Trapping Sunlightwith Silicon Nanowires

While there are now silicon photovoltaics that can convert sunlight into electricity at impressive 20 percent efficiencies,the cost of this solar power is prohibitive for large-scale use.Researchers are developing a new approach that could substantially reduce these costs. The key to their success is a betterway of trapping sunlight.Because of its superior photo-electronic properties,silicon remains the photovoltaic semiconductor of choice but rising demand has inflated the price of the raw material. Furthermore,because of the high-level of crystal purification required,even the fabrication of the simplest silicon-based solar cell is a complex,energy-intensive and costly process. The researchers are now able to reduce both the quantity and the quality requirements for silicon by using vertical arrays of nanostructured radial p-n junctions rather than conventional planar p-n junctions. In a radial p-n junction,a layer of n-type silicon forms a shell around a p-type silicon nanowire core.As a result,photo-excited electrons and holes travel much shorter distances to electrodes,eliminating a charge-carrier bottleneck thatoften arises in a typical silicon solar cell.The radial geometry array also,asphotocurrent and optical transmission measurements by the researchers revealed,greatly improves light trapping.

(From:Light Trapping in Silicon Nanowire Solar Cells)