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

S. NEŠPŮREK1,* , P. TOMAN1, M. MENŠÍK1, I. KRATOCHVÍLOVÁ2, J. SWORAKOWSKI3, T. MALLOUK4

Affiliation

  1. Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Heyrovský Sq. 2, 162 06 Prague 6, Czech Republic
  2. Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, 182 21 Prague 8, Czech Republic
  3. Institute of Physical and Theoretical Chemistry, Wroclaw University of Technology, Wyb. Wyspianskiego 27, 50-370 Wroclaw, Poland
  4. Department of Chemistry, The Pennsylvania State University, University Park, PA 16802, U.S.A

Abstract

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..

Keywords

Charge transport, Molecular wire, Polaron, Charge mobility.

Submitted at: Nov. 28, 2006
Accepted at: Jan. 15, 2007

Citation

S. NEŠPŮREK, P. TOMAN, M. MENŠÍK, I. KRATOCHVÍLOVÁ, J. SWORAKOWSKI, T. MALLOUK, Charge transport in organic materials: From molecular wire to 3D systems, Journal of Optoelectronics and Advanced Materials Vol. 9, Iss. 1, pp. 134-140 (2007)