The charge localization deteriorating the thermoelectric properties: The case of kiddcreekite-type Cu6WSnSe8

In principle, thermoelectric materials with superior performance require high lattice symmetry and heavy components integrated in semiconductors. Cu6WSnSe8, isostructural to kiddcreekite Cu6WSnSe8, possesses the characteristics for being a promising thermoelectric material, including narrow band-gap, high crystal symmetry, heavy constituent elements, and complex crystal structure. In this work, the thermoelectric transport properties of pristine and copper-deficient Cu6WSnSe8 were investigated. The extremely low hole mobility restricts Cu6WSnSe8 as an excellent thermoelectric parent despite the fact that Cu-deficiency can increase the electrical conductivity and boost the power factor of Cu5.94WSnSe8 by four times than that of pristine Cu6WSnSe8. Combined with density functional theory calculations and X-ray photoelectron spectra analysis, we conclude that the extremely low hole mobility derives from the charge localization around W cations. Due to charge transfer and redistribution, the high valence state W6+ seizes electrons from Se2-, and thus localizing carriers.

Automated summary

Cu6WSnSe8 possesses characteristics of being a promising thermoelectric material but is limited as an excellent thermoelectric parent due to extremely low hole mobility. Although copper deficiency can increase electrical conductivity and power factor, the charge localization around W cations restricts the hole mobility, affecting the thermoelectric properties.