The unique evolution of transport bands and thermoelectric performance enhancement by extending low-symmetry phase to high temperature in tin selenide
Thermoelectric conversion is a promising route to convert heat into electricity. In this process, phase transition may induce an unexpected consequence under certain conditions. In this work, we find that the extending of low-temperature phase with low-symmetry lattice structure, which holds excellent electrical properties and low thermal conductivity, enhances the thermoelectric performance in SnSe-based thermoelectric materials. Peak zT values of 1.14 and 0.94 are obtained along b- and c-axes of SnSe0.7S0.3 single crystal at 820 K, which are about 41% and 27% higher than the pristine SnSe single crystals, respectively. Band structure calculations and angle-resolved photoemission spectroscopy (ARPES) suggest that the unique evolution of transport bands with temperature in SnSe-based materials should be responsible for the abnormal electrical behavior and large Seebeck coefficient in the low-symmetry structure.