English | 
Photovoltaic (PV) technology converts energy from the sun (photons) into electricity. Current PV technologies use semiconductor materials also found in computers and other electronic equipment. Semiconductors release electrons from their atomic bonds producing electrical current.
There are two leading manufactured solar photovoltaic (PV) technologies in commercial use today; crystalline silicon PV and thin-film PV. The vast majority of solar module demand comes from crystalline silicon (80%) with thin-film making up the balance. Since 2008, thin-film has gained ground on crystalline silicon largely due to the higher manufacturing costs associated with crystalline silicon PV.
Crystalline silicon PV (c-Si)
C-Si cells were first commercialized by Bell Labs in the 1950s. They are made by slicing high purity silicon into thin wafers the thickness of a human hair. Three types of crystalline silicon are used in the production of solar cells:
Mono-crystalline silicon uses single-crystal wafer cells cut from cylindrical ingots. These are very expensive due to the manufacturing process involved.
Poly or multi-crystalline silicon cells are made from square cast ingots. These cells are less expensive than mono-crystalline but also less efficient.
Ribbon silicon is made by drawing flat thin-films from molten silicon creating a multi-crystalline structure. Their efficiencies are lower but costs are significantly cheaper by saving on material waste.
Mono-crystalline silicon solar modules are the workhorse of the solar industry. They are extremely durable and have the highest commercial power conversion efficiencies. However, growing the single crystalline structure in the manufacturing process is time consuming and extremely expensive.
Poly-crystalline solar modules are made from a block of silicon that contains multiple crystals. These panels are square in shape with a mosaic-like structure. The poly-crystalline modules are much cheaper to produce than mono-crystalline due to their less stringent crystal structures. The trade-off for less expense with polycrystalline cells; however, is their lower efficiencies over mono-crystalline silicon modules.
Thin-film PV (CdTe, a-Si, CIGS)
Thin-film PV is the fastest growing sector of the solar cell manufacturing industry. Thin-film cells are manufactured by applying very thin layers of semiconductor material to inexpensive materials such as glass, plastic or metal. Thin-film semiconductors absorb light more easily than c-Si, therefore requiring less semiconductor material, making them far less expensive than crystalline silicon modules.
There are three leading manufactured thin-film PV modules presently:
CdTe or Cadmium Telluride thin-film, currently has the lowest Wp (watt peak) production cost due to a balance between ease of production and higher cell efficiency (currently 6 – 11%: limited to 31% maximum).
a-Si or Amorphous Silicon thin-film uses a highly a proven but slower layer deposition manufacturing process which results in lower efficiencies (currently 6 – 8%: limited to 12% in-lab). Microcrystalline technology is used as an upgrading technology to boost the amorphous silicon products to efficiencies of around 10%.
CIGS or Copper Indium Gallium Selenide thin-film has been able to reach the highest efficiencies in production: 13 – 14% max, and averaging around 10%. There are difficulties in controlling the uniformity of the active layer on larger formats,and this does not currently work on steel.
All currently manufactured thin-film PV solar cells rely on either rare earth elements (such as Indium or Tellurium). These elements have very finite quantities globally and are often situated in only a few locations with exports strictly controlled by those countries. Despite the lower cost advantages of thin-film PV technologies, none of them can achieve commercially produced efficiencies over 17%. The combination of these factors restricts thin-film from achieving terawatt scale global power production.
