A simple systematic design of phenylcarbazole derivatives for host materials to high-efficiency phosphorescent organic light-emitting diodes

A series of novel blue phosphorescent host materials, namely, CTP-1, CTP-2 and CTP-3 have been designed and synthesized through the Suzuki-Miyaura cross-coupling reaction between N-phenylcarbazole and biphenyl. Their thermal, photophysical and electrochemical properties were systematically investigated. These novel hosts show excellent thermal stability and high glass transition temperatures (T-g) ranging from 113 to 127 degrees C. The triplet energies of these three materials are significantly higher than that of (4,4'-bis(N-carbazolyl)-2,2'-biphenyl) (CBP, 2.56 eV) and that of the most popular blue phosphorescent material iridium(III) bis[(4,6-difluorophenyl)pyridinato-N,C-2'] picolinate (Flrpic, 2.65 eV). These three novel materials have superior thermal and electronic properties for blue and white phosphorescent OLEDs. Blue emitting devices with an Ir-complex Flrpic as the phosphorescent dopant have been fabricated and show high efficiency with low roll-off. In particular, 40.4 cd A(-1) at 100 cd m(-2) and 38.2 cd A(-1) at 1000 cd m(-2) were achieved when CTP-1 was used as the host material. On the basis of this work, an all-phosphor white device with a current efficiency of 64.5 cd A(-1) at 100 cd m(-2) and 61.9 cd A(-1) at 1000 cd m(-2) has also been fabricated.