Efficient multilayer electroluminescence devices with poly(m-phenylenevinylene-co-2,5-dioctyloxy-p-phenylenevinylene) as the emissive layer

The use of a new highly luminescent conjugated polymer as an emissive layer in single and multilayer electroluminescence devices is reported. Poly(⁠$m$-phenylenevinylene-co-2,5 -dioctyloxy-$p$-phenylenevinylene) [PmPV-co-DOctOPV] was prepared via a Wittig synthesis reaction. The resulting polymer has a high photoluminescence quantum efficiency in the solid state with an emission spectrum peaked at 506 nm (2.45 eV) in the green. Electroluminescence devices were fabricated with an ITO anode and a MgAg cathode. Three different structures were studied: (i) single layer devices containing only PmPV-co-DOctOPV; (ii) double layer devices with PmPV-co-DOctOPV and an evaporated film of 1,3-bis(4-tert-butylphenyl-1,3,4-oxadiazoyl) phenylene [OXD-7] as an electron transport layer; (iii) triple layer devices containing PmPV-co-DOctOPV, OXD-7 and in addition a polyvinylcarbazole hole transport layer. Electroluminescence external quantum efficiencies for these devices were found to be up to 0.08%, 0.55%, and 1%, respectively, corresponding to luminous efficiencies of $≈0.5,$ $≈3,$ and $≈6 lm/W$ and power efficiencies of $8.5×10−5,$ $5.9×10−4,$ and $6.0×10−4 W/W.$