Publication date: 28th August 2024
Photodetectors in the short-wave infrared (SWIR: 1-1.7 µm) range have garnered significant attention due to the growing demand for 3D imaging and facial recognition technologies. The inherent transparency of silicon above 1 µm wavelength and the intricate integration processes of III-V materials restrict conventional technologies from effectively addressing this spectral region. In this context, it has become essential to explore alternative photodetector materials. Among the candidates for SWIR sensing, lead sulfide quantum dots (PbS QD) are very promising for integration as active material due to their strong, size-tuneable absorption at targeted infrared wavelengths. However, when exceeding a specific nanocrystal size, these QD are prone to surface oxidation and aggregation limiting their performances and integration in sensor devices. [1]
Among several strategies developed to passivate and deposit these QDs as thin layer, one of the most promising is to combine them with halogenated perovskites. [2] Inspired by this approach, we investigated and optimized all the steps, from the synthesis of the PbS QD to their integration in the perovskite matrix. An efficient solution exchange of long-chain ligands on the surface of QDs with perovskite precursors is performed and confirmed through FTIR, NMR, and XPS measurements. The relevance of this perovskite shell around the QD is explored optically (PL, Abs spectroscopy) revealing significantly improved luminescence stability under ambient atmosphere for more than 2 months in thin films. To facilitate thin film fabrication, we developed a stable ink based on the ligand-exchanged QDs and perovskite precursors. The optimized inks are stable for days in suitable solvents for film deposition. This new approach enables one-step thin film deposition compared to the multi-step approach required to manage organic ligand exchange. The solution-processed perovskite-exchanged PbS QD strategy was devised to produce reproducible and homogenous thin films absorbing in the desired NIR spectral region which are further integrated into devices. This study covers fundamental understanding of the exchanged quantum dot system and explores its photodetector performance.
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