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Boffins find Jackie Chan's SUPERCOP is good for something

Blu-Ray's pit and peak pattern supercharges solar cells

Blu-Ray might not be setting the world afire, but boffins have turned up a surprising upside of the technology that can be applied to solar PV manufacture.

It turns out the pit-and-peak pattern that encodes a movie on the disk helps improve light absorption if reproduced on the surface of a solar cell.

Published in Nature Communications (abstract here), the work was carried out at Northwestern University.

Blu-Ray's high data density means the textures that encode a movie are at the right scale to apply to solar cell fabrication (compared to CDs or DVDs that carry less data), but it turns out that other characteristics are also important.

The compression applied to movies, along with redundancy added to the data sequence, has the effect of creating a quasi-random sequence of 1s and 0s, the university explains – and that randomness is what makes Blu-Ray exploitable as a pattern template.

The researchers found that the Blu-Ray template – they picked Jackie Chan's Supercop for their experiment – lifted a cell's broadband solar absorption by 21.8 per cent compared to a cell with no pattern.

If a random pattern is wanted, why resort to a template rather than generating randomness in manufacturing? The paper's abstract explains that trying to optimise such patterns is an expensive manufacturing process, whereas working to the Blu-Ray template produces a quasi-random array of islands and pits with feature sizes between 150 and 525 nm, and it's suitable for light-trapping over the entire solar spectrum.

Jiaxing Huang, associate professor of materials science and engineering at Northwestern's McCormick School of Engineering, explains that it was only with input from information theorists that he was able to explain why Blu-Ray's patterns worked so well.

“We found a random pattern of texture does work better than no pattern, but a Blu-Ray disk is best of all. Then I wondered, why did it work? If you don't understand why, it's not good science.”

Huang's wife, an IBM database engineer suggested that data compression was part of the answer, and McCormic information theory expert Dongning Guo unravelled the compression-and-redundancy combination that explained the phenomenon.

Making Blu-Ray into a solar cell pattern

An unauthorised copy of Supercop becomes a solar cell pattern. Image: Huang et al, Nature Communications

Since Huang's group was working with finished Blu-Rays, they had to remove the protective layer so as to cast a mold from the surface. In an industrial process, getting the pattern lifted from a Blu-Ray could be done far more efficiently.

Just so long as Hollywood's lawyers don't fire off a sueball for copying Supercop... ®

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