Research output: Contribution to Journal/Magazine › Journal article › peer-review
Research output: Contribution to Journal/Magazine › Journal article › peer-review
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TY - JOUR
T1 - Redox control of thermopower and figure of merit in phase-coherent molecular wires
AU - Garcia-Suarez, Victor M.
AU - Lambert, Colin J.
AU - Manrique, David Zs
AU - Wandlowski, Thomas
PY - 2014/5/23
Y1 - 2014/5/23
N2 - 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 ZelT 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 + kappa(p)/kappa(el)), where kappa(p) is the phonon contribution to the thermal conductance and kappa(el) is the electronic contribution. For unstructured gold electrodes, kappa(p)/kappa(el) >> 1 and therefore strategies to reduce kappa(p) are needed to realize the highest possible figure of merit.
AB - 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 ZelT 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 + kappa(p)/kappa(el)), where kappa(p) is the phonon contribution to the thermal conductance and kappa(el) is the electronic contribution. For unstructured gold electrodes, kappa(p)/kappa(el) >> 1 and therefore strategies to reduce kappa(p) are needed to realize the highest possible figure of merit.
KW - molecular wires
KW - single molecule conductance
KW - thermopower
KW - OPE
KW - quantum interference
KW - SINGLE-MOLECULE
KW - THERMOELECTRIC-MATERIALS
KW - THERMAL CONDUCTANCE
KW - JUNCTIONS
KW - HETEROJUNCTIONS
KW - TRANSPORT
KW - ELECTRONICS
KW - DEVICES
U2 - 10.1088/0957-4484/25/20/205402
DO - 10.1088/0957-4484/25/20/205402
M3 - Journal article
VL - 25
JO - Nanotechnology
JF - Nanotechnology
SN - 0957-4484
IS - 20
M1 - 205402
ER -