Resonant enhancement of dielectric and metal nanoparticle arrays for light trapping in solar cells

We numerically investigate the light trapping properties of twodimensional diffraction gratings formed from silver disks or titanium dioxide pillars, placed on the rear of Si thin-film solar cells. In contrast to previous studies of front-surface gratings, we find that metal particles outperform dielelectric ones when placed on the rear of the cell. By optimizing the grating geometry and the position of a planar reflector, we predict short circuit current enhancements of 45% and 67% respectively for the TiO2 and silver nanoparticles. Furthermore, we show that interference effects between the grating and reflector can significantly enhance, or suppress, the light trapping performance. This demonstrates the critical importance of optimizing the reflector as an integral part of the light trapping structure.