• 한국정보디스플레이학회:학술대회논문집
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• 2006.08a
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• pp.1583-1586
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• 2006

All non-dopant white organic light-emitting diodes (WOLEDs) have been realized by using solid state highly fluorescent red bis(4-(N-(1- naphthyl)phenylamino)phenyl)fumaronitrile (NPAFN) and amorphous bipolar blue light-emitting 2-(4- diphenylamino)phenyl-5-(4-triphenylsilyl)phenyl- 1,3,4-oxadiazole (TPAOXD), together with well known green fluorophore tris(8- hydroxyquinolinato)aluminum $(Alq_3)$. The fabrication of multilayer WOLEDs did not involve the hard-tocontrol doping process. Two WOLEDs, Device I and II, different in layer thickness of $Alq_3$, 30 and 15 nm, respectively, emitted strong electroluminescence (EL) as intense as $25,000\;cd/m^2$. For practical solid state lighting application, EL intensity exceeding $1,000\;cd/m^2$ was achieved at current density of $18-19\;mA/cm^2$ or driving voltage of 6.5-8 V and the devices exhibited external quantum efficiency $({\eta}_{ext})$ of $2.6{\sim}2.9%$ corresponding to power efficiency $({\eta}_P)$ of $2.1{\sim}2.3\;lm/W$ at the required brightness.

• Journal of the Korean Applied Science and Technology
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• v.18 no.3
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• pp.186-190
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• 2001

By fabricating the organic light-emitting devices (OLEDs) based on phosphorescent material, the internal quantum efficiency can reach 100%, compared to 25% in the case of the fluorescent material. Thus, the phosphorescent OLEDs have recently been extensively studied and showed higher internal quantum efficiencies then the conventional OLEDs. In this study, we investigated the characteristics of the phosphorescent OLEDs, with the green emitting phosphor, $Ir(ppy)_{3}$, (tris(2-phenylpyridine)iridium). The devices with a structure of $ITO/TPD/Ir(ppy)_{3}$ doped in the host material $/BCP/Alq_{3}/Li:Al/Al$ were fabricated, and its electrical and optical characteristics were studied. By changing the doping concentration of $Ir(ppy)_{3}$, we fabricated several devices and investigated the device characteristics. OLEDs doped into BCP by 10% showed the best characteristics. For 10% doped OLEDs, the maximum luminance of was over 10000 $cd/m^{2}$, and the maximum power efficiency was 7.14 lm/W.

• 한국정보디스플레이학회:학술대회논문집
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• 2005.07b
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• pp.1416-1418
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• 2005

A new DCM derivative containing a phenothiazine moiety, 4-(dicyanomethylene)-2-t-butyl-6-(9-ethylphenothiazine-2- enyl)-4H-pyran (DCPTZ), has been synthesized as an orange-red fluorescent dye molecule for organic lightemitting diodes (OLEDs). EL devices with the structure of $ITO/PEDOT-PSS/{\alpha}-NPD/Alq_3:DCPTZ/Alq_3/LiF/Al$ have been fabricated with changing the doping concentration of the DCPTZ. Maximum EL spectra of the devices ranged from $580{\sim}620$ nm depending on the doping concentration of the dye molecule. An EL device with 0.5 % doping concentration showed CIE coordinate (0.51, 0.47) at luminance of 100 $cd/m^2$. White light-emitting devices with the structure of $ITO/PEDOT-PSS/{\alpha}-NPD/{\alpha}-NPD:DCPTZ/DPVBi/Alq_3/$ LiF/Al have been also fabricated. The thickness of blue light-emitting 1,4-bis(2,2- diphenylvinyl)benzene (DPVBi) layer was changed to obtain a white light-emission. A white light-emission from the device was observed when the thickness of the DPVBi layer became thicker than 10 nm.

• Proceedings of the KIEE Conference
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• 1998.07d
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• pp.1373-1376
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• 1998

Electroluminescent(EL) devices based on organic materials have been of great interest due to their possible applications for large-area flat-panel displays. They are attractive because of their capability of multicolor emission, and low operation voltage. In this study, glass substrate/ITO/TPD/$Eu(TTA)_3(phen)/Alq_3/Al$ structures were fabricated by evaporation method, where aromatic diamine(TPD) were used as a hole transporting material, $Eu(TTA)_3(phen)$ as an emitting material, and tris(8-hydroxyquinoline)Aluminum ($Alq_3$) as an electron transporting layer. Electroluminescent(EL) and I-V characteristics of $Eu(TTA)_3(phen)$ with a variety thickness was investigated. This structure shows the red EL spectrum, which is almost the same as the PL spectrum of $Eu(TTA)_3(phen)$. I-V characteristics of this structure show that turn-on voltage was 9V and current density of $0.01A/cm^2$ at a dc drive voltage of 9V. Details on the explanation of electrical transport phenomena of these structures with I-V characteristics using the trapped-charge-limited current model will be discussed.

• Applied Chemistry for Engineering
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• v.9 no.5
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• pp.710-714
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• 1998

Organic electroluminescence devices (ELD) with hetero-junction structure were fabricated utilizing poly(p-phenylne vinylene) (PPV) as emitting layer and electron transport layer (ETL). 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD) was used as an electron transport agent. Copolymers with stilbene type comonomers, such as poly(styrene-co-PVTS), poly(styrene-co-MeO-PVTS) and poly(styrene-co-MeO-ST) were synthesized to be used as a matrix polymer to disperse electron transport agent (PBD). Among the hetero-junction EL devices fabricated with the above materials, the device with poly(styrene-co-PVTS) as matrix polymer for ETL gave the highest luminance ($120.7cd/m^2$, 13 V). EL devices made with poly(styrene-co-MeO-PVTS) or poly(styrene-co-MeO-ST) matrix exhibited lower luminance than the one with polystyrene matrix and the single layer EL (ITO/PPV/Mg) device.

• Polymer(Korea)
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• v.25 no.3
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• pp.399-405
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• 2001

Poly[3-octylthiophene-co-3-(4-fluorophenyl)thiophene]s were synthesized in 2:1, 1:1, and 1:2 mole ratios, and organic electroluminescent devices were fabricated using the copolymers. The opto-electrical properties of the copolymers were studied by PL, EL spectra, I-V, and V-L curves of the organic electroluminescent devices in conjunction with the energy band diagrams which were obtained from the cyclic voltammogram and the electronic absorption spectra. The LUMO energy level of P(OT/FPT)(1:1) is the lowest as -3.35 eV. In the copolymers P(OT/FPT)(2:1) and P(OT/FPT)(1:1) the ${\lambada}_{max}$ in the PL and EL spectra red-shifted as the mole ratio of fluorophenyl group increased while in P(OT/FPT)(1:2) it showed a blue-shift. This indicates that the backbone chain is twisted due to the steric hinderance of the fluorophenyl group leading to shorter ${\pi}$-conjugation length. P(OT/FPT)(1:1) showed the highest EL intensity and the highest power efficiency among the three copolymers. In P(OT/FPT)(1:2) the roughness of the film surface causes unusually high local leakage current leading to the low efficiency of electroluminescence.

• Journal of the Korean Applied Science and Technology
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• v.21 no.1
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• pp.24-30
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• 2004

New electroluminescent materials based on anthracene chromophore with naphthylethenyl substituent, 9,10-bis($\alpha$-naphthylethenyl)anthracene (a-BNA), as well as four kinds of its derivatives were synthesized, and luminescent properties of these materials were investigated. Electrolumineecent(EL) emission band was discussed based on their substituent structure differences. It was found that the emission band strongly depends on the molecular structure of introduced substituent. It can be tuned from 557 nm to 591 nm by changing the substituent structures. On the other hand, the anthracene chromophore with bulky substituent possessed high melting point and they gave stable films through vacuum-sublimation. The double layer EL device of ITO/TPD/emission layer/Mg:Ag was employed, and exhibited efficient orange light originating from emitting materials. EL emission with a maximum luminance was observed in the b-BNA emitting material, : maximum luminance was about 8,060 cd $m^{-2}$ at an applied voltage of 10 V and current density of 680 $mA/cm^2$. In conclusion, the electroluminescent properties also showed good difference with their substituent structure.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1998.11a
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• pp.53-56
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• 1998

Electroluminescent(EL) devices based on organic materials have been of great interest due to their possible applications for large-area flat-panel displays, where they are attractive because of their capability of multicolor emission, and low operation voltage. In this study, glass substrate/ITO/Eu(TTA)$_3$(Phen)/Al(A), glass substrate/ITO/TPD/Eu(TTA)$_3$(p-hen)/Al(B) and glass substrate/ITO/TPD/Eu(TTA)$_3$(phen)/AlQ$_3$/Al(C) structures were fabricated by vacuum evaporation method. where aromatic diamine(TPD) was used as a hole transporting material, Eu(TTA)$_3$(phen) as an emitting material. and tris(8-hydroxyquinoline)Aluminum(AlQ$_3$) as an electron transporting layer. Electroluminescent(EL) and I-V characteristics of Eu(TTA)$_3$(Phen) with a various thickness were investigated. This structure shows the red EL spectrum, which is almost the same as the PL spectrum of Eu(TTA)$_3$(phen). I-V characteristics of this structure show that turn-on voltage was 9V and current density was 0.01A/$\textrm{cm}^2$ at a dc operation voltage of 9V. Electrical transporting phenomena of these structures was explained using the trapped- charge-limited current model with I-V characteristics.

• 한국정보디스플레이학회:학술대회논문집
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• 2002.08a
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• pp.336-339
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• 2002

Fluorenevinylene-based EL polymers, poly(9,9-dioctylfluorene-2,7-vinylene) (PFV) and poly[(9,9-dioctylfluorene-2,7-vinylene)-co-{2-methoxy-5-(2 ethylhexyloxy)-1,4-phenylenevinylene}] (PFV-co-MEH-PPV), have been synthesized by Gilch polymerization method. The resulting polymers were soluble in common organic solvents and easily spin cast onto the indium-tin oxide (ITO) substrate. The weight average molecular weight and polydispersity of PFV and PFV-co-MEH-PPV were in the range of 22.2 - 43.2 x $10^4$ and 1.9 - 3.0, respectively. Double-layer light-emitting diodes with ITO/PEDOT/Polymer/Al configuration were fabricated. PFV-co-MEH-PPV showed better EL properties than those of PFV and MEH-PPV The turn-on voltage of poly(9,9dialkylfluorene) derivatives were dramatically decreased to the 2.5 V compared to fluorene-based EL polymers. The maximum brightness and luminescence efficiency were up 7 to 1350 cd/$m^2$ and 0.51 Cd/A.

• Journal of Information Display
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• v.5 no.4
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• pp.12-17
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• 2004

A series of statistical random copolymers of dioctylfluorene (DOF) and 3,4-ethylenedioxythiophene (EDOT) were synthesized by Ni (0) mediated polymerization and their light-emitting properties were compared with poly (9,9-di-n-octylfluorene) (PDOF). The synthesized polymers were characterized using UV-vis spectroscopy, TGA, photoluminescence (PL) & electroluminescence (EL) spectroscopy and by conducting molecular weight studies. The resulting polymers were found to be thermally stable and readily soluble in organic solvents. The UV-visible absorption and PL emission spectra of the copolymers were gradually red-shifted as the fraction of EDOT in copolymers increased. Light-emitting devices were fabricated in an ITO (indium-tin oxide)/PEDOT/polymer/Ca/Al configuration. Interestingly, the EL spectra of these devices were similar to the PL spectra of the corresponding polymer film. However, the EL devices constructed from the copolymer showed more than 10 times higher efficiency level than the devices constructed from the PDOF homopolymer. This higher efficiency is possibly the result of better charge carrier balance in the copolymer systems due to the lower HOMO levels of the copolymers in comparison to that of PDOF homopolymer.