Trap origin of field-dependent mobility of the carrier transport in organic layers

In the measurements of space-charge limited current (SCLC) transport in disordered organic semiconductors, it is often observed that carrier mobility depends on bias voltage. Two continuous models have been applied for the description of this dependence. One interpretation assumes the charge carrier mobility dependent on the local electrical field. In the other one, the mobility at the transport state is affected by the trapping–detrapping dynamics of an exponential distribution of localized states (traps) in the band-gap. Analysing the frequency dependent capacitance and conductance (corresponding to measurements of impedance spectroscopy, IS), we demonstrate that the apparent field-dependent mobility found in experiments can be interpreted in terms of the multiple trapping approach.