Superexchange Coupling-Induced Enhancements of Thermoelectric Performance in Saturated Molecules

Abstract

To develop thermoelectric devices, it is of the utmost importance to design organic building blocks to have efficient thermopower. Whereas conjugated and aromatic molecules with intrinsic narrow band gaps are attractive candidates to achieve efficient thermoelectric properties, saturated molecules are usually avoided owing to intrinsically poor thermopower. Here we demonstrate that thermopower of saturated molecules can be enhanced by superexchange coupling. Specifically, thermoelectric properties of large-area junctions that contain self-assembled monolayers of oligo­(ethylene glycol) thiolates and alkanethiolates are compared. Through large-area thermopower measurements using a liquid metal top electrode, we show that the superexchange coupling enhances the Seebeck coefficient and counterintuitively leads to an increase in the Seebeck coefficient with increasing the length in a certain conformation. The improved thermoelectric performance is attributed to the superexchange-induced enhanced ability to mediate metal wave function in junctions. Our work offers new insights for improving the thermoelectric performance of nonconjugated, saturated molecules.

Validating the Mott Formula with Self-Assembled Monolayer (SAM)-Based Large-Area Junctions: Effect of Length, Backbone, Spacer, Substituent, and Electrode on the Thermopower of SAMs

“…Upon insertion of a short (−CH 2 −) spacer (from n = 0 to 1) into benzenethiolate (to afford SC 1 Ph), the value of S increased by ∼23% (Figure a). Our observation is rather surprising given that increased S with increasing the saturated hydrocarbon component is rare in molecular thermoelectrics; to our knowledge, few examples based on oligo­(ethylene glycol) thiolates and oligothiophene thiolates on Au were reported. , To examine the origin of the increased S , we conducted electronic structural analysis with SLM and TVS over the same junction that we used for S measurements. Figure S14 shows F–N plots for the Au TS /SC n Ph//Ga 2 O 3 /EGaIn junctions from which values of − V t and + V t were obtained.…”

Enhanced Thermopower of Saturated Molecules by Noncovalent Anchor‐Induced Electron Doping of Single‐Layer Graphene Electrode

“…Hence, thermopower in saturated molecules would be, in principle, sensitive to the molecule-electrode contact. [5,24]…”

High‐Resolution Capillary Printing of Eutectic Gallium Alloys for Printed Electronics

“…Overall, our results confirm the nanometer‐sized thickness of the native oxide layer as also estimated in other studies. [ 33,36 ]…”

“…Overall, our results confirm the nanometer-sized thickness of the native oxide layer as also estimated in other studies. [33,36] In order to expand the LM-direct writing techniques to fully printed electronic devices, we have focused on the fabrication and functionality of resistors, diodes, and FETs. These devices are particularly interesting for the development of bioelectronic applications [47][48][49] and wearables [9,10,50] where large numbers of them are placed in active arrays and microelectrode applications.…”

“…Similarly, Boley et al reported a direct writing method for gallium-indium based inks in which the LM ink is printed on substrate using a syringe pump, and a computer-controlled stage providing patterns with micron scales. [32] Nozzle based LM deposition can even result in 3D structures: the oxide layer building up on Ga-In-Sn based alloys under ambient conditions, though being only 1-3 nm thick, [33][34][35][36] provides sufficient stability to structures which would ordinarily be untenable due to the extremely high surface tension (>500 mN m −1 ). [37][38][39] However, at the same time, this oxide layer is further complicating printing of gallium-based LM alloys, thus is removed with HCl or NaOH treatment in some approaches.…”