Charge transport in organic materials: From molecular wire to 3D systems

The main limitation on the charge carrier mobility in polymer-based molecular wires follows from polaron formation and the dispersion of transfer integrals among the monomer units. The electrical current passing through a single molecule is influenced by charge tunnelling - the Fowler-Nordheim model seems to be a good approximation for the description of charge transport. The presence of dipolar species results in a mobility decrease, due to the increase of the transfer integral dispersion. Polar groups, chemically attached to the molecular wire, can causeorbital localization. The charge transport in 3D samples can be described by the theory of disordered polarons, which postulates that the activation energy of the charge carrier mobility is composed of contributions both from the dynamic disorder, i.e. the polaronic barrier, and from the static disorder, i.e. the variation of the energy of transport states as a result of the environment. The main contribution to the polaron binding energy results from molecular deformation; the electron-phonon term makes only a 5 % contribution. Dipolar additives make the distribution of hopping states broadened and new localized states for charge carriers are formed which results in a reduction of the charge mobility.