  We propose a back-reflecting scheme in order to enhance the maximum
achievable current in one micron thick crystalline silicon solar cells. We
perform 3-dimensional numerical investigations of the scattering properties of
metallic nanostructures located at the back side, and optimize them for
enhancing absorption in the silicon layer. We validate our numerical results
experimentally and also compare the absorption enhancement in the solar cell
structure, both with quasi-periodic and random metallic nanostructures. We have
looked at the interplay between the metallic nanostructures and an integrated
back-reflector. We show that the combination of metallic nanoparticles and a
metallic reflector results in significant parasitic absorption. We compared
this to another implementation based on titanium dioxide nanoparticles which
act as a lambertian reflector of light. Our simulation and experimental results
show that this proposed configuration results in reduced absorption losses and
in broadband enhancement of absorption for ultra-thin solar cells, paving the
way to an optimal back reflector for thin film photovoltaics.
