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

AgSbSe₂ is regarded as a promising p-type I-V-VI₂ 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 AgSbSe₂. Here, a novel approach is initiated to enhance the thermoelectric properties of AgSbSe₂ 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-yBi_xSe₂ 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 cm² V^-1 s^-1 for pristine AgSbSe₂ to 11.16 cm² V^-1 s^-1 for Ag_1.01Sb_0.9Bi_0.09Se₂, and a high power factor of ≈7.2 µW cm^-1 K^-2 is achieved in Ag_1.01Sb_0.9Bi_0.09Se₂. Simultaneously, the amplified localized off-centering behavior drives a low lattice thermal conductivity of ≈0.37 W m^-1 K^-1 for Ag_1.01Sb_0.9Bi_0.09Se₂ at 673 K, representing a 20% reduction in lattice thermal conductivity than that of pristine AgSbSe₂. As a result, Ag_1.01Sb_0.9Bi_0.09Se₂ 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 AgSbSe₂ thermoelectric materials.