Advancing Thermoelectrics in Lead-Free Rhombohedral GeTe via Interfacial Engineering With MXene

Lead-containing GeTe-based thermoelectric (TE) materials exhibit outstanding performance, but the toxicity of lead (Pb) limits their practical applications. Lead-free GeTe-based TE materials present a promising alternative for environmentally sustainable and scalable applications. Here, Bi doping is used to reduce the majority carrier concentration in GeTe, combined with uniform incorporation of nanoscale layered MXene via high-energy ball milling. This approach significantly enhances the structural symmetry of GeTe, while MXene further reduces carrier concentration and improves carrier mobility. Consequently, the Ge_0.93Bi_0.07Te-0.6 mass% MXene sample achieves an impressive average power factor of ≈28.40 µW m⁻¹ K⁻² across 303–603 K. Moreover, point defects, multilayer nanostructures, and grain boundaries reduce thermal conductivity to ≈1.04 W m⁻¹ K⁻¹ at 603 K. A maximum ZT_max of ≈2.1 at 603 K, an average ZT_avg of ≈1.1, and a Vickers microhardness of ≈ 236.75 H_v are obtained. In particular, a high power density of ≈1.54 W cm⁻² and a maximum conversion efficiency of ≈7.5% at a temperature difference of 300 K are achieved in a 7-pair TE module. These outcomes represent the highest performance levels for lead-free GeTe-based materials. This work uncovers a straightforward method to enhance the structural symmetry of GeTe-based compounds, providing insights for advancing lead-free TE technologies.