XPS and sputtering study of the Alq3/electrode interfaces in organic light emitting diodes

The interface formed between tris(8-hydroxyquinoline) aluminum (Alq3) and electrodes (Al and ITO) of light emitting diodes was examined by X-ray photoelectron spectroscopy (XPS). Upon deposition of aluminum layer, Alq3 reacts partially with the metal, forming metallic carbide and/or Al±O±C complex in the interfacial region. On the Alq3/ITO side, no noticeable change in the spectra was observed. Analysis of the organic material/electrode interface was also performed on the devices after several working cycles up to their complete destruction. Compared to non-degraded samples, the interface between Alq3 and Al of degraded samples was modi®ed by the diffusion of indium from the ITO base electrode to the upper Alq3/Al interface and aluminum from the upper electrode to the Alq3 layer. In the ITO/Alq3 interface, partial decomposition of the oxide layer occurred, leaving indium to diffuse throughout the emitting layer. The structural changes of the contact region is proposed to be one of the possible causes of the diode failure. # 2001 Elsevier Science B.V. All rights reserved