High triplet energy exciplex host derived from a CN modified carbazole based n-type host for improved efficiency and lifetime in blue phosphorescent organic light-emitting diodes

High triplet energy exciplexes which can improve the lifetime of blue phosphorescent organic light-emitting diodes were developed by mixing a carbazole based hole transport type host with a CN modified carbazole based electron transport type host. The electron transport type host was designed to have an electron withdrawing CN functional unit at the central core and CN substituted carbazole for electron transport properties. The mixing of the two hosts generated an exciplex which has a high triplet energy of 2.94 eV and singlet energy of 3.30 eV. The exciplex host realized a high external quantum efficiency of 18.8% and extended the lifetime by more than 1.8 times in blue phosphorescent organic light-emitting diodes.