Electronic properties of C60 thin films

The electronic structure of polycrystalline C-60 thin films has been investigated using surface photovoltage spectroscopy (SPS) and conductivity measurements. The films show n-type semiconductivity with an activation energy of approximate to 0.8 eV as found from the temperature dependence of the conductivity at high temperatures. The electronic structure emerging from our SPS results comprises a 1.6 eV photo-conduction gap, a mobility gap of about 2.25 eV and two gap states, a donor and an acceptor, at 0.35 eV and (1.0-1.1) eV, respectively, below the photo-conduction edge. The results indicate the possibility of the existence of band tails, extending into the optical gap of these films, as well as other deep gap states.