Ecofriendly Highly Robust Ag₈SiSe₆-Based Thermoelectric Composites with Excellent Performance Near Room Temperature

Bi₂(TeSe)₃ is a dominant n-type thermoelectric material used in commercial applications. However, its toxicity and rarity hamper further large-scale industrial applications. Herein, we develop a Ag₈SiSe₆-based composite as a promising n-type semiconductor with the advantages of nontoxicity and elemental abundance. Ag₈SiSe₆ composites with Ag₂Se and Si nanoprecipitation are fabricated by a unique precipitation reaction sensitive to the hot pressing process. The energy-filtering effect between these phases optimizes electrical resistivity (∼14.59 μΩ·m) and the Seebeck coefficient (above -150 μV·K^-1) of the composites, resulting in a maximum power factor of ∼1772 μW·m^-1·K^-2(@125 °C), which is the highest value in an argyrodite system near room temperature. Nanoprecipitation of Ag₂Se and Si can also scatter more phonons and further reduce the lattice thermal conductivity to 0.20 W·m^-1·K^-1. As a result, a maximum ZT value of ∼0.9 (@125 °C) and an average ZT value of ∼0.7 (25-200 °C) are obtained in the composite with 12 vol % Ag₂Se and 0.23 vol % Si, which is sintered at 525 °C. These thermoelectric properties are comparable to those of a commercial n-type Bi₂Te₃ compound. In addition, the Ag₈SiSe₆ composite has robust mechanical properties (Vickers hardness of >110 HV and bending strength of 70.6 MPa), much better than those of other thermoelectric compounds, because of which Ag₈SiSe₆ has great commercial application as an alternative to Bi₂Te₃-based compounds.