Hierarchically Etched Silicon Lotus Effect Surface Structures for Reduced Light Reflection

Superhydrophobic self-cleaning lotus effect surfaces are of interest for a variety of applications such as self-cleaning, water repellency and anticorrosion properties. Numerous approaches to generate superhydrophobic surfaces have been proposed. In these studies, high contact angles and reduced contact angle hysteresis were intensively investigated. In our study, we invoked a surface etching technique for the preparation of multi-functional (self-cleaning, non-reflecting, water repellent) surface micro/nano structures for potential photovoltaic applications. A facile way of forming superhydrophobic surfaces is reported that uses Au assisted HF/H₂O₂ etching of silicon wafers. The Au layer was deposited onto a silicon wafer via e-beam evaporation. By controlling the evaporation and etching times, the surface roughness can be manipulated and superhydrophobic surfaces with different optical properties can be generated. Contact angles were measured with a CCD camera equipped goniometer; these values determined the water repellency. Light reflection on the as prepared black surfaces was measured to assess the efficiency for low cost solar cell applications. It is expected that by controlled manipulation of surface structures via the etching process, multifunctional silicon surfaces can be achieved and cost-effective photovoltaics may be possible[1].