Ultra-Thin Organic Imager Makes the Invisible Visible by Peering Into the Infrared Spectrum

A team of researchers from the University of California San Diego, the University of Southern Mississippi, and the Samsung Advanced Institute of Technology (SAIM) have unveiled a large-area yet surprisingly-thin infrared imager which, they say, is flexible, low-cost, and safe for biomedical use.

Shortwave infrared visualisers have a range of uses: Peering through smoke and fog, mapping a person's veins through their skin, remotely monitoring heart rate without physical contact, inspecting electronics through the surface of silicon wafers, and more. Traditional infrared imagers, though, are expensive, bulky, and difficult to build — which is where a new design created by Professor Tina Ng and colleagues comes in.

Described in the team's paper as an "organic upconversion imager", the ultra-thin prototype device is built using organic semiconductors - resulting in a biomedical-safe, flexible, and low-cost device. Despite this, it also boasts improved resolution over many of its more expensive inorganic competitors - and over a wider part of the infrared spectrum. Finally, it also offers a larger viewing area: 2 square centimetres, with scale-up theoretically simple to even bigger sizes.

The team's design is made up of multiple ultra-thin layers of semiconductors, three of which combine tasks normally given over to separate devices: An OLED display layer, an electron-blocking layer, and the photodetector layer. Unlike rival designs, the upconversion process — converting the low-energy photons absorbed by the photodetector layer into high-energy photons emitted by the OLED display layer - is electronic.

"The advantage of this is it allows direct infrared-to-visible conversion in one thin and compact system," explains first author Ning Li. "In a typical IR imaging system where upconversion is not electronic, you need a detector array to collect data, a computer to process that data, and a separate screen to display that data. This is why most existing systems are bulky and expensive."

The team's work has been published under open-access terms in the journal Advanced Functional Materials.