Saturday, February 5, 2011

Berkeley Researchers Create Cheap Full-Spectrum Solar Cell

Discovery sparks hopes of mass-marketing a highly efficient solar cell

Researchers at Lawrence Berkeley National Laboratory have developed a solar cell that responds to almost all wavelengths of light, potentially creating high-efficiency solar cells that could affordably be produced in volume.

Wladek Walukiewicz, leader of the Solar Energy Material Research Group in the Materials Sciences Division at the US Department of Energy's Berkeley Lab, used a new design that enables traditional solar materials to produce layers of material that respond to different parts of the light spectrum.

Traditionally, commercially available solar cells have been able to respond to a relatively narrow part of the solar spectrum, while the few solar cells developed to absorb energy from the entire light spectrum have so far proved extremely expensive and limited to specific applications, such as spacecraft.

However, Walukiewicz's team, working in conjunction with Arizona-based Sumika Electronics Materials, may have discovered a commercially viable solution.

Prior research involved stacking layers of different semiconductors and wiring them together, but these are complicated to produce, making them commercially unreliable, Walukiewicz explained. A second approach involved using the same alloy to create two mismatched semiconductors, and enabling the alloy to create a further layer sandwiched between them.

This created a third band gap. A band gap is the energy needed to free electrons that are bound to atoms on the top layer, enabling them to move into the conductive layer of material. Introducing a third band of material enables the semiconductor to respond to lower- and middle-energy wavelengths.

The research team had created triple-layer semiconductors based on a single alloy before, but the materials used in the past had been difficult to manufacture, again precluding the research from being commercialised.

But the scientists have now discovered that it is possible to create mismatched alloy semiconductors with a third band using a common gallium arsenide nitrate alloy, which is very similar to the gallium arsenide used in many semiconductors. It replaces some arsenic atoms with nitrogen to create the intermediate energy band.

The researchers said that the alloy can be made using metal organic chemical vapour deposition, which is a common method for creating semiconductors.

During testing, the solar cell responded to a broad spectrum of light, ranging from infrared into ultraviolet, the researchers found.


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