Nanotechnologists’ new material harvests sun’s invisible rays

Toronto, ON – Researchers at University of Toronto have invented an infrared-sensitive material that is five times more efficient at converting solar energy than today’s best plastic solar cells.

In a paper published on the Nature Materials website on January 9, senior author Professor Ted Sargent, Nortel Networks Canada Research Chair in Emerging Technologies at the university’s department of electrical and computer engineering, and his team report on their achievement in tailoring matter to harvest the sun’s invisible rays.

“We made particles from semiconductor crystals which were exactly two, three or four nanometres in size,” he says. “The nanoparticles were so small they remained dispersed in everyday solvents just like the particles in paint.

Then, they tuned the tiny nanocrystals to catch light at very long wavelengths. The result was a sprayable infrared detector. Existing technology can create solution-processible, light-sensitive materials making large, low-cost solar cells, displays, and sensors possible, but these materials have so far only worked in the visible light spectrum, says Sargent. “These same functions are needed in the infrared for many imaging applications in the medical field and for fibre optic communications,” he says.

The discovery may also help in the quest for renewable energy sources. Flexible, roller-processed solar cells have the potential to harness the sun’s power, but efficiency, flexibility and cost are going to determine how that potential becomes practice, says Josh Wolfe, managing partner and nanotechnology venture capital investor at Lux Capital in Manhattan. Wolfe, who was not part of the research team, says the findings in the paper are significant: “These flexible photovoltaics could harness half of the sun’s spectrum not previously accessed.”

Professor Peter Peumans of Stanford University, who has reviewed the U of T team’s research, also acknowledges the groundbreaking nature of the work. “Our calculations show that, with further improvements in efficiency, combining infrared and visible photovoltaics could allow up to 30% of the sun’s radiant energy to be harnessed, compared to 6% in today’s best plastic solar cells,” he says.

University of Toronto electrical and computer engineering graduate student Steve MacDonald carried out many of the experiments that produced the world’s first solution-processed photovoltaic in the infrared. “The key was finding the right molecules to wrap around our nanoparticles,” he explains. “Too long and the particles couldn’t deliver their electrical energy to our circuit; too short, and they clumped up, losing their nanoscale properties. It turned out that one nanometer – eight carbon atoms strung together in a chain – was just right.”

Other members of the research team are Gerasimos Konstantatos, Shiguo Zhang, Paul W Cyr, Ethan JD Klem, and Larissa Lavina of electrical and computer engineering; Cyr is also with the department of chemistry. The research was supported in part by the government of Ontario through Materials and Manufacturing Ontario, a division of the Ontario Centres of Excellence; the Natural Sciences and Engineering Research Council of Canada through its collaborative research and development program; Nortel Networks; the Canada Foundation for Innovation; the Ontario Innovation Trust; the Canada Research Chairs Programme; and the Ontario Graduate Scholarship.

Reported by Sonnet L’Abb