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Cheap Templates For Solar Cells Now On Blu-Ray

Nanofabrication: Structures patterned by Blu-ray discs could boost the efficiency of photovoltaic devices

by Matt Davenport
November 26, 2014 | A version of this story appeared in Volume 92, Issue 48

A photoactive polymer is patterned with a mold made from a Blu-ray disc.
Credit: Nat. Commun.
Researchers used patterned polymers (right) to create solar cells that are more efficient than nonpatterned devices (left). Pits (dark brown) are roughly 25 nm deep.

Even with the advent of streaming video, Blu-ray Discs may yet escape the fate of obsolete Betamax videotape cassettes. A team of engineers at Northwestern University has shown that Blu-ray movies can be converted into inexpensive templates for efficient solar cells (Nat. Commun. 2014, DOI: 10.1038/ncomms6517).

Researchers have long known that arrays of nanostructures can boost solar-cell efficiency. Patterns that are too random or too regular often fail to maximize a cell’s interaction with sunlight. Patterns in a middle ground—known as quasi-random—best facilitate this interaction. But fabricating these arrays is expensive.

Cheng Sun of Northwestern was preparing to pay thousands of dollars for such an array when he and Jiaxing Huang, a colleague in the engineering department, decided to turn to the bargain Blu-ray bin first.

Sun, Huang, and their team realized that Blu-ray Discs are already pocked with quasi-random patterns of nanoscopic pits and islands that correspond to the zeroes and ones of digitized information. These patterns allow Blu-ray players to read sequences of nanostructures without confusing them for fingerprints or scratches. Sequences range in length from about 150 to 525 nm.

These patterns couple strongly with sunlight, Huang says. “Engineers in the Blu-ray industry have been working on these patterns for years,” he explains. “We realized that they’ve been subconsciously doing our jobs.”

By coating recorded discs—featuring such Hollywood fare as “Supercop” and “Family Guy”—with a silicone elastomer, the team created stamps that can be used to transfer patterns to a photoactive polymer called PTB7:PC71BM. Solar cells made using polymers patterned this way absorbed more light and converted it to electricity more efficiently than nonpatterned ones.

“This is a very clever idea,” says Xiang Zhang of the University of California, Berkeley, and director of the Materials Sciences Division at Lawrence Berkeley National Laboratory. The new nanopatterning method, he says, “amazingly works so well and costs so little.”

Computer simulations also suggest this technique could enhance perovskite and silicon solar cells. And Huang suspects its utility won’t end with photovoltaics. “This is a very cheap, very accessible patterning technique,” he says. “I have a hunch there are applications beyond photonics.”



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