• 한국정보디스플레이학회:학술대회논문집
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• 2009.10a
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• pp.184-187
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• 2009

In this paper, we study effect of charge balance on performance of blue phosphorescent organic light emitting diodes (OLEDs). Charge balance determines the location of recombination zone in the OLEDs. By tuning the charge balance in iridium (III) bis[(4,6-difluorophenyl)-pyridinate-N,C2']picolinate (FIrpic) based blue phosphorescent organic light-emitting devices (PHOLEDs) with a high mobility and high triplet energy electron transporting material, we were able to achieve a high current efficiency of 60 cd/A which is a 3X improvement over previous devices with 3,5'-N,N'-dicarbazole-benzene (mCP) host.

• 한국정보디스플레이학회:학술대회논문집
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• 2009.10a
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• pp.38-41
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• 2009

We demonstrate a new commercial green phosphorescent organic light emitting device (OLED) in a bottom emission device and top emission microcavity. The bottom and top emitting phosphorescent OLEDs (PHOLED$^{TM}$s) had luminance efficiencies of 60cd/A and 137cd/A respectively, at a luminance of 1,000cd/$m^2$. The top emission microcavity was close to 1953 NTSC color requirements with 1931 CIE color coordinates of 0.231, 0.718. A record green PHOLED lifetime of >3,500hrs to LT95 from 4000cd/$m^2$ is demonstrated for the microcavity device.

• Proceedings of the Materials Research Society of Korea Conference
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• 2012.05a
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• pp.69.2-69.2
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• 2012

Graphene films have a strong potential to replace indium tin oxide anodes in organic light-emitting diodes (OLEDs), to date. However, the luminous efficiency of OLEDs with graphene anodes has been limited by a lack of efficient methods to improve the low work function and reduce the sheet resistance of graphene films to the levels required for electrodes. Here, we fabricate flexible OLEDs by modifying the graphene anode to have a high work function and low sheet resistance, and thus achieve extremely high luminous power efficiencies (37.2 lm/W in fluorescent OLEDs, 102.7 lm/W in phosphorescent OLEDs), which are significantly higher than those of optimized devices with an indium tin oxide anode (24.1 lm/W in fluorescent OLEDs, 85.6 lm/W in phosphorescent OLEDs). We also fabricate flexible white OLED lighting devices using the graphene anode. These results demonstrate the great potential of graphene anodes for use in a wide variety of high-performance flexible organic optoelectronics.

• 한국정보디스플레이학회:학술대회논문집
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• 2008.10a
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• pp.1414-1417
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• 2008

Using a $Ir(ppy)_3$ doped in the TCTA:$Bepp_2$ mixed host and N- and P-doped in TCTA:$Bepp_2$ charge transport layers, an ideal energy level alignment technology is developed. A very low roll-off current efficiency of 7.4 % at a luminance of $10,000\;cd/m^2$ with this technology is demonstrated in green phosphorescent OLEDs.

• Applied Chemistry for Engineering
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• v.26 no.6
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• pp.725-729
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• 2015

Organic light emitting diodes (OLEDs) are regarded as the next generation display and solid-state lighting due to their superb achievements from extensive research efforts on improving the efficiency and stability of OLEDs in addition to developing new materials. Herein, efficient green phosphorescent OLEDs were obtained by using hexaazatrinaphthylene (HAT) derivatives as a hole injection layer. External quantum and current efficiencies of OLEDs were enhanced from 8.8% and 30.8 cd/A to 13.6% and 47.7 cd/A, respectively by inserting a thin layer of HAT derivatives between the ITO and hole transporting layer. The enhancement of OLEDs was found to be originated from the inserted HAT derivatives, which resulted in the optimized hole-electron balance inside the emission layer.

• 한국정보디스플레이학회:학술대회논문집
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• 2008.10a
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• pp.1516-1519
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• 2008

We report extremely low doping technology in phosphorescent organic light emitting diodes(PHOLEDs). Highly efficient red PHOLEDs with excellent energy transfer characteristics even under 1 % doping condition have been demonstrated. Results reveal efficient host-dopant system to realize highly efficient PHOLEDs and useful cost saving way by reduction of expensive Ir complex dopants.

• 한국정보디스플레이학회:학술대회논문집
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• 2007.08a
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• pp.694-697
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• 2007

We demonstrate the use of screen printing in the fabrication of highly efficient phosphorescent polymer organic-light-emitting devices (OLEDs) based on a green-emitting $Ir(ppy)_3$ and a host polymer PVK. We incorporate PBD in the polymer host as an electron-transporting dopant and ${\alpha}-NPD$ as a hole transporting dopant. The best screen printed single-layer device exhibits very high peak luminous efficiency of 63 cd/A at a relatively high operating voltage of 17.1 V at the luminance of $650\;cd/m^2$. We observed the highest luminance of $21,000\;Cd/m^2$ at 35V. Due to the high operating voltage, despite of the high peak luminous efficiency the peak power efficiency was found to be 12.2 lm/W at the luminance of $470\;cd/m^2$ (15.9 V).

• 한국정보디스플레이학회:학술대회논문집
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• 2007.08a
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• pp.663-666
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• 2007

High-efficiency red phosphorescent OLEDs employing a novel red emitter and a multifunctional oligofluorene host are reported. With qazIr(acac) as the red phosphorescent dopant, a maximum external quantum efficiency of 19% and maximum power efficiency of 11 lm/W are achieved. In addition, single layer devices using such host and dopant materials have efficiencies up to 13%.

• Bulletin of the Korean Chemical Society
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• v.31 no.12
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• pp.3711-3717
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• 2010

Four orange-red phosphorescent Ir(III) complexes were designed and synthesized based on the benzoylphenylpyridine ligand with a fluorine substituent. Multilayered OLEDs with the device structure, ITO/2-TNATA/NPB/CBP : 8% Ir(III) complexes/BCP/Liq/Al, were fabricated using these complexes as dopant materials. All the devices exhibited orange-red electroluminescence and their electroluminescent properties were quite sensitive to the structural features of the dopants in the emitting layers. Among these, the maximum luminance ($14700\;cd/m^2$ at 14.0 V) was observed in the device containing Ir(III) complex 1 as the dopant. In addition, its luminous, power and quantum efficiency were 11.7 cd/A, 3.88 lm/W and 9.58% at $20\;mA/cm^2$, respectively. The peak wavelength of electroluminescence was 606 nm with CIE coordinates of (0.61, 0.38) at 12.0 V. The device also showed stable color chromaticity with various voltages.

• 한국정보디스플레이학회:학술대회논문집
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• 2008.10a
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• pp.1513-1515
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• 2008

High efficiency phosphorescent organic light emitting devices ($PHOLED^{TM}s$) are now widely used in commercial displays. In this paper we describe some of the work behind the development of high efficiency stable green PHOLEDs capable of fulfilling display specifications.