Synergistically optimizing the thermoelectric properties of polycrystalline Ag8SnSe6 by introducing additional Sn

Recently, Ag8SnSe6-based materials, belonging to the family of argyrodite compounds, have been considered as promising thermoelectric candidates due to their intrinsically ultralow lattice thermal conductivity. However, their thermoelectric properties have been rarely investigated because of the intrinsic low carrier concentration. In this work, polycrystalline Ag8SnSe6 bulk materials were successfully synthesized by a bottom-up method by using hydrothermally synthesized Ag8SnSe6 nanocrystals as the precursors. The carrier concentration and mobility of Ag8SnSe6 are successfully enhanced by introducing additional Sn, which should manipulate the self-defects and improve the crystallinity. Thanks to the synergistic optimization of crystal and composition engineering, a maximum ZT value of about 1.22 is achieved for Ag8Sn1.005Se6 at 715 K, which is about 11% higher than that of the pristine sample, and the average ZT is also improved from about 0.65 to about 0.87. This study indicates that crystal engineering and composition engineering play an important role in the thermoelectric properties of Ag8SnSe6 and may provide guidance to improve the thermoelectric performance of other argyrodite compounds.