Combined effect of N-methyl pyrrolidone and ferrocene derivatives on thermoelectric performance of n-type single-wall carbon nanotube-based composites

Abstract Organic/single-walled carbon nanotube (SWCNT) composites as thermoelectric (TE) materials have been developed rapidly in recent years; however, research on n-type organic/SWCNTs is relatively lagging, and their performance needs to be further improved. In this work, three low-cost organometallic complexes (OMCs) with reducing abilities, including ferrocene (FeCp2), FeCp2 with an acetenyl group (EtFc) to extend the conjugation degree, and FeCp2 with a (dimethylamino)methyl group (FcMA) to increase the electron-donating ability, were developed to enhance the TE properties of n-type SWCNT-based composites. In addition, the effect of solvents was also studied, and it was determined that a synergistic effect of N-methyl pyrrolidone (NMP) and ferrocene derivatives occurred in enhancing the n-type properties. Among the three OMCs, SWCNT/FcMA prepared from NMP displayed the highest TE performance, indicating that the ferrocene and (dimethylamino)methyl group can also form synergistic effects. When the mass ratio of the SWCNTs and FcMA was 1:7, the highest power factor of 567.54 ± 27.18 μW m−1 K−2 at room temperature was achieved, which is among the state-of-the-art n-type SWCNT/organic molecule-based TE materials in literature. A combination of field emission scanning electron microscopy and photoelectron spectroscopy indicated that the electrons could be transferred from NMP, FeCp2 and its derivatives to SWCNTs, leading to an upshift in the Fermi level and an increase in conductivity. Moreover, a TE device containing five p (SWCNTs) − n (SWCNT/FcMA) junctions was assembled, and an open-circuit voltage of 22.7 mV with an output power of 0.75 µW at a temperature difference of 54.1 K was achieved. These results showed that OMCs possess promising applications in future n-type carbon nanotube-based TE materials.