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 ( 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 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 μ_DC/μ_OP 35, corresponding to a calculated DC conductivity of over 7000 S cm^-1. When very thin (T₅₅₀ 96%), smooth (RMS roughness, R_q 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 20-30 nm) and less conductive (peak μ_DC/μ_OP 2.5) films formed by common vacuum filtration of the same starting material, and having the same transmittance.