Thermoelectric Effect - Figure of Merit

Figure of Merit

The figure of merit Z for thermoelectric devices is defined as

where σ is the electrical conductivity, κ is the thermal conductivity, and S is the Seebeck coefficient. The dimensionless figure of merit ZT is formed by multiplying Z with the average temperature.

A greater ZT indicates a greater thermodynamic efficiency, subject to certain provisions, particularly that the two materials in the couple have similar Z. ZT is therefore a method for comparing the potential efficiency of devices using different materials. Values of 1 are considered good; values in the 3–4 range are essential for thermoelectrics to compete with mechanical devices in efficiency. To date, the best reported ZT values are in the 3–4 range. Currently this goal of high ZT values is referred to as: "high-figure-of-merit" Much of the research in thermoelectric materials has focused on increasing S and reducing κ by manipulating the nanostructure of the materials.