Blu-ray Discs Spin Their Way Into Making Solar Cells More Efficient
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Researchers at Northwestern University have hit upon a way to give Blu-ray discs a second chance at usefulness: They make excellent molds for imprinting solar cells with quasi-random nanostructures. Even the ones with terrible movies on them.
The efficiency of a solar cell is dependent on how many photons it can absorb. Quasi-random nanostructures on the subwavelength scale can be imprinted on solar cells to increase the number of photons that get trapped, but it’s very expensive to create the molds required for fabrication. Experiments have been done to see whether blank optical media could be used to cheaply and efficiently imprint these nanostructures, but the periodicity of the pattern on a blank disc wasn’t very effective at trapping photons.
The binary data on a full Blu-ray disc, on the other hand, has a nanostructure that’s very different. It consists of compressed binary sequences that have been applied with an error control modulation, so that all those segments of ones and zeros (physically translated into islands and pits on the surface of the disc) are always between two and seven digits long. Since the length of a single digit is 75 nanometers, a full disc ends up being etched with a quasi-random pattern of islands and pits ranging in length from 150 nm to 525 nm. These dimensions happen to be “near optimal” for trapping photons in the visible and near infrared portions of the spectrum.
The Northwestern researchers chose to experiment with a Blu-ray copy of Police Story 3: Supercop for reasons that we can all understand. They delaminated the surface of the disc to expose the pattern of bits, and then created a negative mold. The mold was then pressed onto a pre-fabricated polymer active layer to transfer the pattern, and evaporative electrode deposition completed the solar panel.
http://spectrum.ieee.org/energywise/energy/renewables/bluray-discs-find-useful-application-in-increasing-solar-cell-efficiency
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