Ambipolar charge transport in organic field-effect transistors

A model describing charge transport in disordered ambipolar organic field-effect transistors is presented. The basis of this model is the variable-range hopping in an exponential density of states developed for disordered unipolar organic transistors. We show that the model can be used to calculate all regimes in unipolar as well as ambipolar organic transistors, by applying it to experimental data obtained from ambipolar organic transistors based on a narrow-gap organic molecule. The threshold voltage was determined independently from metal insulator semiconductor diode measurements. An excellent agreement between theory and experiment is observed over a wide range of biasing regimes and temperatures.