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

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