Lighter, More Efficient Solar Cells Look Like Your Retina

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Solar cells for your handheld devices may yet be around corner. A recent discovery in the exotic optical effects on the nanoscale allows thinner and lighter solar cells to absorb a broader spectrum of light.

Today solar cells are expensive and bulky--far out of reach for the common consumer, and not terribly practical for small devices that you want to carry around in your pocket. According to Technology Review the typical solar at least 100 micrometers thick. While the research centers and businesses around the world are pushing toward thinner solar cells, these thinner cells have one major drawback: they don't absorb as much light as their thicker counterparts.

Fortunately, a new technology could someday change all of this and bring lighter, thinner, and more efficient solar cells to even the smallest of our gadgets. Harry Atwater, a professor of Applied Physics and Materials at Caltech, and Koray Aydin, assistant professor of Electrical Engineering and Computer Science Northwestern University, have discovered that by creating nanoscale wedge shapes with a wide base and a pointy tip, a material could capture a broader spectrum of light.

The wavelengths for waves on the electromagnetic spectrum range from picometers (10^-12) to the 100s of megameters (10^6), so there's a lot of ground to cover. The typical solar cell can only make use of waves within a narrow band of the already-narrow visible spectrum which covers only about 390- to 750-nanometer wavelengths.

Atwater and Aydin worked together to develop a super-absorbant solar cell using a property called optical resonance. When a radio wave hits an antenna, the antenna will resonate, absorbing certain radio waves depending the antenna's size. The same can be said for light; when light hits a certain size structure, the structure resonates at a certain frequency, and that structure can only absorb certain wavelengths of light. This is also similar to how the rods and cones work in your eye--each size of rods and cones absorbs a different wavelength.

The solar material developed by Atwater and Aydin uses nanoscale wedges that are of all different lengths ,with pointed tops and wide bases. Blue light (440–500 nm) is absorbed at the tip and red light (625–740 nm) is absorbed at the base.

The material is made from a silver base with a layer of silicon dioxide above it, and finally a layer of silver with the carved out wedges. The wedges are 40 nanometers at their tips and the total thickness of the film material has been demonstrated at 260 nm, however, according to Technology Review, the group has also made a film 220 nm that can absorb the same amount of light as an unpatterned film that's 25 times thicker.

According to their published findings in the journal Nature (you'll need a subscription or to buy the article to see it), the film can also absorb light over the entire visible spectrum with an average measured absorbtion of 71% and a simulated absorption of 85%.

Some day this new material could make it to your laptop, or even your cell phone. That coupled with super-fast charging batteries, the future sure looks bright!

[Nature via Technology Review]

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