Nitrocatechol/ZnO Interface: The Role of Dipole in a Dye/Metal-Oxide Model System

The electronic properties of a prototype system suitable for dye-sensitized solar cell applications are investigated both experimentally and theoretically by means of electron spectroscopies (high-resolution electron energy loss spectroscopy, HREELS, and ultraviolet and X-ray photoemission spectroscopies, UPS and XPS) and first-principles density functional theory (DFT)-based calculations. The comparison of HREELS and UPS data with the DFT results allows the microscopic description of electronic structure modifications upon interface formation, and provides a quantitative evaluation of the ionization energy and electron affinity changes induced by functionalization: these variations can be associated to the electric dipole of the functional species and, thus, to the formation of an interface dipole layer.