Power by sun: Nano-based plastic could be the key

Researchers at the University of Toronto have developed a plastic material that could significantly increase the efficiency of converting sunlight into electrical energy compared with current materials and processes. The material is sensitive to infra-red light, an untapped source of energy which accounts for about one-half of the sun’s emitted energy.

In a paper published in the February issue of Nature Materials, Ted Sargent, professor of electrical and computer engineering at U of T, reported that his team first made particles from semiconductor crystals which were exactly two, three or four nanometers in size. The nanoparticles remained dispersed in everyday solvents, like particles in paint. The researchers then “tuned” the nanocrystals to catch light at very long wavelengths. The key was finding the right polymer to wrap around the nanoparticles.

“Too long and the particles couldn’t deliver their electrical energy to our circuit; too short and they clumped up, losing their nanoscale properties,” said Steve Macdonald, a U of T graduate student who conducted many of the experiments.

The right molecule turned out to be octylamine, an eight-carbon atom chain, which happens to be approximately one nanometer in length.

Scientists have previously developed solution-processible, light-sensitive materials used in low-cost solar cells, displays and sensors, but these materials only work in the visible light spectrum. This is the first such material sensitive to light in the infra-red spectrum. Combining infra-red and visible photovoltaics could allow up to 30% of the sun’s radiant energy to be harnessed, compared to just 6% in today’s best plastic solar cells. In addition, the material might be used for imaging applications in the medical field and for fibre optic communications, noted Sargent.

“It’s a sprayable, spalashable, paintable material that dries on surfaces, like paint. When the solvent evaporates a thin continuous film is left behind.”