Thermoactivated Electrical Conductivity in Perylene Diimide Nanofiber Materials

Thermoactivated electrical conductivity has been studied on nanofibers fabricated from the derivatives of perylene tetracarboxylic diimide (PTCDI) both in the dark and under visible light illumination. The activation energy obtained for the nanofibers fabricated from donor-acceptor (D-A) PTCDIs are higher than that for symmetric n-dodecyl substituted PTCDI. Such difference originates from the strong dependence of thermoactivated charge hopping on material disorder, which herein is dominated by the D-A charge-transfer and dipole-dipole interactions between stacked molecules. When the nanofibers were heated above the first phase transition temperature (around 85 °C), the activation energy was significantly increased because of the thermally enhanced polaronic effect. Moreover, charge carrier density can be increased in the D-A nanofibers under visible light illumination. Consistent with the theoretical models in the literature, the increased charge carrier density did cause decrease in the activation energy due to the up-shifting of Fermi level closer to the conduction band edge.