p-type Sn0.98Ag0.02Se with low thermal conductivity synthesized by hydrothermal method

Tin selenide exhibits outstanding thermoelectric properties. Among its various forms, multicrystalline SnSe stands out as a more practical choice compared to single-crystal SnSe, owing to its straightforward chemical synthesis process, enhanced processability, and scalability. Herein, we synthesized p-type polycrystalline Sn1-xAgXSe bulk materials (x=0, 0.01, 0.015, 0.02, 0.025, 0.03) using a simple hydrothermal and hot pressing method. Characterization methods such as XRD, Raman and XPS were used to demonstrate the successful doping of Ag+ into the SnSe matrix. When the doping concentration reached Sn0.98Ag0.02Se (x = 0.02), Ag+ reached the optimal concentration in the SnSe matrix, causing significant lattice distortion which increased phonon scattering and lowered the thermal conductivity, resulting in Sn0.98Ag0.02Se achieving ZTmax=1.14. However, when the doping concentration exceeded Sn0.98Ag0.02Se (x>0.02), excess silver ions precipitated, partially acting as charge carriers, leading to a significant increase in electrical conductivity, resulting in Sn0.97Ag0.03Se having an electrical conductivity of 6860 s/m at 773 K. Compared to the pure phase, the electrical conductivity of Sn0.97Ag0.03Se increased by 259%, and the ZT value of Sn0.98Ag0.02Se increased by 178%. This work demonstrates that Ag+ is an effective p-type dopant in the SnSe system and indicates that high ZT values in SnSe can be achieved through a simple, low-cost, and environmentally friendly method.