The charge carrier mobility's activation energies and pre-factor dependence on dopant concentration in molecularly doped polymers

The elucidation of the charge transport mechanism in molecularly doped polymers MDP has been confused by disagreement on the role of disorder, which has led to disagreement on how to analyze the experimental mobility data. Plotting the mobility vs. T-1 or T-2 where T is temperature gives an Arrhenius activation energy or disorder energy respectively, which cannot be compared. A methodology is suggested to convert disorder energies into activation energies. This allows a compilation of a list of the activation energies of all MDP's which have been characterized as a function of dopant concentration and a correlation of the activation energies with material properties. In addition, it is argued that the intrinsic mobility in MDP's is activated with an activation energy that is independent of dopant concentration, and has a pre-factor which is exponential in rho, the calculated distance between dopant molecules, as expected for a hoping theory. The experimental observations of other behaviors, activation energies that depend on rho and pre-factors independent of rho, are attributed to either interactions among the dopant molecules or the failure of the lattice gas model to properly calculate rho at high dopant concentrations. (C) 2009 Elsevier B. V. All rights reserved.