Bipolaron formation in organic semiconductors at the interface with dielectric gates

The formation of the electron-phonon induced bipolaron is shown to be feasible in organic semiconductors at the interface with dielectric gates due to the coupling of the carriers with interface vibrational modes and to the weak to intermediate strength of bulk electron-electron interaction. The polaronic bound states are found to be quite robust in a model with realistic strengths of electron coupling to both bulk and interface phonons. The crossover to nearly on-site bipolarons occurs for coupling values much smaller than those for nearly on-site polarons, but, on the other hand, it gives rise to an activated behavior of mobility with much larger activation energies. The results are discussed in connection with rubrene field-effect transistors.