Your answer is in your penultimate sentence ("The hard part is purifying it.") and at the end of the article. >>The German scientists said the cells were fabri

Your answer is in your penultimate sentence ("The hard part is purifying it.") and at the end of the article. >>The German scientists said the cells were fabricated only with wafers relying on recycled silicon and that no commercial ultrapure silicon was added during the manufacturing process. >>The performance of the first trial PERC cells was tested and the devices were found to achieve a power conversion efficiency of 19.7%. “This is below the efficiency of today’s premium PERC solar cells, which have an efficiency of around 22.2 percent, but it is certainly above that of the solar cells in the old, discarded modules,”