• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.493-494
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• 2006

We have demonstrated highly efficient WOLED with two separated emissive layers using a blue fluorescent dye and a red phosphorescent dye. we also obtain stable $CIE_{x,y}$ coordinates with two-layered WOLEDs. The device structure was ITO/2-TNATA/NPB/two separated emissive layers/Bphen/Liq/Al. The maximum luminous efficiency of the device was 11.6 cd/A at $20\;mA/cm^2$ and $CIE_{x,y}$ coordinates varied from (x = 0.33, y = 0.37) at 6V to (x = 0.28, y = 0.35) at 14V.

• 한국정보디스플레이학회:학술대회논문집
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• 2006.08a
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• pp.1067-1070
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• 2006

We have demonstrated highly efficient WOLED with two separated emissive layers using a blue fluorescent dye and a red phosphorescent dye. The maximum luminous efficiency of the device was 11.2 cd/A at $20\;mA/cm^2$ and $CIE_{x,y}$ coordinates varied from (x = 0.33, y = 0.37) at 6V to (x = 0.25, y = 0.33) at 14V.

• 한국정보디스플레이학회:학술대회논문집
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• 2007.08b
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• pp.1437-1439
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• 2007

We fabricated white organic light emitting device (WOLED) with the layered fluorescent blue material and phosphorescent green/red dye-doped materials. Addition of the non-doped phosphorescent host material between the fluorescent and phosphorescent light emitting layers provided the result of broadband white spectrum, with improved balance, higher efficiency, and lower power consumption. In our devices, there was no need of exciton-blocking layer between the each emission layer for the further confinement of the diffusion of excitons.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.11
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• pp.1192-1198
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• 2004

Hole transporting polymer(poly［N-(p-diphenylamine)phenylmethacrylamide］, PDPMA) was doped with nile red dye at various concentrations to study the influence of doping on the energy transfer during light emitting processes. Organic LEDs composed of ITO/blend(PDPMA -nile red)/ Alq$_3$/Al as well as thin films of blend(PDPMA -nile red)/ Alq$_3$ were manufactured for investigating photoluminescence, electroluminescence, and current-voltage characteristics. Atomic Force Microscopy was also used to observe surface morphology of the blend films. It was found that such doping. significantly influences the efficiency of the energy transfer from the Alq$_3$ layer to blended layer and the optical/electrical properties could be optimized by choosing the right concentration of the dye molecule. The results also showed a interesting correlation with the morphological aspect, i.e. the optimum luminescence at the concentration with the least surface roughness. When the concentration of nile red was 0.8 wt%, the maximum energy transfer could be achieved.

• 한국정보디스플레이학회:학술대회논문집
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• 2008.10a
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• pp.477-480
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• 2008

A highly efficient white phosphorescent OLED with a "tetra-chromatic" emission was fabricated by using an external color tuning layer (ECTL) which is composed of a layer of greenish yellow organic dye dispersed in PMMA on the outside of the glass. The ECTL combining with a lower red dopant concentration in the device has been found to improve the efficiency of a conventional WOLED by more than 27%.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.73-74
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• 2006

New iridium complexes that have carbonyl group were synthesized and demonstrated various red light emission in organic light-emitting diodes (OLEDs). The maximum luminance of $57000{\sim}15300\;cd/m^2$ at 15 V and the luminance efficiency of 22.8~5.6 cd/A at $20\;mA/cm^2$ were achieved respectively. The peak wavelength of the electroluminescence were at 570~604 nm and the device also showed a stable color chromaticity with various voltages.

• Journal of Information Display
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• v.8 no.2
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• pp.15-19
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• 2007

We have studied the effect of host materials on the electrophosphorescence properties by comparing three different host materials such as tris(8-hydroxyquinoline)-aluminum (III) $(Alq_3)$, bis(8-hydroxyquinoline)-zinc (II) $(Znq_2)$, and 4,4'-N,N' dicarbazole-biphenyl (CBP) doped with a red-emissive phosphorescent dye, 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin platinum (II) (PtOEP). The EL spectra show a strong red emission (peak at 650 nm) from the triplet excited state of PtOEP and a very weak emission from an electron transport layer of $Alq_3$ and a hole transport layer of N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1-biphenyl-4,4'-diamine (TPD). We find that the triplet exciton lifetime and the quantum efficiency decrease in the order of CBP, $Alq_3$, and $Znq_2$ host materials. The results are interpreted as a poor exciton confinement in $Alq_3$, and $Znq_2$ host compared with in CBP. Therefore, it is very important for the triplet-exciton confinement in the emissive layer for obtaining a high efficiency.