Dynamical study of polaron-bipolaron scattering in conjugated polymers

We simulate the scattering processes between a negative polaron and a positive bipolaron in a conjugated polymer chain using mixed quantum classical molecular dynamics. The simulations are performed based on the Su-Schrieffer-Heeger (SSH) model modified to include electron-electron interactions, a Brazovskii-Kirova symmetry-breaking term, and an external electric field. It is found that there exist a critical electric field, below which the polaron and bipolaron can scatter into an excited polaron. If the external electric field is higher than the critical electric field, the polaron and bipolaron will pass through each other and continue moving as isolated ones. Because the excited polaron can decay to the polaron state through emitting a photon, our results indicate that the interactions between polarons and bipolarons can open a channel for electroluminescence.