Efficient bottom cathodes for organic light-emitting devices

Bilayers of aluminum and an alkali fluoride are well-known top cathode contacts for organic light-emitting devices but have never been successfully applied as bottom contacts. We describe a bilayer bottom cathode contact for organic electronic devices based on reversing the well-known top cathode structure such that the aluminum, rather than the alkali fluoride, contacts the organic material. Electron-only devices were fabricated showing enhanced electron injection from this bottom contact. Kelvin probe, x-ray photoelectron spectroscopy experiments, and thermodynamic calculations suggest that the enhancement results from n doping of the organic material by dissociated alkali metals.