Decoupling Electron‐Phonon Transport in AgSbSe ₂ via Stepwise Cd‐Sb Substitution and Interstitial Se Compensation

ABSTRACT P‐type AgSbSe ₂ ‐based thermoelectric materials are promising candidates for power generation due to their high Seebeck coefficient, low thermal conductivity, and earth‐abundant constituent elements. However, their intrinsically low electrical conductivity limits further improvement in thermoelectric performance. Herein, a stepwise atom‐site tuning strategy is employed to progressively enhance the electrical properties and decouple electrical‐phonon transport. Cd doping at the Sb site raises carrier concentration and mobility via acceptor doping and the formation of grain boundary phases, achieving a high σ of ∼90 S cm ⁻¹ at 323K. Subsequent Se enrichment introduces interstitial atoms, enabling counter‐doping while maintaining grain growth, thereby optimizing carrier concentration. As a result, AgSb _0.96 Cd _0.04 Se _2.02 exhibits a significantly enhanced power factor over the entire temperature range, reaching 7.84 µW cm ⁻¹ K ⁻² at 673 K. Moreover, the synergistic effect of Ag ₅ Cd ₈ grain boundary phases, Ag‐rich nanoprecipitates, and dislocations strengthen phonon scattering, leading to an ultralow κ _L that decreases from 0.49 W m ⁻¹ K ⁻¹ at 323 K to 0.35 W m ⁻¹ K ⁻¹ at 673 K. Consequently, a peak zT of ∼1.23 and average zT of ∼0.73 are achieved between 323 and 673 K in AgSb _0.96 Cd _0.04 Se _2.02 . This work demonstrates an effective strategy to decouple the electron and phonon transport, thereby improving the thermoelectric performance of AgSbSe ₂ ‐based materials.