Bilayers of aluminum (Al) and alkali fluoride (such as sodium fluoride) are well-known top cathode contacts for organic light-emitting devices (OLEDs) in which the alkali fluoride is inserted in between the Al and organic materials. However, the configuration, to date, has never been successfully applied as bottom cathode contacts. In this article, we describe a novel bilayer bottom cathode contact for OLEDs utilizing the same materials but with a reversed structure, i.e. the Al rather than the alkali fluoride contacts the organic material. Electron-only devices were fabricated showing enhanced electron injection from this bottom contact with respect to an Al-only contact. Kelvin probe, X-ray photoelectron spectroscopy, Auger electron spectroscopy experiments and thermodynamic calculations suggest that the enhancement results from n-doping of the organic material by dissociated alkali metals.
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