Publications (14)23.02 Total impact
- [Show abstract] [Hide abstract] ABSTRACT: We have designed and synthesized five blue emitters based on diphenylaminofluorenylstyrene emitting core groups. Multilayered OLEDs were fabricated using these materials as dopants in a 2-methyl-9,10-di(naphthen-2-yl)anthracene (MADN) host. One of them in particular a deep blue OLED using dopant 9-[4-(2-diphenylamino-9,9-diethylfluoren-7-yl)phenyl]-9-phenylfluorene (3) at 15% doping concentration exhibited a maximum luminance of 4720 cd m−2 at 9.0 V, a luminous efficiency of 5.3 cd A−1 at 20 mA cm−2, a power efficiency of 2.9 lm W−1 at 20 mA cm−2, an external quantum efficiency of 4.8% at 20 mA cm−2, and CIE coordinates (x = 0.15, y = 0.13) at 8.0 V. Furthermore, this deep blue device had very stable CIE coordinates of (x = 0.15, y = 0.13) that did not vary with doping concentration from 5% to 15%.
- [Show abstract] [Hide abstract] ABSTRACT: Multilayered organic light-emitting diodes (OLEDs) were fabricated by using the new fluorine derivatives end-capped with arylaminofluorenylethylenes as dopant materials. The device structure was ITO/NPB/15% blue dopants doped in MADN/Bphen/Liq/Al. Among those, a device shows the maximum luminance of 40800 cd/m2 at 12 V, the luminous efficiency of 12.8 cd/A at 20 mA/cm2, power efficiency of 9.13 Im/W at 20 mA/cm2 and CIE(x,y) coordinates of (x = 0.188, y = 0.372) at 8 V.
- [Show abstract] [Hide abstract] ABSTRACT: The authors have demonstrated efficient and color-stable white organic light-emitting diodes (WOLEDs) by using three emitters, 4"-(2,2-diphenylvinyl)-1-[4-(N,N-diphenylamino)-styryl]-terphenyl (PVAS-tPh), fac tris(2-phenypyridine) irdium(III) (Ir(ppy)3), and Bis(5-benzoyl-2-phenylpyridinato-C,N)iridium(III) (acetylacetonate) (Bzppy)2Ir(III)acac). In this WOLEDs, 4,4'-N, N'-dicarbazole-biphenyl (CBP) were used as a spacer among three emitting layers. CBP between red and green emitting layers prevented the Commission Internationale de L'Eclairage (CIE(x,y)) coordinates change of white emission. As a result, WOLEDs showed a minimal change of deltaCIE(x,y) < (0.01,0.02) for the brightness change form 100 to 20 000 cd/m2.
- [Show abstract] [Hide abstract] ABSTRACT: A series of seven diarylaminofluorene-derived fluorescent molecules demonstrating a blue emission in organic light-emitting diodes (OLEDs) were synthesized via the Horner-Wadsworth-Emmons reaction and the Suzuki-cross coupling reaction. Among the molecules, one device exhibited blue emission with a maximum luminance of 28900 cd/m2 at 12 V. A luminous efficiency of 11.5 cd/A at 20 mA/cm2 was achieved. The peak wavelength of the electroluminescence (EL) was 459.5 nm with the CIE coordinates of (x = 0.173, y = 0.281) at 8 V. The device also showed a stable color chromaticity at various voltages.
- [Show abstract] [Hide abstract] ABSTRACT: We studied the use of N,N'-dicarbazolyl-3,5-benzene (mCP) of the triplet energy level 2.90 eV and p-bis(triphenylsilyly)benzene (UGH2) of the wide triplet energy band gap 3.50 eV as triplet exciton blocking layer (TEBL) to get high efficiency in phosphorescent blue organic light-emitting diodes. Five devices (Devices I-V) with different structures were fabricated to investigate the effect of mCP and UGH2 TEBLs on device performances. The maximum quantum efficiencies of devices I, II, III, IV and V were 5.10%, 1.41%, 5.90%, 4.98% and 0.61%, respectively.
- [Show abstract] [Hide abstract] ABSTRACT: A series of diphenylaminofluorene- and phenylcarbazole-derived, blue fluorescent molecules have been synthesized via the Hornor–Wadsworth–Emmons and Suzuki-cross coupling reactions. To explore the electroluminescent properties of these molecules, multilayer devices were fabricated with a structure of ITO/NPB/(1–6) doped in MADN/Bphen/Liq/Al, yielding a device that exhibited highly efficient sky-blue emissions with the luminous efficiency of 11.2cd/A at 20mA/cm2, a power efficiency of 7.35lm/W at 20mA/cm2, and CIEx,y coordinates of (x=0.16, y=0.26) at 8V. Also, a deep blue OLED with CIEx,y coordinates of (x=0.16, y=0.13) at 8V showed a luminous efficiency of 2.13cd/A and power efficiency of 1.20lm/W at 20mA/cm2, respectively.
- [Show abstract] [Hide abstract] ABSTRACT: We have demonstrated the structure optimization of white organic light-emitting diodes with two separated emissive layers for better efficiency. For efficient optimization of white organic light-emitting diodes, we carried out a insertion of hole buffer layer, a thickness change of emission layer, and a change of electron transport layer. The optimized device showed maximum luminance of 29 600 cd/m2 at 14 V and the maximum luminous efficiency of 14.30 cd/A at 7.34 mA/cm2, respectively. All devices showed white emission at operating voltages without change of CIEx,y coordinates.
- [Show abstract] [Hide abstract] ABSTRACT: A series of blue fluorescent materials based on asymmetric mono-triphenylamine-substituted anthracenes have been synthesized and characterized using spectroscopic analysis. Multilayered organic light-emitting diodes (OLED) were fabricated using these materials as dopants. A maximum luminance of 27900 cd/m at 11 V and a luminous efficiency of 10.1 cd/A at 20 mA/cm were achieved. The peak wavelength of the electroluminescence was 459 nm with CIE coordinates of (0.174, 0.288) at 10 V and the device also showed a stable color chromaticity at various voltages.
- [Show abstract] [Hide abstract] ABSTRACT: We investigated the electrical characteristics of three devices which were fabricated with phosphorescent blue emitter, iridium(III) bis(4,6-difluorophenylpyridinato-N,C)picolinate (FIrpic), doped in host materials, 4,4,N,N′-dicarbazolebiphenyl (CBP), N,N′-dicarbazolyl-3,5-benzene (mCP) of the carbazole-type and p-bis(triphenylsilyly)benzene (UGH2) of the wide-energy-gap, respectively. We demonstrated the efficient blue electrophosphorescence using exothermic energy transfer between mCP and FIrpic with triplet energy level of 2.90 eV and 2.65 eV, respectively. Device property for a mCP-based structure was found to be superior to that employing the endothermic host-guest combination consisting of the CBP and FIrpic with triplet energy level of 2.57 eV and 2.65 eV, respectively. In case the device with UGH2, despite of the very wide band gap (4.40 eV), it is inefficient given the large energy barrier (1.70 eV) for hole injection into the highest occupied molecular orbital (HOMO) of UGH2 as the drive voltage increases. The device with mCP host material shows a maximum luminous efficiency and power efficiency of 17.00 cd/A and 10.9 lm/W, respectively.
- [Show abstract] [Hide abstract] ABSTRACT: The authors have demonstrated highly efficient deep-blue phosphorescent organic light-emitting diodes (BPHOLEDs) using iridium(III) bis[(5-cyano-4-fluorophenyl)pyridinato-N,C2']picolinate (FCNIrpic) as a blue emitter. FCNIrpic has a deeper-blue color than iridium(III) bis[4,6-(difluorophenyl)pyridinato-N,C2']picolinate. The BPHOLEDs with FCNIrpic showed a maximum luminous efficiency of 19.00 cd/A, a maximum external quantum efficiency of 10.70%, and Commission Internationale de L'Eclairage coordinates (CIEx,y) of (0.16,0.26).
- [Show abstract] [Hide abstract] ABSTRACT: We have demonstrated high-efficiency white organic light-emitting diodes (WOLEDs) using codoped blue-emitting layers with three light emitters, 4 ''-(2,2-diphenylvinyl)-1-[4-(N,N-diphenylamino)-styryl]-terphenyl, fac-tris(2-phenypyridine) iridium(III), and bis(5-benzoyl-2-phenylpyridinato-C,N)iridium(III) (acetylacetonate). Blue-emitting layers (BEMLs) were codoped with the different functional materials, N,N'-bis(1-naphyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine and 4,7-diphenyl-1,10-phenanthroline, which are used as charge-transporting materials in OLEDs. An optimized device with centralized carriers in emitting layers showed a maximum luminance of 19710 cd/m(2) at 12V, a maximum luminous efficiency of 23.20 cd/A at 0.14 mA/cm(2), and an external quantum efficiency of 10.20% at 32.19 cd/m(2). (C) 2009 The Japan Society of Applied Physics
- [Show abstract] [Hide abstract] ABSTRACT: A new red fluorescent material, (2Z,2′Z)-3,3′-[4,4″-bis(dimethylamino)-1,1′:4′,1″-terphenyl-2′,5′-diyl]bis(2-phenylacrylonitrile) (ABCV-P), preventing concentration quenching in solid state was synthesized. Studies on the device performance of ABCV-P doped OLEDs with variation of the doping concentration and thickness of the emitting layer as well as the optical properties of ABCV-P were carried out. The effective doping concentration of ABCV-P dopant was in the range of 40%–50%. ABCV-P doped OLEDs showed maximum luminance of 11000 cd/m (40%) and 6800 cd/m (50%), CIExy coordinates of (0.588, 0.410) (40%) and (0.597, 0.402) (50%) and full width at half maxima of 71 nm and 72.5 nm, respectively. Accordingly, ABCV-P doped OLED showed much lower sensitivity to doping concentration than the typical red doped ones.
- [Show abstract] [Hide abstract] ABSTRACT: Newly prepared hydrido iridium(III) complexes [Ir(ppy)(PPh3)2(H)L](0,+) (ppy = bidentate 2-phenylpyridinato anionic ligand; L = MeCN (1b), CO (1c), CN(-) (1d); H being trans to the nitrogen of ppy ligand) emit blue light at the emission lambda(max) (452-457, 483-487 nm) significantly shorter than those (468, 495 nm) of the chloro complex Ir(ppy)(PPh3)2(H)(Cl) (1a). Replacing ppy of 1a-d with F2ppy (2,4-difluoro-2-phenylpyridinato anion) and F2Meppy (2,4-difluoro-2-phenyl-m-methylpyridinato anion) brings further blue-shifts down to the emission lambda(max) at 439-441 and 465-467 nm with CIE color coordinates being x = 0.16 and y = 0.18-0.20 to display a deep-blue photoemission. No significant blue shift is observed by replacing PPh3 of 1a with PPh2Me to produce Ir(ppy)(PPh2Me)2(H)(Cl) (1aPPh 2Me), which displays emission lambda max at 467 and 494 nm. The chloro complexes, [Ir(ppy)(PPh3)2(Cl)(L)](0,+) (L = MeCN (2b), CO (2c), CN(-) (2d)) having a chlorine ligand trans to the nitrogen of ppy also emit deep-blue light at emission lambda(max) 452-457 and 482-487 nm.
- [Show abstract] [Hide abstract] ABSTRACT: High-efficient white organic light-emitting diodes (WOLEDs) were fabricated by using the following three different emitting materials: 4″-(2,2-diphenylvinyl)-1-[4-(N,N-diphenylamino)-styryl]-terphenyl for blue emission, fac-tris(2-phenypyridine) iridium(III) for green emission, and bis(5-benzoyl-2-phenylpyridinato-C,N)iridium(III) (acetylacetonate) for red emission. For higher efficiency, a hybrid spacer (HS) was inserted between each emissive layer (blue-red, red-green, and green-blue emissive layers). It was found that the WOLEDs using HS showed maximum power efficiency of 28.69 lm/W, maximum external quantum efficiency of 13.1%, and Commission Internationale de I’Eclairage coordinates (CIEx,y) of (x = 0.37,y = 0.37).
Hongik UniversitySŏul, Seoul, South Korea