In thin-film silicon solar cells (TFSC) efficient light management is essential in order to increase energy conversion efficiency. The application of nano-scale periodic gratings (PG) is a promising method to enhance absorption in the absorber layers of TFSC since they can efficiently scatter the incident light. Carefully designed gratings give a possibility to increase the photocurrent over a wavelength range where silicon exhibits a weak absorption. Maxwell's equations solver was employed to carry out optical simulations of TFSC with PG. Atomic force microscopy (AFM) measurements demonstrate that film deposition smoothens the morphology of PG. In the simulations we used the results of AFM measurements to define the morphology of interfaces between the layers of TFSC. An optimum smoothing of interface roughness was determined that resulted in maximum absorption in thin-film silicon solar cells.