Diameter and thermal treatment dependent structure and optical properties of poly(3-hexylthiophene) nanotubes

Abstract

Poly(3-hexylthiophene) (P3HT) nanotubes were prepared using anodized aluminum oxide (AAO) templates with two different diameters of ca. 240 nm and 60 nm. The structure and optical properties of the P3HT nanotubes were studied by using X-ray diffraction and UV-vis spectrometry. The results show that annealing and melt-crystallization can enhance the crystallinity and content of the well-ordered crystalline P3HT aggregates capped in the wider AAO template (240 nm). While melt-recrystallization leads to the highest crystallinity of the P3HT nanotubes, annealing leads to the formation of P3HT aggregates with the highest content of ordered structure (55.1%) and the narrowest free exciton bandwidth (w = 6.9 meV). By contrast, both annealing and melt-recrystallization do not remarkably influence the crystallinity and structural order of the P3HT nanotubes capped in the narrower AAO template (60 nm). The annealing and melt-recrystallization treatments show even a negative effect on the UV absorption properties of P3HT nanotubes. After releasing the P3HT nanotubes from the AAO, the existence of free surface results in a tremendous enhancement of crystallinity and an increase of the lateral size of crystals independent of the diameter. With respect to the optical properties, a further improvement in the optical properties of the released P3HT nanotubes with larger diameters is achieved through annealing; but annealing has a negative effect on the optical properties of the released P3HT nanotubes with smaller diameters.