Improved Light Extraction in Organic Light-Emitting Diodes via Semiconductor Dilution

Increasing the internal light extraction efficiency of organic light-emitting diodes (OLEDs) is key to improving their performance for solid-state lighting applications; however, it is challenging to do this in a way that is compatible with high volume manufacturing. Here, it is shown that the outcoupling efficiency of OLEDs can be improved by diluting their hole transport layer (HTL) with the low refractive index material trifluoropropyl oligomeric silsesquioxane (F-POSS). Specifically, co-evaporating 40 vol.% F-POSS in the HTL of single and multi-stack phosphorescent OLEDs decreases its refractive index by Delta n approximate to 0.2, which in turn yields a approximate to 12% increase in their outcoupling efficiency with no impact on electrical performance or operational lifetime. This result is significant because F-POSS is a small molecule that sublimes cleanly, does not aggregate, and is compatible with state-of-the-art HTL materials, making it a realistic path to increase light extraction in commercial OLEDs manufactured on existing production lines. Co-evaporating a low refractive index small molecule in the hole transport layer of organic light-emitting diodes is shown to increase their light extraction efficiency without sacrificing electrical performance or operational lifetime.image