Ag-Substituted Nanocrystal Building Blocks for Enhanced Thermoelectric Performance in Earth-Abundant Cu ₁₂ Sb ₄ S ₁₃ Tetrahedrite

Earth-abundant tetrahedrite Cu 12 Sb 4 S 13 is a promising p-type thermoelectric (TE) material owing to its intrinsically low lattice thermal conductivity, yet its performance remains limited by insufficient electrical transport and the persistent trade-off between charge and phonon transport. In this study, we present a colloidal route for the scalable synthesis of Ag-substituted Cu 12 Sb 4 S 13 nanocrystals and use these nanocrystal building blocks to construct bulk tetrahedrite TE materials with improved transport balance. Ag incorporation preserves the tetrahedrite framework while inducing lattice expansion, increased microstrain, local bond softening, and enhanced structural disorder, which can be retained to a meaningful extent after densification. These structural perturbations are accompanied by a marked enhancement in electrical conductivity and weighted mobility, together with a substantial suppression of lattice thermal conductivity. The optimally substituted Cu 11.92 Ag 0.08 Sb 4 S 13 sample exhibits the best overall transport performance, reaching a lattice thermal conductivity of 0.30 W m –1 K –1 and a maximum zT max of 1.23 at 690 K, representing an approximately 1.8-fold improvement over pristine Cu 12 Sb 4 S 13, as well as competitive theoretical conversion efficiency and slightly improved hardness. These results highlight Ag-substituted nanocrystals as effective building blocks for improving the TE performance of earth-abundant tetrahedrites through coordinated control of structure and transport.