Electrical characteristics in unipolar conjugated polymer devices: the case of modified transport properties in the neighbourhood of the top electrode/polymer interface

We discuss charge transport in a conjugated polymer thin film device with t hermionic and tunnelling charge-carrier injection. We consider that the pol ymer transport properties along the polymer are position dependent, with th e charge-carrier mobility being smaller near the top electrode/polymer neig hbourhood. We also assume a charge density distribution that decreases expo nentially from this interface. At high applied voltages the electric field produced by the space charge induces a minimum of electric potential inside the polymer layer simulating an ohmic contact. We determine a parameter th at indicates how deep material properties are altered. The model fits exper imental data in the entire measured applied voltage interval permitting app arently anomalous charge transport characteristics to be understood. We als o discuss possible reasons for the position dependence of the electrical fe atures of the polymer layer in terms of the device fabrication process.