• Journal of the Korean institute of surface engineering
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• v.49 no.2
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• pp.196-201
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• 2016

We studied white tandem organic light-emitting diodes using blue and red phosphorescent materials. Optimized white single phosphorescent OLED was fabricated using CBP : FIrpic (12 vol.%, 9 nm) / CBP : $Ir(mphmq)_2acac$ : $Ir(ppy)_3$ (1 vol.%, 1 vol.%, 1 nm) as emitting layer (EML). The single phosphorescent OLED showed maximum current efficiency of 22.5 cd/A, white emission with a Commission Internationale de l'Eclairage (CIE) coordinates of (0.342, 0.37) at $1,000cd/m^2$, and variation of CIE coordinates with ($0.339{\pm}0.008$, $0.371{\pm}0.001$) from 500 to $3,000cd/m^2$. Optimized white tandem phosphorescent OLED was fabricated using CBP : FIrpic (12 vol.%, 7 nm) / CBP : $Ir(mphmq)_2acac$ : $Ir(ppy)_3$ (1 vol.%, 1 vol.%, 3 nm) as EML. The tandem phosphorescent OLED showed maximum current efficiency of 49.2 cd/A, white emission with a CIE coordinates of (0.376, 0.366) at $1,000cd/m^2$, variation of CIE coordinates with ($0.375{\pm}0.004$, $0.367{\pm}0.002$) from 500 to $3,000cd/m^2$. Maximum current efficiency of tandem phosphorescent OLED was more twice as high as single phosphorescent OLED. Our results suggest that tandem phosphorescent OLED was possible to control CIE coordinates and produce excellent color stability.

• Journal of the Korean Applied Science and Technology
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• v.32 no.1
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• pp.1-6
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• 2015

We investigated green phosphorescent organic light-emitting diodes with stepwise doping to improve efficiency roll-off and operational lifetime by efficient distribution of triplet excitons. The host material which was 4,4,N,N'-dicarbazolebiphenyl (CBP) of bipolar characteristic that can control the carrier in emitting layer (EML). When the EML devided into four parts with different doping concentration, each devices shows various efficiency roll-off and lifetime enhancement. The distribution of the carrier and excitons in the EML can be confirmed by using stepwise doping structure. The properties of device C exhibited luminous efficiency of 51.10 cd/A, external quantum efficiency of 14.88%, respectively. Lifetime has increased 73.70% compared to the reference device.

• Journal of the Korean Applied Science and Technology
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• v.30 no.2
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• pp.244-250
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• 2013

We investigated green phosphorescent organic light-emitting diodes (PHOLEDs) with charge control layer (CCL) to produce high efficiency. The CCL and host material which was 4,4,N,N'-dicarbazolebiphenyl (CBP) of bipolar property can control the carrier movement in emitting layer (EML). The performance improvement by the insertion of CCL was realized to the well confined exciton and the reduced triplet exciton quenching effect in EML. Five types of devices (Device A, B, C, D, and E) were fabricated following the thickness of CCL within EML. The properties of device D using optimized thickness of CCL showed external quantum efficiency of 16.22% and luminous efficiency of 55.76 cd/A, respectively.

• Proceedings of the Materials Research Society of Korea Conference
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• 2007.11a
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• pp.77.1-77.1
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• 2007

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.22 no.9
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• pp.781-785
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• 2009

We have fabricated simple triple-layer blue-emitting phosphorescent organic light emitting diodes (OLEDs) using different thicknesses (25 and 55 nm) of 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) electron transport layers. 1,1-bis[4-bis (4-methylphenyl)- aminophenyllcyclohexane (TAPC), bis[(4,6-di-fluorophenyl)-pyridinate-$N,C^{2'}$]picolinate (FIrpic) and N,N' -dicarbazolyl-3,5-benzene (mCP) were used as hole transport, blue guest and host materials, respectively. The driving voltage, electroluminescence (EL) efficiency and emission characteristics of devices were investigated. The maximum EL efficiency was 20 cd/A in the device with 55 nm BCP layer, which efficiency was about 33% higher than the device with 25 nm BCP layer. The higher efficiency in the 55 nm BCP device resulted from the enhanced electron-hole balance. In the EL spectrum of blue phosphorescent OLED with BCP layer, the relative intensity between 470 and 500 nm peaks was related to the location of emission zone.

• 한국정보디스플레이학회:학술대회논문집
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• 2005.07b
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• pp.1143-1146
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• 2005

Novel series of electron-transporting hosts, pentavalent aluminum complexes containing 8 hydroxyquinoline ligands and various phenolato ligands were synthesized, and organic light-emitting diodes (OLEDs) were fabricated using these complexes as host materials of phosphorescent emitting device and the fabricated phosphorescent emitting device showed low driving voltage, high efficiency at high current density and good stability under conventional driving condition.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.05a
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• pp.153-156
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• 2005

In this study, we have investigated transient properties of top emission organic light emitting diode (OLED) with a red electrophosphorescent dopant. The emission spectrum shows a strong peak at 620 nm accompanied with a small peak at 675 nm in the red region. Time evolution of electrophosphorescence reveals a decay time of 703 ms at a voltage pulse of 5 V in a device with an emitting area of 20 $mm^2$. Rise and delay times vary from 450 to 14 ms and 73 to 3 ms, respectively, as the voltage amplitude increases from 4.5 to 10 V. These results are compared with the red emitting device without an electron injection layer.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.402-403
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• 2007

High-efficiency white organic light-emitting diodes (WOLEDs) were fabricated with two emissive layers and a spacer was sandwiched between two phosphorescent dyes which were, bis(3,5-Difluoro-2-(2-pyridyl)phenyl-(2-carboxypyridyl) iridium III (FIrpic) as the blue emission and bis(5-acetyl-2-phenylpyridinato-N,C2') acetylacetonate $((acppy)_2Ir(acac))$ as the red emission. This spacer effectively prevented a triple-triple energy transfer between the two phosphorescent emissive layers with blue and red emission that was showed a improved lifetime. The white device showed Commission Internationale De L'Eclairage $(CIE_{x,y})$ coordinates of (0.33, 0.42) at $22400\;cd/m^2$, a maximum luminance of $27300\;cd/m^2\;at\;0.388\;mA/cm^2$, and a maximum luminous efficiency of 26.9 cd/A.

• 한국정보디스플레이학회:학술대회논문집
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• 2005.07b
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• pp.1381-1382
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• 2005

We report improved efficiency in blue electrophosphorescent organic light emitting diodes by introducing an interfacial exciton blocking layer between light emitting layer (EML) and hole transport layer (HTL). Iridium(III) bis [(4,6-di-fluorophenyl)- pyridinato -N,C2']picolinate (FIrpic) was used as blue phosphorescent dopant and JHK6-3 with carbazole and electron transporting group as host and also as the interfacial layer, resulting in drastic increase in quantum efficiency.

• Transactions on Electrical and Electronic Materials
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• v.10 no.6
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• pp.208-211
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• 2009

The authors have demonstrated the various characteristics of hybrid white organic light-emitting diodes (HWOLED) using fluorescent blue and phosphorescent red emitters. We also demonstrated that two devices showed different characteristics in accordance with thickness of the 4,4′-N,N′-dicarbazole-biphenyl (CBP) spacer (CS) inserted between the blue and the red emitting layer. It was found that the device with a CS thickness of 70 $\AA$ showed a current efficiency 2.5 times higher than that of the control device with a CS thickness of 30 $\AA$ by preventing the triplet Dexter energy transfer from the red to the blue emitting layer. The HWOLED with the CS thickness of 70 $\AA$ exhibited a maximum luminance of 24500 cd/$m^2$, a maximum current efficiency of 42.9 cd/A, a power efficiency of 37.5 lm/W, and Commission Internationale de I'Eclairage coordinates of (0.37, 0.42).