Blu-ray discs have proven themselves superior to DVDs as storage media in light of their high capacity, high definition, and higher transfer rate. Now researchers claim that Blu-ray discs have one more advantage over DVDs: they also have the ability to help markedly improve the efficiency of solar cells, when their etched information patterns are repurposed for use as light concentrators.

Blu-ray discs have proven themselves superior to DVDs as storage media in light of their high capacity, high definition, and higher transfer rate. Now researchers claim that Blu-ray discs have one more advantage over DVDs: they also have the ability to help markedly improve the efficiency of solar cells, when their etched information patterns are repurposed for use as light concentrators.

According to new research from a team at Northwestern University, Illinois, it has been discovered that the scattering effect on light shone through the arrangement of data etched on a Blu-ray disc improves energy absorption across the spectrum of light used by solar cells.

"We had a hunch that Blu-ray discs might work for improving solar cells, and, to our delight, we found the existing patterns are already very good," said Associate Professor Jiaxing Huang, of the McCormick School of Engineering and Applied Science at Northwestern. "It’s as if electrical engineers and computer scientists developing the Blu-ray technology have been subconsciously doing our jobs, too."

The quasi-random pattern applied to Blu-ray discs – formed as part of the development of their higher-density makeup – has proven to be of the right texture to significantly improve the scattering effect of light when applied to the surface of solar cells. That is, the arrangement of troughs and peaks (zeroes and ones) etched into the surface are sized at between 150 and 525 nanometers, making them ideal for improved light-trapping and concentration.

In fact, the researchers claim, the overall broadband absorption improvement of a solar cell with its surface etched with a Blu-ray pattern was around 21.8 percent; much greater than a standard solar cell.

Associate Professor Huang, working with his team and in collaboration with Associate Professor of mechanical engineering at McCormick, Cheng Sun, tested a range of different movies and TV shows across the genres of action, drama, documentaries, and cartoons: they even tested Blu-ray discs containing old black-and-white movies. However, no matter the content, the patterns of these all performed alike in improving solar cell light absorption.

Whether as a favorite film or selected at random the researchers didn't say, but the first movie they selected to test was the Jackie Chan film Supercop. It was the pattern from the Blu-ray disc of this movie that they copied onto the active coating of a polymer solar cell, and discovered that the cell displayed greater efficiency than a comparable control solar cell with a haphazard surface pattern.

"We found a random pattern or texture does work better than no pattern, but a Blu-ray disc pattern is best of all," Huang said. "Then I wondered, why did it work? If you don’t understand why, it’s not good science."

The answer to Huang’s dilemma came to pass when – after some time cogitating over it – he talked to his wife, a database engineer at IBM, who proffered the idea that the data compression on the pattern of the discs could be responsible. This was a light-bulb moment for Huang.

Working with Dongning Guo, a colleague and expert in information theory, Huang and Sun examined the algorithms used in processing data in Blu-ray. From this study, the collaborators observed that the algorithms realized an exceptionally high degree of compression by converting video signals into a seemingly random sequence of data bits, and that error tolerance was increased by controlling data sequence redundancy, thereby limiting the consecutive number of ones and zeroes.

As a result, the team has been able to determine that these algorithms create blue-laser-etched patterns that – serendipitously – also provide a new and unexpected method of precise scattering that improves light absorption for solar cells and possibly other photovoltaic devices, that simple random patterning is unable to replicate.

"In addition to improving polymer solar cells, our simulation suggests the Blu-ray patterns could be broadly applied for light trapping in other kinds of solar cells," said Professor Sun.

No announcement has been made as to further research or any commercial availability of the technique in future devices.