Enhanced pure red electroluminescence intensity of Eu(o-BBA)3(phen) by red dye co-doping and inorganic semiconductor as charge carrier function layer

Abstract

There is an emission peak at 494nm in the electroluminescence (EL) of PVK [poly(n-vinylcarbazole)]: Eu(o-BBA)3(phen) besides PVK exciton emission and Eu3+ characteristic emissions. Both the peaking at 494nm emission and PVK emission influenced the color purity of red emission from Eu(o-BBA)3(phen). In order to restrain these emissions and obtain high intensity red emission, 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7,-tetramethyljulolidy-9-enyl)-4Hpyran (DCJTB) and Eu(o-BBA)3(phen) were co-doped in PVK solution and used as the active emission layer. The EL intensity of co-doped devices reached to 420cd/m2 at 20V driving voltage. The chromaticity coordinates of EL was invariable (x=0.55, y=0.36) with the increase of driving voltage. For further improvement of EL intensity, organic–inorganic hybrid devices (ITO/active emission layer/ZnS/Al) were fabricated. The EL intensity was increased by a factor of 2.5 [(420cd/m2)/(168cd/m2)] when the Eu complex was doped with an efficient dye DCJTB, and by a factor of ≈4 [(650cd/m2)/(168cd/m2)] when in addition ZnS layer was deposited on such an emitting layer prior to evaporation of the Al cathode.