Engineering the electronic band structures of novel cubic structured germanium monochalcogenides for thermoelectric applications

Abstract

Germanium mono-chalcogenides have received considerable attention for being a promising replacement for the relatively toxic and expensive chalcogenides in renewable and sustainable energy applications. In this paper, we explore the potential of the recently discovered novel cubic structured (π-phase) GeS and GeSe for thermoelectric applications in the framework of density functional theory coupled with Boltzmann transport theory. To examine the modifications in their physical properties, the across composition alloying of π-GeS and π-GeSe (such as π-GeS1- xSex for x =0, 0.25, 0.50, 0.75, and 1) has been performed that has shown important effects on the electronic band structures and effective masses of charge carriers. An increase in Se composition in π-GeS1- xSex has induced a downward shift in their conduction bands, resulting in the narrowing of their energy band gaps. The thermoelectric coefficients of π-GeS1- xSex have been accordingly influenced by the evolution of the electronic band structures and effective masses of charge carriers. π-GeS1- xSex features sufficiently larger values of Seebeck coefficients, power factors and figures of merit (ZTs), which experience further improvement with an increase in temperature, revealing their potential for high-temperature applications. The calculated results show that ZT values equivalent to unity can be achieved for π-GeS1- xSex at appropriate n-type doping levels. Our calculations for the formation enthalpies indicate that a π-GeS1- xSex alloying system is energetically stable and could be synthesized experimentally. These intriguing characteristics make π-GeS1- xSex a promising candidate for futuristic thermoelectric applications in energy harvesting devices.