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Crystalline Silicon Technology

Crystalline silicon is currently used in the majority of PV cells. They are three major types of crystalline silicon, mono, poly and ribbon. The commercial efficiency of this product is between 12-18%.

Monocrystalline Silicon is made from very pure Monocrystalline Silicon. Monocrystalline Silicon has a single and continuous crystal lattice structure with practically zero defects or impurities.  One of the many reasons Monocrystalline Silicon is superior to other types of silicon cells are their high efficiencies - which are typically around 18%. Because the manufacturing process required to produce Monocrystalline Silicon is more involved and detailed than other types, this results in slightly higher costs for Monocrystalline Silicon than other technologies.

Polycrystalline Silicon - also referred to as "polysilicon" or "Poly-Si" or known as multisilicon is a material consisting of multiple small silicon crystals and has long been used as the conducting gate material in MOSFET and CMOS processing technologies. For these technologies, Polycrystalline Silicon is deposited using LPCVD reactors at high temperatures and is usually heavily n or p-doped. The main advantage of Polycrystalline Silicon over other types of silicon is that the mobility can be orders of magnitude larger and the material also shows greater stability under electric field and light-induced stress. This allows far more complex, high-speed electrical circuits that can be created on the glass substrate along with the amorphous silicon devices, which are still needed for their low-leakage characteristics.

Ribbon Silicon -  describes a method of producing multi-crystalline silicon strips suitable for the photovoltaic industry.  The name describes the manufacturing process, where high temperature resistant wires are pulled through molten silicon to form a multi-crystalline ribbon of silicon crystals. The ribbon is then cut into lengths which are treated with traditional processes to form solar cells.

String Ribbon technology offers a less expensive manufacturing technique but is not capable of achieving the same electrical performance as wafer technology. Typically a cut wafer will convert 15-18% of the incoming light into electricity where String Ribbon Solar Cells are capable of converting 13-14%. In research laboratories the technology has reached as high as 18.3%, however it cannot be produced commercially to this specification. Wafer technologies have reached as high as 25% in laboratory conditions.

While String Ribbon technology has certain advantages as to the shape of the crystals, the overall thickness varies enough so that not every 'silicon strip' can be processed directly into a solar cell. In addition to this drawback, the growth process is thermally very in-efficient. The radiating area/gram of crystal is extremely high, leading to very high energy expenses which offset the reduced silicon use/expense.