Evaluate dimensionless figure of merit for thermoelectric materials based on the intrinsic carrier concentration and bipolar effect

Abstract

Based on the relationship between the carrier concentration and the dimensionless figure of merit (ZT), we develop a method to evaluate the ZT corresponding to the experimental measurement using the transport coefficients, intrinsic carrier concentration, and bipolar effect. Bi2S3 is used to demonstrate the details and confirm the validity. The transport coefficients relative to carrier concentration are obtained by employing the semiclassical Boltzmann theory, while intrinsic carrier concentrations are calculated with the density of states. The ZT free of carrier type and concentration at a specific temperature is evaluated with the bipolar effect caused by the coexistence of two types of carriers. The present results correspond well to the reported experimental data of Bi2S3, confirming the reliability of our method. It is expected that the present method could become a useful basis for identifying more high ZT thermoelectric materials as the candidates for the experimental preparations.