Amorphous or thin-film cells entail the precipitation of a layer of silicon on glass or other substrate. Such layers are less than 1 um thick (the thickness of a human hair is 50-100 um), which means less material and, in turn, reduced production costs. On the other hand, amorphous cells are much less efficient than other types. They are mainly used in low-power devices (watches, calculators) or as façade elements.