Atomic Off‐Centering and Grain Boundary Engineering Drive Extraordinary Thermoelectric Properties in AgSbSe₂

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.