Researchers crack full-spectrum solar challenge

June 26, 2011, University of Toronto

In a paper published in Nature Photonics, U of T Engineering researchers report a new solar cell that may pave the way to inexpensive coatings that efficiently convert the sun's rays to electricity.

The U of T researchers, led by Professor Ted Sargent, report the first efficient tandem solar cell based on colloidal (CQD). "The U of T device is a stack of two light-absorbing layers – one tuned to capture the sun's visible rays, the other engineered to harvest the half of the sun's power that lies in the infrared," said lead author Dr. Xihua Wang.

"We needed a breakthrough in architecting the interface between the visible and infrared junction," said Sargent, a Professor of Electrical and Computer Engineering at the University of Toronto, who is also the Canada Research Chair in Nanotechnology. "The team engineered a cascade – really a waterfall – of nanometers-thick materials to shuttle electrons between the visible and infrared layers."

According to doctoral student Ghada Koleilat, "We needed a new strategy – which we call the Graded Recombination Layer – so that our visible and infrared light-harvesters could be linked together efficiently, without any compromise to either layer."

The team pioneered made using CQD, nanoscale materials that can readily be tuned to respond to specific wavelengths of the visible and invisible spectrum. By capturing such a broad range of light waves – wider than normal solar cells – tandem CQD solar cells can in principle reach up to 42 per cent efficiencies. The best single-junction solar cells are constrained to a maximum of 31 per cent efficiency. In reality, solar cells that are on the roofs of houses and in consumer products have 14 to 18 per cent efficiency. The work expands the Toronto team's world-leading 5.6 per cent efficient colloidal quantum dot solar cells.

"Building efficient, cost-effective solar cells is a grand global challenge. The University of Toronto is extremely proud of its world-class leadership in the field," said Professor Farid Najm, Chair of The Edward S. Rogers Sr. Department of Electrical & Computer Engineering.

Sargent is hopeful that in five years solar cells using the graded recombination layer published in today's paper will be integrated into building materials, mobile devices, and automobile parts.

"The solar community – and the world – needs a solar cell that is over 10% efficient, and that dramatically improves on today's photovoltaic module price points," said Sargent. "This advance lights up a practical path to engineering high-efficiency that make the best use of the diverse photons making up the sun's broad palette."

Explore further: Researchers discover new lead-free perovskite material for solar cells

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Vendicar_Decarian
2 / 5 (4) Jun 26, 2011
Photosynthesis is 7% efficient.
Yahp
5 / 5 (1) Jun 26, 2011
Which is only true for certain plants. Typically it's well below 1% considering somekind of a light-to-biomass effiency.
Wulfgar
5 / 5 (4) Jun 26, 2011
Its always five years away from deployment...
sender
not rated yet Jun 26, 2011
Solar-pumped optical lasing equipment fades still, suppose miniaturization could help.
concern_person
5 / 5 (5) Jun 26, 2011
Very poor writing as usual for this site in the 4th paragraph they state ?In reality, solar cells that are on the roofs of houses and in consumer products have 14 to 18 per cent efficiency."
Then the come up with this statement "The solar community and the world needs a solar cell that is over 10% efficient, and that dramatically improves on today's photovoltaic module price points," What price point? what about life time ? durability?
_etabeta_
4 / 5 (1) Jun 27, 2011
"The solar community and the world needs a solar cell that is over 10% efficient,"
What is the author try to say? I hope he meant "10% more efficient than the present 14 to 18% efficiency"
If PV panels were commercially available (at a reasonable cost) with a 25% efficiency, I would be able to cover my 100m2 roof and have a peak output of 25kW, with sufficient battery storage (or a presently unobtainable better storage system) a system like this would surely make a big dent in my energy bill.
lengould100
5 / 5 (1) Jun 27, 2011
Regarding the "10%", I think they might have meant "When applied as a cheap additional coating to standard metal roofing or siding".

Photosynthesis is 7% efficient.
Only in your dreams. The most efficient C4 plants such as sugar cane, MAY achieve efficiencies up to about 4% for only those times when the plant's leaves completely cover the surface in question. Obviously, that drops dramatically immediately after harvest, or during winter in tempearte climates. Many other issues as well (including fresh water availability, world's declining phosphate resources scheduled to be all used up in less than 100 years at present rates, and the high energy inputs required for nitrogen fertilizers, harvesting, transporting, drying and processing) combine to argue STRONGLY against mass dependence on photosynthesis.

Any non-photosynthesis system of harvesting solar energy is better in all respects, from area efficiency to resource use.
El_Nose
not rated yet Jun 27, 2011
question -- can't this be retyped to read that they have created a solar panal that captures light and has a heat conversion as well?? isn't IR capture simply heat capture? Doesn't heat propagate through IR radiation?
Eikka
5 / 5 (1) Jun 27, 2011
You know, they do this shoddy writing stuff on purpose to create rabble on otherwise uninteresting or pointless articles so that they'd get more pageviews and more ad reloads from their sponsors.

The same reason why they sometimes re-publish old articles as new articles.

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