Roles of SiN$_{\mathrm{x}}$ layers in light trapping and carrier collection of nanostructured crystalline Si solar cells

We investigated optical properties and photovoltaic (PV) performance of nanostructured Si solar cells with and without SiN$_{\mathrm{x}}$ dielectric layers. The SiN$_{\mathrm{x}}$ layer contributed to the enhancement of internal quantum efficiency of the nanostructured cells at both short and long wavelengths. In contrast, the surface passivation of SiNx layers on flat cells helped the carrier collection mainly at short wavelength. The surface nanopatterned array enhanced the optical absorption and also concentrated incoming light near the surface in broad wavelength range, revealed by experimental data and optical simulation results. As a result, the nanostructured cells had high density of photo-generated carriers near the surface. This could lead to significant recombination loss of the cells without SiN$_{\mathrm{x}}$ layers. Our work suggested that the SiNx layer played a crucial role in the improved carrier collection of the nanostructured Si PV devices.