Systematic Investigation of Surface Modification by Organosiloxane Self-Assembled on Indium-Tin Oxide for Improved Hole Injection in Organic Light-Emitting Diodes

Various works on modification of the indium-tin oxide (ITO) substrate have been carried out so as to enhance hole injection in organic light-emitting devices. Herein, a simple and efficient approach to tuning the work function of the ITO substrate is described by surface modification of ITO with an organosiloxane self-assembled monolayer. The influences of the electronegativity on modification of the ITO substrate are systematically investigated by attaching electron-withdrawing groups (Cl, Br, and I) and an electron-donating group (NH2) to the organosiloxane materials. The preparation and modification of the ITO substrate has been studied using primarily atomic force microscopy and X-ray photoelectron spectroscopy and vacuum-ultraviolet spectroscopy, and remarkable changes have been observed after modification. The device based on a 3Cl-Si-ITO-modified anode exhibits the best efficiency among the devices, better than the control devices based on bare ITO, UV-treated ITO, and even Cl-ITO.