XPS and sputtering study of the Alq(3)/electrode interfaces in organic light emitting diodes

The interface formed between tris(8-hydroxyquinoline) aluminum (Alq(3)) and electrodes (Al and ITO) of light emitting diodes was examined by X-ray pho toelectron spectroscopy (XPS). Upon deposition of aluminum layer, Alq(3) re acts partially with the metal, forming metallic carbide and/or Al-O-C compl ex in the interfacial region. On the Alq(3)/ITO side, no noticeable change in the spectra was observed. Analysis of the organic material/electrode int erface was also performed on the devices after several working cycles up to their complete destruction. Compared to non-degraded samples, the interfac e between Alq(3) and Al of degraded samples was modified by the diffusion o f indium from the ITO base electrode to the upper Alq(3)/Al interface and a luminum from the upper electrode to the Alq(3) layer. In the ITO/Alq(3) int erface, partial decomposition of the oxide layer occurred, leaving indium t o diffuse throughout the emitting layer. The structural changes of the cont act region is proposed to be one of the possible causes of the diode failur e. (C) 2001 Elsevier Science B.V. All rights reserved.