Effect Of Electron-Phonon Interactions On Transport Properties In Organic Polymers

Most of the conjugated polymers have the quasi-one-dimensional structure with strongelectron-phonon interactions. Especially, the additional charge will induce lattice deformation,on the contrary, the lattice defect will have effect on the energy band structure of the organicsystem, which is fundamental important for the transport properties and photoluminescence ofconjugated polymers. Based on the tight-binding SSH model and nonadiabatic moleculardynamic method, we have investigated the effect of electron-phonon interactions on thecarrier transport properties in the sandwiched structures of open system.First, comparison between the non-adiabatic molecular dynamics and non-equilibriumGreen’s function was made, which is shown the feasibility and correctness of the moleculardynamics. Then, we investigated the effect of electron-phonon interactions on I-V propertiesof molecular devices in steady state by the molecular dynamics. It is shown that the transportcurrent reduced with the increase of the electron-phonon interactions. The electron-phononinteractions reflected the lattice scattering of electrons. As the electron-phonon interactionsincreased, the lattice scattering of electrons increased, electrons were no easily transmittedand the transport current decreased. With the Fermi level of the electrode gradually closing tothe resonance level, the influence of electron-phonon coupling on current became larger andthe greatest impact occurs when the Fermi level equals the resonance energy level.Meanwhile, we also found that the current platform appeared with the increasing of the lengthof the organic molecules. The introduction of electron-phonon coupling leads to the fall of thecurrent platform, which makes the transport current to be level trends more obviously.Moreover, the effect of the lattice distortion, by the electron-phonon coupling caused, onthe carrier transport properties has been investigated, when the system reached any transientstate. The results show that, with the introduction of electron-phonon coupling, the structureof lattice atomic was changed and the transport current fluctuated. As the electron-phononinteractions increased, the amplitude increased. Accordingly, the energy of lattice atomsoscillated and the amplitude increased with the electron-phonon interactions increased. Withthe variation curve of the transport current and the energy of lattice atoms, we know that the approximately uniformed lattice structure is similar to the metal structure, and because of thesmall energy gap, the electron can easily transmit through the organic molecular layer, so thetransport current is comparatively large. The dimerization makes the energy gap larger, so theelectron can’t easily transmit through the organic molecular layer and transport current iscomparatively smaller.