Nickel Silicide Nanowire Arrays for Anti-Reflective Electrodes in Photovoltaics

Conductive nanowires (NWs) provide several advantages as a template and electrode material for solar cells due to their favorable light scattering properties. While the majority of NW solar cell architectures studied are based on semiconductor materials, metallic NWs could provide equivalent anti-reflection properties, while acting as a low-resistance back contact for charge transport, and facilitate light scattering in thin layers of semiconductors coated on the surface. However, fabrication of single-crystalline highly anti-reflective NWs on low-cost, flexible substrates remains a challenge to drive down the cost of NW solar cells. In this study, metallic NixSi NW arrays are fabricated by a simple, bottom-up, and low-cost method based on the thermal decomposition of silane on the surface of flexible Ni foil substrates without the need for lithography, etching or catalysts. The optical properties of these NW arrays demonstrate broadband suppression of reflection to levels below 1% from 350 nm to 1100 nm, which is among the highest values reported for NWs. A simple route to control the diameter and density of the NWs is introduced based on variations in a carrier gas flow rate. A high-resolution TEM, XRD and TEM-EDS study of the NWs reveals that they are single crystalline, with the phase and composition varying between Ni2Si and NiSi. The nanowire resistivity is measured to be 10-4 O-cm, suggesting their use as an efficient back electrode material for nanostructured solar cells with favorable light scattering properties.