Defect engineering synergistically modulates power factor and thermal conductivity of CuGaTe2 for ultra-high thermoelectric performance

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• The vacancy of Cu atom can increase the band gap and reduce the sound velocity. • Cu vacancies increase the density of the samples, and significantly increase the carrier concentration. • Cu vacancies generate many defects, which scatter phonons at multiple scales and realize thermoelectric decoupling. • The highest ZT value of Cu 0.96 GaTe 2 reaches 1.23 at 823 K, and the average ZT value reaches 0.575. The ternary chalcopyrite CuGaTe 2 has emerged as a promising p -type thermoelectric material with its advantages of low cost, good stability, and non-toxic elements. However, its thermoelectric performance is limited by the intrinsic low electrical conductivity and high lattice thermal conductivity. In this work, A deficiency of Cu in Cu 1– x GaTe 2 semiconductors can be used to optimize the electrical properties by improving the carrier concentration and to reduce thermal conductivity through multi-scale phonon scattering, which is predicted and guided by the First-principles density functional theory calculations. The carrier concentration is increased to 10 20 , which compensates for the low electrical performance caused by the intrinsic low n H of CuGaTe 2 . The average power factor of Cu 0.96 GaTe 2 reaches 106.3% higher than that of the original CuGaTe 2 . In addition, the lattice thermal conductivity of the defective samples is greatly reduced at high temperatures, which is mainly due to the reduction of sound speed and phonon scattering. All the above factors contribute to the highest dimensionless figure of merit (ZT) value of 1.23 at 823 K in Cu 0.96 GaTe 2 , which is 114% higher than the pristine CuGaTe 2 , and the average ZT is 171.4% higher.