High-Performance Quantum Dot Near-Infrared Upconversion Devices Based on the Hole-Only Injection Mechanidsm

Colloidal quantum dot (CQD) near-infrared (NIR) upconversion devices (UCDs) can directly convert low-energy NIR light into higher energy visible light without the need for additional integrated circuits, which is advantageous for NIR sensing and imaging. However, the state-of-the-art CQD NIR upconverters still face challenges, including high turn-on voltage (V on), low photon-to-photon (p-p) upconversion efficiency, and low current on/off ratio, primarily due to inherent limitations in the device structure and operating mechanisms. In this work, we developed a CQD NIR UCD based on a hole-only injection mechanism. Our device effectively suppresses electron injection from the cathode without hindering hole injection from the anode. As a result, the dark current of the device is reduced to a low level, which is favorable for the balance of photogenerated carriers and injected charges. Furthermore, we employed a liquid-phase ligand-exchange process to treat the PbS CQD photosensitive layer (PSL), which enhances the uniformity and charge transport capability of PSL, further optimizing the utilization of photogenerated carriers. We achieved a record high current on/off ratio exceeding 3.5 x 105 for the CQD NIR UCD. Additionally, the device exhibits a high p-p upconversion efficiency of 12.8% and a low V on of 1.8 V.