• Transactions on Electrical and Electronic Materials
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• 제9권1호
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• pp.20-23
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• 2008

Organic light-emitting diodes (OLEDs) are attractive because of possible application in display with low-operating voltage, low-power consumption, self-emission and capability of multicolor emission by the selection of emissive materials. To investigated the optical effects, we studied the electrical and optical characteristics due to thickness variation of electron injection materials LiF on organic light-emitting diodes in the ITO (indium-tin-oxide)/N,N'-diphenyl-N, N'-bis(3-methyphenyl)-1,1'-biphenyl-4,4'-diamine(TPD)/tris(8-hydroxyquinoline) aluminum $(Alq_3)/LiF$ layer/Al device. We maintained the thicknesses of TPD and $Alq_3$ layers at 40 nm and 60 nm, respectively. The deposition rates of TPD and $Alq_3$ were in the $1.5{\AA}/s$ under a base pressure of $5{\times}10^{-6}$ Torr. It was found that luminance and luminous efficiency of the device with 0.7 nm LiF layer improve 25 times and 7 times than the device without the LiF layer, respectively.

• Transactions on Electrical and Electronic Materials
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• 제8권5호
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• pp.218-221
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• 2007

High-efficiency white organic light-emitting diodes(WOLEDs) were fabricated with two emissive layers and an blocking layer was sandwiched between two phosphorescent dopants, bis(3,5-difluoro-2-(2-pyridyl)phenyl-(2-carboxypyridyl) iridium III(FIrpic) as the blue emission and a newly synthesized red phosphorescent material guest, bis(5-acetyl-2-phenylpyridinato-N,C2') acetylacetonate($(acppy)_2Ir(acac)$). This blocking layer prevented a T-T annihilation in a red emissive layer, and balanced with blue and red emission as blocking of hole carriers. The white device showed Commission Internationale d'Eclairage($CIE_{x,y}$) coordinates of (0.317, 0.425) at 22400 $cd/m^2$, a maximum luminance of 27300 $cd/m^2$ at 268 $mA/cm^2$, a maximum luminous efficiency and power efficiency of 26.9 cd/A and 18.6 lm/W.

• 한국생산제조학회지
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• 제24권1호
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• pp.49-55
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• 2015

This paper reports solution-processed, high-efficiency organic light-emitting diodes (OLEDs) fabricated by a knife coating method under ambient air conditions. In addition, indium tin oxide (ITO), traditionally used as the anode, was substituted by optimizing the conductivity enhancement treatment of poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) films on a polyethylene terephthalate (PET) substrate. The transmittance and sheet resistance of the optimized PEDOT:PSS anode were 83.4% and $27.8{\Omega}/sq$., respectively. The root mean square surface roughness of the PEDOT:PSS anode, measured by atomic force microscopy, was only 2.95 nm. The optimized OLED device showed a maximum current efficiency and maximum luminous density of 5.44 cd/A and $8,356cd/m^2$, respectively. As a result, the OLEDs created using the PEDOT:PSS anode possessed highly comparable characteristics to those created using ITO anodes.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2009년도 9th International Meeting on Information Display
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• pp.418-420
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• 2009

The Authors have demonstrated high efficiency hybrid white organic light-emitting diodes (HWOLED) for reduced efficiency roll-off and color stability. It was shown that HWOLED fabricated in this study have the maximum luminance of 46 420 cd/$m^2$ at 8 V (turn-on voltage of 2.7 V), external quantum efficiency of 13.18%, power efficiency of 28.75 lm/W at 1 000 cd/$m^2$, and reduced efficiency roll-off of 2.7 times than control white device. The HWOLED also showed the stable color shift with $\Delta$Commission Internationale de I'Eclairage coordinates coordinates of ${\pm}$ (0.00, 0.00) from 100 to 10000 cd/$m^2$.

• ETRI Journal
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• 제27권4호
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• pp.405-410
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• 2005

High quality indium tin oxide (ITO) thin films were grown by pulse laser deposition (PLD) on flexible polyethersulphone (PES) substrates. The electrical, optical, and surface morphological properties of these films were examined as a function of substrate temperature and oxygen pressure. ITO thin films, deposited by PLD on a PES substrate at room temperature and an oxygen pressure of 15 mTorr, have a low electrical resistivity of $2.9{\times}10^{-4}{\Omega}cm$ and a high optical transmittance of 84 % in the visible range. They were used as the anode in organic light-emitting diodes (OLEDs). The maximum electro luminescence (EL) and current density at 100 $cd/m^2$ were 2500 $cd/m^{2}$ and 2 $mA/m^{2}$, respectively, and the external quantum efficiency of the OLEDs was found to be 2.0 %.

• Journal of Information Display
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• 제4권1호
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• pp.29-33
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• 2003

We have investigated the effects of hole-injection buffer layer in organic light-emitting diodes using copper phthalocyanine (CuPc), poly(vinylcarbazole)(PVK), and Poly(3,4-ethylene dioxythiophene):poly(styrenesulfonate) (PEDOT: PSS) in a device structure of $ITO/bufferr/TPD/Alq_3/Al$. Polymer PVK and PEDOT:PSS buffer layer were produced using the spin casting method where as the CuPc layer was produced using thermal evaporation. Current-voltage characteristics, luminance-voltage characteristics and efficiency of device were measured at room temperature at various a thickness of the buffer layer. We observed an improvement in the external quantum efficiency by a factor of two, four, and two and half when the CuPc, PVK, and PEDOT:PSS buffer layer were used, respectively. The enhancement of the efficiency is assumed to be attributed to the improved balance of holes and elelctrons resulting from the use of hole-injection buffer layer. The CuPc and PEDOT:PSS layer function as a hole-injection supporter and the PVK layer as a hole-blocking one.

• 한국전기전자재료학회논문지
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• 제16권5호
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• pp.409-417
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• 2003

We have studied electrical properties and luminous efficiency of organic light-emitting diodes(OLEDs) with different buffer layer and cathodes in a temperature range of 10 K and 300 K. Four different device structures were made. The OLEDs are based on the molecular compounds, N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD) as a hole transport, tris(8-hydroxyquinolinato) aluminum(III) (Alq$_3$) as an electron transport and omissive layer, and poly(3,4-ethylenedioxythiophene) :poly (styrenesulfonate) (PEDOT:PSS ) as a buffer layer. And LiAl was used as a cathode. Among the devices, the ITO/PEDOT:PSS/TPD/Alq$_3$/LiAl structure has a low energy-barrier height for charge injection and show a good luminous efficiency. We have got a highly efficient and low-voltage operating device using the conductive PEDOT:PSS and low work-function LiAl. From current-voltage characteristics with temperature variation, conduction mechanisms are explained SCLC (space charge limited current) and tunneling one. We have also studied energy barrier height and luminous efficiency at various temperature.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2007년도 추계학술대회 논문집
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• pp.31-32
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• 2007

Built-in voltage in organic light-emitting diodes was studied using modulated photocurrent technique ambient conditions. A device was made with a structure of anode/$Alq_3$/cathode to study a built-in voltage. An ITO was used as an anode, and $Li_2O$/Al was used as a cathode. From the bias voltage-dependent photocurrent, built-in voltage of the device is determined. The applied bias voltage when the magnitude of modulated photocurrent is zero corresponds to a built-in voltage. Built-in voltage in the device is generated due to a difference of work function of the anode and cathode. It was found that for 0.5nm thick $Li_2O$ layer built-in voltage is the higher than the others. It indicates that a very thin alkaline metal compound $Li_2O$ lowers an electron barrier height.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2007년도 추계학술대회 논문집
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• pp.434-435
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• 2007

We have demonstrated the characteristics on the variation of hole transporting layer in blue organic light-emitting diodes (OLEDs) using new blue fluorescent emitter. We fabricated two types of hole transporting layer structures that one is 4,4',4"-Tris(N-(2-naphthyl)-N-phenyl-amino)-triphenylamine (2-TNATA) of $600{\AA}$ as a hole injection layer, N,N'-diphenyl-N,N'- (2-napthyl)-(1,1'-phenyl)-4,4'-diamine (NPB) of $200{\AA}$ as a hole transporting layer and another device is NPB of $500{\AA}$ without the 2-TNATA. The devices without the 2-TNATA showed improved characteristic of the luminance and efficiency.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2007년도 추계학술대회 논문집
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• pp.490-491
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• 2007

We have investigated dielectric polarization in organic light-emitting diodes using 8-hydroxyquinoline aluminum$(Alq_3)$ as an electron transport and emissive material. We analyzed the dielectric polarization of organic light emitting diodes using impedance. Impedance characteristics was measured complex impedance Z and phase ${\theta}$ in the frequency range of 40Hz to $10^8Hz$. We obtained dielectric constant and loss tangent (tan ${\delta}$) of the device. From these analyses, we are able to interpret a dielectric dispersion and dielectric absorption contributed by an interfacial and orientational polarization.