Thermoelectric materials and transport physics

Thermoelectrics is attractive as a green and sustainable way for harnessing waste heat and cooling applications. Designing high performance thermoelectrics involves navigating the complex interplay between electronic and heat transports. This fundamentally involves understanding the scattering physics of both electrons and phonons, as well as maximizing symmetry-breaking in entropy and electronic transports. In the last two decades, thermoelectrics have progressed in leaps and bounds thanks to parallel advancements in scientific technologies and physical understandings. Figure of merit zT of 2 and above have been consistently reported in various materials, especially Chalcogenides. In this review, we provide a broad picture of physically driven optimization strategies for thermoelectric materials, with emphasis on electronic transport aspect of inorganic materials. We also discuss and analyzes various newly coined metrics such as quality factors, electronics quality factor, electronic fitness function, weighted mobility, and Fermi surface complexity factor. More importantly, we look at the non-trivial interdependencies between various physical parameters even at a very fundamental level. Moving forward, we discuss the outlook for the potential of 3D printing and device oriented research in thermoelectrics. The intuition derived from this review will be useful not only to guide materials selection, but also research directions in the coming years.