A general light trapping theory for grating structures

We use a rigorous electromagnetic approach to analyze the fundamental limit of light-trapping enhancement in grating structures. This limit can exceed the bulk limit of 4n², but has significant angular dependency. We explicitly show that 2D gratings provide more enhancement than 1D gratings. We also show the effects of the grating profile´s symmetry on the absorption enhancement limit. Our findings provide general guidance for the design of grating structures for light-trapping solar.