Technician holding a polycrystalline silicon solar cell. The first silicon photovoltaic solar cells (seen in the background) were made by single crystals of silicon. They are characterised by a relatively high efficiency, up to 35%, but at the same time are very expensive to manufacture. Polycrystalline cells, also known as amorphous silicon cells, are made by very small silicon crystals. They are less efficient (up to 15%) but much cheaper to produce.