IBM Canada's Research and Development Centre, a consortium of seven universities that include the University of Toronto, has made significant headway in making spray-on solar cells a reality. The secret ingredient is collodial quantum dots, stated Illan Kramer, an IBM employee who works as a post-doctoral fellow in professor Ted Sargent's group at the University of Toronto.

"Colloidal quantum dots are semiconductor nanoparticles that are suspended in the solution phase. Because the nanoparticles are so small, they cannot be seen by eye, but they do make the solution look black, much like an ink. When you have materials like this, you can allow your imagination to run wild with respect to how you want to deposit them into a film: ink-jet printing, slot-dye coating or through a spraying method. We played with both the ink solution and the spray droplet size to arrive at a scenario where the colloidal quantum dots were 'almost dry' by the time the spray reached the substrate," Kramer stated.

Quantum dots are increasingly being used for brighter LEDs as well as novel solar cells built into windows. Now the IBM Canada's Research and Development Centre and the University of Toronto believe they are on the road to spray-on solar cells using quantum dots in this century. Kramer calls the devices sprayLD, a play on ALD, atomic layer deposition.

"We have sprayed onto flat glass substrates, flexible plastic substrates and hemispherical glass substrates. We were able to make functional devices on all three types of substrates. The glass substrates represented a perfect analogue to our batch-processed counterparts for comparative purposes, while the flexible and hemispherical substrates were more directly linked to manufacturability. In the flexible case, one could envision a roll-to-roll manufacturing plant where deposition occurred much like it would at a newspaper printing press," added Kramer. "Whereas in the hemispherical class case, we considered that a proof-of-concept for directly applying our solar cell materials to non-flat surfaces like airplane wings or car fenders."

SprayLD can be applied directly to nearly any surface, no matter the shape, for mass production. Kramer's vision is to use roll-to-roll manufacturing to create films that can be applied to nearly any surface from patio furniture to airplane wings to the surface of your car. Next the researchers want to optimise the process to boost its efficiency.

"The current record we achieved is 8.1 per cent power conversion efficiency, the ratio of electrical power output to sunlight power input. While this is a great achievement for spray-coated films, we consider 10 per cent to be a critical threshold for getting seriously commercially compelling," noted Kramer. "We are continuously working towards improving our efficiency, but also towards scaling up our process towards larger and larger cells. We hope that within 5 to 10 years, you will see solar cells like these being commercialised."

Funding for spray-on solar cells was provided by the IBM Canada Research and Development Centre, and by King Abdullah University of Science and Technology.

By: DocMemory
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