• 한국정보디스플레이학회:학술대회논문집
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• 2006.08a
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• pp.1692-1696
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• 2006

Dopant and host molecules for charge transport layer in OLED have been developed. They enable implementation of the PIN OLED technology in mass production. We review the status of PIN OLED with main focus on top-emission structures and operation stability at elevated temperatures. A green phosphorescent top-emission device with 2.5 V operating voltage and 90 lm/W at 1000 $cd/m^2$ is presented. For a red top-emission device, lifetime exceeding 100,000 h at 500 $cd/m^2$ initial brightness is reported. Operational stability at $80^{\circ}C$ has been investigated. A lifetime of 17,000 h at 500 $cd/m^2$ has been achieved. Finally, we comment on further reduction of the operating voltage in OLED.

• 한국정보디스플레이학회:학술대회논문집
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• 2005.07b
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• pp.1408-1409
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• 2005

Organic light-emitting diodes (OLEDs) of metalsemiconductor-metal (MSM) structure have been fabricated by using m-MTDATA [4,4',4"-tris (3-methylphenylphenylamino) triphenylamine] as a hole-injection layer (HIL). The m-MTDATA is shown to be an effective hole-injecting material for the OLED, in that the insertion of m-MTDATA greatly reduces the roughness of anode surface and improves the device performance.

• Bulletin of the Korean Chemical Society
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• v.34 no.1
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• pp.167-173
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• 2013

A series of highly efficient red phosphorescent heteroleptic iridium(III) complexes 1-6 containing two cyclometalating 2-(2,4-substitued phenyl)quinoxaline ligands and one chromophoric ancillary ligand were synthesized: (pqx)$_2Ir$(mprz) (1), (dmpqx)$_2Ir$(mprz) (2), (dfpqx)$_2Ir$(mprz) (3), (pqx)$_2Ir$(prz) (4), (dmpqx)$_2Ir$(prz) (5), (dfpqx)$_2Ir$(prz) (6), where pqx = 2-phenylquinoxaline, dfpqx = 2-(2,4-diflourophenyl)quinoxaline, dmpqx = 2-(2,4-dimethoxyphenyl)quinoxaline, prz = 2-pyrazinecarboxylate and mprz = 5-methyl-2-pyrazinecarboxylate. The absorption, emission, electrochemical and thermal properties of the complexes were evaluated for potential applications to organic light-emitting diodes (OLEDs). The structure of complex 2 was also determined by single-crystal X-ray diffraction analysis. Complex 2 exhibited distorted octahedral geometry around the iridium metal ion, for which 2-(2,4-dimethoxyphenyl)quinoxaline N atoms and C atoms of orthometalated phenyl groups are located at the mutual trans and cis-positions, respectively. The emission spectra of the complexes are governed largely by the nature of the cyclometalating ligand, and the phosphorescent peak wavelengths can be tuned from 588 to 630 nm with high quantum efficiencies of 0.64 to 0.86. Cyclic voltammetry revealed irreversible metal-centered oxidation with potentials in the range of 1.16 to 1.89 V as well as two quasi-reversible reduction waves with potentials ranging from -0.94 to -1.54 V due to the sequential addition of two electrons to the more electron-accepting heterocyclic portion of two distinctive cyclometalated C^N ligands.

• Korean Journal of Optics and Photonics
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• v.32 no.5
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• pp.235-243
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• 2021

Photobiomodulation (PBM)-based therapy, which uses a phenomenon in which a light source of a specific wavelength band promotes ATP production in mitochondria, has attracted much attention in the fields of biology and medicine because of its effects on wound healing, inflammation reduction, and pain relief. Research on PBM-based therapy has mainly used lasers and light-emitting diodes (LEDs) as light sources and, despite the advantages of organic light-emitting diodes (OLEDs), there have been only a few cases where OLEDs were used in PBM-based therapy. In this research, the skin-care effect of PBM was analyzed using red (λ = 620 nm), green (λ = 525 nm), and blue (λ = 455 nm) OLED lighting modules, and was compared to the PBM effect of LEDs. We demonstrated the PBM-based skin-care effect of the red, green, blue OLED lighting modules by measuring the increase in the amount of collagen type-1 synthesis, the inhibition of melanin synthesis, and the suppression of nitric oxide generation, respectively.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.28 no.11
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• pp.704-710
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• 2015

We studied white organic light-emitting diodes using blue fluorescent and red phosphorescent materials. White single OLEDs were fabricated using SH-1 : BD-2 (3 vol.%) and CBP : $Ir(mphmq)_2(acac)$ (2 vol.%) as emitting layer (EML). The white single OLED using SH-1 : BD-2 (3 vol.% 8 nm) / CBP : $Ir(mphmq)_2(acac)$ (2 vol.% 22 nm) as emitting layer showed maximum current efficiency of 8.8 cd/A, Commission Internationale de l'Eclairage (CIE) coordinates of (0.403, 0.351) at $1,000cd/m^2$, and variation of CIE coordinates with ($0.402{\pm}0.012$, $0.35{\pm}0.002$) from 500 to $3,000cd/m^2$. The white tandem OLED using SH-1 : BD-2 (3 vol.% 12 nm) / CBP : $Ir(mphmq)_2(acac)$ (2 vol.% 18 nm) showed maximum efficiency of 19.6 cd/A, CIE coordinates of (0.354, 0.365) at $1,000cd/m^2$, and variation of CIE coordinates with ($0.356{\pm}0.016$, $0.364{\pm}0.002$) from 500 to $3,000cd/m^2$. Maximum current efficiency of the white tandem OLED was more twice as high as the single OLED. Our findings suggest that tandem OLED was possible to produce improved efficiency and excellent color stability.

• 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.

• 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.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.04a
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• pp.36-36
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• 2008

Organic light-emitting device (OLED) have become very attractive due to their potential application in flat panel displays. One important problem to be solved for practical application of full-color OLED is development of three primary color (Red, Green and Blue) emitting molecule with high luminous operation. Particularly, the development of organic materials for blue electroluminescence (EL) lags significantly behind that for the other two primary colors. For this reason, Flu-Si was synthesized and characterized by means of high-resolution mass spectro metry and elemental analyses. Flu-Si has the more wide optical band gap (Eg = 3.86) than reference material (Cz-Si, Eg = 3.52 eV). We measured the photophysical and electrochemical properties of Flu-Si. The HOMO-LUMO levels were estimated by the oxidation potential and the onset of the UV-Vis absorption spectra. The EL properties were studied by the device fabricated as a blue light emitting material with FIrpic.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.12
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• pp.983-987
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• 2010

In order to investigate the emission characteristics of the phosphorescent white organic light-emitting diodes (PHWOLEDs) according to various hole transport layers (HTLs), PHWOLEDs composed of HTLs whose structure are NPB/TCTA, NPB/mCP and NPB/TCTA/mCP, two emissive layers (EMLs) which emit two-wavelengths of light (blue and red), and electron transport layer were fabricated. The applied voltage, power efficiency, and external quantum efficiency at a current density of $1 mA/cm^2$ for the fabricated PHWOLEDs were 7.5 V, 11.5 lm/W, and 15%, in case of NPB/mCP, 5 V, 14.8 lm/W, and 13.7%, in case of NPB/TCTA, and 5.5 V, 14.6 lm/W, and 15%, in case of NPB/TCTA/mCP in the hole transport layer, respectively. High emission efficiency can be obtained when the amount of hole injection from anode is balanced out by the amount of electron injection from the cathode to EML by using NPB/TCTA/mCP structured HTL.

• 한국정보디스플레이학회:학술대회논문집
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• 2002.08a
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• pp.780-783
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• 2002

We report very efficient white OLEDs consisting of a blue-emitting 4,4'bis[N-(1-napthyl)-N-phenyl-amino]-biphenyl (${\alpha}$-NPD), a hole-blocking layer of 2,9-dimethyl-4, 7-diphenyl-1, 10-phenanthroline (BCP) doped with red fluorescent dye of 4-dicyanomethylene-2-methyl-6-[2-(2,3,6,7-tetrahydro- 1H, 5H-benzo[i,j]quinolizin-8-yl) vinyl]-4H-pyran) (DCM2), and green-emitting tris(8-hydroxyquinoline) aluminum ($Alq_3$). The device with the structure of ITO/${\alpha}$-NPD (50 nm)/BCP:DCM2 (0.8 %, 4 nm)/$Alq_3$ (50 nm)/LiF (0.5 nm)/Al shows a white emission with the CIE coordinates (0.329, 0.333). The maximum luminance of 20,800 cd/$m^2$ is obtained at 15.4 V. The power efficiency is 2.6lm/W and the external quantum efficiency is 2.1 % at a luminance of 100 cd/$m^2$ at the bias voltage of 6 V.