Thermoelectric property enhancement of single-wall carbon nanotube network by ICl intercalation and filling: a first-principles study

Abstract

CNTs are promising candidates for wearable thermoelectric applications because of their simultaneously prevailing features of flexibility, lightweight, and quantum confinement due to low dimensionality. The unique advantages of CNT's one-dimensionality can be extracted by tuning the Fermi level near the singularity points of the density of states at the band edges by doping the CNT network. Though interhalogen compounds act as excellent dopants among the various dopants in the CNT system, the impact of their orientation and placement in the CNT system is rarely explored. Here, we investigated the impact of ICl molecule filling and intercalation and its orientation on the thermoelectric properties of a semiconducting single-wall carbon nanotube (SWCNT) network through density functional theory (DFT)-based ab initio calculations and Boltzmann transport theory. Our calculated ICl-doped SWCNT system showed improved thermoelectric performance. Notably, the system's power factor can be increased from 0.28 to 2.4 mW m⁻¹ K⁻², more than an eight-fold increment of its value obtained at the Fermi level. On the other hand, ICl intercalation of the SWCNT bundle shifted the peak thermoelectric power factor below its Fermi level, and it can be attained by doping the CNT bundle with additional acceptor atoms. We achieved the best enhancement of the thermoelectric power factor from zero for pristine CNTs to 0.3 mW m⁻¹ K⁻² when the ICl molecules were horizontally aligned outside the CNTs in close spacing with adjacent dopants. It can further be pulled up to 1.82 mW m⁻¹ K⁻² by doping the CNT with an acceptor concentration of 7.1 × 10²¹ cm⁻³. The insights gained in this investigation will help design and fabricate substrate-supported and flexible thermoelectric nanogenerators and coolers for applications to power up wearable electronics and IoT-based remote devices where thermal energy is abundant.