Chemical Composition Modulation Realizing Remarkable Improvement of Thermoelectric Performance in CuInTe₂-Based Alloy

CuInTe₂ (CIT) is one of the typical ternary chalcogenides known for its characteristic mixed polyanionic/polycationic site defects, making it a subject of continuous interest in the field of thermoelectrics. In this work, we propose a chemical composition modulation strategy for CIT by alloying GeTe and then introducing a copper deficiency (denoted by V_Cu). This strategy aims to unpin its Fermi level (F_r) and shift F_r into the valence band (VB) while simultaneously enabling coupling between the optical and acoustic phonon, thereby providing an extra phonon scattering path at low frequencies. The simultaneous composition regulations not only enhance the carrier concentration (n_H) to 10¹⁹-10²⁰ cm^-3 but also significantly reduce the lattice thermal conductivity (κ_L) to ∼0.48 W m^-1 K^-1, thus effectively realizing electro-acoustic coordination in the present material. As a consequence, the thermoelectric (TE) performance is remarkably improved with the highest TE figure of merit (ZT) of 1.51 at ∼838 K. This value ranks at a higher level among CIT-based materials, which showcases the great significance of chemical composition modulation.