US Patent 7517595 Electroluminescent devices with mixed electron transport materials

An OLED device comprises a cathode, an anode, a light emitting layer, and on the cathode side of said emitting layer, a further layer, wherein the further layer is an electron-transporting layer containing:a) a first compound that has the lowest LUMO value of the compounds in the layer, the amount being greater than 40% by volume and less than 100% by volume of the layer; andb) at least one second compound that is a low voltage electron transport material, exhibiting a higher LUMO value than the first compound, the total amount of said compound(s) being less than 60% by volume and more than 0% by volume of the layer.