First-principles study of thermoelectric and lattice vibrational properties of chalcopyrite CuGaTe2

• The electronic structure of CuGaTe2 was calculated by first-principles.
• The features of electronic structure show good thermoelectric performance.
• The thermoelectric properties were investigated by Boltzmann transport theory.
• The optimal p- or n-type doping concentrations have been estimated.
• The vibrational properties of CuGaTe2 were calculated and analyzed.

The electronic structure of CuGaTe2 has been investigated using first-principles calculations, and it was discovered that it has a mixture of heavy and light bands near the valence band maximum and a combination of electronically conducting and insulating units near the gap edges, highly desirable for good thermoelectric performance. Semi-classic Boltzmann transport theory was then used to calculate the thermoelectric properties of CuGaTe2, and the optimal p- or n-type doping concentrations have been estimated based on the predicted maximum power factors. The phonon dispersion, phonon density of states, and specific heat of CuGaTe2 were evaluated by density functional perturbation theory in combination with the quasi-harmonic approximation, and the calculated phonon frequencies at the Γ point as well as the specific heat are in agreement with experimental data. The relatively high thermal conductivity of CuGaTe2 at low temperature is attributed to the lack of low-frequency vibrational modes, suggesting that its thermal conductivity can be reduced by introducing additional phonon scattering.

It was reported before that the bulk CuGaTe2 compound exhibits a high ZT value of 1.4 at the temperature about 950 K. The thermoelectric properties of CuGaTe2 have been investigated using first-principles calculations and semi-classic Boltzmann transport theory. According to the carrier concentration dependence of transport properties of CuGaTe2, we can see that there is very little anisotropy, where the transport properties along the xx direction (a-axis) are only slightly larger than the zz direction (c-axis). Furthermore, the p-type CuGaTe2 exhibits a higher value of thermopower S compared with n-type with the same carrier concentrations. The optimum doping levels can be obtained on the basis of the maximum power factors. The optimum doping level of p-type CuGaTe2 is in the range from 2.0 × 1020 cm−3 to 6.0 × 1020 cm−3. As for n-type, the good performance may be obtained in the range of 1.0 × 1020–5.0 × 1020 cm−3.Figure optionsDownload as PowerPoint slide