Organic near-infrared upconversion devices: Design principles and operation mechanisms

Optical upconversion devices up-converting near-infrared (NIR) light to visible light have attracted a great deal of research interest in the past decades. Among these devices, organic upconversion devices have been presented as an alternative strategy for simplifying the fabrication process and reducing the cost. In recent years, along with the development of organic electronics, several types of organic NIR upconversion devices have been reported. However, there have been very few systematic studies of the design principles and operation mechanisms of organic NIR upconversion devices. In order to illustrate the structural design principles and operation mechanisms, organic upconversion devices based on donor/acceptor planar heterojunction (PHJ) as NIR sensitizer and inverted OLED structure as emitter are fabricated and studied. Significantly, two types of photo-generated electron and hole based organic upconversion devices are realized by ingeniously exchanging the position of the PHJ and the inverted OLED in the devices, respectively. The light emission in the former results from the recombination of photo-generated electrons with the injected holes from the anode, while that of the later from the recombination of photo-generated holes with the injected electrons from the cathode. Both types of the upconversion devices demonstrated great potentials for future pixel-less NIR imaging applications.