Preparation method of chlorine-doped PbS colloidal quantum dot film

Abstract

The invention discloses a preparation method of a chlorine-doped PbS colloidal quantum dot film, and relates to the technical field of PbS colloidal quantum dot film doping, in particular to a Cl-doped colloidal quantum dot. The chlorine-doped PbS colloidal quantum dot film is formed by doping 1 * 10 <-3 > M Cl in PbS colloidal quantum dots. The preparation method comprises the steps of preparation of PbS colloidal quantum dot powder, preparation of a PbS colloidal quantum dot film, preparation of an HCl / ethanol solution and doping. According to the solution method doping, expensive equipment of doping technologies such as ion implantation and thermal diffusion does not need to be used, the experiment cost is greatly reduced, and commercialized application becomes possible.

Description

Technical Field

[0001] This invention relates to the field of PbS colloidal quantum dot thin film doping technology, specifically to a Cl-doped colloidal quantum dot. Background Technology

[0002] PbS colloidal quantum dot materials exhibit excellent infrared photosensitivity due to the tunable band gap in the near-infrared to mid-infrared spectral region, allowing their absorption to be adjusted within the range of 800~4000 nm, making them ideal photoelectric detection materials.

[0003] PbS colloidal quantum dots (PbS CQDs) and their nanocrystals offer a wide range of tunable band gaps, high absorption coefficients, and large Bohr exciton radii, exhibiting unique potential in infrared and optoelectronic applications. Due to their Pb-rich surface, PbS CQDs typically exhibit n-type conductivity. New material combinations to construct pn junctions can effectively improve carrier transport efficiency. Doping is an effective method to improve carrier transport efficiency and directionally control the conductivity type of PbS CQD devices. Common doping strategies include thermal diffusion and ion implantation, but these methods are complex, require expensive equipment, and are unsuitable for large-area PbS CQD devices and flexible device fabrication due to high costs, hindering mass production. Therefore, achieving mass production, low-cost manufacturing, and flexible detector fabrication is crucial for the practical and commercial application of PbS CQDs. Summary of the Invention

[0004] The purpose of this invention is to provide a low-cost PbS CQDs thin film doping technology that can precisely control the doping concentration. The doping is performed using a chemical solution method, which is simple and efficient.

[0005] A chlorine-doped PbS colloidal quantum dot film, characterized in that the PbS colloidal quantum dots are doped with 1×10⁻⁶ PbS. -3 M Cl.

[0006] A method for preparing chlorine-doped PbS colloidal quantum dot thin films, characterized by the following steps: S1, using PbO as lead precursor and S powder as sulfur precursor, synthesizes PbS CQDs solution by hot injection method, and then obtains PbS CQDs powder after ligand exchange and vacuum drying. S2, Weigh out PbS CQDs powder and dissolve it in a mixed solution of DMF and BTA; S3, PbS CQDs thin films were obtained by spin coating; S4, dilute the HCl solution with ethanol to a concentration of 1×10⁻⁶. -3 HCl and ethanol solutions of molar concentration; S5, PbS CQDs film is doped by immersing it in a solution of HCl and ethanol for 15-60s; S6, after doping is completed, the film is cleaned and annealed to obtain Cl-doped PbS CQDs thin film.

[0007] In ligand exchange engineering, iodides and bromides can passivate the lead-rich (111) facet well, while chlorides are more conducive to the passivation of the (100) facet. Therefore, based on the lead iodide / lead bromide mixed ligand exchange, HCl was used as Cl dopant to dop PbS CQDs thin films.

[0008] This invention employs a solution method to dope PbS CQDs thin films, achieving mass production and low-cost processing of PbS CQDs thin film doping under precise control of doping concentration and doping time, thus making the fabrication of doped flexible detectors possible.

[0009] The solution-based doping method of this invention does not require expensive equipment for doping techniques such as ion implantation and thermal diffusion, greatly reducing experimental costs and making commercial applications possible. Attached Figure Description

[0010] Figure 1 The image shows the TEM image of undoped lead sulfide quantum dots.

[0011] Figure 2 The graphs are infrared absorption curves of the thin films in Example 1 and Comparative Example 1. The vertical axis represents the absorption intensity, and the horizontal axis represents the absorption wavelength.

[0012] Figure 3 The image shown is the AFM image of the thin film in Example 1.

[0013] Figure 4 The XRD spectra of Example 1 and Comparative Example 1 are shown, where the vertical axis represents the diffraction intensity and the horizontal axis represents the diffraction angle 2θ.

[0014] Figure 5 The imaginary part of the dielectric constant of the elliptically polarized spectrum of undoped lead sulfide quantum dots in Comparative Example 1. ε 2 Wajitsube ε 1 The figure shows that the vertical axis is... ε 1 and ε 2 Values, with the horizontal axis representing wavelength.

[0015] Figure 6 The imaginary part of the dielectric constant of the quantum elliptically polarized spectrum of Cl-doped lead sulfide in Example 1. ε 2 Wajitsube ε 1The figure shows that the vertical axis is... ε 1 and ε 2 The horizontal axis represents the wavelength.

[0016] Figure 7 The diagram shows the parameters of the Lorentz oscillator model for Example 1 and Comparative Example 1. Detailed Implementation

[0017] Example 1: Preparation of 1×10 -3 The preparation steps for MCl-doped PbS CQDs thin films are as follows: S1, using PbO as lead precursor and S powder as sulfur precursor, synthesized a PbS CQDs solution with uniform size and good dispersibility by hot injection method, and then obtained PbS CQDs powder after ligand exchange and vacuum drying. S2, Weigh 0.1185g of PbS CQDs powder and dissolve it in 395μL of a mixed solution with a volume ratio of DMF:BTA=2:1 to prepare a solution with a concentration of 300mg / mL; S3, a PbS CQDs film with good reflectivity and uniform thickness was prepared by spin coating process at 2500r / 30s.

[0018] S4, take 333 μL of analytical grade HCl reagent and add it to a beaker containing 40 mL of anhydrous ethanol to prepare a 0.1 M HCl / ethanol solution. Then, take 400 μL of the 0.1 M HCl / ethanol solution and dilute it in 40 mL of anhydrous ethanol to obtain 1 × 10⁻⁶ HCl / ethanol solution. -3 M's HCl / ethanol dopant; S5, Use tweezers to pick up the PbS film and immerse it in 1×10⁻⁶ molten metal. -3 After 15s in the HCl / ethanol solution of M, the excess dopant was removed by spin-coating at 2500r / 10s. Then, 120μL of anhydrous ethanol was taken with a pipette and cleaned twice with the same spin-coating process. S6. The cleaned film is annealed on a 45°C heating table for 3 minutes to obtain a 1×10 film with good reflectivity. - 3 M HCl / ethanol doped PbS thin film.

[0019] Comparative Example 1: Preparation method of undoped PbS CQDs thin film, the preparation steps are as follows: S1, using PbO as lead precursor and S powder as sulfur precursor, synthesized a PbS CQDs solution with uniform size and good dispersibility by hot injection method, and then obtained PbS CQDs powder after ligand exchange and vacuum drying. S2, Weigh 0.1138g of PbS CQDs powder, dissolve it in 379μL of DMF / BTA (2:1) mixed solution, and prepare a solution with a concentration of 300mg / mL; S3, using a 2500r / 30s spin coating process, yielded a PbS CQDs film with good reflectivity and uniform thickness.

[0020] S4. The film is annealed on a 45°C heating stage for 3 minutes to obtain an undoped PbS film.

[0021] Compared with traditional doping techniques such as thermal diffusion and ion implantation, solution doping exhibits significant advantages. Thermal diffusion and ion implantation are typically complex processes with expensive equipment, and it is difficult to achieve uniform and precise doping of quantum dot films at low temperatures. Solution doping, on the other hand, not only significantly reduces process costs but also allows for precise control of the doping concentration and distribution of PbS CQDs films by accurately adjusting the dopant concentration and reaction time. This efficient and controllable doping strategy provides a feasible technical path for developing high-performance flexible photodetectors and has broad application prospects in fields such as infrared sensing and wearable optoelectronic devices.

[0022] The prepared Cl-doped PbS CQDs thin films were tested, and the results are as follows: like Figure 2 As shown, 1×10 can be clearly observed. -3 The first exciton peak of the HCl-doped quantum dots was 1914 nm, showing a slight redshift of 6 nm compared to the absorption curve of the undoped PbS CQDs film. This confirms that the HCl / ethanol dopant successfully introduced and fine-tuned the band structure of the quantum dots. This effective modulation of absorption characteristics provides a material basis for optimizing the response wavelength of optoelectronic devices, such as infrared detectors.

[0023] like Figure 3 As shown, 1×10 -3 The MCl-doped PbSCQDs film has a roughness of 28.5 nm and exhibits good reflective properties.

[0024] like Figure 4 As shown, four diffraction peaks can be clearly observed, which accurately match the rock salt mineral structure of PbS (PDF#65-0132) crystals, proving the successful synthesis of undoped PbS CQDs; XRD analysis in the figure confirms that 1×10⁻³ M Cl doping successfully introduced the PbSCQDs system. The spectrum shows a fifth diffraction peak that precisely matches the PbCl₂ (PDF# 78-2050) standard card. The diffraction pattern of the doped film exhibits sharp peaks and flat baselines. In particular, the newly added PbCl₂ diffraction peak has significant intensity and a high signal-to-noise ratio, indicating that the film possesses excellent long-range order and crystal integrity. By comparing the XRD patterns before and after doping, a fifth diffraction peak is clearly identifiable at a doping concentration of 1×10⁻³ M, and its position perfectly matches that of the orthorhombic PbCl₂ (PDF# 78-2050). This diffraction peak is sharp and has a clear signal, not a broad, diffuse peak. Both the phase and morphology dimensions demonstrate that the Cl doping was not only successful but also induced the formation of a well-crystallized new phase, resulting in excellent overall crystallinity of the doped PbSCQDs film.

[0025] like Figure 6 As shown, after elliptic polarization spectroscopy testing, a result of 1×10⁻⁶ was obtained. -3 Imaginary part of dielectric constant of MCl-doped PbS CQDs thin films ε 2 Wajitsube ε 1 Ellipsometry analysis revealed that 1×10⁻³ MCl doping significantly modulated the optical constants of the PbSCQDs thin film. Compared to the undoped PbS CQDs thin film, the real part of the dielectric function of the 1×10⁻³ MCl-doped sample ( ε 1 (correlated refractive index) and imaginary part ( ε2 Both the dielectric function and the correlated absorption show a systematic improvement, a change consistent with the self-consistency verification of the Kramers-Kronig relationship. Fitting based on the Lorentz oscillator model reveals that this enhancement in dielectric function directly corresponds to a deterministic narrowing of the material's intrinsic bandgap (En) from 0.64369 eV to 0.64 eV. The reduction in bandgap means that electrons can be excited more efficiently at the same photon energy, which directly translates into enhanced optical response and light absorption efficiency in the near-infrared band, providing a key material advantage for fabricating high-performance infrared photonic devices.

[0026] like Figure 7As shown, the modulation effect of 1×10⁻³ MgCl doping on the optical properties of PbS is directly reflected in the oscillator strength. The oscillator strength of the doped sample jumps from 0.22924 eV² to 0.55539 eV², a significant change that reveals an optimization of the material's internal optical properties from a quantum mechanical perspective, with a substantial enhancement in the oscillator strength due to electron transitions. This is because the impurity energy levels or band structure modified by 1×10⁻³ MgCl doping allow more electrons per unit volume to effectively participate in the light absorption process. The direct result is an overall improvement in the material's optical constants (such as the absorption coefficient), laying a crucial material foundation for the development of high-sensitivity photodetectors.

[0027] Doping with 1×10⁻³ MCl significantly enhanced the optical oscillator intensity of PbSCQDs, increasing it by as much as 142% ((0.55539- 0.22924) / 0.22924 ≈ 142%), while precisely narrowing its optical bandgap by 3.7 meV. This synergistic optimization of optical constants demonstrates the decisive advantage of this doping strategy in fabricating high-performance, strong-absorption, wavelength-tunable infrared optoelectronic devices.

Claims

1. A film of chlorine-doped PbS colloidal quantum dots, characterized in that Doping of 1 x 10 -3 M Cl.

2. The method for preparing chlorine-doped PbS colloidal quantum dot thin films as described in claim 1, characterized in that... The preparation method comprises the following steps: S1, synthesizing a PbS CQDs solution by a hot injection method with PbO as a lead precursor and S powder as a sulfur precursor, and performing ligand exchange and vacuum drying to obtain a PbS CQDs powder; S2, weighing the PbS CQDs powder and dissolving the PbS CQDs powder in a DMF and BTA mixed solution; S3, obtaining a PbS CQDs film by using a spin coating method; S4, dilute the HCl solution with ethanol to 1 x 10 -3 molar concentration of HCl with ethanol solution; S5, doping the PbS CQDs film by immersing the PbS CQDs film in a HCl and ethanol solution for 15-60s; S6, cleaning and annealing after the doping is completed, and obtaining a Cl-doped PbS CQDs film.

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