Point defects control in non-stoichiometric CuInTe₂ compounds and its corresponding effects on the microstructure and thermoelectric properties

Thermoelectric properties of CuInTe₂ compounds are constrained by characteristic low carrier concentration (~10¹⁷/cm³) and high thermal conductivity (~6 W/mK) at room temperature. These limitations need to be enhanced in order to make these compounds better thermoelectric materials. To resolve the aforementioned issues, we opted to introduce diverse point defects in pristine CuInTe₂ through elemental composition control by either removing cation or adding anion, leading to non-stoichiometric compounds. Compounds with the general chemical composition of Cu_1−xIn_1−yTe_2+z (x, y, z = 0, 0.05), representing Cu poor, In poor and Te rich, were studied in this work. The introduced charged point defects alter both the carrier concentration and tunes phonon scattering. It was found that the carrier concentration of the Cu poor sample increased by about 50 times to ~ 10¹⁹/cm³ compared to the pristine sample. As a result, the highest power factor of ~16.1 μW/cmK² at 723 K was obtained in the Cu poor compound. In addition, a superlattice structure formed by partially ordered Cu vacancies was observed through field-emission transmission electron microscopy, which contributed enhanced phonon scattering. A high ZT value of ~0.98 was obtained at 823 K resulting from decreased lattice thermal conductivity and a record high power factor in the Cu poor condition.