Black silicon—formed by the irradiation of silicon with an ultrafast laser in a sulfur-based atmosphere, or by various etching processes—is finding applications as varied as IR detection and terahertz emission. Now, researchers at the National Renewable Energy Laboratory (NREL; Golden, CO) have discovered that a similar black-silicon layer made nanoporous by a nanocatalyzed etch can be used as an effective antireflection coating for silicon solar cells.
Although black-silicon (bSi) solar cells have been previously demonstrated with conversion efficiencies ranging from 8.8% to 13.9%, systematic analysis of the loss mechanisms was not performed. Researchers at NREL, by studying the reflectance and optical properties of bSi and optimizing the solar-cell fabrication process, developed bSi solar cells with efficiency values of 16.8%. Analysis of bSi solar cells fabricated with a nanoporous etch of different depths (and pore sizes, as well as levels of inhomogeneity) within the silicon substrate revealed that cell efficiency can be maximized by optimizing etch depth and pore size, and by increasing scattering from the backside metallization layer. A 500-nm-deep bSi surface from a three-minute etch allowed routine fabrication of 16.8% efficient solar cells without requiring any antireflection coating. Contact Hao-Chih Yuan at [email protected].