Large batches of nominal 10 cm×10 cm solar cells of 14% efficiency have been made from improved lifetime silicon sheet octagons grown by the Edge‐defined Film‐fed Growth (EFG) technique. At the level of bulk material quality achieved, limitations to further increases in cell efficiencies start to arise from solar cell design. The potential is examined for producing over 16% cell efficiencies with current EFG octagon material as its thickness is decreased from 400 to 200 &mgr;m.