• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.151.2-151.2
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• 2015

본 연구에서는 indium-tin-oxide(ITO)/1,4,5,8,9,11-hexaazatriphenylene-hexacarbonitrile(HAT-CN)/N,N'-di(naphthalene-lyl)-N,N'-diphenyl-benzidine(NPB)/4,4'-Bis(N-carbazolyl)-1,1'-biphenyl(CBP)/2,2',2"-(1,3,5-Benzinetriyl)-tris(1-phenyl-1-H-benzimidazole)TPBi/tris-(8-hydroxyquinoline) aluminum($Alq_3$)/LiF/Al 구조를 가진 유기 발광 다이오드 소자의 발광층에 $Ir(ppy)_3$(2% wt)을 도핑하여 소자의 특성 변화를 살펴보았다. $Ir(ppy)_3$의 두께는 5nm이고 도핑 위치는 정공 수송층과 발광층 계면의 0nm에서부터 25nm까지 5nm간격으로 도핑을 하였다. 실험 결과 소자의 효율은 도핑 위치가 정공 수송층에서 25nm떨어진 위치일 때 가장 높았고, 10nm일 때 가장 낮았다. 이는 도핑 부분의 위치가 정공 차단층에 가까워질수록 정공과 전자의 균형이 좋아지는 것이 소자 성능을 향상시키는 원인으로 추측된다.

• KIEE International Transactions on Electrophysics and Applications
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• v.11C no.3
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• pp.53-57
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• 2001

The organic light-emitting devices (OLEDs) based on fluorescence have low efficiency due to the requirement of spin-symmetry conservation. By using the phosphorescent material, internal quantum efficiency can reach 100%, compared with 25% in the case of the fluorescent material. Thus, phosphorescent OLEDs have recently been extensively studied and shown higher internal quantum efficiency than 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 device with a structure of ITO/TPD$Ir(ppy)_3$ doped in BCP/BCP/$Alq_3$/Li:Al/Al was fabricated, and its electrical and optical characteristics were studied. By changing the doping concentration of $Ir(ppy)_3$, we fabricated several devices and investigated their characteristics.

• Proceedings of the Polymer Society of Korea Conference
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• 2006.10a
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• pp.166-166
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• 2006

The photoluminescence (PL) efficiency of $Ir(ppy)_{3}$:PVK is lower than $Ir(ppy)_{3}$:CBP for the whole range of doping concentration and this low PL efficiency can be a reason of the lower efficiency of PhPLED than PhOLED. The lower efficiency is originated from the large bi-excitonic quenching such as the triplet-triplet annihilation. The PhPLEDs showed very short lifetime. The short lifetime was found to be originated from the instability of the doubly reduced $Ir(ppy)_{3^{-2}}$. The double reduction takes place because of the low electron mobility of PVK and large energy difference of LUMO level between PVK and $Ir(ppy)_{3}$.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.226-226
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• 2016

PHOLED devices which have the structure of ITO/HAT-CN(5nm)/NPB(50nm)/EML(30nm)/TPBi(10nm)/Alq3(20nm)/LiF(0.8nm)/Al(100nm) are fabricated to investigate the green emission profile in EML by using a gasket doping method. CBP and Ir(ppy)3 (2% wt) are co-deposited homogeneously as a background material of EML for green PHOLED, then a 5nm thickness of additionally doped layer by Ir(btp)2 (8% wt) is formed as a profiler of the green emission. The total thickness of the EML is maintained at 30nm while the distance of the profiler from the HTL/EML interface side (x) is changed in 5nm steps from 0nm to 25nm. As shown in Fig. 1, the green (513nm) peak from Ir(ppy)3 is not observed when Ir(btp)2 is also doped homogeneously because Ir(ppy)3 works as an gasket dopant of the Ir(btp)2 :CBP system. Therefore, in this experment, Ir(btp)2 can be used as a profiler of the green emission in CBP:Ir(ppy)3 system. The emission spectra from the PHOLED devices with different x are shown in Fig. 2. In this gasket doping system, stronger red peak means more energy transfer from green to red dopant or higher exciton density by green dopant. To find the green emission profile, the external quantum efficiency (EQE) at 3mA/cm2 for red peaks are calculated. More green light emission at near EML/HBL interface than that of HTL/EML is observed (insert of Fig. 2). This means that the higher exciton density at near EML/HBL interface in homogeneously doped CBP with Ir(ppy)3. As shown in Fig. 3, excitons can be quenched easily to HTL(NPB) because the T1 level of HTL(2.5eV) is relatively lower than that of EML(2.6eV). On the other hand, the T1 level of HBL(2.7eV) is higher than that of EML.

• Proceedings of the KAIS Fall Conference
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• 2010.05a
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• pp.363-365
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• 2010

고분자 발광다이오드(polymer light emitting diode, PLED)는 초박막화, 초경량화가 가능하며 간단한 용액공정 으로 향후 휨성(flexible) 디스플레이로의 응용이 가능할 것으로 기대되고 있다. 본 연구에서는 녹색 고분자 유기 발광다이오드를 제작하고, 효율을 향상 시키고자 이중 발광층을 두어 전기 광학적 특성을 평가하였다. ITO/Glass기판 위에 정공주입층으로 PEDOT:PSS [poly(3,4-ethylenedio xythiophene):poly(styrene sulfolnate)]를 발광물질로는 형광 발광물질인 PVK(poly-vinylcarbazole)와 인광 발광 물질인 Ir(ppy)$_3$[tris(2-phenylpyridine) iridium(III)]를 각각 host와 dopant로 사용하였다. 정공 차단층 및 전자 수송층 두 개의 역할로 사용 가능한 TPBI(1,3,5-tris(2-N-phenylbenzimidazolyl) benzene)를 진공 열증착법으로 막을 형성하였다. 전자주입층으로 LiF(lithium flouride)와 음극으로 Al(aluminum)을 증착하여 최종적으로 ITO/PEDOT:PSS/PVK:Ir(ppy)$_3$/TPBI/LiF/Al 구조를 갖는 녹색 형광:인광 혼합 유기 발광 다이오드를 제작하였다.

• Journal of the Microelectronics and Packaging Society
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• v.15 no.2
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• pp.1-6
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• 2008

New devices with the structure of ITO/2-TNATA/NPB/TCTA/CBP:$7%Ir(ppy)_3$/BCP/SFC-137/LiF/Al were designed and fabricated to develop high efficiency green phosphorescent organic light emitting diodes and their electroluminescence properties were evaluated. Among the devices with different thicknesses of CBP in a range of $150{\AA}{\sim}350{\AA}$, the best luminance was obtained in the device with $300{\AA}$-thick CBP host. Nearly saturated current efficiencies indicates that the maximum efficiency value can be obtained with CBP thicknesses of $300{\AA}{\sim}350{\AA}$. The current density, luminance, and current efficiency of the PhOLED(phosphorescent organic light emitting diode) with $CBP(300{\AA}):7%Ir(ppy)_3-emissive$ layer at an applied voltage of 10V were $40mA/cm^2,\;10000cd/m^2$, and 25 cd/A, respectively. The maximum current efficiency was 40.5cd/A under the luminance of $160cd/m^2$. The peak wavelength and FWHM(full width at half maximum) in the electroluminescence spectral were 512nm and 60nm, respectively. The color coordinate was (0.28, 0.63) on the CIE (Commission Internationale de I'Eclairage) chart.

• 한국정보디스플레이학회:학술대회논문집
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• 2009.10a
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• pp.1511-1514
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• 2009

Organic light emitting layer in OLED device was formed by gravure printing process in this work. Organic surface coated by gravure printing typically showed relatively bad uniformity. Thickness and roughness control was characterized by applying various mixed solvents in this work. Poly (N-vinyl carbazole) (PVK) and fact-tris(2-phenylpyridine)iridium($Ir(ppy)_3$) are host dopant system materials. PVK was used as a host and Ir(ppy)3 as green-emitting dopant. To luminance efficiency of the plasma treatment on etched ITO glass and then PEDOT:PSS spin coated. The device layer structure of OLED devices is as follow Glass/ITO/PEDOT:PSS/PVK+Ir(ppy)3-Active layer /LiF/Al. It was printed by gravure printing technology for polymer light emitting diode (PLED). To control the thickness multi-printing technique was applied. As the number of the printing was increased the thickness enhancement was increased. To control the roughness of organic layer film, thermal annealing process was applied. The annealing temperature was varied from room temperature, $40^{\circ}C$, $80^{\circ}C$, to $120^{\circ}C$.

• Transactions on Electrical and Electronic Materials
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• v.12 no.2
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• pp.80-83
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• 2011

We have fabricated phosphorescent white organic light-emitting devices (WOLEDs) with a spin-coated poly(Nvinylcarbazole) [PVK] host layer. Iridium(III) bis[(4,6-difluorophenyl)-pyridinato-N,$C^{2'}$]picolinate (FIrpic), tris(2-phenylpyridine)iridium(III) [$Ir(ppy)_3$], and tris(2-phenyl-1-quinoline)iridium(III) [$Ir(phq)_3$], were used as the blue, green, and red guest materials, respectively. The PVK was mixed with FIrpic, $Ir(ppy)_3$, and $Ir(phq)_3$ molecules in a chlorobenzene solution and spin-coated in order to prepare the emission layer; 3-(4-biphenylyl)-4-phenyl-5-(4-tertbutylphenyl)-1,2,4-triazole (TAZ) was used as an electron transport material. The resultant device structure was ITO/PVK:FIrpic:$Ir(ppy)_3:Ir(phq)_3$/TAZ/LiF/Al. The electroluminescence, efficiency, and electrical conduction characteristics of the WOLEDs based on the doped PVK host layer were investigated. The maximum current efficiency of the three wavelength WOLED with the doped PVK host was 19.2 cd/A.

• 한국정보디스플레이학회:학술대회논문집
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• 2008.10a
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• pp.1509-1512
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• 2008

Monomer and aggregate of $Bebq_2$ give fluorescence at 492 and 511 nm at 12 K, respectively. Intense T1 emission with vibronic structure was observed from $Bebq_2$ and $Alq_3$ below 70 K by heavily doping with phosphorescent $Ir(ppy)_3$. Energy transfer from $Ir(ppy)_3$ was clarified by photoluminescence excitation spectra.

• Bulletin of the Korean Chemical Society
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• v.32 no.4
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• pp.1415-1418
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• 2011