Blu-ray discs can hold a higher density of data than DVDs or CDs. A team led by Jiaxing Huang and Cheng Sun has now found that when a Blu-ray disc’s strings of binary code, 0s and 1s (embedded as quasi-random nanopatterns of pits and islands), are transferred onto the surface of a polymer solar cell, they improve the amount of light absorbed by the cell. And this is across the entire range of solar spectrum wavelengths.

“Solar cells absorb sunlight and convert it into electricity,” explains Huang. “If the cell surface is textured, it absorbs light more strongly, thanks to light scattering, which helps the light travel longer distances through the cell before exiting it.”

"Surprisingly well suited"

Scientists already know that quasi-random structures (so-called because they are somewhere between periodic and completely random) are the best for such applications, he says. “However, making optimized quasi-random textures is not easy, and is expensive. We found that the patterns in Blu-ray movie discs are surprisingly well suited for this purpose."

The researchers obtained their result by first peeling off the protective coating on a Blu-ray movie disc (in their case, an old Jackie Chan film: Police Story 3, but the film or video content is irrelevant here). They then used an elastomer to copy and transfer the patterns onto a polymer solar cell by an imprinting technique.

Quasi-random pattern works best

“We found that a random pattern or texture does work better than no pattern, but a Blu-ray disc’s quasi-random pattern works best of all,” says Huang.

But why does this pattern work so well? As luck would have it, it was Huang’s wife, Shaorong Liu, herself a database engineer at IBM (and not involved in this work) who rightly suggested that it had something to do with data compression. By looking more closely at the data-processing algorithms in Blu-ray technology, the Northwestern team realized that these discs convert video signals into seemingly random sequences of 0s and 1s, which make for the quasi-random arrays of island and pits unique to Blu-ray discs (and allows them to store much more data than ordinary DVDs).

Happily, the pits and islands have feature sizes of between 150 and 525 nm, a range over which all frequencies of sunlight can be trapped. Indeed, the researchers calculated that a Blu-ray patterned solar cell was able to absorb nearly 22% more light than a device that was not patterned at all.

Our work shows that Blu-ray movie discs are a readily available source of sub-wavelength, quasi-random patterns that are well suited to enhancing light absorption in solar cells, says Huang. These discs could provide us with a cheap and easy way to increase the performance of solar cells, and indeed why not that of other photonic devices.

“It has also been extremely fun to see some exciting new science come out from seemingly unrelated fields – in this case, information theory, photonics and materials science,” he told nanotechweb.org.

The work is described in Nature Communications doi:10.1038/ncomms6517.