• Proceedings of the IEEK Conference
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• 2003.07b
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• pp.999-1002
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• 2003

In this study, the white organic light emitting device was fabricated using ITO/a-NPD:DCM/a-NPD/BCP/Alq3/Al structure. Blue emission by a-NPD and orange emission by energy transfer between a-NPD and DCM embodied the white emission. The optimal structure of the white OLED is ITO/a-NPD:DCM(50$\square$)/a-NPD(150$\AA$)/BCP(100$\square$)/Alq$_3$(200$\square$)/Al. We varied the doping concentration of DCM properly and obtained high purity white emitting light. The CIE coordinate and maximum luminance of the devices was obtained (0.310, 0.333) and 400cd/$m^2$ at 11Volt.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.1491-1492
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• 2011

In this study, we investigated about the effect of hole transport layer materials(${\alpha}$-NPD, TPD) depending on the electrical properties of organic light emitting diode. In deposition method, we used thermal evaporation and it was a method for performing thin film by attaching vaporizing a molecule to substrate in a high thermal and vaccum. We analyzed luminance, current density, external quantum efficiency and current efficiency in 40 [nm] as optimization thickness of ${\alpha}$-NPD and TPD. In result of experiment, maximum luminance of TPD had 1.1 times higher than ${\alpha}$-NPD, but ${\alpha}$-NPD had luminance, external quantum efficiency, and current efficiency higher than TPD in low operating voltage. Actually, ${\alpha}$-NPD had efficiency higher than TPD in low operating voltage.

• 한국정보디스플레이학회:학술대회논문집
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• 2006.08a
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• pp.1038-1041
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• 2006

We report low operating voltage and long lifetime organic light-emitting diodes (OLEDs) with a vanadium oxide $(V_2O_5)-doped$ N,N'-di(1-naphthyl)- N,N'-diphenylbenzidine $({\alpha}-NPD)$ layer between indium tin oxide and ${\alpha}-NPD$. At a luminance of $1000\;cd/m^2$, $V_2O_5$ doped ${\alpha}-NPD$ device shows a operation voltage of 5.1V, while the device without $V_2O_5$ shows 5.8V. The $V_2O_5$ doped $({\alpha}-NPD)$ device also shows a longer lifetime and smaller operation voltage variation over time. It is suggested that the improved device performance can be attributed to the higher hole-injection efficiency and stability of the $V_2O_5$ doped $({\alpha}-NPD)$ layer.

• Proceeding of EDISON Challenge
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• 2015.03a
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• pp.412-414
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• 2015

유기 반도체의 전하 이동 특성은 그 구조적 특성에 매우 민감하다. 따라서 재료의 특성을 정확히 예측하기 위해서는 정확하게 구조를 모델링할 필요가 있다. 본 연구에서는 OLED에 널리 쓰이는 ${\alpha}$-NPD의 구조를 분자동역학을 통해 예측하기 위하여 OPLS-AA force field를 기반으로 하여 dihedral coefficient를 최적화하였다. DFT 계산을 기준으로 이를 근사하는 dihedral coefficient를 계산하였으며 ${\alpha}$-NPD의 중앙에 위치한 biphenyl dihedral의 경우, $K_2=2.74kcal/mol$, $K_4=-0.12kcal/mol$을 얻었다. 또한 이를 이용하여 melt-quench 방법을 통해 ${\alpha}$-NPD의 비정질 구조를 모델링하였다. 계산으로 얻어진 밀도는 $1.11g/cm^3$이며 실험값은 $1.12g/cm^3$이다.

• JSTS:Journal of Semiconductor Technology and Science
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• v.8 no.1
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• pp.40-45
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• 2008

We developed small molecular organic nonvolatile $4F^2$ memory cells using metal layer evaporation followed by $O_2$ plasma oxidation. Our memory cells sandwich an upper ${\alpha}$-NPD layer, Al nanocrystals surrounded by $Al_2O_3$, and a bottom ${\alpha}$-NPD layer between top and bottom electrodes. Their nonvolatile memory characteristics are excellent: the $V_{th},\;V_p$ (program), $V_e$ (erase), memory margin ($I_{on}/I_{off}$), data retention time, and erase and program endurance were 2.6 V, 5.3 V, 8.5 V, ${\approx}1.5{\times}10^2,\;1{\times}10^5s$, and $1{\times}10^3$ cycles, respectively. They also demonstrated symmetrical current versus voltage characteristics and a reversible erase and program process, indicating potential for terabit-level nonvolatile memory.

• Korean Journal of Materials Research
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• v.15 no.7
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• pp.448-452
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• 2005

This study was based on organic electroluminescence display. Especially, TPD and $\alpha-NPD$ for the hole transport materials were synthesized by Ullmann reaction. This reaction was conducted between 3­methylphenylamine, 1-naphthylamine and 4,4'-diiodobiphenyl in toluene containing CuCl catalyst and KOH base. The structural property of reaction products were analyzed by FT-IR, $^1H-NMR$ spectroscopy, and thermal stability, reactivity and PL property were analyzed by melting point, yield and emission spectrum, respectively. The photoluminescence spectra of a pure TPD and $\alpha-NPD$ were observed at approximately 416nm and 438nm respectively. In this study, it was known that the melting point, yield, PL properties of TPD and $\alpha-NPD$ were changed by substituent group of amines.

• Journal of the Microelectronics and Packaging Society
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• v.10 no.1
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• pp.1-5
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• 2003

The multi-layered OELDs(organic electroluminescent devices) were prepared on the patterened ITO (indium tin oxide)/glass substrates by the vacuum thermal evaporation method. The $Alq_3$ (tris-(8-hydroxyquinoline)aluminum) low molecule compound was used as the light emission layer. TPD(triphenyl-diamine) and $\alpha-NPD$ were used as the hole transport layer. CuPc (Copper phthalocyanine) was also used as the hole injection layers. In addition, QD2 (quinacridone2) organic material with $10\AA$ thickness was deposited in the $Alq_3$ emission layer to improve the luminance efficiency. The threshold voltage was about 7V for all devices. The luminance and efficiency of devices was improved by substitution the $\alpha-NPD$ for TPD as the hole as the hole transport layer. The luminance efficiency of the OELD sample with QD2 thin film in the $Alq_3$ emission layer was found to be 1.55 lm/W, which is about 8 times larger value compared to the sample without QD2 thin layer.

• Journal of Information Display
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• v.9 no.3
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• pp.23-27
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• 2008

This paper reports that well-balanced white emission with three primary colors can be achieved with a simple white organic light-emitting diode (WOLED) structure of ITO / $\alpha$-NPD (50 nm) / $\alpha$-NPD: Btp2Ir(acac) (8 wt%, 6 nm) / $\alpha$-NPD (5 nm) / BCP (3 nm) / $Alq_3$: C545T (0.5 wt%, 10 nm) / $Alq_3$ (40 nm) / LiF (0.5 nm) / Al (100 nm). The external quantum efficiency of the device reached 3.8% at a current density (luminance) of 4.6 mA/$cm^2$ (310 cd/$m^2$), and the maximal luminance of the device reached 19,000 cd/$m^2$ at 11.5 V. The insignificant blue shift of the emitting color with an increasing current density can be attributed to the narrowing of the exciton formation zone width.

• 한국정보디스플레이학회:학술대회논문집
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• 2003.07a
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• pp.940-943
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• 2003

We report the fabrication and the characterization of white organic light-emitting devices consisting of a red-emitting layer of a new DCM derivative doped into 4,4'bis[N-(1-napthyl)-N-phenyl-amino]-biphenyl (${\alpha}-NPD$) and a blue-emitting layer of 1,4-bis(2,2-diphenyl vinyl)benzene (DPVBi). The device structure is ITO/PEDOT:PSS/${\alpha}-NPD$ (50 nm)/${\alpha}-NPD$:DCM (5 nm, 0.2 %)/DPVBi (x)/Alq3 (40 nm)/LiF (0.5 nm)/Al. The electroluminescence (EL) spectra consist of two broad peaks around 470 nm and 580 nm with the spectral emission depending on the thickness of DPVBi. The device with the DPVBi thickness of about 20 nm show a white light-emission with the Commission Internationale d'Eclairage(CIE) chromaticity coordinates of (0.33, 0.36). The external quantum efficiency is 2.6% and luminous efficiency is 2.0 lm/W at a luminance of 100 $cd/m^{2}$. The maximum luminance is about 30,270 $cd/m^{2}$ at 13.9 V.

• 한국정보디스플레이학회:학술대회논문집
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• 2006.08a
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• pp.1050-1053
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• 2006

We fabricated white organic light emitting diodes consisting of three emitting layers of red-emitting DCM2 doped ${\alpha}-NPD$, blue-emitting DPVBi and green-emitting C545T doped Alq3. By optimizing the thickness of the hole-transport layer of ${\alpha}-NPD$ and the electron-transport layer of Alq3, efficient white OLEDs were obtained with a luminous efficiency of 4.40lm/W at luminance of $1000cd/m^2$, and a max-imum luminance of $51,939cd/m^2$