Indolo[3,2-b]carbazole/benzimidazole hybrid bipolar host materials for highly efficient red, yellow, and green phosphorescent organic light emitting diodes
Journal
Journal of Materials Chemistry
Journal Volume
22
Journal Issue
17
Pages
8399-8407
Date Issued
2012
Author(s)
Ting, H.-C.
Chen, Y.-M.
You, H.-W.
Hung, W.-Y.
Lin, S.-H.
Chaskar, A.
Chou, S.-H.
Chi, Y.
Liu, R.-H.
Abstract
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) 2Ir(acac), yellow (Bt) 2Ir(acac), and two new red emitters (35dmPh-6Fiq) 2Ir(acac) (i3) and (4tBuPh-6Fiq) 2Ir(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) 2(PPhMe 2) 2] achieved a maximum external quantum efficiency, current efficiency, and power efficiency of 22%, 28 cd A -1, and 22.1 lm W -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 -2, suggesting balanced charge fluxes within the emitting layer, rendering devices with limited efficiency roll-off. © The Royal Society of Chemistry 2012.
SDGs
Type
journal article