N-DMBI Doping of Carbon Nanotube Yarns for Achieving High n-Type Thermoelectric Power Factor and Figure of Merit

The application of carbon nanotube (CNT) yarns as thermoelectric materials for harvesting energy from low-grade waste heat including that generated by the human body, is attracting considerable attention. However, the lack of efficient n-type CNT yarns hinders their practical implementation in thermoelectric devices. This study reports efficient n-doping of CNT yarns, employing 4-(1, 3-dimethyl-2, 3-dihydro-1H-benzimidazole-2-yl) phenyl) dimethylamine (N-DMBI) in alternative to conventional n-dopants, with o-dichlorobenzene emerging as the optimal solvent. The small molecular size of N-DMBI enables highly efficient doping within a remarkably short duration (10 s) while ensuring prolonged stability in air and at high temperature (150 degrees C). Furthermore, Joule annealing of the yarns significantly improves the n-doping efficiency. Consequently, thermoelectric power factors (PFs) of 2800, 2390, and 1534 mu W m-1 K-2 are achieved at 200, 150, and 30 degrees C, respectively. The intercalation of N-DMBI molecules significantly suppresses the thermal conductivity, resulting in the high figure of merit (ZT) of 1.69x10-2 at 100 degrees C. Additionally, a pi-type thermoelectric module is successfully demonstrated incorporating both p- and n-doped CNT yarns. This study offers an efficient doping strategy for achieving CNT yarns with high thermoelectric performance, contributing to the realization of lightweight and mechanically flexible CNT-based thermoelectric devices. N-type dry-spun CNT yarns using N-DMBI doping are successfully fabricated. Joule annealing at high temperatures (<= 2900 degrees C) significantly enhances crystallinity, resulting in higher power factors. A suitable solvent of o-dichlorobenzene is determined to realize efficient N-DMBI doping. A maximum power factor of 2800 mu W m-1 K-2 at 200 degrees C and high figure of merit of 1.69x10-2 at 100 degrees C are reported owing to the enhanced crystallinity and optimized N-DMBI doping. image