One-Step Carrier Modulation and Nano-Composition Enhancing Thermoelectric and Mechanical Properties of p-Type SnSe Polycrystals by Introducing Ag9GaSe6 Compound

The group IV–VI semiconductor, SnSe, is abundant on the earth and is a promising thermoelectric (TE) material due to its low thermal conductivity. However, the p-type SnSe polycrystals have low electrical conductivities due to their low carrier concentration, significantly limiting their further applications. This study introduced the argyrodite-type Ag₉GaSe₆ compound into the SnSe matrix to effectively increase the hole carrier concentration, increasing the electrical conductivity. A high electrical conductivity of 50.5 S cm⁻¹ was obtained for the SnSe + 0.5 wt% Ag₉GaSe₆ sample at 323 K. Due to the increased electrical conductivity, the SnSe + 0.5 wt% Ag₉GaSe₆ sample had an average power factor (PF_ave) value of ~ 410 μW m^–1 K^–2 in the 323–823 K temperature range, a nearly four times enhancement compared to the undoped SnSe sample. Additionally, the thermal conductivity slightly increased due to the introduction of the Ag₉GaSe₆ compound. However, the electrical transport properties were significantly enhanced, making up for the improvement in thermal conductivity. Consequently, the SnSe + 0.5 wt% Ag₉GaSe₆ sample obtained a peak thermoelectric figure of merit ZT value of ~1.2 at 823 K and a ZT_ave value of 0.58 in the 323–823 K temperature range. The proposed strategy improved the ZT and ZT_ave values of SnSe-based TE materials at room temperature and provided a systematic strategy for modifying SnSe-based TE materials. Moreover, the thermoelectric properties of SnSe can be effectively improved by introducing the Ag₉GaSe₆ compound for doping, and waste heat power generation can be effectively carried out in the middle temperature region.