Realizing the High Thermoelectric Performance of CuGaTe₂ via Cd–Ag Codoping Driven Synergistic Band and Defect Engineering

CuGaTe2 is considered a p-type thermoelectric material with great potential due to its high Seebeck coefficient. However, its low carrier concentration and high thermal conductivity remain major bottlenecks, limiting its performance. This study proposes and applies a synergistic approach integrating band and defect engineering to concurrently optimize its thermoelectric performance. First-principles calculations demonstrate that Cd doping shifts the Fermi level into the valence band, narrows the band gap, and introduces additional density of states near the Fermi level. Co-doping with Ag further promotes band flattening, leading to a marked enhancement in density-of-states effective mass, thereby enabling the sample to maintain a power factor exceeding 1200 μW·m–1·K–2. Furthermore, codoping with Cd and Ag induces an “avoided crossing” effect reduces the phonon group velocity and weakens chemical bonding, thereby leading to a reduction in thermal conductivity. Microstructural analyses indicate that co-dopants induce lattice expansion along with the generation of point defects and high-density dislocations. These defects effectively scatter phonons, achieving low thermal conductivity of 0.77 W·m–1·K–1 at 823 K. As a result, Cu0.97Ag0.03Ga0.995Cd0.005Te2 exhibits a ZT value of 1.20 at 823 K. This study not only advances insights into codoping-driven thermoelectric improvements but also introduces a practical band–defect coengineering strategy for developing high-efficiency thermoelectric materials.