Boron-Doped Single-Walled Carbon Nanotubes with Enhanced Thermoelectric Power Factor for Flexible Thermoelectric Devices
Y. Liu, V. Khavrus, T. Lehmann, H. L. Yang, L. Stepien, M. Greifzu, S. Oswald, T. Gemming, V. Bezugly, and G. Cuniberti
ACS Appl. Ener. Mat. 3 3 (2020)
We report a detailed experimental and theoretical study on thermoelectric properties of boron-doped single-walled carbon nanotubes (B-SWCNTs), which are versatile building blocks of flexible thermoelectric devices. Implantations of substitutional boron dopants (0.1-0.5 atom %) in SWCNTs are realized using thermal diffusion. The after-synthesis boron doping simultaneously improves the Seebeck coefficient (S) and electrical conductivity (σ) of SWCNT networks, leading to an S2σ value of 226 μW/mK2. First-principle calculations indicate that a few tenths atom % of substitutional boron atoms improve the S value of semi-conducting SWCNTs but reduce the electron conductance in individual SWCNTs. The high σ of B-SWCNT networks is attributed to the improved electrical transport between laterally contacted metallic and semi-conducting nanotubes. The produced B-SWCNTs are stable over high-temperature annealing or processing in liquid media, which inspired us to fabricate thermoelectric modules by a low-cost printing method. The modules demonstrate an increased thermoelectric efficiency by 76% compared to those with undoped SWCNTs. This work provides a feasible fabrication strategy and physical insights for B-SWCNT-based flexible thermoelectrics.