Temperature dependence of charge carrier creation in poly(p-phenylene vinylene) [PPV]

The photocurrent decays measured in poly(p-phenylene vinylene) [PPV] from r oom temperature (RT) down to 77 K in the presence of air traces have been s tudied. We have observed long-lived decays, between RT and similar to 200 K , which can be fitted to the well known Kohlrausch's law: i(p)(t) = i(p)(0) exp-(t/tau)(beta) characteristic of dispersive transport. A detailed tempe rature dependence study has been carried our to investigate the behavior of the exponent beta and the relaxation time tau in order to understand the o rigin of the observed complex transport mechanism. At lower temperature, es pecially below 160 K, a fast component is detected alone, where the slow on e is frozen. The associated interpretation is based on a recent work of sim ulated yield of geminate pair dissociation in an energetically random disor der. Modulated experiments show that both components are superimposed at en ough high temperature. In our model, the long-lived contribution is interpr eted as being extrinsic due to dissociation of polaron pairs assisted by el ectronegative defects and the fast one as being intrinsic due to dissociati on of excitons assisted by the intrinsic energetic disorder, created by the distribution of conjugation length in PPV.