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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 - Quantum and Phonon Interference Enhanced Molecular-Scale Thermoelectricity
AU - Sadeghi, Hatef
PY - 2019/5/14
Y1 - 2019/5/14
N2 - Simultaneous engineering of electron and phonon transport through nanoscale molecular junctions is fundamental to the development of high-performance thermoelectric materials for the conversion of waste heat into electricity and cooling. Here, we demonstrate a systematic improvement of the room-temperature thermoelectric figure of merit (ZT) of molecular junctions. This is achieved by phonon interference (PI)-suppressed thermal conductance and quantum interference-enhanced electrical conductance and Seebeck coefficient. This strategy leads to a significant enhancement of ZT from low values ca. 10–6 in oligo(phenylene-ethynylene) (OPE2) to the record values of 2.4 in dinitro-functionalized OPE2 (DOPE2). The dinitro functionalization also considerably enhances ZT of biphenyl-dithiol (BDT) and bipyridyl molecular junctions. Remarkably, the energy levels of electron-withdrawing nitro groups are hardly changed from one molecule to the other. Because of this generic feature, a resonance transport in the vicinity of Fermi energy of electrodes is formed leading to a significant improvement of Seebeck coefficient and ZT of all derivatives. For example, the Seebeck coefficient enhances from 10.8 μV/K in BDT to −470 μV/K in dinitro-BDT (DBDT). In addition, destructive PI due to the nitro groups suppresses phonon thermal conductance, for example, from 20 pW/K in BDT to 11 pW/K in DBDT at room temperature. We also demonstrate that quantum and PI-enhanced single-molecule thermoelectric efficiency is conserved when parallel molecules are placed between gold electrodes. These results promise to remove the key roadblocks and open new avenues to exploit functionalized organic molecules for thermoelectric energy harvesting and cooling.
AB - Simultaneous engineering of electron and phonon transport through nanoscale molecular junctions is fundamental to the development of high-performance thermoelectric materials for the conversion of waste heat into electricity and cooling. Here, we demonstrate a systematic improvement of the room-temperature thermoelectric figure of merit (ZT) of molecular junctions. This is achieved by phonon interference (PI)-suppressed thermal conductance and quantum interference-enhanced electrical conductance and Seebeck coefficient. This strategy leads to a significant enhancement of ZT from low values ca. 10–6 in oligo(phenylene-ethynylene) (OPE2) to the record values of 2.4 in dinitro-functionalized OPE2 (DOPE2). The dinitro functionalization also considerably enhances ZT of biphenyl-dithiol (BDT) and bipyridyl molecular junctions. Remarkably, the energy levels of electron-withdrawing nitro groups are hardly changed from one molecule to the other. Because of this generic feature, a resonance transport in the vicinity of Fermi energy of electrodes is formed leading to a significant improvement of Seebeck coefficient and ZT of all derivatives. For example, the Seebeck coefficient enhances from 10.8 μV/K in BDT to −470 μV/K in dinitro-BDT (DBDT). In addition, destructive PI due to the nitro groups suppresses phonon thermal conductance, for example, from 20 pW/K in BDT to 11 pW/K in DBDT at room temperature. We also demonstrate that quantum and PI-enhanced single-molecule thermoelectric efficiency is conserved when parallel molecules are placed between gold electrodes. These results promise to remove the key roadblocks and open new avenues to exploit functionalized organic molecules for thermoelectric energy harvesting and cooling.
U2 - 10.1021/acs.jpcc.8b12538
DO - 10.1021/acs.jpcc.8b12538
M3 - Journal article
VL - 123
SP - 12556
EP - 12562
JO - The Journal of Physical Chemistry C
JF - The Journal of Physical Chemistry C
SN - 1932-7447
IS - 20
ER -