Thermally stable efficient hole transporting materials based on carbazole and triphenylamine core for red phosphorescent OLEDs

In this work, a series of hole transporting materials with carbazole and triphenylamine cores have been synthesized and characterized. In the carbazole's 3rd and 6th positions, two site tryphenylamine para positions are end capped with the same types of branching derivatives to compare the overall performances of constructed devices. All of our hole transporting materials showed good thermal stabilities without any crystallized features which expressed in higher decomposition temperature (Over 500 degrees C at 5% weight reduction). All synthesized materials revealed HOMO energy levels between -5.62 and -5.48 eV, which values are lying between HOMO energy values of anode and emission layer; as a result, it made an effective path for hole transportation. Higher lying LUMO values between -2.51 and -2.31 can block the electrons from adjacent layer to ensure the perfect recombination in the middle layer. Triphenylamine based HTMs indicated better performances than carbazole based HTMs. Further comparisons were done by using NPB as hole transporting material with the same red phosphorescent based OLED device. HTM2A based device IV was exhibited higher maximum current efficiency of 30.6 cd/A and higher maximum external quantum efficiency of 26.7% than reference NPB based device. Measured Hole mobility value of HTM2A with hole dominant device was 5.3 x 10(-4) cm(2) V-1 s(-1), which was better than NPB. Synthesized HTM2A would be a promising hole transporting material for various phosphorescent based OLEDs.