• ETRI Journal
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• v.34 no.5
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• pp.690-695
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• 2012

We investigate the light-emitting performances of blue phosphorescent organic light-emitting diodes (PHOLEDs) with three different electron injection and transport materials, that is, bathocuproine(2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline) (Bphen), 1,3,5-tri(m-pyrid-3-yl-phenyl)benzene (Tm3PyPB), and 2,6-bis(3-(carbazol-9-yl)phenyl)pyridine (26DCzPPy), which are partially doped with cesium metal. We find that the device characteristics are very dependent on the nature of the introduced electron injection layer (EIL) and electron transporting layer (ETL). When the appropriate EIL and ETL are combined, the peak external quantum efficiency and peak power efficiency improve up to 20.7% and 45.6 lm/W, respectively. Moreover, this blue PHOLED even maintains high external quantum efficiency of 19.6% and 16.9% at a luminance of $1,000cd/m^2$ and $10,000cd/m^2$, respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.174-177
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• 2001

We have seen the effects of buffer layer in organic light-emitting diodes using poly(N-vinylcarbazole)(PVK). Polymer PVK buffer layer was made using spin casting techniques. Two different types of spin casting have been applied; static coating and dynamic coating. Two device structures were fabricated; one is ITO/TPD/Alq$_3$/Al as a reference, and the other is ITO/PVK/TPD/Alq$_3$/Al to see the effects of buffer layer in organic light-emitting diodes. Current-voltage characteristics and luminous efficiency were measured with a variation of spin-casting methods and rpm speeds. We have obtained an improvement of luminous efficiency by a factor of two and half when the PVK buffer layer is used.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.11a
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• pp.293-294
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• 2005

We have investigated dielectric properties depending on frequency in organic light -emitting diodes using 8-hydroxyquinoline aluminum ($Alq_3$) as an electron transport and emissive material. We analyzed the dielectric properties of organic light-emitting diodes using impedance of characteristics. impedance characteristics was measured complex impedance Z and phase $\Theta$ in the frequency range of 40 Hz to $10^8$ Hz. We obtained complex electrical conductivity, dielectric constant, and loss tangent (tan$\delta$) of the device at room temperature. From these analyses, we are able to interpret a conduction mechanism and dielectric properties contributed by an interfacial and orientational polarization.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.04a
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• pp.74-75
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• 2006

We have investigated dielectric properties depending on temperature in organic light-emitting diodes using 8-hydroxyquinoline aluminum ($Alq_3$) as an electron transport and emissive material. We analyzed the dielectric properties of organic light-emitting diodes using characteristics of impedance. he Impedance characteristics was measured complex impedance Z and phase $\theta$ in the temperature range of 10 K to 300 K. We obtained complex electrical conductivity, dielectric constant and loss tangent ($tan{\delta}$) of the device at room temperature. From these analyses, we are able to interpret a conduction mechanism and dielectric properties contributed by an interfacial and orientational polarization.

• Proceedings of the Optical Society of Korea Conference
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• 2008.02a
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• pp.95-96
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• 2008

We theoretically investigated the influence of side surface texturing on the light extraction efficiency in nitride-based light-emitting diodes (LEDs). The light extraction efficiency was expected as 1.2 times larger in a LED with textured surfaces compared to without ones.

• 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.

• Journal of the Optical Society of Korea
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• v.17 no.1
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• pp.16-21
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• 2013

In this paper, we report the effect of GaN/graded-composition AlGaInN/GaN quantum barriers in active regions on the electrical and optical properties of GaN-based vertical light emitting diodes (VLEDs). By modifying the aluminum composition profile within the AlGaInN quantum barrier, we have achieved improvements in the output power and the internal quantum efficiency (IQE) as compared to VLEDs using conventional GaN barriers. The forward voltages at 350 mA were calculated to be 3.5 and 4.0 V for VLEDs with GaN/graded-composition AlGaInN/GaN barriers and GaN barriers, respectively. The light-output power and IQE of VLEDs with GaN/graded-composition AlGaInN/GaN barriers were also increased by 4.3% and 9.51%, respectively, as compared to those with GaN barriers.

• Polymer(Korea)
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• v.29 no.2
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• pp.107-121
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• 2005

Electrophosphorescent light emitting diodes (LEDs) using phosphorescent dyes as triplet emitter, which incorporate a heavy metal atom to mix singlet and triplet states by the strong spin-orbit coupling, can achieve the theoretically $100\%$ internal quantum efficiency. In this paper, we report on the performance and the energy transfer mechanism of polymer based highly efficient electrophosphorescent LEDs. The effect of phase separation and aggregation to the energy transfer between polymer hosts and phosphorescent guests and performance of polymer electrophosphorescent LEDs were investigated. Finally, the effect of introducing substitute group and ligand modification of phosphorescent dyes on optical and electrical properties are reported.

• 제어로봇시스템학회:학술대회논문집
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• 1991.10b
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• pp.1956-1960
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• 1991

This paper describes the measured results upon monochromatic light, compound light, and light emanated from light emitting diodes by a simplified wavemeter with a semiconductor color sensor. Since a single unit element of a semiconductor color sensor with two PN junction photodiodes has been developed, the author has fabricated the simplified wave detector by using the element. The simplified wive detector has been measured results upon monochromatic light, compound light, and light emanated from light emitting diodes. Since luminescent color of each diode locates in luminosity region, comparison of measured values of PD-150 and PD-151 resulted no remarkable difference in averaged wave length. As for monochromatic light, PD-151 showed very cross value to the color filter peak value rather than PD-150. As for compound light, PD-150 has shown such influence of long wave length light which reaches to near infrared ray with respect to PD-151.

• Proceedings of the Optical Society of Korea Conference
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• 2008.02a
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• pp.355-356
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• 2008

The light extraction efficiencies of GaN-based light-emitting diodes (LEDs) grown on differently patterned sapphire substrates were investigated by using the ray tracing method. It was found that angle of the pattern surface against the sapphire surface, the number of pattern per unit area were important structural factors for high extraction efficiency.