Engineering host materials for high efficiency and long operational lifetime in blue phosphorescent organic light-emitting diodes

Two host materials for blue phosphorescent organic light emitting diodes (PhOLEDs) were developed to exhibit high external quantum efficiency (EQE) and long device lifetime, By substituting strong electron deficient CN moiety in different positions, the highest occupied molecular orbital and the lowest unoccupied molecular orbital energy levels were controlled. Although the CN substitution position is different between the two hosts, both of the host materials showed high triplet energy of 2.98 eV. The CN modification in dibenzothiophene was effective to improve electron injection and high EQE. The new host materials also showed long device operational lifetime when CN modified phenylimidazole ligand based blue phosphorescent emitter was used as a blue triplet emitter.