An electrostatic adsorption and covalent bonding synergistic induced infrared quantum dot film assembly process

Abstract

This application relates to an infrared quantum dot thin film assembly process synergistically induced by electrostatic adsorption and covalent bonding. The process includes: modifying the surface charge of a conductive substrate to make the substrate surface positively charged; preparing an infrared quantum dot dispersion with a negatively charged surface; rapidly and densely adsorbing infrared quantum dots onto the substrate surface under electrostatic attraction to form a monolayer or quasi-monolayer quantum dot adsorption structure; subsequently, performing in-situ ligand replacement on the adsorption layer using a short-chain bifunctional crosslinking agent to form a stable covalent bonding network between the quantum dots and the substrate and adjacent quantum dots; and constructing an infrared quantum dot thin film of the desired thickness layer by layer through multiple cycles of repeated adsorption and bonding steps. This application utilizes electrostatic adsorption to achieve rapid and uniform assembly of quantum dots, and effectively reduces the ligand insulation effect and enhances the electrical coupling between quantum dots through covalent bonding to achieve layer-by-layer stress release and avoid thick film cracking.

Description

Technical Field

[0001] This application relates to the field of infrared optoelectronic functional thin film preparation, and in particular to an infrared quantum dot thin film assembly process synergistically induced by electrostatic adsorption and covalent bonding. Background Technology

[0002] Infrared colloidal quantum dots (such as HgTe and PbS) have great potential in infrared imaging, photovoltaic devices and other fields due to their solution processing characteristics and tunable band gap. In order to achieve high photoelectric conversion efficiency, it is usually necessary to prepare dense quantum dot films with a thickness of 300 nm to 1 μm.

[0003] Currently, the fabrication of infrared quantum dot films mainly relies on the "layer-by-layer spin coating with solid-state ligand exchange" technique. However, existing technologies have the following significant drawbacks: 1. Volume shrinkage leading to cracks: Initially synthesized quantum dots are usually coated with long-chain organic ligands (such as oleic acid and oleylamine). When ligand exchange with short-chain ligands such as EDT and TBAI occurs after film formation, the film volume shrinks dramatically, with a shrinkage rate of 30%-50%. This shrinkage generates huge tensile stress inside the film, leading to a large number of microcracks on the film surface, severely interrupting the carrier transport path and increasing device noise; 2. Poor interfacial adhesion: Traditional physical spin coating mainly relies on van der Waals forces for adhesion. There is a lack of strong interaction between the quantum dot layer and the substrate. In subsequent multilayer stacking or photolithography processes, the film is prone to detachment or delamination. 3. Low material utilization: In the spin coating process, more than 90% of the quantum dot solution is wasted. For expensive infrared quantum dot materials, especially expensive mercury-containing materials, the cost is extremely high and it is not only environmentally unfriendly. 4. Limitations of simple electrostatic assembly: Although layer-by-layer self-assembly (LbL) technology based on electrostatic attraction exists, traditional LbL usually introduces an insulating polymer electrolyte as a connecting layer, which hinders the transfer of charge between quantum dots, resulting in poor device performance and failing to meet the high mobility requirements of infrared detectors.

[0004] Therefore, there is an urgent need for a new assembly process that can achieve rapid and dense pre-deposition using electrostatic adsorption, and can also eliminate the insulating layer and lock the morphology through covalent bonding, thereby obtaining high-quality infrared quantum dot films with no cracks and high conductivity. Summary of the Invention

[0005] To address the technical problems of existing infrared quantum dot films, this application provides an infrared quantum dot film assembly process synergistically induced by electrostatic adsorption and covalent bonding.

[0006] The infrared quantum dot thin film assembly process synergistically induced by electrostatic adsorption and covalent bonding provided in this application adopts the following technical solution: An infrared quantum dot thin film assembly process synergistically induced by electrostatic adsorption and covalent bonding includes the following steps: Step 1: Charge modification of the substrate The cleaned conductive substrate is surface-modified to acquire a positive charge. Method A is physical adsorption: The substrate is immersed in a low-concentration polyelectrolyte solution for 1-5 minutes, washed with water and dried. The polyelectrolyte solution is polydiallyldimethylammonium chloride (PDDA) with a concentration of 0.1-1 mg / mL. Method B is chemical grafting: The substrate is silanized using aminosilanes, allowing positively charged amino groups to be grafted onto the surface. Step 2: Pretreatment of Quantum Dot Ink An infrared quantum dot dispersion with a negatively charged surface was prepared. The infrared quantum dots were selected from either HgTe or PbS. If the synthesized quantum dots are oil-soluble, liquid-phase ligand exchange must be performed first to transfer them into a polar solvent, and it must be ensured that their Zeta potential is negative. Step 3: Electrostatic Induction Adsorption. The positively charged substrate is immersed in the negatively charged quantum dot ink. Under the action of strong electrostatic attraction, the quantum dots will quickly migrate to the substrate and fill the gaps. The electrostatic repulsion restricts the aggregation between quantum dots. The adsorption layer shows a highly uniform monolayer or quasi-monolayer arrangement. The time is 10 seconds to 60 seconds. Step 4: Covalent bonding and ligand substitution. The substrate with adsorbed quantum dots is immersed in a solution containing a short-chain bifunctional crosslinking agent. The crosslinking agent can be selected from 1,2-ethanedithiol (EDT), 1,3-benzenedithiol (BDT), or ammonium thiocyanate (NH4SCN). Solvents selected: acetonitrile, ethanol Reaction mechanism: One end of the short-chain crosslinking agent forms a strong covalent bond (such as Hg-S bond) with the metal site (Hg or Pb) on the surface of the quantum dot, replacing the weaker electrostatically stable ligand in step two; the other end of the crosslinking agent can bond with the substrate or adjacent quantum dots. The reaction process transforms the "soft" electrostatic adsorption into a "hard" covalent network. At the same time, the extremely short ligand length (<0.5nm) ensures the quantum tunneling effect between quantum dots and eliminates the insulating layer. Step 5: Repeat steps 3 and 4 in multiple cycles until the film reaches the required thickness. Each layer undergoes an "adsorption-locking" process, and the stress is released layer by layer, avoiding cracking caused by the accumulation of stress in the thick film.

[0007] By employing the above technical solution, rapid, controllable, and high-quality assembly of infrared quantum dot films is achieved without relying on complex vacuum processes or high-temperature treatments. First, by positively charging the substrate and negatively charging the quantum dot ink, strong electrostatic attraction drives the quantum dots to migrate uniformly and densely adsorb onto the substrate surface in a very short time. Simultaneously, electrostatic repulsion effectively suppresses random aggregation between quantum dots, resulting in a monolayer or quasi-monolayer quantum dot adsorption structure with uniform distribution and complete coverage. Second, after electrostatic adsorption, a short-chain bifunctional crosslinking agent is introduced for in-situ ligand replacement, forming a bond between the quantum dots and the substrate, as well as between adjacent quantum dots. A stable covalently bonded network is formed, transforming the originally environmentally susceptible physical adsorption structure into a chemically more stable solidified structure, significantly improving the mechanical stability and environmental durability of the film. At the same time, short-chain ligands effectively shorten the spacing between quantum dots, significantly reducing the insulation barrier introduced by organic ligands and enhancing the electron or hole tunneling ability between quantum dots, thereby improving the overall conductivity and carrier transport efficiency of the film. Furthermore, through a multi-cycle repeated "electrostatic adsorption-covalent locking" layer-by-layer construction method, the film thickness can be precisely controlled, and the internal stress of each layer is gradually released during the formation process, avoiding problems such as cracking and warping that are prone to occur in traditional one-time thick film deposition.

[0008] Optionally, the conductive substrate is any one of indium tin oxide (ITO) substrate, fluorine-doped tin oxide (FTO) substrate, or doped silicon substrate.

[0009] By adopting the above technical solutions and selecting indium tin oxide, fluorine-doped tin oxide, or doped silicon as the conductive substrate, a good conductive channel and stable mechanical support can be provided for the quantum dot film. At the same time, its surface is easy to be charged and modified, which is conducive to forming a stable and uniform electrostatic adsorption interface, thereby improving the film formation consistency, electrical performance and device operation stability of the infrared quantum dot film.

[0010] Optionally, the charge modification of the substrate in step one is achieved by physical adsorption, specifically by immersing the substrate in a polyelectrolyte solution, so that the positively charged polyelectrolyte is adsorbed onto the substrate surface.

[0011] By adopting the above technical solution, the substrate can be charged by physical adsorption of polyelectrolytes. A stable positive charge layer can be introduced into the substrate surface rapidly and uniformly under mild conditions. The process is simple and reproducible, which is conducive to enhancing the electrostatic attraction between the substrate and the negatively charged quantum dots, thereby improving the quantum dot adsorption efficiency and the uniformity of thin film assembly.

[0012] Optionally, the polyelectrolyte is polydiallyldimethylammonium chloride, the concentration of the polyelectrolyte solution is 0.1–1 mg / mL, and the immersion time is 1–5 minutes.

[0013] By adopting the above technical solution and selecting polydiallyldimethylammonium chloride and controlling its concentration and impregnation time within a reasonable range, a dense and stable positive charge modification layer can be formed on the substrate surface. This ensures sufficient electrostatic adsorption capacity and avoids the adverse effects of excessively thick polyelectrolyte layer on subsequent quantum dot assembly and electrical transport, thereby improving the film formation quality and stability.

[0014] Optionally, the charge modification of the substrate in step one is achieved by chemical grafting, specifically by silanizing the substrate with aminosilane to graft positively charged amino groups onto the substrate surface.

[0015] By adopting the above technical solution, a positively charged amino functional layer that is firmly bonded to the substrate can be formed on the substrate surface through chemical grafting with aminosilane. This modified layer has high stability and is not easy to fall off, which is beneficial to continuously provide stable electrostatic adsorption force in subsequent assembly processes, thereby improving the consistency, reliability and long-term stability of infrared quantum dot film assembly.

[0016] Optionally, the infrared quantum dots mentioned in step two are HgTe quantum dots or PbS quantum dots, and their surfaces exhibit negative charges.

[0017] By adopting the above technical solution, HgTe quantum dots or PbS quantum dots with negative surface charge can form a stable and effective electrostatic attraction relationship with the positively modified substrate. This is beneficial for the rapid directional adsorption and uniform spreading of quantum dots on the substrate surface, while meeting the requirements of infrared band response, thereby improving the film quality of infrared quantum dot films and the performance of device applications.

[0018] Optionally, when the infrared quantum dots are initially oil-soluble, the long-chain organic ligands on the surface of the quantum dots are replaced with mercaptopropionic acid or short-chain halide ions through liquid-phase ligand exchange, so that the quantum dots are dispersed in a polar solvent.

[0019] By adopting the above technical solution, replacing the long-chain organic ligands on the surface of oil-soluble infrared quantum dots with mercaptopropionic acid or short-chain halide ions can effectively improve the dispersion stability of quantum dots in polar solvents and make their surface negatively charged, which is convenient for subsequent electrostatic adsorption assembly. At the same time, it reduces the obstruction of long-chain ligands to charge carrier transport and improves the electrical performance of the film.

[0020] Optionally, the electrostatic induction adsorption time in step three is 10 to 60 seconds, so that the infrared quantum dots form a uniform adsorption structure of monolayer or quasi-monolayer under the electrostatic attraction and electrostatic repulsion between particles.

[0021] By adopting the above technical solution, the electrostatic induction adsorption time is controlled between 10 and 60 seconds, which allows infrared quantum dots to migrate and adsorb onto the substrate surface rapidly and uniformly under the synergistic effect of strong electrostatic attraction and electrostatic repulsion between particles, forming a monolayer or quasi-monolayer arrangement structure. This ensures the compactness and uniformity of the film while effectively inhibiting quantum dot aggregation, thereby improving the film formation quality and subsequent photoelectric properties of the infrared quantum dot film.

[0022] Optionally, the short-chain bifunctional crosslinking agent in step four is 1,2-ethylenedithiol, 1,3-phenyldithiol, or ammonium thiocyanate, and the crosslinking agent is dissolved in acetonitrile or ethanol solvent.

[0023] By adopting the above technical solution, using 1,2-ethanedithiol, 1,3-benzenedithiol, or ammonium thiocyanate as short-chain bifunctional crosslinking agents and dissolving them in acetonitrile or ethanol, in-situ ligand substitution and covalent bonding can be achieved in the quantum dot adsorption layer, transforming weak electrostatic adsorption into a stable chemical bonding network, shortening the quantum dot spacing, and enhancing the electron or hole tunneling effect, thereby improving the mechanical stability, electrical properties, and working efficiency of the thin film and infrared devices.

[0024] Optionally, infrared quantum dot films can be constructed by repeatedly performing steps three and four to achieve a film thickness of 300–500 nm, and internal stress can be released by layer-by-layer covalent locking to prevent the film from cracking.

[0025] By adopting the above technical solution and repeatedly constructing the infrared quantum dot film through electrostatic adsorption and covalent bonding, the precise thickness control of the infrared quantum dot film to 300–500 nm can be achieved. At the same time, during the formation of each layer, the internal stress is gradually released through covalent locking, avoiding cracking or warping problems during the thick film deposition process. This results in an infrared quantum dot film with high mechanical stability, uniform density and excellent electrical properties, which is suitable for the fabrication of high-performance infrared optoelectronic devices.

[0026] In summary, this application includes at least one of the following beneficial technical effects: By leveraging the synergistic effect of electrostatic adsorption and covalent bonding, infrared quantum dots can be rapidly, uniformly, and densely assembled on the substrate surface to form a monolayer or quasi-monolayer adsorption structure, thereby improving the uniformity and coverage integrity of the thin film.

[0027] By using short-chain bifunctional crosslinking agents to transform electrostatic adsorption into a stable covalently bonded network, the mechanical stability and environmental durability of the film are significantly enhanced.

[0028] Extremely short ligand lengths ensure quantum tunneling between quantum dots, reduce insulation barriers, and improve the carrier transport efficiency and overall conductivity of thin films.

[0029] By using a multi-cycle "adsorption-locking" layer-by-layer construction method, the film thickness can be controlled (300–500 nm), and the internal stress is released layer by layer, effectively avoiding thick film cracking or warping.

[0030] The process is mild and does not require complex vacuum or high-temperature conditions, making it suitable for the efficient preparation of high-quality infrared quantum dot films under conventional laboratory conditions.

[0031] By selecting conductive substrates such as indium tin oxide, fluorine-doped tin oxide, or silicon-doped substrates, which combine good conductivity, mechanical support, and surface modifiability, the quality of thin film assembly and device stability can be further improved.

[0032] Liquid-phase ligand exchange technology can convert oil-soluble quantum dots into polar solvent dispersion, ensuring uniform distribution of negative charges, facilitating electrostatic adsorption assembly, and reducing the obstruction of electron transport by long-chain ligands. Attached Figure Description

[0033] Figure 1 This is a flowchart of an embodiment of this application.

[0034] Figure 2 This is a SEM image of the film edge in Embodiment 1 of this application.

[0035] Figure 3 This is a SEM image of the film edge in Comparative Example 1 of this application.

[0036] Figure 4 This is a transfer characteristic curve of Embodiment 1 of this application. Detailed Implementation

[0037] The following is in conjunction with the appendix Figure 1-4 This application will be described in further detail.

[0038] This application discloses an infrared quantum dot thin film assembly process synergistically induced by electrostatic adsorption and covalent bonding, aiming to solve the problems of volume shrinkage cracks and poor film adhesion caused by ligand exchange in the traditional preparation process of infrared quantum dot thin films.

[0039] By constructing a synergistic mechanism of "electrostatic pre-adsorption-in-situ covalent replacement", a high-density assembly of quantum dots on a substrate is achieved without introducing insulating polymers, and ligand exchange is completed simultaneously, thus preparing an infrared optoelectronic thin film with no cracks, low defect states, and high carrier transport efficiency.

[0040] The thin film assembly method of "electrostatic adsorption traction and covalent bonding locking" utilizes the charge difference between the substrate and quantum dots to achieve rapid and dense adsorption, and then uses short-chain bifunctional ligands to perform in-situ displacement, transforming physical adsorption into permanent chemical bonding.

[0041] Reference Figure 1An infrared quantum dot thin film assembly process synergistically induced by electrostatic adsorption and covalent bonding includes the following steps: Step 1: Charge modification of the substrate The cleaned conductive substrate is surface-modified to acquire a positive charge. Method A is physical adsorption: The substrate is immersed in a low-concentration polyelectrolyte solution for 1-5 minutes, washed with water and dried. The polyelectrolyte solution is polydiallyldimethylammonium chloride (PDDA) with a concentration of 0.1-1 mg / mL. Method B is chemical grafting: The substrate is silanized using aminosilanes, allowing positively charged amino groups to be grafted onto the surface. Step 2: Pretreatment of Quantum Dot Ink An infrared quantum dot dispersion with a negatively charged surface was prepared. The infrared quantum dots were selected from either HgTe or PbS. If the synthesized quantum dots are oil-soluble, liquid-phase ligand exchange must be performed first to transfer them into a polar solvent, and it must be ensured that their Zeta potential is negative. Step 3: Electrostatic Induction Adsorption. The positively charged substrate is immersed in the negatively charged quantum dot ink. Under the action of strong electrostatic attraction, the quantum dots will quickly migrate to the substrate and fill the gaps. The electrostatic repulsion restricts the aggregation between quantum dots. The adsorption layer shows a highly uniform monolayer or quasi-monolayer arrangement. The time is 10 seconds to 60 seconds. Step 4: Covalent bonding and ligand substitution. The substrate with adsorbed quantum dots is immersed in a solution containing a short-chain bifunctional crosslinking agent. The crosslinking agent can be selected from 1,2-ethanedithiol (EDT), 1,3-benzenedithiol (BDT), or ammonium thiocyanate (NH4SCN). Solvents selected: acetonitrile, ethanol Reaction mechanism: One end of the short-chain crosslinking agent forms a strong covalent bond (such as Hg-S bond) with the metal site (Hg or Pb) on the surface of the quantum dot, replacing the weaker electrostatically stable ligand in step two; the other end of the crosslinking agent can bond with the substrate or adjacent quantum dots. The reaction process transforms the "soft" electrostatic adsorption into a "hard" covalent network. At the same time, the extremely short ligand length (<0.5nm) ensures the quantum tunneling effect between quantum dots and eliminates the insulating layer. Step 5: Repeat steps 3 and 4 in multiple cycles until the film reaches the required thickness. Each layer undergoes an "adsorption-locking" process, and the stress is released layer by layer, avoiding cracking caused by the accumulation of stress in the thick film. An infrared quantum dot thin film assembly process synergistically induced by electrostatic adsorption and covalent bonding can achieve efficient, controllable, and high-quality assembly of infrared quantum dot thin films without relying on complex vacuum processes or high-temperature treatments. First, by modifying the substrate with a positive charge, whether by physical adsorption of polyelectrolytes or chemical grafting of aminosilanes, a stable positive charge layer can be formed on the substrate surface, providing a strong electrostatic attraction for the negatively charged infrared quantum dots. At the same time, through liquid-phase ligand exchange treatment, oil-soluble quantum dots are transformed into a polar solvent-dispersed, negatively charged quantum dot dispersion, which forms a stable and uniform electrostatic interaction between the dispersion and the substrate. Building upon this, the electrostatically induced adsorption time was controlled to be between 10 and 60 seconds, allowing quantum dots to rapidly migrate and uniformly adsorb under electrostatic attraction and interparticle repulsion, forming a monolayer or quasi-monolayer dense arrangement. This effectively prevents quantum dot aggregation and improves the uniformity and coverage integrity of the film. Subsequently, a short-chain bifunctional crosslinking agent was introduced for in-situ ligand replacement, enabling the formation of a stable covalent bond network between the quantum dots, the substrate, and adjacent quantum dots. This transforms the originally environmentally susceptible physical adsorption structure into a chemically more stable solidified structure, significantly improving the film's mechanical stability, environmental durability, and long-term reliability. The short-chain ligand can shorten the quantum dot spacing, reduce insulation barrier, enhance the electron or hole tunneling effect between quantum dots, and improve the film's carrier transport efficiency and overall conductivity. Furthermore, by repeatedly performing a layer-by-layer construction method of "electrostatic adsorption-covalent locking" over multiple cycles, the film thickness was precisely controlled to 300–500 μm. nm, each layer gradually releases stress during the formation process, avoiding the cracking, warping or stress accumulation problems common in traditional one-time thick film deposition, and achieving significant improvements in the structural uniformity, mechanical stability, electrical performance and thickness controllability of infrared quantum dot films, meeting the stringent requirements of high-performance infrared optoelectronic devices for thin film materials.

[0042] The core technology of this application has the following breakthroughs: using "electrostatic attraction" as the driving force for rapid assembly and "covalent coordination" as the final fixation method, the two work together to solve the contradiction that infrared quantum dot films are difficult to balance "density" and "conductivity".

[0043] The protected aspects of the technical solution in this application are: 1. Assembly process: A method for preparing an infrared colloidal quantum dot film, comprising alternating steps of "electrostatic adsorption of quantum dots on charged substrate" and "chemical replacement / crosslinking of short-chain ligands"; 2. Specific charge-matching systems: Protecting the combined use of "positively charged modified substrates (such as PDDA / APTES modification)" and "negatively charged stable quantum dots (such as carboxyl / halogen ligands)"; 3. In-situ conversion mechanism: During the film formation process, the electrostatic adsorption layer is replaced in-situ using bidentate or multidentate short-chain ligands (EDT, BDT, TBAI), which simultaneously achieves film densification and conductivity.

[0044] Example 1: Crack-free assembly of HgTe quantum dots on a silicon substrate Materials preparation: Quantum dots: MPA (mercaptopropionic acid) coated HgTe quantum dots, Zeta potential -35 mV; Substrate: Cleaned n-type silicon wafer. Modifier: PDDA aqueous solution (2 wt%); Crosslinking agent: acetonitrile solution (0.02 M) of 1,2-ethylenedithiol (EDT); Process: Immerse the silicon wafer in PDDA solution for 2 minutes, then rinse with water to make the surface positively charged; Cycle start: Immerse in HgTe quantum dot dispersion for 30 seconds (electrostatic adsorption); Acetonitrile rinse; Immerse in EDT acetonitrile solution for 30 seconds (covalent displacement, Hg-S bond formation, film shrinkage and locking); Acetonitrile rinse; Repeat the above cycle 40 times; Test results reference Figure 2 , Figure 4 ; SEM observation: Dense structure; no microcracks or pinholes were found on the surface. FET transport test: It shows a low carrier concentration, indicating that interface defects are suppressed.

[0045] Example 2: Effects of different substrates The difference compared to Example 1 is as follows: The silicon substrate was replaced with an ITO / PET flexible substrate, and hydroxyl groups were introduced by oxygen etching. The substrate was then immersed in a 1% APTES ethanol solution for 10 minutes. After removal, it was heat-treated in a 60°C oven for 15 minutes to firmly graft amino groups onto the substrate surface, giving it a positive charge. Results: Dense quantum dot films were obtained in the same way, with no significant difference in quality.

[0046] Comparative Example 1: Preparation of thin films using the traditional spin coating method Reference Figure 3Compared with Example 1, the difference is that: in the process, a thin film is prepared by spin coating at 4000 rpm, followed by EDT ligand exchange and post-drying treatment; this process is repeated 40 times. Test results: SEM observation: When a film of the same thickness is prepared by the traditional spin coating method, obvious cracks and grids appear on the surface.

[0047] Alternative solutions to the technical solution of this application: Alternative Option A: Traditional Spin-coating method Description: Add quantum dots -> spin coating -> Add ligands -> spin coating -> clean.

[0048] Disadvantages: It is very prone to cracking, resulting in significant material waste and a noticeable edge effect.

[0049] Alternative B: Langmuir-Blodgett (LB) membrane technology Description: A quantum dot monolayer is compressed at the gas-liquid interface and then transferred to a substrate.

[0050] Disadvantages: The equipment is expensive, the production efficiency is extremely low, it is difficult to achieve the industrial preparation of micron-level thick films, and the interlayer bonding is weak.

[0051] Alternative Option C: Inkjet Printing Description: Direct printing quantum dot ink.

[0052] Disadvantages: The prepared thin film is relatively porous and contains a large number of microscopic voids, which affects its photoelectric properties.

[0053] The implementation principle of the infrared quantum dot thin film assembly process synergistically induced by electrostatic adsorption and covalent bonding in this application embodiment is as follows: By constructing a stable charge difference between the substrate and the infrared quantum dots, electrostatic attraction is first used as the driving source to enable the negatively charged quantum dots to migrate and adsorb onto the positively charged substrate surface rapidly and orderly in a short time. At the same time, the like charge repulsion between quantum dots inhibits agglomeration behavior, thereby forming a dense and uniform monolayer or quasi-monolayer adsorption structure. On this basis, a short-chain bifunctional crosslinking agent is introduced to perform in-situ ligand replacement on the adsorbed quantum dots, so that the metal sites on the surface of the quantum dots form stable covalent bonds with the crosslinking agent. The original "soft connection" that relied on electrostatic interaction is transformed into a structurally stable "hard connection" covalent network, which significantly shortens the quantum dot spacing and reduces the interfacial insulation barrier. By alternately repeating the layer-by-layer construction process of "electrostatic adsorption-covalent locking", the film thickness can be controlled to increase. During the layer-by-layer curing process, internal stress is released, avoiding the cracking problem caused by volume shrinkage in traditional thick film deposition, thereby obtaining an infrared quantum dot thin film with high density, high conductivity and excellent mechanical stability.

[0054] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. An infrared quantum dot thin film assembly process synergistically induced by electrostatic adsorption and covalent bonding, characterized in that: Includes the following steps: Step 1: Charge modification of the substrate The cleaned conductive substrate is surface-modified to acquire a positive charge. Method A is physical adsorption: The substrate is immersed in a low-concentration polyelectrolyte solution for 1-5 minutes, washed with water and dried. The polyelectrolyte solution is polydiallyldimethylammonium chloride (PDDA) with a concentration of 0.1-1 mg / mL. Method B is chemical grafting: The substrate is silanized using aminosilanes, allowing positively charged amino groups to be grafted onto the surface. Step 2: Pretreatment of Quantum Dot Ink An infrared quantum dot dispersion with a negatively charged surface was prepared. The infrared quantum dots were selected from either HgTe or PbS. If the synthesized quantum dots are oil-soluble, liquid-phase ligand exchange must be performed first to transfer them into a polar solvent, and it must be ensured that their Zeta potential is negative. Step 3: Electrostatic Induction Adsorption. The positively charged substrate is immersed in the negatively charged quantum dot ink. Under the action of strong electrostatic attraction, the quantum dots will quickly migrate to the substrate and fill the gaps. The electrostatic repulsion restricts the aggregation between quantum dots. The adsorption layer shows a highly uniform monolayer or quasi-monolayer arrangement. The time is 10 seconds to 60 seconds. Step 4: Covalent bonding and ligand substitution. The substrate with adsorbed quantum dots is immersed in a solution containing a short-chain bifunctional crosslinking agent. The crosslinking agent can be selected from 1,2-ethanedithiol (EDT), 1,3-benzenedithiol (BDT), or ammonium thiocyanate (NH4SCN). Solvents selected: acetonitrile, ethanol Reaction mechanism: One end of the short-chain crosslinking agent forms a strong covalent bond (such as Hg-S bond) with the metal site (Hg or Pb) on the surface of the quantum dot, replacing the weaker electrostatically stable ligand in step two; the other end of the crosslinking agent can bond with the substrate or adjacent quantum dots. The reaction process transforms the "soft" electrostatic adsorption into a "hard" covalent network. At the same time, the extremely short ligand length (<0.5 nm) ensures the quantum tunneling effect between quantum dots and eliminates the insulating layer. Step 5: Repeat steps 3 and 4 in multiple cycles until the film reaches the required thickness. Each layer undergoes an "adsorption-locking" process, and the stress is released layer by layer, avoiding cracking caused by the accumulation of stress in the thick film.

2. The infrared quantum dot thin film assembly process according to claim 1, characterized in that, The conductive substrate is any one of indium tin oxide (ITO) substrate, fluorine-doped tin oxide (FTO) substrate, or doped silicon substrate.

3. The infrared quantum dot thin film assembly process according to claim 1, characterized in that, The charge modification of the substrate in step one is achieved through physical adsorption, specifically by immersing the substrate in a polyelectrolyte solution, so that the positively charged polyelectrolyte is adsorbed onto the substrate surface.

4. The infrared quantum dot thin film assembly process according to claim 3, characterized in that, The polyelectrolyte is polydiallyldimethylammonium chloride, the concentration of the polyelectrolyte solution is 0.1–1 mg / mL, and the immersion time is 1–5 minutes.

5. The infrared quantum dot thin film assembly process according to claim 1, characterized in that, The charge modification of the substrate in step one is achieved by chemical grafting, specifically by silanizing the substrate with aminosilane to graft positively charged amino groups onto the substrate surface.

6. The infrared quantum dot thin film assembly process according to claim 1, characterized in that, The infrared quantum dots mentioned in step two are HgTe quantum dots or PbS quantum dots, and their surfaces exhibit negative charges.

7. The infrared quantum dot thin film assembly process according to claim 6, characterized in that, When the infrared quantum dots are initially oil-soluble, the long-chain organic ligands on the surface of the quantum dots are replaced with mercaptopropionic acid or short-chain halide ions through liquid-phase ligand exchange, so that the quantum dots are dispersed in a polar solvent.

8. The infrared quantum dot thin film assembly process according to claim 1, characterized in that, The electrostatic induction adsorption time in step three is 10 to 60 seconds, so that the infrared quantum dots form a uniform adsorption structure of monolayer or quasi-monolayer under the electrostatic attraction and electrostatic repulsion between particles.

9. The infrared quantum dot thin film assembly process according to claim 1, characterized in that, The short-chain bifunctional crosslinking agent mentioned in step four is 1,2-ethylenedithiol, 1,3-phenyldithiol, or ammonium thiocyanate, and the crosslinking agent is dissolved in acetonitrile or ethanol solvent.

10. The infrared quantum dot thin film assembly process according to claim 1, characterized in that, Infrared quantum dot films are constructed by repeatedly performing steps three and four to achieve a film thickness of 300–500 nm. Internal stress is released through layer-by-layer covalent locking, thereby preventing the film from cracking.

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