Surface treatment of indium-tin-oxide substrates and its effects on initial nucleation processes of diamine films

The effects of several surface treatment techniques for indium-tin-oxide (ITO) substrates on the surface properties and the initial nucleation processes of trisphenyldiamine (TPD) have been investigated. Mechanical rubbing, HCl treatment, and O-2-plasma irradiation smoothen the ITO surface and enhance the cohesion of TPD molecules. As-received ITO surfaces promote amorphous structure of the TPD molecules; this results in effective carrier transport, but the substrate surface is too rough on a molecular scale for the fabrication of very thin (e.g., less than or equal to 200 Angstrom) layered structures. Layer-by-layer amorphous nucleation on flat surfaces is a key technology for the fabrication of future organic electroluminescence (EL) device structures with very thin constituent layers. O-2-plasma treatment reduces the potential barrier for hole injection from ITO to TPD with moderate cohesion of TPD molecules, and results in brighter EL devices than those on as-received ITO substrates.