Experimental solar panel, consisting of circular photovoltaic cells. The first silicon photovoltaic solar cells were made using single crystals of silicon. Although these are relatively efficient, they are very expensive to manufacture. Polycrystalline cells (or 'amorphous' silicon cells) are comprised of many small crystals. They are less efficient than single crystal cells, but are very much cheaper to produce. This makes them more attractive for large-scale applications where space or weight are not critical.