Method for high temperature nanoimprint of an organic semicrystalline polymer

Abstract

Performance and functionality of devices prepared from organic semicrystalline polymers strongly depend on the size and the orientation of the ordered crystalline domains, as the conductivity is distinctly different in the different lattice directions. This investigation addresses the potential of thermal nanoimprint to control the size of the ordered domains as well as their orientation with respect to the substrate. Poly-3-hexylthiophene (P3HT) is chosen as one of the prominent semicrystalline polymers available at high quality. In order to control the ordering of the domains freely, the imprint is performed at a temperature beyond the melting point to eliminate the domains already existing after spin-coating and soft-bake. To avoid a degradation of P3HT at such a high temperature under oxygen contact—the imprint system used operates in air—a novel imprint procedure is employed, where a distinct prepressure is applied already during the heating of the imprint stack (stamp/substrate with P3HT layer). To enable efficient recrystallization in the form “shaped” by the imprint mold, the novel procedure features, in addition, a slow cool-down from the processing temperature (245 °C) down to 150 °C. During recrystallization the orientation of the ordered domains is driven primarily by the interaction of the side-chains of the P3HT molecules with the antisticking layer of the mold, where the pressure still applied forces ordering, too. The potential of this approach is characterized by x-ray diffraction measurements. The results clearly show that the novel procedure investigated here is effective not only to avoid the degradation of P3HT at a high temperature but also to provide ordered domains that are more than two times larger than those existing before imprint, after spin-coating. The results obtained so far with grating patterns are encouraging and indicate new possibilities of controlling the conductivity of devices prepared from semicrystalline organic polymers.