Ultralow Thermal Conductivity and High Thermoelectric Performance in AgCuTe1–xSex through Isoelectronic Substitution

In this paper, we report a series of x polycrystalline AgCuTe1–xSe samples with high thermoelectric performance. X-ray photoelectron spectroscopy data suggest the observation of Ag+, Cu+, Te2–, and Se2– states of Ag, Cu, Te, and Se. Meanwhile, the carrier concentration of the obtained p-type samples changes from 9.12 × 1018 to 0.86 × 1018 cm–3 as their carrier mobility varies from 698.55 to 410.12 cm2·V–1·s–1 at 300 K. Compared with undoped AgCuTe, an ultralow thermal conductivity is realized in AgCuTe1–xSex due to the enhanced phonon scattering. Ultimately, a maximum figure of merit (ZT) of ∼1.45 at 573 K and a high average ZT above 1.0 at temperatures ranging from room temperature to 773 K can be achieved in AgCuTe0.9Se0.1, which increases by 186% compared to that of the undoped AgCuTe (0.82 at 573 K). This work provides a viable insight toward understanding the effect of the Se atom on the lattice structure and thermoelectric properties of AgCuTe and other transition-metal dichalcogenides.