As far as threequels go, Jackie Chan’s 1992 movie Police Story 3: Supercop has done pretty well for itself. It has a 7.3 rating on Rotten Tomatoes and a 6.9 on IMDb. But those ratings have nothing to do with Northwestern University researchers’ decision to purchase three copies of the flick in Blu-ray for their lab. According to them, the film was just a means to an end — a random purchase that helped them discover that the etchings that cover Blu-ray discs can actually improve the way solar cells absorb light.

"Now there's a new purpose of unwanted Blu-ray discs."

"Now there's a new purpose of unwanted Blu-ray discs," says Jiaxing Huang, an engineer at Northwestern University and a co-author of the study published today in Nature Communications.

Solar cells work by absorbing sunlight and converting it to electricity. But some cells are more efficient than others. For instance, studies have shown that cells that sport surfaces with "quasi-random" patterns etched into them — partners that aren't completely uniform or completely random — trap light more easily. Unfortunately, making cells with these kinds of patterns isn't particularly straightforward or cheap, Huang says. So researchers at Northwestern decided to look into using movie discs to imprint patterns into the cells. And that's where Police Story 3 came in.

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

It took a few months to run the necessary experiments, but when they were over, the researchers concluded that Blu-rays could be used to produce rubber stamps that can then be pressed into polymer solar cells. And the resulting patterns, the researchers say, can enhance the overall light absorption of solar cells by 20 percent.

Blu-ray discs enhance the overall light absorption of solar cells by 20 percent

"Of course, other Blu-ray movies would work as well," Huang says. "The main excitement of our paper is that movie content does matter, because the Blu-ray algorithms convert the video and audio signals into universally quasi-random patterns."

The finding was unexpected, the researcher says, and the technique will need to be perfected. "To achieve thicker cells or other types of materials, we will need to refine the imprinting process." But if they can work through the kinks, Huang says, it might be possible to give "the Blu-ray industry, which already have quite mature nanofabrication and nanomanufacturing toolsets, a new purpose."