First-principles calculations of anisotropic charge-carrier mobilities in organic semiconductor crystals

The orientational dependence of charge-carrier mobilities in organic semiconductor crystals and the correlation with the crystal structure are investigated by means of quantum chemical first-principles calculations combined with a model using hopping rates from Marcus theory. A master equation approach is presented which is numerically more efficient than the Monte Carlo method frequently applied in this context. Furthermore, it is shown that the widely used approach to calculate the mobility via the diffusion constant along with rate equations is not appropriate in many important cases. The calculations are compared with experimental data, showing good qualitative agreement for pentacene and rubrene. In addition, charge-transport properties of core-fluorinated perylene bisimides are investigated.