Back-side diffractive gratings enhance a solar cell's efficiency by trapping light inside the cell and increasing the probability of absorption. We introduce a three-dimensional, polarization-sensitive optical model combining ray tracing and rigorous coupled-wave analysis to investigate silicon solar cells with pyramidal front-side texturing and back-side gratings. Parameter optimization is performed to increase the short-circuit current density for a linear binary grating with grating period p and height h. For the investigated 180-µm-thick pyramidally textured silicon solar cells, the simulation yields a maximum enhancement of the short-circuit current density by ΔJSC = 1.79 mA/cm2 corresponding to an absolute efficiency increase of Δη = 0.90%. Furthermore, we report on fabrication and reflectance measurements of solar cells with gratings and key challenges in achieving efficiency gains using back-side diffractive gratings. Copyright © 2012 John Wiley & Sons, Ltd.