POLYMER LIGHT-EMISSION - CONTROL OF PROPERTIES THROUGH CHEMICAL-STRUCTURE AND MORPHOLOGY

We report on recent work concerning polymers for improved electron inj ection and transport, for enhanced photoluminescence quantum efficienc y and for polarised emission. A new blue-emitting triazole containing co-polymer with high photoluminescence efficiency is described. This p olymer acts to enhance the electroluminescence efficiency when used in two layer devices with poly(p-phenylene-vinylene) [PPV] as a hole tra nsporting emitter. The two layer device has an external quantum effici ency of approximate to 0.08% at a luminance of 250 cd/m(2) for a curre nt density of 100 mA/cm(2). Use of a meta-phenylene-vinylene conjugati on interrupting unit as a means of enhancing photoluminescence quantum efficiency is also described. The resulting co-polymer allows fabrica tion of three layer devices that have an external efficiency of approx imate 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 conj ugated polymer via alignment of its liquid crystal phase on rubbed sub strates. Thermotropic liquid crystal phases offer an approach to polar ised electroluminescence emission and we discuss the merits of this an d various other approaches. (C) 1998 Elsevier Science B.V.