Charge transport in organic crystals: Theory and modelling

Efficient charge transport in organic semiconductors is the key for their application in Organic Electronics. Therefore the most important design ansatz is directed to improve carrier mobilities by means of available tools such as chemical and/or structural modifications of the organic materials. Thereby theoretical input can provide guidelines towards possible realizations of high-mobility or, more general, highly functional materials. In particular the structure-property relationship is at the heart of theoretical studies which are extremely helpful if they achieve predictive power. In this paper we systematically review several charge-transport approaches and illustrate their relationship in order to display their capabilities regarding this goal. Special focus is put on the transport mechanism, the mobility anisotropy and temperature dependence of charge-carrier transport. As the central concept the inclusion of the strong coupling of the carriers with the vibrating lattice and, hence, the dressing of carriers to polarons is described. The availability of material parameters is tremendously important for transport description. We highlight their computation by ab initio theory in order to arrive at a satisfactory level beyond phenomenological approaches.