Probing the band structure and phonon dynamics in Fe mediated Cu2SnS3 for thermoelectric applications

Abstract

Ternary Cu2SnS3 (CTS) is a less toxic, earth abundant, and low-cost p-type semiconductor material, suitable for thermoelectric applications, which can work at mid-temperature. This work aims to investigate the effect of substituting Fe on the thermoelectric properties of the CTS system. It is found that the electrical conductivity enhanced after Fe substitution due to the simultaneous enhancement of carrier concentration, as well as a reduced bandgap from 0.88 to 0.5 eV. The high power factor of ∼514 μW/mK2 was obtained for the Cu2Sn0.7Fe0.3S3 sample. The Fe substitution generated different types of phonon scatterings, such as mass fluctuation scattering arising from the difference in atomic mass of Sn and Fe and strain field scattering as a result of size and interatomic coupling force difference between Sn and Fe. Accordingly, the Fe-substituted CTS samples obtained the thermal conductivity of 0.45 W/mK at 753 K. In addition, the density functional theory calculations reveal that the substitution of Fe in Cu2SnS3 significantly alters the electronic structure and reduces the bandgap, resulting in enhanced electrical conductivity and power factor, thereby a high zT of ∼0.5 is obtained in Cu2Sn0.7Fe0.3S3.