The impact of the tortuosity of the charge transport pathways through a bulk heterojunction film on the charge carrier mobility are theoretically investigated using model morphologies and kinetic Monte Carlo simulations. The tortuosity descriptor provides a quantitative metric to characterize the quality of the charge transport pathways, and model morphologies with controlled domain size and tortuosity are created using a new anisotropic domain growth procedure. The tortuosity is found to be dependent on the anisotropy of the domain structure and is highly tunable. Time-offlight charge transport simulations on morphologies with a range of tortuosity values reveal that tortuosity can significantly reduce the magnitude of the mobility and the electric field dependence relative to a neat material. These reductions are found to be further controlled by the energetic disorder and temperature. Most significantly, the sensitivity of the electric field dependence to the tortuosity can explain the different experimental relationships previously reported, and exploiting this sensitivity could lead to simpler methods for characterizing and optimizing charge transport in organic solar cells.
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