Publication date: 15th December 2025
Extended shortwave infrared (eSWIR) photodetectors based on solution-processable semiconductors are attracting growing interest for applications including ranging, night vision, and gas sensing. Colloidal quantum dots (CQDs) are particularly appealing owing to their solution processability and facile bandgap tunability from the visible to the mid-infrared. However, most eSWIR-absorbing CQDs are based on toxic elements such as Hg and Pb, which are incompatible with RoHS directives. Moreover, the frequent need for cryogenic cooling and the intrinsically slow temporal response of many CQD devices significantly hinder their commercial deployment.
Here, we demonstrated an eSWIR photodetector employing silver telluride (Ag2Te) CQDs as a RoHS-compliant active material. Ag2Te CQDs feature a small effective mass, which is beneficial for achieving high carrier mobility and rapid response. To accommodate the complex monoclinic structure of Ag2Te, we rationally selected thiol ligands that enable efficient solid-state ligand exchange, thereby lowering trap density and enhancing carrier transport in the CQD films. These optimized CQD solids are integrated into a vertical p–n photodiode with a well-aligned energy-level landscape that promotes efficient charge extraction. The resulting device operates at room temperature and is free of regulated toxic elements, while exhibiting ultrafast temporal characteristics. Our best-performing photodetector achieved a fall time of 72 ns at 298 K, which, to our knowledge, represents the fastest response reported for CQD-based eSWIR photodetectors, including those based on toxic CQDs.
Conference participation is supported by a National Research Foundation of Korea grant funded by the Korean government (MSIT) (No. RS-2025-24523595).
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