Chemical Reactivity‐Controlled Synthesis of Silver Chalcogenide Colloidal Quantum Dots for Efficient Shortwave Infrared Photodetectors

Abstract Eco‐friendly Ag 2 Te colloidal quantum dots (CQDs) have emerged as promising candidates for shortwave infrared (SWIR) optoelectronic applications owing to their size‐tunable bandgaps with high optical properties. However, conventional synthesis methods relying on high temperatures and long reaction times yield low‐quality Ag 2 Te CQDs because of their low chemical stability, resulting in decomposition under synthetic conditions and, thus, a non‐uniform size distribution. Here, chemical reactivity‐controlled synthesis is presented to regulate the crystal size and bandgap of Ag 2 Te CQDs. This involves adjusting the concentration and type of ligands, as well as the precursor ratio. The rapid termination of the reaction in this method prevents Ag 2 Te CQD decomposition, yielding monodisperse CQDs with a 1.66 peak‐to‐valley ratio at the first exciton absorption peak (≈1440 nm) and enabling absorption and emission in the 1100−1600 nm range. Furthermore, polar antisolvents in the purification process cause surface ligand removal from Ag 2 Te CQDs, resulting in surface defects and CQD aggregation. To mitigate these issues by enhancing their chemical stability, core/shell‐type Ag 2 Te/Ag 2 S CQDs are synthesized. The photoluminescence (PL) intensity of Ag 2 Te/Ag 2 S CQDs significantly increased fivefold compared to Ag 2 Te core CQDs, and after purification, their size distribution remained uniform with preserved PL intensity. This is attributed to a significant reduction in surface defects. Consequently, the Ag 2 Te/Ag 2 S CQD‐based SWIR photodetector exhibits a high external quantum efficiency of 8.4% and a specific detectivity of 1.1 × 10 11 Jones at 1550 nm, with a fast response time of 38 ns.