Compositional modification for efficient near-room-temperature Ag2Se thermoelectrics through modulation decoration of amorphous Sb2S3

Compositing a secondary phase in Ag₂Se can usually tune the electron and phonon scattering to improve the thermoelectric performance. However, the intrinsically high carrier concentration still limits the performance optimization. Here, we employ a modulation decoration strategy to simultaneously achieve submicron-scale constituents and compositional modification for synergistic optimization of thermoelectric properties. Amorphous nano Sb₂S₃ has been decorated on the surface of Ag₂Se powders, and S was added into the Ag₂Se matrix through an ion exchange reaction accompanied by the formation of a crystal/amorphous mixed secondary phase of Sb₂(S, Se)₃. The S doping reduced the excessive intrinsic carrier concentration, leading to modified electrical transport properties and significantly reduced electrical thermal conductivity. On the other hand, introducing the S dopants and the crystal/amorphous interfaces into the Ag₂Se matrix could increase the lattice anharmonicity, further contributing to the reduced thermal conductivity. Consequently, the Ag₂Se-0.4% Sb₂S₃ sample obtains a high average zT value of > 1 in the temperature range of 300–390 K. In addition, the maximum cooling temperature difference of over 85 K can be predicted in an Ag₂Se/Ag₂Se-0.4% Sb₂S₃ segregated module at the hot side temperature of 350 K.