Size identified as key to more efficient nanowire solar cells
By Leon Gettler
January 22, 2013
In a breakthrough that could lead to more efficient and cheaper solar cells, scientists at Sweden's Lund University claim to have identified the ideal diameter for nanowires to convert sunlight into electricity.
While the use of nanowires in solar cells is still in the research phase, they promise advantages over conventional silicon solar cells. Because they are based on a single material, silicon cells can only convert a limited part of the solar spectrum. Approaches that use different types of semiconductor material on the other hand, are more efficient because they utilize more of the spectrum, but they are also more complicated and expensive to produce. The advantage of nanowires is that they are simpler to synthesize with different semiconductor materials, resulting in a lower cost. According to the Lund researchers, the nanowires can generate power at the same level as a thin film of the same material, even if they only cover around 10 percent of the surface rather than 100 percent.
Scientists have previously been unable to attain efficiency of greater that 10 percent using solar nanowires, but using array of four million nanowires made of the semiconductor material indium phosphide on surfaces of just one square millimeter, the researchers have reported a figure of 13.8 percent.
Identifying the exact dimensions for the nanowires is critical to this result. “The right size is essential for the nanowires to absorb as many photons as possible. If they are just a few tenths of a nanometre too small their function is significantly impaired”, says Magnus Borgström, a researcher in semiconductor physics and the principal author.
While there is still some way to go, scientist believe that once a higher level of efficiency is reached, the technology could be used in large solar power plants.
“Our findings are the first to show that it really is possible to use nanowires to manufacture solar cells”, says Borgström.
The findings have been published in the latest edition of Science.
Source: Lund University