High‐Performance GeSe‐Based Thermoelectrics via Cu‐Doping

Abstract 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 0.895 Cu 0.005 Se 0.9 (AgBiTe 2 ) 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 AgBiTe 2 and doping with Cu successfully induce dense point defects, secondary Ag 2 Te 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.