Figure of merit ZT of a thermoelectric device defined from materials properties†
While the thermoelectric materials figure of merit is a well defined metric to evaluate thermoelectric materials, it can be a poor metric for maximum thermoelectric device efficiency because of the temperature dependence of the Seebeck coefficient S, the electrical resistivity ρ, and the thermal conductivity κ where T is the absolute temperature. Historically the field has used a thermoelectric device figure of merit ZT to characterize a device operating between a hot side temperature Th and cold side temperature Tc. While there are many approximate methods to calculate ZT from temperature dependent materials properties, an exact method is given here that uses a simple algorithm that can be performed on a spreadsheet calculator. The figure of merit is defined for a thermoelectric generator using the maximum efficiency of the thermoelectric device η calculated from the exact method.