Long-term stable MAPbBr3 nanocrystal polymer optical film in blue light irradiation environment as well as preparation method and application of long-term stable MAPbBr3 nanocrystal polymer optical film

Abstract

The invention belongs to the technical field of optical films, and relates to a long-term stable MAPbBr3 nanocrystal at polymer optical film in a blue light irradiation environment and application of the long-term stable MAPbBr3 nanocrystal at polymer optical film. On the basis of improvement of an in-situ synthesis method in a water solvent, N-oxalylglycine (NOG) is introduced into an MAPbBr3 precursor solution to improve the blue light irradiation stability of an MAPbBr3 nanocrystal-polyvinyl alcohol (PVA) polymer film, and C-O-Pb covalent bonds are formed on the surfaces of the nanocrystals by using-COOH double sites of the NOG to inhibit the interaction of excitons and phonons and ligand desorption on the surfaces of the MAPbBr3 nanocrystals under continuous irradiation of blue light.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical films and relates to a MAPbBr3 nanocrystal@polymer optical film that is stable for a long time under a blue light irradiation environment, and a preparation method and application thereof. Background Art

[0002] Since their discovery in 2014, organic-inorganic lead halide hybrid perovskite nanocrystals have shown great potential in various applications due to their high photoluminescence quantum yield (PLQY), narrow emission full-width at half-maximum (FWHM), and ease of preparation. In particular, perovskite nanocrystals grown in situ within polymer films have attracted attention due to their excellent film-forming ability for display applications, scalability for roll-to-roll production, and improved water and oxygen stability through polymer encapsulation. However, the ionic crystal nature of perovskites leads to their instability under blue light irradiation, severely limiting their commercial applications.

[0003] The instability of perovskite nanocrystals under light irradiation mainly stems from charge accumulation caused by defects. Specifically, continuous illumination causes photoexcited carriers to localize at vacancies, interstitials, and / or surface defects. These localized carriers accumulate, generating local electric fields that promote the migration of halide ions and the desorption of surface ligands. These processes together exacerbate structural degradation, increase non-radiative recombination pathways such as trap-assisted recombination and Auger recombination by creating additional defects, and ultimately reduce the optical properties and stability of perovskite nanocrystals. To mitigate these adverse effects, two approaches can be implemented: suppress defect states to minimize trap sites, or reduce the free carrier concentration to reduce charge accumulation.

[0004] While surface ligand engineering and metal doping can be used to suppress defect states and minimize trap sites, thereby mitigating or inhibiting perovskite decomposition or failure caused by blue light irradiation, increasing the exciton binding energy of perovskite nanocrystals to enhance electron and hole confinement, thereby reducing exciton dissociation into free carriers and increasing the probability of radiative recombination, and thus improving stability under continuous blue light irradiation, remains understudied. The instability of perovskite nanocrystals under blue light irradiation remains a significant challenge for perovskite materials and their optoelectronic devices, and a significant factor restricting their commercial application in liquid crystal display backlights.

[0005] A Chinese patent application document (CN117050352A) discloses a MAPbBr3 nanocrystal@polymer film with high humidity and heat stability and a preparation method thereof. The main focus is on the stability of the prepared MAPbBr3 nanocrystal@polymer film in a high temperature and high humidity environment, and no research is conducted on the stability under blue light irradiation. The selected preparation solvent is N,N-dimethylformamide (DMF), which is not only toxic, but also has a certain degree of toxicity. During the experiment, the patent tested its stability under blue light irradiation and found that the stability of its composite film was poor. It is speculated that the MAPbBr3 nanocrystals in the composite film still have surface defects that have not been effectively passivated, thereby inducing the migration of halogen ions and the desorption of surface ligands under blue light irradiation, thereby further deteriorating the stability under blue light irradiation.

[0006] A Chinese patent application document (CN115521561A) discloses a ligand-modified highly stable MAPbBr3 perovskite quantum dot@polymer optical film. The prepared MAPbBr3 perovskite quantum dot@polymer optical film focuses on thermal stability and water immersion stability at 60°C, and does not involve blue light irradiation stability. In addition, the fluorescence quantum efficiency of the material is low, indicating that there are still some defect states on its surface, which will weaken its blue light stability. Summary of the Invention

[0007] The purpose of the present invention is to address the above-mentioned problems existing in the prior art and propose a MAPbBr3 nanocrystal@polymer optical film that is stable for a long time under blue light irradiation environment. The short-chain ligand N-oxalylglycine with strong binding force and double-site structure is used to improve the blue light irradiation stability of the polymer film.

[0008] The purpose of the present invention can be achieved through the following technical solutions:

[0009] A MAPbBr3 nanocrystal@polymer optical film with long-term stability under blue light irradiation environment is obtained by adding a bromine-containing compound and N-oxalylglycine to a precursor solution for ligand modification.

[0010] Among the bromides, methylamine bromide and lead bromide are the raw materials for the synthesis of MAPbBr3 nanocrystals. Octylamine bromide and hydrobromic acid can be considered as defect inhibitors or regulators for improving the crystallinity of MAPbBr3 nanocrystals. Specifically, octylamine bromide and hydrobromic acid can increase a certain amount of bromine source, which can effectively fill the surface bromine vacancy defects of the synthesized MAPbBr3 nanocrystals to a certain extent. At the same time, hydrobromic acid can regulate the pH of the precursor solution, which is beneficial to regulating the growth dynamics of the nanocrystals.

[0011] N-oxalylglycine is a short-chain surface ligand with a dual coordination site (hydroxyl: COO-). Its short-chain structure can match the distance between adjacent lead atoms in MAPbBr3 nanocrystals on a spatial scale, achieving effective coordination at the atomic scale. At the same time, its dual-site coordination makes N-oxalylglycine more firmly bound to the surface of MAPbBr3 nanocrystals, achieving strong binding, so it is not easy to fall off under blue light irradiation. By regulating the concentration of N-oxalylglycine, the growth dynamics of MAPbBr3 nanocrystals can be affected. The quantum confinement effect enhances the exciton binding energy, accelerates the radiative recombination rate, and thus reduces charge accumulation, thereby improving the overall blue light stability of the composite film.

[0012] In the above-mentioned MAPbBr3 nanocrystal@polymer optical film that is stable for a long time under blue light irradiation environment, the bromine-containing compounds include methylamine bromide, lead bromide, octylamine bromide, and hydrobromic acid, wherein the mass ratio of methylamine bromide, lead bromide, octylamine bromide, hydrobromic acid and N-oxalylglycine is (5-30):(10-40):1:(1-30):(1-20).

[0013] In the above-mentioned MAPbBr3 nanocrystal@polymer optical film that is stable for a long time under blue light irradiation environment, the added amount of N-oxalylglycine in the precursor solution is 1-150 mg / 100 mL.

[0014] In the above-mentioned MAPbBr3 nanocrystal@polymer optical film that is stable for a long time under blue light irradiation environment, the precursor solution includes PVA powder and water in a mass ratio of (70-85): (900-1000).

[0015] The present invention ensures that the reaction is further completed by controlling the ratio of MABr, PbBr2 and PVA powder and water within the above range, and does not cause excessive residue of one of the reactants. At the same time, the formed MAPbBr3 nanocrystals can be evenly distributed in the polymer matrix.

[0016] The present invention also provides a method for preparing the above-mentioned MAPbBr3 nanocrystal@polymer optical film with long-term stability under blue light irradiation environment, the method comprising the following steps: adding a bromine-containing compound and N-oxalylglycine to a precursor solution for ligand modification, and then dropping the ligand-modified mixed solution onto the surface of a flat glass after centrifugation to form a transparent precursor layer by a blade coating technique.

[0017] In the above-mentioned method for preparing a long-term stable MAPbBr3 nanocrystal@polymer optical film under a blue light irradiation environment, the coating thickness during the coating process is 50-200 microns, and the coating area is 1-100 square centimeters.

[0018] In the preparation method of the MAPbBr3 nanocrystal@polymer optical film with long-term stability under blue light irradiation environment, the transparent precursor layer after being scraped is required to be subjected to a heating treatment, wherein the heating temperature is 80-120 DEG C, and the time is 1-10 min.

[0019] In the preparation method of the MAPbBr3 nanocrystal@polymer optical film with long-term stability under blue light irradiation environment, after the heating treatment, the optical film is required to be subjected to a standing treatment, wherein the standing temperature is 15-25 DEG C, the humidity is 60-80%, and the time is 10-24 h. Through the standing treatment, the growth rate of the MAPbBr3 nanocrystal and the size and uniformity of the nanocrystal can be stably controlled.

[0020] In the preparation method of the MAPbBr3 nanocrystal@polymer optical film with long-term stability under blue light irradiation environment, the optical film has a fluorescence emission efficiency of 88-97%, a half-peak width of 19-25 nm, and an adjustable emission peak position within 518-528 nm.

[0021] As preferred, the optical film still maintains more than 99% of the initial value of PLQY after being continuously irradiated by 460 nm blue light (13 mW·cm -2 ) for 1444 hours.

[0022] The application further provides an application of the MAPbBr3 nanocrystal@polymer optical film with long-term stability under blue light irradiation environment in a liquid crystal display backlight source.

[0023] Compared with the prior art, the application has the following beneficial effects:

[0024] 1. The application realizes effective control of the optical performance of the MAPbBr3 nanocrystal@polymer film by adjusting parameters such as ligand (N-oxalyl glycine) concentration, heat curing time and temperature, and water absorption temperature, humidity and time, which makes the optical film have excellent fluorescence emission efficiency (88-97%), narrow half-peak width (19-25 nm), and adjustable emission peak position (518-528 nm).

[0025] 2. The application effectively fills the bromine vacancy defects on the surface of the MAPbBr3 nanocrystal by using specific bromine-containing compounds (methylamine bromide, lead bromide, octylamine bromide, hydrobromic acid) for ligand modification and adding N-oxalyl glycine as a surface ligand, thereby improving the crystallinity of the nanocrystal, and enhancing the stability of the composite film under blue light irradiation, especially the PLQY still maintains more than 99% of the initial value after being continuously irradiated by 460 nm blue light for 1444 hours, which shows excellent blue light stability.

[0026] 3. The application adopts water as a solvent, and has the characteristics of simple and controllable synthesis process, easy large-scale preparation, green environmental protection, reduced production cost and increased economic benefit.

[0027] 4. The optical film is particularly suitable for a wide color gamut liquid crystal display backlight device, and compared with an existing material system, provides better blue light irradiation stability, and expands the application prospect in high-end display technology.

[0028] Drawings accompanying the specification

[0029] Figure 1 A preparation flowchart of all embodiments of the application;

[0030] Figure 2 A transmission electron microscope (TEM) image of the MAPbBr3 nanocrystal@PVA film prepared in Example 1 of the application;

[0031] Figure 3 A size distribution graph of the transmission electron microscope (TEM) image of the MAPbBr3 nanocrystal@PVA film prepared in Example 1 of the application;

[0032] Figure 4 A PLQY change graph of the MAPbBr3 nanocrystal@PVA film prepared in Example 1 of the application after 460nm blue light (13mW·cm -2 ) continuous irradiation for 1444 hours;

[0033] Figure 5 A PLQY change graph of the MAPbBr3 nanocrystal@PVA film prepared in Example 2 of the application after 460nm blue light (13mW·cm -2 ) continuous irradiation for 1444 hours;

[0034] Figure 6 A PLQY change graph of the MAPbBr3 nanocrystal@PVA film prepared in Example 3 of the application after 460nm blue light (13mW·cm -2 ) continuous irradiation for 1444 hours;

[0035] Figure 7 A PLQY change graph of the MAPbBr3 nanocrystal@PVA film prepared in Example 4 of the application after 460nm blue light (13mW·cm -2 ) continuous irradiation for 1444 hours;

[0036] Figure 8 A transmission electron microscope (TEM) image of the MAPbBr3 nanocrystal@PVA film prepared in Comparative Example 1 of the application;

[0037] Figure 9This is a size distribution diagram of the transmission electron microscope (TEM) image of the MAPbBr3 nanocrystal@PVA film prepared in Comparative Example 1 of the present invention;

[0038] Figure 10 The MAPbBr3 nanocrystal@PVA film prepared in Comparative Example 1 of the present invention was subjected to 460nm blue light (13mW·cm -2 ) PLQY change diagram after continuous irradiation for 1444 hours;

[0039] Figure 11 X-ray diffraction (XRD) patterns of the MAPbBr3 nanocrystal@PVA films prepared in Examples 1 to 4 of the present invention and Comparative Example 1;

[0040] Figure 12 PL and UV absorption spectra of MAPbBr3 nanocrystals@PVA films prepared in Example 1-Example 4 and Comparative Example 1;

[0041] Figure 13 GSB decay dynamics of femtosecond transient absorption (TA) spectra of MAPbBr3 nanocrystals@PVA films prepared in Example 1 and Comparative Example 1;

[0042] Figure 14 Time-resolved photoluminescence (TRPL) spectra of the MAPbBr3 nanocrystals@PVA films prepared in Example 1 and Comparative Example 1;

[0043] Figure 15 Huang Kun factor fitting of the change of half-peak width of PL of MAPbBr3 nanocrystal@PVA film prepared in Example 1 and Comparative Example 1 at 200K to 400K;

[0044] Figure 16 Exciton binding energy fitted by the peak intensity change of PL of MAPbBr3 nanocrystal@PVA film prepared in Example 1 and Comparative Example 1 at variable temperature from 200K to 400K. DETAILED DESCRIPTION

[0045] The following are specific embodiments of the present invention, which further describe the technical solutions of the present invention, but the present invention is not limited to these embodiments.

[0046] Example 1:

[0047] according to Figure 1 Preparation of MAPbBr3 nanocrystals@PVA film as shown in the process:

[0048] S1. Place 8.0 g of polyvinyl alcohol powder and 100 mL of deionized water into a conical flask and stir at 85 °C for 1 hour to fully dissolve into a uniform precursor solution; then, add 112 mg of MABr, 220 mg of PbBr2, 10.8 mg of OABr, 110 μL of HBr, 97 mg of NOG and 50 mL of toluene, and mechanically stir at room temperature for 3 hours to fully mix; centrifuge at 10,000 rpm for 1 hour to remove unreacted impurities and undissolved particles to ensure a uniform mixed precursor solution.

[0049] S2. Take 1 mL of the above-mentioned mixed precursor solution to one end of the glass substrate, and apply it on a scraper at a scraping speed of 28 mm / s to 25 square centimeters to obtain a composite wet film with a thickness of 200 microns. The glass substrate with a wet film evenly coated on the surface is then placed on a heating plate at 115°C to evaporate the water, causing the precursor solution to be converted into a transparent and colorless film. Subsequently, the film is placed in a constant temperature and humidity chamber (20°C, 70% relative humidity) for 24 hours of humidity treatment, so that the film gradually absorbs water to promote the growth of perovskite nanocrystals, and finally obtains MAPbBr3 nanocrystals @PVA film.

[0050] The flow chart of preparing MAPbBr3 nanocrystal@PVA film in this embodiment is as follows Figure 1 The transmission electron microscope (TEM) image of the prepared composite film is shown in FIG. Figure 2 As shown, it shows that MAPbBr3 nanocrystals uniformly distributed in the PVA polymer film were successfully prepared, and the size distribution diagram ( Figure 3 ) showed that its average size was 10.59 nm; Figure 4 The prepared MAPbBr3 nanocrystal@PVA film was exposed to 460nm blue light (13mW·cm -2 ) After 1444 hours of continuous irradiation, the PLQY still maintained more than 99% of the initial value.

[0051] Example 2:

[0052] The only difference from Example 1 is that the mass of NOG in this example is 24.3 mg. The rest is the same as Example 1 and will not be repeated here.

[0053] The MAPbBr3 nanocrystal@PVA film prepared in this example was exposed to 460nm blue light (13mW·cm -2 ) After 1444 hours of continuous irradiation, the PLQY still maintained more than 36% of the initial value ( Figure 5 ).

[0054] Example 3:

[0055] The only difference from Example 1 is that the mass of NOG in this example is 48.5 mg. The rest is the same as Example 1 and will not be repeated here.

[0056] The MAPbBr3 nanocrystal@PVA film prepared in this example was exposed to 460nm blue light (13mW·cm -2 ) After 1444 hours of continuous irradiation, the PLQY still maintained more than 78% of the initial value ( Figure 6 ).

[0057] Example 4:

[0058] The only difference from Example 1 is that the mass of NOG in this example is 145.6 mg. The rest is the same as Example 1 and will not be repeated here.

[0059] The MAPbBr3 nanocrystal@PVA film prepared in this example was exposed to 460nm blue light (13mW·cm -2 ) After 1444 hours of continuous irradiation, the PLQY still maintained more than 70% of the initial value ( Figure 7 ).

[0060] Example 5:

[0061] The only difference from Example 1 is that the relative humidity during the humidity treatment in step S2 is 5%.

[0062] Because the growth environment of nanocrystals is too dry, its normal crystallization process is affected, resulting in inconsistent nanocrystal size and uneven distribution, which greatly affects the photophysical properties of the material. Especially for optical films that require high blue light irradiation stability, too low humidity will affect the growth quality of nanocrystals and thus weaken their stability.

[0063] Example 6:

[0064] The only difference from Example 1 is that the relative humidity during the humidity treatment in step S2 is 95%.

[0065] A high humidity environment will introduce additional moisture into the material system. Excessive moisture will cause material hydrolysis, structural collapse, and increased defects, thereby reducing its optical properties and stability. In addition, excessive humidity may cause condensation on the surface of the film, resulting in surface unevenness or other defects.

[0066] Comparative Example 1:

[0067] The only difference from Example 1 is that the NOG ligand is not added in this comparative example. The rest is the same as Example 1 and will not be repeated here.

[0068] The transmission electron microscopy (TEM) image and size distribution of the MAPbBr3 nanocrystal@PVA film prepared in this comparative example are shown in FIG.Figure 8 and Figure 9 As shown, the size of the synthesized nanocrystals is 15.28 nm; under 460 nm blue light (13 mW·cm -2 ) After 1444 hours of continuous irradiation, the PLQY remained at about 26% of the initial value ( Figure 10 ).

[0069] Comparative Example 2:

[0070] The only difference from Example 1 is that no constant temperature and humidity static treatment is performed.

[0071] Due to the lack of constant temperature and humidity static treatment, the nanocrystals grow unevenly and have large size differences, which leads to a decrease in the stability of the optical film and is prone to performance degradation in actual applications.

[0072] Comparative Example 3:

[0073] The only difference from Example 1 is that the bromine-containing compound in the raw material is only methylamine bromide.

[0074] Since the raw materials only contain methylamine bromide, MAPbBr3 nanocrystals cannot be synthesized.

[0075] Comparative Example 4:

[0076] The only difference from Example 1 is that the bromine-containing compound in the raw material is only lead bromide.

[0077] Since the raw materials only contain lead bromide, MAPbBr3 nanocrystals cannot be synthesized.

[0078] Comparative Example 5:

[0079] The only difference from Example 1 is that the bromine-containing compound in the raw material is only octylamine bromide.

[0080] Since the raw material contains only octylamine bromide, MAPbBr3 nanocrystals cannot be synthesized.

[0081] Comparative Example 6:

[0082] The only difference from Example 1 is that the bromine-containing compound in the raw material is only hydrobromic acid.

[0083] Since the raw material only contains hydrobromic acid, MAPbBr3 nanocrystals cannot be synthesized.

[0084] X-ray diffraction (XRD) patterns of the MAPbBr3 nanocrystals@PVA films prepared in Examples 1-4 and Comparative Examples ( Figure 11 ), indicating that cubic phase MAPbBr3 nanocrystals were successfully synthesized in the prepared composite film; the PL and UV absorption spectra of the MAPbBr3 nanocrystals@PVA films prepared in Examples 1-4 and Comparative Example 1 are as follows Figure 12As shown, it shows that the quantum confinement of MAPbBr3 nanocrystals prepared after adding NOG ligand is enhanced;

[0085] Figure 13 The GSB decay dynamics of the femtosecond transient absorption (TA) spectra of the MAPbBr3 nanocrystal@PVA films prepared in Example 1 and Comparative Example 1 show that the defect state density of the two films is similar, and the addition of the NOG ligand accelerates the band-edge radiative recombination; Figure 14 The TRPL spectra of the MAPbBr3 nanocrystals@PVA films prepared in Example 1 and Comparative Example 1 show that after adding an appropriate amount of NOG ligand, the exciton radiative recombination rate is faster and the exciton recombination ratio is increased. Figure 15 It is the Huang Kun shadow fitted by the change of the half-peak width of the PL of the MAPbBr3 nanocrystal@PVA film prepared in Example 1 and Comparative Example 1 at 200K to 400K, indicating that the exciton-phonon interaction of the ligand with the addition of an appropriate amount of NOG is suppressed; Figure 16 It is the exciton binding energy fitted by the peak intensity change of the PL of the MAPbBr3 nanocrystal@PVA film prepared in Example 1 and Comparative Example 1 at a temperature ranging from 200K to 400K, indicating that the exciton binding energy increases after adding an appropriate amount of NOG ligand.

[0086] In summary, the present invention utilizes the -COOH double site of NOG to form a CO-Pb covalent bond with the nanocrystal surface, inhibiting the exciton-phonon interaction and ligand desorption from the surface of MAPbBr3 nanocrystals under blue light irradiation. The steric hindrance effect of NOG reduces the grain size, and the quantum confinement effect enhances the exciton binding energy, accelerates the radiative recombination rate, and thus reduces charge accumulation. -2 ) After continuous irradiation for 1444 hours, the PLQY of the MAPbBr3 nanocrystal@PVA film can still maintain more than 99% of the initial value. The good blue light irradiation stability makes it suitable for use in the backlight source of wide color gamut liquid crystal displays.

[0087] The specific embodiments described herein are merely illustrative of the spirit of the present invention. Persons skilled in the art may make various modifications, additions, or substitutions to the described specific embodiments without departing from the spirit of the present invention or exceeding the scope of the appended claims.

Claims

1. A MAPbBr3 nanocrystal@polymer optical film with long-term stability under blue light irradiation environment, characterized in that: The optical film is obtained by adding a bromine-containing compound and N-oxalylglycine into a precursor solution for ligand modification.

2. The MAPbBr3 nanocrystal@polymer optical film with long-term stability under blue light irradiation environment according to claim 1, characterized in that: The bromine-containing compound includes methylamine bromide, lead bromide, octylamine bromide and hydrobromic acid, wherein the mass ratio of methylamine bromide, lead bromide, octylamine bromide, hydrobromic acid and N-oxalylglycine is (5-30):(10-40):1:(1-30):(1-20).

3. The MAPbBr3 nanocrystal@polymer optical film with long-term stability under blue light irradiation environment according to claim 1, characterized in that: The amount of N-oxalylglycine added to the precursor solution is 1-150 mg / 100 mL.

4. The MAPbBr3 nanocrystal@polymer optical film with long-term stability under blue light irradiation environment according to claim 1, characterized in that: The precursor solution includes PVA powder and water in a mass ratio of (70-85): (900-1000).

5. A method for preparing a MAPbBr3 nanocrystal@polymer optical film that is stable for a long time under blue light irradiation as claimed in claim 1, characterized in that: The method comprises the following steps: adding a bromine-containing compound and N-oxalylglycine to a precursor solution for ligand modification, then dropping the ligand-modified mixed solution onto a flat glass surface after centrifugation and forming a transparent precursor layer by a blade coating technique.

6. The method for preparing a long-term stable MAPbBr3 nanocrystal@polymer optical film under blue light irradiation environment according to claim 5, characterized in that: The coating thickness is 50-200 microns and the coating area is 1-100 square centimeters during the coating process.

7. The method for preparing a long-term stable MAPbBr3 nanocrystal@polymer optical film under blue light irradiation environment according to claim 6, characterized in that: The transparent precursor layer needs to be heated after being scraped, wherein the heating temperature is 80-120° C. and the heating time is 1-10 minutes.

8. The method for preparing a long-term stable MAPbBr3 nanocrystal@polymer optical film under blue light irradiation environment according to claim 7, characterized in that: After the heating treatment, a standing treatment is required, wherein the standing temperature is 15-25°C, the humidity is 60-80%, and the time is 10-24 hours.

9. The MAPbBr3 nanocrystal@polymer optical film with long-term stability under blue light irradiation environment according to claim 1, characterized in that: The optical film has a fluorescence luminous efficiency of 88-97%, a half-peak width of 19-25 nm, and a luminous peak position adjustable within 518-528 nm.

10. Use of the optical film according to any one of claims 1 to 4 or the optical film prepared by the preparation method according to any one of claims 5 to 8 in a liquid crystal display backlight source.

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