Comparison of Surface Modifications by Wet and Dry Methods on Indium Tin Oxide Using Self-Assembled Monolayers

Abstract

We developed a self-assembled monolayer (SAM) surface modification of an indium tin oxide (ITO; SnO2–In2O3) by a dry method for ink-jet printing processes and compared this with the SAM surface modifications by wet and dry methods. We focused on an analysis of the work function increase and changes in chemical bonding at the ITO surface interface with the SAM. In addition, we demonstrated that the causes of the work function increase of the ITO were the binding energy changes of the oxygen atoms on the ITO surface and an improvement in the hole injection from the ITO with the SAM to an organic layer in the organic device. The SAM surface modification decreased the threshold voltage and increased the current density in the organic device. These changes were due to the energy barrier caused by the work function difference being removed at the interface between the ITO with a high work function (5.3 to 5.5 eV) and the organic layer. Additionally, it was observed that the current density and luminance characteristics of the device were improved by the SAM surface modification. There was less organic solvent contamination at the interface between the ITO and the SAM by the dry method because no organic solvent was used.