Green’s function approach for a dynamical study of transport in metal/organic/metal structures

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Abstract
We develop an efficient Green’s function formalism to study transport in organic tunneling devices. We find a crossover behavior of the transport from free-electron-like to polaronlike as the ratio between the electronic and organic lattice vibration time scales is varied. If the electronic time scale is fast compared to the lattice vibration time scale, the lattice motion lags behind the incoming wave packet and the transmission is similar to that in a static case where the lattice is frozen. In the opposite limit, the lattice follows the electron and the first transmission peak shifts from the conduction-band edge toward the self-trapped polaron level. We investigate the transmission coefficient, the transfer of energy between the incident electron and the lattice, and the time evolution of the electron energy distribution function as the ratio of these time scales is changed. To simulate lattice fluctuations we study a preexisting lattice distortion and find enhanced subgap transmission. Our results are important for understanding electrical injection in polymer light-emitting diodes and other organic-based electronic device structures, and electrical transport in molecular wires.