Enhancing thermoelectric performance of (Cu1-xAgx)2Se via CuAgSe secondary phase and porous design

In the field of thermoelectrics, Cu2Se has attracted extensive attention due to its ultralow lattice thermal conductivity (κl) deriving from its superionicity. Here, we develop a solvothermal method to synthesize Ag-alloyed Cu2Se powders, subsequently sintered to form porous pellets by spark plasma sintering. After detailed characterization, we found that CuAgSe secondary phase forms when Ag has easily surpassed its solubility limit of ~1 at. % and the chemical reaction during the spark plasma sintering causes the formations of the porous structure. Benefiting from these structural features, a very low κl of ~0.23 W m−1 K−1 and in turn an improved figure of merit of ~1.1 at 773 K were secured in the (Cu0.93Ag0.07)2Se pellet. This study suggests that the thermoelectric performance of Cu2Se can be further enhanced by reducing κl via effective engineering methods, such as porosity engineering and introducing additional secondary phase.