Oligomers containing pyridinyl-substituted carbazole rings as host materials for phosphorescent OLEDs

Abstract

Two oligoethers containing electroactive pendent pyridinyl-carbazole moieties have been synthesized by the multi-step synthetic route. Full characterization of their structures is presented. The oligomers represent derivatives of very high thermal stability with initial thermal degradation temperatures exceeding 400 °C. Glass transition temperatures of the amorphous materials were also very high and reached values of 124 °C and 145 °C, respectively. Bipolar chemical structure having oligomer, i.e. poly{3-(2-methoxy-3-pyridinyl)-9-(3-methyloxetan-3-yl)methyl-carbazole} was tested as host material for green phosphorescent organic light emitting diode using tris(2-phenylpyridine)iridium(III) as a triplet emitter. A green device containing 10 wt% of the green guest demonstrated among all the devices the best performance with current efficiency of 8.8 cd/A and power efficiency of 5.1 lm/W at 100 cd/m². At higher brightness, such as 1000 cd/m², used for illumination applications, this PhOLED showed enhanced efficiency of 11.7 cd/A (5.4 lm/W) with brightness exceeding 4000 cd/m².

Keywords:

• Carbazole derivative
• oligomer
• thermal stability
• organic light emitting diode

Acknowledgements

The OLED materials were developed in the frame of project funded by the Kaunas University of Technology (grant No. PDN2/18).