X-ray photoelectron core level spectroscopy has been used to probe the buried metal (Au, Ag, Mg, Mg:Ag alloy)/AlQ3 interface structures from working organic light-emitting diodes. It is found that there is no chemical reaction between (Au,Ag)/AlQ3 interfaces, while there is a significant reaction/diffusion at (Mg,Mg:Ag)/AlQ3 interfaces. The reaction is AlQ3 oxidation-reduction reaction in nature, and is well explained by thermodynamic consideration of equivalent type of reaction. The reaction involves formation of MgO, metallic Al and fragmented hydroxyquinolines, gaseous N, and then followed by metallic Mg diffusion to the interface and metallic Al diffusion into the metal cathodes.
