Electronic Structure of Single Crystal $\alpha $-Perylene

In organic electronics, the highest estimated charge mobility in a device is typically achieved when the organic semiconductor is a single crystal. However, the measurement of the electronic and chemical structure of organic single crystals by photoemission lags far behind of the thin-film counterpart. The measurement challenge is due to two reasons: the insulating nature of the crystal surface and relatively small size of the crystals (millimeter to a few hundred micrometers). X-ray and ultraviolet-based photoemission measurements are achievable on single crystal $\alpha $-perylene with measurement assistance from a blue light emitting laser to enhance photoconductivity of the crystal surface. We are able to clearly resolve multiple highest molecular orbitals and determine the ionization energy of $\alpha $-perylene. We are able to obtain high-resolution C 1s spectrum which we can clearly distinguish contribution from carbon atoms in the two inequivalent sites and shake-up satellite features. Electronic ``band'' structure measurements of $\alpha $-perylene are realized using a novel angle-resolved time-of-flight electron spectrometer and the complete $\alpha $-perylene electronic structure and impact on electrical performance will be discussed.