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2013-01-04. Space Solar Cells With A Down-to-Earth Cost

posted Jan 5, 2013, 10:59 PM by Alan Gould
| Robert F. Service, Science: Vol. 339 no. 6115 p. 21. Relevant to GSS Energy Use chapter 10. Excerpt: …gallium arsenide (GaAs) … has been used for decades to make ultrahigh-efficiency solar cells for spacecraft. But the out-of-this-world cost of GaAs itself makes these too expensive for mass-market uses. Now, researchers at the University of Michigan may have found a way not only to drop the cost of producing GaAs cells, but also to drop the cost of the power they produce to near that of grid power from fossil fuels…. Crystals of GaAs are typically grown in 200-millimeter-diameter cylinders that are then sliced into thin wafers. …But this tends to use too much of the expensive GaAs. More recently, groups … have used GaAs as a substrate on which to grow other semiconductor alloys … and recover the GaAs wafer so that it can be reused. Unfortunately, …it can only be used a few times before engineers must replace it with a fresh wafer. Three years ago, Stephen Forrest, a materials scientist at the University of Michigan, Ann Arbor, came up with a … strategy … to add two additional very chemically different layers to the sandwichlike stack of materials. … enabling it to be reused again and again. … additional steps also allowed them to bond the final GaAs layer to a clear plastic substrate, giving them a flexible solar cell with more than 22% efficiency. If cheap solar concentrators are added to focus more light onto the cell, Forrest says he believes that they should be able to convert more than 30% of the energy in sunlight into electricity. If that's the case, Forrest says his calculations show that they can reduce the cost of power from the cells to less than $1 per watt, roughly the current cost for silicon-based solar cells. If they can muster further improvements, that price could drop close to grid parity—the holy grail for solar power…. Read the full article: http://www.sciencemag.org/content/339/6115/21.full