Efficient light emitting diodes from polyfluorene copolymer blends

Highly efficient light emitting diodes were obtained by blending blue-emitting poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-co-(N,N′-diphenyl)-N,N-di(p-butyl-oxyphenyl)-1,4-diaminobenzene] (I) with green-emitting poly[(9,9-dioctyl-2,7-divinylene-fluorenylene)-alt-co-{2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene}] (II). Only green emission was obtained from the films of polymer blends and from corresponding double-layer LEDs, indicating an almost complete Förster energy transfer from I to II. These devices show enhanced external quantum efficiency, higher brightness and lower turn on voltages. Luminance and efficiency of 2.6 × 104 cd/m2 and 2.55%, respectively, were obtained.