Weon-Jong Kim

Efficiency Improvement of OLEDs depending on the Hole-size of Crucible Boat

In the device structure of ITO/tris(8-hydroxyquinoline) aluminum ()/Al device, we investigated the efficiency improvement of organic light-emitting diodes (OLEDs) depending on the hole-size of crucible boat. The device was manufactured using a thermal evaporation under the base pressure of . The organics were evaporated to be 100 nm thick at a deposition rate of , and in order to investigate the optimal surface roughness of , the was thermally evaporated to be 0.8 mm, 1.0 mm, and 1.5 mm as a hole-size of the boat, respectively. We found that luminance and external quantum efficiency are superior when the hole-size of the boat is 1.0 mm. The external quantum efficiency of the device made with the hole-size of 1.0 mm boat were improved by a factor of ten compared to the devices made with the hole-size of non boat.

Effect on the Electrical Characteristics of OLEDs Depending on Amorphous Fluoropolymer

In this research, the electric characteristic of organic light-emitting diodes(OLEDs) was studied depending on thickness of amorphous fluoropolymer(Teflon-AF) which is the material of hole injection layer to improve electric characteristic of OLEDs. Sample composition was fabricated in double layer. The basic structure was fabricated by ITO/tris(8-hydroxyquinoline) aluminum (Alq3)/Al and the 2 layer was fabricated by ITO/2,2-Bistrifluoromethyl-4,5-Difluoro-1,3-Dioxole(Teflon-AF)/tris(8-hydro xyquinoline) aluminum (Alq3)/Al. The experiment was carried with variation of thickness of Teflon-AF at 1.0, 2.0, 2.5, 3.0 nm. The result showed when Teflon-AF thickness was 2.5 nm, the electric and optical characteristic were well performed. Moreover, when it was compared with Teflon-AF without materials, it was improved 15.1 times more on luminance, 12.7 times more on luminous efficiency and 12.1 times more on external quantum efficiency. Therefore, OLEDs element with optimum hole injection layer reduced energy barrier and driving voltage, and confirmed that it improved efficiency widely.

Electrical Properties of OLEDs due to the Hole-size of Crucible Boat and Deposition Rate of Hole Transport Layer

In the structure of ITO/N,N`-diphenyl-N,N` bis (3-methylphenyl)-1,1`-biphenyl-4,4`-diamine(TPD)/tris (8-hydroxyquinoline)aluminum()/Al device, we studied the efficiency improvement of organic light-emitting diodes due to variation of deposition rate of hole transport layer (TPD) materials using hole-size of crucible boat. The thickness of TPD and was manufactured 40 nm, 60 nm, respectively under a base pressure of Torr using a thermal evaporation. The used for an electron-transport and emissive layer were evaporated to be at a deposition rate of . When the deposition rate of TPD increased from 1.5 to , we studied the efficiency improvement of TPD using the hole-size of crucible is 1.0 mm. When the deposition rate of TPD is , we found that the average roughness is rather smoother, the luminous efficiency the external quantum efficiency is superior to the others. Compared to the two from the devices made with the deposition rate of TPD is and , the external quantum efficiency was improved by four-times and two-times, respectively.

Efficiency Improvement of Organic Light-emitting Diodes depending on the Thickness Variation of BCP using Electron Transport Layer

In the devices structure of ITO/N,N`-diphenyl-N,N` bis (3-methylphenyl)-1,1`-biphenyl-4,4`-diamine (TPD) /tris (8-hydroxyquinoline)aluminumelectron-transport-layer(ETL)(2,9-Dimethyl-4,7-diphenyl-1,10-phenanthroline(BCP))/Al, we have studied the efficiency improvement of organic light-emitting diodes depending on the thickness variation of BCP using electron transport layer. The thickness of TPD and was manufactured 40 nm, 60 nm under a base pressure of Torr using at thermal evaporation, respectively. The TPD and layer were evaporated to be deposition rate of . And the BCP was evaporated to be a4 a deposition of . As the experimental results, we found that the luminous efficiency and the external quantum efficiency of the device is superior to others when thickness of BCP is 5 nm. Also, operating voltage is lowest. Compared to the ones from the devices without BCP layer, the luminous efficiency and the external quantum efficiency were improved by a factor of four hundred ninty and five hundred, respectively. And operating voltage is reduced to about 2 V.

Influence of the Optical Characteristics and Conductive Mechanism depending on the Deposition Condition of BCP

In a triple-layered structure of ITO/N,N`-diph enyl-N,N`bis(3-methylphenyl)-1,1` - biphenyl-4,4`-diamine(TPD)/tris(8-hydroxyquinoline)aluminum()/(2,9-Dimethyl-4,7-diphenyl-1,10-phenanthroline(BCP)/Al device, we have studied the electrical and optical characteristics of organic light-emitting diodes(OLEDs) depending on the deposition condition of BCP layer. Several different sizes of holes on boat and several different deposition rates were employed in evaporating the organic materials. And then, electrical properties of the organic light-emitting diodes were measured and the performance of the devices was analyzed. It was found that the hole-size of crucible boat and the evaporation rate affect on the surface roughness of BCP layer as well as the performance of the device. When the hole-size of crucible boat and the deposition rate of BCP are 1.2 mm and , respectively, average surface roughness of BCP layer is lower and the efficiency of the device is higher than the ones made with other conditions. From the analysis of current density-luminance-voltage characteristics of a triple layered device, we divided the conductive mechanism by four region according to applied voltage. So we have obtained a coefficient of in schottky region is , a coefficient of in Poole-Frenkel region is , and a potential barrier of in Fower-Nordheim region is 0.39 eV.

Electrical Characteristics of Organic Light-emitting Diodes Fabricated by Varying a Hole-size in Evaporation Boat

Electrical characteristics of organic light-emitting diodes were investigated by varying a hole-size in evaporation boat in the device structure of ITO/tris(8-hydroxyquinoline) aluminum/Al. The device was manufactured using a thermal evaporation under a base pressure of Torr. The emitting organics were evaporated to be a thickness of 100 nm at a deposition rate of . A cylindrical-shaped evaporation boat was made out of stainless steel with a small size of hole on top of the boat. Several evaporation boats were made having a different hole size on top; 0.8 mm, 1.0 mm, 1.5 mm, and 3.0 mm. We found that when the hole size on top of the evaporation boat is 1.0 mm, the average roughness is rather smoother compared to the other ones. Also, luminance and external quantum efficiency are superior to the others. Compared to the ones from the devices made with the hole-size of 0.8 mm boat. The luminance and external quantum efficiency of the device made with the hole-size of 1.0 mm boat were improved by a factor of seventy and thirty three, respectively. Also operating voltage is reduced to 2 V.

Electrical Characteristics on the Variation of Thickness and Deposition Rate in Organic Layer of OLEDs

OLEDs(Organic Light Emitting Diodes) are attractive as alternative display components because of their relative merits of being self-emitting, having large intrinsic viewing angle and fast switching speed. But because of their relatively short history of development, much remains to be studied in terms of their basic device physics and design, manufacturing techniques, stability and so on. We investigated electrical properties of N, N-diphenyl-N, N bis (3-methyphenyl-l,1`-biphenyl-4,4`-diamine (TPD) and tris-8-hydroxyquinoline aluminum when their thicknesses were changed variedly from 3:7 to 5:5 of their thickness ratios. And we also studied properties of OLED depend on their deposition rate between nm/s.

Insulation deterioration diagnosis on ultra high voltage power cables

Tests were performed for an insulation deterioration diagnosis on ultra high voltage power cables from the generator to the main transformer at the Daecheong hydroelectric power plant. These cables have been in service for over 22 years. With this mind, an investigation concerning the present conditions and the securing of basic data toward a life span diagnosis was conducted over 3 months, beginning in April of last year. In this diagnosis, we conducted the following tests: insulating voltage measurement, D.C. leakage current measurement, recovery voltage measurement, tan /spl delta/ measurement and partial discharge. According to our findings, for power cables from both generator 1 and 2, there was only a slight possibility of equipment failure or defect and this only during the recovery voltage measurement testing. At present its not severe, but follow-up checks will be needed again in 3 or 4 years.