Decoupling of Carrier‐Phonon Transport in PbSe with Dumbbell‐Like Occupied Cu ⁺ by Referencing Hume–Rothery Rule

PbSe is considered a candidate for Te‐free thermoelectric materials with the same crystal structure and similar band structure as PbTe. Cu is predicted to introduce impurity energy levels near the valence band of PbSe and increase the Seebeck coefficient. However, the low solid solubility of Cu greatly restricts the improvement of thermoelectric performance for p‐type PbSe. The Hume‐Rothery rule can guide the study of solid solution formation conditions and stability. In this study, one Pb 2+ is successfully replaced with two Cu + in the PbSe matrix, referencing the Hume–Rothery rule, facilitating three‐valence‐band convergence. Meanwhile, the Pb off‐centered caused by the Coulomb force of two Cu + results in the softening phonon mode, synergistically enhancing the power factor and reducing the lattice thermal conductivity. Furthermore, the lowest valence band convergence onset temperature of ≈500 K is achieved for Pb 0.98 Ag 0.02 Se‐2%Cu 2 Se with further Ag‐doping. An average power factor of ≈15.1 µW cm −1 K −2 and an average ZT of ≈0.66 from 300 to 773 K are obtained, which are better than other p‐type PbSe thermoelectric materials. These results indicate that referring to the Hume–Rothery rule can be a promising strategy for enhancing solid solubility and thermoelectric performance.