Amorphous silicon, a disordered form of silicon with dangling bonds, is used to produce thin films for electronic components. It can be applied more evenly and at lower temperatures than crystalline silicon, and absorbs up to 40 times more solar radiation. Hydrogenation is required for stability and durability, and the material may experience a voltage output reduction after initial exposure to sunlight.
Amorphous silicon is a form of silicon, the second most abundant naturally occurring element on Earth. However, it differs from silicon in that it is not crystallized and disordered in the same way as ordinary glass, meaning that some of the atoms in its chemical structure resist bonding. These so-called “dangling” bonds affect the intrinsic properties of the material, i.e. giving it a higher defect density, which refers to the amount of natural imperfections. This substance, often abbreviated to a-Si, still offers several advantages over crystalline silicon making it preferable for use in the production of thin films for coating a variety of electronic components, especially photovoltaic (PV) systems. For example, it can be applied over large areas more evenly than silicon and at very low temperatures, allowing it to adhere to glass, plastics and metals.
Before amorphous silicon can be applied as a thin film to certain materials, such as solar cells, it must go through hydrogenation to give the material greater stability and durability. This means that the dangling bonds must undergo “passivation,” a process in which the random bonds in each layer of silicon cells are saturated with atomic hydrogen while under pressure between layers of transparent conductor and a metallic support, usually oxide. of tin and aluminum, respectively. This change allows for more flexibility in how the material is deposited, as well as giving you more control over its tensile properties. As a result, amorphous silicon can be used in thin-film processes used to make a variety of low-voltage devices, such as pocket calculators and watches.
Another advantage of using amorphous silicon thin film over crystalline silicon is that the former absorbs up to 40 times more solar radiation. This being the case, only a very thin film coating is needed to absorb 90% or more of direct sunlight. In fact, the coating need only be 0.000 039 37 inches, or one micrometer thick. To put this into perspective, a single strand of human hair is 100 times thicker. This attribute adds to the cost effectiveness of using amorphous silicon in thin film technologies.
The only drawback of using amorphous silicon in solar cell applications is known as the Staebler-Wronski effect. For reasons not fully understood, cells in the material tend to reduce their voltage output by up to 20% after initial exposure to natural sunlight. However, the material reaches a point of electrical power stability after one to two months.
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