Comparative study of bulk and interface transport in disordered fullerene films

The characterization of the charge carrier transport in disordered fullerene films, grown by physical vapor deposition, is important for organic electronics in order to improve carrier mobility and understand transport processes. In this contribution, the electron mobility in the bulk of the fullerene film and at the interface with dielectrics are compared. The bulk mobility is measured in diode structures using the Charge Extraction by Linearly Increasing Voltage (CELIV) technique, which allows a simultaneous study of the electric field, concentration and temperature dependence. The interface mobility is determined using organic field effect transistor (OFET) geometry. The electron mobility values are lower and the dependence on carrier density, field and temperature is stronger in diodes compared to OFETs. In both structures different temperature dependence of the mobility on the carrier concentration and on the electric field is obtained. The dependence shows Meyer-Neldel rule (MN-rule) behavior with similar MN temperatures and MN energies. Activation energy for electron transport plotted as a function of the square root of electric field is linear (Gill's law behavior), in accordance with Poole-Frenkel-type charge carrier transport