Polymer light emission: control of properties through chemical structure and morphology

We report on recent work concerning polymers for improved electron injection and transport, for enhanced photoluminescence quantum efficiency and for polarised emission. A new blue-emitting triazole containing co-polymer with high photoluminescence efficiency is described. This polymer acts to enhance the electroluminescence efficiency when used in two layer devices with poly(p-phenylene-vinylene) [PPV] as a hole transporting emitter. The two layer device has an external quantum efficiency of approximate to 0.08% at a luminance of 250 cd/m(2) for a current density of 100 mA/cm(2). Use of a meta-phenylene-vinylene conjugation interrupting unit as a means of enhancing photoluminescence quantum efficiency is also described. The resulting co-polymer allows fabrication of three layer devices that have an external efficiency of approximate to 1% at a luminance of 96 cd/m(2) for a current density of 3.7 mA/cm(2). Finally, we report on the orientation of a polyfluorene conjugated polymer via alignment of its liquid crystal phase on rubbed substrates. Thermotropic liquid crystal phases offer an approach to polarised electroluminescence emission and we discuss the merits of this and various other approaches. (C) 1998 Elsevier Science B.V.