Decoupling Electron-Phonon Transport in AgSbSe₂ via Stepwise Cd-Sb Substitution and Interstitial Se Compensation

P-type AgSbSe₂-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_0.96Cd_0.04Se_2.02exhibits 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 Ag₅Cd₈ 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_0.96Cd_0.04Se_2.02. This work demonstrates an effective strategy to decouple the electron and phonon transport, thereby improving the thermoelectric performance of AgSbSe₂-based materials.