Blu-ray discs are already one of the best ways to store high-definition movies and TV shows because of their high-density data storage. Now, new research from Northwestern University states they also improve the performance of solar cells.
An interdisciplinary research team has discovered that the pattern of information written on a Blu-ray disc works great for improving light absorption across the solar spectrum.
“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 Jiaxing Huang, a materials chemist and an associate professor of materials science and engineering in the McCormick School of Engineering and Applied Science. “It is as if electrical engineers and computer scientists developing the Blu-ray technology have been subconsciously doing our jobs, too.”
Blu-ray discs contain a higher density of data than DVDs or CDs, and it is this pattern, perfected by engineers over decades for data storage that, when it is transferred to the surface of solar cells, provides the right texture to improve the cells’ light absorption and performance.
Working with Cheng Sun, an associate professor of mechanical engineering at McCormick, Huang and his team tested a wide range of movies and television shows stored of Blu-ray discs, including action movies, dramas, documentaries, cartoons and black-and-white content. They found that the video content did not matter. All of them worked equally well for enhancing light absorption in solar cells.
If the texture is placed on the surface of a solar cell, light is scattered more efficiently, increasing a cell’s efficiency. Scientists have been searching for the most effective and inexpensive texture for a long time.
The Northwestern researchers have demonstrated that a Blu-ray disc’s strings of binary code 0s and 1s, embedded as islands and pits to store video information, give solar cells the near-optimal surface texture to improve their absorption over the broad spectrum of sunlight.
The researchers first selected the Jackie Chan movie “Super Cop” for their study. They replicated the pattern on the active layer of a polymer solar cell and found the cell was more efficient than a solar control cell with a random pattern on its surface.
“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 do not understand why it is not good science.”
For a while, Huang could not figure out why, until one day his wife, Shaorong Liu, a database engineer at IBM, suggested it likely had something to do with data compression. This was the answer that he had been looking for.
Huang and Sun then turned to McCormick colleague Dongning Guo, an expert in information theory, to investigate the idea. Guo is an associate professor of electrical engineering and computer science.
The researchers looked carefully at the data processing algorithms in the Blu-ray standard and noted the algorithms serve main purposes:
- Achieving as high a degree of compression as possible by converting the video signals into a seemingly random sequence of 0s and 1s
- Increasing error tolerance by adding controlled redundancy into the data sequence, which also limits the number of consecutive 0s and 1s.
The researchers said that these two purposes have resulted in a quasi-random array of islands and pits (0s and 1s) with feature sizes between 150 and 525 nanometers. As it turns out, this range works quite well for light-trapping applications over the entire solar spectrum.
The overall broadband absorption enhancement of a Blu-ray patterned solar cell was measured to be 21.8 percent, the researchers report.
“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,” Sun said.
“It has been quite unexpected and truly thrilling to see new science coming out of the intersection of information theory, nanophotonics, and materials science,” Huang said.
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