Surface Modification of Indium–Tin Oxide with Functionalized Perylene Diimides: Characterization of Orientation, Electron-Transfer Kinetics and Electronic Structure

Abstract

Charge-transfer efficiency at the active layer/transparent conducting oxide (TCO) interface is thought to be a key parameter contributing to the overall efficiency of organic electronic devices such as organic photovoltaics (OPVs). Modification of the TCO surface with a redox-active surface modifier is a possible approach toward enhancing OPV efficiency by providing an efficient charge-transfer pathway between either hole- or electron-harvesting contacts and the organic active layer. Here we report on the modification of indium–tin oxide (ITO) electrodes with two perylene diimides (PDIs), coupled to phosphonic acid (PA) binding groups through a p-phenylene bridge or a biphenyl-4,4′-diyl bridge (PDI–phenyl–PA and PDI–diphenyl–PA, respectively). We used two different deposition techniques: adsorption from solution (SA) and spin coating (SC), to create three types of monolayer films on ITO: SA PDI–phenyl–PA, SA PDI–diphenyl–PA, and SC PDI–phenyl–PA. These thin films, designed to act as “charge-transfer media...