Effect of dipolar arrays on the localization of charge carriers in molecular materials

Abstract

Recent decades have seen a revival of the interest in studies of the transport and localization of charge carriers in molecular solids, stimulated by several current and emerging applications of these materials. Of particular interest to the matter of this paper is the situation when a molecular system consisting of nonpolar molecules is doped with polar guest species. In this case, permanent dipole moment of the dopant molecules modifies locally the polarization energy, the changes resulting in the appearance of local states in the vicinity of the dopant. Earlier calculations of the author demonstrated that the presence of dipoles in non-polar molecular lattices may result in creation of traps as deep as several tenths of an electronvolt. While the earlier papers considered the effect of isolated dipoles (thus reflecting the situation in nearly-perfect molecular crystals), this contribution will report on results of similar calculations performed on systems mimicking molecularly doped polymers and molecular glasses in which the concentration of dopants is so high that the dipoles cannot be treated as isolated.