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 Ge0.895Cu0.005Se0.9(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. P-type rhombohedral GeSe as Ge0.895Cu0.005Se0.9(AgBiTe2)0.1 has a peak ZT of 1.24 at 623 K and an ultra-low lattice thermal conductivity of 0.35 W m-1 K-1, which is attributed to the dense point defects, Ag2Te phases, and nanoprecipitates with strong phonon scattering. A theoretical energy conversion efficiency of 8.5% highlights the potential of GeSe for medium-temperature applications. image