|Greczmiel, M.; Pösch, P.; Schmidt, H.-W.; Strohriegl, P.; Buchwald, E.; Meier, M.; Rieß, W.; Schwoerer, M.: Polymer Light Emitting Diodes, Macromolecular Symposia, 102, 371-380 (1996) -- DOI: 10.1002/masy.19961020144|
Monolayer light emitting diodes from poly(1,4-phenylenevinylene) (PPV) usually exhibit relatively low quantum efficiencies. So the external efficiency of an ITO/PPV/Ca LED is typically 0.01%. In order to increase the quantum yield in bilayer devices, oxadiazole polymers have been used. The syntheses of a number of novel polymethacrylates with pendant oxadiazole groups and some aromatic polyethers with oxadiazole units in the main chain are described. These polymers with the electron withdrawing oxadiazole units facilitate electron injection and transport in bilayer LEDs with PPV as hole transport layer. Thus an LED with a top layer of the polyether 3a exhibits a tenfold increase of the external quantum efficiency to 0.1%. Compared to conventional PPV LEDs, the improved bilayer devices show intense emission at low current densities.