Isovalent substitution in metal chalcogenide materials for improving thermoelectric power generation – A critical review

The adverse effect of fossil fuels on the environment is driving research to explore alternative energy sources. Research studies have demonstrated that renewables can offer a promising strategy to curb the problem, among which thermoelectric technology stands tall. However, the challenge with thermoelectric materials comes from the conflicting property of the Seebeck coefficient and the electrical conductivity resulting in a low power factor and hence a lower figure of merit. Researchers have reported various techniques to enhance the figure of merit, particularly in metal chalcogenide thermoelectric materials. Here we present a review on isovalent substitution as a tool to decouple the interdependency of the electrical conductivity and Seebeck coefficient to facilitate simultaneous enhancement in these two parameters. This is proven true in both cationic and anionic side substitutions in metal chalcogenide thermoelectric materials. Numerous publications relating to isovalent substitution in metal chalcogenide thermoelectric are reviewed. This will serve as a direction for current and future research to enhance thermoelectric performance and device application. This review substantiates the role of isovalent substitution in enhancing metal chalcogenide thermoelectric properties compared with conventional systems.