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New Types of Solar Cells

by J.T. Barett, Demand Media
    Innovative solar cell designs help to lower costs and permit new applications.


    Government incentives and requirements such as the Renewable Portfolio Standards have helped fund research and development for new types of solar cells. Although traditional solar cells have seen many useful applications, they suffer from high costs and low efficiency. Research has focused on reducing costs, increasing output and making them easier to manufacture.


    A standard solar cell is made from brittle materials such as silicon and glass; these aren’t suitable for applications requiring flexibility. However, a new technique developed by the Massachusetts Institute of Technology prints solar-cell materials on paper, plastic and other flexible materials. Printing solar cells onto sheets and rolls lowers the cost of making them and creates new possibilities such as solar-powered backpacks, magazines and window shades.


    An innovative, three-dimensional solar cell captures light from wider range of angles than standard cells can. Panels made of traditional solar cells must be pointed directly at the Sun; when light falls at an angle, it reflects off instead of being absorbed by the solar material. The three-dimensional design uses a multifaceted solar cell instead of a simple, flat one. In addition, the 3D approach moves the necessary electrical wiring from the front to the back of the cell where it doesn’t block the incoming light. Many applications can benefit from 3D technology, including mobile devices, rooftop solar panels and commercial solar farms. Commercial power plants that use traditional solar cells solve the light angle problem by steering solar panels with electric motors; the panels track the Sun’s movement throughout the day. The 3D technology eliminates the need for tracking motors, reducing installation and maintenance costs.


    A process that sprays solar cell materials onto a glass surface makes them easier to manufacture. Standard techniques typically involve creating solar cells at high temperatures and in a vacuum, which is slow and expensive. The sprayed-on material is thin enough to be transparent. Applications for spray-on solar cells include windows for residential and commercial buildings; the windows let sunlight through and produce electricity at the same time.


    On a bright summer day, the Earth receives about 1,000 watts per square meter of energy from sunlight. However, because the efficiency of traditional solar cells ranges from 5 to 20 percent, you get only 50 to 200 watts of useful energy from a panel a square meter in size. To increase efficiency, scientists have used a multi-layered approach in which each layer absorbs different colors of light as opposed to a standard cell, which typically uses a very narrow range of colors. However, compatibility problems arise between layers, compromising the cell’s performance. A newer design, called the “inverted metamorphic multijunction,” makes solar cells by growing layers of silicon and other materials “upside-down” compared to standard devices. This reduces compatibility issues and allows the cell to convert more of the Sun’s light into electrical energy -- increasing efficiency to as much as 40 percent, or more than double the output of a standard cell. Improved efficiency means you get more energy from the same light or the same energy from a smaller area of light.

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