Interfacial Reconstruction Enables Enhanced Thermoelectric Performance in Bismuth Telluride‐Based Alloys

Bismuth telluride‐based alloys are the benchmark thermoelectric materials for near‐room‐temperature power generation and solid‐state cooling, yet further performance improvements through conventional optimization strategies remain challenging. Here, we introduce an interfacial reconstruction strategy by incorporating SnSe into Bi 0.4 Sb 1.6 Te 3 . Interdiffusion and chemical reconstruction at the Bi 0.4 Sb 1.6 Te 3 /SnSe heterointerfaces synergistically regulate charge‐carrier transport and phonon scattering. As a result, the optimized composite achieves a peak dimensionless figure of merit ( ZT ) of ∼1.38 at 363 K and an average ZT of ∼1.25 across 303–423 K. Moreover, a single‐leg thermoelectric device fabricated from this material delivers an energy conversion efficiency of ∼6.47% under a temperature difference of 200 K. These results establish interfacial reconstruction as a simple and effective approach to improving the thermoelectric performance of bismuth telluride‐based alloys.