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

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) is introduced, defined as Φ = ΔE - δ, where ΔE is the valence band offset and δ accounts for interface-induced barrier softening. This enables the direct extraction of extrinsic thermoelectric contributions, including ΔS (Seebeck coefficient), Δσ (electrical conductivity), and ΔP (power factor). An inverse relationship between ΔS and Δσ is revealed, resulting in a nonmonotonic dependence of ΔP on Φ. An analytical volcano plot identifies an optimal ΔE of≈0.48 eV for maximizing ΔP. 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.