Browsing by Author "Wu, Fang-Iy"

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Bright-white light-emitting devices based on a single polymer exhibiting simultaneous blue, green, and red emissions
(2007-01-23)
Chuang, Chu-Ying
;
Shih, Ping-I
;
Chien, Chen-Han
;
Wu, Fang-Iy
;
Shu, Ching-Fong
We have developed efficient white-light-emitting polymers through the incorporation of low band gap green-light-emitting benzothiadiazole and red-light-emitting bisthiophenylbenzothiadiazole moieties into the backbone of a blue-light-emitting bipolar polyfluorene copolymer. Partial energy transfer from the blue-fluorescent polyfluorene backbone to the green- and red-fluorescent components resulted in individual emissions from the three emissive species. By carefully controlling the concentrations of the low-energy-emitting species in the resulting copolymers, the emission of white light, with contributions from each of the three primary colors, was achieved. Efficient polymer light-emitting devices prepared using these copolymers exhibited luminance efficiencies as high as 4.87 cd/A with color coordinates (0.37, 0.36) that were very close to the ideal CIE chromaticity coordinates for pure white light (0.33, 0.33). In addition, the color coordinates remained almost unchanged over a range of operating potentials. A mechanistic study suggested that energy transfer from the fluorene segments to the low band gap units, rather than charge trapping, was the main operating process involved in the electroluminescent process.
Efficient red-emitting electrophosphorescent polymers
(2008-02-26)
Yang, Xiao-Hui
;
Wu, Fang-Iy
;
Neher, Dieter
;
Chien, Chen-Han
;
Shu, Ching-Fong
We report the synthesis and characterization of a series of electrophosphorescent polymers with a polyfluorene backbone, containing a red-emitting iridium complex and carrier-transporting units as the substitutes of the C-9 position of fluorene. Different specimens and contents of the hole-transporting moieties were found to influence the electroluminescent properties of the polymers. Incorporation of a hole-transporting/electron-blocking interfacial layer and utilization of an efficient electron injection cathode led to the saturated red-emitting electrophosphorescent polymer devices with the peak luminance efficiency and power conversion efficiency of 9.3 cd A(-1) and 10.5 lm W-1, respectively. The efficiencies were 8 cd A(-1)/8 lm W-1 and 5.9 cd A(-1)/4.6 lm W-1, respectively, at 100 and 1000 cd m(-2).
Efficient white-electrophosphorescent devices based on a single polyfluorene copolymer
(2007-05-07)
Wu, Fang-Iy
;
Yang, Xiao-Hui
;
Neher, Dieter
;
Dodda, Rajasekhar
;
Tseng, Ya-Hsien
An efficient white-light-emitting polymer (W3) is realized by covalently attaching a green fluorophore and a red phosphor into the backbone and the side chains, respectively, of polyfluorene at a concentration of 0.04 mol %. In addition, charge-transporting pendant units are included to improve carrier injection and transport. White-electrophosphorescent devices with the structure ITO/PEDOT.PSSiW3/CsF/Al (ITO: indium tin oxide; PEDOT.PSS: poly(styrenesulfonate)-doped poly(3,4-ethylenedioxythiophene)) exhibit a low turn-on voltage of 2.8 V and a luminance of ca. 10(3) cd m(-2) at below 6 V. The peak luminance and power-conversion efficiencies are 8.2 cd A(-1) and 7.2 lm W-1, respectively. Furthermore, the device shows relatively stable white emission: the Commission Internationale d'Eclairage (CIE) chromaticity coordinates of the devices change only slightly from (0.35,0.38) at 10 mA cm(-2) to (0.33,0.36) at 100 mA cm(-2), with an almost constant color render index (CRI) value of 82 at all measured current densities.
Highly efficient white-electrophosphorescent devices based on polyfluorene copolymers containing charge-transporting pendent units
(2007)
Wu, Fang-Iy
;
Shih, Ping-I
;
Tseng, Ya-Hsien
;
Shu, Ching-Fong
;
Tung, Yung-Liang
We have developed an efficient green-emitting polymer (FTO-BT5) through the incorporation of low-bandgap 2,1,3-benzothiadiazole (BT) moieties into the backbone of a blue-light-emitting polyfluorene copolymer (PF-TPA-OXD), which contains hole-transporting triphenylamine (TPA) and electron-transporting oxadiazole (OXD) pendent groups. A polymer light-emitting device based on this BT-containing copolymer exhibited very bright green emission having Commission Internationale d'E'nclairage (CIE) chromaticity coordinates (0.32, 0.61); the maximum brightness was 10232 cd m(-2) and the maximum luminance efficiency was 8.9 cd A(-1). In addition, a highly efficient three-band white-light-emitting diode was prepared using PF-TPA-OXD as a blue-light-emitting host doped with this green-light-emitting FTO-BT5 copolymer and a red-light-emitting Os phosphor Os(fppz). Without co-doping any other electron-and/or hole-transporting molecules, this white-light-emitting device reached a maximum external quantum efficiency of 4.1% (8.3 cd A(-1)) at a luminance of 402 cd m(-2) and a current density of 4.8 mA cm(-2). When the luminance increased from 26 cd m(-2) (0.36, 0.32) to 5258 cd m(-2) (0.33, 0.31), the corresponding CIE chromaticity coordinates remain almost unaltered and very close to the emission of pure white light; the value of eta(ext) remained above 3% in this high-luminance region.
Polyfluorene presenting dipolar pendent groups and its application to electroluminescent devices
(2007-06-01)
Chien, Chen-Han
;
Shih, Ping-I
;
Wu, Fang-Iy
;
Shu, Ching-Fong
;
Chi, Yun
We have synthesized a blue-light-emitting polyfluorene derivative (PF-TPAOXD) that presents sterically hindered, dipolar pendent groups functionalized at the C-9 positions of alternating fluorene units. The incorporation of the dipolar side chains, each comprising an electron-rich triphenylamine group and an electron-deficient oxadiazole group connected through a pi-conjugated bridge, endows the resultant polymer with higher highest occupied molecular orbital and lower lowest unoccupied molecular orbital energy levels, which, consequently, lead to an increase in both hole and electron affinities. An electroluminescent device incorporating this polymer as the emitting layer exhibited a stable blue emission with a maximum brightness of 2080 cd/ m(2) at 12 V and a maximum external quantum efficiency of 1.4% at a brightness of 137 cd/m(2). Furthermore, atomic force microscopy measurements indicated that the dipolar nature of PF-TPAOXD, in contrast to the general nonpolarity of polydialkylfluorenes, provided a stabilizing environment allowing the polar organometallic triplet dopant to be dispersed homogeneously. We also fabricated an electrophosphorescent device incorporating PF-TPAOXD as the host material doped with a red-emitting osmium complex to realize red electroluminescence with Commission Internationale de l'Eclairage color coordinates of (0.66, 0.34). The resulting device exhibited a maximum external quantum efficiency of 7.3% at a brightness of 1747 cd/m(2) and a maximum brightness of 7244 cd/ m(2). (C) 2007 Wiley Periodicals, Inc.
Stable and efficient white electroluminescent devices based on a single emitting layer of polymer blends
(2006-08-04)
Shih, Ping-I
;
Tseng, Ya-Hsien
;
Wu, Fang-Iy
;
Dixit, Ajay Kumar
;
Shu, Ching-Fong
An efficient orange-light-emitting polymer (PFTO-BSeD5) has been developed through the incorporation of low-bandgap; benzoselenadiazole (BSeD) moieties into the backbone of a blue-light-emitting polyfluorene copolymer (PFTO poly{[9,9-bis(4-(5-(4-tert-butylphenyl)-[1,3,4]-oxadiazol-2-yl)phenyl)-9',9'-di-n-octyl-[2,2']-bifluoren-7,7'-diyl]-stat-[9,9-bis(4-(NN-di(4-n-butylphenyl)amino)phenyl)-9',9'-di-n-octyl-[2,2']-bifluoren-7,7'-diyl]}) that contains hole-transporting triphenylamine and electron-transporting oxadiazole pendent groups. A polymer light-emitting device based on this copolymer exhibits a strong, bright-orange emission with Commission Internationale de L'Eclairage (CIE) color coordinates (0.45,0.52). The maximum brightness is 13716 cd m(-2) and the maximum luminance efficiency is 5.53 cd A(-1). The use of blends of PFTO-BSeD5 in PFTO leads to efficient and stable white-light-emitting diodes - at a doping concentration of 9 wt%, the device reaches its maximum external quantum efficiency of 1.64% (4.08 cd A(-1)). The emission color remains almost unchanged under different bias conditions: the CIE coordinates are (0.32,0.33) at 11.0 V (2.54 mA cm(-2), 102 cd m(-2)) and (0.31,0.33) at 21.0 V (281 mA cm(-2), 7328 cd m(-2)). These values are very close to the ideal CIE chromaticity coordinates for a pure white color (0.33,0.33).