A lithium carboxylate ultrathin film on an aluminum cathode for enhanced electron injection in organic electroluminescent devices

The effects of new insulating materials of lithium fluoride and lithium carboxylates at an aluminum cathodic interface on the performance of organic electroluminescent (EL) devices are described. Three different cathode interface materials are used: lithium salts of fluoride, acetate, and benzoate. We compare the current density-voltage (I-V) and the luminance-voltage (L-V) characteristics of the devices with Al/lithium carboxylates with those of the devices with Al/LiF or an Al cathode. We find that the bilayer cathodes with lithium carboxylates exhibit better device performance than the cathodes with LIF or the Al cathode itselt. In particular, the device with lithium benzoate gives the best performance of all the devices studied. The improvements are attributed to the lowering in work function of the cathode due to lithium metal formation by the higher reactivity of lithium carboxylates than LiF. with hot Al atoms impinging on these insulating materials.