DIPOLE-MOMENTS, ENERGETIC DISORDER, AND CHARGE-TRANSPORT IN MOLECULARLY DOPED POLYMERS

The mobility of holes has been compared for polystyrene (PS) doped with tri-p-tolylamine (TTA) or a derivative with an ethyl propionate side group (ESTER). The mobility in ESTER+PS is smaller and more strongly dependent on temperature and electric field strength than the mobility in TTA+PS at the same molecular concentration. The difference between the two materials increases with increasing concentration, indicating that the cause is mainly an intermolecular interaction. Of several possible explanations, the most cogent is offered by the Gaussian disorder model [Bassler, H. Phys. Status Solidi B 1993, 175, 15]: The polar side group of ESTER increases the degree of energetic disorder, presumably via random charge-dipole interactions. At high concentrations, however, the dielectric constant of ESTER+PS is larger than that of TTA+PS, and the difference is large enough that the possible effects of dielectric polaron formation cannot be discounted a priori.