Pushing PbS/Metal‐Halide‐Perovskite Core/Epitaxial‐Ligand‐Shell Nanocrystal Photodetectors beyond 3 µm Wavelength

PbS nanocrystals have been proven to be highly suitable for photodetector fabrication by facile solution processing, and have been successfully tested as photosensitive material in imaging devices. So far, their spectral response has been blue‐shifted with respect to that of commercial bulk PbS detectors, due to quantum confinement in nanostructures smaller than the exciton Bohr radius. Here, a PbS nanocrystal synthesis approach is introduced, allowing to surpass this limit, and thus to push the cut‐off wavelength to the value of the bulk material. To avoid self‐absorbance from ligands within the spectral range of the photoconducting signal, an all inorganic metal‐halide‐perovskite is applied to form a semiconducting ligand shell. The photoconductors, which are provided from a single drop, do not only show a record in long wavelength operation for PbS nanocrystal detectors but also a room temperature detectivity > 1010 Jones, which is on par with that of commercial bulk PbS detectors. Combining these properties might find application in future low‐cost infrared imagers, which are currently still elusive due to their high prices. Presented is a synthesis for lead sulfide colloidal nanocrystals with variable sizes from 6 nm to well beyond the excitonic Bohr radius. Ligand exchange with zero dimensional perovskite ligands that form an epitaxial shell results in a semiconducting ink that is used to cast a photoconductive film sensitive to a mid‐infrared light with a wavelength beyond 3 µm.