Hierarchical charge carrier motion in conjugated polymers

Motion of photogenerated charge carriers in π-conjugated polymer films with different disorder and chain orientation and also in a blend of conducting and insulating polymers has been investigated by means of time-resolved electric field-induced second harmonic generation technique. Experimental results and Monte Carlo simulation enabled us to distinguish three time domains of charge transport. The charge carriers become separated by about 10 nm in a strong electric field within 1 ps. Subsequently, carriers drift another 10–15 nm on a picosecond time scale with a high mobility. The third and the slowest carrier motion phase is well described by the stochastic drift and determines the macroscopic equilibrium mobility. We attribute the two ultrafast drift phases to carrier motion inside a conjugated segment and along a single polymer chain, respectively, whilst the slow motion phase involves interchain jumps.