The physical properties of polymers strongly depend on the molecular or supermolecular order and orientation. Here we demonstrate the preferential orientation of lamellar crystals and the enhancement of ferro/piezoelectric properties in individual poly-(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) nanowires fabricated from anodic alumina oxide (AAO) templates. The crystallographic a axis of P(VDF-TrFE) was found to be aligned along the long axis of nanowires due to geometrical confinement and grapho-expitaxial crystals growth. The alignment of lamellar crystals in P(VDF-TrFE) nanowires and enhancement of crystallization translated into improved ferro/piezoelectric properties such as lower coercive field and higher piezoelectric coefficient, testified by piezoresponse force microscopy images and piezoresponse hysteresis loops.

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 π–π 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.

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We develop a solvent-assisted room temperature nanoimprint lithography (SART-NIL) technique to fabricate an ideal active layer consisting of poly(3-hexylthiophene) nanopillar arrays surrounded by [6,6]-phenyl-C61-butyric acid methyl ester. Characterization by scanning electron microscopy, two-dimensional grazing incidence wide angle X-rays diffraction, and conducting atomic force microscopy reveals that the SART-NIL technique can precisely control the size of P3HT nanopillar arrays. With the decrease in diameters of P3HT nanopillar arrays, the P3HT nanopillar arrays exhibit a more preferable face-on molecular orientation, enhanced UV-vis absorption and higher conducting ability along the direction perpendicular to the substrate. The ordered bulk heterojunction film consisting of P3HT nanopillar arrays with a diameter of ∼45 nm (OBHJ-45) gives face-on orientation, a high interfacial area of 2.87, a high conducting ability of ∼130 pA and efficient exciton diffusion and dissociation. The polymer solar cell (PSC) based on an OBHJ-45 film exhibits a significantly improved device performance compared with those of PSCs based on the P3HT nanoapillar arrays with diameters ∼100 nm and ∼60 nm. We believe that the SART-NIL technique is a powerful tool for fabricating an ideal active layer for high performance PSCs.