The Contribution of Energetic Disorder to Charge Transport in Molecularly Doped Polymers

Abstract

Energetic disorder plays a central role in many of the theories of charge transport in molecularly doped polymers, MDP. In these theories, energetic disorder determines the energy width of the hopping site manifold. It is generally assumed that the disorder-created energy width arises from interactions between the charge on a dopant molecule and its environment, including the dipole moments of neighboring dopant molecules, the dipole moments of the molecules of the polymer matrix, and van der Waals interactions with neighboring molecules. This assumption can be tested experimentally. Bassler's formulation of the Gaussian Disorder Model predicts that the energy width can be obtained from the temperature dependence of the mobility: it appears as an activation energy. A review of experimentally characterized MDP systems reveals that there is almost no experimental evidence to support the prediction that the experimentally observed activation energy is due to energetic disorder. Instead, the data appear to suggest that the activation energy is primarily intramolecular in origin.