General strategies to improve thermoelectric performance with an emphasis on tin and germanium chalcogenides as thermoelectric materials

Abstract

Thermoelectric (TE) materials have attracted tremendous research interests over the past few decades, due to their application in power generation technology from waste heat, almost without producing any pollution in the environment. The energy conversion efficiency depends on a dimensionless quantity called the “Figure of merit” (ZT) of the material. The higher value of ZT indicates a material to be a good thermoelectric. So the aim is to find materials with a high ZT value and can commercially be used in devices like thermoelectric generators (TEGs) or thermoelectric coolers (TECs). Some decades ago, the benchmark value of ZT for the available TE materials was ∼1. Still, the application of various novel strategies made it possible to set the target to achieve ZT > 2 or even higher. This review will discuss the traditional and modern strategies for the generic improvement of thermoelectric materials and the progress in thermoelectric performance of Tin and Germanium chalcogenides (SnTe, SnSe, SnS, GeTe, GeSe, and GeS-based materials) over the past few years. Lead chalcogenides have already been one of the best representative materials for TE applications in mid and high-temperature regions for the past few decades. But the toxicity of Pb and related ecological problems restrict their usage for commercial purposes. Sn- and Ge-chalcogenides belong to the same class of (IV–VI) Pb-chalcogenides but cause no serious environmental issues. This article will provide an overview of the progress of Sn- and Ge-chalcogenides as TE materials.