Ag₂Te Colloidal Quantum Dots for Near-Infrared-II Photodetectors

Ag2Te colloidal quantum dots (QDs) are an excellent nanomaterial for applications in the second near-infrared window (NIR-II, 1000–1700 nm). However, synthesis with narrow size distribution and high photoluminescence quantum yield (PL QY) is challenging. In this study, we systematically investigate critical synthesis parameters affecting an organic phase process. We show that high Ag/Te feed ratio leads to smaller size and higher PL QY; under 4:1 Ag/Te feed molar ratio, addition of secondary phosphine leads to narrower size distribution and excellent colloidal stability; under 6:1 Ag/Te feed molar ratio, excess 1-dodecanethiol as a strong ligand slows the nucleation and results in fewer nuclei, leading to a broad size distribution and poor optical properties; additional trioctylphosphine as a weak ligand provides better colloidal stability; and another weak ligand tributylphosphine improves QD colloidal stability, focuses size distribution, and enhances PL QY. A noninjection method maintains narrow size distribution in upscaling syntheses. After optimization, relatively large Ag2Te QDs with distinct excitonic absorption peaks (∼1050–1450 nm) and PL emission peak 1.3–1.7 μm (QY up to 6.2%) were obtained. NIR-II photodetection has been demonstrated with a responsivity of ∼1.5 mA/W at 1400 nm.