Band Structure and Transport of Holes and Electrons in Anthracene

Previous mobility measurements indicate that the band approximation can be used to describe the behavior of injected holes and electrons in anthracene, and the present theoretical investigation appears to confirm this. The structures of the bands appropriate to a hole or electron are calculated with the tight binding approximation. Hückel linear combinations of Slater-type atomic orbitals are used for the molecular basis functions. Both bands are highly anisotropic and each is found to be approximately 0.56 kT wide at room temperature. Mobility tensors are derived using a simplified treatment of scattering which assumes isotropic scattering parameters. The calculated mobilities exhibit roughly the anisotropy that has been observed experimentally. Magnitudes of the scattering parameters are estimated from the observed mobilities, and these are found to be reasonable (e.g., free path>lattice distances).