High-Performance GeSe-Based Thermoelectrics via Cu-Doping

Rhombohedral GeSe is a promising p-type thermoelectric material, noted for its low toxicity, environmental friendliness, and greater affordability compared with tellurides. However, its thermoelectric performance still requires further enhancement for practical applications. In this work, a highly competitive peak figure of merit (ZT) of 1.24 at 623 K for p-type polycrystalline Ge_0.895Cu_0.005Se_0.9(AgBiTe₂)_0.1, along with a high average ZT of 0.74 between 323 K and 623 K is reported. Comprehensive micro/nanostructural characterization reveals that alloying with AgBiTe₂ and doping with Cu successfully induce dense point defects, secondary Ag₂Te phases, and various nanoprecipitates in the GeSe matrix. These abundant crystalline and lattice defects result in strong phonon scattering, leading to an ultra-low lattice thermal conductivity of 0.35 W m⁻¹ K⁻¹ at 623 K. Moreover, Cu doping enhances carrier mobility, promoting decoupling between carriers and phonons. This allows for low thermal conductivity and high power factor coexistence to achieve a high ZT. Additionally, with a temperature difference of 325 K, the theoretical energy conversion efficiency reaches up to 8.5%, indicating great potential for medium-temperature device applications. This work suggests that Cu doping is an effective strategy for achieving high thermoelectric performance in rhombohedral GeSe-based materials.