Modeling Electron and Hole Transport in Fluoroarene-Oligothiopene Semiconductors: Investigation of Geometric and Electronic Structure Properties

p-Conjugated molecular, oligomeric, and polymeric materials are of immense interest as alternatives to traditional inorganic materials for many low-cost organic-based electronics applications–including thin-film transistors (OTFTs), light-emitting diodes (OLEDs), and photovoltaic cells –owing to device processing ease, mechanical flexibility, and a large synthetic palette from which properties can be designed into the molecular or polymeric structures. However, many fundamental questions concerning how charge is transported through these functional organic molecular solids remain unresolved. In particular, why certain molecular materials favor the transport of holes versus electrons (i.e., positive and negative polarons, respectively) and how molecular and crystal structure parameters influence relative carrier mobility magnitudes are far from being completely understood. In typical organic transport media, very small bandwidths (< 1 eV) dictate that charge motion occurs by hopping. The electron-hopping process is generally portrayed as a self-exchange electron-transfer reaction between neighboring molecules within the framework of Marcus theory and extensions thereof. The rate constant for electron transfer (i.e., polaron hopping) is then defined in an Arrhenius-like form: