From Wikipedia, the free encyclopedia. A wafer, also called a slice or substrate, is a thin slice of semiconductor material, such as a crystalline silicon, used in electronics for the fabrication of integrated circuits and in photovoltaics for conventional, wafer-based solar cells.he size of wafers for photovoltaics is 100–200 mm square and the thickness is 200–300 μm. In the future, 160 μm will be the standard. Electronics use wafer sizes from 100–450 mm diameter. (The largest wafers made have a diameter of 450 mm but are not yet in general use.).