How are solar cells manufactured?
Depending on the Semiconductor material, material thickness or crystal structure, different types of solar cells can be distinguished. The most common are thick-film solar cells, in which the main material is silicon. Silicon is a common raw material present in various chemical compounds, mainly in silicate minerals, sand, and quartz. The extraction of pure silicon is an energetically expensive process because silicon already reacts with oxygen at room temperature. The purest silicon is also required for chip production, but a somewhat lower purity is sufficient for so-called "solar silicon". Silicon wafers are the semi-finished products from which solar cells are manufactured.
The ingot is the intermediate step from which the so-called wafers are produced. A distinction is made between monocrystalline and polycrystalline ingots, with monocrystalline ingots being the more expensive variant made from high-purity silicon. In the production of monocrystalline ingots, silicon is heated to high temperatures in a crucible and the melt is deposited on rods while the crucible is rotated. Upon cooling, crystal growth, once induced, continues on the rods, producing a single crystal in cylindrical form.
These silicon crystals are sawn into 0.15 to 0.25 mm thin wafers. Due to the manufacturing process, the crystal structure in monocrystalline wafers is homogeneous. In the production of polycrystalline ingots, the silicon is heated in square crucibles. As it cools, many differently sized and differently oriented crystal zones subsequently form.
In the next step, the wafers are then "doped". This is the term used to describe the incorporation of foreign atoms into the existing silicon lattice so that a charge difference is created between the individual layers. To make particularly effective use of sunlight, an anti-reflective layer of silicon nitride or titanium oxide is applied to the wafer. The contacts are then screen-printed onto the wafers and then solidified by baking. On the reverse side, the contacts are made by silver contact points on an aluminum layer.
Hydrogen is used in the process for manufacturing thin-film solar cells. This is reacted with silicon to form monosilane (SiH4). This gaseous compound is evaporated onto a carrier material and decomposed at low temperatures; whereby amorphous, non-crystalline silicon is separated. In further layers, electrically conductive oxides that serve as contacts are deposited. These layers are structured either mechanically or by laser, resulting in the individual cells.
Monocrystalline solar cells are characterized by a long service life of over 20 years. In addition, with an efficiency of between 14 and 18 percent, they are the most efficient solar cells currently available on the market, but their production is comparatively expensive and more complex. The highest efficiencies (up to 30 percent), however, were achieved with so-called tandem solar cells. These cells consist of two or more solar cells that are layered on top of each other. This allows light with different wavelengths to be absorbed by the cell. Organic solar cells, whose special features we have already described in an earlier article, consist of hydrocarbon compounds and are still a relatively new technology with many new potential applications.
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https://www.energie-experten.org/erneuerbare-energien/photovoltaik/solarmodule/monokristalline-module, accessed: 3/26/2022 at 2 p.m.
https://de.wikipedia.org/wiki/Solarzelle#Einteilung, accessed: 3/28/2022 at 9 a.m.