Thermoelectric properties of low-cost transparent single wall carbon nanotube thin films obtained by vacuum filtration

The dispersions of semiconducting (sc-) and metallic (m-) SWCNTs with purity more than 98 and 86%, correspondingly, were obtained by using the aqueous two-phase extraction method. The unseparated (un-) SWCNTs contained ~3/4 of semiconducting and ~1/4 of metallic nanotubes. Thin films based on unseparated, semiconducting and metallic SWCNTs were prepared by vacuum filtration method. An Atomic Force Microscopy (AFM) and a Transmission Electronic Microscopy (TEM) were used to investigate the thin film microstructure. The thin SWCNT film transmittance was measured in the wavelength range of 300–1500 nm. Thermoelectric properties were carried out in the temperature range up to 200 °C. The largest Seebeck coefficient was observed for thin films based on semiconducting SWCNTs. The maximum value was 98 μV/K under the temperature of 170 °C. The lowest resistivity was 7.5·10⁻⁴·Ohm·cm at room temperature for thin un-SWCNT films. The power factor for m-SWCNT and un-SWCNT films was 47 and 213 μW m⁻¹ K⁻², correspondingly, at room temperature and 74 and 54 μW m⁻¹ K⁻² at 200 °C, respectively. For a thin sc-SWCNT film the maximum power factor was 2.8 μW m⁻¹ K⁻² at 160 °C. The un-SWCNT film thermal conductivity coefficient was 5.63 and 3.64 W m⁻¹ K⁻¹ and a thermoelectric figure of merit was 0.011 and 0.016 at temperatures of 23 and 50 °C, respectively.