Solar cell characteristics of a-Si/nc-Si tandem devices as a function of substrate texture. Symbols indicate the characteristics of the best (closed) and average of best 5 (open) cells on a substrate, based on conversion efficiency. Symbol type indicates results of devices with high-E_G a-Si (diamond) and low-E_G a-Si (circle). J_sc is obtained from EQE-measurements and is presented separately for the bottom nc-Si junction, top a-Si junction and sum of both junctions.