The phase-transfer ligand exchange of PbS quantum dots (QDs) has substantially simplified device fabrication giving hope for future industrial exploitation. However, this technique when applied to QDs of large size (>4 nm) gives rise to inks with poor colloidal stability, thus hindering the development of QDs photodetectors in short-wavelength infrared range. Here, it is demonstrated that methylammonium lead iodide ligands can provide sufficient passivation of PbS QDs of size up to 6.7 nm, enabling inks with a minimum of ten-week shelf-life time, as proven by optical absorption and solution-small angle X-ray scattering. Furthermore, the maximum linear electron mobility of 4.7 × 10-2 cm2 V-1 s-1 is measured in field-effect transistors fabricated with fresh inks, while transistors fabricated with the same solution after ten-week storage retain 74% of the average starting electron mobility, demonstrating the outstanding quality both of the fresh and aged inks. Finally, photodetectors fabricated via blade-coating exhibit 76% external quantum efficiency at 1300 nm and 1.8 × 1012 Jones specific detectivity, values comparable with devices fabricated using ink with lower stability and wasteful methods such as spin-coating.
Keywords: MAPbI3; lead sulfide; phase-transfer ligand exchange; quantum dot photodetector; short-wavelength infrared; stability.
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