  Random surface texturing of an optically-thick film to increase the path
length of scattered light rays, first proposed nearly thirty years ago, has
thus far remained the most effective approach for photon absorption over the
widest set of conditions. Here using recent advances in computational
electrodynamics we describe a general strategy for the design of a silicon thin
film applicable to photovoltaic cells based on a quasi-resonant approach to
light trapping where two partially-disordered photonic-crystal slabs, stacked
vertically on top of each other, have large absorption that surpasses the
Lambertian limit over a broad bandwidth and angular range.
