Electric-field effects on the competition between polarons and bipolarons in conjugated polymers

The charge transport on a single conducting polymer chain is investigated. The dynamics of polarons and bipolarons is numerically studied using the Su -Schrieffer-Heeger model combined with the Pariser-Parr-Pople model extende d to include an external electric field and a Brazovskii-Kirova symmetry br eaking interaction. The time-dependent unrestricted Hartree-Fock approximat ion is used. It is found that dynamical effects do not reverse the stabilit y relation between polarons and bipolarons. On the other hand, as the elect ric held intensity gets stronger the moving polarons structure is blurred ( destroyed) faster than the structure of moving bipolarons. This effect is r educed with increasing doping concentration. Therefore, it is shown within the present model that the applied external electric field as well as the d oping concentration are fundamental in determining the relative prevalence of polarons or bipolarons.