Efficient light-trapping nanostructures in thin silicon solar cells

We examine light-trapping in thin crystalline silicon periodic nanostructures for solar cell applications. Using group theory, we show that light-trapping can be improved over a broad band when structural mirror symmetry is broken. This finding allows us to obtain surface nanostructures with an absorptance exceeding the Lambertian limit over a broad band at normal incidence. Further, we demonstrate that the absorptance of nanorod arrays with symmetry breaking not only exceeds the Lambertian limit over a range of spectrum but also closely follows the limit over the entire spectrum of interest for isotropic incident radiation. These effects correspond to a reduction in silicon mass by two orders of magnitude, pointing to the promising future of thin crystalline silicon solar cells.