both nitro-DPVT for blue~emitting material, orange emission as a host material and Rubrene for orange emission as a guest material. The basic structure of the fabricated white OLED is glass/ITO/NPB$(200{\AA})$/nitro-DPVT$(100{\AA})$/nitro-DPVT:$Rubrene(100{\AA})/BCP(70{\AA})/Alq_3(150{\AA})/Al(600{\AA})$. To evaluate the. characteristics of the devices, firstly, we varied the doping concentrations of fluorescent dye Rubrene from 0.5 % to 0.8 % to 1.3 % to 1.5 % to 3.0 % by weight. A nearly pure white-emission was obtained in CIE coordinates of (0.3259, 0.3395) when the doping concentration of Rubrene was 1.3 % at an applied voltage of 18 V. Secondly, we varied the thickness of the NPB layer from $150{\AA}\;to\;200{\AA}\;to\;250{\AA}\;to\;300{\AA}$ by fixing doping with of Rubrene at 1.3 %. A nearly pure white-emission was also obtained in CIE coordinates of (0.3304, 0.3473) when the NPB layer was $250-{\AA}$ thick at an applied voltage of 16 V. The two devices started to operate at 4 V and to emit light at 4.5 V. The external quantum efficiency was above 0.4 % when almost all of the current was injected.

• Fiber Technology and Industry
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• v.2 no.3
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• pp.355-375
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• 1998

• Proceedings of the Optical Society of Korea Conference
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• 2007.07a
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• pp.231-232
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• 2007

• Rapid Communication in Photoscience
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• v.1 no.2
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• pp.63-63
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• 2012

• Proceedings of the Optical Society of Korea Conference
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• 2006.07a
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• pp.239-240
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• 2006

• Journal of the Korean Society for Precision Engineering
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• v.29 no.11
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• pp.1183-1189
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• 2012

Organic light-emitting diodes (OLEDs) using microcavity effect have attracted great attention because they can reduce the width of emission spectra from organic materials, and enhance brightness from the same material. We demonstrate the simulation results of the radiation properties from top-emitting organic light-emitting diodes (TE-OLEDs) with microcavity structures based on the general electromagnetic theory. Organic materials such as N,N'-di (naphthalene-1-yl)-N,N'-diphenylbenzidine (NPB) as a hole transport layer and tris (8-hydroxyquinoline) ($Alq_3$) as emitting and electron transporting layer are used to form the OLEDs. The organic materials were sandwiched between anode such as Ni or Au and cathode such as Al, Ag, or Al:Ag. The devices were characterized with electroluminescence phenomenon. We confirmed that the simulation results are consistent with experimental results.