We have investigated the effect of small amounts of a highly polar additive, t‐amylphthalonitrile (TAP), on the mobility of holes in polystyrene doped with tri‐p‐tolylamine. The mobility decreases rapidly and becomes more steeply dependent on electric field strength and temperature as the concentration of TAP is increased. The experimental results are compared with two current models. A ‘‘dipolar trap’’ model fails to reproduce the observed dependence of the mobility on TAP concentration. The Gaussian disorder model of Bässler and co‐workers [Phys. Status Solidi 175, 15 (1993)] can fit the dependencies on field strength and temperature at each concentration, but the concentration dependencies of the fitting parameters are problematic.
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