THE EFFECT OF DOPANT CONCENTRATION ON THE MOBILITY OF A TRIPHENYLMETHANE DOPED POLYMER

Hole mobilities have been measured in poly(styrene) (PS) doped with bi s(4-N,N-diethylamino-2-methylphenyl) (4-4-methoxyphenyl) methane (TPM) . TPM is a weakly polar donor molecule with a dipole moment of 2.1 D. The results are described by a formalism based on disorder. The formal ism is based on the assumption that charge transport occurs by hopping through a manifold of localized states with superimposed energetic an d positional disorder. The parameters of the formalism are sigma, the energy width of the hopping site manifold, Sigma the degree of positio nal disorder, mu(0) a prefactor mobility, and rho(0) a wavefunction de cay constant. The energy widths are between 0.105 and 0.113 eV, increa sing with increasing TPM concentration. The concentration dependence o f the widths is described by an argument based on dipolar disorder. Va lues of Sigma are between 2.4 and 3.8, increasing with increasing dilu tion. The prefactor mobilities are between 1.6 x 10(-5) and 7.4 x 10(- 2) cm(2)/Vs and can be described by a wavefunction decay constant of 1 .2 Angstrom.