The mobility of holes and electrons in organic crystals

Overlap integrals between the molecular orbitals of different anthracene molecules in the crystal lattice have been calculated. In the c′ direction the highest occupied orbitals overlap to a greater extent than the lowest vacant orbitals (a ratio of 4·7 : 1). This result explains the experimental fact that holes are more mobile than electrons in this direction. It is predicted that in the ab plane the mobilities of the holes and electrons should be approximately equal, and considerably greater than in the c′ direction.