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

CuGaTe-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 antisite defects in the CuGaTe compound promotes the formation of Cu vacancies, and vice versa, which tends to form the charge-neutral structure defects combination with one Ga antisite defect and two Cu vacancies. The accumulation of Cu vacancies in the structure of the (CuTe)(GaTe) compounds evolves into twins and stacking faults. This in conjunction with Ga antisite defects intensify the point defects phonon scattering, yielding a dramatic reduction on lattice thermal conductivity from 6.95 W m K for the pristine CuGaTe sample to 2.98 W m K for the (CuTe)(GaTe) 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/mK at 600 K for the (CuTe)(GaTe) sample, which is 41% higher than for the pristine CuGaTe sample. Consequently, the highest value of 0.82 is achieved at 915 K for Cu(CuTe)(GaTe), which represents an enhancement of about 22% over that of the pristine CuGaTe compound.