• Proceedings of the Polymer Society of Korea Conference
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• 2006.10a
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• pp.166-166
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• 2006

The photoluminescence (PL) efficiency of $Ir(ppy)_{3}$:PVK is lower than $Ir(ppy)_{3}$:CBP for the whole range of doping concentration and this low PL efficiency can be a reason of the lower efficiency of PhPLED than PhOLED. The lower efficiency is originated from the large bi-excitonic quenching such as the triplet-triplet annihilation. The PhPLEDs showed very short lifetime. The short lifetime was found to be originated from the instability of the doubly reduced $Ir(ppy)_{3^{-2}}$. The double reduction takes place because of the low electron mobility of PVK and large energy difference of LUMO level between PVK and $Ir(ppy)_{3}$.

• 한국정보디스플레이학회:학술대회논문집
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• 2008.10a
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• pp.499-502
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• 2008

Effects of a dielectric capping layer on the luminous characteristics of top emitting organic light emitting diodes (TOLEDs) have been analyzed using a classical electromagnetic theory. Special attention was given to the influence of the cavity length on the effectiveness of the capping layer. The luminance characteristics of the TOLEDs influenced by the combined effects of the cavity length and the capping layer thickness. Furthermore, these combined effects also modify the emission spectrum and pattern of the TOLEDs, which result in the improvement of total luminance of the device, but no significant change in the device out-coupling efficiency.

• Journal of the Korean Applied Science and Technology
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• v.22 no.4
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• pp.299-305
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• 2005

In this study, we designed color of tunable and high efficient organic materials using the quantum dynamics and the semi-empirical calculation, and applied this results to the fabrication of organic light-emitting diodes. Also we optimized the molecular structure of phosphorescent materials and the energy transfer from a host to a dye which makes organic light-emitting diodes improve. Using quantum dynamics method, the molecular structures of ligand only and the whole metal chelate were optimized, and these energy levels were calculated. From this test results, we could understand the emission mechanism of phosphors with various ligands as well as design the proper ligands reducing the T-T annihilation and the carrier lifetime. We also could design ligands with various colors using this test method.

• 한국정보디스플레이학회:학술대회논문집
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• 2006.08a
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• pp.357-362
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• 2006

OLEDs are becoming established as a commercially viable flat panel display technology of choice of the $21^{st}$ century because of its lightweight, fast response time, lower thickness than LCD's and potentially low cost (1-2). For the OLEDs to function effectively, highly thermally stable materials, which offer high efficiency and long operational lifetimes are required. To achieve long lifetime, highly stable charge (both holes and electrons) transporters are essential. OLED-T provides these materials as well as fluorescent and phosphorescent dopants. This paper reports a unique patented hole injector (E9363) and an electron transporter (E246) that increases the lifetime and efficiency and reduces operating voltage. Further, an electron injector, EEI-101, which evaporates at a very low temperature of $300^{\circ}C$ as opposed to the conventional LiF, which requires $580^{\circ}C$, is also presented.

• 한국정보디스플레이학회:학술대회논문집
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• 2009.10a
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• pp.192-195
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• 2009

We developed highly efficient blue PHOLEDs with reduced roll-off by using a mixed host structure. The balanced charge carrier injection and the distributed recombination zone within emissive layer resulted in a highly stable efficiency roll-off with quantum efficiencies of 20.1 and 18.1 % at a luminance of 1000 and 10000 cd/$m^2$.

• Bulletin of the Korean Chemical Society
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• v.32 no.12
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• pp.4321-4326
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• 2011

A new series of heteroleptic cyclometalated iridium(III) complexes has been synthesized and characterized by absorption, emission and cyclic voltammetry studies: $(pqx)_2Ir(acac)$ (1), $(dmpqx)_2Ir(acac)$ (2) and $(dfpqx)_2Ir(acac)$ (3) where pqx=2-phenylquinoxalinate, dmpqx=2-(2,4-dimethoxyphenyl)quinoxalinate, dfpqx=2-(2,4-difluorophenyl) quinoxalinate and acac=acetylacetonate anion. The reaction of excess acetylacetone with ${\mu}$-chloride-bridged dimeric iridium complex, $[(C\^N)_2Ir({\mu}-Cl)]_2$, gives a complex 1 and an unusual hydridoiridium(III) complex, $(pqx)IrH(acac)_2$ (4). The complex 1, 2 and 3 show their emissions in an orangered region (${\lambda}_{PL,max}$ = 583-616 nm), and the emission maxima can be tuned by the change of substituent at phenyl ring of 2-phenylquinoxaline ligand. The phosphorescent line shape indicates that the emissions originate predominantly from $^3MLCT$ states with little admixture of ligand-based $^3({\pi}-{\pi}^*)$ excited states. The structures of complex 3 and 4 are additionally characterized by a single crystal X-ray diffraction method. The complex 3 shows a distorted octahedral geometry around iridium(III) metal ion. A strong trans influence of the phenyl ring is examined. In complex 4, there are two discrete molecules which are mirror images each other at the ratio of 1:1 in an unit cell. We propose that the phosphorescent complex 1, 2 and 3 are possible candidates for the phosphors in OLEDs applications.

• Korean Journal of Materials Research
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• v.18 no.7
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• pp.347-351
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• 2008

We have fabricated and evaluated newNew high high-efficiency green green-light light-emitting phosphorescent devices with an emission layer of [$TCTA/TCTA_{1/3}TAZ_{2/3}/TAZ$] : $Ir(ppy)_3$ were fabricated and evaluated, and compared the electroluminescence characteristics of these devices were compared with the conventional phosphorescent devices with emission layers of ($TCTA_{1/3}TAZ_{2/3}$) : $Ir(ppy)_3$ and (TCTA/TAZ) : $Ir(ppy)_3$. The current density, luminance, and current efficiency of the a device with an emission layer of ($80{\AA}-TCTA/90^{\circ}{\AA}-TCTA_{1/3}TAZ_{2/3}/130{\AA}-TAZ$) : 10%-$Ir(ppy)_3$ were $95\;mA/cm^2$, $25000\;cd/m^2$, and 27 cd/A at an applied voltage of 10 V, respectively. The maximum current efficiency was 52 cd/A under the a luminance value of $400\;cd/m^2$. The peak wavelength and FWHM (FWHM (full width at half maximum) in the electroluminescence spectral were 513 nm and 65 nm, respectively. The color coordinate was (0.30, 0.62) on the CIE (Commission Internationale de I'Eclairage) chart. Under the a luminance of $15000\;cd/m^2$, the current efficiency of the a device with an emission layer of ($80{\AA}-TCTA/90{\AA}-TCTA_{1/3}TAZ_{2/3}/130{\AA}-TAZ$) : 10%-$Ir(ppy)_3$ was 34 cd/A, which has beenshowed an improvement of improved 1.7 and 1.4 times compared to those of the devices with emission layers of ($300{\AA}-TCTA_{1/3}TAZ_{2/3}$) : 10%-$Ir(ppy)_3$ and ($100{\AA}-TCTA/200{\AA}$-TAZ) : 10%-$Ir(ppy)_3$, respectively.

• Journal of the Korean Applied Science and Technology
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• v.24 no.1
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• pp.74-78
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• 2007

A new blue phosphorescent material for organic light emitting diodes (OLEDs), Iridium(III)bis[2-(4-fIuoro-3-benzonitrile)-pyridinato-N,C2'] picolinate (Firpic-CN), was synthesized and studied. We compared characteristics of Firpic-CN and Bis(3,5-Difluoro-2-(2-pyridyl)phenyl-(2-carboxypyridyl) iridium III (FIrpic) which has been used for blue dopant materials frequently. The devices structure were indium tin oxide (ITO) (1000 ${\AA}$)/N,N'-diphenyl-N,N'-(2-napthyl)-(1,1'-phenyl)-4,4'-diamine (NPB) (500 ${\AA}$)/4,4'-N,N'-dicarbazole-biphyenyl (CBP) : FIrpic and FIrpic-CN (X wt%)/4,7-diphenyl-1,10-phenanthroline (BPhen) (300 ${\AA}$)/lithum quinolate (Liq) (20 ${\AA}$)/Al (1000 ${\AA}$). 15 wt% FIrpic-CN doped device exhibits a luminance of $1450\;cd/m^2$ at 12.4 V, luminous efficiency of 1.31 cd/A at $3.58mA/cm^2$, and Commission Internationale d'Eclairage $(CIE_{x,y})$ coordinates of (0.15, 0.12) at 12 V which shows a very deep blue emission. We also measured lifetime of devices and was presented definite difference between devices of FIrpic and FIrpic-CN. Device with FIrpic-CN as a dopant presented lower longevity due to chemical effect of CN ligand.

• 한국정보디스플레이학회:학술대회논문집
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• 2007.08b
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• pp.1425-1428
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• 2007

The amorphous IZO on flexible substrate (PC) shows similar electrical conductivity and optical transmittance with commercial ITO glass even though it was prepared at $<50\;^{\circ}C$. Moreover, it exhibits little resistance change during 5000 bending cycles, demonstrating good mechanical robustness. A green phosphorescent OLED fabricated on amorphous IZO on flexible PC shows maximum external quantum efficiency of ${\eta}_{ext}=13.7\;%$ and power efficiency of ${\eta}_p=32.7\;lm/W$, which are higher than a device fabricated on a commercial ITO on glass (${\eta}_{ext}=12.4%$ and ${\eta}_p=30.1\;lm/W$) and ITO on flexible PC (${\eta}_{ext}=8.5%$ and ${\eta}_p=14.1\;lm/W$).

• 한국정보디스플레이학회:학술대회논문집
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• 2008.10a
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• pp.454-457
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• 2008

We report the syntheses, photophysical properties and device performances of solution processible host material for green-phosphorescent OLEDs. The butterfly-shaped new host materials with nonconjugated linkage of carbazole and fluorene moieties have large triple energy band gap around 2.8 eV. All of the EL devices exhibited turn-on voltages in the range of 4.8-5.0 V. GH-4 exhibited the best performance with a maximum current efficiency and power efficiency of 21.1 cd/A and 7.9 lm/W.