Work-function changes of treated indium-tin-oxide films for organic light-emitting diodes investigated using scanning surface-potential microscopy

Local surface work-function (WF) measurement on indium-tin-oxide (ITO) films prepared by different cleaning methods for use as anode materials in organic light-emitting diodes were studied using scanning surface-potential microscopy. The ITO WF changes with standard wet-cleaning treatment correspond directly to asperities on the film surface. The maximum difference value (MDV) in the local WF reached 0.41 eV. However, after wet-cleaning ITO with the ultraviolet ozone or O-plasma treatment, the WF distribution is more uniform than the original distribution. Owing to the sufficient ITO surface oxidization, the mean local WF value increases effectively to more than 5.00 eV and the MDV is less than 0.05 eV. Furthermore, the changes in roughness and conductivity on the ITO surface at different treatment times are also discussed. The proper exposure time for the O-plasma treatment can thereby be determined. (C) 2005 American Institute of Physics.