Enhanced thermoelectric performance of Cu₂Se realized by Ag₂S doping

In this paper, Cu2Se samples doped with different concentrations of Ag2S were prepared by mechanical alloying and spark plasma sintering. Ag and S elements diffused during the preparation process and appeared aggregation in EDS mapping images. AgCuSe impurity phase can be observed in Cu2Se samples after Ag2S doping. Because of the enhanced scattering of the low- and mid-frequency phonons by AgCuSe nano inclusion, the total thermal conductivity of the Ag2S doped samples exhibits a significant decrease. Additionally, the diffusion and substitution of S can efficiently impede the formation of Cu vacancies. Ag ions can also fill the Cu vacancies, leading to the decreasing carrier concentration. Finally, the thermoelectric property is improved and the maximum ZT value similar to 1.5 is achieved at 820 K in Cu2Se/ 2% Ag2S, which is about 1.5 times of the undoped Cu2Se sample.