The blackness of black silicon comes from the near-total absence of reflected light from the surface. This is desirable because it means that incident light is being absorbed for conversion to energy, rather than being reflected and wasted. A panel made with black silicon solar cells will produce significantly more energy than one made with cells having a standard antireflective coating – firstly because it reflects less light, and secondly because it performs better during the morning and afternoon when the sun hits it at an angle.
Conventional solar cells with antireflective coatings produced by chemical vapor deposition have a reflectance of about 4%. Previous black silicon technology reduced this to about 2%, but a new technology developed by researchers at Natcore Technology achieves a tenfold improvement. They have shown that simple liquid bath processes can produce a black surface on silicon wafers with an average reflectance in the visible and near-infrared region of just 0.3%, the blackest surface ever measured on silicon solar cells.
The process starts with an uncoated, textured silicon wafer. Nanoscale pores are first etched in the wafer surface by briefly submerging it in a liquid solution at room temperature. A liquid phase deposition process is then used to fill the pores and coat them with silicon dioxide. In addition to reducing the reflectance, the coating passivates the surface.