Synergistic enhancement of Cu2Se thermoelectric properties via Te and S co-doping: aqueous synthesis and cold-press sintering for power generation

Abstract

A series of materials, including Cu₂Se, Cu₂Se_0.96−xS_xTe_0.04 (x = 0.00, 0.01, 0.02, 0.03), and Cu_2−ySe_0.94S_0.02Te_0.04 (y = 0.00, 0.02, 0.04), were synthesized using aqueous solution processing at room temperature, followed by cold-press sintering under vacuum at 923 K for 6 hours. The samples were extensively characterized by X-ray diffraction and evaluated for their electronic and thermal transport properties. Sulfur doping in Cu₂Se_0.96−xS_xTe_0.04 simultaneously reduces electrical resistivity and thermal conductivity. The composition Cu₂Se_0.96−xS_xTe_0.04 with x = 0.02 exhibits the zT of 1.54 at 915 K and the highest average zT of 1.34 between 750 K and 915 K, a 27.62% improvement over Cu₂Se_0.96−xS_xTe_0.04. In the Cu_2−ySe_0.94S_0.02Te_0.04 series, copper deficiency increases thermal conductivity, leading to a decrease in zT, despite an improved power factor. The sample Cu_1.96Se_0.94S_0.02Te_0.04 achieves the highest power factor of 10.64 μW cm⁻¹ K⁻², a 5% increase compared to Cu₂Se_0.94S_0.02Te_0.04. To assess the practical potential of these materials, a thermoelectric generator (TEG) with eight pairs of p-leg Cu₂Se_0.94S_0.02Te_0.04 and n-leg Cu_0.7Ni_0.3 was constructed. The TEG delivers a maximum output voltage of 0.127 V and a peak output power of 21.86 μW at a temperature difference (ΔT) of 120 K. Maximum efficiencies of the p-leg, n-leg, and TEG were 2.0%, 2.25%, and 2.07%, respectively, at ΔT = 120 K and a hot-side temperature of 413 K. These results highlight the potential of the synthesized materials for practical thermoelectric applications.