Revisiting Light Trapping in Silicon Solar Cells with Random Pyramids

Random pyramids are the most widely used texture in monocrystalline silicon solar cells for reducing front-surface reflection and trapping weakly absorbed light. In prior efforts to evaluate the light-trapping performance of random pyramids through optical simulations, the base angle of the pyramids was assumed to be 54.7 degrees, as is expected from the orientation of the crystallographic planes. In this contribution, we benchmark the light-trapping capability of real random pyramids-which have a distribution of base angles-against both ideal, 54.7 degrees random pyramids, and a Lambertian scatterer. We do so by calculating the path length enhancement and fraction of rays remaining trapped as a function of passes through the wafer, and this information is used to calculate short-circuit current density as a function of wafer thickness. Interestingly, the excellent performance of real random pyramids-they are close to Lambertian-arises precisely because they are imperfect and have a distribution of angles.