Aligned Carbon Nanotube Thin Films from Liquid Crystal Polyelectrolyte Inks

Single walled carbon nanotube thin films are fabricated by solution shearing from high concentration sodium nanotubide polyelectrolyte inks. The solutions are produced by simple stirring of the nanotubes with elemental sodium in dimethylacetamide, and the nanotubes are thus not subject to any sonication-induced damage. At such elevated concentrations (similar to 4 mg mL(-1)), the solutions exist in the liquid crystal phase and during deposition this order is transferred to the films, which are well aligned in the direction of shear with a 2D nematic order parameter of similar to 0.7 determined by polarized absorption measurements. Compared to similarly formed films made from superacids, the polyelectrolyte films contain smaller bundles and a much narrower distribution of bundle diameters. After p-doping with an organic oxidizer, the films exhibit a very high DC electrical to optical conductivity ratio of sDC/sOP similar to 35, corresponding to a calculated DC conductivity of over 7000 S cm(-1). When very thin (T-550 similar to 96%), smooth (RMS roughness, R-q similar to 2.2 nm), and highly aligned films made via this new route are used as the front electrodes of carbon nanotube-silicon solar cells, the power conversion efficiency is almost an order of magnitude greater than that obtained when using the much rougher (R-q similar to 20-30 nm) and less conductive (peak sigma(DC)/sigma(OP) similar to 2.5) films formed by common vacuum filtration of the same starting material, and having the same transmittance.