Morphology and Electronic Properties of N,N'-Ditridecylperylene-3,4,9,10-tetracarboxylic Diimide Layered Aggregates: From Structural Predictions to Charge Transport

The morphology of layered aggregates of N,N '-ditridecylperylene-3,4,9,10-tetracarboxylic diimide (PTCDI-C13), a prototypical n-type semiconductor for organic electronic devices, was investigated by molecular dynamics and corroborated by metadynamics simulations. Calculations were targeted to ordered 3D aggregates, differing in the relative orientation of the perylene pi-cores and on the degree of interdigitation among contiguous planar layers. Our simulations indicated the noninterdigitated cofacial structure as the thermodynamically most stable form of ordered PTCDI-C13 aggregates, in both bulk crystals and bilayers. Other structures, however, may occur in the growth of PTCDI-C13 under kinetic conditions. Density functional theory calculations were also performed to evaluate the relative total electronic energy of 3D crystals of PTCDI-C13 and related transfer integrals, correlating structure with potential charge-transport properties in devices. The most stable ordered aggregated form of PTCDI-C13 exhibits significant transfer integrals for electrons and accounts for the remarkable n-type charge-transport properties observed in thin films grown under thermodynamic conditions. The effect of structural disorder on charge-transport properties was also assessed by computing transfer integrals in PTCDI-C13 layers at the interface with a model surface. Targeting a strategic material for organic electronics, this work also highlights an integrated computational approach to simulate the structure and energetics of competing 3D morphologies in thin films and to shed light on the details of ordered structures that are responsible for the charge transport in small-molecule organic semiconductors.