Preparation method of perovskite quantum dot with polyfluorinated passivation layer

Abstract

The invention relates to a preparation method of a perovskite quantum dot with a multi-fluorine passivation layer. The preparation method comprises the following steps: providing a monovalent cation precursor containing one or more of cesium, formamidine, methyl ammonium, rubidium and gallium; providing a lead source precursor containing a halogen element; providing a B-site cation doped precursor containing one or more of tin, copper, strontium, barium, zinc and calcium; a poor solvent containing fluorine ions is provided; respectively adding the monovalent cation precursor, the lead source precursor and the B-site cation doped precursor into a carrier solvent for dissolving and stirring treatment to obtain a perovskite precursor solution; and injecting the perovskite precursor solution into a poor solvent containing fluorine ions, carrying out a stirring reaction, and carrying out centrifugal purification to obtain the perovskite quantum dots. According to the method, the perovskite quantum dots and the multi-fluorine common passivation layer are synthesized through a one-step method, and the multi-fluorine common passivation layer not only can coat the perovskite quantum dots, but also can effectively passivate surface defects of the perovskite quantum dots.

Description

Technical Field

[0001] The present invention belongs to the field of perovskite quantum dot preparation methods, and in particular relates to a perovskite quantum dot preparation method with a polyfluoride passivation layer. Background Art

[0002] In recent years, perovskite quantum dots (PQDs), with their unique properties such as full-band wavelength tunability, narrow emission wavelengths, and ease of synthesis, have attracted widespread attention and have become a candidate material for high-efficiency photoelectric conversion devices such as solar cells, photodetectors, LEDs, display technologies, and bioimaging. However, their inherent structural instability can easily lead to their decomposition and failure in humid and high-temperature environments, which in turn reduces the PQDs' fluorescence efficiency (PLQY) and stability, hindering their application development.

[0003] To further improve the PLQY and stability of perovskite quantum dots (PQDs) to meet the needs of lighting and display applications, effective passivation and encapsulation of PQDs is a feasible approach. Currently, the passivation of PQDs typically uses long-chain organic ligands, such as Lewis base organic compounds like oleic acid and oleylamine, to passivate the perovskite surface. This is to passivate the surface defects of the PQDs and improve the PQY and stability of the PQDs. However, these organic compounds are not stable in high-temperature and high-humidity environments and are prone to falling off, losing their passivation effect.

[0004] Some current patents (publication numbers CN110734758A and CN115772401A) employ the collapse of micro- or mesoporous templates (mesoporous silica, molecular sieves) to encapsulate perovskite quantum dots. However, these encapsulation structures fail to effectively passivate the perovskite nanocrystal surface while simultaneously encapsulating it, resulting in the presence of numerous surface defects. These defects can lead to a decrease in the fluorescence intensity of the perovskite nanocrystals under high temperatures or light exposure, thus requiring further improvement. Summary of the Invention

[0005] This paper proposes a method for preparing perovskite quantum dots with a polyfluoride passivation layer. This method involves a simple one-step synthesis of perovskite quantum dots and a polyfluoride co-passivation layer. This polyfluoride co-passivation layer not only coats the perovskite quantum dots but also effectively passivates surface defects, resulting in the prepared perovskite quantum dots with high PLQY and high stability.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] A method for preparing perovskite quantum dots with a polyfluoride passivation layer comprises the following steps:

[0008] Providing a monovalent cation precursor containing one or more of cesium (Cs), formamidine (FA), methylammonium (MA), rubidium (Rb), and gallium (GA);

[0009] Providing a lead source precursor containing a halogen element;

[0010] Provide a B-site cation doping precursor containing one or more of tin (Sn), copper (Cu), strontium (Sr), barium (Ba), zinc (Zn), and calcium (Ca);

[0011] providing a poor solvent containing fluoride ions;

[0012] The monovalent cation precursor, the lead source precursor and the B-site cation doping precursor are respectively added into a carrier solvent for dissolution and stirring to obtain a perovskite precursor solution;

[0013] The perovskite precursor solution is injected into a poor solvent containing fluoride ions for stirring reaction, and the perovskite quantum dots with a polyfluoride common passivation layer are obtained after centrifugal purification.

[0014] In the above description, poor solvents are common knowledge in the fields of chemistry and materials, such as toluene, octane, hexane, etc. The polarity difference between the poor solvent and the carrier solvent is large. The present invention utilizes a ligand-assisted reprecipitation method to synthesize perovskite quantum dots. The precursor of the target material is first dissolved in a carrier solvent (such as DMSO, DMF, etc.) to form a uniform solution. It is then injected into a poor solvent (with a polarity significantly different from that of the precursor solvent). The solubility of the precursor material is reduced by the change in solvent polarity, triggering the nucleation and precipitation of quantum dot molecules and the growth of quantum dots.

[0015] In the present invention, after the perovskite quantum dots are nucleated, the X-site halogen anions and the insufficiently coordinated B-site cations on the surface first coordinate with the fluoride ions in the poor solvent, and an anion exchange reaction occurs simultaneously to epitaxially generate a multi-component fluoride shell. The multi-component fluoride shell can not only modify and passivate the surface defects of the perovskite quantum dots but also form a dense coating layer to protect the perovskite quantum dot core, ensuring that the perovskite quantum dots can stably emit light in high-light, high-heat, and high-humidity environmental conditions.

[0016] Furthermore, the polyfluorinated common passivation layer includes at least two of lead fluoride, tin fluoride, copper fluoride, strontium fluoride, barium fluoride, zinc fluoride and calcium fluoride.

[0017] Further, the monovalent cation precursor includes one or more of methylammonium halide, methylammonium acetate (MA-), cesium oleate, cesium halide, formamidine acetate, formamidine hydrohalide, gallium halide and rubidium halide;

[0018] The lead source precursor containing halogen elements is lead halide;

[0019] The B-site cation doping precursor is at least one of tin halide, copper halide, strontium halide, barium halide, zinc halide, and calcium halide.

[0020] Furthermore, the preparation method of the poor solvent containing fluoride ions comprises the following steps:

[0021] A fluoride-containing compound is dissolved in a poor solvent, wherein the fluoride-containing compound comprises at least one of ammonium fluoride, ammonium bifluoride, potassium fluoride, sodium fluoride, cesium fluoride, and didecyldimethylammonium fluoride (DDAF).

[0022] Furthermore, the preparation method can be carried out at normal temperature or room temperature.

[0023] Furthermore, the carrier solvent includes at least one of dimethylformamide (DMF), dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), toluene, and tetrahydrofuran (THF).

[0024] Furthermore, the synthesis of the perovskite quantum dots is carried out simultaneously with the formation of the polyfluorinated common passivation layer.

[0025] Furthermore, the lead source precursor and the B-site cation doping precursor together constitute a B-site metal cation precursor;

[0026] The molar ratio of the B-site metal cation precursor to the monovalent cation precursor is greater than 1:1.

[0027] Furthermore, the molar amount of fluoride ions in the poor solvent is greater than (the molar amount of the B-site metal cation precursor minus the molar amount of the monovalent cation precursor), thereby providing excess fluoride ions to the reaction system.

[0028] The present invention essentially provides a B-site metal cation precursor in excess of that required for synthesizing perovskite quantum dots, enabling subsequent reaction with fluoride ions in a poor solvent to form a polyfluorinated common passivation layer. This polyfluorinated common passivation layer, as a film, coats the surface of the perovskite quantum dots, providing passivation, reducing surface defects, and improving the stability and optical properties of the quantum dots.

[0029] Furthermore, in a solution environment, excess fluoride ions exchange with halogen anions in perovskite quantum dots and coordinate with B-site cations to form a polyfluoride common passivation layer;

[0030] The polyfluoride common passivation layer encapsulates the perovskite quantum dots to form a core-shell structure.

[0031] With the gradual formation of perovskite quantum dots, the active sites on its surface provide sites for the formation of a multi-fluorine co-passivation layer (such as lead vacancies, halogen exchange, F ion coordination provided by B-site metal), and the formation of a multi-fluorine co-passivation layer further stabilizes the structure of the perovskite quantum dots, preventing aggregation or degradation, thereby improving the performance of the quantum dots.

[0032] For perovskite quantum dots with an ABX3 structure, B-site metal cations and halogen atoms are located outside the perovskite structure, and the maximum coordination number forms an octahedron, while in this system, excess fluoride ions are provided, which have the following effects:

[0033] (1) Fluoride ions are used to modify the insufficient lead coordination on the surface of perovskite: F ions form lead fluoride with lead vacancies on the surface of perovskite quantum dots.

[0034] (2) Fluoride ions are used for halogen anion exchange: F ions undergo halogen exchange with halogen X located at the apex of the Pb-X octahedron to form Pb-F, and ultimately form a Pb-F shell layer.

[0035] (3) Fluoride ions and B-site doped metal cations (such as lead, strontium, barium, etc.) form multiple fluorides.

[0036] The above-mentioned co-effects form a multi-fluorine co-passivation layer.

[0037] Advantages of the present application: The present application first forms a B-site component doped perovskite quantum dot in the reaction, and then generates a multi-fluoride shell layer with the B-site cations (such as lead, strontium, barium, etc.) in the perovskite structure through fluoride ions in the solution environment, passivating and coating the defects of the perovskite quantum dots. The principle is to use fluoride ions to exchange with anions in perovskite and coordinate with B-site cations (such as lead, strontium, barium, etc.) to form a multi-fluoride co-coated shell layer to passivate the perovskite surface and Pb vacancies. Only one simple operation can obtain high-quality perovskite quantum dots with high PLQY and high stability after fluorine passivation. The multi-component fluorine layer passivated quantum dot material prepared by the present application has the advantages of simple preparation process, high repeatability, wide adjustment range, high luminous efficiency, and good photo-thermal stability. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 XRD pattern of the product obtained in Example 1 of the present application;

[0039] Figure 2 XRD pattern of the product obtained in Comparative Example 1 of the present application;

[0040] Figure 3 XRD pattern of the product obtained in Comparative Example 2 of the present application. DETAILED DESCRIPTION

[0041] To make the purpose, technical solution and effect of the present invention clearer and more specific, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0042] Example 1:

[0043] Step 1: Mix 125 mg (1 mmol) of formamidine hydrobromide (FABr), 367 mg (1 mmol) of lead bromide, 25 mg (0.1 mmol) of strontium bromide, 15 mg (0.05 mmol) of barium bromide, and 10 mg (0.05 mmol) of calcium bromide with 3 mL of N,N-dimethylformamide (DMF), 750 μL of hexanoic acid, and 200 uL of n-octylamine and stir until dissolved. The stirring time is 1 h to obtain a perovskite quantum dot precursor solution.

[0044] Step 2: Add 1 ml of didecyldimethylammonium fluoride (DDAF) (concentration 1 mmol / ml) to 16 mL of toluene solvent, mix and stir for 1 hour to obtain a toluene solution of DDAF.

[0045] Step 3: Take 2 mL of the precursor obtained in step 1 and inject it into the toluene solution of DDAF in step 2 to obtain perovskite quantum dots, then stir for 30 minutes, and then centrifuge and purify to obtain the target product.

[0046] Experimental Analysis: The fluorescence quantum yield (PLQY) of the treated powder was measured. As shown in Table 1, the PLQY for this sample was 98.5%. By comparison, the PLQY for the perovskite quantum dots (QDs) treated with fluoride ions to form a single fluoride shell, as described in Comparative Example 1, was 85.3%, and the PLQY for the untreated B-site cation-doped QDs, as described in Comparative Example 2, was 75.9%. This improvement in PLQY demonstrates that the fluoride shell formed by the fluoride ion treatment of the multi-component B-site perovskite not only better than that of the untreated perovskite, but also more densely packed than the shell formed by the fluoride ion treatment of the single-component B-site perovskite, resulting in superior passivation and coating.

[0047] The stability of the powder after the above treatment was tested in a strong blue light environment. See Table 1 for details. 2 After continuous irradiation with blue light (450nm) for 100 hours, the luminescence intensity of the quantum dots can maintain 96% of the original intensity. The luminescence intensity of the perovskite quantum dots provided in Comparative Example 1, which have only been treated with fluoride ions to form a single fluoride shell, can maintain 86% of the original intensity. The luminescence intensity of the perovskite quantum dots provided in Comparative Example 2, which have not been treated with any B-site cations, can maintain 52% of the original intensity. The blue light stability test proves that the shell formed by the fluoride ion treatment of the multi-component B-site perovskite has higher photostability.

[0048] Comprehensive fluorescence quantum yield and blue light stability test data demonstrate that the fluoride shell formed by fluoride ion treatment of multi-component B-site perovskites improves both PLQY and photostability. XRD data also demonstrates that the crystallinity of the examples is significantly improved compared to the comparative examples. The relationship between PLQY and crystallinity is: high crystallinity → low defect density → suppression of non-radiative recombination → increased radiative recombination efficiency → high PLQY. Therefore, the increased crystallinity demonstrated by the XRD data of the present invention further demonstrates improved material stability (e.g., resistance to light and heat).

[0049] Example 2:

[0050] The difference from Example 1 is that formamidine hydrobromide (FABr) in step 1 is replaced with an equal molar amount of cesium bromide, and the rest are the same to prepare CsPbBr3 perovskite quantum dots.

[0051] Example 3:

[0052] The difference from Example 1 is that formamidine hydrobromide (FABr) in step 1 is replaced with an equal molar amount of methylammonium bromide, and the rest are the same to prepare MAPbBr3 perovskite quantum dots.

[0053] Comparative Example 1:

[0054] The difference from Example 1 is that: only a lead monofluoride shell is provided, and the perovskite quantum dots do not have B-site metal doping.

[0055] Step 1: Mix 125 mg (1 mmol) of formamidine hydrobromide (FABr), 440 mg (1.2 mmol) of lead bromide, 3 mL of N,N-dimethylformamide (DMF), 750 μL of hexanoic acid, and 200 μL of n-octylamine and stir until dissolved. The stirring time is 1 hour to obtain a perovskite quantum dot precursor solution.

[0056] Step 2: Add 1 ml of didecyldimethylammonium fluoride (DDAF) (concentration 1 mmol / ml) to 16 mL of toluene solvent, mix and stir for 1 hour to obtain a toluene solution of DDAF.

[0057] Step 3: Take 2 mL of the precursor obtained in step 1 and inject it into the toluene solution of DDAF in step 2 to obtain perovskite quantum dots, then stir for 30 minutes, and then centrifuge and purify to obtain the target product.

[0058] Experimental analysis: The product obtained in Comparative Example 1 has only lead as the B-site cation in the perovskite, and can only form a lead fluoride shell. The tested fluorescence quantum yield and blue light stability are 85.3% and 86%.

[0059] Comparative Example 2:

[0060] The difference from Example 1 is that only the B-site polycation component is doped, and no fluoride ion treatment is performed, so there is no fluoride shell layer grown.

[0061] Step 1: Mix 125 mg (1 mmol) of formamidine hydrobromide (FABr), 367 mg (1 mmol) of lead bromide, 25 mg (0.1 mmol) of strontium bromide, 15 mg (0.05 mmol) of barium bromide, 10 mg (0.05 mmol) of calcium bromide with 3 mL of N,N-dimethylformamide (DMF), 750 μL of hexanoic acid, and 200 uL of n-octylamine and stir until dissolved. The stirring time is 1 hour to obtain a perovskite quantum dot precursor solution.

[0062] Step 2: Add 2 mL of the precursor obtained in step 1 to 16 mL of toluene solvent to obtain a toluene solution of perovskite quantum dots, which is then stirred for 30 minutes and then centrifuged and purified to obtain the target product.

[0063] Experimental analysis: The product obtained in Comparative Example 2, in which only the B-site component is doped but the fluoride shell cannot be formed, has a fluorescence quantum yield and a blue light stability of 75.9% and 52%.

[0064] Comparing Example 1 with Comparative Examples 1 and 2, it can be seen that the use of only a single fluoride layer coating method cannot effectively solve the PLQY and photostability problems. The fluoride shell formed by treating the multi-component B-site perovskite with fluoride ions is denser and has a better passivation effect, which can greatly improve the PLQY and photostability of the perovskite.

[0065] The final products were prepared from the above examples. The PLQY and photothermal stability of each product under 450nm blue laser are shown in Table 1.

[0066] Table 1: Comparison of PLQY and stability test results of samples from different embodiments (comparative examples)

[0067]

[0068]

[0069] The crystallinity of the product of Example 1 of the present invention is much higher than that of the products of Comparative Example 1 and Comparative Example 2. Figure 1 It can be seen that doping / substitution of metal elements at the B site increases the unit cell parameters. The added impurity atoms (such as Ba, Sr, and Ca in Example 1) cause lattice expansion and increase the d value, thereby shifting the XRD diffraction peak toward smaller angles. Simultaneously, the formed fluorides (PbF2, BaF2, SrF2, etc.) can restructure the perovskite surface, modify defects, and recrystallize the surface, resulting in excellent crystallinity as shown by XRD.

[0070] By comparison Figure 2 、 Figure 3 It can be seen that we can qualitatively or quantitatively evaluate the degree of crystallinity by comparing the relative intensity and shape of the sharp diffraction peaks and the broad amorphous scattering packets:

[0071] 1) The sharpness and intensity of the diffraction peak (high crystallinity: sharp diffraction peak, high intensity, and flat baseline);

[0072] 2) Half-height width: Under the same sample preparation and testing conditions, the narrower the half-height width, the higher the crystallinity.

[0073] 3) Flatness of the baseline and amorphous scattering package (the baseline with high crystallinity is flat, while the baseline with low crystallinity is raised, forming a wide bulge).

[0074] 4) Signal-to-noise ratio (the diffraction peak corresponding to high crystallinity is very high compared to the background noise (baseline), and the baseline fluctuation range is small).

[0075] It can be clearly concluded that the crystallinity of the product of the present invention is significantly better than that of Comparative Example 1. The relationship between PLQY and crystallinity is: high crystallinity → low defect density → suppression of non-radiative recombination → improvement of radiative recombination efficiency → high PLQY.

[0076] While the present invention is described through the above-described embodiments to illustrate the detailed preparation methods of the present invention, the present invention is not limited to the above-described detailed preparation methods. This does not necessarily mean that the present invention must rely on the above-described products and detailed preparation methods in order to be implemented. Those skilled in the art will appreciate that any improvements to the present invention, or any combination or equivalent substitution of raw materials in the products of the present invention, fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for preparing perovskite quantum dots with a polyfluoride passivation layer, characterized in that: The steps include: Providing a monovalent cation precursor containing one or more of cesium (Cs), formamidine (FA), methylammonium (MA), rubidium (Rb), and gallium (GA); Providing a lead source precursor containing a halogen element; Provide a B-site cation doping precursor containing one or more of tin (Sn), copper (Cu), strontium (Sr), barium (Ba), zinc (Zn), and calcium (Ca); providing a poor solvent containing fluoride ions; The monovalent cation precursor, the lead source precursor and the B-site cation doping precursor are respectively added into a carrier solvent for dissolution and stirring to obtain a perovskite precursor solution; The perovskite precursor solution is injected into a poor solvent containing fluoride ions for stirring reaction, and the perovskite quantum dots with a polyfluoride common passivation layer are obtained after centrifugal purification.

2. The method for preparing perovskite quantum dots with a polyfluoride passivation layer according to claim 1, characterized in that: The polyfluoride common passivation layer includes at least two of lead fluoride, tin fluoride, copper fluoride, strontium fluoride, barium fluoride, zinc fluoride and calcium fluoride.

3. The method for preparing perovskite quantum dots with a polyfluoride passivation layer according to claim 1, characterized in that: The monovalent cation precursor includes one or more of methylammonium halide, methylammonium acetate (MA-), cesium oleate, cesium halide, formamidine acetate, formamidine hydrohalide, gallium halide and rubidium halide; The lead source precursor containing halogen elements is lead halide; The B-site cation doping precursor is at least one of tin halide, copper halide, strontium halide, barium halide, zinc halide, and calcium halide.

4. The method for preparing perovskite quantum dots with a polyfluoride passivation layer according to claim 1, wherein: The preparation method of the poor solvent containing fluoride ions comprises the following steps: A fluoride-containing compound is dissolved in a poor solvent, wherein the fluoride-containing compound comprises at least one of ammonium fluoride, ammonium bifluoride, potassium fluoride, sodium fluoride, cesium fluoride, and didecyldimethylammonium fluoride (DDAF).

5. The method for preparing perovskite quantum dots with a polyfluoride passivation layer according to claim 1, characterized in that: The preparation method can be carried out at normal temperature or room temperature.

6. The method for preparing perovskite quantum dots with a polyfluoride passivation layer according to claim 1, characterized in that: The carrier solvent includes at least one of dimethylformamide (DMF), dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), toluene, and tetrahydrofuran (THF).

7. The method for preparing perovskite quantum dots with a polyfluoride passivation layer according to claim 2, wherein: The synthesis of the perovskite quantum dots is carried out simultaneously with the formation of the polyfluoride common passivation layer.

8. The method for preparing perovskite quantum dots with a polyfluoride passivation layer according to claim 7, characterized in that: The lead source precursor and the B-site cation doping precursor together constitute a B-site metal cation precursor; The molar ratio of the B-site metal cation precursor to the monovalent cation precursor is greater than 1:

1.

9. The method for preparing perovskite quantum dots with a polyfluoride passivation layer according to claim 8, characterized in that: The molar amount of fluoride ions in the poor solvent is greater than (the molar amount of the B-site metal cation precursor minus the molar amount of the monovalent cation precursor), thereby providing excess fluoride ions to the reaction system.

10. The method for preparing perovskite quantum dots with a polyfluoride passivation layer according to claim 9, characterized in that: In a solution environment, excess fluoride ions exchange with halogen anions in perovskite quantum dots and coordinate with B-site cations to form a polyfluoride common passivation layer; The polyfluoride common passivation layer encapsulates the perovskite quantum dots to form a core-shell structure.

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