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 T_h and cold side temperature T_c. 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.