Realizing high thermoelectric performance of CuGaTe2 via CdTe-doping-driven band engineering and chemical bond modulation

Abstract

CuGaTe₂ is p-type thermoelectric material with high thermoelectric potential. However, its performance is hindered by its intrinsic high resistivity and thermal conductivity. In this study, a synergistic strategy combining band engineering and chemical bonding modulation is employed to simultaneously optimize the electrical and thermal transport properties of CuGaTe₂. First-principles calculations reveal that Cd preferentially occupy Ga sites, leading to bandgap narrowing and increasing density of states near Fermi level. Consequently, both carrier concentration and density-of-states effective mass are simultaneously optimized, ultimately power factor reaches 1359 μW·m⁻¹·K⁻². Phonon dispersion analysis reveals that Cd doping induces acoustic-optical phonon avoided crossing behavior, decelerating phonon velocity. Combined with the increase of Grüneisen parameter and weakened chemical bonding, which significantly enhances lattice anharmonicity, leading to effectively reduce in lattice thermal conductivity. Microstructural characterization further reveals that CdTe doping leads to the formation of three-dimensional defect network consisting of point defects, dislocations, and stacking faults enhances phonon scattering. Ultimately, lattice thermal conductivity of doped sample is reduced to 0.81 W·m⁻¹·K⁻¹. Consequently, (CuGaTe₂)_0.9975(2CdTe)_0.0025 sample achieves enhanced zT of 1.05 at 823 K. This work provides insights into the synergistic effects of band engineering and chemical bonding modulation, offering pathway for the design of thermoelectric materials.