Resonant level and band splitting boost the thermoelectric performance of p-type polycrystalline SnSe

Due to its abundant raw-material resources, high intrinsic Seebeck coefficient, and low intrinsic thermal conductivity, SnSe has emerged as a standout among numerous thermoelectric materials. However, achieving thermoelectric performance in polycrystalline SnSe that approaches the high-performance single-crystal materials remains a challenge. Here, we design high-performance p-type polycrystalline SnSe co-doped with Ge and Ga by validating through first-principles calculations. Ge-doping causes band splitting and reduced bandgap of SnSe, while Ga-doping introduces resonant levels, thereby synergistically enhancing its originally low intrinsic carrier concentration to improve electrical conductivity. Additionally, co-doping introduces intensive point defects and other lattice defects, which strengthen phonon scattering and effectively reduce thermal conductivity. As a result, the ZT value of polycrystalline Sn0.955Ge0.005Ga0.04Se reached 1 at 773 K. The findings highlight the significant importance of rational band engineering in achieving excellent thermoelectric performance and advancing the progress of thermoelectric technology.