Langevin recombination and space-charge-perturbed current transients in regiorandom poly(3-hexylthiophene) -: art. no. 125205

We have studied photogenerated charge carrier transport and recombination in thick films of regiorandom poly (3-hexylthiophene) by using the current mode time-of-flight technique. We measured the extracted charge as a function of light intensity and applied voltage, and found that for α d&MGT; 1 it saturates at a value that can be stored on the contacts Q(e)=CUo as expected for diffusion controlled bimolecular recombination, i.e., Langevin recombination. As a consequence we can only measure space charge perturbed current transients. We measured a field-dependent hole mobility of the order of 10(-5) cm(2)/V s, which extrapolated to zero field determines the Langevin bimolecular recombination coefficient 4 x 10(-12) cm(3)/s.