Effects of defects on thermoelectric properties of carbon nanotubes

Abstract

Carbon nanotubes (CNTs) have recently attracted attention as materials for flexible thermoelectric devices. To provide theoretical guideline of how defects influence the thermoelectric performance of CNTs, we theoretically studied the effects of defects (vacancies and Stone-Wales defects) on its thermoelectric properties; thermal conductance, electrical conductance, and Seebeck coefficient. The results revealed that the defects mostly strongly suppresses the electron conductance, and deteriorates the thermoelectric performance of a CNT. By plugging in the results and the intertube-junction properties into the network model, we further show that the defects with realistic concentrations can significantly degrade the thermoelectric performance of CNT-based networks. Our findings indicate the importance of the purification of CNTs for improving CNT-based thermoelectrics.

Thermoelectric properties of sorted semiconducting single-walled carbon nanotube sheets

“…The inplane thermal conductivity of SWNT sheets varied within two orders of magnitude in the literatures as summarized in Table S3. Therefore, the difference of the thermal conductivity range between our results (9.16-17.9 W m −1 K −1 ) and reported values (80-370 W m −1 K −1 ) was probably due to the difference of either SWNT diameter [53], length [54,55], bundle size [56], anisotropy [57,58], defect density [43], mass density [59] of SWNTs or measurement accuracy [42,[60][61][62]. We also recognized that the s-SWNT sheets had lower thermal conductivity than that of the unsorted SWNT sheet.…”

“…We assumed that an introduction of defects and shortening of the SWNTs during DGU sorting caused the lowering of the conductivity as pointed out previously [42], which is also supported by our Raman spectra (Supporting information, Figure S1) and AFM images (Supporting information, Figure S2). Such a lowering of the electrical conductivity is supported by the theoretical simulation as well [43].…”

“…We also recognized that the s-SWNT sheets had lower thermal conductivity than that of the unsorted SWNT sheet. Similar to the electrical conductivity, it can also be explained by the introduction of defects (Supporting Information, Figure S4) or the shortening of SWNTs upon sorting, which leads to additional phonon scattering in the defective regions of SWNTs and the SWNT junctions inside the sheets as predicted by theoretical simulations [43,63,64].…”

Thickness-dependent thermoelectric power factor of polymer-functionalized semiconducting carbon nanotube thin films

“…Slight doping with 0.1 mg mL −1 AgTFSI dramatically increased electrical conductivity to 7.8 S cm −1 , and the reduction of film resistivity down to less than a mega-ohm enabled the reliable measurement of the Seebeck coefficient. The order of the obtained Seebeck coefficient (~ 235 μV K −1 ) corresponds approximately to the theoretical value of slightly doped s-SWNTs [19]. Using identical feedstock films, we examined the doping effect on the thermoelectric transport.…”

Magnetic nanotubes: A new material platform to realize a robust spin-Seebeck effect and a perfect thermal spin-filtering effect

“…Recent research works have demonstrated that finite-layer nanotubes are promising thermoelectric materials with many advantages [22][23][24] . First, nanotubes are one-dimensional materials, leading to high Seebeck coefficient due to the quantum confinement effect [25][26][27] . Second, the natural network structures with multiple intertube junctions significantly reduce the thermal conductivity, leading to large figureof-merit values 28,29 .…”