Toward the Thermoelectric ZT Limit via the Quantification of Interface‐Driven Carrier Sorting

Abstract Interfacial engineering is a promising strategy to enhance thermoelectric performance, but identifying and optimizing the interfacial carrier transport mechanisms required to approach the theoretical ZT limit remains challenging. Here, a unified, quantitative framework is presented to describe and correlate cross‐interface transport with thermoelectric properties in heterostructures. Using SnSe/GeSe superlattices as a model, an effective interfacial energy‐sorting potential ( Φ _eff ) is introduced, defined as Φ _eff = Δ E − δ , where Δ E is the valence band offset and δ accounts for interface‐induced barrier softening. This enables the direct extraction of extrinsic thermoelectric contributions, including Δ S (Seebeck coefficient), Δ σ (electrical conductivity), and Δ P (power factor). An inverse relationship between Δ S and Δ σ is revealed, resulting in a nonmonotonic dependence of Δ P on Φ _eff . An analytical volcano plot identifies an optimal Δ E of≈0.48 eV for maximizing Δ P . At this condition, a four‐layer SnSe/GeSe structure is predicted to achieve a ZT of 2.01, which is remarkable among reported nanoscale thermoelectric materials. This work offers a generalizable strategy for quantifying interface‐governed transport and provides valuable insights into the design of high‐performance nano‐thermoelectric materials and devices.