Significant Improvement in Thermoelectric Performance of AgInSe₂-Based Composites through In Situ Formation of Ag₂Se

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 (nH) 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.