Multifunctional Optical Outcouplers for Efficient and Stable White OLEDs (Final Technical Report)
Replacing fluorescence by phosphorescence in OLED-based solid-state lighting can realize the Department of Energy’s efficiency target of 83% Internal Quantum Efficiency (IQE). The principal challenge, however, is to fix the poor stability of phosphorescent blue OLEDs. To address this, we have fabricated novel plasmonic architectures that improve device stability by decreasing the exciton lifetime of the emitters without drastically decreasing the light extraction efficiency. We describe the impact on stability of these structures in high efficiency blue phosphorescent OLEDs. Although the benefit is appreciable, we find that targeting ‘bright’ triplets on phosphorescent emitter molecules is an incomplete solution, and that it is also necessary to stabilize ‘dark’ triplets formed in the host and blocking layers. We demonstrate substantial improvements in stability using the latter approach, and conclude with a discussion of potential approaches to managing dark triplets in OLEDs.