Intermolecular energy-band dispersion in PTCDA multilayers

Abstract

The electronic structure of a well-oriented perylene-3,4,9,10-tetracarboxylic acid-dianhydride multilayer prepared on ${\mathrm{MoS}}_2$ single crystal surface were studied by angle-resolved ultraviolet photoemission spectroscopy using synchrotron radiation. From the photon energy dependence of normal emission spectra, we observed an intermolecular energy-band dispersion of about 0.2 eV for the highest occupied molecular orbital (HOMO) band of single $\pi$ character. The observed energy-band dispersion showed a cosine curve, which originates from the intermolecular $\pi -\pi$ interaction. Analyses using the tight-binding model gave that the transfer integral of about 0.05 eV for the $\pi -\pi$ interaction, the effective mass of HOMO hole $m_h^{*}{=5.28m}_0,$ and the hole mobility ${\mu }_h>3.8\mathrm{}{\mathrm{cm}}^2/\mathrm{V}\mathrm{}\mathrm{s}.$ This is the first observation of the intermolecular energy-band dispersion of a conventional single-component organic semiconductor only with the weak intermolecular van der Waals interaction.