Synergistic Optimization of Thermoelectric Performance in SnSe2 through co-doping: Anionic Vacancy Formation and Band Engineering

SnSe2 is a layered crystal structure material that is abundant in the Earth's crust and considered non-toxic. However, its thermoelectric properties are anisotropic due to the differences in its interlayer and intralayer electrical and thermal transport properties. The intrinsically poor thermoelectric performance of SnSe2 can be attributed to its lower electrical transport properties in its pristine condition. To address this, we developed a method involving combined mechanical alloying (MA) and spark plasma sintering (SPS) to synthesize n-type Sn-rich Cu-Br co-doped SnSe2 polycrystals. Optimization of Sn enrichment facilitated superior material selection for subsequent doping. The resulting substitutional doping induced a substantial rise in carrier concentration, leading to improved thermoelectric performance. Notably, the power factor displayed a significant increase, reaching approximately 795 µWm-1K-2 at 765 K through Cu-Br co-doping. Furthermore, density functional theory (DFT) analysis elucidated a reduced bandgap and increased degeneracy within the electronic band structure and density of states, affirming the enhancement of thermoelectric properties in Cu-Br co-doped Sn-rich SnSe2 polycrystals. Finally, a maximum figure of merit (ZT) value of 0.46 was achieved at 765 K for the Sn0.985Cu0.015Se1.92Br0.03 sample, perpendicular to the SPS pressing direction, which was nearly threefold higher than the pure SnSe1.95. This compelling outcome highlights the improved thermoelectric performance of the co-doped SnSe2 polycrystals.