Potential of functionalized single walled carbon nanotubes in flexible thermoelectrics

It is well known that chemical functionalization of surfaces has demonstrated to be an important strategy to modify electron transport mechanism of single walled carbon nanotubes (SWNTs). In this work, with the aim to explore the potential of functionalized single walled carbon nanotubes (f-SWNTs) in flexible thermoelectrics for the development of thermal energy harvesting devices, we present a systematic study on the thermoelectric behavior of SWNTs and f-SWNTs based films, and demonstrate the impact that functional groups play in modifying their thermoelectric performance. The selected functional groups were carboxylic acid (COOH), octadecyl amine (ODA), poly (m-amino benzenesulfonic acid) (PABS) and amide (NH 2 ). Experimental measurements reveal that, at room temperature the thermoelectric power factor (TPF) of the films based on SWNTs is up to two orders of magnitude higher than the f-SWNTs based films, whereas despite of slight thermoelectric differences among f-SWNTs, the SWNTs-COOH material presents the best TPF in comparison to the rest of the f-SWNTs. Likewise, by realizing proof-of-concept flexible thermoelectric devices using SWNTs and SWNTs/ABS(acrylonitrile butadiene styrene copolymer), the SWNTs based device presents three and a half fold more maximum output power than the SWNTs/ABS based device. Thereby, as unveiled by X-Ray photoelectron spectroscopy and Raman spectroscopy analyses, in SWNTs chemical functionalization disrupts the conducting π-bonding, and a substantial content of organic molecules covalently attached to the SWNTs surface are detected, giving rise to the formation of localized defect sites, which act as scattering centers for electrons and phonons. Meanwhile, in SWNTs films the creation of random networks promote the formation of high contact resistances between nanotubes due to functionalizers, as a consequence, the thermal and electron transfer mechanisms are seriously altered, affecting significantly the thermoelectric performance of the devices based on f-SWNTs based films.