High performance thermoelectric materials and devices based on GeTe

Abstract

Thermoelectric materials have received recent attention due to their ability to convert waste heat to electrical energy directly and reversibly. Inorganic materials, especially Bi₂Te₃, PbTe and Si–Ge based alloys, have been investigated in the temperature range of 300–1000 K, among which PbTe based materials have been extensively studied, and reported to be the leading thermoelectric materials for mid-temperature power generation. However, environmental concern limits their large scale production due to the toxic nature of Pb. As an alternative, GeTe-rich alloys such as TAGS (GeTe–AgSbTe₂) have been largely investigated since the 1960s. Most recently, some of the new materials in the GeTe family have been introduced such as Ge_0.87Pb_0.13Te, the homologous series of Sb₂Te₃(GeTe)_n and Ge_0.9Sb_0.1Te, and are reported to exhibit high thermoelectric performance, inherently formed nano and microstructure modulations, and high thermal and mechanical stability. These collective enhanced properties of GeTe-rich alloys have generated great interest in investigating further new GeTe based alloys for intermediate temperature thermoelectric applications. In order to provide the fundamental understanding, technological insights, and to further promote the GeTe based alloys, we hereby present a review on (i) the crystal structure, nano/microstructure, phase transition, electronic structure, and thermoelectric properties of GeTe, (ii) correlation of compositional and microstructure modulations and thermoelectric properties of doped GeTe, TAGS based alloys, Ge–Pb–Te materials, and Ge–Sb–Te materials, (iii) mechanical properties, (iv) past and present devices based on GeTe materials and (v) future directions.