Atomic‐Plane Distance as a Structural Indicator for Carrier‐Phonon Decoupling and Band Convergence in Doped BiCuSeO

Although doping is widely applied to enhance the thermoelectric performance of BiCuSeO, little attention is given to how doping‐induced lattice parameter changes affect it. These changes are primarily used to confirm successful dopant substitution. Here, Pb‐doped BiCuSeO serves as a model to reveal structural changes concealed in lattice changes and their critical role. Specifically, the weaker Coulomb interaction between Bi and Se sites induced by doping leads to changes in the Se─Cu─Se angle and Cu─Se bond length. These changes induce band convergence and reduce the bandgap. Additionally, they promote high carrier mobility, reduce phonon group velocity, and expand phonon scattering phase space, realizing carrier‐phonon decoupling. Combined with Pb 2+ substitution, which optimizes carrier concentration, activates multiple converged valence bands, and suppresses phonon transport, the ZT value increases to 1.21. Notably, the extent of bonding configuration change in (Cu 2 Se 2 ) 2− layers can be reflected by the reduced distance between the Cu and Se atomic planes, which may serve as a descriptor for advanced BiCuSeO‐based TE materials design.