Co-doping enables band convergence, dopability preservation and dislocation engineering in PbTe thermoelectrics
Thermoelectric materials enable direct and reversible conversion between heat and electricity, offering unique advantages for waste heat recovery, solid-state refrigeration, and deep-space power systems. The performance is evaluated by the dimensionless figure of merit, zT = S²σT/κ, where S is the Seebeck coefficient, σ is the electrical conductivity, T is the absolute temperature, and κ is the total thermal conductivity. Achieving high zT requires simultaneous realization of a large power factor (S²σ) and low thermal conductivity. However, these parameters are intrinsically coupled, posing a fundamental challenge. PbTe is a representative thermoelectric material operating in the intermediate temperature range, with outstanding performance originating from its unique electronic band structure featuring multiple nearly degenerate valence band maxima near the L points. Band convergence via alloying with mono-tellurides such as MgTe, MnTe, CdTe, YbTe, SrTe, and EuTe effectively modifies the valence band structure, increasing band degeneracy and density-of-states effective mass, thereby enhancing electrical conductivity without decreasing the Seebeck coefficient. However, increasing the content of these mono-tellurides limits acceptor dopability, making conventional dopants like Na difficult to incorporate. This study demonstrates that co-doping strategies can preserve dopability while achieving band convergence and dislocation engineering, leading to significantly reduced lattice thermal conductivity and extraordinary peak zT values. The decoupling of electronic and thermal transport through this approach offers a promising route for high-performance thermoelectrics.