A percolation approach to exciton diffusion and carrier drift in disordered media

Abstract

Previous data on triplet exciton diffusion in high concentrations (>0·l) of naphthalene in durene melts and carrier drift in molecularly doped polymers are re-examined from a percolation point of view. This is a departure from the view that hopping sites in these disordered media can be represented as an ideal gas with the average distance between sites being a continuous function of the concentration and this average distance determining the diffusion rate. Instead, the correlated motion imposed by the random media, determines the rate of diffusion. From numerical modelling the rate of diffusion and drift is found to be proportional to (C—C _o)^1.8 where C ₀ is the threshold concentration for percolation. Comparison with experiment shows excellent agreement.