Thermoelectricity at the molecular scale: a large Seebeck effect in endohedral metallofullerenes

Abstract

Single molecule devices provide a unique system to study the thermoelectric energy conversion at an atomistic level and can provide valuable information for the design of organic thermoelectric materials. Here we present a comprehensive study of the thermoelectric transport properties of molecular junctions based on C(82), Gd@C(82), and Ce@C(82). We combine precise scanning tunneling microscope break-junction measurements of the thermopower and conductance with quantitatively accurate self-energy-corrected first-principles transport calculations. We find that all three fullerene derivatives give rise to a negative thermopower (n-conducting). The absolute value, however, is much larger for the Gd@C(82) and Ce@C(82) junctions. The conductance, on the other hand, remains comparable for all three systems. The power factor determined for the Gd@C(82) based junction is so far the highest obtained for a single-molecule device. Although the encapsulated metal atom does not directly contribute to the transport, we show that the observed enhancement of the thermopower for Gd@C(82) and Ce@C(82) is elucidated by the substantial changes in the electronic- and geometrical structure of the fullerene molecule induced by the encapsulated metal atom.

Electronic Properties of Single Atom and Molecule Junctions

“…The sign and magnitude of the thermopower of the Sc 3 N@C 80 single‐molecule junction can be controlled by the applied pressure. Here, Sc 3 N inside the cage produces a resonance state around the Fermi level, whose energy, and thus the thermopower, is tuned by applying the mechanical force …”

“…Fluctuation in the electronic properties of the single‐molecule junctions reflects the character of the metal‐molecule bonds at the interfaces, which enables us to study the molecular adsorption process on the metal electrodes. The electronic energy levels in single molecules are discretized and quantum effects can play an important role in thermoelectric transport for the single atom and molecule junctions . We describe the thermopower of the single atom and molecule junctions.…”

“…The thermopower has been successfully measured for the single‐molecule junctions ,. Due to their discrete energy levels, large thermopower can be expected.…”

Thermal and Thermoelectric Properties of Molecular Junctions

“…In addition, Lee et al studied the thermoelectric properties of three fullerene derivatives (C82, Gd@C82, and Ce@C82). They found that the Seebeck coefficient for all three fullerene derivatives is negative (electron‐conduction).…”

High cross-plane thermoelectric performance of metallo-porphyrin molecular junctions

“…Fullerenes also exhibit negative Seebeck coefficients, ranging from À10 to À30 mV K À1 for C 60 14 to À33 mV K À1 for C 60 dimers 15 and up to À31.6 mV K À1 C 82 endohedral fullerenes. 16 The sign of the endohedral fullerene Sc3N@C 80 was shown to be sensitive to pressure, ranging from À25 mV K À1 to +25 mV K…”