Correlation between the air stability of n-type thermoelectric properties and defects in single-walled carbon nanotubes with anionic surfactants

Abstract

Single-walled carbon nanotubes (SWCNTs) are promising thermoelectric materials for use as sustainable power sources for the Internet of Things technology due to their flexibility and excellent thermoelectric properties near 300 K. One of the most important challenges in the development of SWCNTs is achieving n-type thermoelectric properties with long air stability. Here, we investigated the correlation between the air stability of the n-type property and the defects of SWCNTs using two types of SWCNTs with different defect densities. SWCNT films with anionic surfactants were prepared using drop-casting, followed by heat treatment. Both types of SWCNT films exhibited approximately the same n-type Seebeck coefficient values at appropriate heat treatment temperatures. The SWCNT films with low defect density exhibited high electrical conductivity, but the n-type Seebeck coefficient was converted into a p-type one at 14 d. Conversely, the SWCNT films with high defect density exhibited low electrical conductivities but maintained the n-type Seebeck coefficient for 35 d. Therefore, the defect density of SWCNTs impacted the air-stability of the thermoelectric properties. This phenomenon possibly indicates that SWCNT films with high defect density were homogeneously coated with surfactants, thus preventing oxygen atoms from adhering to the film.