Realizing Improved Thermoelectric Performance in BiI₃-Doped Sb₂Te₃(GeTe)₁₇ via Introducing Dual Vacancy Defects

The superior performance of GeTe-based materials has drawn increased attention in the community of thermoelectrics. Originating mainly from the low lattice thermal conductivity (κl) caused by vast planar cation vacancy defects, Sb2Te3-alloyed Sb2Te3(GeTe)17 (Ge17Sb2Te20) samples are able to realize peak ZT values of over ∼2.0 at high temperatures, displaying more promising aptitude than traditional Sb-doped Ge18-xSb2Te20 samples. In this work, BiI3 was doped into Sb2Te3(GeTe)17 samples in order to produce further improvement in thermoelectric behavior. Electron microscopy characterization revealed that BiI3 doping introduced vast anion (Te) vacancies that cluster together as additional phonon scattering sources and that these anion defects can further weaken the potential carrier concentration reduction at high temperatures, thus retaining a large power factor (∼3.4 mW m–1 K–2 at 773 K). The discovery of this anion vacancy defect, together with the planar cation vacancies, allows realization of the simultaneous modulation of electrical and thermal transport properties, resulting in a high maximum ZT value of ∼2.2 at 723 K. Our findings offer an alternative strategy for pursuing thermoelectric performance enhancement of GeTe-based systems.