A team of researchers from The Barcelona Institute of Science and Technology and Barcelona-based startup Qurv Technologies have made flexible, nearly transparent image sensors that could be hidden in plain sight. The sensors, made of graphene and quantum dots, could be integrated directly onto eyeglasses or curved windshields, placed right in front of a user’s eyes. This could make eye-tracking hardware less bulky, improve the accuracy of gaze detection, and reduce computational complexity. To make semi-transparent image sensors, researchers combined the properties of two nanomaterials. Atoms-thick graphene is an excellent conductor and is also very good at converting photons into electrons and positively charged holes. But it absorbs very little light. On the other hand, quantum dots, which are semiconductor nanocrystals, are excellent light absorbers.
So, the team deposited graphene on a clear quartz substrate, and then coated it with an ultrathin layer of quantum dots just a few tens of nanometers thick. The quantum dots absorb photons and pass them on to the graphene, which converts them into voltage. As a demonstration, the researchers made an 8-by-8 array of graphene–quantum dot photodetector pixels, each 60 by 140 micrometers in size. The pixels are connected to the signal-processing electronics via wires made of indium tin oxide, a commonly used transparent electrode material. The researchers projected pixelated black and white images on the array and reconstructed them by reading the signals from each photodetector. Most of the patterns could be reconstructed by the array, but the results weren’t perfect. Researchers now plan to further improve the resolution and speed of the image sensors and develop methods to reliably make them on larger scale.
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