Hybridizing ZnO Nanowires with Micropyramid Silicon Wafers as Superhydrophobic HighEfficiency Solar Cells

Low conversion efficiency is still the main limiting factor for current solar-cell technologies. A large portion of the energy loss during solar-cell operation is attributed to optical loss, namely the loss of the incoming light by reflection.[1] To reduce the reflection loss, surface texturing and antireflection coatings are the most-commonly used strategies.[2–4] Surface texturing is able to enhance light trapping by multiplying the internal reflections. The industrial standard for the current Si-based photovoltaic (PV) industry process is alkaline fabrication of micrometer-sized pyramid textures. An emerging focus today is the incorporation of nanostructures as surface-texturing materials.[5–8] For example, porous Si and Si nanowires (NWs) have been applied to solar cells to effectively reduce the reflection loss.[9–11] Xiu et al. developed a hierarchical structure through a two-tier texturing method for lower light reflection.[12] Using an antireflection coating (ARC) is another method to reduce light reflectance via destructive interference of the reflected light at the air–ARC–substrate interfaces. A single-layer ARC, such as silicon nitride (SiNx), is the industry standard ARC on Si PVs.[13] A further reduction of reflection can be achieved through a multilayer ARC or fine control of the ARC geometry, which enables a gradual transition of the refraction index from air to the silicon.[14,15] As an outstanding 1D nanostructure, ZnO NWs have a high transparency due to the wide bandgap, appropriate refractive index (n ≈ 2 at 600 nm), and the capability of forming a textured coating on virtually any substrate.[16–19] These characteristics make it an attractive dielectric ARC material for PV applications. By the integration of ZnO NWs with optical fibers and quartz waveguides, an enhancement of the efficiency by a factor of 4–6 has been shown by utilizing a three-dimensional approach.[20,21] The application of ZnO nanostructures on planar Si as an ARC for solar cells has achieved a weighted reflectance