Direct Measurement of the Absolute Seebeck Coefficient Using Graphene as a Zero Coefficient Reference

Despite the importance of the Seebeck coefficient to thermoelectric materials, the current methods to determine the absolute Seebeck coefficient, S, have not progressed much in 90 years. A clear limitation comes from the superconducting reference material, which requires measurements performed at low temperature. For most thermoelectric applications, S values are deduced at higher temperatures using the Kelvin relation, which, in turn, requires difficult measurements of the Thomson effect. In this work, we present a simple method with graphene transistors to measure the absolute Seebeck coefficient at and above room temperature. As a zero coefficient reference material, graphene naturally provides a zero absolute Seebeck coefficient when the Fermi level is tuned to the charge neutrality (Dirac) point. Here we use a graphene reference device to acquire direct and accurate measurements of the absolute Seebeck coefficient of five different materials (chromel, molybdenum, gold, tungsten, and constantan) from 230 to 390 K. We also highlight how graphene's unique characteristics, including its stability, insensitivity to impurities, and ease of tunable electrical properties, allow for in situ calibration. This work presents graphene as an ideal and robust reference standard of the absolute Seebeck coefficient.