Significantly Enhanced Thermoelectric Performance Achieved in CuGaTe 2 through Dual-Element Permutations at Cation Sites.

CuGaTe 2 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 CuGaTe 2 . 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 CuGaTe 2 to nearly zero for Cu 0.97 GaTe 2 , 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 0.72 Ag 0.25 Ga 0.6 In 0.4 Te 2 , while a large average ZT avg value of ∼0.7 (323-873 K) is obtained in the Cu 0.67 Ag 0.3 Ga 0.6 In 0.4 Te 2 sample, both of which are significant improvements over pristine CuGaTe 2 .