Revisiting thermoelectric transport properties through a band nonparabolicity factor

Thermoelectric materials are advanced functional semiconductors for the forthcoming era of energy conversion. The development in this field critically depends on the understanding of their band structures. However, many analyses rely on the parabolic band model that oversimplifies the realistic electron behavior. Such simplification leads to significant deviations in the predicted behavior of electrical transport properties due to the non-local characteristics of the Seebeck coefficient and the Lorenz number. This study introduces a nonparabolicity factor ξ, which quantitatively measures the deviations from parabolic dispersion in semiconductor band structures and can also directly predict the thermoelectric performance change induced by the band nonparabolicity. Notably, our results reveal that the influence of band nonparabolicity is significant when estimating the Lorenz number. We have formulated a universal ξ modified solution for the Lorenz number, which can effectively correct the non-physical lattice thermal conductivity derived from the typical parabolic band model in various representative thermoelectric semiconductors, establishing a basis for further insights into the underlying mechanisms of electrical and thermal transport.