Identification of a positive-Seebeck-coefficient exohedral fullerene†
If fullerene-based thermoelectricity is to become a viable technology, then fullerenes exhibiting both positive and negative Seebeck coefficients are needed. C60 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 C50Cl10 connected to gold electrodes and found that it indeed possesses a positive Seebeck coefficient. Furthermore, in common with C60, the Seebeck coefficient can be increased by placing more than one C50Cl10 in series. For a single C50Cl10, we find S = +8 μV K−1 and for two C50Cl10's in series we find S = +30 μV K−1. We also find that the C50Cl10 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.