SWIR imaging enables precise, long-range sensing for applications such as LiDAR, which require high intensity illumination at eye-safe SWIR wavelengths. However, conventional InGaAs-based sensors rely on costly manufacturing processes, including epitaxial growth and flip-chip bonding, which significantly increase production costs. Colloidal quantum dots (QDs) offer an alternative pathway toward scalable and cost-effective infrared sensors, as they are compatible with low-cost solution processing and large area deposition. Among infrared QDs, lead chalcogenide QDs exhibit large exciton Bohr radii, enabling facile quantum confinement-based bandgap tuning and thus wavelength selective absorption across the NIR–SWIR region. In particular, PbSe is known to be favorable for charge transport due to its relatively high dielectric constant.

Despite these advantages, lead chalcogenide QDs face severe stability challenges. As larger QD sizes are required for SWIR absorption, exposure of the oxidation prone (100) facet increases, and this facet dependent instability is especially pronounced in PbSe, leading to rapid surface degradation under ambient conditions. To address this issue, we focus on alloyed PbSe_xS_1-x QDs that can retain PbSe-like transport characteristics while improving ambient stability. Although the potential of ternary PbSe_xS_1-x QDs has been suggested in prior studies, systematic comparisons of band structure and transport related trends under identical optical conditions remain limited in the SWIR regime, where compositional changes inevitably shift the absorption wavelength. To mitigate this confounding factor, we designed and synthesized composition controlled PbSe_xS_1-x QDs while maintaining SWIR absorption around ~1400 nm, enabling evaluation of composition dependent transport trends under matched wavelength conditions. However, in OA-capped PbSe_xS_1-x QD systems, ambient stability remained limited and deteriorated with increasing Se content, indicating that alloying alone is insufficient and that stronger surface passivation and defect control strategies are required.

Motivated by prior PbSe QD literature reporting that cation exchange strategies can improve ambient robustness through defect reduction and strengthened surface passivation, we propose a cation exchange-based route to synthesize PbSe_xS_1-x QDs from metal chalcogenide precursor nanocrystals. The formation of the precursors and their subsequent conversion to PbSe_xS_1-x QDs were confirmed by well-matched XRD patterns and TEM analysis, which verified uniform conversion and the formation of highly monodisperse alloyed QDs. Importantly, the absorption spectra exhibited minimal change even after one month of storage under ambient conditions, suggesting a substantially improved resistance to oxidation induced spectral drift. This enhanced stability is attributed to defect reduction via recrystallization during cation exchange and to deactivation of surface trap sites. Overall, these results demonstrate that cation exchange derived PbSe_xS_1-x QDs provide a promising pathway for robust, solution-processed SWIR materials, and they establish a foundation for systematically elucidating the relationships among composition, surface chemistry, and charge transport under matched optical conditions.