Browsing by Author "Liu, MS"

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Bright red-emitting electrophosphorescent device using osmium complex as a triplet emitter
(2003-07-28)
Kim, JH
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Liu, MS
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Jen, AKY
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Carlson, B
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Dalton, LR
A series of efficient and bright double-layer light-emitting devices have been fabricated using the osmium (Os) complex as the triplet emissive dopant in both a blue-emitting polyfluorene derivative (PF-TPA-OXD) containing hole-transporting triphenylamine (TPA) and electron-transporting oxadiazole (OXD) as side chains and a blend of 2-(4-t-butylphenyl)-5(4-biphenylyl)-1,3,4-oxadizole (PBD) in poly(N-vinylcarbazole) (PVK). Due to a balanced charge injection and transport in PF-TPA-OXD and very efficient energy transfer from this polymer to the Os complex, the resulting device (indium tin oxide/HTL/OsCF3:PF-TPA-OXD/Ca/Ag) reaches a maximum external quantum efficiency of 2.1% with a peak brightness of 2920 cd/m(2). These results are significantly higher than those obtained from the commonly used host, PVK:PBD (0.49% and 1270 cd/m(2)). (C) 2003 American Institute of Physics.
Highly efficient blue-light-emitting diodes from polyfluorene containing bipolar pendant groups
(2003-09-09)
Shu, CF
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Dodda, R
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Wu, FI
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Liu, MS
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Jen, AKY
A highly efficient blue-light-emitting copolymer with bulky hole-transporting triphenylamine (TPA) and electron-transporting oxadiazole (OXD) pendant groups at the C-9 position of fluorene was synthesized. The results from photoluminescence and electrochemical measurements reveal that both the side chains and the polyfluorene main chain retain their own electronic characteristics in the copolymer. It shows a pure blue emission with no aggregates or excimers formed even after being annealed at 150 degreesC under nitrogen for 20 h. In addition, it also demonstrates improved charge injection and balanced charge transport in electroluminescence. The maximum external quantum efficiency of a single-layer device using this copolymer as the emitting layer is 1.21% (at a brightness of 354 cd/m(2) with driving voltage of 7.6 V). The maximum luminance of the device reaches 4080 cd/m(2) at a bias of 12.0 V and a current density of 640 mA/cm(2).
Material and interface engineering for high-performance light-emitting diodes.
(2005-03-13)
Jen, AKY
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Niu, YH
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Liu, MS
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Yip, H
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Kang, MS
Novel oxadiazole-containing polyfluorene with efficient blue electroluminescence
(2003-01-14)
Wu, FI
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Reddy, DS
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Shu, CF
;
Liu, MS
;
Jen, AKY
A novel oxdiazole-containing polyfluorene copolymer (PF-OXD) was synthesized by attaching two electron-deficient, 4-tent-butylphenyl-1,3,4-oxadiazole groups onto the C-9 position of the alternating fluorene unit to form a 3-D cardo-structure. This polymer possesses a very high glass transition temperature (T-g: 213 degreesC) and very good thermal stability due to its rigid cardo-linkage. The results from the photoluminescence measurements of the isothermally heated PF-OXD thin film (150 degreesC for 20 h) show that the commonly observed aggregate/excimer formation in polyfluorenes is very effectively suppressed in this polymer due to its 3-D structure and high T-g. A double-layer LED device using this polymer as the emitting layer shows a bright blue emission with a low turn-on voltage at 5.3 V and a high brightness of 2770 cd/m(2) at a drive voltage of 10.8 V. The maximum external quantum efficiency is 0.52% at 537 cd/m(2) with a bias of 7.4 V. The improved device performance over that of poly(9,9-dioctylfluorene) (POF) may be due to better electron injection and transport in PF-OXD and the efficient energy transfer from the OXD side chain to the polyfluorene main chains.