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

Abstract

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 > 10 10 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.devices are prepared via a drop and dry procedure with no high temperature steps or aggressive ligand exchange procedures required, making them ideal candidates for integration onto delicate read out electronics, as is used for imaging devices.

Field-Effect Transistor and Photo-Transistor of Narrow-Band-Gap Nanocrystal Arrays Using Ionic Glasses

“…Narrow band gap nanocrystals [1][2][3] are currently generating a strong interest for the design of high performance and low cost infrared sensors in the short-wave (SWIR: up to 1.7 µm) and mid-wave infrared (MWIR : 3-5 µm). 4,5 Recent developments include high detectivity photodiodes, 6 multicolor devices, [7][8][9] demonstration of focal plane arrays 10 and detectors with enhanced light matter coupling.…”

Bringing Colloidal Quantum Dots to Detector Technologies

“…Lead sulfide (PbS) CQDs have an absorption that is tunable from 1–3 μm (Fig. ) , and their photoconductors, 6 phototransistors, 7 and photodiodes 8 have demonstrated sensing capabilities from the visible to short‐wave infrared (SWIR) spectral regions. Despite the progress with PbS CQDs, their quantum efficiency—that is, the percentage of light detected and converted to measurable signal—is quite low, with values of 10–15 percent compared to 65–80 percent for epitaxial InGaAs (Fig.…”

“…Unless otherwise specified, the data presented are for a detector operating at room temperature. Green circle = HgTe CQD photodiodes; 12 , 13 green triangle = phototransistors; 11 green square = photoconductors; 10 blue circle = PbS CQD photodiodes; 8 blue triangle = phototransistors; 7 blue square = photoconductors; 6 red circle = HgCdTe photodiodes; 14 , 15 orange circle = InGaAs photodiodes; 16 , 17 and yellow circle = InSb photodiodes 18…”

Quantum Dot Light‐Emitting Transistors—Powerful Research Tools and Their Future Applications

“…Here, PbS is a particular attractive candidate due to its narrow bandgap and the potential for multiple exciton generation . Similarly, CQDs allow for the precise tuning of the photodetector sensitivity to a desired photon energy . It was furthermore shown that bandwidth limitations due to their modest carrier mobilities could be overcome when using CQCs in synergy with 2D materials, such as graphene or transition metal dichalcogenides …”