Blue polymer electrophosphorescent devices with different electron-transporting oxadiazoles

We report that the performances of blue polymer electrophosphorescent devices are crucially depending on the choice of the electron transporting material incorporated into the emissive layer. Devices with 1,3-bis[(4-tert-butylphenyl)-1,3,4-oxidiazolyl]phenylene (OXD-7) doped at ∼40wt% into a poly(vinylcarbazole) matrix exhibited significantly higher efficiencies than those with 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD), yielding maximum luminous and power efficiency values of 18.2 Cd∕A and 8.8 lm∕W, respectively. Time resolved photoluminescence measurements revealed a long lifetime phosphorescence component in layers with PBD, which we assign to significant triplet harvesting by this electron-transporting component.