Identification of a positive-Seebeck-coefficient exohedral fullerene

Abstract

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.