Multilayer Polymer Light-emitting Diodes for Solid State Lighting Applications
Multilayer polymer light-emitting diodes (PLEDs) are demonstrated using semiconducting polymers blended with organometallic emitters as the emissive layer and one or both of an electron transport layer and a hole transparent layer on the appropriate electron injection and hole injection sides of the emissive layer. The transport layers reduce energy potential gaps between the hole injection electrode and the emissive polymer and between the electron injection electrode and the emissive polymer. A solvent-processing based procedure for preparing these devices is also disclosed It uses nonpolar solvent-based solutions of emissive polymers to form the emissive layer and polar solvent-based solutions to form the transport layers to minimize etching and other undesirable interactions as the multiple layers are being laid down. Illumination quality white light can be obtained with stable Commission Internationale de l'Eclairage coordinates, stable color temperatures, and stable color rendering indices, all close to those of “pure” white light. These multilayer white light-emitting PLEDs are useful as backlights for liquid crystal displays and for solid state lighting applications.