EFFECT OF POLAR ADDITIVES ON DIELECTRIC-PROPERTIES AND CHARGE-TRANSPORT IN A MOLECULARLY DOPED POLYMER - A TEST OF DIELECTRIC POLARIZATION MODELS

The mobility of holes in a molecularly doped polymer (tri-p-tolylamine doped polystyrene) is dramatically diminished by the presence of a few wt % of a highly polar additive (t-amylphthalonitrile, TAP). Thermal and dielectric data indicate that the TAP is molecularly dissolved and held rigidly by the matrix up to approximately the glass transition temperature (Tg). The dielectric constant increases with increasing TAP concentration to a degree that is small except above Tg. Two proposed mechanisms for the effect of a polar additive on charge-carrier mobility, involving enhanced dielectric polarization of the medium surrounding a charge carrier, are tested. The observed increases in dielectric constant in the presence of TAP are too small for these mechanisms to explain the large decreases in hole mobility and increases in its activation energy. © 1995 American Institute of Physics.