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MemberSeptember 9, 2021 at 3:58 pm
The imager is made up of multiple semiconducting layers, each hundreds of nanometers thin, stacked on top of one another. Three of these layers, each made of a different organic polymer, are the imager’s key players: a photodetector layer, an organic light-emitting diode (OLED) display layer, and an electron-blocking layer in between.
The photodetector layer absorbs shortwave infrared light (low energy photons) and then generates an electric current. This current flows to the OLED display layer, where it gets converted into a visible image (high energy photons). An intermediate layer, called the electron-blocking layer, keeps the OLED display layer from losing any current. This is what enables the device to produce a clearer image.
This process of converting low energy photons to higher energy photos is known as upconversion. What’s special here is that the upconversion process is electronic. “The advantage of this is it allows direct infrared-to-visible conversion in one thin and compact system,” said first author Ning Li, a postdoctoral researcher in Ng’s lab. “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.”
Another special feature is that the imager is efficient at providing both optical and electronic readouts. “This makes it multifunctional,” said Li. For example, when the researchers shined infrared light on the back of a subject’s hand, the imager provided a clear picture of the subject’s blood vessels while recording the subject’s heart rate.
The researchers also used their infrared imager to see through smog and a silicon wafer. In one demonstration, they placed a photomask patterned with “EXIT” in a small chamber filled with smog. In another, they placed a photomask patterned with “UCSD” behind a silicon wafer. Infrared light penetrates through both smog and silicon, making it possible for the imager to see the letters in these demonstrations. This would be useful for applications such as helping autonomous cars see in bad weather and inspecting silicon chips for defects.