(554d) Optoelectronic Evaluation of MEP-PPV and P3HT Nanotubules Fabricated Via Template Wetting Nanofabrication

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) and (2-methoxy-5-(2x-ethylhexyloxy)-1,4-phenylene vinylene) (MEH-PPV) nanotubules made using one of the simplest of these techniques, template wetting nanofabrication. A bathochromic shift in the Uv-vis absorption along with a greater degree of fine structure was observed in nanotubules of both polymers when compared to thin films. These are indicative of increased long range order and a greater effective conjugation length in the polymer. Polarized FTIR spectroscopy was used to evaluate the degree of orientation of the polymer chains in the nanotubules. Carrier mobility was also evaluated by fitting current voltage characteristics of simple devices to space charge limited conduction models. While an order or magnitude increase in mobility was observed in MEH-PPV nanotubules, the mobility of P3HT nanotubules was roughly the same as observed in thin films. This trend is consistent with the degree of redshift and the dichroic ratio observed in Uv-vis and polarized FTIR spectra. Confinement within the nanopores of the template leads to increased molecular order in the polymer. We speculate that a greater degree of order can be induced in the amorphous MEH-PPV than is possible in the already somewhat ordered, semicrystalline P3HT, accounting for the differences observed in the behavior of these conjugated polymer nanostructures.