Modeling of the temperature dependence of the field-effect mobility in thin film devices of conjugated oligomers

A simple model is proposed for charge carrier transport across grain boundaries with an acceptor-like trap level. Potential wells between the grains are formed due to negatively charged grain boundaries. Based on this model, a variety of temperature dependencies of the charge carrier mobility can be described. Using realistic parameters, this model reproduces very well the measured temperature dependencies of the field-effect mobility in polycrystalline pentacene and oligothiophene thin film devices. Therefore, it seems to be difficult to investigate the intrinsic material properties of organic semiconductors using only polycrystalline field-effect devices, since they may be masked by the effects of traps and grain boundaries.