Evaluation of Hole Doping Performance of Single-Walled Carbon Nanotubes with Boron Compounds

Neutral organoboron compounds often show electron acceptance due to the vacant 2p orbital on boron and act as p-type dopants for organic semiconductors with electron-donating properties.¹ Therefore, most of the organic semiconductors have heteroatoms such as nitrogen, oxygen, and thiophene with lone pair electrons that can coordinate to vacant orbitals on the boron. On the other hand, for carbon materials such as single-walled carbon nanotubes (SWCNTs) consist of only carbon atoms without lone pair electrons, the effect of doping with organoboron compounds has not rarely been studied. In this study, we investigated p-type doping of SWCNTs by monoboranes and diboranes as organoboron compounds and the thermoelectric properties of the p-type doped SWCNT sheets.<br/>P-type doped SWCNT sheets were prepared by immersed SWCNT sheets (4 mm × 14 mm × 30 µm) into THF solution of boron compounds and shaking at 30 °C for 24 hours. Electrical conductivity measurements of the SWCNT sheets revealed a significant increase in conductivity compared with pristine SWCNT sheets when using tris(pentafluorophenyl)borane (BCF) and bis(catecolato)diboron (B₂cat₂). In addition, the Seebeck coefficient of the SWCNT sheets were lower than that of pristine SWCNT. From these results, these dopants can serve as efficient hole-dopants for SWCNTs. Interestingly, the electrical conductivity of these doped SWCNT sheets increased with exposure to air. We considered that the proton generated by the reaction of boron dopants on the surface of SWCNTs with water in air caused hole doping in the SWCNTs.²<br/><br/>References-<br/>[1] G. C. Bazan and T.-Q. Nguyen et al., <i>Nature Materials</i> <b>2019</b>, <i>18</i>, 1327. [2] J. Jang et al., <i>Adv. Energy Mater.</i> <b>2020</b>, <i>10</i>, 2003521.