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HgTe nanocrystals (NCs) possess advantages including tunable infrared absorption spectra, solution processability, and low fabrication costs, offering new avenues for the advancement of next‐generation infrared detectors. In spite of great synthetic advances, it remains essential to achieve customized synthesis of HgTe NCs in terms of industrial applications. Herein, by taking advantage of a high critical nucleation concentration of HgTe NCs, a continuous‐dropwise (CD) synthetic approach that features the addition of the anion precursors in a feasible drop‐by‐drop fashion is demonstrated. The slow reaction dynamics enable size‐customized synthesis of HgTe NCs with sharp band tails and wide absorption range fully covering the short‐ and mid‐infrared regions. More importantly, the intrinsic advantages of CD process ensure high‐uniformity and scale‐up synthesis from batch to batch without compromising the excitonic features. The resultant HgTe nanocrystal photodetectors show a high room‐temperature detectivity of 8.1 × 1011 Jones at 1.7 µm cutoff absorption edge. This CD approach verifies a robust method for controlled synthesis of HgTe NCs and might have important implications for scale‐up synthesis of other nanocrystal materials. [ABSTRACT FROM AUTHOR]

Colloidal quantum dots (CQDs) have attracted considerable attention owing to their potential applications in low-cost and high-performance optoelectronic devices. Achieving electronic-grade CQD materials requires precise control over their semiconducting properties via surface management. Herein, we developed a new surface modification strategy that allows for enhanced control over both the type and the amount of ligands by decoupling colloidal-stabilization and property-engineering ligands. This enables the fine control of the electronic properties of CQD materials. Using PbS CQDs, we showed improved passivation and suppressed band tail states. The resultant solar cells exhibited a higher power conversion efficiency of 13.3% compared to the 10.4% efficiency of the control device, and photodetectors showed a detectivity (D*) of 1.8 × 1012 Jones, which is a more than four-fold improvement in comparison to the control devices. Moreover, the versatility of this approach was evaluated in other CQD systems, including emissive CdSe/ZnCdSe/ZnSe core/shell and infrared HgTe CQDs. The high photoluminescence quantum yield of CdSe/ZnCdSe/ZnSe core/shell CQDs was well preserved in polar solvents following a solution ligand exchange process, and tunable doping of HgTe CQDs was achieved. Overall, this ligand-customization approach verifies the significance of fine control of ligands towards the development of electronic-grade CQD materials, which might have implications for other QD materials. [ABSTRACT FROM AUTHOR]

Lead sulfide (PbS) colloidal quantum dots (CQDs) are promising candidates for infrared photodetectors (PDs). However, solution-processed PbS CQDs with spectra ranging up to the mid-infrared range are completely absent because long-chain organic ligands capped on large size CQDs provide insufficient steric hindrance to separate the adjacent particles for dispersion in solvents, limiting their application in infrared PDs. Herein we report a strategy that addresses the extension of the response spectra of PbS CQDs by incorporating PbNO2 impurities. This is achieved by photo-carrier transition from the valence band (VB) of PbS CQDs to the unoccupied in-gap states (IGSs) near the conduction band. The device exhibits an obvious response with responsivity of 0.11 A W−1 and a detectivity of 5.38 × 108 Jones under the illumination of 3000 nm light rays at room temperature. Once the temperature decreased to 78 K, the device exhibited a response with a responsivity of 0.03 A W−1 and a detectivity of 3.77 × 108 Jones. The X-ray photoelectron spectroscopy results indicate that these IGSs are formed by using potassium nitrite (KNO2) to remove the oleate ligands and induce oxidation impurities on the CQD surface. Additionally, detailed characterization is carried out to investigate the mechanism of the infrared response of PbS CQDs. We are optimistic that this strategy could provide an alternative avenue toward the use of CQDs in optoelectronic devices with a broad response range. [ABSTRACT FROM AUTHOR]