Nanostructured back side silicon solar cells

In this paper, we report our investigation on the light trapping enhancement of silicon solar cells via the introduction of nanoscale gratings on the back side of solar cells. The grating is designed to diffract long wavelengths, typically from 900 nm to 1100 nm, leading to an enhancement of the photons path length in the solar cell. Therefore, a gain in current and then efficiency can be expected. The optimal grating parameters were first calculated via RCWA simulations, and were found to be a period of 310 nm for a flat front side and 410 nm for a textured front side. Test structures, with flat and textured front and back side and various silicon dioxide thicknesses on the back side, were then fabricated to confirm the simulation results. Reflection measurements performed on these test structures show a decrease of the reflection in that particular wavelength range for a flat front side. However, spectral response measurements of solar cells will be the only characterisation that can assure us that this decrease in reflection is inducing an increase of absorption in the silicon, as expected by simulation and not in the aluminium layer.