Dissociation of bipolaron in non-degenerate polymer chain at high electric fields

We investigate the dynamics of bipolaron in non-degenerate polymer (e.g. PPV) in an external electric field by using a nonadiabatic evolution method, which allows transition between instantaneous electronic states. When the applied electric field exceeds a critical value, a bipolaron is found to dissociate like the case of polaron due to the lattice distortion not being able to follow the fast moving electrons. The critical value is estimated to be of order 106 V/cm. This result is consistent with experiment in that a large increase in current in PPV occurs at high fields. At a given electric field, the saturation velocity of bipolaron will decrease with the increase of non-degenerate parameters te.