Indolo[3,2-b]carbazole/benzimidazole hybrid bipolar host materials for highly efficient red, yellow, and green phosphorescent organic light emitting diodes

By incorporating electron-accepting benzimidazole and electron-donating indolo[3,2-b]carbazole into one molecule, two novel donor-acceptor bipolar host materials, TICCBI and TICNBI, have been synthesized. The photophysical and electrochemical properties of the hybrids can be tuned through the differ...

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Bibliographic Details
Published in:Journal of materials chemistry 2012-01, Vol.22 (17), p.8399-8407
Main Authors: Ting, Hao-Chun, Chen, You-Ming, You, Hong-Wei, Hung, Wen-Yi, Lin, Sheng-Hsun, Chaskar, Atul, Chou, Shu-Hua, Chi, Yun, Liu, Rai-Hsung, Wong, Ken-Tsung
Format: Article
Language:English
Subjects:
Acceptors (electronic)
Charge
Devices
Electronics
Emitters
Light-emitting diodes
Quantum efficiency
Rendering
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Summary:By incorporating electron-accepting benzimidazole and electron-donating indolo[3,2-b]carbazole into one molecule, two novel donor-acceptor bipolar host materials, TICCBI and TICNBI, have been synthesized. The photophysical and electrochemical properties of the hybrids can be tuned through the different linkages (C- or N-connectivity) between the electronic donor and acceptor components. The promising physical properties of these two new compounds made them suitable for use as hosts doped with various Ir or Os-based phosphors for realizing highly efficient phosphorescent organic light emitting diodes (PhOLEDs). PhOLEDs using TICCBI and TICNBI as hosts incorporated with Ir-based emitters such as green (PPy) sub(2)Ir(acac), yellow (Bt) sub(2)Ir(acac), and two new red emitters (35dmPh-6Fiq) sub(2)Ir(acac) (i3) and (4tBuPh-6Fiq) sub(2)Ir(acac) (i6) accomplished high external quantum efficiencies ranging from 14 to 16.2%. Nevertheless, the red PhOLED device incorporating TICNBI doped with the red emitter osmium(ii) bis[3-(trifluoromethyl)-5-(4-tert-butylpyridyl)-1, 2,4-triazolate]dimethylphenylphosphine [Os(bpftz) sub(2)(PPhMe sub(2)) sub(2)] achieved a maximum external quantum efficiency, current efficiency, and power efficiency of 22%, 28 cd A super(-1), and 22.1 lm W super(-1), respectively, with CIE coordinates of (0.65,0.35). The external quantum efficiency remained high (20%) as the brightness reached to 1000 cd m super(-2), suggesting balanced charge fluxes within the emitting layer, rendering devices with limited efficiency roll-off.
ISSN:0959-9428
1364-5501
DOI:10.1039/c2jm30207a