Photon-Trapping Cu2S Architectures for Next-Generation Solar Thermal Conversion

Abstract

Solar energy harvesting using photothermal nanofluids (NFs) depends greatly on how well light interacts with the suspended particles and how stable those particles remain in the base fluid. This work presents a geometrically engineered hierarchical design of hollow-core copper sulfide (H-Cu₂S) nanostructures (NSs) dispersed in ethylene glycol (EG) to enhance photothermal performance. The tailored shell morphology with hollow-core facilitates multiple light scattering and extended photon trapping, significantly enhancing solar absorption, particularly in the near-infrared region. This morphology-driven approach addresses limitations of conventional polymer or surfactant coatings, which, while improving colloidal stability, often compromise light accessibility and thermal conversion efficiency. The synthesized H-Cu₂S/EG NF demonstrated exceptional colloidal stability, negligible sedimentation, low viscosity enhancement, and robust thermal cycling, even at ultra-low loading of 0.01 wt%. Compared to 2D Cu₂S counterparts, this enhanced photon trapping, combined with the material's intrinsic semiconductor properties, yields an exceptional photothermal conversion efficiency of 86.8%, representing a 64.72% increase over EG as the base fluid. These features are achieved without the need for surface modification, benefiting from the intrinsically low density and optimized geometry of the NS. The resulting NFs exhibit significantly enhanced solar absorption and efficient light-to-heat conversion, establishing H-Cu₂S/EG NFs as promising candidates for next-generation solar thermal technologies.