Cocrystal Growth in Organic Semiconductor Thin Films: Simulation of Pentacene, Perfluoropentacene, and Their 1:1 Blend Deposited On Graphite

The understanding of crystal formation in thin films and the precise knowledge of the relation between structure and surface diffusion are two important requirements for the efficient (nano)fabrication of organic electronic devices. Here a computational approach for simulating vapor-phase deposition is employed to obtain and investigate three types of crystalline thin films on graphite. All systems, namely pentacene, perfluoropentacene, and their 1:1 blend, which forms an alternate cocrystal, are constituted by recumbent molecules in accordance with experimental findings. The contributions of intermolecular interactions and of molecular rearrangements occurring during the deposition are analyzed to rationalize the final morphologies. Then, the generated structures are employed to evaluate the energy barriers that prevent molecular diffusion at terraces and step-edges, and to study the reorganization of the films upon high-temperature annealing. The broad agreement with experimental observations and the possibility of evaluating the potential energy surface at the molecular detail render the proposed approach a promising tool to make predictions for other systems.