AgInTe2 compound has not received enough recognition in thermoelectrics, possibly due to the fact that the presence of Te vacancy (VTe) and antisite defect of In at Ag site (InAg) degrades its electrical conductivity. In this work, we prepared the Ag1-xInTe2 compounds with substoichiometric amounts of Ag and observed an ultralow lattice thermal conductivity (κL = 0.1 Wm−1K−1) for the sample at x = 0.15 and 814 K. This leads to more than 2-fold enhancement in the ZT value (ZT = 0.62) compared to the pristine AgInTe2. In addition, we have traced the origin of the untralow κL using the Callaway model. The results attained in this work suggest that the engineering of the silver vacancy (VAg) concentration is still an effective way to manipulate the thermoelectric performance of AgInTe2, realized by the increased point defects and modified crystal structure distortion as the VAg concentration increases.

As the development of n-type ternary chalcopyrite semiconductors in thermoelectrics (TEs) is relatively slow compared to that of their p-type counterparts, it greatly restricts the fabrication of their modules and real applications. In this work, we prepare n-type AgInSe2-based composites via mixing with their electrical property-counter Ag2Se, where each species plays a role in improving the TE performance. The results confirm that the presence of the minor Ag2Se enhances the Hall carrier concentration (n H) significantly and thereby improves the electrical property of the system. At the same time, it reduces the lattice thermal conductivity (κL) at low temperatures as the phonon scattering in the AgInSe2/Ag2Se heterointerface increases. On another note, the internal lattice distortion (ψ) in the main phase AgInSe2 strengthens as the content of Ag2Se increases, which reduces the κL significantly at high temperatures. As a consequence, the resultant ZT value reaches ∼0.9 at 846 K, about 2.7 times that of the pristine AgInSe2.

The rational synthesis of high‐performance thermoelectric (TE) materials guided by theoretical design is still in its infancy. Here by computationally exploiting the possibilities of materials’ dopability and hence the electron–phonon transport/scattering, a new defective compound, AgGaTe2, with simultaneous Ag deficiency and isoelectronic substitution of In on Ga‐site (InGa) is predicted, and its high performance is then confirmed via experiments. Using density functional theory and density functional perturbation theory calculations, it is identified that controlled defects viz. Ag vacancy and In substitution in AgGaTe2 system can lead to extremely low lattice thermal conductivity (κL) of around 0.13 WK−1 m−1 at 850 K. This ultralow κL results from both the Ag vacancy that serves as a better rattler and the extra phonon scattering due to the defect induced internal lattice distortion (ψ). The synthesized compounds Ag0.85Ga1−xInxTe2 (x = 0–0.3) indeed achieve the extremely low κL (0.08 WK−1 m−1 for x = 0.15). As a result, the highest TE figure of merit (ZT) of 1.44 is obtained, which is the highest recorded value for silver‐based ternary chalcopyrite semiconductors to date.