Favorable Face-on Orientation of a Conjugated Polymer on Roll-to-Roll-Transferred Graphene Interface

The use of dry transferred graphene as a templating layer to enhance face-to- face stacking in poly(3-hexylthiophene) (P3HT) systems which is widely used for organic optoelectronics is investigated. In contrast to conventional poly(methyl methacrylate) (PMMA) assisted wet transferred graphene, dry transferred graphene is found in the current work to be quite suitable for use in the roll-to-roll process due to its lack of PMMA residue, whose removal would require high-temperature annealing. Grazing-incidence wide-angle X-ray scattering (GIWAXS) is used to determine the percentages of P3HT molecules adopting a face-on orientation on the various substrates tested. When a P3HT film with a thickness of 30 nm is produced, the face-on populations of P3HT are prominent on both the dry and wet transferred graphene layers. As the film thickness is increased to 50 nm, the face-on population decreases on the wet transferred graphene surface, but retains high levels on the dry transferred graphene. GIWAXS, near-edge X-ray absorption fine structure, and atomic force microscopy data are combined to propose schematic models for the molecular stacking of P3HTs on the two differently transferred graphene surfaces.