Tetramer of triphenylamine and similar derivatives with bromine atoms as hole injecting/transporting materials for efficient red phosphorescent OLEDs

Abstract Tetramer of triphenylamine and similar compounds having bromine atoms have been synthesized, characterized and tested as hole injecting/transporting layers of organic light-emitting diodes (OLEDs). Rather high glass transition temperatures of the derivatives were determined to be in a range of 99–163 °C. Some of the materials have suitable ionization potentials and adequate triplet state energies, which make them useful hole injecting/transporting layer materials for application in red phosphorescent devices. A simplified tri-layer device architectures of red OLEDs were prepared by adopting N-(1-diphenylamino[4,4′-biphenyl])-N,N-bis(4-bromophenyl)amine (1) or N,N-bis (1-diphenylamino[4,4′-biphenyl])-N-(4-bromophenyl)amine (2) as hole transporting layer (HTL) material. Tris(1-diphenylamino[4,4′-biphenyl])amine (3) was selected for the hole injecting layer (HIL) to combine with 1 or 2 to construct step-wise hole injection in the devices. Peak efficiencies of the device with a single 1-based HTL were 12.5%, 18.6 cd/A, and 13.1 lm/W, all of which were slightly lower than those of a step-wise device having an additional 3-based HIL (i.e. 14.0%, 22.8 cd/A, and 17.8 lm/W). Similarly, the device with 2-based HTL exhibited peak efficiencies up to 13.5%, 21.3 cd/A, and 17.6 lm/W; while those of the device with an additional 3-based HIL achieved higher values of 13.8%, 22.6 cd/A, and 18.4 lm/W. The results indicate a high potential of these newly synthesized hole injecting/transporting materials.