Redox control of thermopower and figure of merit in phase-coherent molecular wires

García-Suárez, Víctor M; Lambert, Colin J; Manrique, David Zs; Wandlowski, Thomas (2014). Redox control of thermopower and figure of merit in phase-coherent molecular wires. Nanotechnology, 25(20), p. 205402. Institute of Physics Publishing IOP 10.1088/0957-4484/25/20/205402

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We demonstrate how redox control of intra-molecular quantum interference in phase-coherent molecular wires can be used to enhance the thermopower (Seebeck coefficient) S and thermoelectric figure of merit ZT of single molecules attached to nanogap electrodes. Using first principles theory, we study the thermoelectric properties of a family of nine molecules, which consist of dithiol-terminated oligo (phenylene-ethynylenes) (OPEs) containing various central units. Uniquely, one molecule of this family possesses a conjugated acene-based central backbone attached via triple bonds to terminal sulfur atoms bound to gold electrodes and incorporates a fully conjugated hydroquinonecentral unit. We demonstrate that both S and the electronic contribution Z el T to the figure of merit ZT can be dramatically enhanced by oxidizing the hydroquinone to yield a second molecule, which possesses a cross-conjugated anthraquinone central unit. This enhancement originates from the conversion of the pi-conjugation in the former to cross-conjugation in the latter, which promotes the appearance of a sharp anti-resonance at the Fermi energy. Comparison with thermoelectric properties of the remaining seven conjugated molecules demonstrates that such large values of S and Z el T are unprecedented. We also evaluate the phonon contribution to the thermal conductance, which allows us to compute the full figure of merit ZT = Z el T/(1 + κ p/κ el), where κ p is the phonon contribution to the thermal conductance and κ el is the electronic contribution. For unstructured gold electrodes, κ p/κ el Gt⃒ 1 and therefore strategies to reduce κ p are needed to realize the highest possible figure of merit.

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Departement of Chemistry and Biochemistry

UniBE Contributor:

Wandlowski, Thomas

Subjects:

500 Science > 570 Life sciences; biology
500 Science > 540 Chemistry
500 Science

ISSN:

0957-4484

Publisher:

Institute of Physics Publishing IOP

Language:

English

Submitter:

Beatrice Niederhauser

Date Deposited:

26 Mar 2015 11:01

Last Modified:

25 Aug 2015 10:26

Publisher DOI:

10.1088/0957-4484/25/20/205402

BORIS DOI:

10.7892/boris.65950

URI:

https://boris.unibe.ch/id/eprint/65950

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