Photoconductivity in solid films of C60/70

Abstract We report photoeffects in the visible and near-infrared spectrum in submitted films of C 60/70 . The peak photoefficiency (photocarrier per absorbed photon) is ≈ 10 −4 . Since for wavelengths > 7000 A, absorption in C 60/70 films is very weak, carrier photoinjection from the electrodes into the conduction states of C 60/70 must be considered. Evidence, based on the energy level structure of C 60 films, is discussed which suggests this may not be the source of the photocurrents. Alternatively, the observed threshold may be photoconductive edge associated with the reported weak absorption due to forbidden transitions in the lowest direct bandgap, which recent calculations place at 1.5 eV.