Highest-Occupied-Molecular-Orbital Band Dispersion of Rubrene Single Crystals as Observed by Angle-Resolved Ultraviolet Photoelectron Spectroscopy

The electronic structure of rubrene single crystals was studied by angle-resolved ultraviolet photoelectron spectroscopy. A clear energy dispersion of the highest occupied molecular orbital-derived band was observed, and the dispersion width was found to be 0.4 eV along the well-stacked direction. The effective mass of the holes was estimated to be 0.65(+/-0.1)m0. The present results suggest that the carrier conduction mechanism in rubrene single crystals can be described within the framework of band transport.