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 Ag₈Sn_1.005Se₆ 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.