Electronic structure and thermoelectric performance of SnSe with controlled vacancy population

We report the electronic structure of thermoelectric material SnSe studied by angle-resolved photoemission spectroscopy and first principles calculations. We found that the thermoelectric performance of SnSe strongly depends on its low‑energy electron band structure that provides high density of states in a narrow energy window due to the multi‑valley valence band maximum. Moreover, the binding energy of the valence band maximum can be tuned by the population of Sn vacancy, which can be controlled by the cooling rate during the sample growth. The shift in the valence band maximum follows precisely the behavior of the thermoelectric power factor, while the effective mass is barely modified upon changing the population of Sn vacancies. These findings indicate that the low‑energy electronic structure is closely related with the high thermoelectric performance of hole‑doped SnSe, providing a viable route toward engineering the intrinsic defect‑enhanced thermoelectric performance.