Photomultiplication Enables Efficient NIR Quantum Dot Organic Upconversion Devices

Infrared (IR)-to-visible upconversion devices integrate IR photodetection and visible light emission into a single device. Such devices selectively emit visible photons from regions irradiated by IR photons, enabling simplified and low-cost pixel-less imaging. Recently, the integration of colloidal quantum dots (CQDs)-based IR photodetection units with organic semiconductor–based visible emitters has attracted significant attention. These quantum dot organic upconversion devices (QOUDs) benefit from solution processability and tunable infrared absorption. However, their performance has so far been limited by inefficient coupling between the absorption and emission units as well as the relatively low efficiency of the photodetection layer. In this work, a high-performance QOUD is demonstrated by incorporating an improved interconnection layer (ICL) and introducing a photomultiplication (PM) mechanism. A photon-to-photon efficiency of 23% is achieved, which is 143 times higher than that of a gain-free device. The low-barrier interconnection is achieved by using an ultrathin MoO3 ICL, which provides favorable energy level alignment. The turn-on voltage of the QOUD under infrared illumination was greatly reduced to 1.9 V. In addition, the PM effect originates from the absorption layer, where defect states trap photogenerated carriers and induce image-charge-assisted carrier injection from the electrode. The QOUD is further demonstrated for pixel-less IR imaging, combining low turn-on voltage with high PM and showing strong potential for practical infrared imaging applications.