Inorganic-metal composite cathodes boost performance of organic LEDs
A cathode structure based on composites of aluminum and cesium fluoride (Al:CsF), aluminum and lithium fluoride (Al:LiF), or aluminum and sodium fluoride (Al:NaF) greatly enhances the performance of organic light-emitting devices (OLEDs), according to Ghassan Jabbour and Nasser Peyghambarian at the University of Arizona (Tucson, AZ). In devices with the Al:LiF cathode, for example, green light was visible at 3 V; at 7 V, they showed forward light output of more than 830 cd/m2 and a quantum efficiency of about 1.4%. "At the same voltage, OLEDs with magnesium cathodes had a light output of only about 17 cd/m2 and 0.4% quantum efficiency, and OLEDs with aluminum cathodes did not show any light output." Jabbour said.
The data show for the first time that CsF, LiF, and NaF do not have to be in a buffer-layer form to provide efficient OLEDs based on an aluminum cathode, but that the use of inorganic-metal composite cathodes allows fabrication of efficient and bright OLEDs. Jabbour said that, at any given voltage, the forward light output and quantum efficiency were at least an order of magnitude higher in OLEDs with the composite cathode.