XPS investigation of electrode/polymer interfaces of relevance to the phenylene vinylene polymer-based LEDs

X-ray photoelectron spectroscopy (XPS) was employed for the study of the ph ysicochemical interactions at electrode/polymer interfaces involving metals of high and low work functions and thin films of poly(p-phenylene vinylene ) (PPV) and poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene] vinylene (M EH-PPV), The changes in the C Is core-level line shape of the polymers, the evolution of the metal core-level spectra and the changes in chemical comp ositions at the interfaces involving polymer coated on indium-tin oxide (IT O), sputtered ITO on polymer, and in situ evaporated magnesium (Mg) on poly mer were carefully monitored. Indium of the ITO in both the ITO/polymer and polymer/ITO assemblies was found to diffuse towards the polymer at the int erface. Oxygen migration was also observed at the ITO/polymer interfaces, T he results obtained from in situ analysis by angle-resolved XPS of the inte ractions between thermally evaporated Mg and PPV and Mg and MEH-PPV indicat ed the formation of an interfacial layer in each case. The surface diffusio n of adsorbed oxygen from the bulk of the conjugated polymer film played a dominant role in the interfacial reactions. The interfacial layer consisted of Mg oxides, Mg clusters, Mg metal and Mg-polymer complexes. Copyright (C ) 2000 John Wiley & Sons, Ltd.