Significantly Enhanced Thermoelectric Performance Achieved in CuGaTe₂ through Dual-Element Permutations at Cation...

CuGaTe₂ has become a widely studied mid-temperature thermoelectric material due to the advantages of large element abundance, proper band gap, and intrinsically high Seebeck coefficient. However, the intrinsically high lattice thermal conductivity and low room-temperature electrical conductivity result in a merely moderate thermoelectric performance for pristine CuGaTe₂. In this work, we found that Cu deficiency can significantly reduce the activation energy E_a of Cu vacancies from ∼0.17 eV for pristine CuGaTe₂ to nearly zero for Cu_0.97GaTe₂, thus leading to dramatic improvements in hole concentration and power factor. More remarkably, element permutations (Ag/Cu and In/Ga) at both cation sites can effectively reduce the lattice thermal conductivity at the entire testing temperatures by producing intensive atomic-scale mass and strain fluctuations. Eventually, an ultrahigh peak ZT_max value of ∼1.5 at 873 K is achieved in the composition of Cu_0.72Ag_0.25Ga_0.6In_0.4Te₂, while a large average ZT_avg value of ∼0.7 (323-873 K) is obtained in the Cu_0.67Ag_0.3Ga_0.6In_0.4Te₂ sample, both of which are significant improvements over pristine CuGaTe₂.