Empa researchers Roland Hany, Karen Strassel, Wei-Hsu and Michael Bauer have developed a short-wave infrared (SWIR) camera with a single component. The device is basically an OLED display with three additional layers (see graphic). IR light falls through an electrically conductive glass pane onto a dye layer in a photodetector. Therein, electrons begin to migrate, their motion being amplified by an electrical voltage. The electrical charges then migrate into the OLED layer, where they produce a green light spot. Electronic signal processing by a computer is not necessary: The incoming SWIR light is amplified in an “analogue” way and displayed directly on the screen. The colour of the emitted visible light—blue, green, yellow or red—can be adjusted by selecting the dye in the OLED.
The key to Roland Hany’s SWIR screen is special dyes, squaraines, that he and his colleagues have been investigating for a while. Their name comes from the basic structure of squaric acid. This class of dyes was first discovered in the 1960s and is characterised by deep colours and a high temperature stability. The researchers chemically modified the squaric acid so that it absorbs in the range of SWIR light. “Right now, we’re working with dyes that absorb at just under 1000 nm”, Hany says. “But we’re already working on shifting the absorption to longer wavelengths, further into the IR range. If we succeed, our sensor will be able to detect water and moisture much better than it does now.”