Multifunctional Cu Doping Enhances Electron Transport and Thermoelectric Performance in n-Type BiSbSe₃

The thermoelectric material BiSbSe₃ possesses an intrinsically low lattice thermal conductivity through its weakly bonded chain-like structure. However, these weak inter-chain bonds also severely limit carrier mobility. Herein, we demonstrate that Cu doping effectively alleviates this limitation through dual mechanisms. The incorporation of Cu atoms into both substitutional and interstitial sites increases the charge density, directly facilitating electron transport. Concurrently, Cu-doping optimizes carrier concentration at elevated temperatures, reducing band degeneracy and lowering the effective mass, contributing to the improvement in high-temperature carrier mobility. This synergistic optimization yields a 135% enhancement in the average power factor between 600 and 800 K, obtaining a maximum ZT of ∼1.2 at 800 K and an average ZT of ∼0.85. A single-leg device fabricated from an optimal BiSbSe₃-0.05Cu sample attains a thermoelectric conversion efficiency of ∼6.3% under a temperature difference of 475 K. These results validate the Cu-mediated charge-density modulation as an effective strategy for decoupling electron and phonon transport, underscoring the practical promise of this low-cost BiSbSe₃-based thermoelctric material.