Studies of Alq/Mg: Ag Interface in Organic Light-Emitting Diodes by XPS

The organic/cathode interface plays an important role in device degradation of organic light-emitting diodes (OLEDs). The interface between 8-hydroxyquinolino aluminium (Alq) and Mg:Ag cathode in OLEDs, operated for some time, was characterized using Xray photoemission spectroscopy (XPS). An in-vacuum peel-off method was used to separate the buried interfaces. XPS results indicate that Alq molecules break down, resulting in formation of fragmented hydroxyquinolino, Mg oxides, and metallic Al at the interface. It is also found by XPS depth-profiling measurement that metallic Al diffuses into the cathode electrode, and that the fraction of oxidized Mg decreases gradually from the interface but extended very deep into the cathode.