Spectroscopic and electrical evaluation of poly(3-hexylthiophene) nanotubules made using template wetting nanofabrication

Abstract

The unique properties of conjugated polymer nanostructures as compared to thin films of the same materials have fueled the investigation of a number of different polymer nanofabrication techniques. Here we examine the optoelectronic properties of poly(3-hexylthiophene)P3HT nanotubules made using one of the simplest of these techniques, template wetting nanofabrication. Comparison is made with results from our previous study in which in poly(2-methoxy-5-(2́-ethylhexyloxy)-1,4-phenylene vinylene) (MEH-PPV) nanotubules prepared in this manner were shown to have dramatically different properties in comparison with thin films due to increased molecular order in the nanostructures. With semicrystalline P3HT, the differences are much more subtle, we believe due to the greater inherent order in this material. In P3HT nanotubules, a small bathochromic shift (∼0.05 eV) in the onset of Uv–vis absorption was observed indicating increased long range order and a greater effective conjugation length in the polymer. Polarized FTIR spectroscopy indicated a small degree of preferential alignment of the inter-ring C–C bond with the axis of the nanotubules as the stretching vibration for this bond showed a dichroic ratio of 1.73. The degree of increased conjugation length and chain alignment in P3HT nanotubules indicated by both the UV–vis and polarized FTIR spectra were much smaller than that previously observed for MEH-PPV. No significant improvement in mobility as measured from the current voltage characteristics of simple single carrier devices based on the P3HT nanotubules was observed, in sharp contrast to previously studied MEH-PPV where more than an order of magnitude increase was seen. Unlike in amorphous MEH-PPV, the increase in molecular order suggested by spectral data was insufficient to significantly impact mobility of semicrystalline P3HT when using template wetting nanofabrication for either of the 100 or 200 nm nanotubules examined.