Browsing by Author "Tam, Hoi Lam"

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High efficiency and small roll-off electrophosphorescence from a new iridium complex with well-matched energy levels
(2008-02-18)
Gao, Zhi Qiang
;
Mi, Bao Xiu
;
Tam, Hoi Lam
;
Cheah, Kok Wai
;
Chen, Chin Hsin
Phenylpyridazine ligands coordinating to the iridium(III) atom yield a thermally stable (5 % weight loss at 439 degrees C) homoleptic iridium complex with a high phosphorescent quantum yield (0.32 at room temperature). This material has well-matched energy levels with the host, and highly efficient electrophosphorescence (52 cd A(-1); see figure) with a small roll-off (23 % at 70 mA cm(-2)) in device efficiency is achieved.
New Host Containing Bipolar Carrier Transport Moiety for High-Efficiency Electrophosphorescence at Low Voltages
(2009-02-09)
Gao, Zhi Qiang
;
Luo, Meiming
;
Sun, Xiao Hua
;
Tam, Hoi Lam
;
Wong, Man Shing
A new host material for use in phosphorescent OLEDs with desirable electronic properties has been synthesized. The material exhibits superior carrier-transport properties, a narrow optical band gap, relatively high triplet energy, and high thermal stability. It is synthesized by integrating hole-transporting carbazole groups into an electron-transporting phenanthroline core (see figure), and is demonstrated to be an excellent host for phosphorescent dopant emitters.
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.