Analysis of charge transport path ways in disordered organic conductors

Charge mobilities in disordered organic conductors have a high impact on the functionality of the number of devices, but simulation methods for a detailed analysis of the transport mechanisms and material-dependent effects are still in their infancy. Here we present a model of charge transport in organic solids which explicitly considers the packing and electronic structure of individual molecules. We first develop molecular models for disordered films of tris(8-hydroxyquinoline) aluminium (Alq3 ) on the basis of all-atom simulations. We use density functional theory to determine the electronic couplings between molecules and simulate the time-of-flight mobility measurement. We find electron mobilities in the crystalline and disordered phases of ~ 1 cm2 V-1 s-1 and ~ 10-4 cm2 V-1 s-1 respectively. A detailed analysis of the conduction pathways suggests the existence of kinetic traps for electrons and holes on localized molecular clusters. Our results suggest that charge transport in disordered Alq3 is dominated by a few highly conducting pathways.