Novel Host Materials Based on Dibenzothiophene and Carbazolylcarbazole for Extended Lifetime in Blue Phosphorescent Organic Light-Emitting Diodes

High triplet energy materials based on dibenzothiophene and carbazolylcarbazole are developed as hosts for lifetime extension in blue phosphorescent organic light-emitting diodes. Two host materials with or without a biphenyl linker between dibenzothiophene and carbazolylcarbazole are synthesized to get insight about the effect of aromatic linkers on the photophysical properties of the hosts and the device performances of a blue triplet emitter doped phosphorescent organic light-emitting diodes. It is described that the host design with dibenzothiophene and carbazolylcarbazole at 4-position of dibenzothiophene is effective for both high efficiency and improved lifetime. In particular, the new hosts improved the lifetime of the blue devices by more than five times while enhancing the quantum efficiency compared to a common triplet host.