Effect of dipoles on carrier drift and diffusion of molecularly doped polymers

Abstract

Drift mobilities and diffusion coefficients of molecularly doped polymers, with dipole moment as a parameter, have been measured by fitting a theoretical equation to time-of-flight photocurrent transients. The slope of the logarithm of mobility vs the square root of electric field is proportional to the dipole moment squared. A similar relationship is observed for diffusion coefficients. We analyze the results using disorder formalism and estimate the dipolar contribution ${\ensuremath{\sigma}}_{d}$ to the width of the density of states. The constant of proportionality in the relation between ${\ensuremath{\sigma}}_{d}$ and the dipole moment squared coincides with the theoretical value given by the dipole trap model. This result provides an important demonstration of the validity of both the disorder formalism and the dipole trap model.