Rational Design of Cu Vacancies and Antisite Defects for Boosting the Thermoelectric Properties of CuGaTe₂-Based...

CuGaTe₂-based compounds show great promise in the application for high-temperature thermoelectric power generation; however, its wide bandgap feature poses a great challenge for enhancing thermoelectric performance via structural defects modulation and doping the system. Herein, it is discovered that the presence of Ga_Cu antisite defects in the CuGaTe₂ compound promotes the formation of Cu vacancies, and vice versa, which tends to form the charge-neutral structure defects combination with one Ga_Cu antisite defect and two Cu vacancies. The accumulation of Cu vacancies in the structure of the (Cu₂Te)(Ga₂Te₃)_1- compounds evolves into twins and stacking faults. This in conjunction with Ga_Cu antisite defects intensify the point defects phonon scattering, yielding a dramatic reduction on lattice thermal conductivity from 6.95 W m^-1 K^-1 for the pristine CuGaTe₂ sample to 2.98 W m^-1 K^-1 for the (Cu₂Te)_0.45(Ga₂Te₃)_0.55 sample at room temperature. Furthermore, the high concentration of charge-neutral defects combination narrows the band gap and increases the carrier concentration, leading to an improved power factor of 1.58 mW/mK² at 600 K for the (Cu₂Te)_0.49(Ga₂Te₃)_0.51 sample, which is 41% higher than for the pristine CuGaTe₂ sample. Consequently, the highest ZT value of 0.82 is achieved at 915 K for Cu_0.015(Cu₂Te)_0.48(Ga₂Te₃)_0.52, which represents an enhancement of about 22% over that of the pristine CuGaTe₂ compound.