Rationally Designing High-Performance Bulk Thermoelectric Materials.

There has been a renaissance of interest in exploring highly efficient thermoelectric materials as a possible route to address the worldwide energy generation, utilization, and management. This review describes the recent advances in designing high-performance bulk thermoelectric materials. We begin with the fundamental stratagem of achieving the greatest thermoelectric figure of merit ZT of a given material by carrier concentration engineering, including Fermi level regulation and optimum carrier density stabilization. We proceed to discuss ways of maximizing ZT at a constant doping level, such as increase of band degeneracy (crystal structure symmetry, band convergence), enhancement of band effective mass (resonant levels, band flattening), improvement of carrier mobility (modulation doping, texturing), and decrease of lattice thermal conductivity (synergistic alloying, second-phase nanostructuring, mesostructuring, and all-length-scale hierarchical architectures). We then highlight the decoupling of the electron and phonon transport through coherent interface, matrix/precipitate electronic bands alignment, and compositionally alloyed nanostructures. Finally, recent discoveries of new compounds with intrinsically low thermal conductivity are summarized, where SnSe, BiCuSeO, MgAgSb, complex copper and bismuth chalcogenides, pnicogen-group chalcogenides with lone-pair electrons, and tetrahedrites are given particular emphasis. Future possible strategies for further enhancing ZT are considered at the end of this review.