Heterointerface Electronic States and Charge Transport of Crystalline N,N′-1H,1H′-Perfluorobutil Dicyanoperylene Diimide in Field-Effect Transistor Configuration

We present a theoretical study on the nature and origin of charge carriers, charge transfer, and currents at the interface of an organic field-effect transistor (OFET) structure composed of the N,N′-1H,1H′-perfluorobutil dicyanoperylene diimide (PDIFCN2) organic crystal adsorbed on the (001)-oriented, clean, silicon surface. Starting from the knowledge of the structural and electronic bulk properties of the organic crystal and of the surface of the dielectric substrate, we have evaluated the band structure, density of states, charge transfer, and surface currents in a model crystal made of a reconstructed silicon surface on which a single layer of PDIF-CN2 molecules was deposited in the same packing arrangement as in the bulk PDIF-CN2 organic crystal. In this way alignment of energy bands of the separate PDIF-CN2 and silicon crystals are naturally considered in the model crystal and information on the states involved in charge transport is evidenced. In particular, the analysis of the charge transfer between the dielectric substrate and the adsorbed PDIF-CN2 molecules, of the interface densities of states, and of the currents at the interface allows us to confirm existing experimental results on the distribution and origin of the currents in the FET structure. Namely, that these are essentially determined by the conducting channel made of the π orbitals of the perylene cores of the face-to-face packed PDIF-CN2 molecules on the dielectric substrate. Our results support the description of coherent bandlike transport in OFETs based on the n-type PDIF-CN2 organic crystal.