Browsing by Author "Xia, Ping Fan"

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Efficient deep-blue organic light-emitting diodes: Arylamine-substituted oligofluorenes
(2007-11-05)
Gao, Zhi Qiang
;
Li, Zhong Hui
;
Xia, Ping Fan
;
Wong, Man Shing
;
Cheah, Kok Wai
Novel deep-blue-light-emitting diphenylamino and triphenylamino end-capped oligofluorenes were synthesized by double palladium-catalyzed Suzuki cross- coupling of dibromo-oligofluorene with the corresponding boronic acid as a key step. These oligofluorenes exhibit deep-blue emission (lambda(em)(max) = 429-432 nm), low and reversible electrochemical oxidation (highest occupied molecular orbital = 5.15-5.20 eV), high fluorescence quantum yield (Phi(FL) = 0.61-0.93), and good thermal properties (glass-transition temperature, T-g = 99-195 degrees C and decomposition temperature, T-dec > 450 degrees C). Remarkably, saturated deep-blue organic light-emitting diodes, made from these oligofluorenes as dopant emitters, have been achieved with excellent performance and maximum efficiencies up to 2.9 cd A(-1) at 2 mA cm(-2) (external quantum efficiency of 4.1 %) and with Commission Internationale de l'Eclairage (x,y) coordinates of (0.152,0.08), which is very close to the National Television System Committee standard blue.
p-Doped p-phenylenediamine-substituted fluorenes for organic electroluminescent devices
(2009-07-01)
Gao, Zhi Qiang
;
Xia, Ping Fan
;
Lo, Pik Kwan
;
Mi, Bao Xiu
;
Tam, Hoi Lam
Two novel p-phenylenediamine-substituted fluorenes have been designed and synthesized. Their applications as hole injection materials in organic electroluminescent devices were investigated. These materials show a high glass transition temperature and a good hole-transporting ability. It has been demonstrated that the 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) doped p-phenylene-diamine-substituted fluorenes, in which F4-TCNQ acts as p-type dopant, are highly conducting with a good hole-transporting property. The organic light emitting devices (OLEDs) utilizing these F4-TCNQ-doped materials as a hole injection layer were fabricated and investigated. The pure Alq(3)-based OLED device shows a current efficiency of 5.2 cd/A at the current density of 20 mA/cm(2) and the operation lifetime is 1500 h with driving voltage increasing only about 0.7 mV/h. The device performance and stability of this hole injection material meet the benchmarks for the commercial requirements for OLED materials. (C) 2009 Elsevier B.V. All rights reserved.