News Article: Feb 2003
http://www.newscientist.com/article.ns?id=dn3380
Unlike conventional solar cells, the new, cheap material has no rigid silicon base. Instead, it is made of thousands of inexpensive silicon beads sandwiched between two thin layers of aluminium foil and sealed on both sides with plastic. Each bead functions as a tiny solar cell, absorbing sunlight and converting it into electricity. The aluminium sheets give the material physical strength and act as electrical contacts.
The manufacturing process uses waste silicon from the chip-making industry, which is melted down and shaped into spheres about one millimetre across. Next, the cores of the silicon spheres are doped with boron atoms, which turn it into a "p-type" (positive) semiconductor. Then phosphorus atoms are diffused into the outer layer of the beads, converting it into a negative "n-type" material. The bumpy surface presented by the spheres offers a large area for absorbing light, giving the material an overall efficiency of 11 per cent.
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