Enhanced Electroluminescent Efficiency Based on Functionalized Europium Complexes in Polymer Light-Emitting Diodes

Efficient red polymer light-emitting diodes are fabricated with the single active layer from the blends of poly(N-vinylcarbazole) (PVK) in the presence of 30wt.% electron-transporting compound 2-(4-biphenylyl)-5-(p-tert-butylphenyl)-1,3,4-oxadiazole (PBD) and europium complexes. The polyphenylene functionalized europium complex shows an enhanced electroluminescent efficiency due to the large site-isolation effect. For the polyphenylene functionalized europium complex, the maximum external quantum efficiency of 1.90% and luminous efficiency of 2.01cd A^-1 are achieved with emission peak at 612nm. The maximum brightness is more than 300cd m^-2.