High‐Performance Bi₂Te₃‐Based Thermoelectrics Enabled by ≈1 nm Metal Chalcogenide Clusters with Size‐Dependent Electron and Phonon Structures

Abstract The untapped potential of sub‐nanometric materials (SNMs) in constructing high‐performance thermoelectrics (TE) presents a promising yet unexplored avenue. This study investigates the utilization of supertetrahedral CdS clusters, representing SNMs, in conjunction with state‐of‐the‐art Bi₂Te₃‐based systems. The CdS cluster with size‐dependent electronic structure enables selective interface scattering of carriers, while its 1 nm size and size‐dependent phonon density of states (DOS) contribute to significant interfacial thermal resistance. Furthermore, interfacial dislocations and significant grain refinement induced by the incorporation of the CdS cluster boost the mechanical properties. Consequently, a remarkable peak figure of merit (ZT) value of 1.47 at 350 K and a record‐high Vickers hardness of 1.08 GPa is achieved in the Bi_0.5Sb_1.5Te₃/0.1 wt% CdS cluster composite. The robust TE module achieves an excellent conversion efficiency of about 6.1% under a ΔT of 241 K. This work opens up exciting possibilities for utilizing 1 nm clusters in thermoelectrics and even inspires other fields involving size‐dependent electrical and thermal transport behaviors.