Tuning Counterion Chemistry to Reduce Carrier Localization in Doped Thermoelectric Carbon Nanotube Networks

Abstract

Semiconducting single-walled carbon nanotubes (s SWCNTs) have demonstrated promising performance for several electronic and energy harvesting devices such as low-temperature thermoelectric converters. A fundamental challenge for incorporating s-SWCNTs (and other pi-conjugated semiconductors) into such applications is exerting fine control over charge carrier densities via electronic doping while simultaneously ensuring these charge carriers are not localized due to the inherently low Coulomb screening. Here, we compare a series of molecular charge-transfer dopants based on functionalized icosahedral dodecaborane (DDB) clusters with small molecules to explore the impact of the dopant’s chemical and electronic structure on the doping efficacy and charge carrier transport in s-SWCNT networks. Analysis of the thermoelectric properties indicates that localization of electron density on the DDB core counterion reduces the coulombic interactions that contribute to hole localization in the s-SWCNTs, thereby increasing the charge carrier mobility. The enhanced delocalization ultimately allows for an increase in the thermopower and electrical conductivity at lower charge carrier densities, yielding enhanced thermoelectric transport and a thermoelectric power factor that surpasses the previous best-in-class for enriched s-SWCNT thin film networks.

Keywords: carbon nanotubes, charge transfer, carrier doping, carrier transport, thermoelectric, delocalization, dodecaborane