Direct Measurement of Absolute Seebeck Coefficient Using Graphene As a Zero Coefficient Reference

Abstract

With increasing interest in thermoelectrics for energy applications, determining the thermoelectric power (also known as the Seebeck coefficient) is critical for the characterization and optimization of thermoelectric materials. Obtaining the absolute Seebeck coefficient, however, is difficult due to induced response in the probes contributing to the observed Seebeck effect. Current methods for obtaining the absolute Seebeck coefficient require using a reference material as probes and: estimating it via the Thomson effect, or measuring it directly using a superconductor as a zero coefficient reference. These methods are either cumbersome or are limited to low temperatures, respectively. Graphene, like superconductors, has a zero absolute Seebeck coefficient at the dirac point; additionally, it offers many advantages over superconductors as a reference material as it is stable over a wider range of temperatures and conditions. In this work, we use graphene as a zero coefficient reference to obtain direct measurements of the absolute Seebeck coefficient of five different materials (Au, W, Mo, chromel and constantan) from 250 K to 390 K, and compare to known results with good agreement. Here, we show that graphene’s unique characteristics, including its stability, insensitivity to impurities and ease of tunable electrical properties allowing for in-situ calibration, make it an excellent candidate as a reference standard for direct measurements of the absolute Seebeck coefficient. This work minds an important 75 years pending gap in the field of thermoelectricity.