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Abstract
We prepare thin single-walled carbon nanotube networks on a transparent and flexible substrate with different densities, using a very simple spray method. We measure the electric impedance at different frequencies Z(f) in the frequency range of 40 Hz to 20 GHz using two different methods: a two-probe method in the range up to 110 MHz and a coaxial (Corbino) method in the range of 10 MHz to 20 GHz. We measure the optical absorption and electrical conductivity in order to optimize the conditions for obtaining optimum performance films with both high electrical conductivity and transparency. We observe a square resistance of 1 to 8.5 kΩ for samples showing 65% to 85% optical transmittance, respectively. For some applications, we need flexibility and not transparency: for this purpose, we deposit a thick film of single-walled carbon nanotubes on a flexible silicone substrate by spray method from an aqueous suspension of carbon nanotubes in a surfactant (sodium dodecyl sulphate), thereby obtaining a flexible conducting electrode showing an electrical resistance as low as 200 Ω/sq. When stretching up to 10% and 20%, the electrical resistance increases slightly, recovering the initial value for small elongations up to 10%. We analyze the stretched and unstretched samples by Raman spectroscopy and observe that the breathing mode on the Raman spectra is highly sensitive to stretching. The high-energy Raman modes do not change, which indicates that no defects are introduced when stretching. Using this method, flexible conducting films that may be transparent are obtained just by employing a very simple spray method and can be deposited on any type or shape of surface.
Highlights
Flexible conducting thin films are useful in flexible electronic devices for different applications such as sensors, transistors, or flexible electrodes
Transparent, flexible electrodes could be used in photovoltaic solar cells as an alternative material to conducting oxides as ITO
The density, film thickness, and transparency are controlled by the single-walled carbon nanotubes (SWCNTs) concentration in sodium dodecyl sulphate (SDS) and the number of spray passes over the substrate, which is from three to ten in our samples: as the number of spray passes increases, the density increases and the transparency decreases
Summary
Flexible conducting thin films are useful in flexible electronic devices for different applications such as sensors, transistors, or flexible electrodes. Transparent, flexible electrodes could be used in photovoltaic solar cells as an alternative material to conducting oxides as ITO. Different research groups have obtained and studied the performances of flexible electrodes and transistors based on carbon nanotubes [5,6,7,8]. With this objective, in this paper, we present our results in two different series of samples: Part 1: We measure the frequency-dependent electrical impedance on transparent, flexible SWCNT networks by varying the SWCNT density and using different sample geometries up to 20 GHz. We analyze the cutoff frequency (f0) dependence on carbon nanotube density. After measuring the optical transmittance (%T), we can correlate the transmittance T with impedance
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