Researchers from the Northwestern University bought three copies of Jackie Chan's Police Story 3 in Blu-ray disc, but it was not to watch the Chinese star's movie. It was actually a random purchase that they needed for a study on finding an inexpensive way of improving the efficiency of solar cells used in solar panels.

The efficiency of a solar cell is influenced by the amount of photons it can absorb. Cells with surfaces that are etched with patterns that are neither too orderly nor too random, a pattern known as quasi-random, trap light more easily.

The fabrication techniques that are required to create such quasi-random patterns for solar cells, however, are very expensive, limiting its widespread use. The researchers looked at the possibility of using Blu-ray discs, which are widely available, as an option to create quasi-random patterns on solar cells at a much cheaper cost.

For their study published in the journal Nature Communications on Nov. 25, Jiaxing Huang from the department of materials science and engineering at the Northwestern University in Illinois and colleagues used Blu-ray discs of Jackie Chan's action flick Police Story 3: Supercop to create a mold with quasi-random patterns that they stamped into the solar cells to transfer the patterns.

"Picking Police Story 3 was somewhat serendipitous," Huang recalled. "My student, Alex Smith, found it among a few other movies on sale at BestBuy, so he bought a number of copies."

Huang and colleagues found that the pattern significantly improved the cells' light absorption with the quasi-random patterned panels absorbing 21.8 percent more light compared with the non-patterned panel, boosting power conversion efficiency by almost 12 percent.

"As a proof-of-concept, imprinting polymer solar cells with the Blu-ray patterns indeed increases their efficiencies," the researchers wrote. "Simulation suggests that Blu-ray patterns could be broadly applied for solar cells made of other materials."

By testing other movies and television shows, Huang and colleagues also found that the video content on the Blu-ray discs do not matter because they all improved the light-absorbing efficiency of the solar cells.

What actually matters is the algorithm used in encoding data on the discs, which convert the audio and video signals into quasi-random patterns that turn out to be well suited for trapping light. Huang and his colleagues, however, pointed out that there is still room for improvement. The imprinting process involved, for instance, still needs to be refined.

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