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

• Published in: Journal of physical chemistry. C Vol. 125; no. 36; pp. 20035 - 20047
• Main Authors: Park, Sohyun, Jang, Jiung, Yoon, Hyo Jae
• Format: Journal Article
• Language: English
• Published: American Chemical Society 16-09-2021
• Subjects: C: Physical Properties of Materials and Interfaces
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.1c05623

Understanding how the Seebeck effect of organic thermoelectric devices is associated with the chemical structure of active molecules within the devices is a key goal in organic and molecular thermoelectrics. This paper describes a series of physical–organic studies that investigate structure–thermopower relationships in self-assembled monolayers (SAMs) through measurements of the Seebeck coefficient (S, μV/K) using the eutectic gallium–indium (EGaIn)-based junction technique. Several hypotheses were derived from a transmission function-based simple toy model, the Lorentzian transmission function-based Mott formula. These hypotheses were tested by comparing values of S for simple alkyl and aryl molecules with different structures in terms of backbone, length, spacer, anchor, and substituent, and for different electrodes (Au vs Ag), and by monitoring responses of S to the structural modifications. Experimentally obtained S values were further reconciled with values simulated by the Mott formula and with interfacial electronic structure and molecule-electrode coupling strength, independently measured by ultraviolet photoelectron spectroscopy and transition voltage spectroscopy.