Efficient red phosphorescent OLEDs employing 2-phenylcarbazoles-based hole transport materials

A new series of 9-hexylcarbazole-based hole transporting materials (HTMs) with naphthyl or pyrenyl substitutions (i.e. compounds 1 and 2) were synthesized and characterized. Compound 2 possesses an adequate ionization potential and triplet energy gap of 5.54 eV and 2.48 eV respectively, which makes 2 a suitable HTM for use in red phosphorescent organic light-emitting diodes (OLEDs). In contrast, a rather higher ionization potential of 1 was estimated to be 5.72 eV, thus the p-type conducting dopant should be introduced in device fabrication. The respective peak efficiencies of compounds 1 and 2-based OLEDs with the p-type dopant were recorded at 15.4 % (26.0 cd/A and 24.2 lm/W) and 17.3 % (26.1 cd/A and 19.1 lm/W), demonstrating their high potential for EL applications.