Colloidal quantum dots and methods of making the same

Abstract

The application relates to the technical field of quantum dots, and discloses a colloidal quantum dot and a preparation method thereof. The preparation method of the colloidal quantum dot comprises the following steps: providing a cesium-based precursor solution and a lead-based precursor solution; filtering the cesium-based precursor solution and the lead-based precursor solution respectively; providing isopropyl alcohol solvent and n-hexane solvent, mixing the isopropyl alcohol solvent, the n-hexane solvent and the filtered cesium-based precursor solution to form a pre-solution; injecting the filtered lead-based precursor solution into the pre-solution to form a mixed solution; performing first centrifugal treatment on the mixed solution; providing organic precursor solvent, dispersing the mixed solution after the first centrifugal treatment into the organic precursor solvent, and then performing second centrifugal treatment; providing low-polarity solvent, dispersing the mixed solution after the second centrifugal treatment into the low-polarity solvent, and obtaining the colloidal quantum dot. The colloidal quantum dot prepared by the method is also provided. The method avoids the problem that the existing thermal injection method is strict in temperature control.

Description

Technical Field

[0001] This invention relates to the field of quantum dot technology, and in particular to a colloidal quantum dot and its preparation method. Background Technology

[0002] Compared to traditional perovskite thin film materials, all-inorganic perovskite quantum dot materials, due to their unique organic surface ligand interconnection structure and nanoscale grains, not only possess excellent optoelectronic properties, but also exhibit better chemical and structural stability thanks to their inorganic chemical components and high surface energy.

[0003] However, most methods for synthesizing all-inorganic perovskite quantum dots involve hot injection. Since the reaction rate between metal ions and the halogen source is rapid at higher temperatures, a constant reaction temperature is required to obtain a uniform crystal structure. Therefore, using existing hot injection methods to synthesize all-inorganic perovskite quantum dot materials requires extremely strict control over temperature and environmental atmosphere. Furthermore, the photoelectric conversion efficiency of all-inorganic perovskite quantum dots is currently limited and needs further improvement and optimization. Therefore, there is an urgent need to find a novel method for preparing all-inorganic perovskite quantum dots to address these issues. Summary of the Invention

[0004] The purpose of this invention is to address the issues that the existing hot-injection synthesis process requires strict temperature control and that the photoelectric conversion efficiency of all-inorganic perovskite quantum dots is currently limited, necessitating further improvement and optimization. This invention provides a colloidal quantum dot and its preparation method.

[0005] To achieve the above objectives, the present invention specifically adopts the following technical solution:

[0006] A method for preparing colloidal quantum dots includes the following steps:

[0007] Cesium-based precursor solutions and lead-based precursor solutions are available.

[0008] The cesium-based precursor solution and the lead-based precursor solution were filtered separately.

[0009] Isopropanol solvent and n-hexane solvent are provided. The isopropanol solvent, n-hexane solvent and filtered cesium-based precursor solution are mixed to form a presol.

[0010] The filtered lead-based precursor solution is injected into the pre-solution to form a mixed solution;

[0011] The mixed solution was subjected to a first centrifugation treatment;

[0012] An organic precursor solvent is provided, and the mixed solution after the first centrifugation is dispersed in the organic precursor solvent and then subjected to a second centrifugation.

[0013] A low-polarity solvent is provided, and the mixed solution after a second centrifugation is dispersed into the low-polarity solvent to obtain colloidal quantum dots.

[0014] Optionally, cesium-based precursor solutions and lead-based precursor solutions are provided, including:

[0015] Cesium carbonate powder and lead iodide powder are available;

[0016] Propionic acid solvent is provided, and propionic acid solvent is used as the first solvent;

[0017] Provide n-butylamine solvent, isopropanol solvent and propionic acid solvent, and mix n-butylamine solvent, isopropanol solvent and propionic acid solvent to form a second solvent;

[0018] Cesium carbonate powder was dissolved in a first solvent to obtain a cesium-based precursor solution;

[0019] Lead iodide powder was dissolved in a second solvent to obtain a lead-based precursor solution.

[0020] Optional,

[0021] The concentration of the cesium-based precursor solution is 2 mol / L;

[0022] The concentration of the lead-based precursor solution is 0.6 mol / L.

[0023] Optionally, the volume ratio of the n-butylamine solvent, isopropanol solvent, and propionic acid solvent is 1:1:1.

[0024] Optionally, filtration of the cesium-based precursor solution and the lead-based precursor solution includes:

[0025] A polytetrafluoroethylene (PTFE) filter membrane with a pore size of 0.18–0.25 micrometers is provided to filter cesium-based precursor solutions and lead-based precursor solutions through the PTFE filter membrane.

[0026] Optionally, the volume ratio of isopropanol solvent, n-hexane solvent, filtered cesium-based precursor, and filtered lead-based precursor solution in the mixed solution is in the range of 1:9 to 1:12.

[0027] Optionally, the first centrifugation of the mixed solution includes:

[0028] When the mixed solution turns into brown flocculent matter, the mixed solution is subjected to a first centrifugation treatment, wherein the first centrifugation speed range is 5000-8000 rpm and the centrifugation time is 1-2 minutes.

[0029] Optionally, the organic precursor solution is a precursor solution containing a trioctylphosphine oxide organic group;

[0030] The second centrifugation process involves a centrifugation speed of 5000–8000 rpm and a centrifugation time of 1–2 minutes.

[0031] Optionally, the low-polarity solvent includes toluene or chlorobenzene solution.

[0032] To achieve the above objectives, the present invention specifically adopts the following technical solution: a colloidal quantum dot is also provided, which is prepared by the above-mentioned colloidal quantum dot preparation method.

[0033] Compared with the prior art, the advantages of the present invention are as follows:

[0034] 1. This invention proposes an innovative method for preparing colloidal quantum dots by reprecipitation of ligands in a mixed solvent with high dielectric constant. Compared with the traditional hot-injection method, the proposed method uses an environmentally friendly mixed solvent with a low boiling point and short-chain ligands with a high dielectric constant. On the one hand, it can control the synthesis temperature at room temperature without strict temperature and atmosphere control. On the other hand, it can enhance the dielectric shielding effect in perovskite quantum dots and weaken their dielectric confinement effect, thereby obtaining a smaller exciton binding energy.

[0035] Furthermore, the introduction of short-chain ligands can reduce the surface barrier of quantum dots caused by alkyl groups, enhance electrical coupling, and thus promote carrier transport between adjacent quantum dots, ultimately achieving high photoelectric conversion efficiency. Finally, the addition of high-formation-energy TOPO organic groups during the centrifugation and dispersion process of the final perovskite colloidal quantum dots can further enhance the interaction between alkyl chains and quantum dots, thereby improving the monodispersity of the colloidal quantum dots and providing support for subsequent device fabrication.

[0036] 2. The colloidal quantum dot provided by this invention is of high quality and high performance, and has superior advantages.

[0037] Attached image captions:

[0038] Figure 1 This is a first reference diagram for a method of preparing colloidal quantum dots provided by the present invention.

[0039] Figure 2 This is a second reference diagram for a method of preparing colloidal quantum dots provided by the present invention.

[0040] Figure 3 This is a third reference figure for a method of preparing colloidal quantum dots provided by the present invention.

[0041] Figure 4 This is a statistical diagram showing the size distribution of colloidal quantum dots in quantum dot solution 1 prepared in Example 1 of the present invention.

[0042] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0043] Therefore, the following detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. Detailed Implementation

[0044] Compared to traditional perovskite thin film materials, all-inorganic perovskite quantum dot materials, due to their unique organic surface ligand interconnection structure and nanoscale grains, not only possess excellent optoelectronic properties but also exhibit better chemical and structural stability thanks to their inorganic chemical components and high surface energy. Quantum dots specifically refer to semiconductor particles with nanoscale dimensions, typically between 2 and 10 nanometers, possessing quantum effect characteristics (such as quantized energy levels and size-dependent optical properties). They are called quantum dots because they exhibit a quantum confinement effect; that is, when the particle size is shrunk to the nanoscale, the movement of electrons and holes is restricted, thus exhibiting unique optoelectronic properties different from bulk materials.

[0045] However, most methods for synthesizing all-inorganic perovskite quantum dots are the hot-injection method.

[0046] The main process of the hot-injection method includes: first, preparing a perovskite precursor solution; heating the precursor solution to a certain temperature, and then rapidly injecting a metal source and a halide source into the solvent while heating; after the metal source and halide source are injected, the solution reacts rapidly to form perovskite crystals, thus forming quantum dots.

[0047] Because the reaction rate between metal ions and halogen sources is faster at higher temperatures, a constant reaction temperature needs to be maintained to obtain a uniform crystal structure. Furthermore, since the synthesis of perovskite quantum dots is typically very sensitive to oxygen and moisture, the environmental atmosphere must be strictly controlled to prevent material degradation.

[0048] Therefore, the synthesis of all-inorganic perovskite quantum dots using the existing hot-injection method requires extremely strict control over temperature and environmental atmosphere. Furthermore, the photoelectric conversion efficiency of all-inorganic perovskite quantum dots is currently limited and needs further improvement and optimization. To address these issues, a novel method for preparing all-inorganic perovskite quantum dots is urgently needed.

[0049] Please see Figure 1 The first embodiment of the present invention provides a method for preparing colloidal quantum dots, comprising the following steps:

[0050] S1. Provide cesium-based precursor solutions and lead-based precursor solutions;

[0051] S2. Filter the cesium-based precursor solution and the lead-based precursor solution respectively;

[0052] S3. Provide isopropanol solvent and n-hexane solvent, and mix isopropanol solvent, n-hexane solvent and filtered cesium-based precursor solution to form a pre-solution;

[0053] S4. Inject the filtered lead-based precursor solution into the pre-solution to form a mixed solution;

[0054] S5. Perform the first centrifugation on the mixed solution;

[0055] S6. Provide an organic precursor solvent, disperse the mixed solution after the first centrifugation into the organic precursor solvent, and then perform a second centrifugation.

[0056] S7. Provide a low-polarity solvent, and disperse the mixed solution after the second centrifugation into the low-polarity solvent to obtain colloidal quantum dots.

[0057] Understandably, in this embodiment, cesium-based (Cs) materials are first prepared using a pre-defined method. + ) and lead-based (Pb) 2+ Precursor solution of cesium (Cs). + ) and lead-based (Pb) 2+ The precursor solution of cesium ions (Cs) is the basis for the formation of perovskite quantum dots. + ) and lead ions (Pb 2+ These react with halide ions in solution to form the basis of the perovskite structure. They are the main source of the reaction during synthesis and ensure that the final perovskite quantum dots have a high-quality crystal structure.

[0058] Furthermore, filtration removes large particulate impurities from the cesium-based and lead-based precursor solutions, ensuring the purity and homogeneity of the solution. It should be understood that the mixed solution formed in this embodiment achieves the adjustment of ligands and solvents with high dielectric constants. Solvents with high dielectric constants (e.g., propionic acid, isopropanol, etc.) help enhance the electrical shielding effect between quantum dots, reduce the interaction between charges, and thus lower the exciton binding energy.

[0059] Furthermore, the first centrifugation separates the formed quantum dots, and an organic precursor solution is added before the second centrifugation. The organic groups of the organic precursor help to further enhance the interaction between the alkyl chain and the quantum dots, thereby improving the monodispersity of the colloidal quantum dots.

[0060] Furthermore, in this embodiment, a low-polarity solvent is provided, containing short-chain ligands, specifically shorter alkyl groups or low-polarity organic groups. The introduction of these short-chain ligands reduces the surface barrier caused by longer alkyl chains, thereby improving the conductivity and photoelectric conversion efficiency of the quantum dots. Additionally, a second centrifugation further purifies the quantum dots, removing excess solvent and byproducts, ultimately ensuring higher purity quantum dots.

[0061] It should be understood that this embodiment innovatively proposes a method for preparing colloidal quantum dots by reprecipitation of high dielectric constant mixed solvent ligands. Compared with the traditional hot injection method, the proposed method uses environmentally friendly mixed solvents with low boiling points and short-chain ligands with high dielectric constants. On the one hand, it can control the synthesis temperature at room temperature without strict temperature and atmosphere control; on the other hand, it can enhance the dielectric shielding effect in perovskite quantum dots and weaken their dielectric confinement effect, thereby obtaining a smaller exciton binding energy.

[0062] It should be noted that the colloidal quantum dots used in this embodiment are all-inorganic perovskite quantum dots, which will not be elaborated on further below.

[0063] Specifically, please refer to Figure 2 In step S1 above, providing the cesium-based precursor solution and the lead-based precursor solution includes:

[0064] S11 provides cesium carbonate powder and lead iodide powder;

[0065] S12, providing propionic acid solvent, using propionic acid solvent as the first solvent;

[0066] S13 provides n-butylamine solvent, isopropanol solvent and propionic acid solvent, and mixes n-butylamine solvent, isopropanol solvent and propionic acid solvent to form a second solvent;

[0067] S14, Cesium carbonate powder is dissolved in a first solvent to obtain a cesium-based precursor solution;

[0068] S15, lead iodide powder is dissolved in a second solvent to obtain a lead-based precursor solution.

[0069] It should be understood that the main chemical raw materials in this example are cesium carbonate (Cs₂CO₃) and lead iodide (PbI₂). These two chemicals are the basic precursors for the synthesis of perovskite quantum dots. Cesium carbonate provides cesium ions (Cs₂CO₃, Cs₂O ... + Lead iodide provides lead ions (Pb). 2 + These two metal ions can combine with iodide ions (I-) in lead iodide (PbI2) to form key components of the perovskite structure.

[0070] Specifically, in step S12, propionic acid (PrAc) is used as the solvent in the first solvent, mainly to dissolve cesium carbonate powder. The polarity of propionic acid can effectively dissolve cesium carbonate and is compatible with the subsequent solvent system, providing a suitable solvent environment for the preparation of the precursor solution.

[0071] Furthermore, in steps S14 and S15: n-Butylamine (BuAm) helps improve the solubility of the lead compound and helps adjust the pH of the solution. Isopropanol (IPA) provides a certain degree of polarity, helping to dissolve the lead source and optimize the stability of the solution. Propionic acid (PrAc), as a solvent for dissolving cesium carbonate, is also present as a component of the solvent in this solution.

[0072] The concentration of the cesium-based precursor solution is 2 mol / L; the concentration of the lead-based precursor solution is 0.6 mol / L.

[0073] In step S13 above, the volume ratio of the n-butylamine solvent, isopropanol solvent, and propionic acid solvent is 1:1:1. The purity of the n-butylamine solvent, isopropanol solvent, and propionic acid solvent is greater than 99%.

[0074] By mixing n-butylamine solution, isopropanol solvent, and propionic acid solvent in a volume ratio of 1:1:1 to form a second solution, the solubility and reactivity of the second solution can be optimized by specifically controlling the volume ratio of the three solutions, which helps to dissolve lead iodide powder.

[0075] Furthermore, in steps S14 and S15, the key components for forming the perovskite structure are respectively formed in the obtained cesium-based precursor solution and lead-based precursor solution. It should be understood that the cesium-based precursor solution contains cesium ions (Cs). + The lead-based precursor solution contains lead ions (Pb). 2+ ) and iodide ions (I - ).

[0076] Understandably, in this embodiment, cesium-based and lead-based precursor solutions were prepared, and these precursor solutions will react to form the core structure of perovskite quantum dots in the subsequent synthesis process. Different solvents were used in the precursor solution synthesis steps to optimize solubility, stability, and reaction conditions, thereby providing an ideal chemical environment for the synthesis of perovskite quantum dots. These solutions play a crucial role in subsequent mixing and reaction, ensuring the quality and performance of the perovskite quantum dots.

[0077] Specifically, the filtration treatment of cesium-based precursor solutions and lead-based precursor solutions includes:

[0078] A polytetrafluoroethylene (PTFE) filter membrane with a pore size of 0.18–0.25 micrometers is provided to filter cesium-based precursor solutions and lead-based precursor solutions through the PTFE filter membrane.

[0079] It should be understood that the function of the polytetrafluoroethylene (PTFE) filter membrane is to remove large particulate impurities from the precursor solution, ensuring the purity and homogeneity of the solution. Filtration removes any particulate matter and impurities that may be present in the solution, preventing them from adversely affecting subsequent quantum dot synthesis.

[0080] Specifically, the volume ratio of isopropanol solvent, n-hexane solvent, filtered cesium-based precursor, and filtered lead-based precursor solution in the mixed solution ranges from 1:9 to 1:12. It should be understood that the mixed solution is obtained by controlling the ratio of isopropanol solvent, n-hexane solvent, cesium-based precursor, and lead-based precursor. The high dielectric constant of the solvent in the mixed solution helps to enhance the electrical shielding effect between quantum dots, reduce the interaction between charges, and thus lower the exciton binding energy.

[0081] Specifically, in step S5 above, the first centrifugation of the mixed solution includes:

[0082] When the mixed solution turns into brown flocculent matter, it is subjected to a first centrifugation treatment. The first centrifugation speed range is 5000-8000 rpm, and the centrifugation time is 1-2 minutes.

[0083] It should be understood that the liquid turning into a brown flocculent substance indicates that quantum dots have begun to form. The first centrifugation is to remove unreacted solvent and other potentially dissolved substances, while simultaneously separating the formed quantum dots.

[0084] Furthermore, after the first centrifugation, the mixed solution can be dissolved in an organic precursor solution for a second centrifugation. The organic precursor solution contains a trioctylphosphine oxide organic group. It should be understood that adding a high-formation-energy TOPO organic group during the final centrifugation and dispersion process of the perovskite colloidal quantum dots can further enhance the interaction between the alkyl chain and the quantum dots, thereby improving the monodispersity of the colloidal quantum dots and providing support for subsequent device fabrication.

[0085] Specifically, the second centrifugation process involves a centrifugation speed of 5000–8000 rpm for 1–2 minutes. It should be understood that this second centrifugation further purifies the quantum dots, removing excess solvent and byproducts to ensure higher purity quantum dots.

[0086] Furthermore, in this embodiment, the low-polarity solvent includes toluene or chlorobenzene solution. Specifically, the mixed solution after two centrifugations is redispersed in a low-polarity solvent. Specifically, the dispersion process can be carried out by mechanical stirring or ultrasonic dispersion. Colloidal quantum dots are finally obtained. It should be understood that this invention addresses the problems existing in the above-mentioned all-inorganic perovskite quantum dots by developing a method for preparing colloidal quantum dots through the redeposition of ligands in a mixed solvent with high dielectric constant. On the one hand, the dielectric constant of the ligands in the mixed solvent is controlled to reduce the exciton binding energy of the material; on the other hand, the alkyl chains of the ligands in the mixed solvent are optimized to promote electrical coupling and carrier transport, thereby forming high-quality and high-performance colloidal quantum dots.

[0087] This invention also provides a colloidal quantum dot, which is prepared using the colloidal quantum dot preparation method described above. The colloidal quantum dot provided in this embodiment has the same beneficial effects as the colloidal quantum dot preparation method, therefore, it will not be elaborated upon further here.

[0088] Example 1

[0089] In this embodiment, please refer to Figure 1 , Figure 2 and Figure 3 The specific operation is as follows:

[0090] At room temperature, cesium carbonate (Cs₂CO₃) powder was dissolved in propionic acid (PrAc), and lead iodide (PbI₂) powder was dissolved in a mixed solvent of n-butylamine (BuAm), isopropanol (IPA), and propionic acid (PrAc) (volume ratio 1:1:1). The mixture was thoroughly mixed until the solution became clear, thus yielding cesium-based (Cs⁺) and lead-based (PbI₂) compounds. 2+ Precursor solution;

[0091] The precursor solutions were filtered using polytetrafluoroethylene (PTFE) membranes with a pore size of 0.22 micrometers; and Pb 2+ The precursor solution was rapidly injected into a mixed solution containing Cs+ precursor solution, isopropanol (IPA), and n-hexane (HEX). After the solution turned into a brown flocculent precipitate (within seconds), residual solvent was removed by centrifugation at 6000 rpm for 1 minute.

[0092] The quantum dots after centrifugation were redispersed in a precursor containing trioctylphosphine oxide (TOPO) organic groups and centrifuged a second time at 6000 rpm for 1 minute.

[0093] The centrifuged quantum dots were dispersed again in a low-polarity solvent such as toluene or chlorobenzene and mixed thoroughly to form a high-quality all-inorganic perovskite quantum dot solution 1.

[0094] Experimental Example 1: Statistical analysis of the size distribution of quantum dot solution 1 prepared in Example 1.

[0095] 1.1 Test Operation

[0096] The size distribution of quantum dot solution 1 prepared in Example 1 was statistically analyzed using transmission electron microscopy. The size distribution statistical graph is shown below. Figure 4 .

[0097] 1.2 Results Analysis

[0098] See Figure 4 It can be seen that the average size of the quantum dot solution 1 prepared in Example 1 is 7.92 nm. Colloidal quantum dots have high monodispersity and excellent performance.

[0099] The foregoing has provided a detailed description of a method for preparing colloidal quantum dots and the colloidal quantum dots themselves, as disclosed in the embodiments of the present invention. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention. Any modifications, equivalent substitutions, and improvements made within the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing colloidal quantum dots, characterized in that, Includes the following steps: A cesium-based precursor solution and a lead-based precursor solution are provided, wherein the cesium-based precursor solution is obtained by dissolving cesium carbonate powder in propionic acid as a first solvent, and the lead-based precursor solution is obtained by dissolving lead iodide powder in a second solvent formed by mixing n-butylamine, isopropanol and propionic acid in a volume ratio of 1:1:

1. The cesium-based precursor solution and the lead-based precursor solution were filtered using polytetrafluoroethylene filter membranes with pore sizes of 0.18–0.25 micrometers, respectively. Isopropanol solvent, n-hexane solvent, and the filtered cesium-based precursor solution are mixed to form a pre-solution, wherein the volume ratio of isopropanol solvent to n-hexane solvent is 1:9 to 1:12; the filtered lead-based precursor solution is injected into the pre-solution to form a mixed solution; when the mixed solution turns into brown flocculent matter, it is subjected to a first centrifugation treatment at a speed of 5000 to 8000 rpm for 1 to 2 minutes; An organic precursor solvent containing a trioctylphosphine oxide organic group is provided. The precipitate after the first centrifugation is dispersed in the organic precursor solvent, followed by a second centrifugation at a speed of 5000-8000 rpm for 1-2 minutes. A low-polarity solvent is provided to disperse the precipitate after the second centrifugation process into the low-polarity solvent to obtain colloidal quantum dots.

2. The method for preparing colloidal quantum dots as described in claim 1, characterized in that, The concentration of the cesium-based precursor solution is 2 mol / L; The concentration of the lead-based precursor solution is 0.6 mol / L.

3. The method for preparing colloidal quantum dots as described in claim 1, characterized in that, The low-polarity solvent includes toluene or chlorobenzene solution.

4. A colloidal quantum dot, characterized in that, The colloidal quantum dots are prepared using the colloidal quantum dot preparation method as described in any one of claims 1-3.

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