The effect of nano-planarization of pyramidally textured wafer surfaces by wet-chemical treatment on solar cell parameters is investigated. The obtained significant increase of the photocurrent at long wavelengths is attributed to the improvement of the back side reflectance, whereas the higher fill factor is assigned to a lowering of the back contact resistance. Theoretical estimate and numerical modeling support these assumptions. (C) 2012 Elsevier B.V. All rights reserved.