Published on November 26th, 2014 | by Tina Casey9
New Solar Cell Efficiency From Old Blu-Ray Discs
November 26th, 2014 by Tina Casey
Talk about your upcycling, a research team from Northwestern University has figured out how you can boost your solar cell efficiency and get rid of your old Blu-ray discs all at the same time. We’re not about to repurpose Blade Runner because we still luvs it, but not to worry — apparently you can get the same results with just about anything on Blu-ray.
More And Better Solar Cell Efficiency
So, what’s the secret sauce? The team was inspired to tinker around with Blu-ray discs because of their superior data storage capability compared to DVDs or CDs.
The idea sounds simple enough: transfer the data storage pattern of nanoscale “islands” and “pits” from the disc to the surface of a solar cell, and you get a nano-textured surface that enhances the ability of the cell to absorb light.
The reason why that sounds simple is that texturizing is a known thing for solar cell efficiency. You can check out our friends over at Natcore for an example of “black silicon” solar cells with improved efficiency from a textured surface.
The sticky wicket, of course, is bringing the cost of the texturizing process down. That’s where the Northwestern discovery gets really interesting, because it provides a pathway for reclaiming value out of old products while lowering the cost of the process.
The team found that it literally doesn’t matter what’s on the Blu-Ray disc (they started with a copy of “Supercop”), so if you share a household with persons who have super-annoying viewing habits, you can ditch all of their discs for a good cause.
Sooo…How Does This Actually Work?
Actually, the really interesting thing about the Northwestern solar cell efficiency discovery is that the team found that a randomly textured surface is better than no texture at all, but for some reason the purpose-based pattern on Blu-ray discs outperforms a random texture.
The question is, why does that happen, and for an answer we turn to the wife of one of the researchers, Shaorong Liu, who happens to be a database engineer at IBM. She dropped a hint that the mechanics could involve the enhanced data compression of Blu-ray, and the rest is history.
As described by Northwestern, the team took a good look at the algorithms used to fabricate Blu-ray discs in a binary sequence of 0s and 1s (that’s the nanoscale “islands” and “pits” on the discs).
They noted two main features that drive the algorithms, one of which is the aforementioned compression of video signals into 0s and 1s.
The other factor is an element of “controlled redundancy” that limits how many 0s and 1s can appear consecutively.
So, you get more seeming randomness while creating a texture in the range of 15-525 nanometers:
And this range, it turns out, 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.
If you want to take a look at the study, check out “Repurposing Blu-ray Movie Discs as Quasi-random Nanoimprinting Templates for Photon Management” in the journal Nature.
For those of you on the go, here’s a snippet from the abstract:
…While the algorithms in the Blu-ray industrial standard were developed with the intention of optimizing data compression and error tolerance, they have also created quasi-random arrangement of islands and pits on the final media discs that are nearly optimized for photon management over the solar spectrum, regardless of the information stored on the discs.
And Then There’s This…
By the way, aside from improving solar cell efficiency, the ubiquitous disc could also have some application in energy storage, at least in the form of a DVD.
A couple of years ago we noticed that a team from UCLA was on the way to figuring out how you could use a blank DVD to make a high efficiency supercapacitor (for those of you new to the topic, supercapacitors store energy like batteries but they charge and discharge in quick, powerful bursts).
Here’s the breakdown:
…an ordinary DVD pre-treated with graphite oxide can be inscribed by laser into components for a graphene-based supercapacitor using a commercially available CD/DVD label burning drive, in this case from the company LightScribe.
We’re guessing that for everybody who’s piling up stacks of worn out Blu-rays, somebody else is hoarding stacks of unused CD/DVD blanks, so we’ll keep you posted if the two of them ever get together.
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