Plasmon-like Optical–Thermal Coupling in Nano-Engineered Solar Absorber Coatings Integrated Structural, Spectral, and Photothermal Analysis

This work involves preparing photothermal absorber coatings with nanoparticle additives and their characterization for photo-thermal conversion applications. It includes the correlation between additions of metallic and metal oxide particles, the optical properties of the composite coatings and their photo-thermal conversion characteristics. Coatings incorporating Ni, Fe3O4, CuO, NiO, and MnO₂ are characterized using SEM–EDS, UV–Vis spectroscopy (200–1000 nm), specular reflection measurements. The coatings are also subjected to time-resolved photothermal analysis. Ni-incorporated coatings exhibited the highest measured thermal performance among the investigated coatings. A maximum surface temperature of 93.93 °C and stored thermal energy of 213.10 J with a peak heating rate indicator of 0.360 are obtained corresponding to a visible absorption peak at approximately 540 nm. A high spectral absorptance (AUCα) of about 1.717 and a low reflectivity of 4.6% are also obtained. The results are in agreement with the proposed plasmon-like absorption behavior in metallic Ni nanoparticles that can lead to the transformation of photons into heat. The Fe3O4- and CuO-incorporated coatings show competitive performance due to broadband absorption mechanisms. The NiO- and MnO2-incorporated coatings are found to exhibit lower efficiency due to UV-dominated absorption. Despite its high absorptance, the primary coating thermal response remains limited due to the absence of conductive pathways. Correlation analysis indicates that no individual spectral parameter alone governs photothermal performance. The results demonstrate that effective photo–thermal conversion requires the combined effect of broadband absorption, plasmon-assisted or defect-mediated mechanisms in addition to suitable microstructural characteristics.