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 Bi 2 Te 3 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 0.93 Bi 0.05 Te over the entire temperature range by introducing Ge deficiency. Further AgSbTe 2 alloying leads to a remarkable increase in density-of-states effective mass and high weighted mobility. Thermally, the addition of AgSbTe 2 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 0.93 Bi 0.05 Te) 85 (AgSbTe 2 ) 15 material, and its maximum single-leg conversion efficiency reaches 8.6 % at Δ 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. • A high average zT of 1.34 (323–573 K) in the lead-free GeTe material. • The maximum single-leg conversion efficiency reaches 8.6 % at Δ T = 273 K. • Ge deficiency and AgSbTe 2 alloying enhance the carrier effective mass, resulting in excellent weighted mobility. • The introduction of multiscale hierarchical defects strongly blocks phonon transport.