Hole transport in poly(styrene) doped with p-diarylaminostilbene molecules

Abstract

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 approximately 20, decreasing with increasing dipole moment. The results are described by a model based on disorder, due to Bässler and coworkers. The model is based on the argument that charge transport occurs by hopping through a manifold of localized states that are distributed in energy. The key parameter of the model is the energy width of the hopping site manifold. For DAS doped PS, the energy widths are between 0.092 and 0.107 eV, increasing with increasing dipole moment and increasing DAS concentration. The width is described by a model based on dipolar disorder. According to the model, the width is comprised of a dipolar component and a van der Waals component. Describing the dipolar component 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 concentration. A comparison of these results with literature results for a wide range of doped polymers suggests that differences in the van der Waals component is the principal reason for the very considerable differences in mobility of these materials.