High-performance low-cost sulfide/selenide thermoelectric devices

Thermoelectric (TE) materials with high figure-of-merit, ZT, are critical to the development of energy harvesting devices that directly convert heat to electricity. This chapter surveys recent developments in earth abundant high ZT metal selenides and sulfides. Key physical mechanisms leading to high ZT are discussed first, including anharmonicity, band structure engineering by doping, nanoscale size effect and topological defects. The impact of synthesis and consolidation processes on the thermoelectric performance of a range of chalcogenides is described. In particular, factors including changes in stoichiometry, phase separation and precipitation arising from volatilization of the chalcogen at elevated temperatures are discussed. The significant challenges presented by devices constructed from copper chalcogenides exhibiting phonon-liquid electron-crystal (PLEC) behavior are outlined, and strategies to ameliorate the deleterious effects of ionic diffusion in PLEC-based devices reviewed. Material synthesis, spark plasma sintering and emerging TE processing techniques such as screen-printing are described.