U of T engineers crack solar challenge

University of Toronto
June 27, 2011

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 researchers, led by Professor Ted Sargent of electrical and computer engineering, report the first efficient tandem solar cell based on colloidal quantum dots (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 co-author Xihua Wang, a post-doctoral fellow.

“We needed a breakthrough in architecting the interface between the visible and infrared junction,” said Sargent, 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, lead co-author of the paper, “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 solar cells made using CQDs, 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.
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