Are Topological Insulators Promising Thermoelectrics?

Some of the best thermoelectric (TE) materials to date are also topological insulators (TIs). While many studies have investigated the effects of topologically-protected surface states on TE properties, it is still unclear how the bulk band structure of a TI can benefit the TE performance. Here, we perform high-throughput transport calculations using density functional theory (DFT) to reveal that TIs, when properly optimized, tend to outperform normal insulators as TEs. Models based on Boltzmann transport theory show that warping driven by band inversion, a key characteristic of TIs, is beneficial for TE performance because of reduced transport mass and effectively higher valley degeneracy. The model also reveals that the band inversion strength is a critical material property dictating the TE performance, where TIs with strongly inverted bands exhibit higher <i>zT</i>. We suggest potential avenues for tuning the band inversion strength and, as a result, enhancing the TE performance in TIs, such as alloying and strain engineering. The study marks TIs as serious candidates for TE applications owing to band inversion-driven warping.