Researchers from the Beijing Institute of Technology (BIT) have developed an infrared-to-visible upconversion device (night goggles) that stacks a mercury telluride (HgTe) colloidal quantum dot photodetector directly underneath a dual-emissive-layer OLED. Unlike previous upconverters, which output a single color and encode the infrared signal only as brightness, this device changes both its emitted color and its luminance depending on the wavelength and intensity of the incoming infrared light - effectively giving the wearer full-color infrared vision.
The OLED unit is the key to the color-coding scheme. It uses two separate emissive layers - a red one based on Ir(piq)3 doped in CBP, and a cyan one based on FIrpic doped in CBP - with a deliberately engineered 0.82 eV hole-injection barrier between the HOMO levels of the two dopants.
Under weak infrared illumination, the small number of photogenerated holes arriving from the quantum dot detector gets trapped in the red dopant and cannot cross into the cyan layer, so the device emits red. Under stronger or shorter-wavelength infrared light, the extra holes saturate the red traps, migrate through the CBP host, overcome the barrier and reach the cyan layer as well - producing a mixed red and cyan emission at higher luminance. The full OLED stack is ITO / HATCN (5 nm) / NPB (30 nm) / TCTA (10 nm) / 8% Ir(piq)3:CBP (15 nm) / 15% FIrpic:CBP (20 nm) / CzPhPy (10 nm) / TPBi (30 nm) / LiF/Al.
