Charge transport in organic semiconductors

In this review, we have discussed the major advances that have recently been achieved in the description of the parameters impacting charge transport in organic semi-conductors. Once again, the picture emerging in organic semiconductors appears to be more complex than in conventional inorganic semiconductors; this was the case already when comparing the electronic structure of these materials: while inorganic semiconductors can usually be well described via one-electron (band structure) approaches, organic semi-conductors often require a treatment that takes both electron-electron and electron-phonon interactions into account. In the case of transport, we emphasized in sections 3 and 4 some of the shortcomings of the current models used to depict organic semiconductors and the paths to be followed to achieve significant improvements. An important element is that it has become clear that organic semiconductors require that both local and nonlocal electron-phonon couplings be considered. Thus, we can conclude that a comprehensive understanding will come from the development of models allowing the calculations of the vibrational couplings: (i) with all modes, optical as well as acoustical since the actual strength of acoustic-type nonlocal interactions is not well-established yet; (ii) at a high level of theory; and (iii) over a much larger range of systems than those that have been examined to date. We hope that this review will provide the impetus for these calculations to be undertaken.