Heating and acid doping thin film carbon nanotube assemblies for high transparency and low sheet resistance
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Transparent electrodes made from metal oxides suffer from poor flexibility and durability. Highly transparent and electrically conductive thin films were assembled as a potential indium tin oxide (ITO) replacement using layer-by-layer (LbL) assembly of single-walled carbon nanotubes (SWNTs), stabilized with negatively charged deoxycholate (DOC), and positively charged poly(diallyldimethylammonium chloride) [PDDA]. Ellipsometry, quartz crystal microbalance, and UV-vis were used to measure the linear growth of these films as a function of the number of bilayers deposited, while TEM and SEM were used to visualize the morphology of these films. The PDDA/(SWNT + DOC) system produced transparent (>82% visible light transmittance) and electrically conductive (160 S cm -1 ) 20-bilayer films with a 38.4 nm thickness. Moreover, a series of post-treatments, involving heating and nitric acid doping, were used to increase conductivity to 1430 S cm -1 (Rs 300 sq -1 ), with no change in transparency, owing to the removal of PDDA and the charge transfer doping. This study demonstrates high visible light transmittance and electrical conductivity of SWNT-based thin films, which are potentially useful as flexible transparent electrodes for a variety of optoelectronic applications. 2011 The Royal Society of Chemistry.
