Efficient LEDs with a conjugated co-polymer as the emissive layer

We report on the use of a new highly luminescent conjugated polymer as an emissive layer in single and multi-layer electroluminescence devices. 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 peaking at 506 nm (2.45 eV) in the green. Three different electroluminescence devices were fabricated: (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 [PVK] hole transport layer. All the devices utilised an ITO anode and a MgAg cathode. Electroluminescence external quantum efficiencies for these devices were found to be respectively up to 0.08%, 0.55% and 1% respectively, corresponding to luminous efficiencies of ≈ 0.5, ≈ 3 and ≈ 6 1m/W and power efficiencies of 8.5 × 10-5, 5.9 × 10-4 and 6.0 × 10-4 W/W. © 1998 Published by Elsevier Science B.V.