Toronto Researchers Increase Solar Efficiency by 35 Percent in Quantum Dot Photovoltaics
March 11, 2013 4:26 PM
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This mean an 11 percent solar power conversion efficiency increase overall
A Canadian research team has used a certain type of nanoparticle to increase the efficiency of
Ted Sargent, study leader and a professor at the University of Toronto's Engineering Department, along with Dr. Susanna Thon, has improved the efficiency of colloidal quantum dot photovoltaics through the use of plasmonic nanoparticles.
While colloidal quantum dot photovoltaics offer a lot of potential for large-area, low-cost solar power, they're not quite as efficient in the infrared area of the sun's spectrum.
To address this, the team used plasmonic nanoparticles that are spectrally tuned, meaning that they offer control over light absorption. The gold nanoshells were embedded directly into the quantum dot absorber film to do so.
The team added that gold is not the only material that can be used for this, since it isn't the most economical. Lower-cost materials can be used as well.
Using this technique, the team saw a 35 percent
increase in efficiency
in the near-infrared spectral region. This mean an 11 percent solar power conversion efficiency increase overall.
"There are two advantages to colloidal quantum dots," Thon said. "First, they're much cheaper, so they reduce the cost of electricity generation measured in cost per watt of power. But the main advantage is that by simply changing the size of the quantum dot, you can change its light-absorption spectrum. Changing the size is very easy, and this size-tunability is a property shared by plasmonic materials: by changing the size of the plasmonic particles, we were able to overlap the absorption and scattering spectra of these two key classes of nanomaterials."
From here, the team plans to look into cheaper metals to build a better cell.
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RE: Gaps in information.
3/12/2013 3:20:58 PM
Thank you for that excellent reply! So is the amorphous nature of quantum dots the reason for the much higher theoretical efficiency of 87%? That would completely obsolete traditional Si solar cells considering that any gains in Si past the Shockley-Queisser limit involve intricate magnification techniques that would not be easily applied into a commercial setting. Assuming of course that quantum dots can indeed to tuned to reach it's theoretical maximum!
As for cost, from what I remember in school, quantum dots could be printed using already existing inkjet printers adapted for suitable use. That would mean that QD solar cells could be produced using the extremely cheap thin film method which could produce large sheets of solar panels relatively quickly and inexpensively.
At any rate, thank you for all the fantastic info! You answered my question well and then some!
RE: Gaps in information.
3/12/2013 7:53:06 PM
I'm happy I was able to answer it.
I wouldn't go so far as to call the quantum dots amorphous. They are "quasi-crystals" in that their atomic structure has long range order... over their small diameter. The fact that they can easily produce these crystals in a test tube by chemistry, chemically modify the surface, and electrically connect the quantum dots to a matrix material that is both conductive and allows for the separation of the electron-hole pairs is what makes this work. It is entirely different than any other kind of solar cell out there, which are usually crystalline films. It is really more similar to organic solar cells in principle, but using inorganic semiconductors instead.
Now while I said the theoretical maximum could be up to 87%, I wouldn't expect it to get anywhere near that. If they could get 30% though (especially in a production cell), that would be massively impressive.
The process they use to make these does lend itself to cheap manufacturing methods like you said, so we'll see if they can scale it up!
RE: Gaps in information.
3/13/2013 4:35:23 PM
That's interesting, although since quantum dots are able to be infinitely tuned I wouldn't be surprised if QDs can be tuned for the entire spectrum of sunlight to absorb as much energy as possible. Heck, one could even use a multi-layered approach where one layer is tuned for say infrared and visible light while the next layer is tuned for ultra violet and visible light. The materials science is really the meaty and interesting part of this research in that the potential applications are truly limitless. :)
However, do you think that you may be a tad conservative about the practical limits QD solar cells? Commercialized solar panels can reach ~22% CE for polycrystalline panels and ~15% for the much cheaper thin film variety, or roughly 67% and 50% of the Shockley-Queisser limit respectively. So just carrying over the ratios, if researchers can reach even 50% of the theoretical limit that would translate to a CE of 44%!
Considering that a square meter of sunlight that reaches the Earth's surface contains 1100 watts of energy, a one square meter panel could harness 484 watts of energy on a sunny day! Also consider that the roof size of an average middle class home is 223 square meters and if you can allocate 75% for panel coverage then you can collect almost 81kW of energy just in one sunny day! Plus, seeing as how that's much more energy than what most people use in a day, you could make a fortune selling energy back to the utility company! Being a personal energy tycoon sounds rather appealing, wouldn't you say? :)
"And boy have we patented it!" -- Steve Jobs, Macworld 2007
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