The current-voltage dependence of nominally undoped thin conjugated polymer films

The charge transport in conjugated polymer films sandwiched between metallic electrodes is described by means of a one-dimensional master equation where the hopping rates are given by thermally activated jumps over barriers separating trapping sites of same energy. An applied electric field along the chain reduces the barrier height leading to a field-dependent mobility, mu(E) similar to sinh(E)/E. We exactly derive the current-voltage characteristics of such a system assuming that the injected carriers generate space charge effects inside the polymer. We find an excellent agreement with the experimental data for different types of conjugated materials and compare our model with other models that predict exp(JE) for the field dependence of the mobility, discussing the essential differences between them. (C) 2000 American Institute of Physics. [S0003-6951(00)01131-1].