ELECTROLUMINESCENCE FROM SINGLE-LAYER MOLECULARLY DOPED POLYMER-FILMS

Light emission from single layer thin film devices comprised of a hole transport polymer, poly(N-vinylcarbazole) (PVK) doped with 2-(4-biphenyl)-5-(t.-butyl-phenyl)-1,3,4-oxadiazole (Bu-PBD) and variety of emitter molecules is described. The single layer nature and the use of soluble materials simplifies the fabrication of devices by common solution coating techniques. The color of the emitted light can be tuned across the visible spectrum by using appropriate dyes. Evidence is presented that the luminance from any given device increases linearly with the current density and that the luminance observed from different devices is independent of the hole mobility. This shows that the critical determinant of the light output is the quality of the injecting contact or the number of injected carriers and not the speed with which the carriers migrate. Some criteria for tuning the emission color are presented.