Use of an organic strong acid ligand in regulating halogen activity of perovskite nanocrystals

Abstract

This invention relates to the use of an organic strong acid ligand in regulating the halogen activity of perovskite nanocrystals, wherein the perovskite nanocrystals are ABBr with blue luminescence. y Cl 3‑y The structure describes an organic strong acid ligand that acts as a chloride ion scavenger in an organic solvent. The hydrogen ions provided by the organic strong acid ligand combine with halide ions in the organic solvent, reversing the ionization reaction of hydrogen halides to form non-ionized HX molecules. The halogens in the organic solvent consist of chlorine and bromine elements. The organic strong acid ligand selectively and preferentially combines with chlorine to form non-ionized HCl molecules. By reducing the activity of chlorine in the reactants, the chlorine-bromine ratio of the perovskite nanocrystals is controlled. Furthermore, with increasing amounts of the organic strong acid ligand, the emission wavelength of the perovskite nanocrystals gradually red-shifts. This invention regulates halogen activity through acidic ligands, thereby controlling the emission wavelength and internal defects of the inorganic core (i.e., perovskite nanocrystals).

Description

Technical Field

[0001] This invention belongs to the field of perovskite quantum dot preparation technology, and particularly relates to the use of an organic strong acid ligand in regulating the halogen activity of perovskite nanocrystals. Background Technology

[0002] The intriguing characteristics arising from the surface and size effects of nanomaterials have spurred unprecedented rapid development of colloidal nanocrystals in next-generation luminescence and photovoltaic fields. Against this backdrop, perovskite nanocrystals have become a research hotspot in electroluminescence due to their wide color gamut, narrow emission, and easy spectral tunability. Efficient blue electroluminescence represents the most challenging step towards further development of perovskite nanocrystals.

[0003] A simple method to achieve blue emission is to introduce chlorine into the CsPbBr3 system through halogen doping. This allows for continuous spectral tuning across the entire range from green to deep blue, and the spectral emission can be easily adjusted by composition, providing great synthetic flexibility for perovskite nanocrystals with various wavelengths. For example, our earlier Chinese patent application, CN116904184B, discloses a method for precisely controlling the emission wavelength of mixed halogen blue quantum dots.

[0004] However, mixed-halogen perovskite nanocrystals suffer from low photoluminescence quantum yield (PLQY) due to chlorine defects. Controlling the chlorine content and reducing chlorine defects are key to improving luminescence efficiency, especially for soft-lattice perovskites. On the other hand, during synthesis, two factors synergistically dominate the properties of colloidal nanocrystals: the perovskite precursor and the organic ligand, which respectively evolve into the inorganic core (i.e., perovskite nanocrystals) and the organic ligand shell. Specifically, the concentration and activity of the perovskite precursor affect the composition and intrinsic properties of the inorganic core, while the organic ligand manipulates the structure, morphology, dispersibility, and surface properties of the nanocrystals. In this case, the influence of the organic ligand on the inorganic core of the nanocrystal is often neglected.

[0005] Therefore, studying the influence of organic ligands on the inorganic core of nanocrystals, and further studying the influence of organic ligands on the composition and internal defects of the inorganic core (i.e., perovskite nanocrystal) system, is of great significance for the synthesis of nanocrystals and thus needs to be improved. Summary of the Invention

[0006] This invention proposes the use of an organic strong acid ligand in regulating the halogen activity of perovskite nanocrystals. By adjusting the halogen activity through the acid ligand, the emission wavelength and internal defects of the inorganic core (i.e., perovskite nanocrystals) can be controlled.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] The use of an organic strong acid ligand in regulating the halogen activity of perovskite nanocrystals, wherein the perovskite nanocrystals are ABBr with blue luminescence. y Cl 3-y The structure is as follows: 0 < y < 3; A site is at least one of Cs, Rb, FA, MA, GA; B site is at least one of Pb, Sn, or Cu.

[0009] The organic strong acid ligand acts as a chloride ion scavenger in the organic solvent. The hydrogen ions provided by the organic strong acid ligand combine with the halide ions in the organic solvent and reverse the ionization reaction of hydrogen halide to form non-ionized HX molecules.

[0010] The halogen in the organic solvent is composed of chlorine and bromine. The organic strong acid ligand selectively and preferentially binds to chlorine to form non-ionized HCl molecules. By reducing the activity of chlorine in the reactants, the chlorine-bromine ratio of the perovskite nanocrystals is controlled. As the amount of organic strong acid ligand added increases, the emission wavelength of the perovskite nanocrystals gradually increases (wavelength redshift).

[0011] Furthermore, the organic strong acid ligand partially ionizes in the organic solvent to form hydrogen ions (H+) and corresponding acid radical ions, wherein the hydrogen ions (H+) are used to bind with halide ions in the organic solvent.

[0012] Furthermore, the halogen in the organic solvent originates from a B-site metal precursor and a mixed halogen source; the B-site metal precursor and the mixed halogen source together provide chlorine and bromine elements.

[0013] Furthermore, the B-site metal precursor includes at least one of lead halide, copper halide, and tin halide;

[0014] The mixed halogen source includes one or more of tetra-n-octylammonium bromide (TOAB), tetra-octylammonium chloride (TOAC), dodecylammonium bromide (DDAB), and dodecylammonium chloride (DDAC);

[0015] The organic solvent includes one or more of toluene, xylene, and mesitylene.

[0016] Furthermore, the organic strong acid ligand includes at least one of benzenesulfonic acid, 4-dodecylbenzenesulfonic acid (DBSA), and trifluoromethanesulfonic acid (TFMSA).

[0017] Furthermore, the preparation method of the perovskite nanocrystals includes the following steps:

[0018] The organic strong acid ligand is added to the mixed precursor and mixed evenly. Then, a mixture of monovalent cation precursors is added to react. After nucleation and growth until the quantum dots are fully grown, the crude solution of the mixed halide perovskite blue light nanocrystals is obtained. Finally, the crude solution of the mixed halide perovskite blue light nanocrystals is purified to obtain the mixed halide perovskite nanocrystals.

[0019] The mixed precursor is a mixture of B-site metal precursor, mixed halogen source and organic solvent;

[0020] The monovalent cation precursor mixture is a mixture of a monovalent cation precursor containing one or more cations selected from cesium (Cs), rubidium (Rb), formamidinium (FA), methylammonium (MA), and aminoformamidinium (GA) and a weakly acidic ligand.

[0021] Furthermore, the B-site metal precursor is lead halide, which is lead chloride and lead bromide.

[0022] Furthermore, the purification process is as follows:

[0023] Ethyl acetate was added to the crude solution of mixed halide perovskite blue light nanocrystals as an antisolvent. After centrifugation, the precipitate was dispersed in n-octane. The purification process was repeated two to three times to obtain the mixed halide perovskite nanocrystals.

[0024] Furthermore, the monovalent cation precursor includes one or more of cesium carbonate (Cs2CO3), cesium formate (CsHCOO), cesium acetate (CsAc), cesium trifluoroacetate (CsTFA), formamidine formate (FAHCOO), formamidine acetate (FA-Ac), methylamine acetate (MAAc), rubidium carbonate (Rb2CO3), rubidium formate (RbHCOO), and rubidium acetate (RbAc);

[0025] The weakly acidic ligand is bis(2,4,4-trimethylpentyl)phosphoric acid (PA).

[0026] Furthermore, the organic strong acid ligand enables controllable adjustment of the emission wavelength of the perovskite nanocrystals within the range of 445-482 nm. The perovskite nanocrystals are used to prepare perovskite light-emitting diodes, perovskite inks, or light conversion films / plates.

[0027] The beneficial effects of this invention are:

[0028] (1) The synthesis of perovskite nanocrystals is usually carried out in weakly polar organic solvents, such as 1-octadecene, octane, or toluene, to minimize damage to the perovskite nanocrystals (because preparation under high polarity will destroy the structure of the perovskite nanocrystals). In this invention, the strong organic acid ligand (taking DBSA as an example) has strong acidity and will partially ionize into H in the solvent for synthesizing the nanocrystals. +and DBS - It can regulate halogen activity.

[0029] After DBSA was added to the reactants, the pH of the solution dropped from 6.0 to 1.0, indicating the ionization process of DBSA in toluene. The hydrogen ions generated by DBSA can reverse the ionization reaction of hydrogen halides by combining with halogens, forming HX with lower reactivity. Since chlorine (3.16) is more electronegative than bromine (2.96), chloride ions tend to be depleted from the organic solvent, forming unionized HCl molecules. This will greatly reduce the reactivity of halogens in the reactants, especially chlorine, causing a red shift in wavelength, thus enabling controllable adjustment of the chlorine-bromine ratio in the nanocrystals. It is important to emphasize that only ionic halogens can participate in the synthesis of perovskite nanocrystals.

[0030] (2) In this invention, as the amount of organic strong acid ligand added changes, the emission wavelength of the resulting perovskite nanocrystals can be controllably adjusted within the range of 445–482 nm. Simultaneously, as the amount of organic strong acid ligand added increases, the PLQY of the perovskite nanocrystals generally shows an increasing trend.

[0031] (3) This invention provides a method for controlling the halogen ratio and properties in nanocrystals by changing the content of acidic ligands. This allows for a wide range of adjustment of the emission wavelength of nanocrystals and a reduction of internal defects without altering the halogen ratio in the precursor raw materials. It achieves controllable adjustment of the emission wavelength of nanocrystals using only acidic ligands and complete passivation of surface and internal defects in the nanocrystals. The synthesized nanocrystals exhibit superior optical properties, and the prepared perovskite light-emitting diodes have high external quantum efficiency. This expands the function of acidic ligands in the nanocrystal synthesis process and promotes the application of perovskite nanocrystals in the field of full-color displays. Attached Figure Description

[0032] Figure 1 The reaction mechanism for regulating halogen activity using organic strong acid ligands (taking DBSA as an example) of this invention;

[0033] Figure 2 The ultraviolet-visible spectra of the perovskite nanocrystals obtained in Examples 1-5 and Comparative Example 1 of this invention;

[0034] Figure 3 The fluorescence spectra of the perovskite nanocrystals obtained in Examples 1-5 and Comparative Example 1 of this invention;

[0035] Figure 4 The photoluminescence quantum yield of perovskite nanocrystals obtained in Examples 1-5 and Comparative Example 1 of this invention;

[0036] Figure 5Comparison of UV-Vis spectra and fluorescence spectra of halogen activity modulated using different organic strong acid ligands in Examples 1 and 6;

[0037] Figure 6 The fluorescence lifetime comparison diagram shows the perovskite nanocrystals prepared in Example 1 and Example 6.

[0038] Figure 7 The ultraviolet-visible spectra of the perovskite nanocrystals prepared in Examples 6-10 are shown.

[0039] Figure 8 External quantum efficiency-current density curves for perovskite light-emitting diodes prepared using the perovskite nanocrystals prepared in Examples 1 and 6. Detailed Implementation

[0040] To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0041] Example 1:

[0042] A solution of cesium carbonate (Cs₂CO₃, 0.085 mol / L), formamidine acetate (FA-Ac, 0.015 mol / L), and rubidium carbonate (Rb₂CO₃, 0.0085 mol / L) in bis(2,4,4-trimethylpentyl)phosphoric acid (PA) was prepared as a monovalent cation precursor. 0.4 mmol of lead bromide (PbBr₂), 0.1 mmol of lead chloride (PbCl₂), and 0.725 mmol of tetraoctylammonium bromide (TOAB) were weighed and added to a 20 mL sample vial. 5 mL of ultra-dry toluene was added to the vial, and the mixture was stirred continuously for 4–5 h to ensure complete dissolution of the reagents, thus preparing a mixed precursor of lead and halogen. A 100 mg / mL ultra-dry toluene solution of dodecyl ammonium chloride (DDAC) was prepared for later use. 0.6 mL of 4-dodecylbenzenesulfonic acid (DBSA, 1 g / mL dissolved in ultra-dry toluene) was added to the mixed precursor, and the mixture was stirred for 4 min. Then, 0.5 ml of a monovalent cation precursor solution was rapidly injected, and after the reaction proceeded for 2.5 min, 1 ml of ultra-dry toluene solution of DDAC was added, and stirring was continued for another 4 min. After a series of subsequent purification processes, blue perovskite nanocrystals with an emission wavelength of 470 nm, treated with DBSA, were obtained.

[0043] In some embodiments, the method for purifying nanocrystals may include, but is not limited to, the following steps: transferring the stock solution to a centrifuge tube for low-speed centrifugation, taking the supernatant after centrifugation, adding a certain amount of antisolvent to precipitate the perovskite nanocrystals and centrifuging at high speed; dispersing the precipitate in octane or toluene, and collecting it by filtration through a 0.22 μm organic filter to obtain a blue light-emitting perovskite nanocrystal solution. Under certain conditions, the above steps may be repeated two to three times.

[0044] Examples 2-5:

[0045] The difference from Example 1 is that different amounts of DBSA were used for treatment to obtain a series of nanocrystals with different wavelengths.

[0046] Prepare a solution of cesium carbonate (Cs₂CO₃, 0.085 mol / L), formamidine acetate (FA-Ac, 0.015 mol / L), and rubidium carbonate (Rb₂CO₃, 0.0085 mol / L) in bis(2,4,4-trimethylpentyl)phosphoric acid (PA) as a monovalent cation precursor. Weigh 0.4 mmol of lead bromide (PbBr₂), 0.1 mmol of lead chloride (PbCl₂), and 0.725 mmol of tetraoctylammonium bromide (TOAB) and add them to a 20 mL sample vial. Add 5 mL of ultra-dry toluene to the sample vial and stir continuously for 4–5 h to ensure complete dissolution of the reagents, thus preparing a mixed precursor of lead and halogen. Prepare a 100 mg / mL ultra-dry toluene solution of dodecyl ammonium chloride (DDAC) for later use. 0.2 ml, 0.4 ml, 0.8 ml, and 1.0 ml of 4-dodecylbenzenesulfonic acid (DBSA, 1 g / ml dissolved in ultra-dry toluene) were added to the mixed precursor, respectively, and stirred for 4 min. Then, 0.5 ml of the monovalent cation precursor solution was rapidly injected, and after reacting for 2.5 min, 1 ml of ultra-dry toluene solution of DDAC was added, and stirring continued for another 4 min. After a series of subsequent purification processes, blue perovskite nanocrystals with emission wavelengths of 460 nm, 465 nm, 476 nm, and 482 nm, respectively, were obtained after DBSA treatment.

[0047] Figure 1 This invention describes the reaction mechanism by which the acidic ligand DBSA modulates halogen activity. The strongly acidic ligand DBSA ionizes into DBS in a nonpolar solvent. - and H + They combine with quaternary ammonium and halogens respectively, resulting in a decrease in the activity of halide anions, especially chloride ions, which in turn reduces defects on the surface and inside of the nanocrystals and improves the optical properties of the nanocrystals.

[0048] Figure 2 and Figure 3The images show the UV-Vis spectra and fluorescence spectra of the perovskite nanocrystals obtained in Examples 1-5 and Comparative Example 1 of this invention, respectively. With increasing DBSA content, the wavelength of the nanocrystals gradually red-shifts, which is attributed to the modulation of halogen activity by DBSA. Simultaneously, the optical properties of the nanocrystals also gradually improve.

[0049] like Figure 4 The comparison of photoluminescence efficiency shown is due to the reduction in chlorine content in the system caused by DBSA-mediated halogen activity regulation, which reduces internal defects in the nanocrystals.

[0050] Example 6:

[0051] The difference from Example 1 is that DBSA was replaced with 0.04 mL of trifluoromethanesulfonic acid (TFMSA), while the other steps remained the same. This yielded blue perovskite nanocrystals with an emission wavelength of 470 nm after treatment with 0.04 mL of TFMSA.

[0052] Figure 5 Comparison of UV-Vis spectra and fluorescence spectra of nanocrystals used in Examples 1 and 6 to regulate halogen activity and internal defects.

[0053] Figure 6 The image shows a comparison of the fluorescence lifetime of the perovskite nanocrystals prepared in Examples 1 and 6.

[0054] Examples 7-10:

[0055] The difference from Example 6 is that different amounts of trifluoromethanesulfonic acid (TFMSA) were added (0 ml, 0.01 ml, 0.02 ml, 0.03 ml), while the other steps were the same.

[0056] Figure 7 The images show the UV-Vis spectra of the perovskite nanocrystals prepared in Examples 6-10. It is evident that adding a certain amount of trifluoromethanesulfonic acid (TFMSA) can modulate the wavelength redshift of the perovskite nanocrystals.

[0057] Comparative Example 1:

[0058] The difference from Example 1 is that DBSA treatment was not used; all other steps were the same. The resulting perovskite nanocrystals, without DBSA treatment, emitted light at a wavelength of 445 nm.

[0059] Application example:

[0060] A perovskite light-emitting diode includes an ITO conductive glass, a hole injection layer, a hole transport layer, a perovskite nanocrystal light-emitting layer, an electron transport layer, and an electrode layer arranged sequentially, wherein the perovskite nanocrystal light-emitting layer is a perovskite nanocrystal spin-coated film prepared according to Examples 1 and 6 above.

[0061] The hole injection layer may include one or more of nickel oxide (NiOx) and poly(3,4-ethylenedioxythiophene):poly(4-benzenesulfonic acid) (PEDOT:PSS).

[0062] The hole transport layer may include one or more of the following: poly(9-vinylcarbazole) (PVK), poly[(4,4′-(N-(4-sec-butylphenyl)diphenylamine)] (PolyTPD), poly[9,9-dioctylfluorene-co-N-[4-(3-methylpropyl)]-diphenylamine] (TFB), poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA), and poly(9,9-n-dioctyl-2,7-fluorene-alt-9-isooctyl-3,6-carbazole) (pF8Cz).

[0063] The electron transport layer may include one or more of 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene (TPBi), 2,4,6-tris[3-(diphenylphosphino)phenyl]-1,3,5-triazole (PO-T2T), and 3,3'-[5'-[3-(3-pyridyl)phenyl][1,1':3',1”-terphenyl]-3,3”-diyl]dipyridine (TmPyPB).

[0064] Figure 8 The figures show the external nanocrystal efficiency-current density curves for perovskite light-emitting diodes (LEDs) prepared using the perovskite nanocrystals prepared in Examples 1 and 6. It can be seen that the nanocrystals treated with DBSA achieved a PLQY of 89%, and the corresponding perovskite nanocrystal LEDs obtained an external quantum efficiency of 24.5%.

[0065] In summary, we have demonstrated the control of halogen activity and internal defects in nanocrystals mediated by organic strong acid ligands. Taking the organic strong acid ligand DBSA as an example, it ionizes into DBS in a low-polarity solvent. - and H +The ligands interact with quaternary ammonium and halogens respectively, thereby modulating the activity of halogens. This reveals a novel function of organic strong acid ligands, allowing for controllable tuning of the nanocrystal composition, thereby suppressing the formation of halogen-related internal defects. Example 1 of this invention achieved approximately 89% PLQY with a blue emitting nanocrystal centered at 470 nm, and produced a perovskite nanocrystal light-emitting diode with an EQE as high as 24.5%, representing the highest efficiency to date for pure blue perovskite nanocrystal light-emitting diodes. Further research into the role of surface ligands in controlling surface and internal defects of nanocrystals is of great significance for promoting the development and application of perovskite nanocrystals in semiconductor devices such as light-emitting diodes and solar cells.

[0066] The present invention has been illustrated with the above embodiments to explain the detailed preparation method of the present invention. However, the present invention is not limited to the above detailed preparation method, that is, it does not mean that the present invention must rely on the above product and detailed preparation method to be implemented. Those skilled in the art should understand that any improvement to the present invention, or the combination or equivalent substitution of the raw materials of the present invention, falls within the protection scope and disclosure scope of the present invention.

Claims

1. Use of an organic strong acid ligand in modulating halogen activity of perovskite nanocrystals, characterized in that, The perovskite nanocrystal is an AB Br y Cl 3-y structure, wherein: 0 < y < 3; A site is at least one of Cs, Rb, FA, MA, GA; B site is at least one of Pb, Sn or Cu. The organic strong acid ligand in the organic solvent acts as a chloride ion scavenger, the hydrogen ion provided by the organic strong acid ligand combines with the halogen ion in the organic solvent, and reverses the ionization reaction of hydrogen halide to form a non-ionized HX molecule; The halogen in the organic solvent is composed of chlorine and bromine elements, the organic strong acid ligand selectively and preferentially combines with chlorine to form a non-ionized HCl molecule; the chlorine-to-bromine ratio of the perovskite nanocrystal is regulated by reducing the activity of chlorine in the reactant, and as the amount of the organic strong acid ligand increases, the luminescence wavelength of the perovskite nanocrystal red shifts; The halogen in the organic solvent comes from the B-site metal precursor and the mixed halogen source; the B-site metal precursor and the mixed halogen source together provide chlorine and bromine elements; the mixed halogen source includes one or more of tetra-n-octylammonium bromide, tetraoctylammonium chloride, dodecylammonium bromide, and dodecylammonium chloride; The organic strong acid ligand includes at least one of 4-dodecylbenzenesulfonic acid and trifluoromethanesulfonic acid.

2. Use of an organic strong acid ligand according to claim 1 for the regulation of halogen activity in perovskite nanocrystals, characterized in that, The organic strong acid ligand partially ionizes in the organic solvent to form hydrogen ions and corresponding acid ions, and the hydrogen ions are used to combine with halogen ions in the organic solvent.

3. Use of an organic strong acid ligand according to claim 1 for the regulation of halogen activity in perovskite nanocrystals, characterized in that, The B-site metal precursor includes at least one of lead halide, copper halide, and tin halide; The organic solvent includes one or more of toluene, xylene, and mesitylene.

4. Use of an organic strong acid ligand according to any one of claims 1-3 for the regulation of halogen activity in perovskite nanocrystals, characterized in that, The preparation method of the perovskite nanocrystal includes the following steps: The organic strong acid ligand is added to the mixed precursor and mixed uniformly, then a monovalent cation precursor mixture is added for reaction, nucleation and growth to complete quantum dot growth to obtain a mixed halogen perovskite blue nanocrystal crude solution, and finally the mixed halogen perovskite blue nanocrystal crude solution is purified to obtain a mixed halogen perovskite nanocrystal; The mixed precursor is a mixture of a B-site metal precursor, a mixed halogen source, and an organic solvent; The monovalent cation precursor mixture is a mixture of a monovalent cation precursor containing one or more of cesium, rubidium, formamidinium, methylammonium, and aminomethylformamidinium and a weak acid ligand.

5. Use of an organic strong acid ligand according to claim 4 for the regulation of halogen activity in perovskite nanocrystals, characterized in that, The B-site metal precursor is lead halide, and the lead halide is lead chloride and lead bromide.

6. Use of an organic strong acid ligand according to claim 4 for the regulation of halogen activity in perovskite nanocrystals, characterized in that, The purification process is as follows: The mixed halogen perovskite nanocrystal is obtained by adding an anti-solvent ethyl acetate to the mixed halogen perovskite blue nanocrystal crude solution, centrifuging, and then dispersing the precipitate in n-octane, and repeating the purification process two to three times.

7. Use of an organic strong acid ligand according to claim 4 for the regulation of halogen activity in perovskite nanocrystals, characterized in that, The monovalent cation precursor includes one or more of cesium carbonate, cesium formate, cesium acetate, cesium trifluoroacetate, formamidinium formate, methylammonium acetate, methylamine acetate, rubidium carbonate, rubidium formate, and rubidium acetate; The weak acid ligand is bis(2,4,4-trimethylpentyl)phosphoric acid.

8. Use of an organic strong acid ligand according to claim 1 for the regulation of halogen activity in perovskite nanocrystals, characterized in that, The organic strong acid ligand can achieve controllable adjustment of the luminescence wavelength of the perovskite nanocrystal in the range of 445-482 nm; The perovskite nanocrystal is used to prepare a perovskite light-emitting diode or a perovskite ink or a light conversion film / panel.

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