Time-dependent Langevin-type bimolecular charge carrier recombination in regiorandom poly(3-hexylthiophene)

We have studied transport and recombination of photogenerated charge carriers in thin films of regiorandom poly(3-hexylthiophene) (RRaPHT). Time-of-Flight studies show space charge perturbed current transients with a saturation of current level at high light intensities as a result of diffusion controlled Langevin-type bimolecular charge carrier recombination. We have been able to measure the time-dependent charge carrier mobility by using the carrier extraction by linearly increasing voltage technique. We found that the hole mobility follows a power law dependence over a few orders of magnitude in time as μ = μ0t−0.42. By using the carrier extraction by pulsed voltage technique we measured the photogenerated charge carrier concentration decay as a function of delay time and found that the decay can be fitted using a dispersive time-dependent bimolecular recombination coefficient governed by the time-dependent hole mobility.