A team of scientists headed up by Princeton University has achieved a whopping 47 percent increase in electricity generation from flexible plastic solar cells, simply by texturing the surface to mimic the wrinkles of a typical leaf. The biomimicry approach has resulted in a low cost, elegant solution for polymer-based solar cells, which are relatively cheap to manufacture but don’t pack the efficiency punch of typical silicon solar cells.
Navy and Air Force support solar research
By now it should come as no surprise that the U.S. Navy and the U.S. Air Force have provided funding in support of the Princeton biomimicry research, as the Department of Defense aggressively transitions to solar energy and other low cost, reliable alternatives to fossil fuel. The National Science Foundation also chipped in, and the University of Pennsylvania contributed to the research.
Plastic solar cell efficiency on the rise
Polymer (aka plastic) solar cells are notoriously inefficient compared to silicon solar cells, but what they lack in punch they make up for in flexibility, durability light weight and above all, low manufacturing costs.
Lately the efficiency of polymer solar cells has been creeping closer to the commercial viability level. In one new development, a team from UCLA achieved a 10.6 percent efficiency, putting it just within the desired range of 10-15 percent. One more tweak and the technology could just about make it — and according to the Princeton team, their biomimicry solution could be applied to almost any kind of plastic solar cell.
The biomimicry solar cell solution
In a report from Princeton University, the principal investigator on the research team, Yueh-Lin Loo, explains the simple principle behind the biomimicry solution. The surface was manipulated to create channels similar to those found in leaves:
“On a flat surface, the light either is absorbed or it bounces back. By adding these curves, we create a kind of wave guide. And that leads to a greater chance of the light’s being absorbed.”
Mimicking nature to make light channels
In practice, the folding technique involved a complicated mathematical exercise. The team used an aerospace engineering lab to develop a technique for introducing different levels of stress to a layer of liquid photographic adhesive. Depending on the rate at which the liquid was allowed to dry, shallow wrinkles and deeper channels or folds were formed.
The team found that a mix of wrinkles and folds performed better than texturing the surface with only one or the other. In fact, the textured surface performed even better than the researchers predicted for the long (red) end of the light spectrum. Absorption at this end is a particular challenge for conventional solar cells, and the textured surface increased it by about 600 percent.
According to Loo, despite the fancy mathwork the actual fabrication process is fairly practical as applied to commercial development, especially for portable solar power applications such as solar powered backpacks and other wearable items, which are of increasing interest to the U.S. military.
Image: Frank Wojciechowski (via Princeton University).
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