Correlation of the molecular structure of host materials with lifetime and efficiency of blue phosphorescent organic light-emitting diodes

Bicarbazole derivatives, 9,9′-bis(dibenzo[b,d]thiophen-2-yl)-9H,9′H-3,3′-bicarbazole (BCzDBT), 9,9′-bis(dibenzo[b,d]furan-2-yl)-9H,9′H-3,3′-bicarbazole (BCzDBF), and 9,9′-di([1,1′-biphenyl]-3-yl)-9H,9′H-3,3′-bicarbazole (BCzBP), were designed and examined as the hole transport type host materials of the tris[1-(2,4-diisopropyldibenzo[b,d]furan-3-yl)-2-phenylimidazole] (Ir(dbi)₃) blue triplet emitter. BCzDBT performed better than BCzDBF and BCzBP as the hosts of Ir(dbi)₃ and could demonstrate 24.8% quantum efficiency and long lifetime in the blue phosphorescent devices. Strong hole carrying properties of the bicarbazole derivatives were proposed as the main factors for the high quantum efficiency of the BCzDBT devices, and thermal and chemical stability of BCzDBT were suggested as crucial factors for the long lifetime of the BCzDBT devices.