HOLE TRANSPORT IN POLY(STYRENE) DOPED WITH P-DIARYLAMINOSTILBENE MOLECULES

Hole mobilities have been measured in poly(styrene) (PS) doped with a series of p-diarylaminostilbene molecules (DAS) with different dipole moments. At room temperature, the mobilities vary by a factor of appro ximately 20, decreasing with increasing dipole moment. The results are described by a model based on disorder, due to Bassler and coworkers. The model is based on the argument that charge transport occurs by ho pping through a manifold of localized states that are distributed in e nergy. The key parameter of the model is the energy width of the hoppi ng site manifold. For DAS doped PS, the energy widths are between 0.09 2 and 0.107 eV, increasing with increasing dipole moment and increasin g DAS concentration. The width is described by a model based on dipola r disorder. According to the model, the width is comprised of a dipola r component and a van der Waals component. Describing the dipolar comp onent by the expression due to Young leads to the conclusion that the van der Waals component is 0.092 eV, and independent of the DAS concen tration. A comparison of these results with literature results for a w ide range of doped polymers suggests that differences in the van der W aals component is the principal reason for the very considerable diffe rences in mobility of these materials. (C) 1997 Elsevier Science S.A.