Univ. of Utah Students Cut Germanium for Solar Cells
University of Utah engineers devised a new way to slice thin wafers of the element germanium for use in the most efficient type of solar power cells. They say the new method should lower the cost of such cells by using less raw material and reducing waste.
Germanium solar cells, the most efficient solar cells, now are used mainly on spacecraft, but with the improved wafer-slicing method, "the idea is to make germanium-based, high-efficiency solar cells for uses where cost now is a factor," particularly for solar power on Earth, says Eberhard "Ebbe" Bamberg, assistant professor of mechanical engineering.
Dinesh Rakwal, a doctoral student in mechanical engineering, adds: "We're coming up with a more efficient way of making germanium wafers for solar cells - to reduce the cost and weight of these solar cells and make them defect-free."
Bamberg and Rakwal are publishing their findings in the Journal of Materials Processing Technology. Their study has been accepted, and a final version will be published online late this month or in early October, and in print in 2009.
Their novel process uses a brass-coated, steel-wire to slice round wafers of germanium from cylindrical ingots. The brittle germanium cracks easily, requiring a saw with a soft touch. The width of the saw creates waste. In the past a significant amount of germanium is lost during the cutting process. The new U of U sawing method improves efficiency by about 10%.
The new method for slicing solar cell wafers - known as wire electrical discharge machining (WEDM) - wastes less germanium and produces more wafers by cutting thinner wafers with less waste and cracking. The method uses an extremely thin molybdenum wire with an electrical current running through it.
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