Imagine a home with “smart” walls responsive to the environment in the room, a digital camera sensitive enough to work in the dark, or clothing with the capacity to turn the sun’s power into electrical energy. Researchers at the University of Toronto have invented an infrared-sensitive material that could shortly turn these possibilities into realities.

A nanometer-resolved microscope image of one of the nanoparticles, or quantum dots, used to make the infrared detectors. The particle is four nanometers – billionths of a meter – in diameter. Individual atoms of lead and sulfur can be resolved in the image. The nanoparticles were suspended in a solvent and dried like paint to make a large-area device. Image: Advanced Materials

“We made particles from semiconductor crystals which were exactly two, three or four nanometres in size. The nanoparticles were so small they remained dispersed in everyday solvents just like the particles in paint,” explains Sargent. Then, they tuned the tiny nanocrystals to catch light at very short wavelengths. The result – a sprayable infrared detector.

Existing technology has given us solution-processible, light-sensitive materials that have made 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.”

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