(A) Percentage chart of worldwide energy consumption, in which low-grade waste heat, high-grade waste heat, useful parts, and others account for ~30%, ~30%, ~33% and ~6%, respectively. (B) Schematic illustration of pseudo-nanostructure design in PbTe. (C) Cartoon of structure-dependent hole trap and release. By introducing Na and Ge doping into the PbTe, the size of the pseudo-nanostructure is shrunk, forming a vacancy cluster, which effectively increased the scattering of phonons. Meanwhile, by replacing the Pb with Ge, the carrier is captured at low temperature and released at high temperature, and the carrier concentration can be dynamically controlled. Adapted from Ref. [9]. Reprint with permission from AAAS.