Impact of breaking symmetry on the light trapping properties of periodic nanostructures for ultra-thin silicon solar cells

Achieving high optical absorption with crystalline silicon absorber layers which are only a few micrometers thick remains a challenge. Periodic nanostructures can be used for this purpose but need to be optimised in order to achieve the best light trapping properties. In this work we theoretically investigate and quantify the impact of breaking the symmetry on the light trapping properties of periodic nanostructures. By comparing highly symmetric baseline periodic nano-pyramids and asymmetric skewed periodic nano-pyramids, we demonstrate that the absorbed photocurrent density of periodic nanostructures can be enhanced by this measure. For the investigated structure we found an increase of up to 1.6 mA/cm² in absorbed photocurrent density by introducing asymmetry. Moreover, we further demonstrate that such enhancement is due to the stronger coupling of light into high diffraction orders and stronger near-field enhancement by asymmetric structures.