Composition Tuning of Nanostructured Binary Copper Selenides through Rapid Chemical Synthesis and their Thermoelectric Property Evaluation.

Reduced energy consumption and environmentally friendly, abundant constituents are gaining more attention for the synthesis of energy materials. A rapid, highly scalable, and process-temperature-sensitive solution synthesis route is demonstrated for the fabrication of thermoelectric CuSe. The process relies on readily available precursors and microwave-assisted thermolysis, which is sensitive to reaction conditions; yielding CuSe at 200 °C and CuSe at 250 °C within 6-8 min reaction time. Transmission electron microscopy (TEM) revealed crystalline nature of as-made particles with irregular truncated morphology, which exhibit a high phase purity as identified by X-ray powder diffraction (XRPD) analysis. Temperature-dependent transport properties were characterized via electrical conductivity, Seebeck coefficient, and thermal diffusivity measurements. Subsequent to spark plasma sintering, pure CuSe exhibited highly compacted and oriented grains that were similar in size in comparison to CuSe, which led to its high electrical and low thermal conductivity, reaching a very high power-factor (24 µW/Kcm). Density-of-states (DOS) calculations confirm the observed trends in electronic properties of the material, where Cu-deficient phase exhibits metallic character. The TE figure of merit () was estimated for the materials, demonstrating an unprecedentedly high at 875 K of 2.1 for CuSe sample, followed by 1.9 for CuSe. Synthetic and processing methods presented in this work enable large-scale production of TE materials and components for niche applications.