Relationship between thermoelectric figure of merit and energy conversion efficiency

TLDR

Thermoelectric materials generate electricity from temperature gradients, and the dimensionless figure of merit ZT, calculated from the Seebeck coefficient, electrical resistivity, and thermal conductivity, is unreliable for efficiency predictions when these properties vary with temperature. The study aims to establish a new efficiency formula by introducing an engineering figure of merit (ZT_eng) and an engineering power factor (PF_eng) to predict material efficiency across large temperature differences. The authors derived this formula by incorporating temperature‑dependent Seebeck coefficient, resistivity, and thermal conductivity into the engineering figure of merit and power factor, thereby extending performance predictions beyond specific temperatures. These new formulas are expected to profoundly impact the search for new thermoelectric materials.

Abstract

Significance Thermoelectric materials generate electricity from temperature gradients. The dimensionless figure of merit, ZT = S 2 ρ −1 κ −1 T , is calculated from the Seebeck coefficient ( S ), electrical resistivity ( ρ ), and thermal conductivity ( κ ). The calculated efficiency based on ZT using the conventional formula is not reliable in some cases due to the assumption of temperature-independent S , ρ , and κ . We established a new efficiency formula by introducing an engineering figure of merit ( ZT ) eng and an engineering power factor ( PF ) eng to predict reliably and accurately the efficiency of materials at a large temperature difference between the hot and cold sides, unlike the conventional ZT and PF providing performance only at specific temperatures. These new formulas will profoundly impact the search for new thermoelectric materials.