Browsing by Author "Wu, Chung-Chih"

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Dibenzothiophene/oxide and quinoxaline/pyrazine derivatives serving as electron-transport materials
(2006-07-21)
Huang, Tai-Hsiang
;
Whang, Wha-Tzong
;
Shen, Jiun Yi
;
Wen, Yuh-Sheng
;
Lin, Jiann T.
A series of 2,8-disubstituted dibenzothiophene and 2,8-disubstituted dibenzothiophene-SS-dioxide derivatives containing quinoxaline and pyrazine moieties are synthesized via three key steps: i) palladium-catalyzed Sonogashira coupling reaction to form dialkynes; ii) conversion of the dialkynes to diones; and iii) condensation of the diones with diamines. Single-crystal characterization of 2,8-di(6,7-dimethyl-3-phenyl-2-quinoxalinyl)-5H-5 lambda(6)-dibenzo[b,d]thiophene-5,5-dione indicates a triclinic crystal structure with space group P1 and a non-coplanar structure. These new materials are amorphous, with glass-transition temperatures ranging from 132 to 194 degrees C. The compounds (Cpd) exhibit high electron mobilities and serve as effective electron-transport materials for organic light-emitting devices. Double-layer devices are fabricated with the structure indium tin oxide (ITO)/Qn/Cpd/LiF/Al, where yellow-emitting 2,3-bis[4-(N-phenyl-9-ethyl-3-carbazolylamino)phenyl]quinoxaline (Qn) serves as the emitting layer. An external quantum efficiency of 1.41 %, a power efficiency of 4.94 lm W-1, and a current efficiency of 1.62 cd A(-1) are achieved at a current density of 100 mA cm(-2).
Effects of Mechanical Strains on the Characteristics of Top-Gate Staggered a-IGZO Thin-Film Transistors Fabricated on Polyimide-Based Nanocomposite Substrates
(2012-07-01)
Lin, Chang-Yu
;
Chien, Chih-Wei
;
Wu, Chung-Chih
;
Yeh, Yung-Hui
;
Cheng, Chun-Cheng
In this paper, we had successfully implemented flexible top-gate staggered amorphous In-Ga-Zn-O (a-IGZO) thin-film transistors (TFTs) on colorless and transparent polyimide (PI)-based nanocomposite substrates using fully lithographic and etching processes that are compatible with existing TFT mass fabrication technologies. The use of the selectively coated release layer between the nanocomposite PI film and the glass carrier ensured smooth debonding of the plastic substrate after TFT fabrication. The TFTs showed decent performances (with mobility > 10 cm(2)/V . s) either as fabricated or as debonded from the carrier glass. By bending the devices to different radii of curvature (from a flat state to an outward bending radius of 5 mm), influences of mechanical strains on the characteristics of flexible a-IGZO TFTs were also investigated. In general, the mobility of the flexible a-IGZO TFT increased with the tensile strain, whereas the threshold voltage decreased with the tensile strain. The variation of the mobility in a-IGZO TFTs versus the strain appeared smaller than those observed for amorphous silicon TFTs.
Multifunctional red phosphorescent bis-cyclometallated iridium complexes based on 2-phenyl-1,2,3-benzotriazole ligand and carbazolyl moieties
(2011-03-11)
Malinauskas, Tadas
;
Daskeviciene, Maryte
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Kazlauskas, Karolis
;
Su, Hai-Ching
;
Grazulevicius, Juozas Vidas
Multifunctional phosphorescent bis-cyclometallated iridium(III) complexes based on the 2-phenyl-1,2,3-benzotriazole moiety and bearing branched hole-transporting carbazole fragments were synthesized. The isolated compounds were found to be amorphous and expressed very good solubility. Introduction of flexible aliphatic chains of various lengths into the iridium complexes enabled manipulation of their glass transition temperature. The iridium complexes exhibited red phosphorescence emission at 650 nm with the lifetime of 5.7 mu s and phosphorescence quantum yields of 0.22 and 0.17 in solution and solid state, respectively, at room temperature. The shielding effect of the carbazolyl moieties on the concentration quenching of phosphorescence of the iridium centers was found to result in the increased excited state lifetime and quantum yield due to the suppressed exciton migration. Non-optimized OLED devices, based on the phosphorescent bis-cyclometallated iridium(III) complex without host material were fabricated and their electroluminescence properties were evaluated. (C) 2011 Elsevier Ltd. All rights reserved.
Solid-State Light-Emitting Electrochemical Cells Based on Cationic Transition Metal Complexes for White Light Generation
(2010)
Su, Hai-Ching
;
Wong, Ken-Tsung
;
Wu, Chung-Chih
;
照明與能源光電研究所
;
Institute of Lighting and Energy Photonics
Solid-state light-emitting electrochemical cells (LECs) based on cationic transition metal complexes (CTMCs) exhibit several advantages over conventional light-emitting diodes such as simple fabrication processes, low-voltage operation, and high power efficiency. Hence, white CTMC-based LECs may be competitive for lighting applications. In this chapter, we review previous important works on CTMC-based LECs, such as increasing device efficiency, color tuning, lengthening device lifetime, and shortening turn-on time. Our demonstration of white CTMC-based LECs by using the host-guest strategy is then described.
Solid-state light-emitting electrochemical cells employing phosphor-sensitized fluorescence
(2010)
Su, Hai-Ching
;
Lin, You-Heng
;
Chang, Chih-Hao
;
Lin, Hao-Wu
;
Wu, Chung-Chih
We report highly efficient phosphor-sensitized solid-state light-emitting electrochemical cells (LECs) utilizing a phosphorescent cationic iridium complex [Ir(dFppy)(2)(SB)](+)(PF(6)(-)) as the host and a fluorescent cationic dye (R6G) as the guest. Photophysical studies show that R6G retains a high photoluminescence quantum yield (PLQY) in highly polar media, revealing its suitable use as an emitting guest in an ionic host matrix. Such solid-state LECs achieve quantum efficiency (cd A(-1)) efficiency, and power efficiency up to 5.5% photon/electron, 19 cd A(-1) and 21.3 lm W(-1), respectively. The device quantum efficiency achieved is among the highest reported for fluorescent LECs and is higher than one would expect from the PLQY of the R6G fluorescent dye in the host film, thus indicating that phosphor-sensitization is useful for achieving highly efficient fluorescent LECs. Moreover, using narrow-band fluorescent emitters, such as R6G (FWHM, similar to 50 nm), is effective in improving the color saturation of solid-state LECs based on cationic complexes.