Dynamical study of impurity effects on bipolaron-bipolaron and bipolaron-polaron scattering in conjugated polymers.

Combining the one-dimensional tight-binding Su-Schrieffer-Heeger (SSH) model and the extended Hubbard model (EHM), the scattering of two oppositely charged bipolarons and a bipolaron-polaron pair is investigated under the influence of impurity effects using a nonadiabatic evolution method. These novel results for bipolarons show that the oppositely charged quasi-particles scatter into a mixed state composed of bipolarons and excitons. The excitation yield depends sensitively on the strength of the applied electric field. In the presence of an impurity, the critical electric field regime for formation of a state composed by bipolarons and excitons is increased. Additionally, we were able to obtain critical values of electric fields that played the role of drastically modifying the system dynamics. These facts suggest that the scattering between bipolarons and a bipolaron-polaron pair in the presence of impurities is crucial for the understanding of electroluminescence in optoelectronics devices, such as polymer light emitting diodes.