How accurate are lattice models with Gaussian energy disorder in describing charge-carrier transport and reactions in amorphous organic semiconductors?

Abstract

We model charge-carrier hopping transport and electron–hole recombination in realistic amorphous structures of different densities and use the obtained results to assess the quality of the lattice models with Gaussian energy disorder, which have been the main theoretical tool in the studies of amorphous organic semiconductors. We find that the hopping-site energy distributions inferred from the amorphous structures deviate from the Gaussian distribution, especially in their low-energy tails. Mostly for this reason, the effect of disorder on charge-carrier mobility is much weaker than predicted by the lattice/Gaussian models and dependent on system density. The lattice models of electron–hole recombination in disordered systems, which assume a Gaussian site energy distribution, are found to be more accurate than those of charge-carrier transport. This is explained by the strong Coulomb trapping of electron–hole pairs before recombination, which makes the role of hopping-site energy disorder less significant.