Understanding the solvent effects on polarity switching and thermoelectric properties changing of solution-processable n-type single-walled carbon nanotube films

Developing high performance solution-processable n-type thermoelectric materials is challenging. In this paper, we report that single-walled carbon nanotubes (SWCNTs) prepared in dimethyl sulfoxide (DMSO) (SWCNTs/DMSO) exhibit a high n-type electrical conductivity of 2298 S/cm at room temperature, which is superior to that of previously reported n-type solution-processable SWCNTs. The maximum n-type electrical conductivity was 3490 S/cm at 373 K. The great electrical conductivity results in a high n-type power factor of 195 μW/m-K² for SWCNTs/DMSO films at 373 K which is larger than most of the n-type solution-processable SWCNTs. The theoretical calculation indicates that the wrapping morphology of the surfactant on SWCNTs is strongly affected by different solvent polarities which lead to different packing densities of the SWCNT films as demonstrated in the scanning electron microscope images, subsequently affecting the n-type doping efficiency and the n-type electrical conductivity. The electrical conductivity affected by the mixed p- and n-type carriers in the film were discussed. A full SWCNT thermoelectric generator has been fabricated to show the heat-to-electricity conversion ability of the materials. This work reveals a potential method to prepare highly conductive n-type SWCNTs by choosing the proper solvent for optimized thermoelectric performance.