Lead-free GeTe Alloys with High Thermoelectric Performance for Low-grade Waste Heat Energy Harvesting

Harvesting and utilization of low-grade waste heat dissipated from industries have garnered immense attention in recent years. Thermoelectric materials, which can directly convert heat into electricity, provide an eco-friendly solution for waste heat recovery. Recently, GeTe-based materials have developed as strong competitors to Bi₂Te₃ near room temperature. Nonetheless, despite exhibiting comparable thermoelectric performance, the majority of these GeTe alloys incorporate toxic Pb, thus limiting the practical application. Herein, a boosted zT was achieved in Ge_0.93Bi_0.05Te over the entire temperature range by introducing Ge deficiency. Further AgSbTe₂ alloying leads to a remarkable increase in density-of-states effective mass and high weighted mobility. Thermally, the addition of AgSbTe₂ forms various phonon scattering centers including domain structures, dislocations, and phase boundaries, contributing to the low lattice thermal conductivity. As a result, a high average zT of 1.34 (323-573 K) is obtained in the lead-free (Ge_0.93Bi_0.05Te)₈₅(AgSbTe₂)₁₅ material, and its maximum single-leg conversion efficiency reaches 8.6% at $\mathrm{\Delta }$T = 273 K. The outstanding thermoelectric performance and the lead-free characteristic presented in our study shed light on the potential of GeTe alloys for applications in recovering low-grade waste heat.