Nanoporous silicon produced by metal-assisted etching: A detailed investigation of optical and contact properties for solar cells

We present a detailed investigation of the optical and contact quality of silicon wafers textured using metal-assisted etching (MAE) to produce a nanoporous silicon (nSi) surface. We show that the solar weighted reflectance (Rw) of the bare optimized MAE nSi structure is only ∼8%, and this is further reduced to 3% with the addition of an Al2O3/TiO2 stack. We also show that the optical path length enhancement can be >20 near the band edge of Si. The contact resistivity measurements of phosphorus-doped MAE nSi samples show that good contact can be made even on lightly doped samples, and we find no significant difference in contact quality between surfaces with different surface area enlargements (between ∼2.2 and 2.7). This loosens constraints on finger width, helping to achieve reduced shading losses.