Exploration into the Valence Band Structures of Organic Semiconductors by Angle-Resolved Photoelectron Spectroscopy

In this chapter, we describe technical essences and several example works of angle-resolved photoelectron spectroscopy (ARPES) that is a surface science methodology to map out the electronic band structures of the matters. Successful results of demonstrating the valence band dispersion relations of crystalline organic semiconductor materials are introduced, which were acquired through resolution of inherent “sample charging” problems in photoelectron spectroscopy techniques. The effective mass of the valence hole and intermolecular transfer integral values of van-der-Waals molecular solids were directly derived as fundamental physical properties regulating the charge carrier transport in these solids. In addition, recent ARPES works on novel interface electronic structures of organic semiconducting molecules in contact with “quantum wells” in nanometer-thick metal thin-films are also reviewed.