Synthesis of Monodisperse Silver Chalcogenide Quantum Dots with Elevated Precursor Reactivity for the Application in Near Infrared Photodetectors

Semiconducting nanocrystals (colloidal quantum dots, QDs) have superior optical properties and solution processibility. Silver selenide quantum dots are important nanomaterials with absorption peak extending from $\sim 880$ nm to $\sim 1200$ nm. Compared to the lead-based counterparts, Ag$_{\mathbf {2}}$ Se QDs are less developed and their application is less explored. This is in part due to the difficult control of their size and size distribution, resulting in broad absorption or even featureless absorption. We employed secondary phosphine to elevate the precursor reactivity and were able to well control the nucleation and growth. After a systematic investigation on a number of synthetic parameters, high quality Ag7/$0_{\mathbf {2}}$ Se QDs have been synthesized with tunable size and narrow size distribution, exhibiting well-defined absorption peaks. The synthesis is scalable with high yield. The application of Ag$_{\mathbf {2}}$ Se QDs has been successfully demonstrated in photodetectors with photoresponse in near infrared region ($\ge 1000$ nm).