Defect Chemistry for Thermoelectric Materials.

Defect engineering, at the core of the field of thermoelectric studies, serves as a scaffold for engineering the intrinsic electrons' and phonons' behaviors to tailor thermoelectric parameters through the direct impacts of band engineering and phonon engineering, which can modify electronic band structure and phonon transport behavior to enhance the power factor (PF = σS2) and reduce the lattice thermal conductivity (κl). By virtue of the implementation of defect engineering, the past decades have witnessed great progress in thermoelectric research through synergistic optimization of the inter-correlated transport parameters, and substantial enhancement has been achieved in the performance of various thermoelectric materials. However, current established optimization strategies based on defect engineering are mainly focused on tuning the electronic and phonon structures, while modulation by additional degrees of freedom caused by defects has long been neglected. In this Perspective, we focus on our interest in the under-exploited aspects of defect engineering, which include defect-related spin effects, defect-mediated atom or charge migration effects, and defect-related interface effects. Through these new points of view, we hope to arouse intense attention to the overlooked parts of defect engineering and combine them with current optimization strategies from the perspective of multiple degrees of freedom modulation, to enable the full potential of defect engineering for boosting thermoelectric performance. Finally, based on the discussion herein and current achievements in thermoelectric research, some personal perspectives on the future of this field are also presented.