Analysis of Impact of C60 Fullerenes on Room-Temperature Seebeck Coefficient and Magnetotransport Properties of Flexible Thermoelectric Bi₂Se₃-C60-MWCNT Heterostructures

Room-temperature thermoelectric properties of heterostructures prepared by direct physical vapor deposition of Bi2Se3 nanostructures on carbon fullerenes (C60)-multiwalled carbon nanotubes (MWCNT) substrates were studied in relation to the C60/MWCNT wt % ratio in the substrate and compared with the properties of similar heterostructures fabricated using bare untreated p-type MWCNTs and nitrogen-doped n-type MWCNTs (nMWCNTs). It is found that Bi2Se3-C60-MWCNT heterostructures exhibit n-type conductance when the total wt % of the C60-MWCNT component does not exceed 10 wt %, and at optimal C60/MWCNT ratios the maximal power factor of ∼58 μW/mK2 is reached, which exceeds previously reported maximal power factor values exhibited by Bi2Se3-MWCNT and Bi2Se3-nMWCNT heterostructures, as well as by C60-based hybrid thermoelectric materials, by factors of ∼11, ∼4, and ∼2, respectively. This effect was attributed to the cluster-like growth mechanism of Bi2Se3 on C60-MWCNT substrates different from that on bare MWCNTs, which was supported by the magnetoresistance studies of the Bi2Se3-C60-MWCNT heterostructures in the 2–300 K temperature range, and to the charge transfer between the Bi2Se3 and C60 molecules, resulting in the formation of a Bi2Se3-dominated heterostructure with enhanced Seebeck coefficient, reaching ∼−110 to −150 μV/K and electrical resistivity not exceeding 1 mΩ·m for optimal C60/MWCNT ratios, which is similar to or lower than that of Bi2Se3-MWCNT and Bi2Se3-nMWCNT heterostructures. In addition, bending tests performed for Bi2Se3-C60-MWCNT heterostructures with the best power factor showed that these structures are stable during 100 consecutive bending cycles down to a 4 mm radius. This work opens the path for significant improvement of thermoelectrical properties of topological insulator–carbon allotrope heterostructures by tuning their charge transport mechanism using different types and concentrations of carbon allotropes and for their application in flexible thermoelectrics.