Enhanced solar reflectance and durability with self-cleaning properties of sputtered multilayer SiO₂-Ag-YSZ-coated aluminum for solar thermal systems

Aluminum (Al)-based solar reflectors (SR) are widely used in concentrated solar power (CSP) due to their broad-spectrum sunlight reflection and high energy capture. However, environmental degradation, including dust accumulation, corrosion, and surface wettability, often compromises reflectance (R) and long-term durability. Here, we report multilayer SiO₂-Ag-YSZ thin films fabricated on Al substrates using magnetron sputtering to simultaneously enhance R, durability, adhesion, and self-cleaning properties. The optimal YSZ deposition parameters (140 W, 220 nm) produced dense, crack-free films with low roughness (10.8 nm), achieved a solar-weighted reflectance (SWR) of 96.72% with a peak R of 98.56% over 300-2500 nm, with angular insensitivity. Mid-infrared reflectance remained high (∼98%) over a 2.5-15 μm, minimizing thermal radiation losses. The multilayer exhibited excellent corrosion resistance and durability with SWR losses of only 1.57% and 1.40% after 240 h of salt spray and 144 h accelerated weathering, respectively. Moreover, the multilayer showed a water contact angle of 130.32°, indicating strong hydrophobicity and favorable self-cleaning properties. Additionally, the nano-mechanical adhesion strength of the multilayer increases from 17.3 mN to 39.5 mN, due to the synergy of SiO₂'s strain accommodation and YSZ hardness, ensuring uniform stress distribution and robust interfacial integrity. These results highlight the potential of multilayer SiO₂-Ag-YSZ films as a high-performance, durable solution for Al-based SR for advanced solar thermal applications.