Efficient white polymer light-emitting diodes (WPLEDs) based on double emitting layers of a PVK:Eu(iii)-complex and Alq₃

Colour-tunable polymer light-emitting diodes (PLEDs) were realized by tuning the concentration of an Eu³⁺-complex in the emitting-layer (EML) and the thickness of the hole-blocking BCP layer (BCP = 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline) in a double-emitting-layer (dEML) configuration. The dEML used PVK:complex 2 (PVK = poly(N-vinylcarbazole); H₂Salen = N,N′-bis(salicylidene)cyclohexane-1,2-diamine and HDBM = dibenzoylmethane for [Zn(Salen)(μ-OAc)Eu(DBM)₂] (2)) as EML1 and Alq₃ as EML2. The efficiencies (0.32-0.39 cd A^-1, 0.54-0.56% and 0.99-1.10 lm W^-1) were obtained from organo-Eu³⁺ incorporated WPLEDs with a complex-2-doping content of 20 or 30 wt% and 20 nm BCP thickness. The WPLEDs exhibited low turn-on voltage (6.0-7.5 V) and low efficiency-roll-off, which are advantageous to organo-Eu³⁺ doped WOLEDs.