Boost the thermoelectric performance of polycrystalline SnSe by combining band engineering and multi-scale defect engineering via K/Ga co-doping

Thermoelectric (TE) materials enable direct conversion between heat and electricity, providing a clean and sustainable solution for waste heat recovery. Single-crystal tin selenide (SnSe) exhibits a record-high figure of merit ZT , but its poor mechanical stability hinders device applications. Polycrystalline SnSe features superior mechanical strength yet suffers from deteriorated electrical transport and abnormally elevated thermal conductivity. Here, we develop a synergistic optimization strategy integrating K/Ga co-doping, carbonate-induced multi-scale defects, and hydrogen reduction to advance the thermoelectric performance of polycrystalline SnSe. Combined first-principles calculations and experimental characterizations reveal that K-rich doping effectively narrows band gap and raises hole concentration to 3.32 × 10 19 cm −3 , Ga-rich doping modulates the valence band structure and reduced the thermal excitation temperature. A peak power factor of 11.42 μW cm −1 K −2 is achieved at 823 K in K 0.01 Ga 0.03 Sn 0.955 Se. The volatilization of carbonates and the artificial introduction of Sn vacancies effectively formed dislocations and point defects. Multi-scale defects spanning point defects, dislocations and grain boundaries strongly scatter full-frequency phonons, and hydrogen removal of high- κ SnO 2 further reduces thermal conductivity κ , yielding a minimum κ of 0.289 W m −1 K −1 at 798 K. Benefiting from the synergistic regulation of electrical and thermal properties, a state-of-the-art ZT max of 2.03 is realized at 823 K. This work offers an effective pathway for designing high-performance polycrystalline SnSe thermoelectric materials.