Highly Enhanced Thermoelectric Performance in Halogen Elements Modified SnSe₂ Materials via Point Defects Engineering

Lead-free SnSe2 materials have intrinsic low thermal conductivities and are promising thermoelectrics. However, their relatively low electrical conductivity limits the improvement of thermoelectric performance. This study successfully introduced halogen elements (X = F, Cl, Br, and I) into SnSe2 to increase carrier concentration for better thermoelectric performance. The defect formation energy calculation results showed the lowest value for SeCl, indicating that incorporating Cl into the SnSe2 matrix could achieve higher thermoelectric performance. Experimental results further verified this conclusion. At 323 K, the electrical conductivity for the SnSe1.94Cl0.06 sample was 86 S cm–1, 61 times higher than that of pristine SnSe2. Combined with the DFT calculation results, the decreased bandgap of the Cl-doped sample benefitted the transport of carriers. Due to the increased electrical conductivity, a peak power factor value of 457μW m–1 K–2 was achieved at 473 K. Meanwhile, the formed point defects decreased the lattice thermal conductivity to 0.38 W m–1K–1 at 773 K, 14% lower than that of the pristine SnSe2 sample. Consequently, the SnSe1.97Cl0.03 sample obtained a peak ZT value of 0.63 at 773 K, five times higher than that of pristine SnSe2. This strategy of thermoelectric performance optimization through the introduction of halogen elements can be applied to other thermoelectric material systems.