High Thermoelectric Performance SnTe-In₂Te₃ Solid Solutions Enabled by Resonant Levels and Strong Vacancy Phonon Scattering

Herein, we report a significantly improved thermoelectric figure of merit ZT of ∼1.1 at ∼923 K in p-type SnTe through In₂Te₃ alloying and iodine doping. We propose that the introduction of indium at Sn sites in SnTe creates resonant levels inside the valence bands, thereby considerably increasing the Seebeck coefficients and power factors in the low-to-middle temperature range. Unlike SnTe-InTe, the SnTe-In₂Te₃ system displays much lower lattice thermal conductivity. Utilizing a model for point defect scattering, we analyze the origin of the low thermal conductivity in SnTe-In₂Te₃ and attribute it mainly to the strong vacancy originated phonon scattering between Sn atoms and the vacancies introduced by In₂Te₃ alloying and partly to the interfacial scattering by In-rich nanoprecipitates present in SnTe matrix. By alloying only In₂Te₃ with SnTe, a ZT value of ∼0.9 at 923 K was achieved. ZT can be further increased to ∼1.1 at 923 K through adjusting the charge carriers by iodine doping at Te sites.