The solar selective absorption film independently developed by Sanrong possesses the following characteristics:
1. Increase the specific surface area of the substrate to form a micro‑rough surface with irregularities ranging from 0.5 to 2.0 μm.
2. Fabrication of highly porous phosphate anodic oxide films;
3. The pores of the anodic oxide film are filled with appropriate materials, enabling the oxide layer to absorb solar wavelengths within the desired range.