Stepwise Vacancy Manipulation for Optimized Carrier Concentration and Blocked Phonon Transport Realizing Record High Figure of Merit zT in CuInTe2

Abstract

Great enhancement in the thermoelectric performance of CuInTe₂ is achieved through stepwise regulation of Cu vacancies. Lowering Cu content can effective introduce large number of Cu vacancies, which is substantiated by positron annihilation measurements. The carrier concentration is thereby successfully tuned from 5.5× 10¹⁸ cm⁻³ to 3.2× 10¹⁹ cm⁻³. The Cu vacancies strongly suppress the lattice thermal conductivity due to both enhanced phonon scattering and lowered phonon velocity. As a consequence, a high zT value exceeding 1.2 at 773 K is achieved in Cu_0.95InTe₂ with optimal carrier concentration of 1.65× 10¹⁹ cm⁻³. The highly Cu deficient Cu_0.90InTe₂ sample is further doped with Bi, which can fill the excessive Cu vacancies. The Bi dopants introduce mass and strain fluctuation, and also cause modulation of lattice structure to form ordered superstructures, which all enhance phonon scattering. In addition, Bi doping results in severe lattice softening, which significantly reduces phonon velocity. As a result, an extremely low lattice thermal conductivity of 1.19 W m⁻¹ K⁻¹ is reached at 300 K. Eventually, a record high zT value of 1.8 at 773 K is achieved in the Cu_0.90Bi_0.06InTe₂ sample, which is almost three times that of the pristine CuInTe₂, reaching the leading level for CuInTe₂-based materials.