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

Abstract

Eco-friendly Ag₂Te 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 Ag₂Te 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 Ag₂Te 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 Ag₂Te 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 Ag₂Te CQDs, resulting in surface defects and CQD aggregation. To mitigate these issues by enhancing their chemical stability, core/shell-type Ag₂Te/Ag₂S CQDs are synthesized. The photoluminescence (PL) intensity of Ag₂Te/Ag₂S CQDs significantly increased fivefold compared to Ag₂Te 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 Ag₂Te/Ag₂S CQD-based SWIR photodetector exhibits a high external quantum efficiency of 8.4% and a specific detectivity of 1.1 × 10¹¹ Jones at 1550 nm, with a fast response time of 38 ns.