Browsing by Author "Tseng, Ya-Hsien"

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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.
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).