Impact of the refractive index on coupling structures for silicon solar cells

Structured surfaces are used to reduce reflection and enhance light-trapping in silicon solar cells. In this simulation study, we investigated the relationship between the refractive index of front-side coupling structures on top of planar wafer-based crystalline silicon solar cells and the light-trapping performance of the structures. A crossed diffraction grating with a period of 1  μm and random pyramid structures with varying refractive indices were considered. Simulations were carried out both at the cell level and at the complete module stack level. It is 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 level and these results deviate from the estimated single pass LPEF. It can also be shown that the refractive index of the structure strongly influences the light-trapping behavior.