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Single-walled carbon nanotubes (SWCNTs) dispersed with Nafion in a solvent mixture containing de-ionized water and 1-propanol (bisolvent) were sprayed on a poly(ethylene terephthalate) substrate to fabricate flexible transparent conducting films (TCFs). Different SWCNT-to-Nafion ratios were used to optimize the film performance of transparence and sheet resistance. The TCFs were then immersed in nitric acid. These steps resulted in p-type doping due to the presence of Nafion in the SWCNT network and de-doping (removal of doping effect) by the acid treatment. X-Ray photoelectron and Raman spectroscopy confirmed that the de-doping effect occurred with the partial removal of Nafion from the nanotube surface by the nitric acid treatment, which improved the film conductivity by a factor of $4 with negligible change in transmittance.

Several single-walled carbon nanotubes (SWCNTs) prepared by different methods have been used to investigate the material dependence on the optimal film performance of flexible transparent conducting films. The nanotubes were dispersed in water with sodium dodecyl sulfate by sonication. These SWCNT solutions were then sprayed onto the Poly(ethylene terephthalate) substrate by a spray coater to form the film. Several factors such as purity, diameter, defects, metallicity, and degree of dispersion were evaluated individually to examine how they affect the film performance. We found that the metallicity of SWCNTs and the degree of dispersion are the most crucial factors in determining the film performance. We also proposed a material quality factor to estimate the material quality of SWCNTs as a figure of merit for the film performance.

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