Identification of a positive-Seebeck-coefficient exohedral fullereneElectronic supplementary information (ESI) available. See DOI: 10.1039/c6nr02291j

If fullerene-based thermoelectricity is to become a viable technology, then fullerenes exhibiting both positive and negative Seebeck coefficients are needed. C 60 is known to have a negative Seebeck coefficient and therefore in this paper we address the challenge of identifying a positive-Seebeck-coefficient fullerene. We investigated the thermoelectric properties of single-molecule junctions of the exohedral fullerene C 50 Cl 10 connected to gold electrodes and found that it indeed possesses a positive Seebeck coefficient. Furthermore, in common with C 60 , the Seebeck coefficient can be increased by placing more than one C 50 Cl 10 in series. For a single C 50 Cl 10 , we find S = +8 μV K −1 and for two C 50 Cl 10 's in series we find S = +30 μV K −1 . We also find that the C 50 Cl 10 monomer and dimer have power factors of 0.5 × 10 −5 W m −1 K −2 and 6.0 × 10 −5 W m −1 K −2 respectively. These results demonstrate that exohedral fullerenes provide a new class of thermoelectric materials with desirable properties, which complement those of all-carbon fullerenes, thereby enabling the boosting of the thermovoltage in all-fullerene tandem structures. If fullerene-based thermoelectricity is to become a viable technology, then fullerenes exhibiting both positive and negative Seebeck coefficients are needed.