Competitive emission process in mixed single layer top-emission organic light emitting device with reduced efficiency roll-off

The authors investigate efficiency roll-off in 5,6,11,12-tetraphenylnaphthacene (rubrene)-based mixed single layer top-emission organic light emitting devices by codoping with special additive dopants. The efficiency roll-off is suppressed after codoping rubrene with phenoxazone (Nile red). Due to dual nature of rubrene acting as electron hopping site and hole trap, it not only captures carrier producing light but also transfers energy to Nile red and then produces light. Meanwhile, Nile red molecules can also get energy from host directly. There exists a competitive process between three emission mechanisms, which depress self-quenching of dye molecules during emission, resulting in improved efficiency and lowered driving voltage. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3516159]