Enhancing the thermoelectric performance of Ag₂Se by non-stoichiometric defects

Ag2Se is an attractive candidate for room temperature thermoelectric applications because of its extremely low thermal conductivity, large power factor, and excellent mechanical properties. However, its performance is difficult to be improved effectively by doping other atoms. The traditional synthesis processes have the disadvantages of low yield, complex steps, and long period. In this study, the Ag2Se1+x samples were rapidly synthesized by the melting method via changing the ratio of Ag and Se. The carrier concentration and mobility of Ag2Se are optimized by adding excess Se, which could regulate non-stoichiometric defects in the process of synthesis. A high Seebeck coefficient of ∼136.0 μV K-1, a large power factor of ∼3000.0 μW m-1 K-2, and the maximum figure of merit (ZT) of ∼1.02 of the Ag2Se1.015 sample have been achieved at 375 K. The ZT value is 2.3 times than that of the pristine sample (Ag2Se). The mechanical properties of the molting sample are comparable to state-of-the-art thermoelectric materials. Finally, the highest ZT value of the material is predicted by factor B. This work provides an idea for further optimizing Ag2Se-based and other non-stoichiometric thermoelectric semiconductors by a slight excess of Se. Moreover, the fast synthesis technology can significantly save time and energy, which manifests great advantages to the wholesale manufacturing industry.