Effect of a Broad Recombination Zone with a Triple-Emitting Layer on the Efficiency of Blue Phosphorescent Organic Light-Emitting Diodes

Abstract

The device characteristics of blue phosphorescent organic light-emitting diodes (PHOLEDs) with a broad recombination region within emitting layers (EMLs) were investigated by changing the combination and the composition of the host materials. Six types of devices were fabricated with the novel host material 9-(4-(triphenylsilyl)phenyl)-9H-carbazole, hole transport-type host material N,N'-dicarbazolyl-3,5-benzene, and electron transport-type host material 2,2',2"-(1,3,5-benzenetriyl)tris-[1-phenyl-1H-benzimidazole] as diverse EML, structures. Balanced charge-carrier injection and a distributed recombination zone within EMLs were achieved through a triple-emitting layer (T-EML). The properties of a device with a T-EML using a stepwise structure without any mixed host system were found to be superior to the other PHOLEDs. This can be explained in terms of improved charge balance and triplet-exciton confinement within the broad recombination region.