Denghui Xu and Chihaya Adachi of the Center for Future Chemistry, Kyushu University, Fukuoka, Japan, have reported an OLED with a liquid host of 9-(2-ethylhexyl)carbazole (EHCz) doped with a guest emitter of 5,6,11,12-tetraphenylnapthacene, otherwise known as rubrene.

To date OLED displays have been made in the solid-state and have the advantage over liquid crystal displays of not requiring a back-light. As OLED is emissive it can be energy efficient and be made very thin. However, manufacturing infrastructure supports cost-efficient LCD manufacture over a large range of sizes while OLED displays have been kept to small size applications.

"Although OLEDs have mainly used complete solid-state organic thin films and partly liquid crystals, no attempt to examine neat liquid organic semiconductors has been reported, except some reports using polymer solutions and solution-phase electroluminescent devices," the authors state in the paper.

As well as being useful for flexible emissive displays liquid semiconductors could also be useful more generally to enhance the reliability and longevity of organic semiconductor systems such as FETs and solar cells.

The authors propose circulated-OLEDs in which the liquid organic semiconductor material is circulated or refilled into the active emitting layer so that fresh organic semiconductors can be supplied.

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