Negative expansion induced anti-abrasive self-cleaning coatings for enhancing output of solar panels

Pollutants on solar panels impede sunlight absorption, leading to a reduction in their output power. Superhydrophilic coatings exhibit effective self-cleaning performance as droplets fully spread on their surfaces. However, one challenge for the commercial development of transparent superhydrophilic coatings is poor abrasion resistance. Frictional heating on the coatings' surface causes the abrasion force to rise uncontrollably, which in turn causes the coatings to either fracture or wear catastrophically. A promising alternative is utilizing novel adaptive materials with a negative thermal expansion coefficient in the coating. The compressive stress on the surface of the coating with negative expansion will enhance its abrasion resistance. Here, we demonstrate a method to achieve compressive stress in the coating by incorporating halloysite (HNTs) nanotubes due to their negative expansive behavior. Hydrolyzed tetraethyl orthosilicate (TEOS) combines HNTs nanotubes with SiO2 nanoparticles, thus forming a hard nano-composite unit. Meanwhile, amino resin and acrylic resin as adhesives participate in constructing the coating's three-dimensional network structure. The surfactant sodium alkenyl sulfonate (AOS) endows the coating with superhydrophilicity. As a result, the nano-composite (NC) coating shows superior superhydrophilicity and anti-abrasive properties. The NC coating retains good hydrophilicity and self-cleaning properties after 2000 cycles of Taber abrasion loading 250 g or 1000-line cycles of steel wool friction loading 500 g. The self-cleaning performance of the robust NC coating on solar panels can improve the output power by up to 33.65 % after 296 days. Hence, introducing shrinkage components such as HNTs may provide a general strategy for developing robust superhydrophilic coatings.