Alkyl Chain Engineering for Enhancing the Thermoelectric Performance of Single-Walled Carbon Nanotubes–Small Organic Molecule Hybrid

Abstract

Alkyl chain engineering of amphiphilic small organic molecules (SOMs) has been widely used for enhancing the performance of organic electronic materials. In this study, three SOMs are synthesized for increasing the thermoelectric (TE) properties of single-walled carbon nanotubes (SWCNTs)-SOM (SWCNTs-SOM) hybrid films. SOMs comprise a bis(bithiophenyl)-terphenyl aromatic rod and tri(ethylene oxide) chains attached at the center of the rod with either hexane (BBTTPH), dodecane (BBTTPD), or octadecane (BBTTPO) at the opposite end. BBTTPO with the largest hydrodynamic radius led to longer and thicker SWCNTs-P in the SWCNTs-SOM hybrid. Therefore, the SWCNTs-BBTTPO film exhibited an electrical conductivity (σ) of 274.5 ± 16.2 S/cm and a power factor (PF) of 54.1 ± 6.1 μW/mK2, which are higher than those of SWCNTs-BBTTPH (56.3 ± 3.5 S/cm S/cm and 19.3 ± 0.5 μW/mK2) and SWCNTs-BBTTPD (92.2 ± 8.6 S/cm and 26.2 ± 4.0 μW/mK2) films. These are attributed to a decreased tunneling energy barrier for charge carrier transport in the SWCNTs-BBTTPO films. Furthermore, 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) doped SWCNTs-BBTTPO film exhibited a PF of 365.9 ± 15.2 μW/mK2 which is higher than those of F4TCNQ doped SWCNTs-BBTTPD film and F4TCNQ doped SWCNTs-BBTTPH film. We thus present alkyl chain engineering of SOMs as a new strategy for enhancing the TE performance of SWCNTs-SOM hybrid films, which will be advantageous to the development of flexible/wearable TE materials.