Quantum dot solar windows go non-toxic, colorless, with record efficiency

August 25, 2015, Los Alamos National Laboratory
The luminescent solar concentrator could turn any window into a daytime power source.

A luminescent solar concentrator is an emerging sunlight harvesting technology that has the potential to disrupt the way we think about energy; It could turn any window into a daytime power source.

"In these devices, a fraction of light transmitted through the window is absorbed by nanosized particles (semiconductor ) dispersed in a glass window, re-emitted at the infrared wavelength invisible to the human eye, and wave-guided to a solar cell at the edge of the window," said Victor Klimov, lead researcher on the project at the Department of Energy's Los Alamos National Laboratory. "Using this design, a nearly transparent window becomes an electrical generator, one that can power your room's air conditioner on a hot day or a heater on a cold one."

This is what becomes possible with new devices – quantum dot LSCs –which will be available in the journal Nature Nanotechnology in the study "Highly efficient large-area colourless luminescent solar concentrators using heavy-metal-free colloidal quantum dots". The work was performed by researchers at the Center for Advanced Solar Photophysics (CASP) of Los Alamos, led by Klimov and the research team coordinated by Sergio Brovelli and Francesco Meinardi of the Department of Materials Science of the University of Milan-Bicocca (UNIMIB) in Italy.

In April 2014, using special composite quantum dots, the American-Italian collaboration demonstrated the first example of large-area free from reabsorption losses of the guided light by the nanoparticles. This represented a fundamental advancement with respect to the earlier technology, which was based on organic emitters that allowed for the realization of concentrators of only a few centimeters in size.

However, the quantum dots used in previous proof-of-principle devices were still unsuitable for real-world applications, as they were based on the toxic heavy metal cadmium and were capable of absorbing only a small portion of the solar light. This resulted in limited light-harvesting efficiency and strong yellow/red coloring of the concentrators, which complicated their application in residential environments.

Klimov, CASP's director, explained how the updated approach solves the coloring problem: "Our new devices use quantum dots of a complex composition which includes copper (Cu), indium (In), selenium (Se) and sulfur (S). This composition is often abbreviated as CISeS. Importantly, these particles do not contain any toxic metals that are typically present in previously demonstrated LSCs."

"Furthermore," Klimov noted, "the CISeS quantum dots provide a uniform coverage of the solar spectrum, thus adding only a neutral tint to a window without introducing any distortion to perceived colors. In addition, their near-infrared emission is invisible to a human eye, but at the same time is ideally suited for most common solar cells based on silicon."

Francesco Meinardi, professor of Physics at UNIMIB, described the emerging work, noting, "In order for this technology to leave the research laboratories and reach its full potential in sustainable architecture, it is necessary to realize non-toxic concentrators capable of harvesting the whole solar spectrum."

"We must still preserve the key ability to transmit the guided luminescence without reabsorption losses, though, so as to complement high photovoltaic efficiency with dimensions compatible with real windows. The aesthetic factor is also of critical importance for the desirability of an emerging technology," Meinardi said.

Hunter McDaniel, formerly a Los Alamos CASP postdoctoral fellow and presently a quantum dot entrepreneur (UbiQD founder and president), added, "with a new class of low-cost, low-hazard quantum dots composed of CISeS, we have overcome some of the biggest roadblocks to commercial deployment of this technology."

"One of the remaining problems to tackle is reducing cost, but already this material is significantly less expensive to manufacture than alternative quantum dots used in previous LSC demonstrations," McDaniel said.

A key element of this work is a procedure comparable to the cell casting industrial method used for fabricating high optical quality polymer windows. It involves a new UNIMIB protocol for encapsulating quantum dots into a high-optical quality transparent polymer matrix. The polymer used in this study is a cross-linked polylaurylmethacrylate, which belongs to the family of acrylate polymers. Its long side-chains prevent agglomeration of the quantum dots and provide them with the "friendly" local environment, which is similar to that of the original colloidal suspension. This allows one to preserve light emission properties of the quantum dots upon encapsulation into the polymer.

Sergio Brovelli, the lead researcher on the Italian team, concluded: "Quantum dot solar window technology, of which we had demonstrated the feasibility just one year ago, now becomes a reality that can be transferred to the industry in the short to medium term, allowing us to convert not only rooftops, as we do now, but the whole body of urban buildings, including windows, into solar energy generators."

"This is especially important in densely populated urban area where the rooftop surfaces are too small for collecting all the energy required for the building operations," he said. He proposes that the team's estimations indicate that by replacing the passive glazing of a skyscraper such as the One World Trade Center in NYC (72,000 square meters divided into 12,000 windows) with our technology, it would be possible to generate the equivalent of the energy need of over 350 apartments.

"Add to these remarkable figures, the energy that would be saved by the reduced need for air conditioning thanks to the filtering effect by the LSC, which lowers the heating of indoor spaces by sunlight, and you have a potentially game-changing technology towards "net-zero" energy cities," Brovelli said.

Explore further: Shiny quantum dots brighten future of solar cells

More information: "Highly efficient large-area colourless luminescent solar concentrators using heavy-metal-free colloidal quantum dots." Nature Nanotechnology (2015) DOI: 10.1038/nnano.2015.178

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5 / 5 (1) Aug 25, 2015
On a good day, one domestic window will generate how many Watts?
3.7 / 5 (7) Aug 25, 2015
On a sunny day? Your windows will generate enough to run an efficient AC system. Easily.

In the end: Every bit helps. We're on the road to where many small providers replace centralized/large providers. And that is certainly a good thing when you thing about resilience of a system against damage (intentional or through natural catastrophes) as well as the effects otherwise monopolized (energy) production has in terms of cost to the consumer.
Aug 25, 2015
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5 / 5 (4) Aug 25, 2015
Can we have that in scientific units please eg kW.
What is the international standard power and energy need of "an apartment"?
2.6 / 5 (5) Aug 25, 2015
But not so efficient, or cost effective, that they have a use.

Carry on.
2 / 5 (4) Aug 25, 2015
Shootist is praying they are not cost-effective.

But they will be.
5 / 5 (3) Aug 25, 2015
Much like regenerative breaking, even if this only picks up a small amount of juice per window, the combination of windows all day + probably solar paint + maybe a small wind turbine and you'll be off the grid entirely. Might want a bank of Tesla batteries in the basement. Maybe a solar water heater on the roof? The more easy power options you can combine, the less you have to worry about fossil fuels and nuclear.
5 / 5 (1) Aug 25, 2015
Record efficiency yet no mention of what that efficiency actually is? I did not read the original paper, but you would think they would mention that in this article.

Can we have that in scientific units please eg kW.
What is the international standard power and energy need of "an apartment"?

What the energy need of an apartment is will be dependent on the apartment. My apologies for a vague answer, but that is the truth of the matter. There are too many variables involved like insulation in the apartment, number of people who live in the apartment, whether they cook in the apartment or eat all their meals elsewhere, etc. The best way for an apartment renter to figure this out is to do an energy survey.

However, the average available solar power on a clear day is approximately 1 kW/m^2. IF, and I emphasize IF these were 100-percent efficient, that is what you would get from a window if it were properly oriented towards the sun all the time - which they won't be.
not rated yet Aug 25, 2015
Quantum dots are entirely awesome.

>On a good day, one domestic window will generate how many Watts?

You mean watt-hours :-) Not many.
It's about 1/30th the efficiency of a solar panel in the same orientation.

From the abstract:"Thanks to the suppressed reabsorption and high emission efficiencies of the quantum dots, we achieve an optical power efficiency of 3.2%."

So, 1000 watts per square meter normal insolation x sine (angle-of-incidence of the sunlight on the window) x .032 x 20% silicon photovoltaic efficiency. It's a little over 0.6 percent efficiency.

Power collection will work best in the morning and evening, and not very well at all at noon in the summertime at lower latitudes. Windows are almost never intentionally positioned as efficient solar collectors, because of the undesirable heat gain.

That assumes that the 3.2% optical power efficiency reported is across the entire spectrum of incoming solar radiation.

not rated yet Aug 25, 2015
On a good day, one domestic window will generate how many Watts?

5 / 5 (3) Aug 25, 2015
This sample we built (energy generating clear glass) produces 7.7 Wp in a vertical window, from 0.25 m2 of energy collection area. https://www.youtu...eXLtoKKU
Aug 26, 2015
This comment has been removed by a moderator.
5 / 5 (3) Aug 26, 2015
We are now ready to reach 23-25W per 1m2 of clear glass packaged into standard Kommerling PVC frames as either an IGU or a single-pane system. The goal is 30-40W/m2 and work is in progress. The model that outputs 43Wp has some externally mounted cells but is ready to be deployed in agricultural glasshouse settings now. New results on upscaling the performance using advanced structures are going to be submitted to Scientific Reports soon, and our older article is at http://www.nature...rep06632
5 / 5 (3) Aug 26, 2015
Regarding the required tinting capability, we are already doing this using polymer-dispersed LC glass from Switchglass Ltd. Plenty of power is still left for driving the fans: https://www.youtu...s_cGd6oI
not rated yet Aug 29, 2015
But not so efficient, or cost effective, that they have a use.
Denial is not a form of intelligence
not rated yet Aug 31, 2015
This story is either the work of fiction or an ad for a a bunch of thieves pretending to be scientists. The story neglects to mention how the energy is concentrated and transmitted to the solar cell as they have not actually done any such thing. the self serving inorg, isc post tells you the so called tech will not power anything 30w for 9 sq ft of glass is a ridiculously low number and would never power an air conditioner. Mine takes 25 amps at 230 volts which is 1725 sq ft of window. No reasonable house has that much glass.
not rated yet Aug 31, 2015
Can we have that in scientific units please eg kW.
What is the international standard power and energy need of "an apartment"?

something like 1/3 of a cubic football field
not rated yet Sep 03, 2015
Ok, 1725 sq ft is only about 160 m2. A floor of windows on a medium building will easily feature 300-400 m2 on its two or three sunny sides. Other calculations show that 300 m2 of window areas averaging 25 Watts/m2 will generate almost 11.25 MegaWatt-hours over 250 sunny days with 6 peak-sunshine-hours per day, over 1 year. EPFL in Switzerland (https://juanbisqu...laronix/ ) built a semitransparent dye-sensitized solar cell facade of 300 m2 which generated 2 MegaWatt-hrs per year. Not to run 1000 aircons, but still something that is worth doing in big buildings with energy storage facilities that are coming to the market.

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