Direct Experimental Evidence of Low Carrier Scattering Potential in High Performance Thermoelectric AgSbSe₂ Crystal

Thermoelectric materials, like other electronic materials, require high carrier mobility, which is governed by carrier scattering potential. In addition to intrinsic acoustic phonon scattering, the extrinsic factors such as microstructure and atomic arrangement also have great influence on carrier transport in solids, e.g., the emerging thermoelectric material AgSbSe₂ with strong cation disorder. However, the experimental evaluation of total carrier scattering potential and distinguishing the contributions from intrinsic and extrinsic scatterings is challenging at present. Here, the time-resolved ultrafast spectroscopy analysis utilizing a pump-probe scheme is performed to characterize the charge carrier dynamics of AgSbSe₂ with femtosecond time resolution quantitatively. A significantly lowered total carrier scattering potential energy in Cd-doped AgSbSe₂ crystal is determined, resulting from the elimination of grain boundaries and the presence of short-range order that leads to a negative extrinsic scattering potential. The reduction in carrier scattering potential leads to a threefold increase in the average power factor from 323 to 723 K. A maximum thermoelectric figure of merit of 1.7 is achieved in high-quality AgSb_0.973Cd_0.017Se₂ crystal at 723 K, with the output efficiency of the single-leg thermoelectric device reaching a competitive value of 8%. This work reveals how to effectively characterize and modulate carrier scattering potential in thermoelectric compounds.