Designs for Upconversion and Photomultiplication in Organic Shortwave Infrared Detectors

Upconversion imagers that combine photosensing and display in a compact structure are attractive since they avoid the costly and complex process of pixilation. This talk will present the designs of polymeric upconversion imagers that combine photo-sensing and display in a compact structure, to enable visualization to 1300 nm (<i>Adv. Func. Mater.</i> 2021, <b>31</b>, 210056). This shortwave infrared spectral region is particularly powerful for a variety of applications including environmental monitoring and medical diagnosis, enabling greater penetration depth and improved resolution in comparison to visible light.<br/><br/>The organic photodetectors are further improved by incorporating a new heterojunction interlayer to trigger trap-assisted photomultiplication. Previous approaches to induce photomultiplication in organic diodes have increased the photosignal but lacked control over reducing background noise. This work presents a new interlayer design based on a heterojunction bilayer that concurrently enables photomultiplication and suppresses the dark current in organic shortwave infrared detectors to improve the overall detectivity (<i>Mater. Horiz</i>. 2022, accepted). The heterojunction bilayer is consisted of a hole-transporting material copper thiocyanate and an electron-transporting material tin oxide. This combination serves to suppress the dark current and enhance the photoresponse, leading to an external quantum efficiency up to 560% and a detectivity of 3.5 x 10^9 Jones. The upconversion efficiency of the imager is doubled with 1.7 fold improvement in contrast compared to the imager without the heterojunction interlayer. The new interlayer design is generalizable to work with different organic semiconductors, making it attractive and easy to integrate with emerging organic infrared systems.