Color-tunable polymer light-emitting diodes with conjugated polymer homojunctions

Abstract

Color-tunable light-emitting diodes with a polymer homojunction structure have been demonstrated. The homojunction structure consisted of two emissive layers, and poly(9,9-dioctylfluorene) (PFO) was used as the host material in both emissive layers. One emissive layer was composed of a blend of blue-emitting PFO and its green-emitting copolymer, and the other one was composed of a blend of green-emitting PFO copolymer and red-emitting poly[2-methoxy-5(20-ethylhexyloxy)-1,4-phenylene vinylene] (MEHPPV). In device characterization, when the injection current was increased, partial electrons could easily pass through the second emissive layer and flow into the first emissive layer near the anode, because there was no potential barrier existing in the homojunction. Therefore, the emission color of our devices could be tuned as orange, yellow, white, and cyan by adjusting the injection current or bias voltage. © 2010 The Japan Society of Applied Physics.