Simultaneously boosting electrical and thermal transport properties of CuGaTe2 through XCl2 (X = Cd, Zn) doping-driven band and defect engineering†

Abstract

The high resistivity and lattice thermal conductivity of CuGaTe₂ have hindered its development. In this work, the thermoelectric and mechanical performances of CuGaTe₂ thermoelectric materials were synergistically optimized by introducing CdCl₂ and ZnCl₂ to regulate the microstructure. Guided by first-principles calculations in composition design, it was found that the introduction of Cd and Zn increases the electronic density of states near the Fermi level, while significantly reducing the sound velocity. By forming Cd_Ga⁻ and Zn_Ga⁻ acceptor defects, the resistivity was significantly decreased. Additionally, detailed micro/nano-structure characterization indicated that doping generated various scale defects, including high-density dislocations, stacking faults, and nanopores. These nanopores contribute to an energy filtering effect, which effectively counteracts the reduction in the Seebeck coefficient caused by acceptor doping. Moreover, these defects significantly scatter phonons of various wavelengths, leading to a decrease in lattice thermal conductivity. Ultimately, the (CuGaTe₂)_0.985(ZnCl₂)_0.015 sample reached a ZT of 1.35 at 823 K. More importantly, the (CuGaTe₂)_0.985(ZnCl₂)_0.015 sample also exhibited good mechanical properties due to the obstruction of dislocation movement by the multi-scale defects. This work illustrates a method to optimize the performance of thermoelectric materials by rationally introducing metal chlorides, presenting new perspectives for the development of high-performance thermoelectric materials.