Atomic Off‐Centering and Grain Boundary Engineering Drive Extraordinary Thermoelectric Properties in AgSbSe ₂

Abstract AgSbSe ₂ is regarded as a promising p‐type I‐V‐VI ₂ thermoelectric material owing to the intrinsically low thermal conductivity and high Seebeck coefficient. However, the intrinsic low electrical conductivity impedes the further enhancement of the thermoelectric performance of AgSbSe ₂ . Here, a novel approach is initiated to enhance the thermoelectric properties of AgSbSe ₂ by combining atomic off‐centering with grain boundary engineering. This work simultaneously promotes the grain growth and amplifies off‐centering behavior for Ag _{1+ y} Sb _{1− x − y} Bi _x Se ₂ by the precise adjustment of the Ag/Sb ratio based on Bi‐doping. The enlarged grain induces the increasing room‐temperature carrier mobility from 2.49 cm ² V ⁻¹ s ⁻¹ for pristine AgSbSe ₂ to 11.16 cm ² V ⁻¹ s ⁻¹ for Ag _1.01 Sb _0.9 Bi _0.09 Se ₂ , and a high power factor of ≈7.2 µW cm ⁻¹ K ⁻² is achieved in Ag _1.01 Sb _0.9 Bi _0.09 Se ₂ . Simultaneously, the amplified localized off‐centering behavior drives a low lattice thermal conductivity of ≈0.37 W m ⁻¹ K ⁻¹ for Ag _1.01 Sb _0.9 Bi _0.09 Se ₂ at 673 K, representing a 20% reduction in lattice thermal conductivity than that of pristine AgSbSe ₂ . As a result, Ag _1.01 Sb _0.9 Bi _0.09 Se ₂ obtains an excellent figure‐of‐merit zT of ≈1.11 at 673 K. The synergistic optimization of cation modulation simultaneously promotes the grain growth and amplifies off‐centering behavior, which provides a new optimization paradigm for designing high‐performance AgSbSe ₂ thermoelectric materials.