Tomoyuki Yoshii

Effect of dipole moment on hole transport in polymers doped with compounds containing two styryltriphenylamine units

Hole mobilities have been measured in molecularly doped polymers and polystyrene (PS). Both polymers were doped with a series of 1,1-bis(4-(N-styryl- phenyl)amino)phenyl)cyclohexane (BTAS) derivatives that have different dipole moments. The measured results are described within the framework of a formalism based on disorder in which it is assumed that charge transport occurs by hopping through a manifold of hopping sites subject to energetic and positional disorder. For each polymer doped with BTAS derivatives, the energy width of its hopping site manifold increased with increasing dipole moments of BTAS derivatives. The BTAS doped PC, which is a highly polar polymer, has a larger energy width than does the BTAS doped PS, and its energy width is also less dependent on the dipole moment. We measured the energy width dependence on BTAS concentration, and found that the energy width decreased with increasing BTAS concentration in the PC systems, but increased in the PS systems. These dependencies may have been attributed to the dipolar fields associated with the dipole moments of not only the BTAS derivatives but also the respective polymers. To explain these dependencies, we proposed a new model which dealt with the effects of the dipole moments of PC on energy width. By using this model, we estimated the dipole moment of a monomer unit of PC to be approximately 2.1 D, which corresponds roughly to that of the carbonyl group within a monomer unit.