Abstract: SnSe₂ single crystals, as novel n-type plastic thermoelectric materials, present advantages such as environmental sustainability and cost-effectiveness. Single crystals of SnSe₂+x%PbBr₂ (x = 0, 0.5, 1, 2, and 3) with large size and high quality were successfully synthesized via the Bridgman method. The significant enhancement in power factor and effective suppression of lattice thermal conductivity can be achieved through PbBr₂ doping, verifying a synergistic optimization of electrical and thermal transport properties. Specifically, Br atoms are effectively incorporated into the Se sites to manipulate the carrier concentration and optimize the power factor, while simultaneously inducing a strong phonon softening effect by introducing Pb atoms at the Sn sites, which leads to a reduced phonon group velocity and a suppression of lattice thermal conductivity. Consequently, SnSe₂+2 %PbBr₂ single-crystal sample achieves a peak figure of merit zT of ∼0.76 and an average zT of ∼0.51, giving rise to corresponding improvements of ∼533 % and ∼538 %, respectively, compared to the pristine SnSe₂ sample, thereby outperforming most of the previously reported SnSe₂-based materials. This work provides a viable approach for promoting the thermoelectric performance of SnSe₂-based single crystals across a broad temperature range and supports the advancement of plastic thermoelectric materials.

Key words: Thermoelectric, SnSe₂ single crystal, Phonon softening, Carrier modulation, Intrinsically low lattice thermal conductivity