Coupling Structures for silicon solar cells: Impact of the refractive index

Structured interfaces to reduce reflection and enhance light trapping are standard concepts for silicon solar cells. Within this simulation study we investigated the influence of the refractive index of front side coupling structures on top of a planar wafer based crystalline silicon solar cell on the light trapping performance. A crossed diffraction grating with a period of 1 µm and random pyramid structures with varying refractive index were considered. Simulations were carried out both at cell level and for the complete module stack. It could be shown that the single pass light path enhancement factor (LPEF) only provides a rough estimate of the light trapping properties. The light trapping behavior can only be reliably assessed in the complete system view and, particularly, can provide results that deviate from the single pass LPEF. It could also be shown that the refractive index of the light trapping structure strongly influences the light trapping behavior.