Design of bicarbazole type host materials for long-term stability in blue phosphorescent organic light-emitting diodes

Two bicarbazole type host materials, 9-(dibenzo [b,d]thiophen-4-yl)-9ʹ-phenyl-9H,9′H-3,3ʹ-bicarbazole (DBTBCz) and 9,9ʹ-bis(dibenzo [b,d]thiophen-4-yl)-9H,9′H-3,3ʹ-bicarbazole (DDBTBCz), were developed as lifetime enhancing host materials for blue phosphorescent organic light-emitting diodes (PhOLEDs). The DBTBCz and DDBTBCz host materials were prepared by substituting one or two dibenzothiophene units to a 3,3ʹ-bicarbazole backbone structure for the purpose of improving thermal stability and rigidity of the host materials for stable operational lifetime. Device characterization of the host materials revealed that the dibenzothiophene modification via 4- position is better than that via 2- position for improved lifetime of blue PhOLEDs.