Abstract

The mobility in crystalline organic semiconductors is believed to be intrinsically limited by the presence of large thermal molecular motions, which are a direct consequence of the weak Van der Waals inter-molecular bonds. These lead to a breakdown of the usual assumptions of semiclassical transport, suggesting that strongly localized carriers are a more natural starting point than free carriers to describe the dynamics of charge carriers in these materials. In this scenario, termed “transient localization”, quantum localization of the carriers occurs on short time scales and is eventually destroyed by the dynamical nature of molecular fluctuations, leading to unconventional charge transport.

I will explore such transient localization mechanism reviewing both microscopic model calculations and a recently developed phenomenological approach which provides useful analytical formulas for the analysis of experiments. I will show that the theory can consistently explain several characteristic experimental features of organic semiconductors, such as the low values of the mobility, its power-law temperature dependence, the crossover to a thermally activated behavior in the presence of extrinsic disorder, as well as the observed non-Drude like behavior of the optical conductivity. Finally I will mention some analogies with other families of organic materials such as organic conductors and superconductors suggesting that transient localization could be a universal characteristic of organic matter.