High thermoelectric performance in rhombohedral GeSe ingots achieved by Pb alloying

GeSe, as a medium-temperature thermoelectric (TE) material, exhibits great potential for power generation. Improving symmetry is a pivotal strategy for enhancing the TE properties of GeSe-based materials. Herein, we incorporated 10 mol% AgBiTe₂ as a solid solution into the GeSe matrix to enhance its structural symmetry. Then, we demonstrate a coordinated Pb-alloying strategy that drastically reduced lattice thermal conductivity (κ_lat) without compromising the electrical properties of GeSe-based materials, achieving an advance in thermoelectric performance and conversion efficiency. The Seebeck coefficient is significantly enhanced by the optimized carrier density and enlarged density of states effective mass, thus preserving electrical properties. The lattice conductivity is driven to the near-theoretical minimum through a concerted effect of chemical bonding softening and intensive point-defect phonon scattering. A minimum κ_lat of 0.44 W m⁻¹ K⁻¹ at 473 K is acquired. These concerted mechanisms culminate in a record ZT of 1.35 at 723 K in the (Ge_0.99Pb_0.01Se)_0.9(AgBiTe₂)_0.1 composition. Besides, a single-leg device of Pb-alloyed GeSe realizes a conversion efficiency of 5.5% at a ΔT of 300 K, underscoring its practical potential. This work not only demonstrates a feasible route toward high-performance GeSe thermoelectrics but also provides a generalizable materials-design paradigm applicable to a broad range of low-symmetry chalcogenides.