Browsing by Author "Ho, Meng-Huan"

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A morphologically stable host material for efficient phosphorescent green and red organic light emitting devices
(2008-11-28)
Ho, Meng-Huan
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Balaganesan, Banumathy
;
Chu, Ta-Ya
;
Chen, Teng-Ming
;
Chen, Chin H.
A carbazole-based host material, 4,4'-N,N'-[di(3, 6-di(t-butyl)carbazole]biphenyl (ttbCBP), with four t-butyl steric spacers on peripheral carbazole moieties was effectively synthesized through Friedel-Crafts Alkylation. Owing to the presence of sterically hindered t-butyl groups, ttbCBP exhibits a high glass transition temperature (175 degrees C) and is morphologically stable. This host material also preserves the characteristics of wide band-gap of 3.2 eV and high triplet energy of 2.64 eV. In addition, ttbCBP has been shown to be effective hosts for green and red phosphorescent emitters in organic electrophosphorescent devices. (C) 2008 Elsevier B.V. All rights reserved.
Ab initio molecular orbital calculation of 1,3,5-triazine derivatives as hosts for phosphorescent organic light emitting devices
(2005)
Chu, Ta-Ya
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Ho, Meng-Huan
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Chen, Jenn-Fang
;
Chen, Chin H.
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電子物理學系
Novel triplet host materials 2,4,6-tris (diarylamino)-1,3,5-triazine derivatives (TRZ1-TRZ4) have been reported and from which TRZ2 as a host for Ir(ppy)(3) was particularly useful in producing high efficiency phosphorescent organic light emitting diodes (OLEDs). This paper reports the molecular orbital and energy level of these derivatives determined by ab initio calculation. The calculated triplet bandgap energy of TRZ1 has been found to be larger than that of TRZ2.
Blue Fluorescence and Bipolar Transport Materials Based on Anthracene and Their Application in OLEDs
(2012-06-01)
Ho, Meng-Huan
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Balaganesan, Banumathy
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Chen, Chin H. (Fred)
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交大名義發表
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National Chiao Tung University
The phenomenon of organic electroluminescence (EL) was first discovered from studies on anthracene crystals in the 1960s. Since then, its derivatives have been studied extensively in applications such as organic light-emitting diodes (OLEDs) and organic thin-film transistors because of their excellent EL, transport, and good electrochemical properties. A blue fluorescence emitter based on anthracene is also important in constructing hybrid tandem white OLEDs for lighting applications. This article provides a review about the development of blue host OLED materials based on molecules designed and derived from the core structure of anthracene and their application as bipolar charge-carrier transport materials in OLEDs. The recent development of efficient, stable, blue-doped p-i-n OLEDs with simplified device architecture based on the single common host 2-methyl-9,10-di(2-napthyl)anthracene, with its stable thin-film morphology, large band gap energy, high fluorescence quantum yield, and ambipolar charge-carrier transport properties, is also highlighted.
Efficient and Color-saturated Inverted Bottom-emitting Organic Light-emitting Devices with a Semi-transparent Metal-assisted Electron Injection Layer
(2009)
Wu, Chang-Yen
;
Ho, Meng-Huan
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Gao, Sin-Min
;
Su, Shang-Yu
;
Lin, Kuan-Hung
We report the development of highly efficient and color-saturated green fluorescent C545T dye-doped inverted bottom-emitting organic light emitting diode (IBOLED) by the insertion of a semi-transparent metal-assisted electron injection layer (SM-EIL) based on silver between the ITO and the n-doped electron injection layer (EIL). This n-i-p device with its synergistic microcavity effect achieved maximum efficiencies of 24 cd/A and 12.9 lm/ W and an external quantum efficiency of 6.2% with a saturated CIE(x,y) (0.24,0.71) which are twice better than those of the conventional OLED and over 60% improvement on IBOLED without the SM-EIL.
Efficient and color-saturated inverted bottom-emitting organic light-emitting devices with a semi-transparent metal-assisted electron injection layer
(2011-01-01)
Ho, Meng-Huan
;
Wu, Chang-Yen
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Chen, Teng-Ming
;
Chen, Chin H.
;
應用化學系
We report the development of highly efficient and color-saturated green fluorescent 10-(2-benzothiazolyl)-1 1 7 7-tetramethyl-2 36 7-tetrahydro-l H 5H 11H-benzo[l]pyrano-[6 7 ij]quinolizin-11-one dye-doped inverted bottom-emitting organic light-emitting diode (IBOLED) This was enabled by the insertion of a silver (Ag) based semi-transparent metal-assisted electron injection layer between the ITO cathode and n-doped electron transporting layer This IBOLED with ITO/Ag bilayer cathode with its synergistic microcavity effect achieved luminous efficiencies of 207 cd/A and 124 1m/W and a saturated ClE(x,y) of (0 22 0 72) at 20 mA/cm(2) which are twice better than those of the conventional OLED and have over 60% improvement on IBOLED without ITO/Ag Mayer cathode (c) 2010 Elsevier B V All rights reserved
Efficient deep blue emitters for organic electroluminescent devices
(2007-08-20)
Ho, Meng-Huan
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Wu, Yao-Shan
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Wen, Shih-Wen
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Chen, Teng-Ming
;
Chen, Chin H.
Highly efficient deep blue organic light emitting devices have been fabricated with a 4-(styryl)biphenyl-core based fluorescent dopant (SK-1) in the wide band gap 2-methyl-9,10-di(1-naphthyl)anthracene (alpha,alpha-MADN) host system which achieved an electroluminescence efficiency of 5.0 cd/A and an external quantum efficiency of 4.2% at 20 mA/cm(2) with a saturated blue Commission Internationale de l'Eclairage coordinates of (0.15, 0.14) and a half-decay lifetime of 8000 h at an initial brightness of 100 cd/m(2). The current efficiency and electroluminescent color of SK-1 doped devices have been shown to be essentially immune to drive current density. (C) 2007 American Institute of Physics.
Efficient electron injection in organic light-emitting diodes using dipotassium phthalate as n-type dopant
(2008)
Ho, Meng-Huan
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Hsieh, Ming-Ta
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Chen, Jenn-Fang
;
Hwang, Shiao-Wen
;
Chen, Chin H.
An efficient n-doped electron transport layer composed of 4,7-diphenyl- 1, 10-phenanthroline (BPhen) and dipotassium phthalate (PAK2) has been developed. By temperature-dependent admittance spectroscopy, the incorporation of PAK2 into BPhen is found to increase electron concentration in BPhen laYer, resulting in raising the Fermi-level to similar to 0.5 eV below its LUMO which further enhances the efficiency of electron injection from Al cathode. When this n-doped layer is adopted in OLED device, the green Alq(3) device can achieve a current efficiency of 3.6 cd/A and a power efficiency of 2.1 lm/W at 20 mA/cm(2) and lower drive voltage of 5.3 V.
Efficient p-i-n Top-emitting Flexible Organic Light Emitting Diodes on Planarized Stainless Steel Foil
(2009)
Su, Shang-Yu
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Ho, Meng-Huan
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Kao, Pei-Yi
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Wu, Chang-Yen
;
Peng, Yi-Hao
A high-efficiency p-i-n top-emitting flexible organic light emitting diode (TFOLED) employing highly reflective Ag as anode and semitransparent Ca/Ag as cathode was fabricated on SS substrate which was insulated and planarized with a specially formulated photoresist coating. By incorporating p-dopant (WO(3)) and a new n-dopant (PAK2) in hole and electron transparent layers, respectively, along with an optimized microcavity structure, a green fluorescent C545T doped Alq(3) TOLED on SS substrate achieved one of the highest efficiencies of 26.7 cd/A and 19.8 lm/W at 20 mA/cm(2) reported for flexible OLEDs.
Electrical characterization of bathophenanthroline doped with dipotassium phthalate
(2007)
Hsieh, Ming-Ta
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Chang, Chan-Ching
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Chen, Jenn-Fang
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Ho, Meng-Huan
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Chen, Teng-Ming
Bathophenanthroline (BPhen) doped with dipotassium phthalate (PAK2) was electrically characterized using current-voltage (I-V) and temperature-dependent admittance spectroscopy measurements which demonstrates that the incorporation of PAK2 into BPhen can increase the electron concentration of the BPhen layer resulting in the transformation of the Fermi-level from deep to shallow (around 0.5 eV below LUMO band) and Accordingly, PAK2 is an alternative n-type organic dopant for n-type doping device.
Electrical characterization of organic light-emitting diodes using dipotassium phthalate as n-type dopant
(2008-08-25)
Ho, Meng-Huan
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Hsieh, Ming-Ta
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Chen, Teng-Ming
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Chen, Jenn-Fang
;
Hwang, Shiao-Wen
An efficient n-doped electron transport layer composed of 4,7-diphenyl-1,10-phenanthroline (BPhen) and dipotassium phthalate (PAK2) has been developed. By temperature-dependent admittance spectroscopy, the incorporation of PAK2 into BPhen is found to raise the Fermi level from 1.7 eV to only around 0.5 eV below BPhen's lowest unoccupied molecular orbital, which further enhances the efficiency of electron injection from an A1 cathode. When this n-doped layer is adopted in an organic light-emitting diode device, the green fluorescent 10-(2-benzothiazolyl)-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H, 5H, 11H-benzo[l]-pyrano[6,7,8-ij]quinolizin-11-one doped device can achieve a current efficiency of 16 cd/A and a power efficiency of 10.9 lm/W at 1000 cd/m(2). (C) 2008 American Institute of Physics.
Flexible inverted bottom-emitting organic light-emitting devices with a semi-transparent metal-assisted electron-injection layer
(2010-01-01)
Wu, Chang-Yen
;
Ho, Meng-Huan
;
Su, Shang-Yu
;
Chen, Chin H.
;
應用化學系
The development of highly efficient and color-saturated green-fluorescent C545T dye-doped flexible inverted bottom-emitting organic light-emitting diode (IBOLED) is reported. This was enabled by the insertion of a silver (Ag) based semi-transparent metal-assisted electron-injection layer between the ITO cathode and n-doped electron-transporting layer on a flexible polyethersulphone substrate. This flexible IBOLED with an ITO/Ag bilayer cathode with its synergistic microcavity effect achieved luminous efficiencies of 20.4 cd/A and 12 lm/W and a saturated CIE(x,y) of (0.28, 0.68) at 20 mA/cm(2), which are 1.5 times higher than those of a conventional OLED.
High color-stability for white organic light emitting devices by using phosphorescent sensitizer fluorescent
(2010)
Juang, Fuh-Shyang
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Hong, Lin-Ann
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Hsiao, Chih-Jen
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Wang, Shun-Hsi
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Ho, Meng-Huan
High color-stability white OLEDs can be achieved by replacing red fluorescent dopant (DCJTB) with yellow dopant (EY-53) in phosphor-sensitized emitter and optimizing the interlayer (CBP) thickness. Device shows the E.Q.E. of 8.2%, the efficiencies of 21.5 cd/A and 8.1 lm/VV with CIE (0.40, 0.46) at 20 mA/cm(2). The shift of ClExy down to (-0.001,-0.001) at a current density of 20 and 200 mA/cm2.
Highly efficient and stable white light organic light-emitting devices
(2007-08-13)
Lin, Mei-Fang
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Wang, Lei
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Wong, Wai-Kwok
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Cheah, Kok-Wai
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Tam, Hoi-Lam
A highly efficient two-element white light organic light-emitting device with a sky blue dopant BUBD-1 and a yellow dopant TBRb was fabricated. The device achieved an electroluminescence efficiency of 17.1 cd/A and 7.9 lm/W at 20 mA/cm(2). From 112 to 32 010 nits, the CIEx,y coordinates variation was Delta(x,y)<+/-(0.01,0.01), which is superior to common white light organic light-emitting devices (OLEDs) that tend to change color with drive conditions. Moreover, the device reached a half-decay t(1/2) lifetime over 40 000 h at an initial luminance of 300 cd/m(2). This result is among the best records of fluorescent white light OLEDs. (C) 2007 American Institute of Physics.
Highly efficient deep blue electroluminescent devices
(2007)
Ho, Meng-Huan
;
Wu, Yao-Shan
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Wen, Shih-Wen
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Chen, Chin H.
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應用化學系
A new deep blue dopant (SK-1) based on "linked" stilbene moiety has been designed and synthesized. When doped in the stable blue host material, 2-methyl-9,10-di(1-naphthyl)anthracene (alpha,alpha-MADM), the SK-1 doped blue device achieved a luminance efficiency of 5.0 cd/A with corresponding CIEx,y of (0.14, 0.14) at 20 mA/cm(2) and an external quantum efficiency of 4.2%. The performance of SK-1 doped device performance under high/low drive current density remains stable for the needs of full color OLED application.
Highly efficient deep blue organic electroluminescent device based on 1-methyl-9,10-di(1-naphthyl)anthracene
(2006-12-18)
Ho, Meng-Huan
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Wu, Yao-Shan
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Wen, Shih-Wen
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Lee, Meng-Ting
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Chen, Teng-Ming
The author have developed 2-methyl-9,10-di(1-naphthyl)anthracene (alpha,alpha-MADN) as an effective wide band gap host material for Forster energy transfer to the unsymmetrical mono(styryl)amine deep blue fluorescent dopant (BD-1). This guest/host emitting system, at the optimal doping concentration of 3%, can also increase the probability of carrier recombination near the hole-transport/emitting layer interface for the blue organic light emitting device which produces electroluminescence efficiencies of 3.3 cd/A and 1.3 lm/W and a deep blue CIEx,y color coordinates of (0.15, 0.13) that are 50% better than those of the traditional beta,beta-isomeric host (MADN) with the same dopant. (c) 2006 American Institute of Physics.
Highly efficient p-i-n white organic light emitting devices with tandem structure
(2007-12-03)
Ho, Meng-Huan
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Chen, Teng-Ming
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Yeh, Pu-Cheng
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Hwang, Shiao-Wen
;
Chen, Chin H.
Highly efficient tandem p-i-n white organic light emitting devices have been fabricated. Utilizing an optical transparent bilayer with doped organic p-n junction that consists of 4,7-diphenyl-1,10-phenanthroline: 2% cesium carbonate (Cs(2)CO(3))/N,N(')-bis(1-naphthyl)-N,N(')-diphenyl-1,1(')-biphenyl-4,4(')-diamine: 50% v/v tungsten oxide (WO(3)) as the connecting layer, the tandem p-i-n white device achieved an electroluminescence efficiency of 23.9 cd/A and a power efficiency of 7.8 lm/W at 20 mA/cm(2) with a Commission Internationale de l'Eclairage coordinates of (0.30, 0.43). The electroluminescent color of this tandem p-i-n white organic light-emitting diode device will not change significantly with respect to drive current variation and forward viewing angle. (c) 2007 American Institute of Physics.
Highly efficient white light organic light-emitting device
(2007-01-01)
Lin, Mei-Fang
;
Wang, Lei
;
Wong, Wai-Kwok
;
Cheah, Kok-Wai
;
Tam, Hoi-Lam
A highly efficient white organic light-emitting device (OLED) with a novel sky blue dopant BUBD-1 in a two-color emission system was fabricated. The device achieved an EL efficiency of 17.1 cd/A and 7.9 lm/W at 20 mA/cm 2 with CIEx,y coordinates of (x=0.29, y=0.41) which was not changed with drive conditions. The white light OLED reached a half-decay t(1/2) lifetime over 40,000 hours at an initial luminance of 300 cd/m(2).
Highly-efficient tandem White Organic light emitting devices
(2007)
Yeh, Pu-Cheng
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Hwang, Shiao-Wen
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Ma, Jia-Wei
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Ho, Meng-Huan
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Hsu, Shih Feng
We demonstrate efficient tandem p-i-n White Organic Light Emitting Diodes (WOLEDs) with the transparent NPB:WO3 interconnecting layer. The CIEx,y coordinate, luminance yield and E.Q.E of the tandem OLEDs (at 20 mA/cm(2)) are (0.30, 0.43), 23.9 cd/A and 8.5%, respectively. The CIEx,y coordinates of the tandem OLEDs neither change (Delta x,y < 0.02) with driving current nor with forward viewing angle (+/- 60 degree). This performance of tandem WOLEDs represents considerable improvement over what have been known in the literature.
Iminodibenzyl-substituted distyrylarylenes as dopants for blue and white organic light-emitting devices
(2008-02-01)
Ho, Meng-Huan
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Chang, Chia-Ming
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Chu, Ta-Ya
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Chen, Teng-Ming
;
Chen, Chin H.
A series of highly efficient blue materials based on iminodibenzyl-substituted distyrylarylene (IDB-series) fluorescent dyes using the concept of steric-compression have been designed and synthesized by means of a rigidized and over-sized ring. The steric-compression effect can shorten the effective conjugation length (chromophore) of the molecule and the added phenyl moiety in the core can alleviate the propensity for molecular aggregation. These materials also possess high glass transition temperature over 100 degrees C. The blue IDB-Ph device achieved a maximum external quantum efficiency of 4.8% with a Commission Internationale de I'Eclairage (CIEx,y) coordinate of (0.16, 0.28). When applied in two-element white OLED system, the IDB-Ph doped device achieved a luminance efficiency of 11.0 cd/A with a CIEx,y color coordinate of (0.29, 0.36). (c) 2007 Elsevier B.V. All rights reserved.
Stable and Efficient Organic Light Emitting Diodes Based on a Single Host of p-doped and n-doped Layers
(2009)
Ho, Meng-Huan
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Hsieh, Ming-Ta
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Chen, Jenn-Fang
;
Lin, Kuan-Heng
;
Chen, Chin H.
A power-efficient and stable organic light emitting diode with a simplified structure based on 2-methyl-9, 10-di(2-naphthyl)anthracene (MADN) has been developed. The incorporation of 10% tungsten oxide (WO(3)) into MADN and 15% cesium carbonate (Cs2CO(3)) into MADN has been found to improve the hole and electron injection, respectively. Based on this work, it is anticipated that p-i-n OLEDs fabrication process can be considerably simplified and the bill of materials cost can reduced by using one ambipolar host for both the p- and n-doped carrier transport layers.