PbS quantum dot film, preparation method thereof and photoelectric device comprising PbS quantum dot film

Abstract

The invention belongs to the technical field of PbS quantum dots, and discloses a PbS quantum dot film, a preparation method thereof and a photoelectric device comprising the PbS quantum dot film, the preparation method comprises the following steps: 1) dissolving oleic acid coated PbS quantum dot solid in a non-polar solvent to form a first solution; 2) dissolving haloid, ammonium acetate and short-chain mercaptan in a polar solvent to form a second solution; (3) mixing the first solution and the second solution to form a mixed solution, standing, layering, removing supernatant, performing centrifugal treatment on subnatant, and drying precipitate subjected to centrifugal treatment to obtain PbS quantum dot solid powder; and 4) dissolving the PbS quantum dot solid powder obtained in the step 3) in a dispersant to obtain a dispersion liquid, coating the dispersion liquid on a substrate, and carrying out annealing treatment on the dispersion liquid to form the PbS quantum dot film. Through the synergistic effect of halogen and short-chain mercaptan, an ionic and covalent dual passivation mechanism is realized, and comprehensive defect passivation of PbS is realized.

Description

Technical Field

[0001] This invention belongs to the field of PbS quantum dot technology, and more specifically, relates to PbS quantum dot thin films, their preparation methods, and optoelectronic devices including them. Background Technology

[0002] PbS quantum dots (Lead Sulfide Quantum Dots, PbS QDs) are a typical class of nanoscale semiconductor materials with tunable band gaps, strong absorption coefficients, and significant quantum confinement effects, thus showing broad application prospects in optoelectronic devices such as infrared detectors, photovoltaic cells, short-wave infrared imaging, and flexible optoelectronics. However, the surface of PbS quantum dots typically contains a large number of uncoordinated atoms (dangling bonds), and these defects easily form nonradiative recombination centers, severely weakening their optoelectronic properties. Therefore, achieving efficient surface passivation has become crucial for improving the performance of optoelectronic devices.

[0003] In existing technologies, long-chain organic ligands such as oleic acid are widely used for the initial passivation of PbS quantum dots in synthesis to maintain the dispersion stability of PbS quantum dots. However, their strong insulating properties significantly hinder charge transport between PbS quantum dots, which is detrimental to improving the efficiency of optoelectronic devices. To overcome this problem, researchers have proposed using inorganic halogen ligands (such as PbX2, CdX2, etc.) for ligand exchange to replace long-chain organic molecules, thereby improving the conductivity of PbS quantum dot films. However, single halogen passivation is difficult to fully cover complex surface defects, resulting in limitations on the stability and interfacial bonding of PbS quantum dot films.

[0004] On the other hand, short-chain thiols, due to their covalent bonding properties, are widely used for ligand exchange on the surface of PbS quantum dots. Compared with halogen ligands, thiols can provide better dispersion stability, but thiols rely solely on the mercapto group to coordinate with the Pb surface, lacking an ion compensation mechanism, and cannot effectively repair various types of surface defects such as Pb or S vacancies.

[0005] Existing PbS quantum dot surface passivation strategies face the following limitations: (1) Incomplete defect passivation makes it difficult to simultaneously cover Pb and S site defects; (2) Charge transport is hindered, and some organic ligands have excessive insulation; (3) Incomplete surface passivation leads to insufficient environmental stability, making it susceptible to oxygen and moisture, resulting in performance degradation. Summary of the Invention

[0006] To address the aforementioned deficiencies or improvement needs of existing technologies, this invention provides PbS quantum dot films, their preparation methods, and optoelectronic devices comprising them. The preparation method achieves a combined "ionic + covalent" passivation mechanism on the PbS quantum dot surface by synergistically introducing halide ions and short-chain thiols, thus simultaneously addressing surface defect repair, charge channel optimization, and molecular encapsulation protection, comprehensively enhancing the optoelectronic performance and environmental stability of PbS quantum dot films.

[0007] To achieve the above objectives, according to one aspect of the present invention, a method for preparing PbS quantum dot thin films is provided, comprising the following steps: 1) Dissolve the PbS quantum dot solid coated with oleic acid in a nonpolar solvent to form the first solution; 2) Dissolve the halogen salt, ammonium acetate and short-chain thiols in a polar solvent to form a second solution, wherein the short-chain thiols have 2 to 6 carbon atoms; 3) Mix the first solution with the second solution to form a mixed solution. After the mixed solution is allowed to stand, it separates into an upper layer and a lower layer. Remove the upper layer and then centrifuge the lower layer. The precipitate after centrifugation is dried to obtain PbS quantum dot solid powder. 4) Dissolve the PbS quantum dot solid powder obtained in step 3) in a dispersant to obtain a dispersion, coat the dispersion onto a substrate, and anneal it to form a PbS quantum dot film.

[0008] Preferably, in step 1), the nonpolar solvent is n-octane; In step 2), the polar solvent is N,N-dimethylformamide.

[0009] As a typical nonpolar solvent, n-octane exhibits intermolecular forces that highly match the hydrophobic groups of oleic acid ligands, enabling it to form good compatibility with the oleic acid ligands on the surface of PbS quantum dots. This allows for the efficient and uniform dissolution of oleic acid-encapsulated PbS quantum dot solids. This uniform dissolution prevents the aggregation of PbS quantum dots in the solvent. Furthermore, n-octane possesses excellent chemical stability. Throughout the entire preparation process (including storage and transfer before mixing with the second solution), it does not react chemically with the oleic acid ligands or PbS quantum dots, nor does it undergo component decomposition or property changes due to minor fluctuations in ambient temperature and humidity. It maintains the long-term stability of the first solution system, ensuring consistent dispersion of PbS quantum dots in each batch of the first solution and guaranteeing process repeatability.

[0010] N,N-Dimethylformamide, as a highly polar solvent, exhibits excellent solubility and dispersion capabilities for three types of substances: halide salts, ammonium acetate, and short-chain thiols. This is a core prerequisite for ensuring the homogeneity of the second solution's composition. Halide salts are ionic compounds, and their dissolution process relies on the polarity of the solvent to achieve ion dissociation. Ammonium acetate is also an ionic compound, requiring dissociation into ammonium and acetate ions in a polar solvent to function. Although short-chain thiols are organic compounds, due to the polarity of their thiol groups, they require a polar solvent to achieve uniform dispersion. The strong polarity of N,N-Dimethylformamide simultaneously satisfies the dissolution requirements of all three types of substances: it provides a sufficient polar environment for halide salts and ammonium acetate to promote ion dissociation and prevent the suspension or sedimentation of solid particles; and through polar interactions with the thiol groups of short-chain thiols, it prevents the aggregation of short-chain thiols due to intermolecular forces, ensuring their uniform distribution in a monomolecular state in the solution.

[0011] The combination of n-octane and N,N-dimethylformamide exhibits a significant synergistic advantage due to their polarity differences, providing crucial assurance for efficient stratification and impurity separation in mixed solutions. The nonpolarity of n-octane contrasts sharply with the strong polarity of N,N-dimethylformamide. After mixing, the extremely weak intermolecular polar interactions allow for rapid and clear stratification upon standing, with well-defined interface boundaries. The upper layer primarily consists of n-octane and oleic acid ligands that have not undergone ligand exchange, while the lower layer comprises N,N-dimethylformamide dissolved with PbS quantum dots that have undergone preliminary ligand exchange. This clear stratification facilitates precise removal of upper impurity liquid and effectively reduces oleic acid ligand residue. If the polarity difference between the two solvents is insufficient (such as using a slightly less polar nonpolar solvent or a slightly more polar polar solvent), it may lead to slow stratification after mixing, blurred interface, or even emulsification. In this case, it is not only difficult to completely separate the upper impurities, but it may also cause some N,N-dimethylformamide phase to be trapped in the upper liquid, resulting in the loss of PbS quantum dots, or some n-octane phase to remain in the lower liquid, introducing organic impurities.

[0012] Preferably, in step 2), the short-chain thiol is selected from at least one of 1,3-propanedithiol, 1,3-ethanedithiol, and 1-propanethiol.

[0013] From the perspective of the coordination mechanism between ligands and the PbS quantum dot surface, all three thiols mentioned above possess the ability to coordinate with PbS quantum dot surface PbS. 2+ The core capability lies in forming stable coordination bonds, and compared to other short-chain thiols, their coordination structure is more suitable for repairing defects on the PbS quantum dot surface. 1,3-Propanedithiol and 1,3-ethanedithiol, as dithiols, contain two thiol groups (-SH) in their molecular structure. These two thiol groups can respectively bond with adjacent PbS quantum dot surfaces. 2+The formation of a bidentate coordination structure significantly enhances the binding strength between the ligand and the PbS quantum dot surface compared to monodentate coordination. This reduces the risk of ligand detachment during subsequent processes (such as centrifugation and annealing), thus preventing the re-exposure of the PbS quantum dot surface and the generation of new defects due to ligand detachment. Simultaneously, the chelate structure formed by bidentate coordination can construct a denser molecular protective layer on the PbS quantum dot surface. This layer not only fills anionic defects such as S vacancies on the PbS quantum dot surface but also hinders the contact between external oxygen and water vapor and the PbS quantum dot surface through steric hindrance, fundamentally improving the environmental stability of the PbS quantum dots and preventing photoelectric performance degradation due to oxidation or hydrolysis.

[0014] 1-Propanthiol, as a monothiol, contains only one thiol group but possesses superior molecular flexibility and solubility. In polar solvents, it can achieve higher dispersion uniformity when contacting the PbS quantum dot surface, making it particularly suitable for scenarios where the PbS quantum dot surface defect distribution is relatively uniform. Its moderate molecular chain length effectively replaces long-chain oleic acid ligands to reduce steric hindrance without causing excessive aggregation between PbS quantum dots due to excessively short chains. The 1-propanethiol molecular chain forms a suitable buffer between PbS quantum dots, preventing aggregation due to insufficient spacing. Compared to thiols with more than 6 carbon atoms, it minimizes charge transport resistance between PbS quantum dots, ensuring efficient charge migration. Furthermore, the moderate reactivity of the thiol group prevents excessively vigorous reactions leading to local overcoordination (ligand accumulation) or incomplete ligand exchange due to insufficient reactivity, allowing it to react with PbS on the quantum dot surface. 2+ The formation of stable and uniform monodentate coordination ensures the consistency of the electrical properties of PbS quantum dot films.

[0015] From a process compatibility perspective, all three thiols exhibit good compatibility with the "halogen salt-ammonium acetate-polar solvent" system. In polar solvents, they can form stable mixed solutions with halogen salts and ammonium acetate, without adverse reactions (such as precipitation or decomposition) with other components due to differences in molecular structure, and without interfering with the promoting effect of ammonium acetate on the dissolution of halogen salts.

[0016] Preferably, in step 2), the halogen salt is selected from at least one of CdX2 and PbX2, wherein X is Cl, Br or I.

[0017] CdX2 and PbX2, as ionic halide salts, can efficiently dissociate into halide ions (Cl-) in polar solvents. - ,Br - I -These halide ions are key active species for filling anionic defects (especially S vacancies) on the surface of PbS quantum dots.

[0018] Compared to other halide salts (such as alkali metal halide salts NaCl, KBr, etc.), the advantage of CdX2 and PbX2 lies more in their metal cations (Cd... 2+ Pb 2+ Lattice compatibility with PbS quantum dots, Cd 2+ Pb 2+ The ionic radius and Pb in the PbS lattice 2+ The ionic radii of PbS quantum dots differ very little, and the introduction of metal cations will not cause lattice distortion; while alkali metal cations (such as Na) + K + Ion radius and Pb 2+ The differences are significant. If used to replace CdX2 and PbX2, it may form lattice stress on the surface of PbS quantum dots, which may introduce new structural defects or even destroy the original lattice structure of PbS quantum dots, thus exacerbating the performance degradation.

[0019] Preferably, steps 1) to 4) are carried out under an inert atmosphere, wherein the inert atmosphere is selected from nitrogen or argon.

[0020] Nitrogen and argon, as chemically inert gases, will not react chemically with PbS quantum dots, nor will they interact with the ligands (oleic acid, short-chain thiols) on the surface of PbS quantum dots. They can form a protective barrier around PbS quantum dots, inhibiting oxidation reactions throughout the entire process. This ensures that the core structure and optical and electrical properties of PbS quantum dots remain stable throughout the entire process from PbS quantum dot dissolution and ligand exchange to PbS quantum dot film formation, laying the foundation for the reliability of subsequent PbS quantum dot film performance.

[0021] Preferably, in the first solution, the mass concentration of the oleic acid-coated PbS quantum dot solution is 5 mg / mL to 20 mg / mL; In the second solution, the molar concentration of the halogen salt is 100 mmol / L to 400 mmol / L, the molar concentration of ammonium acetate is 50 mmol / L to 200 mmol / L, and the molar concentration of the short-chain thiol is 100 mmol / L to 200 mmol / L. In step 3), the volume ratio of the first solution to the second solution is 1:1 to 1:3.

[0022] From the perspective of system stability and reaction compatibility of the first solution, the oleic acid-encapsulated PbS quantum dot solution concentration defined in step 1) ensures that the PbS quantum dots achieve a uniform dispersion and non-agglomeration in a nonpolar solvent, which is ideal. At this concentration, the intermolecular forces between PbS quantum dots are in equilibrium. This prevents aggregation due to excessively high concentrations, which would form difficult-to-disperse clusters (such clusters would reduce the contact area between the PbS quantum dots and the second solution, leading to local ligand exchange failure and ultimately forming performance defect areas in the PbS quantum dot film). Conversely, a low concentration would not result in insufficient PbS quantum dots per unit volume, reducing the efficiency of subsequent mixing reactions and increasing process costs and time. Simultaneously, the first solution at this concentration has suitable viscosity and flowability, facilitating precise mixing with the second solution in the subsequent steps. This avoids uneven mixing due to excessively thick solutions or unbalanced distribution of PbS quantum dots during mixing due to excessively thin solutions, laying the foundation for uniform ligand exchange reactions.

[0023] From the perspective of the reactivity and component synergy of the second solution, the limiting of the molar concentrations of halide salts, ammonium acetate, and short-chain thiols in step 2) constructs an optimal reaction system that maximizes the function of each component without mutual interference. For halide salts, this molar concentration provides sufficient halide ions to fill the S vacancies on the PbS quantum dot surface. It avoids both insufficient ion quantity due to excessively low concentration, which would prevent some defects from being repaired, and excessive accumulation of halide ions on the PbS quantum dot surface due to excessively high concentration, which would introduce new ionic defects and affect the electronic state and charge transport performance of PbS quantum dots. For ammonium acetate, its limited concentration precisely matches the needs of halide salts and short-chain thiols: on the one hand, it can fully enhance the ionic strength of the solution through the ions generated by dissociation, which helps the halide salt to completely dissolve and dissociate, avoiding the suspension of solid particles; on the other hand, it can provide just the right amount of protection for short-chain thiols through weak interactions, inhibiting their self-polymerization and oxidation side reactions, while avoiding excessively high concentration that would lead to excessively high ionic strength in the solution, interfering with the coordination reaction between short-chain thiols and the PbS quantum dot surface. For short-chain thiols, this concentration ensures their uniform distribution in the solution as monomolecules, satisfying the need to replace all oleic acid ligands without causing excessive concentrations that could enhance intermolecular interactions, leading to aggregation or unintended reactions with other components and compromise the homogeneity of the second solution. This synergistic matching of the three concentrations makes the second solution a stable system with triple functions of ion supply, dissolution assistance, and ligand protection, guaranteeing the efficiency and thoroughness of subsequent ligand exchange.

[0024] From the perspective of the sufficiency and controllability of the ligand exchange reaction, the defined volume ratio of the first solution to the second solution is crucial for achieving full contact and reaction between PbS quantum dots and the reactive components. At this volume ratio, the total amount of halide salts and short-chain thiols in the second solution is precisely matched to the total amount of PbS quantum dots in the first solution. This prevents insufficient active components due to an insufficient volume of the second solution, which would cause some PbS quantum dots to fail to complete ligand exchange (residual oleic acid ligands would form an insulating layer between PbS quantum dots, hindering charge transport); conversely, it also prevents an excessive volume of active components due to an excessive volume of the second solution, which would leave unreacted components in the mixed system, increasing the difficulty of subsequent centrifugation and potentially adhering to the surface of the PbS quantum dot solid powder after drying, becoming impurities and defects in the formed PbS quantum dot film. Meanwhile, an appropriate volume ratio ensures that the mixed solution quickly achieves clear stratification after standing. Excessive or insufficient volume of the second solution may disrupt the stratification balance caused by the polarity difference between the two phases, resulting in slow stratification, blurred interfaces, or emulsification. The stratification effect at this ratio can efficiently separate the unreacted oleic acid and nonpolar solvent in the upper layer, reduce impurity residues, and ensure the purity of PbS quantum dots in the lower layer, thus clearing obstacles for the subsequent preparation of high-density and high-purity PbS quantum dot films.

[0025] By precisely controlling the concentration and volume ratio of key reactive components in the solution, the microstructure and interface properties of PbS quantum dot films can be optimized. Uniformly dispersed PbS quantum dots, sufficient ligand exchange, and minimal impurity residue result in a denser microstructure in the subsequently coated PbS quantum dot films. The PbS quantum dots are evenly arranged without significant agglomeration or voids, ensuring unobstructed charge transport paths between them, thereby improving the conductivity and light absorption efficiency of the PbS quantum dot film. Simultaneously, the dense structure and complete passivation layer effectively block the intrusion of oxygen and moisture, reducing the erosion of PbS quantum dot film performance by environmental factors and extending the lifespan of optoelectronic devices based on this PbS quantum dot film.

[0026] Preferably, the mass concentration of PbS quantum dots in the dispersion is 200 mg / mL to 600 mg / mL.

[0027] From the perspective of dispersion system stability, this mass concentration enables PbS quantum dots to form a stable, uniformly dispersed state without agglomeration in the dispersant. The dispersibility of PbS quantum dots in the dispersion depends on the balance between intermolecular forces and the solvation effect of the dispersant. If the concentration is too high, the van der Waals forces and coordination interactions between PbS quantum dots will be significantly enhanced, exceeding the solvation stabilization capacity of the dispersant, leading to the spontaneous aggregation of PbS quantum dots into micro-agglomerates invisible to the naked eye. These agglomerates cannot be effectively dispersed during subsequent coating processes, forming performance islands in the PbS quantum dot film. This not only disrupts the structural continuity of the PbS quantum dot film but also, due to the abnormal reduction in the spacing between PbS quantum dots within the agglomerates, intensifies nonradiative recombination, significantly reducing the photoelectric activity of the PbS quantum dot film. If the concentration is too low, the PbS quantum dots are too sparsely distributed in the dispersant. The solvation effect of the dispersant will excessively occupy the surface of the PbS quantum dots. Although this can prevent aggregation, it will result in insufficient PbS quantum dots per unit volume. This makes it difficult to form a continuous and dense PbS quantum dot film during subsequent coating, easily leading to defects such as missed coating and pinholes. Furthermore, the thickness of the PbS quantum dot film is difficult to control, directly affecting the light absorption efficiency and the integrity of the charge transport path. The limited mass concentration, however, balances the interaction forces between PbS quantum dots and the stabilizing effect of the dispersant. It maintains the monodisperse state of the PbS quantum dots while ensuring a sufficient content of PbS quantum dots per unit volume, providing a stable basis for long-term storage of the dispersion and subsequent coating.

[0028] From the perspective of controllability in the coating process, this concentration provides the dispersion with suitable viscosity and flowability, adapting to the process requirements of various coating methods. Whether spin coating, drop coating, or blade coating, the viscosity and flowability of the dispersion directly determine the uniformity and thickness consistency of the coating. If the concentration is too high, the dispersion viscosity will be too large, and during spin coating, insufficient centrifugal force will easily lead to phenomena such as streaks and edge accumulation in the coating. During blade coating, excessive resistance will cause uneven coating thickness. If the concentration is too low, the dispersion flowability will be too strong, and during drop coating, rapid solvent diffusion will easily lead to an excessively thin coating with irregular edges. During spin coating, insufficient PbS quantum dot concentration will make it difficult to form a coating that meets the thickness requirements, even by adjusting the rotation speed. The dispersion at this concentration has a viscosity that can precisely match the parameter range of conventional coating equipment: when spin-coating, the coating thickness can be made uniform by controlling the rotation speed; when scraping, it can form a continuous and defect-free wet film by advancing the scraper at a uniform speed; and when drop-coating, it can form a stable droplet spreading range on the substrate surface. Standardized coating can be achieved without frequent adjustment of equipment parameters, which greatly reduces the difficulty of process operation and reduces coating defects caused by human factors.

[0029] Preferably, the thickness of the PbS quantum dot film is 200 nm to 500 nm.

[0030] A suitable mass concentration ensures that PbS quantum dots exist in a monodisperse or weakly aggregated state in the dispersion, avoiding aggregation (high concentration easily leads to aggregation) or sparse distribution (low concentration easily leads to sparse distribution) of PbS quantum dots due to improper concentration. The target thickness provides suitable space for the orderly stacking of PbS quantum dots. Within the thickness range of 200nm to 500nm, PbS quantum dots can be uniformly arranged along the thickness direction during the coating process. This avoids insufficient PbS quantum dot layers due to excessive thickness (resulting in gaps and pinholes), and excessive stacking stress of PbS quantum dots due to excessive thickness (resulting in cracks and internal pores). Under this synergistic effect, the PbS quantum dots inside the PbS quantum dot film are uniformly distributed and densely packed, with no obvious structural defects. On the one hand, the dense structure can reduce the scattering loss of light inside the PbS quantum dot film, allowing the target wavelength light (such as the infrared band that PbS quantum dots are sensitive to) to fully interact with the PbS quantum dots, avoiding the increase in light transmittance and decrease in absorption efficiency due to gaps. On the other hand, the uniform distribution of PbS quantum dots can construct continuous charge transport channels, reducing structural obstacles in the charge transport process (such as the breakage of the transport path caused by gaps and the increase in charge recombination caused by aggregation), ensuring efficient charge migration within the PbS quantum dot film, and providing structural protection for the excellent electrical activity of the PbS quantum dot film.

[0031] Preferably, the annealing temperature is 70℃~110℃ and the annealing time is 10min~30min.

[0032] Regarding the control of annealing temperature, a defined annealing temperature range is crucial for balancing the volatilization of dispersant and the stability of the PbS quantum dot surface state. If the annealing temperature is too low, the dispersant cannot volatilize sufficiently, leaving solvent molecules inside the PbS quantum dot film. These residual molecules fill the gaps between PbS quantum dots, forming an insulating barrier layer that hinders charge transfer between PbS quantum dots. They also interact weakly with the ligands on the PbS quantum dot surface, leading to decreased ligand binding stability and ligand detachment over long-term use. If the annealing temperature is too high, it will destroy the crystal structure of PbS quantum dots, causing aggregation or surface oxidation. High temperatures disrupt the coordination balance between the ligands on the PbS quantum dot surface and the PbS quantum dot core, leading to ligand dissociation. The exposed PbS quantum dots aggregate due to excessive surface energy, degrading the photoelectric properties of the PbS quantum dot film. The limited annealing temperature allows for the orderly and complete evaporation of the dispersant, minimizing solvent residue inside the PbS quantum dot film. At the same time, it avoids damage to the PbS quantum dot crystal structure and surface ligands caused by high temperature, ensuring that the PbS quantum dots maintain their original morphology and stable surface coordination state, thus laying the structural foundation for the excellent photoelectric properties of the PbS quantum dot film.

[0033] From the perspective of annealing time adaptability, a defined annealing time is crucial for ensuring the sufficiency and appropriateness of the annealing process. If the annealing time is too short, the dispersant will not evaporate completely, and the ligands on the PbS quantum dot surface will struggle to form stable coordination bonds with the PbS quantum dot core. This will result in a large number of unstable ligand sites on the surface of the PbS quantum dot film. These sites easily adsorb water vapor and oxygen from the environment, causing the performance of the PbS quantum dot film to degrade rapidly over time. If the annealing time is too long, it will lead to over-annealing. Even at suitable temperatures, prolonged heating will cause atoms on the PbS quantum dot surface to migrate, forming surface defects (such as an increase in Pb or S vacancies). It may also promote slight fusion between PbS quantum dots, disrupting the quantum confinement effect of the PbS quantum dots, causing the optical absorption characteristics and electrical response performance of the PbS quantum dot film to deviate from the design goals. The limited annealing time ensures that the dispersant evaporates fully while allowing the PbS quantum dot surface ligands and PbS quantum dot cores to achieve stable coordination. It also prevents surface defects or quantum confinement effects from being caused by excessive heating time, achieving a balance between sufficient treatment and appropriate protection, and ensuring the long-term stability of PbS quantum dot film performance.

[0034] From the synergistic effect of thickness, annealing temperature, and annealing time in PbS quantum dot films, the combination of these parameters forms a complete PbS quantum dot film molding control system. A suitable thickness provides a uniform processing space for the annealing process, ensuring that the annealing temperature and time can act on each layer of PbS quantum dots in the film, avoiding localized over-annealing or insufficient annealing due to uneven thickness. Furthermore, appropriate annealing temperature and time can further optimize the microstructure of the PbS quantum dot film. During annealing, the PbS quantum dots undergo slight self-adjustment under mild temperature and time conditions, filling tiny gaps in the thickness direction and improving the density of the PbS quantum dot film. This synergistic effect ultimately endows PbS quantum dot films with a uniform microstructure, stable surface state, and excellent charge transport capability. It not only reduces the erosion of PbS quantum dot films by oxygen and water vapor in the environment (the dense structure hinders the penetration of impurities), but also ensures the performance consistency of PbS quantum dot films in different batches of preparation. This provides a stable material basis for their application in optoelectronic devices such as colloidal PbS quantum dot infrared detectors and solar cells, avoiding the decline in the yield or shortened lifespan of optoelectronic devices due to performance fluctuations of PbS quantum dot films, and ensuring that optoelectronic devices have stable response speed, signal-to-noise ratio, and energy conversion efficiency during operation.

[0035] Preferably, in step 4), the dispersant is composed of N,N-dimethylformamide and n-butylamine, and the volume ratio of N,N-dimethylformamide to n-butylamine is 1:4 to 1:1.

[0036] From the perspective of PbS quantum dot dispersion stability, N,N-dimethylformamide, as a typical polar solvent, possesses the basic ability to dissolve PbS quantum dot solid powder. However, the N,N-dimethylformamide system alone is prone to local aggregation of PbS quantum dots due to the uneven interaction between the ligands on the PbS quantum dot surface and the solvent. This aggregation directly disrupts the homogeneity of the dispersion, creating a potential problem for subsequent film formation. The introduction of n-butylamine, on the other hand, allows for weak interactions between the amino groups in its molecular structure and the ligands (such as short-chain thiols) on the PbS quantum dot surface. This interaction effectively regulates the charge distribution and steric hindrance on the PbS quantum dot surface, breaking the tendency for PbS quantum dot aggregation in N,N-dimethylformamide alone and ensuring that the PbS quantum dots remain uniformly dispersed in the dispersion. Meanwhile, the specific volume ratio of N,N-dimethylformamide and n-butylamine can precisely adjust the overall polarity and solubility of the dispersant, ensuring that the PbS quantum dots are fully dissolved while avoiding the detachment of ligands from the PbS quantum dots due to excessively strong or weak solvent polarity. This ensures the long-term stability of the dispersion during storage and coating, laying a core foundation for the subsequent preparation of high-quality PbS quantum dot films.

[0037] In terms of improving the film quality of PbS quantum dot films, this dispersant system is crucial for the smoothness of the coating process and the integrity of the microstructure of the PbS quantum dot film. Regardless of the coating method—spin coating, drop coating, or blade coating—the dispersion must possess suitable flowability and viscosity to adapt to the operational requirements of different coating processes. The N,N-dimethylformamide and n-butylamine compound system allows for precise control of the dispersion's viscosity and surface tension by adjusting their ratio, ensuring uniform spreading of the dispersion on the substrate surface during coating and avoiding coating defects (such as streaks, pinholes, and edge shrinkage). During the subsequent annealing process, the dispersant system also exhibited excellent volatility characteristics: n-Butylamine has a relatively low boiling point and can volatilize rapidly and orderly in the early stage of annealing, creating favorable conditions for the gradual volatilization of N,N-dimethylformamide and avoiding the formation of voids or cracks inside the PbS quantum dot film due to the rapid volatilization of the dispersant; at the same time, during the synergistic volatilization process, the two can play a certain supporting role for PbS quantum dots, maintain the uniform arrangement of PbS quantum dots in the PbS quantum dot film, reduce the occurrence of PbS quantum dot aggregation during the annealing stage, and finally form a PbS quantum dot film with high density and uniform microstructure. The high density and uniformity of the PbS quantum dot film are the structural prerequisites for its excellent photoelectric performance.

[0038] Preferably, in step 4), the coating method is selected from one of spin coating, drip coating, and scraping coating.

[0039] According to another aspect of the present invention, a PbS quantum dot thin film is also provided, which is prepared by the preparation method described above.

[0040] From the perspective of surface defect repair, this PbS quantum dot film achieves dual synergistic passivation of "ionic + covalent", completely solving the problem of incomplete defect coverage in traditional single passivation strategies. The halide ions introduced during the preparation process can precisely fill anionic defects (such as S vacancies) on the PbS quantum dot surface through ion compensation, constructing a stable inorganic interface layer. Simultaneously, short-chain thiols form strong covalent coordination bonds with Pb atoms on the PbS quantum dot surface through their thiol groups, effectively repairing cation vacancies and unsaturated dangling bonds. This dual passivation mechanism can comprehensively eliminate nonradiative recombination centers on the PbS quantum dot surface, avoiding ineffective energy loss of charge carriers due to defect sites, significantly improving the optical stability and electrical activity of the PbS quantum dot film, and ensuring that the PbS quantum dot film is not prone to fluctuations in photoelectric performance during long-term use.

[0041] In terms of charge transport performance, this PbS quantum dot film exhibits highly efficient charge transport capabilities. During the fabrication process, halogens replaced traditional long-chain oleic acid ligands, significantly reducing the steric hindrance on the quantum dot surface and shortening the spacing between PbS quantum dots, thus creating a smooth channel for charge transport. Simultaneously, precise control of ligand substitution efficiency during the fabrication process reduced organic residues in the PbS quantum dot film, further lowering charge transport resistance. Compared to traditional PbS quantum dot films containing long-chain organic ligands, this PbS quantum dot film shows a significantly improved charge mobility, enabling rapid and efficient carrier transport, laying a crucial foundation for efficient energy conversion in subsequent optoelectronic devices.

[0042] According to another aspect of the invention, an optoelectronic device is also provided, comprising the aforementioned PbS quantum dot thin film.

[0043] Preferably, the optoelectronic device is a quantum dot infrared detector or a solar cell.

[0044] In quantum dot infrared detector applications, this PbS quantum dot film significantly enhances the core performance and practical value of the detector. Infrared detectors have extremely high requirements for the charge transport efficiency, photoresponse sensitivity, and environmental interference resistance of materials. This PbS quantum dot film eliminates non-radiative recombination centers on the PbS quantum dot surface through "ionic + covalent" dual passivation, greatly extending the carrier lifetime. When the detector receives infrared light signals, more carriers can participate in photoelectric conversion, avoiding response lag or insufficient sensitivity caused by ineffective carrier loss, and significantly improving the detector's accuracy and response speed in capturing infrared signals.

[0045] In solar cell applications, this PbS quantum dot film can help cells achieve higher energy conversion efficiency and longer service life. The core requirements of solar cells are efficient absorption of light energy, rapid transport of photogenerated carriers, and reduced energy loss. In this PbS quantum dot film, short-chain thiols replace long-chain oleic acid ligands, shortening the spacing between PbS quantum dots and reducing organic residues. This significantly improves charge mobility, enabling rapid transport of photogenerated carriers from the PbS quantum dots to the electrodes. This avoids carrier loss due to excessive resistance during transport, effectively improving charge separation and collection efficiency, thereby enhancing the cell's energy conversion efficiency.

[0046] In summary, compared with the prior art, the above-described technical solutions conceived by this invention can achieve the following beneficial effects: 1) The method for preparing PbS quantum dot films of the present invention significantly reduces steric hindrance compared to the initial oleic acid ligand. The charge transport efficiency between PbS quantum dots determines the performance of the PbS quantum dot film. The introduction of halogen ligands can significantly shorten the spacing between PbS quantum dots, reduce steric hindrance in the charge transport path, and lay the structural foundation for the high charge mobility of the subsequent PbS quantum dot film. Simultaneously, the thiol group (-SH) of the short-chain thiol interacts with the Pb group on the surface of the PbS quantum dots. 2+ It has strong coordination ability, which can play a supplementary passivation role and prevent defects on the quantum dot surface from being exposed and oxidized due to ligand detachment.

[0047] In addition, the introduction of halide salts provides a key ion source for the surface state repair of PbS quantum dots. During the preparation of PbS quantum dots, unsaturated coordinated Pb atoms readily form on the surface. 2+ or S 2- These defects become nonradiative recombination centers for charge carriers, where they consume energy through nonradiative transitions, leading to decreased luminescence efficiency and shortened carrier lifetime in PbS quantum dots. Halogen ions, through coordination, can fill these defect sites, forming a stable surface structure, reducing nonradiative recombination, and fundamentally improving the optical stability and electrical activity of PbS quantum dots.

[0048] This invention introduces the synergistic effect of halogens and short-chain thiols during the ligand exchange process of PbS quantum dots, achieving a dual passivation mechanism of ionic and covalent types. The halogen provided by the halide salt can ionically compensate for anionic defects on the PbS quantum dot surface, constructing a stable inorganic interface; while the short-chain thiols form covalent coordination with Pb atoms through –SH groups, effectively repairing cation vacancies and surface dangling bonds, thereby achieving comprehensive defect passivation of PbS. Compared with the traditional single-ligand strategy using only halogens or short-chain thiols, this synergistic passivation method exhibits significant advantages in defect coverage, bonding stability, and electronic coupling. This preparation method significantly improves the structural stability of PbS quantum dot films, substantially reduces dark current, effectively suppresses noise levels, and further enhances response uniformity and signal-to-noise ratio. Simultaneously, the complex complex environment formed by the synergistic passivation of halogens and thiols facilitates the effective stripping of original long-chain ligands from the PbS surface, improving ligand replacement efficiency, reducing organic residues, and increasing the density and charge mobility of the PbS quantum dot film. In addition, the synergistic ligands simultaneously form a dense and stable interfacial coating layer on the surface of PbS quantum dots, effectively blocking the erosion of oxygen and water vapor in the environment. This avoids discontinuities in the reaction area or discontinuities in the interfacial structure on the surface of PbS quantum dots due to batch processing, and greatly improves the passivation integrity and uniformity.

[0049] 2) In the preparation method of the PbS quantum dot film of the present invention, short-chain thiols can replace the long-chain oleic acid ligands on the surface of PbS quantum dots, and the thiol group (-SH) of the short-chain thiols can react with the PbS quantum dots on the surface of PbS quantum dots. 2+ Stable coordination bonds are formed. However, the thiol groups of short-chain thiols are highly reactive and readily undergo self-polymerization in polar solvents (2RSH→RSS-R+H2), leading to thiol group inactivation and preventing ligand exchange. Ammonium acetate provides protection for short-chain thiols through weak interactions, and the NH4+ released from the dissociation of ammonium acetate... + It has weak acidity and can form weak hydrogen bonds with thiol groups (NH4+). + …HS-R), reducing the polarity of the SH bond and inhibiting its tendency for dehydrogenation self-polymerization. If ammonium acetate is not used, a large amount of short-chain thiols will be converted into inactive disulfides (RSSR), resulting in insufficient ligand exchange. This leaves a large amount of long-chain oleic acid on the surface of PbS quantum dots. These long-chain oleic acids will form spatial barriers between PbS quantum dots, which will not only increase the charge transport resistance, but also cause PbS quantum dots to aggregate in subsequent PbS quantum dot films, destroying the electrical continuity and optical consistency of the PbS quantum dot film.

[0050] 3) In the preparation method of the PbS quantum dot film of the present invention, ammonium acetate can be dissociated in a polar solvent. The ammonium ion of ammonium acetate can act as a phase transfer catalyst. The ammonium ion can form ion pairs with halide ions, reducing the energy barrier for halide ions to enter the interface between the nonpolar solvent and the polar solvent from the polar solvent, thereby promoting the halide ions to approach and adsorb onto the surface of the PbS quantum dots more effectively, and completing the replacement of the oleic acid ligand.

[0051] During the dynamic process of ligand exchange, if the original oleic acid ligand is stripped from the PbS quantum dot surface before the new halogen / thiol ligand has fully bonded, a large number of uncoordinated lead atoms will be exposed on the PbS quantum dot surface, making it extremely unstable and prone to aggregation or degradation. The acetate ion of ammonium acetate can act as an L-type ligand (Lewis base), with its lone pair of electrons on its oxygen atom, enabling coordination with the electron-deficient lead sites on the PbS quantum dot surface. This bonding is reversible and relatively weak, acting as a temporary occupant, temporarily stabilizing the exposed PbS quantum dot surface and creating conditions for the subsequent orderly bonding of halogen and thiol ligands to the PbS quantum dot.

[0052] The binding of short-chain thiols to lead atoms on the surface of PbS quantum dots is actually the coordination of the thiolate anions formed after deprotonation with lead. Acetate ions act as Brønsted bases (proton acceptors) in this process, abstracting protons from the short-chain thiols and converting them into more reactive thiolate anions. These thiolate anions are stronger nucleophiles, capable of attacking and bonding to lead atoms on the PbS quantum dot surface more quickly and firmly, thus significantly improving the efficiency of ligand exchange and the coverage of thiols. Attached Figure Description

[0053] Figure 1 This is the absorption spectrum of the PbS quantum dot film prepared in Example 4, before and after treatment at 125°C for 24 hours. Figure 2 This is the absorption spectrum of the PbS quantum dot film prepared in Example 5 before and after treatment at 125°C for 24 hours. Figure 3 This is the absorption spectrum of the PbS quantum dot film prepared in Example 6 before and after treatment at 125°C for 24 hours. Figure 4 This is the absorption spectrum of the PbS quantum dot film prepared in Example 8 before and after treatment at 125°C for 24 hours. Figure 5 The absorption spectra of the PbS quantum dot film prepared in Comparative Example 1 are shown in the untreated state and after treatment at 125℃ for 24h. Figure 6 This is a process flow diagram of the preparation method of the present invention; Figure 7 The current density-voltage curves of the quantum dot infrared detector in Example 6 at the initial (0h) and 500h temperatures at 125°C are shown. Figure 8 The current density-voltage curves of the quantum dot infrared detector prepared in Example 7 at the initial (0h) and 500h temperatures at 125°C are shown. Figure 9 The current density-voltage curves of the quantum dot infrared detector prepared in Comparative Example 2 at the initial (0h) and 500h temperatures at 125℃ are shown. Figure 10 This is an initial (0h) imaging effect of the infrared shortwave imaging detector prepared in Example 6 in an environment of 85℃ / 85% relative humidity; Figure 11 This is an image showing the imaging effect of the infrared shortwave imaging detector prepared in Example 6 after aging for 100 hours in an environment of 85℃ / 85% relative humidity. Detailed Implementation

[0054] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0055] Example 1 The method for preparing PbS quantum dot thin films includes the following steps: 1) Dissolve the PbS quantum dot solid coated with oleic acid in a nonpolar solvent to form a first solution. The nonpolar solvent is n-octane, and the mass concentration of the PbS quantum dot solution coated with oleic acid is 5 mg / mL.

[0056] 2) Dissolve the halogen salt, ammonium acetate, and short-chain thiol in a polar solvent to form a second solution, wherein the polar solvent is N,N-dimethylformamide, the short-chain thiol is selected from 1,3-propanedithiol, the halogen salt is selected from CdCl2, the molar concentration of the halogen salt is 100 mmol / L, the molar concentration of the ammonium acetate is 50 mmol / L, and the molar concentration of the short-chain thiol is 100 mmol / L.

[0057] 3) The first solution and the second solution are mixed to form a mixed solution. After the mixed solution is allowed to stand, it separates into an upper layer and a lower layer. The upper layer is removed, and the lower layer is centrifuged. The precipitate after centrifugation is dried to obtain PbS quantum dot solid powder. The volume ratio of the first solution to the second solution is 1:1.

[0058] 4) Dissolve the PbS quantum dot solid powder obtained in step 3) in a dispersant to obtain a dispersion. The mass concentration of PbS quantum dots in the dispersion is 200 mg / mL. Then, coat the dispersion onto a substrate and anneal it to form a PbS quantum dot film. The dispersant is composed of N,N-dimethylformamide and n-butylamine, and the volume ratio of N,N-dimethylformamide to n-butylamine is 1:4. The coating method is spin coating. The thickness of the PbS quantum dot film is 200 nm, the annealing temperature is 70 °C, and the annealing time is 25 min.

[0059] Steps 1) to 4) above are carried out under an inert atmosphere, wherein the inert atmosphere is selected from nitrogen.

[0060] The PbS quantum dot thin film was prepared using the method described above.

[0061] Optoelectronic devices, including the aforementioned PbS quantum dot thin film.

[0062] Example 2 The method for preparing PbS quantum dot thin films includes the following steps: 1) Dissolve the PbS quantum dot solid coated with oleic acid in a nonpolar solvent to form a first solution. The nonpolar solvent is n-octane, and the mass concentration of the PbS quantum dot solution coated with oleic acid is 20 mg / mL.

[0063] 2) Dissolve the halogen salt, ammonium acetate, and short-chain thiol in a polar solvent to form a second solution, wherein the polar solvent is N,N-dimethylformamide, the short-chain thiol is selected from 1,3-ethanedithiol, the halogen salt is selected from PbBr2, the molar concentration of the halogen salt is 280 mmol / L, the molar concentration of the ammonium acetate is 150 mmol / L, and the molar concentration of the short-chain thiol is 150 mmol / L.

[0064] 3) The first solution and the second solution are mixed to form a mixed solution. After the mixed solution is allowed to stand, it separates into an upper layer and a lower layer. The upper layer is removed, and the lower layer is centrifuged. The precipitate after centrifugation is dried to obtain PbS quantum dot solid powder. The volume ratio of the first solution to the second solution is 1:1.8.

[0065] 4) Dissolve the PbS quantum dot solid powder obtained in step 3) in a dispersant to obtain a dispersion. The mass concentration of PbS quantum dots in the dispersion is 600 mg / mL. Then, the dispersion is coated onto a substrate. After annealing, a PbS quantum dot film is formed. The dispersant is composed of N,N-dimethylformamide and n-butylamine, and the volume ratio of N,N-dimethylformamide to n-butylamine is 1:1. The coating method is selected from drop coating. The thickness of the PbS quantum dot film is 500 nm, the annealing temperature is 110 °C, and the annealing time is 10 min.

[0066] Steps 1) to 4) above are carried out under an inert atmosphere, which is selected from argon.

[0067] The PbS quantum dot thin film was prepared using the method described above.

[0068] Optoelectronic devices, including the aforementioned PbS quantum dot thin film.

[0069] Example 3 The method for preparing PbS quantum dot thin films includes the following steps: 1) Dissolve the PbS quantum dot solid coated with oleic acid in a nonpolar solvent to form a first solution. The nonpolar solvent is n-octane, and the mass concentration of the PbS quantum dot solution coated with oleic acid is 15 mg / mL.

[0070] 2) Dissolve the halogen salt, ammonium acetate, and short-chain thiol in a polar solvent to form a second solution, wherein the polar solvent is N,N-dimethylformamide, the short-chain thiol is selected from 1-propanethiol, the halogen salt is selected from CdI2, the molar concentration of the halogen salt is 400 mmol / L, the molar concentration of the ammonium acetate is 200 mmol / L, and the molar concentration of the short-chain thiol is 200 mmol / L.

[0071] 3) The first solution and the second solution are mixed to form a mixed solution. After the mixed solution is allowed to stand, it separates into an upper layer and a lower layer. The upper layer is removed, and the lower layer is centrifuged. The precipitate after centrifugation is dried to obtain PbS quantum dot solid powder. The volume ratio of the first solution to the second solution is 1:3.

[0072] 4) Dissolve the PbS quantum dot solid powder obtained in step 3) in a dispersant to obtain a dispersion. The mass concentration of PbS quantum dots in the dispersion is 400 mg / mL. Then, coat the dispersion onto a substrate. After annealing, the dispersion forms a PbS quantum dot film. The dispersant is composed of N,N-dimethylformamide and n-butylamine, and the volume ratio of N,N-dimethylformamide to n-butylamine is 1:2. The coating method is selected from blade coating. The thickness of the PbS quantum dot film is 400 nm, the annealing temperature is 95 °C, and the annealing time is 30 min.

[0073] Steps 1) to 4) above are carried out under an inert atmosphere, wherein the inert atmosphere is selected from nitrogen.

[0074] The PbS quantum dot thin film was prepared using the method described above.

[0075] Optoelectronic devices, including the aforementioned PbS quantum dot thin film.

[0076] Example 4 The method for preparing PbS quantum dot thin films includes the following steps: 1) Dissolve the PbS quantum dot solid coated with oleic acid in a nonpolar solvent to form a first solution. The nonpolar solvent is n-octane, and the mass concentration of the PbS quantum dot solution coated with oleic acid is 10 mg / mL.

[0077] 2) Dissolve the halogen salt, ammonium acetate, and short-chain thiol in a polar solvent to form a second solution, wherein the polar solvent is N,N-dimethylformamide, the short-chain thiol is selected from 1,3-propanedithiol, the halogen salt is selected from CdI2 and CdBr2, the molar concentration of CdI2 is 300 mmol / L, the molar concentration of CdBr2 is 150 mmol / L, the molar concentration of ammonium acetate is 100 mmol / L, and the molar concentration of short-chain thiol is 150 mmol / L.

[0078] 3) The first solution and the second solution are mixed to form a mixed solution. After the mixed solution is allowed to stand, it separates into an upper layer and a lower layer. The upper layer is removed, and the lower layer is centrifuged. The precipitate after centrifugation is dried to obtain PbS quantum dot solid powder. The volume ratio of the first solution to the second solution is 1:1.

[0079] 4) Dissolve the PbS quantum dot solid powder obtained in step 3) in a dispersant to obtain a dispersion. The mass concentration of PbS quantum dots in the dispersion is 400 mg / mL. Then, coat the dispersion onto a substrate. After annealing, the dispersion forms a PbS quantum dot film. The dispersant is composed of N,N-dimethylformamide and n-butylamine, and the volume ratio of N,N-dimethylformamide to n-butylamine is 1:2. The coating method is spin coating. The thickness of the PbS quantum dot film is 400 nm. The annealing temperature is 95 °C and the annealing time is 30 min.

[0080] Steps 1) to 4) above are carried out under an inert atmosphere, which is selected from nitrogen or argon.

[0081] The PbS quantum dot thin film was prepared using the method described above.

[0082] Optoelectronic devices, including the aforementioned PbS quantum dot thin film.

[0083] Example 5 The preparation method of PbS quantum dot thin film is basically similar to that of Example 4, except that 1,3-propanedithiol in step 2) of Example 4 is replaced with 1,3-ethanedithiol.

[0084] The PbS quantum dot thin film was prepared using the method described above.

[0085] Optoelectronic devices, including the aforementioned PbS quantum dot thin film.

[0086] Example 6 The preparation method of PbS quantum dot thin film is basically similar to that of Example 4, except that 1,3-propanedithiol in step 2) of Example 4 is replaced with 1-propanethiol.

[0087] The PbS quantum dot thin film was prepared using the method described above.

[0088] Optoelectronic devices, including the aforementioned PbS quantum dot thin film.

[0089] Example 7 The preparation method of PbS quantum dot thin film in this embodiment is basically similar to that in Example 4, except that the mass concentration of PbS quantum dots in step 4) of Example 4 is increased to 600 mg / mL.

[0090] The PbS quantum dot thin film was prepared using the method described above.

[0091] Optoelectronic devices, including the aforementioned PbS quantum dot thin film.

[0092] Example 8 The preparation method of PbS quantum dot thin film in this embodiment is basically similar to that in Example 4, except that CdI2 is replaced with PbI2 and CdBr2 is replaced with PbBr2.

[0093] The PbS quantum dot thin film was prepared using the method described above.

[0094] Optoelectronic devices, including the aforementioned PbS quantum dot thin film.

[0095] Comparative Example 1 The preparation method of PbS quantum dot thin films in this comparative example is basically similar to that in Example 4. However, compared to Example 4, 1,3-propanedithiol is omitted in step 2).

[0096] The PbS quantum dot thin film was prepared using the method described above.

[0097] Optoelectronic devices, including the aforementioned PbS quantum dot thin film.

[0098] Comparative Example 2 Comparative Example 2 involves stepwise ligand exchange between a halide salt and a short-chain thiol and PbS quantum dots.

[0099] The method for preparing PbS quantum dot thin films includes the following steps: 1) Dissolve the PbS quantum dot solid coated with oleic acid in a nonpolar solvent to form a first solution. The nonpolar solvent is n-octane, and the mass concentration of the PbS quantum dot solution coated with oleic acid is 10 mg / mL.

[0100] 2) Dissolve the halogen salt and ammonium acetate in a polar solvent to form a second solution, wherein the polar solvent is N,N-dimethylformamide, the halogen salt is selected from CdI2 and CdBr2, the molar concentration of CdI2 is 300 mmol / L, the molar concentration of CdBr2 is 150 mmol / L, and the molar concentration of ammonium acetate is 100 mmol / L.

[0101] 3) The first solution and the second solution are mixed to form a mixed solution. After the mixed solution is allowed to stand, it separates into an upper layer and a lower layer. The upper layer is removed, and then 150 mmol / L of 1,3-propanedithiol is added to the lower layer for ligand exchange. After the ligand exchange is completed, the mixture is centrifuged. The precipitate after centrifugation is dried to obtain PbS quantum dot solid powder. The volume ratio of the first solution to the second solution is 1:1. The short-chain thiol is selected from 1,3-propanedithiol, and the molar concentration of the short-chain thiol is 150 mmol / L.

[0102] 4) Dissolve the PbS quantum dot solid powder obtained in step 3) in a dispersant to obtain a dispersion. The mass concentration of PbS quantum dots in the dispersion is 400 mg / mL. Then, coat the dispersion onto a substrate. After annealing, the dispersion forms a PbS quantum dot film. The dispersant is composed of N,N-dimethylformamide and n-butylamine, and the volume ratio of N,N-dimethylformamide to n-butylamine is 1:2. The coating method is spin coating. The thickness of the PbS quantum dot film is 400 nm. The annealing temperature is 95 °C and the annealing time is 30 min.

[0103] Steps 1) to 4) above are carried out under an inert atmosphere, which is selected from nitrogen or argon.

[0104] The PbS quantum dot thin film was prepared using the method described above.

[0105] Optoelectronic devices, including the aforementioned PbS quantum dot thin film.

[0106] Performance testing PbS quantum dot films were prepared using typical examples 4-6, Example 8, and Comparative Example 1. These films were then subjected to untreated (initial) and aging treatments at 125°C for 24 hours to obtain samples for UV absorption testing. The samples were then characterized by absorption testing, and the results are as follows: Figures 1-5 As shown, the target PbS quantum dot film prepared in Comparative Example 1 without the addition of short-chain thiols initially exhibited a clear exciton absorption peak characteristic of quantum dots. However, after heating at 125°C for 24 hours, the absorption peak almost disappeared, indicating poor high-temperature stability of the PbS quantum dot film. Based on this, the PbS quantum dot films prepared with different short-chain thiols (Examples 4 (1,3-propanedithiol), 5 (1,3-ethanedithiol), and 6 (1-propanethiol)) still maintained their complete exciton absorption peaks after continuous treatment at 125°C for 24 hours, without significant peak broadening. The PbS quantum dot film prepared in Example 6 showed no significant change in the absorption peak shape after treatment, indicating that it has the best high-temperature stability among the existing examples. Furthermore, when CdX2 was replaced with PbX2 in the preparation of the PbS quantum dot film in Example 8, the exciton absorption peak of the PbS quantum dots remained intact after high-temperature treatment, with a slight blue shift.

[0107] The PbS quantum dot films prepared by the methods in the various embodiments of the present invention have high stability and can be used as the photosensitive layer of a quantum dot infrared detector.

[0108] The structure of the quantum dot infrared detector of the present invention, from bottom to top, consists of a bottom electrode layer, an electron blocking layer, a p-type layer, a photosensitive layer, an electron transport layer, a strong n-type layer, and a top electrode layer.

[0109] Figures 7-9 In the current density-voltage curve, 0h and 500h represent the processing time, 0h is the initial time, P1 represents the test point, dark represents the dark current part, and light represents the photocurrent part.

[0110] Reference Figure 7 In Example 6, the quantum dot infrared detector was continuously heated and aged at 125°C for 500 hours, and the turn-on voltage of the quantum dot infrared detector remained at a relatively normal level (-0.1V).

[0111] Based on this, the mass concentration of PbS quantum dots in the dispersion was adjusted (increased from 400 mg / mL to 600 mg / mL), such as... Figure 8 As shown, Example 7 exhibits excellent high-temperature stability.

[0112] Under the same conditions, the high-temperature stability of the quantum dot infrared detector prepared in Comparative Example 2 was tested, such as... Figure 9As shown, the results indicate that the quantum dot infrared detector prepared in Comparative Example 2 exhibits significant performance degradation after aging at 125℃ for 72 hours. This suggests that the stepwise treatment of the PbS quantum dot surface in Comparative Example 2 leads to discontinuities in the PbS quantum dot surface reaction region or interfacial structural breaks, resulting in incomplete passivation of the PbS quantum dot film surface, which further affects the stability of the PbS quantum dot film. Specifically, in the stepwise ligand exchange process of Comparative Example 2, the first step (halogen salt only) and the replacement of oleic acid ligands with halogen salts cannot achieve 100% coverage of all active sites. Intermediate state: Before the addition of thiols, the quantum dot surface, partially stripped of its original ligands but not completely covered by halogens, is in a highly unstable "naked" state, making it prone to aggregation or the formation of new surface defects. Step 2 (adding thiol): At this point, thiol is added. Since the surface state of the quantum dots has undergone irreversible changes (such as aggregation), thiol molecules are difficult to bind uniformly and effectively to all target sites, ultimately resulting in an uneven and defective passivation layer and incomplete passivation of the PbS quantum dot film surface.

[0113] As shown in Table 1, to further investigate the repeatability of the embodiments of the invention, repeated preparations were performed using Examples 6 and 7, with four samples prepared for each example. Experimental results, as shown in Tables 1 and 2 below, indicate that even after multiple tests, the quantum dot infrared detectors prepared based on Examples 6 and 7 still exhibit excellent consistency.

[0114] Table 1. Dark current and quantum efficiency of Example 6 Table 2. Dark current and quantum efficiency of Example 7 High-temperature and high-humidity stability verification of quantum dot infrared detectors The PbS quantum dot thin film prepared in Example 6 was applied to a quantum dot infrared detector. After encapsulation, it was placed in a high-temperature and high-humidity environment (temperature 85°C, relative humidity 85%) and operated continuously for 100 hours. Its infrared short-wave imaging capability remained clear and stable, without significant degradation or noise enhancement. Figure 10 and Figure 11 As shown in the figure, the results clearly demonstrate that the PbS quantum dot film prepared in Example 6 possesses excellent interfacial stability, antioxidant properties, and adaptability to humid and hot environments, far superior to traditional single-ligand passivated PbS quantum dots. The interfacial passivation structure synergistically constructed with halogens and thiols in this invention exhibits significant weather resistance advantages under extreme humid and hot conditions, providing more reliable material support for the practical application of infrared imaging systems outdoors or in extreme conditions.

[0115] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing PbS quantum dot thin films, characterized in that, Includes the following steps: 1) Dissolve the PbS quantum dot solid coated with oleic acid in a nonpolar solvent to form the first solution; 2) Dissolve the halogen salt, ammonium acetate and short-chain thiols in a polar solvent to form a second solution, wherein the short-chain thiols have 2 to 6 carbon atoms; 3) Mix the first solution with the second solution to form a mixed solution. After the mixed solution is allowed to stand, it separates into an upper layer and a lower layer. Remove the upper layer and then centrifuge the lower layer. The precipitate after centrifugation is dried to obtain PbS quantum dot solid powder. 4) Dissolve the PbS quantum dot solid powder obtained in step 3) in a dispersant to obtain a dispersion, coat the dispersion onto a substrate, and anneal it to form a PbS quantum dot film.

2. The method for preparing PbS quantum dot thin films according to claim 1, characterized in that, In step 1), the nonpolar solvent is n-octane; In step 2), the polar solvent is N,N-dimethylformamide.

3. The method for preparing PbS quantum dot thin films according to claim 1, characterized in that, In step 2), the short-chain thiol is selected from at least one of 1,3-propanedithiol, 1,3-ethanedithiol, and 1-propanethiol.

4. The method for preparing PbS quantum dot thin films according to claim 1, characterized in that, In step 2), the halogen salt is selected from at least one of CdX2 and PbX2, wherein X is Cl, Br or I.

5. The method for preparing PbS quantum dot thin films according to claim 1, characterized in that, Steps 1) to 4) are carried out under an inert atmosphere, which is selected from nitrogen or argon.

6. The method for preparing PbS quantum dot thin films according to claim 1, characterized in that, In the first solution, the mass concentration of the PbS quantum dot solution coated with oleic acid is 5 mg / mL to 20 mg / mL; In the second solution, the molar concentration of the halogen salt is 100 mmol / L to 400 mmol / L, the molar concentration of ammonium acetate is 50 mmol / L to 200 mmol / L, and the molar concentration of the short-chain thiol is 100 mmol / L to 200 mmol / L. In step 3), the volume ratio of the first solution to the second solution is 1:1 to 1:

3.

7. The method for preparing PbS quantum dot thin films according to claim 1, characterized in that, The mass concentration of PbS quantum dots in the dispersion ranges from 200 mg / mL to 600 mg / mL.

8. The method for preparing PbS quantum dot thin films according to claim 7, characterized in that, In step 4), the thickness of the PbS quantum dot film is 200nm~500nm.

9. The method for preparing PbS quantum dot thin films according to claim 8, characterized in that, In step 4), the annealing temperature is 70℃~110℃ and the annealing time is 10min~30min.

10. The method for preparing PbS quantum dot thin films according to claim 1, characterized in that, In step 4), the dispersant is composed of N,N-dimethylformamide and n-butylamine, and the volume ratio of N,N-dimethylformamide to n-butylamine is 1:4 to 1:

1.

11. The method for preparing PbS quantum dot thin films according to claim 1, characterized in that, In step 4), the coating method is selected from one of spin coating, drop coating, and blade coating.

12. A PbS quantum dot thin film, characterized in that, It is prepared by any one of the preparation methods according to claims 1 to 11.

13. An optoelectronic device, characterized in that, Including the PbS quantum dot thin film as described in claim 12.

14. The optoelectronic device according to claim 13, characterized in that, The optoelectronic device is a quantum dot infrared detector or a solar cell.

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