Activation Energies and Diffusion Coefficients of Polarons and Bipolarons in Organic Conductors

Intrachain diffusion of charge carriers in organic conductors is analyzed. Using a tight-binding model Hamiltonian that includes strong electron-phonon coupling combined with a Langevin equation, we simulate both polaron and bipolaron dynamics under quantum-corrected thermal effects. Nonadiabatic molecular time evolution is used to determine how these quasiparticles diffuse through a nondegenerate conjugated polymer. By means of a phenomenological approach, we evaluate the diffusion coefficient and activation energies for the motion of both polarons and bipolarons. The analysis of activation energies, in agreement with available experimental data, suggests that the presence of bipolarons may inhibit the efficiency of organic-based devices. The results presented here point to the importance of taking a closer look at the effects of bipolaron dynamics in organic devices.