Cu₂Te Incorporation-Induced High Average Thermoelectric Performance in p-Type Bi₂Te₃ Alloys

p-Type (Bi, Sb)₂Te₃ alloys are attractive materials for near-room-temperature thermoelectric applications due to their high atomic masses and large spin-orbit interactions. However, their narrow band gaps originating from spin-orbit interactions lead to bipolar excitation, thereby limiting average thermoelectrics within a local temperature region (300-400 K). Here, we introduce Cu₂Te into the Bi_0.3Sb_1.7Te₃ (BST) lattice to implement high thermoelectrics over a wide temperature range. The carrier concentration is synergistically modulated via Cu substitution and the evolution of intrinsic point defects (antisites and vacancies). Furthermore, the chain effect caused by Cu₂Te incorporation in BST is reflected in the improvement of the weighted mobility μ_W, thereby enhancing the power factor in the whole temperature range. Extrinsic and intrinsic defects due to the incorporation of Cu₂Te lead to a significant reduction in the lattice thermal conductivity κ_L, which is further demonstrated by Raman spectroscopy. Combining κ_L and μ_W, the quantity factor B increases from 0.5 to 1 with increasing Cu₂Te content due to not only the reduction of κ_L but also a significant improvement in electrical properties. Eventually, a peak figure of merit (zT) of ∼1.15 at 423 K is achieved in BST-Cu₂Te samples, and an average figure of merit (zT_ave) of ∼1.12 (350-500 K) surpasses other excellent p-type Bi₂Te₃-based thermoelectrics. Such a synergistic effect can facilitate near-room-temperature thermoelectric applications of Bi₂Te₃-based alloys and provide chances for the technology space in thermoelectrics.