  Monte Carlo simulation was carried out to understand the influence of
morphological inhomogeneity on carrier diffusion in organic thin films. The
morphological inhomogeneity was considered in the simulation by incorporating
the regions of low energetic disorder in a host lattice of high energetic
disorder which decreases the overall energetic disorder of the system. For the
homogeneous films, the carrier diffusion was found to decrease upon decreasing
the energetic disorder. In contrast to this, in the case of inhomogeneous films
the carrier diffusion enhanced upon decreasing the overall energetic disorder,
up to an optimum value and beyond which the carrier diffusion decreased.
Through our simulation, we observed that the behavior of carrier diffusion in
the inhomogeneous case is due to the morphology dependent carrier spreading,
which acts in addition to the thermal and non-thermal field assisted diffusion
mechanisms. This morphological dependence of carrier spreading arises due to
the generation of packets of carriers with different jump rates, which is after
effect of slow relaxation of the carriers generated in the less disordered
regions of inhomogeneous system. Our simulation of morphology dependent carrier
spreading and its influence on the basic diffusion process provide deeper
insight into the charge transport mechanisms in organic thin films.
