A convenient and highly tunable way to n-type carbon nanotube thermoelectric composite film using common alkylammonium cationic surfactant

Abstract

Obtaining n-type candidates with high performance is a great challenge for organic and organic/inorganic composite thermoelectric (TE) materials. Here, we report a convenient and highly tunable way to achieve flexible TE films by doping single-walled carbon nanotubes (SWCNT) with common alkylammonium cationic surfactants. Using a simple solution mixing procedure, pristine p-type SWCNT can be effectively changed to n-type form within a short period. The n-type doping mechanism has been investigated by Raman and XPS spectra. The effects of dopant content, dispersion medium as well as alkyl chain length and anion type of the alkylammonium cationic surfactants on the composite TE performance are systematically investigated. The TE performances of both the n-type TE materials and the corresponding device are among the highest so far. The highest power factor at room temperature reaches 185.7 ± 8.5 μW m⁻¹ K⁻². Furthermore, the TE device consisting of five couples of the pristine SWCNT (p-type) and the doped SWCNT (n-type) films generates a high open circuit voltage and a large output power of 37.4 mV and 6.7 μW, respectively, at a temperature gradient of 80 K. The present study opens a convenient and highly tunable avenue to exploit promising n-type TE composites by doping SWCNT with common alkylammonium cationic surfactants.