Bimolecular recombination in molecularly doped polymers

We have investigated the bimolecular recombination of holes and electrons in a typical hole-conducting molecularly doped polymer (DEH-doped polycarbonate). The method used is a variant of the time-of-flight technique with the bulk generation of charge carriers. A small signal regime has been used to extract parameters of the multiple trapping model with an exponential as well as the Gaussian trap distributions. Then, using a large signal regime with the generation rate increasing sequentially in a power of 10, we compared model predictions with experiment. It was found that the best agreement is achieved once the Langevin recombination coefficient is used, this being defined by the microscopic mobility featuring in the models. The relevance of this fact to the published data has been addressed as well. (C) 2013 Elsevier B.V. All rights reserved.