New limits for light-trapping with multi-resonant absorption

We propose a new paradigm for light trapping in solar cells. It is based on multi-resonant absorption (MRA) with a two-dimensional periodical pattern. We develop a simple theoretical model and we derive the upper limit of optical absorption in a slab of semiconductor. This MRA limit exceeds the conventional Lambertian limit (4n2) by a factor of $\pi$ for any absorber thickness: the maximum optical path enhancement factor is F =4$\pi \mathbf{n} ^{2}$. We describe the main results and discuss the strong thickness reduction achievable with multi-resonant light trapping strategy.