Infrared Goes Green

From security cameras to night vision goggles, there are many devices that help us to see after the sun goes down. Most commonly, these devices rely on sensors that detect infrared radiation to make this possible. Anything and everything that has a temperature above absolute zero gives off infrared radiation, so these sensors are perfect for these types of applications. All we need to do is map the intensity of infrared light detected to a similar intensity of visible light, display it on a screen, and we can see in the dark.

Easy enough, but there is one big problem that is jeopardizing our ability to support these applications in the future. Today’s infrared sensors are made with toxic heavy metals like mercury and lead, and governmental regulations are increasingly making it harder (or even impossible) to include these materials in commercial products. So moving forward, new technologies will be needed.

Fortunately, researchers at the NYU Tandon School of Engineering are hard at work on this problem, and have just reported on some significant progress. They have developed a novel system that uses an environmentally friendly method to detect infrared radiation. No toxic heavy metals are involved in the fabrication process.

The team has been exploring colloidal quantum dots as an alternative. Unlike traditional devices that are assembled atom by atom in complex layers, colloidal quantum dots are synthesized in solution. This means that the material can be prepared in bulk and deposited using techniques similar to those used for printing newspapers or packaging. That opens the door to large-scale, low-cost manufacturing.

One of the biggest challenges the team faced with quantum dot films was conductivity. Without efficient charge transport, a detector cannot turn incoming photons into electrical signals. To solve this, a method called solution-phase ligand exchange was used. By tailoring the surface chemistry of the quantum dots, the researchers were able to create smooth, crack-free films that maintain high conductivity.

The new devices show responsivities of about 150 milliamps per watt under modest bias conditions and can detect light on the microsecond timescale. To put that in perspective, that is hundreds of times faster than the blink of a human eye. Even faint signals — as weak as a nanowatt of light — can be detected. The researchers also demonstrated a self-powered photodiode with a detectivity that places it among the highest-performing heavy-metal-free quantum dot detectors reported to date.

There is still ground to cover before quantum dot detectors rival the very best heavy-metal-based systems. But with environmental regulations tightening and demand for infrared technology growing, this line of research provides a sustainable path forward. As one member of the team puts it, “Every infrared camera in a Tesla or smartphone needs detectors that meet environmental standards while remaining cost-effective. Our approach could help make these technologies much more accessible.”

If you are more interested in keeping your face hidden from security cameras in public spaces than in night vision, then you should check out Freedom Shield.