• 한국정보디스플레이학회:학술대회논문집
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• 2007.08b
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• pp.1654-1657
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• 2007

We demonstrate that the reduction of quantum efficiency with increasing current density in phosphorescent light emitting diodes (PhOLEDs) is related to the formation of excitons in hole transporting layer based on the analysis of emission spectra and exciton formation zone. By employing dual emitting layerm we could achieve maintaining quantum efficiency at high current density up to $10000\;cd/m^2$ as 13.1% compared to the devices with single emitting layer (S-EML) (${\eta}_{ext}$= 6.9% at $10000\;cd/m^2$).

• Journal of the Korean institute of surface engineering
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• v.48 no.3
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• pp.121-125
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• 2015

We studied the blue fluorescent OLED with Mg:Ag, Al, Ni as anode materials. Blue fluorescent OLEDs were fabricated using Anode / $MoO_3$ (3 nm) / 2-TNATA (60 nm) / NPB (30 nm) / SH-1 : BD-2 (5 vol.%, 30 nm) / Bphen (40 nm) / Liq (1 nm) / Al (150 nm). Current density of OLED with Mg:Ag was not measured due to too low work function, and that of OLED with Al showed $45.2mA/cm^2$ at 12 V. Luminance and Current efficiency of OLED with Al showed $385.1cd/m^2$ and 0.9 cd/A. Current density of OLED with Ni of 8, 10, 12 nm thickness showed 10, 12.9, $37.2mA/cm^2$, respectively. Luminance and Current efficiency of OLED with Ni of 8, 10, 12 nm thickness showed 670.9, 991.2, $1,320cd/m^2$ and 6.7, 7.7, 3.6 cd/A, respectively. Transmittance of Al was 52.2% at 476 nm wavelength and that of Ni of 8, 10, 12 nm thickness was 79, 77, 74 %, respectively. In spite of best current density, OLED with Al showed the lowest luminance and current efficiency because of low work function and poor transmittance. When thickness of Ni was increased to 12nm, current efficiency was sharply lower owing to bad transmittance and unbalance of holes and electrons. Finally, OLED with Ni of 10 nm thicknes showed the highest current efficiency.

• 한국정보디스플레이학회:학술대회논문집
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• 2005.07b
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• pp.1138-1142
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• 2005

We achieved a highly efficient green OLED with an efficiency of 30cd/A by using a new electron transport material and optimizing the device structure. The luminous efficiency was 16.8lm/W at $3000cd/m^2$ and the lifetime was over 60,000hr at an initial luminance of $1000cd/m^2$. Furthermore, we obtained a threecomponent RGB white OLED by using the highly efficient green material. This RGB white OLED shows more excellent color reproducibility for full color displays with color filters, compared to a twocomponent white OLED.

• Korean Journal of Materials Research
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• v.32 no.7
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• pp.320-325
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• 2022

Single OLED and tandem OLED was manufactured to analyze the electroluminescence characteristics of DC driving, AC driving, and full-wave rectification driving. The threshold voltage of OLED was the highest in DC driving, and the lowest in full-wave rectification driving due to an improvement of current injection characteristics. The luminance at a driving voltage lower than 10.5 V (8,534 cd/m²) of single OLED and 20 V (7,377 cd/m²) of a tandem OLED showed that the full-wave rectification drive is higher than that of DC drive. The luminous efficiency of OLED is higher in full-wave rectification driving than in DC driving at low voltage, but decrease at high voltage. The full-wave rectification power source may obtain higher current density, higher luminance, and higher current efficiency than the AC power source. In addition, it was confirmed that the characteristics of AC driving and full-wave rectification driving can be predicted from DC driving characteristics by comparing the measured values and calculated values of AC driving and full-wave rectification driving emission characteristics. From the above results, it can be seen that OLED lighting with improved electroluminescence characteristics compared to DC driving is possible using full-wave rectification driving and tandem OLED.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.180-180
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• 2010

본 연구에서는 P-Type의 NiO를 Glass기판의 ITO전극위에 RF-스퍼터링 방법으로 증착하였으며, NiO 완충층의 두께 변화에 따른 OLED (Organic Light Emitting Diode) 소자의 발광 특성에 대해 연구하였다[1, 2]. NiO는 우수한 전기 광학적 특성을 가지고 있어 OLED소자의 구동전압, 발광 효율 등의 특성을 향상 시킬 수 있다[3]. NiO 완충층의 두께 변화는 스퍼터링 증착시간을 통해 5-20 nm로 조절하였으며 소자의 구조는 Glass/ITO/NiO(0~20nm)/NPB(40nm)/Alq3(60nm)/LiF(0.5nm)/Al(120nm)형태로 제작하였다. ITO/NPB 계면에 NiO 완충층을 삽입함으로써 OLED 발광소자의 구동전압을 ~8V에서 ~5V (NiO, 10nm)로 낮출 수 있었다.

• 한국정보디스플레이학회:학술대회논문집
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• 2008.10a
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• pp.496-498
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• 2008

We have developed green phosphorescent organic light-emitting diodes (OLEDs) with high quantum efficiency. Wide-energy-gap material, 1,1-bis[(di-4-tolylamino) phenyl]cyclohexane (TAPC), with high triplet energy level was used as a hole transporting layer. Electrophosphorescent devices fabricated using TAPC as a hole-transporting layer and N,N'-dicarbazolyl-4,4'-biphenyl (CBP) doped with fac-tris(2-phenylpyridine) iridium [Ir(ppy)3] as the emitting layer showed the maximum external quantum efficiency ($\eta_{ext}$) of 19.8 %, which is much higher than the devices adopting 4,4'-bis[N-(1-naphthyl)-N-phenyl-amino]biphenyl (NPB) (${\eta}B_{ext}=14.6%$) as a hole transporting layer.

• 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.

• Journal of the Korean institute of surface engineering
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• v.47 no.4
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• pp.210-214
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• 2014

We investigated emission characteristics of tandem organic light emitting devices (OLEDs) with p-type materials as charge generation layer. The tandem OLEDs were fabricated by using $MoO_x$, $WO_x$, C60 and HATCN as p-type material or not using p-type material for charge generation. When HATCN was used as p-type material, it showed high current density at low applied voltage, but increase of efficiency was small because of charge unbalance in emitting layer. In case of tandem OLED not using p-type material, applied voltage increased remarkably because of difficulty of hole injection. In case of $MoO_x$, $WO_x$ or C60 as p-type material, current emission efficiency increased greatly. In particular, current emission efficiency of tandem OLED using $MoO_x$ as p-type material increased up to 3 times than current emission efficiency of single OLED. The Commission Internationale de l'Eclairage (CIE) 1931 color coordinates were changed by overlapping of 504 nm emission wavelength. As a result, emission efficiency of tandem OLED improved compared with single OLED, but driving voltage also increased by increase of organic layer thickness.

• 한국정보디스플레이학회:학술대회논문집
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• 2008.10a
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• pp.503-505
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• 2008

A host material containing tetraphenylsilane, 9-(4-triphenylsilanyl-(1,1'4,1")-terphenyl-4"-yl)-9H-cabazole (TSTC), was synthesized for green phosphorescent organic emitting diodes. $Ir(ppy)_3$ based OLEDs using TSTC host and DTBT (2,4-diphenyl-6-(4'yl)-1,3,5-triazine) hole blocking layer (HBL) showed the maximum external quantum efficiency of 19.8 %, the power efficiency of 59.4 lm and high operational stability with a half lifetime of 160,000 h at an initial luminance of $100\;cd/m^2$.

• Journal of the Korean institute of surface engineering
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• v.52 no.2
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• pp.72-77
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• 2019

To study the characteristics of AC driven OLED, we fabricated the fluorescent OLEDs and analyzed the electroluminescence characteristics of OLEDs with AC negative voltage. The luminance and the current density of the OLED decreased, and the number and size of the dark spots increased in proportion to the duration time and level of the applied AC negative voltage. The current efficiency of the OLED was improved when high AC negative voltage was applied within a short time. When the AC negative voltage of 10 V was applied for 1 minute, the efficiency was improved by 12.4%. Also, the degradation of luminance and current efficiency due to the duration of light emission was improved in the case of OLED applied for 1 minute with 10 V AC negative voltage. These are expected as a result of the improvement of the leakage current characteristics by eliminating the short-circuit region formed by the defect of the OLED at the AC negative high voltage. As a result, the continuous application of AC negative voltage reduced the luminance and the current density of OLED, but the temporary application of AC negative voltage with the proper time and voltage could improve the efficiency and lifetime of OLED.