A challenge in organic thermoelectrics is to relate thermoelectric performance of devices to the chemical and electronic structures of organic component inside them on a molecular scale. To this end, a reliable and reproducible platform relevant to molecular-level thermoelectric measurements is essentially needed. This paper shows a new, efficient approach for thermoelectric characterization of large-area of molecular monolayers using liquid eutectic gallium-indium (EGaIn). Cone-shaped EGaIn microelectrode permits access to non-invasive, reversible top-contact formation onto organic surfaces in ambient conditions, high yields of working devices (up to 97%), and thus statistically sufficient thermoelectric data sets (~6000 data per sample in a few hours). We here estimated thermopowers of EGaIn (3.4 ± 0.1 μV/K) and the Ga2O3 layer (3.4 ± 0.2 μV/K) on the EGaIn conical tip and successfully validated our platform with widely studied molecules, oligophenylenethiolates. Our approach will open the door to thermoelectric large-area molecular junctions.

https://pubs.acs.org/doi/10.1021/acs.nanolett.8b03404