Abstract
We investigate the sign and magnitude of the single-molecule Seebeck coefficient of naphthalenediimide (NDI) under the influence of electrochemical gating and doping. The molecule consists of a NDI core with two alkyl chains in the bay-area position, connected to gold electrodes via benzothiophene (DBT) anchor groups. By switching between the neutral, radical and di-anion charge states, we are able to tune the molecular energy levels relative to the Fermi energy of the electrodes. The resulting single-molecule room-temperature Seebeck coefficents of the three charge states are -294.5 μV K-1, 122 μV K-1 and 144 μV K-1 respectively and the room-temperature power factors are 4.4 × 10-5 W m-1 K-2, 3 × 10-5 W m-1 K-2 and 8.2 × 10-4 W m-1 K-2. As a further strategy for optimising thermoelectric properties, we also investigate the effect on both phonon and electron transport of doping the NDI with either an electron donor (TTF) or an electron acceptor (TCNE). We find that doping by TTF increases the room-temperature Seebeck coefficient and power factor from -73.7 μV K-1 and 2.6 × 10-7 W m-1 K-2 for bare NDI to -105 μV K-1 and 3.6 × 10-4 W m-1 K-2 in presence of TTF. The low thermal conductance of NDI-TTF, combined with the higher Seebeck coefficient and higher electrical conductance lead to a maximum thermoelectric figure of merit of ZT = 1.2, which is higher than that of bare NDI in several orders of magnitude. This demonstrates that both the sign and magnitude of NDI Seebeck coefficient can be tuned reversibly by electrochemical gating and doping, suggesting that such redox active molecules are attractive materials for ultra-thin-film thermoelectric devices.
Highlights
Since the Seebeck coefficient of inorganic nanostructures such as nanotubes, nanowires and nanodots can be tuned by electrostatic gating,[14,15,16,17,18,19,20,21] it is natural to explore the response of organic single-molecule junctions to an external electric field, induced by electrochemical gating or charge transfer complexation with dopants
Electrochemical gating is an interesting research tool for probing transport properties, it is not useful for the purpose of creating high-performance thermoelectric devices formed from molecular films, since the electrochemical environment would conductance heat and reduce the efficiency of the film
After demonstrating the efficacy of electrochemical gating, we proceed to examine the effect of doping by the electron donor TTF and the electron acceptor TCNE and demonstrate that doping is a viable route to large Seebeck coefficients and large thermoelectric efficiencies
Summary
We investigate the sign and magnitude of the single-molecule Seebeck coefficient of naphthalenediimide (NDI) under the influence of electrochemical gating and doping. The low thermal conductance of NDI-TTF, combined with the higher Seebeck coefficient and higher electrical conductance lead to a maximum thermoelectric figure of merit of ZT = 1.2, which is higher than that of bare NDI in several orders of magnitude. This demonstrates that both the sign and magnitude of NDI Seebeck coefficient can be tuned reversibly by electrochemical gating and doping, suggesting that such redox active molecules are attractive materials for ultra-thin-film thermoelectric devices
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
