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 Ag1+ ySb1-x-yBixSe2 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 Ag1.01Sb0.9Bi0.09Se2, and a high power factor of ≈7.2 µW cm-1 K-2 is achieved in Ag1.01Sb0.9Bi0.09Se2. Simultaneously, the amplified localized off-centering behavior drives a low lattice thermal conductivity of ≈0.37 W m-1 K-1 for Ag1.01Sb0.9Bi0.09Se2 at 673 K, representing a 20% reduction in lattice thermal conductivity than that of pristine AgSbSe2. As a result, Ag1.01Sb0.9Bi0.09Se2 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.