Low-Angle Grain Boundary Enabled by Pressure for Enhanced Thermoelectric Performance in Chalcopyrite CuInTe ₂ -Based Alloys

Low-angle grain boundaries (LAGBs), as a typical microstructure, offer a promising pathway to address the coupling of electron and phonon transport behaviors in thermoelectrics. However, designing such structures to unlock high thermoelectric performance remains rare. In this work, we engineer LAGB structures in chalcopyrite CuInTe 2 -based alloys by a unique high-pressure sintering technology and unveil the mechanisms underpinning LAGB formation under gigapascal pressures. The energy filtering effect introduced by LAGBs significantly enhances the Seebeck coefficient, coupled with the modulation of Ag doping and Te excess on the electronic structures and carrier concentration, consequently leading to an enhancement in the electrical transport properties. Additionally, high-density dislocations and point defects induced by high pressure and optimized composition strongly suppress phonon transport, lowering the lattice thermal conductivity to 0.49 Wm –1 K –1 . Benefiting from the synergistic effects of LAGBs and optimized composition, a maximum zT of 1.2 at 773 K is achieved in Cu 0.98 Ag 0.02 InTe 2.03 prepared under 2.5 GPa, corresponding to a potential single-leg thermoelectric module with a power density of ∼7060 Wm –2 at Δ T = 500 K.