Elucidation of molecular-level charge transport in an organic amorphous system

Charge transport in organic amorphous systems has been considered to occur by intermolecular hopping. However, it has been difficult to reveal even the intra- and intermolecular structures because of their amorphous nature. Therefore, the details of charge transport at the molecular level have not been clarified. Here, we investigate a detailed molecular-level insight into the charge transport in an amorphous film by the analysis of multiscale simulation. The charge mobility is normally described by a constant value but is found to be widely distributed with two orders of magnitude even in the 100 nm neat film. From the detailed analysis at the molecular level, it becomes clear that there are three types of charge traps; in addition to (1) the well-known traps due to the site energy difference, we found (2) traps caused by the distribution of molecular packings in the aggregate, and (3) those by charge hopping against the electric field. These traps are the origins of the widely distributed mobilities and the understanding of these traps is important to improve mobility.