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Quantum dot breakthrough could lead to cheap spray-on solar cells


June 10, 2014

A new type of quantum dot could lead to cheaper solar cells and better satellite communica...

A new type of quantum dot could lead to cheaper solar cells and better satellite communication (Image: University of Toronto)

Researchers at the University of Toronto have manufactured and tested a new type of colloidal quantum dots (CQD), that, unlike previous attempts, doesn't lose performance as they keep in contact with oxygen. The development could lead to much cheaper or even spray-on solar cells, as well as better LEDs, lasers and weather satellites.

Quantum dot solar cells

A quantum dot is a nanocrystal made out of a semicondutor material which is small enough to take advantage of the laws of quantum mechanics. Quantum dots are at the center of a very new and rapidly evolving field of research, with the promise for applications in highly efficient solar cells, transistors and lasers, among other things.

In the case of solar cells, quantum dots are used as the absorbing photovoltaic material. The dots have the advantage of having a band gap that can be tuned simply by changing the size of the nanoparticles, and so they can be easily made to absorb different parts of the solar spectrum.

This makes them very attractive for multi-junction solar cells, where you could use a series of quantum dots of different size next to each other to absorb different areas of the spectrum. Crucially, this would drastically cut down the cost and complexity of manufacturing such cells.

The even less expensive option would be for single-junction quantum dot cells. Even here, using quantum dots has definite advantages. Because the band gap can be tuned at will, a single-junction cell can be made to absorb light in the far infrared, where half of the energy from our Sun lies. This would be challenging with standard solar cells, because we don't have materials with the adequate band gaps.

So far, the record efficiency for a quantum dot solar cell is only nine percent, which is roughly half the performance of commercial bulk silicon cells. However, this is a very new field in which progress has been both steady and rapid.

A better dot

Like in standard PV cells, CQD cells use p-type and n-type semiconductors to manipulate charge and generate electricity. However, the n-type quantum dot semiconductor tends to bind with oxygen atoms, giving up its electrons and turning into p-type, which renders the cell useless. N-type semiconductors made using soft matter are notoriously prone to oxidation within minutes of air exposure.

Now, a team led by post-doc researcher Zhijun Ning and Prof. Ted Sargent at the University of Toronto has manufactured and demonstrated a new type of CQD n-type lead-sulfide material that doesn't bind with oxygen, preserving the performance of the cell and opening up a world of new optoelectronic devices that capitalize on the best properties of both light and electricity, including better satellite communication and pollution detectors.

Ning, Sargent and colleagues tested a solar cell manufactured using their material, and achieved a high 8 percent efficiency, just shy of the current efficiency record for quantum dot cells.

"The field of colloidal quantum dot photovoltaics requires continued improvement in absolute performance, or power conversion efficiency," said Sargent. "The field has moved fast, and keeps moving fast, but we need to work toward bringing performance to commercially compelling levels."

Although eight percent efficiency is much less than commercially-available panels, quantum dot solar cells ultimately have the potential to become more efficient than their silicon counterparts because a single photon can be made to excite multiple electrons inside the cell.

With colloidal quantum dots, in which the nanoparticles are evenly distributed, we may eventually have high-efficiency spray-on solar cells that we could apply on our roofs to generate our very own power supply.

A paper detailing the advance was published in the journal Nature Materials.

Source: University of Toronto

About the Author
Dario Borghino Dario studied software engineering at the Polytechnic University of Turin. When he isn't writing for Gizmag he is usually traveling the world on a whim, working on an AI-guided automated trading system, or chasing his dream to become the next European thumbwrestling champion.   All articles by Dario Borghino

Efficiency is less important than cost.

So what if it is only 8%?

If I can cheaply spray these cells on my entire roof then 8% is more than enough to power my house and even charge my car.

10th June, 2014 @ 12:38 pm PDT

Spray-on solar cells are like fusion power: could, might, maybe.... See you in 50 years.

Seriously, people, spray-on solar cells will never make it. You need at least 4 coatings: 2 electrodes and some kind of active structure. Thin film panels are also cheaper than silicon, but where are they today?

Laprivan of the Yellow Eyes
11th June, 2014 @ 07:57 am PDT

This is NOT 50 years away. Konarka perfected the technology to print solar cells using a particular type of ink they invented. Using this ink, they were able to print sheets of paper using low-cost ink jet printers. This wasn't an idea. These printed solar panels worked great! The aholes at Konarka were so eaten up with their invention, they developed this "ivory tower" attitude that led to their demise. I tried doing business with them but they were almost unapproachable.

John Mauldin
11th June, 2014 @ 10:07 am PDT

John M.: So you're saying their product was so "great" that they got conceited and somehow that put them out of business? Do you realize how improbable that sounds? I would posit more likely senarios. 1.They hadn't quite eliminated a fatal defect and finally realized they couldn't. 2. They were a fraud.

Don Duncan
11th June, 2014 @ 02:55 pm PDT

Mass produce this, nice.

Stephen N Russell
11th June, 2014 @ 03:50 pm PDT

Somebody isn't paying enough attention to more recent developments. There are loads of different types of thin film solar cells and yes the more mature thin film technologies already are competing on the market with conventional solar cells. The thing is, is that the prices are going down on both sides and that is why conventional solar cells are still holding an edge, but it is one that is fading because its cost reduction potential isn't as great. Chinese firms have bought up patents for some thin film technologies for a bargain. Guess what they are doing with it?

How long have thin film solar cells been around since they were made in laboratories? A decade or so? Conventional solar cells have been around for 60 years.

Fretting Freddy the Ferret pressing the Fret
12th June, 2014 @ 02:48 pm PDT

There are two major elements to take careful note of here. First, sometimes individual discoveries have been made that are not able to make a complete "thing". It may take time for someone to see this, or not, and discover the matching puzzle pieces that will enable a complete "thing". Also, companies do make a practice of sitting on essential technology, mostly for purely selfish greedy reasons. Patent Law was first conceived and written to create a better society by permitting an inventor to individually profit from their discovery for a while. It is wrong to permit any company, individual, or whomever, including the Chinese to try to corner some market by hiding technology. The point of Patent Law is to create a better society by PROMOTING discovery and not by stalling it.

And to be exact, I do not care if the Chinese, or the Kochs, or whomever do not like that.

13th June, 2014 @ 08:35 am PDT

Unless we're talking about space based solar, it won't mean much of anything (as far as everyone powering their own home) until cheap, reliable, long lasting energy storage is perfected. Modern solar system are expected to last about 25-30 years, but the current lead acid batteries most commonly used to store energy for off-grid systems are expensive and must be replace at LEAST once, probably twice, and possibly 3 times during the life of the rest of the solar system. While there are other battery technologies, none of the currently available proven (in real world) battery technologies can solve this problem. Luckily their are several good candidate battery technologies on the horizon.

14th June, 2014 @ 10:50 am PDT
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