Correlation between host material compositions and performances in organic white-light-emitting diodes with blue/orange/blue emitting stacked structure

Quantum efficiency, driving voltage, color stability and recombination zone of organic white-light-emitting diodes (OWLEDs) with blue/orange/blue stacked emitting structure were correlated with host structure of emitting layer. A mixed host structure of 4,4′,4″-tris(N-carbazolyl)triphenylamine (TCTA) and 1,3,5-tris(N-phenylbenzimidazole-2-yl)benzene (TPBI) was used in orange emitting layer and host composition was critical to device performances of OWLEDs. TPBI host structure was better than other host structures in terms of quantum efficiency and color stability, while TCTA shows poor quantum efficiency in spite of good color stability. TCTA:TPBI mixed host structure showed better driving voltage than other host structures. In addition, recombination zone in blue/orange/blue stacked OWLEDs could be controlled by changing host structure in orange light-emitting layer. OWLEDs with TPBI host in orange emitting layer showed high quantum efficiency of 10.3% at 1000 cd/m² with little change of Commission international De L'Eclairage coordinates of (0.32, 0.34) from 100 cd/m² to 10,000 cd/m².