Correlated Charge Transport in an Organic Coulomb Glass

Advances in the development of organic field-effect transistors (OFETs), electrically gated organic semiconductors (EGOFETs), and organic electrochemical transistors (OECTs) allow for the operation of these devices at very high charge-carrier densities, where Coulomb interactions between carriers can be expected to become significant. We have studied the effects of such Coulomb interactions in an OFET-like structure using Kinetic Monte Carlo (KMC) simulations. Compared to an analogous structure where carrier-carrier interactions are neglected, we find a reduction in carrier mobility and an increase in activation energy. This effect increases with increasing gate voltage, i.e., charge density. We associate this with the emergence of a different transport regime where correlated transport prevails and where a Coulomb gap appears in a dynamic density of states (DOS), consistent with previous work. We demonstrate that at these high densities, the charges in the organic semiconductor behave like those in a Coulomb glass. In this context, the activation energy for transport is reinterpreted to relate to the structural reorganization of the carrier ensemble. Unlike in inorganic semiconductors, for the organic semiconductor system, we find the appearance of a Coulomb gap to occur even at ambient temperature, and it does not require variable-range hopping.