Single-Crystal Technology: Solar Articles: Eco20/20

Single-Crystal Technology

The single crystal or monocrystalline type of silicon forming was invented in 1955. The high purity required for single crystal silicon wafers makes it a highly efficient conductor for photovoltaic panels. These single wafer sheets are known for their long life-time. Many researchers claim that the single crystal wafers never break or tear down.

A single crystal is a solid material where the grouping of points along the atoms repeats systematically at regular intervals in three dimensions. The solid material is entirely united to all edges of the sample. This means there is no grain boundary, which is the border where crystals facing in different directions meet. This lack of boundary limits the number of imperfections such as atoms that have been moved from their original location in the grouping or other impurities. Once a cylinder of single crystal is manufactured, it is cut into circular wafers. Solar panel cells that are available commercially offer an efficiency rating of twenty percent. Solar panel cells that are currently being researched have offered a thirty percent efficiency rate.

The process that is used to grow these cylinders of monocrystalline silicon is called the Czochralski process. The silicon is heated to a melting point in a refractory container called a crucible. Once the silicon is melted, a rod with a single crystal of silicon is dipped into the molten material, and is slowly pulled from the crucible while being rotated. Impurities are added to the extremely pure silicon in order to add electrical conductive value. In order to get a workable size crystal, it is important to constantly check the temperature of the crucible, the speed of the rotation and the speed of the lift on the rod.

Because of the continuity of the wafers and the lack of grain boundaries, the monocrystalline silicon cells are more efficient than polycrystalline silicon cells. They offer more power generated from the same space area. Monocrystalline silicon cells also offer less of a production reduction in higher temperature climates than polycrystalline silicon cells.

Some companies have made improvements to the wafers, as the sheets of film are called. One company, AstroPower, has added bus bars made of silver to both the front and back of the edging of the wafers to prevent the breaking apart of solders. These bus bars also offer an increased electrical conductive source, and interlock the power source and power load.

Using thicker wafers increases the mechanical yield. This increase flows through the complete manufacturing process of making the modules. Clear coatings that diminish the reflective properties of the wafers make the coloring more uniform, and increase the output production of energy.

Because of the extensive work that goes into manufacturing monocrystalline silicon cylinders, this material in slightly more expensive. Because of the few impurities, however, they are also more efficient and long lasting, making this material a good choice for solar panel usage.

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