Ultraviolet photoelectron spectroscopy (UPS) I: Band dispersion measurements of "insulating" organic single crystals

Operation mechanisms and efficiencies of organic electronic devices are principally dominated by the electronic structures of organic semiconductor solids via charge carrier behaviors inside the active materials of the devices; that is the band dispersion for high-mobility crystalline materials being desirable to e.g. organic field effect transistor application. Angle-resolved ultraviolet photoelectron spectroscopy (ARUPS) is one of the most direct and sophisticated techniques to access the valence band of the matters. Several essential physical properties, the effective mass of transport hole and intermolecular transfer integral, in direct relevance to the charge carrier mobility are accessible through accurate analyses of the ARUPS results. In this chapter, we describe technical essences of this methodology and introduce several examples of successful demonstrations of the valence band structures of crystalline organic semiconducting materials.