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Thin Film Solar Cells

As concerns about energy costs and environmental issues continue to escalate, they drive the market for renewable and natural energy sources. have become more mainstream. One “green” energy source is solar energy, specifically the conversion of light from the sun into electricity through the photovoltaic effect. The photovoltaic effect occurs when electromagnetic radiation hits a material and electrons discharge from that material to another, resulting in a voltage build up between two electrodes.

Pholtovoltaic cells are solar cells that capitalize on this effect to harness free energy from the sun by converting electromagnetic radiation from sunlight into electricity. They are made by depositing a thin film layer of photovoltatic material on a wafer made of glass, plastic or metal.

Photovoltaic Thin Films

These so-called “thin films” are tiny particles that are deposited on a substrate in order to make a layer of minimal thickness from half a nanometer to several nanometers thick. They are used for solar applications because the thin layer can affect the substrate’s physical properties in a major way without damaging it. Photovoltaic thin films are made of silicons, such as amorphous, protocrystalline, nanocrystalline or black silicon. Another material used on thin film solar cells is micromorphous silicon, which is a combination of amorphous and microcrystalline silicon. This material is used in a cell that features top and bottom thin cell coatings and protocrystalline silicon between these outer layers.

Thin films are generally applied to cell substrates by chemical vapor deposition. In this process, gaseous forms of silicon are ejected into a chamber with a substrate. The silicon either reacts or decomposes on the substrate surface, causing deposition of small particles that form into a thin coating layer.

Nanotechnology researchers have developed new types of thin film solar cells in an attempt to boost efficiency and lower cost. Some of these developments have included the use of different chemicals and deposition methods as well as finding more durable materials.

Efficiency

Thin film photovoltaic cells are used in many sunny locations around the world to convert sunlight into electricity. The goal is to develop “grid parity,” which will make the construction, deployment and use of photovoltaic cells cost the same amount as fossil fuels and nuclear power, if not less. Efficiency currently measures 6 to 12 percent, while many companies project long term goals of 20 percent. Lots of investment into photovoltaic cells as well as mindfulness about finding more efficient and green sources of energy have resulted in developments of solar energy cells.

One concern about improving thin film photovoltaic cells is the expense of silicon. The types of silicon used in photovoltaic cells are expensive to procure and produce. Additionally, silicon itself presents a number of efficiency issues. For one, silicon has a low energy conversion efficiency because of the twisted bonds of silicon particles. Another issue is the fact that silicon does not absorb infrared light, which represents a large part of the light that could possibly be converted into electricity.

To solve these problems, scientists have been working to develop more robust solar cells to properly absorb the full light range and exhibit greater energy conversion efficiency. For instance, light trapping schemes are becoming more common. This occurs when a film is made more crystalline, resulting in incoming light passing through various parts of the silicon, exhausting the energy conversion possibilities. Layered units are also employed. These tandem cells are composed of different layers of films made of various types of silicon, that can absorb certain types of sun rays while rejecting another. In this way, the most desirable kinds of sunlight are absorbed and converted to electricity.

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