A Path to Heavy Metal-Free Infrared Photodetection Using Silver Selenide Colloidal Quantum Dots

The deployment of infrared cameras has so far been limited to military and defense applications because of the high costs involved in high temperature epitaxy and hybridization (1). The advent of low cost colloidal quantum dot (QD) infrared detectors will help persuade device adoption in the commercial detector markets. However so far toxic heavy metal compounds like Lead and Mercury chalcogenides have dominated the QD Photodetector space (1,2). In this work we establish a route to environmentally benign Near Infrared (NIR: 0.7 - 1.4 μm) and Short Wave Infrared (SWIR: 1.4 - 3 μm) active Ag₂Se CQDs. Herein we study the dynamics of an alternate Ag₂Se synthesis with exquisite size control. We report the effects of various parameters (Synthesis Time, Injection Temperature, Growth Temperature and Precursor Ratios) and highlight the size tunable excitonic peak and room temperature photoluminescence observed in the NIR and SWIR regions. Furthermore, we demonstrate IR active devices using ligand exchanges with short chain molecules such as 3-Mercaptopropionic acid (MPA), Thiocyanate (SCN) and 1,2-Ethanedithiol (EDT). Our results demonstrate that an EDT/HCl/IPA mixture results in a room temperature responsivity ~50mA/W at 1150 nm. To the best of our knowledge, this device provided the highest responsivity at 1150 nm among Ag2Se photoconductors to date. Prior work (3) has shown tunable absorption into the MIR (3-5 μm) as well and future work will involve fabricating photodiodes using these MIR particles.<br/><br/>References:<br/>1) Pejovic, V. (n.d.). Infrared colloidal quantum dot image sensors. IEEE Xplore.<br/>2) Gréboval, C., Chu, A., Goubet, N., Livache, C., Ithurria, S., & Lhuillier, E. (2021). Mercury chalcogenide quantum dots: Material Perspective for Device Integration. Chemical Reviews, 121(7), 3627–3700. https://doi.org/10.1021/acs.chemrev.0c01120<br/>3) Scimeca, M. R., Mattu, N., Paredes, I. J., Tran, M. N., Paul, S. J., Aydil, E. S., & Sahu, A. (2021). Origin of Intraband optical transitions in Ag₂se colloidal quantum dots. The Journal of Physical Chemistry C, 125(31), 17556–17564. https://doi.org/10.1021/acs.jpcc.1c05371<b> </b>