Organic semiconducting polymers are of wide interests for many applications in organic solar cells, field effect transistors, light emitting diodes, and biosensors. The optical and electrical properties of these polymers are anisotropic which largely depends on their nanoscale morphology, crystallinity and the direction of chain configuration. Furthermore, control over direction of chain orientation is essential as certain devices prefer chain alignment in certain directions as determined by device structures, e.g. vertical alignment for solar cells where vertical charge transport occurs, while for FETs, lateral orientation along the channel is preferred instead. Though the significant progress has been made by the development of varieties of techniques for control of nanoscale morphology, crystallinity and orientation of polymer chains for years, the perfect crystallization and preferred chain ordering in nanoscale regime still remains challenging. We report the fabrication of highly-ordered nanostructure arrays of nanopillars and nanogratings in poly (3-hexylthiophene) (P3HT) using nanoimprint lithography and show 3-D chain ordering by x-ray diffraction (XRD) analysis. We have proved for the first time that nanoscale confinement exerted by the mold can induce only one possible configuration of the chain network in the three dimensional P3HT nanostructures during thermal nanoimprint process. Such monodical 3-D chain configuration strongly depends on the geometry of the nanoconfinement. Interestingly the configuration is arranged in a favorable way for solar cell and FET applications, e.g. vertical chain alignment, and π-stacking along gratings.

In this report, uniform 80 nm thin films of rerioregular P3HT were prepared on a Si substrate. The nanograting of 200 nm height, 65 nm wide gratings at a period of 200 nm while hexagonal array of nanopillars of 150 nm high nanopillars with 80 nm diameter were fabricated using nanoimprint lithography. The P3HT nanostructures were characterized by SEM and crystallization and chain orientation were studied by both in-plane, out-of-plane and in-plane grazing incident XRD. The chain ordering of thin film, nanopillar and nanograting structures are proved to be entirely different. The conjugated polythiophene backbones which are horizontal to the substrate in the thin film are reordered into vertical direction in the imprinted structures of P3HT. The interaction of hexyl side chains with hydrophobic mold surface in turn results π-stacking along nanogratings. We will present XRD results analysis and expect to present solar cell device results using these imprinted P3HT nanostructures.