High efficiency and low driving voltage blue/white electrophosphorescence enabled by the synergistic combination of singlet and triplet energy of bicarbazole derivatives

New host materials (BCz-DBT and BCz-DBF) are synthesized by regrouped 3,3-bicarbazole (BCz) and dibenzothiophene (DBT)/dibenzofuran (DBF). Their thermal, electrochemical, electronic absorption and photoluminescent properties are also carefully investigated. The materials exhibit high glass transition temperatures (T-g) of 134 degrees C and 139 degrees C, respectively. This kind of molecular design can effectively achieve high triplet energies and suitable highest occupied molecular orbital and lowest unoccupied molecular orbital (HOMO/LUMO) energy levels. High external quantum efficiencies (EQE) of sky blue (EQE = 25%) and three-color white (EQE = 21.4%) phosphorescent OLEDs have been achieved by using BCz-DBF as the host material. (C) 2015 Elsevier B.V. All rights reserved.