Unleashing the Impact of Topological Surface States on the Thermoelectric Properties of Granular Sb₂Te₃ Thin Films Deposited on Flexible Substrates

Between thermoelectric materials, topological insulators (TIs) such as Sb₂Te₃ can effectively decouple phonon and electronic transport. Recent works mostly focused on TI composites or superlattices, where the contribution of the topological surface states (TSS) to the thermoelectric properties is overshadowed by other mechanisms such as energy filtering or electronic band reorganization. Here, we investigate efficient thermoelectric Sb₂Te₃ polycrystalline thin films deposited on plastic foil. Magneto-transport studies show that the presence of TSS in more granular films is responsible for the 2-orders of magnitude higher electronic conductivity compared to thick films owing to larger crystalline domains (> 100 nm). The prevalence of the bulk states in thick films reduces both their thermal and electronic conductivity; however, they are responsible for an increase in the Seebeck coefficient. Overall, we show that to achieve higher thermoelectric performance of single-component TI films, it is necessary to tune the relative contribution of topological and bulk states. This will potentially allow for the development of cost-effective thermoelectric generators, reducing the complexity of competitive systems based on multicomponent heterostructures.