Polarization Modulated-Infrared Reflectance Absorbance Spectroscopy Of Orientation And Binding Mode Of Pentafluorobenzyl Acid Modifiers On Indium Zinc Oxide

Abstract

Understanding the orientation of small organic acid modifiers on metal oxide electrodes is important in advancing the field of organic photovoltaics (OPVs). In this work, the orientation of a group of these small organic acid modifiers will be investigated on indium zinc oxide (IZO). Polarization modulation-infrared reflectance-absorbance spectroscopy (PM-IRRAS) is the primary technique used to determine these orientations. In order to determine orientations from PM-IRRAS data, other chemical and physical properties of the modifiers, such as density and surface coverage, must be experimentally determined. Neutral buoyancy is used to determine the density of the modifiers, while X-ray photoelectron spectroscopy (XPS) is used to estimate surface coverage of these modifiers on IZO. These techniques are also used to determine binding mode of these modifiers on IZO. The tilt angles (θ) were found to be 50 ± 3°, 64 ± 2°, and 43 ± 3° for F₅BnPA, F₅BnCA, and F₅BnHA, respectively, meaning that the phenyl ring in F₅BnHA is more perpendicular to the surface while the phenyl ring in F₅BnCA more parallel to the surface. All three modifiers were also found to bind to IZO in a bidentate manner. In contrast, F₅BnSA etches away significant portions of the IZO substrate.