Solvent-Assistant Room Temperature Nanoimprinting-Induced Molecular Orientation in Poly(3-hexylthiophene) Nanopillars

Nanoimprinting has been well explored to create nanostructures and to induce molecular orientation in conjugated polymer thin films. We demonstrate here that large area poly(3-hexylthiophene) (P3HT) nanopillar arrays can be fabricated by a simple, cost-effective nanoimprinting method in a solvent-swollen plasticized state at room temperature. In addition, the solvent-assistant room-temperature nanoimprinting induces face-on chain alignment in the P3HT nanopillars; i.e., the pi-pi stacking of P3HT is aligned normal to the substrate, favorable for organic photovoltaic cell applications. The face-on chain alignment solely depends on the diameters of nanopores defined in the nanoimprinting mold, rather than on the initial chain orientation in unprocessed thin films. Furthermore, a critical dimension of ca. 85 nm in diameter is found to be essentially needed to induce the face-on chain alignment within the nanopillars.