A deep blue circularly polarized luminescent thin film and its preparation method and application

Abstract

The present invention discloses a deep blue circularly polarized luminescent thin film, its preparation method and application, which are characterized by including the following steps: S1: Prepare an electrospinning precursor solution: Using chiral aromatic amine salt, alkylamine salt (or formamidine salt or cesium salt) and lead halide as perovskite precursor salts, oleylamine and oleic acid as small molecule ligands, and polymer as the spinning matrix, and using N,N-dimethylformamide as the solvent to prepare the spinning precursor solution; S2: Place the spinning precursor solution described in step S1 in an electrospinning instrument and equipment for spinning, so that quasi-two-dimensional perovskite grows in the polymer to obtain a deep blue circularly polarized luminescent thin film. The synthesis method of the present invention is simple, and the obtained thin film has enhanced circularly polarized luminescence performance. Moreover, the excellent deep blue circularly polarized luminescence performance of the thin film at room temperature also makes it have great potential in circularly polarized luminescence devices.

Description

Technical Field

[0001] The present invention relates to the field of manufacturing perovskite and polymer composite electrospun fibers, and specifically refers to a preparation method of a quasi-two-dimensional perovskite composite polymer nanofiber film with a deep blue circularly polarized light response at room temperature and its application in circularly polarized light-emitting diodes. Background Art

[0002] In recent years, circularly polarized light has received extensive attention from researchers. Since it can carry more dimensional optical information, it plays an important role in fields such as quantum computing, optical information encryption, and magnetic storage.

[0003] Traditional methods for generating circularly polarized light require passing a light source through a linear polarizer and a quarter-wave plate. For example, see the literature shown in Chinese Patent Publication No. CN 105683824 B. These optical devices not only increase the cost of the devices but also are difficult to apply in micro-devices, which limits their application in the field of wearable devices. Therefore, it is of great significance to study materials that can directly emit circularly polarized light without optical elements.

[0004] Chiral metal halide quasi-two-dimensional perovskites are a promising class of circularly polarized light-emitting active materials because they have important chiral optoelectronic properties, such as spin-related optical selection rules, flexible non-centrosymmetric structures, and tunable organic-inorganic compositions. However, chiral quasi-two-dimensional perovskites usually achieve blue circularly polarized (one of the three primary colors) luminescence only at low temperatures. Currently, the research on quasi-two-dimensional perovskites with blue circularly polarized luminescence properties at room temperature is still in its infancy. In addition, achieving long-term stability in air and water is also of great significance for the commercial use of chiral perovskites.

[0005] Therefore, endowing metal halide quasi-two-dimensional perovskites with blue circularly polarized characteristics and improving their stability is of great significance in the field of chiral optoelectronics for realizing their potential applications in circularly polarized light-emitting diodes (LEDs), anti-counterfeiting, and spintronics. Summary of the Invention

[0006] To solve the problems and deficiencies existing in the prior art, the purpose of the present invention is to provide a deep blue circularly polarized light-emitting film, its preparation method and application. The preparation method of this solution is not only simple and effective, can realize the preparation of a large-area light-emitting polymer film material, and realizes the blue circularly polarized light emission of quasi-two-dimensional perovskite materials at room temperature.

[0007] To achieve the above purpose, the first aspect of the present invention is:

[0008] S1: Prepare an electrospinning precursor solution: The molecular formula of the perovskite is A2B nc-1 Pb nc Br3nc+1 , where A is a chiral aromatic amine cation, B is an alkylamine cation, a formamidinium cation or a cesium cation, and n c = 1 to 5; using a chiral aromatic amine salt, an alkylamine salt (or formamidinium salt or cesium salt) and lead halide as a perovskite precursor salt, oleylamine and oleic acid as small molecule ligands, and a polymer as a spinning matrix, and using N,N'-dimethylformamide as a solvent to prepare a spinning precursor solution;

[0009] S2: Place the spinning precursor solution described in step S1 in an electrospinning instrument and equipment for electrospinning, so that quasi-two-dimensional perovskite grows in the polymer to obtain a deep blue circularly polarized luminescent film.

[0010] A further setting is that the electrospinning is carried out in a coaxial manner to obtain a deep blue circularly polarized luminescent film with a coaxial structure.

[0011] A further setting is that the chiral aromatic amine salt in step S1 is any one of R- / S-methylbenzylammonium bromide or R- / S-methylnaphthylamine bromide, the alkylamine salt in step S1 is methylamine bromide, the cesium salt in step S1 is cesium bromide, the formamidinium salt in step S1 is formamidinium bromide, and the lead halide in step S1 is lead bromide.

[0012] A further setting is that the polymer in step S1 is any one of polyacrylonitrile, polymethyl methacrylate, polystyrene, polyvinylidene fluoride or polyvinyl alcohol.

[0013] A further setting is that when n of the quasi-two-dimensional perovskite c = 1 to 5, the molar ratios of methylamine bromide, lead bromide, and methylbenzylammonium bromide in step S1 are 2:0:1, 1:1 / 2:1, 2 / 3:2 / 3:1, 1 / 2:3 / 4:1, and 2 / 5:4 / 5:1, respectively.

[0014] A further setting is that the mass fraction of the polymer in the spinning precursor solution in step S1 is 10wt%-15wt%.

[0015] A further setting is that after the raw materials of the spinning precursor solution in step S1 are mixed, they are stirred at a speed of 600-800 rpm at 40 °C for 3-5 h.

[0016] A further setting is that the electrospinning in step S2 uses a roller to receive, the rotation speed of the roller is 900-1300 rpm / min, the voltage is 15-20 KV, the distance from the syringe needle to the roller is 15-18 cm, the propulsion speed of the propulsion system is 0.10 mL / min, and the electrospinning process in step S2 is carried out under the conditions of an ambient temperature of 25-30 °C and an ambient relative humidity of 40-50%.

[0017] It is further set that: in the step S2, the spinning precursor solution serves as the core, and the polymers of the spinning solution and the shell are any one of polyacrylonitrile, polymethyl methacrylate, polystyrene, polyvinylidene fluoride, and polyvinyl alcohol.

[0018] The second aspect of the present invention is to provide a deep blue circularly polarized luminescent film prepared by the preparation method as described above.

[0019] In addition, the present invention also provides an application of the deep blue circularly polarized luminescent film as described above as a blue circularly polarized luminescent active material in a circularly polarized light emitting diode.

[0020] The beneficial effects of the present invention are as follows:

[0021] 1. Through one-step electrospinning, the present invention in-situ grows stable quasi-two-dimensional perovskites with excellent blue circularly polarized luminescence properties (such as strong blue circularly polarized luminescence at room temperature) in polymer fibers.

[0022] 2. The introduction of electrospinning technology enables the large-scale production of its composite films.

[0023] 3. The excellent deep blue circularly polarized luminescence performance of the film at room temperature also makes it have great potential in future circularly polarized light emitting devices. Description of the Drawings

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, obtaining other drawings based on these drawings still belongs to the scope of the present invention.

[0025] Figure 1 It is the scanning electron microscope image (SEM) of the deep blue circularly polarized luminescent fiber film of S2 in Example 1;

[0026] Figure 2 It is the transmission electron microscope image (TEM) and schematic diagram of the deep blue circularly polarized luminescent fiber film of S2 in Example 1. a and b are the results at different magnifications. The red and yellow dotted circles in a represent the side and front of the chiral perovskite nanosheets;

[0027] Figure 3 It is the X-ray diffraction pattern (XRD) of the deep blue circularly polarized luminescent fiber film of S2 in Example 1;

[0028] Figure 4a is the ultraviolet-visible absorption spectrum (UV-vis) of the dark blue circularly polarized luminescent fiber film of S2 in Example 1, Figure 4 b is the fluorescence spectrum (PL) of the dark blue circularly polarized luminescent fiber film of S2 in Example 2;

[0029] Figure 5 a is the circular dichroism absorption spectrum (CD) of the dark blue circularly polarized luminescent fiber film of S2 in Example 1, Figure 5 b is the circularly polarized fluorescence spectrum (CPL) of the dark blue circularly polarized luminescent fiber film of S2 in Example 1;

[0030] Figure 6 a is the SEM image of the dark blue circularly polarized luminescent fiber film of S3 in Example 1, Figure 6 b is the TEM image of the dark blue circularly polarized luminescent fiber film of S3 in Example 1;

[0031] Figure 7 a is the SEM image of the dark blue circularly polarized luminescent fiber film of S2 in Example 2, Figure 7 b is the SEM image of the dark blue circularly polarized luminescent fiber film of S2 in Example 3;

[0032] Figure 8 a is the SEM image of the dark blue circularly polarized luminescent fiber film of S2 in Example 4, Figure 8 b is the SEM image of the dark blue circularly polarized luminescent fiber film of S2 in Example 5;

[0033] Figure 9 is the stability diagram of the dark blue circularly polarized luminescent fiber films of S2 using different polymer matrices in Examples 1, 4, and 5;

[0034] Figure 10 is the stability diagram of the dark blue circularly polarized luminescent fiber film with a coaxial structure of S3 in Example 1;

[0035] Figure 11 is the LED device diagram of the dark blue circularly polarized luminescent fiber film of S2 in Example 1. Detailed implementation mode

[0036] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings.

[0037] Example 1:

[0038] S1. Preparation of a perovskite spinning precursor with deep blue circularly polarized response, the steps are as follows: Methylammonium bromide (MABr), lead bromide (PbBr2), and methylbenzylammonium bromide (R- / S-MBABr) are precursor salts, and oleic acid (OA) and oleylamine (OAm) are ligands, which are dissolved in N,N-dimethylformamide (DMF). In a typical process, MABr, PbBr2, and R- / S-MBABr (the molar ratios of the precursor solutions with different n c values are shown in Table 1) are added to a 10 mL vial, then 3 mL of DMF, as well as OA (134 μL) and OAm (40 μL) are added to completely dissolve the precursor salts in DMF.

[0039] Specific molar ratios are shown in Table 1:

[0040]

[0041] S2. Dissolve polyacrylonitrile in S1 (mass ratio of polyacrylonitrile: DMF = 3:20), and stir. After the reaction mixture is stirred at room temperature for 3 h, an electrospinning precursor solution is obtained. Transfer 2 mL of the above transparent solution to a 22G (inner diameter 0.4 mm) syringe with a metal needle. Apply a 20 kV high-voltage power supply to the metal needle, set the pushing speed of the propulsion system to 0.5 mL / h, and the electrospun nanofiber film is collected by aluminum foil. The collection distance between the metal needle and the collector is 15 cm. Prepare other n c value samples by adjusting the ratio of MABr2 and R- / S-MBABr.

[0042] S3. Transfer the spinning precursor solution prepared in S2 to a syringe without a metal needle. Dissolve polystyrene in DMF (mass ratio of polystyrene: DMF = 3:20). After the reaction mixture is stirred at room temperature for 3 h, an outer shell solution is obtained. Transfer 2 mL of the outer shell solution to a syringe without a metal needle. The syringes containing the spinning precursor solution and the outer shell solution are installed on a coaxial propulsion system. Apply a 20 kV high-voltage power supply to the metal needle, set the pushing speed of the propulsion system to 0.5 mL / h, and the electrospun nanofiber film is collected by aluminum foil. The collection distance between the metal needle and the collector is 15 cm.

[0043] Performance testing:

[0044] 1. SEM and TEM tests of samples with different n c values

[0045] SEM sample preparation: Paste the electrospun fibers on the sample stage with carbon glue, and then spray gold for 30 s before testing. The test results are as Figure 1 shown. It can be seen from the figure that the size distribution of the prepared electrospun film is uniform and the surface is smooth.

[0046] TEM sample preparation: The micro-grid was pasted on the electrospinning roller with double-sided tape, and then electrospinning was carried out. After one minute, the micro-grid was removed, and n-hexane was dropped on the micro-grid to fix the sample. Then let the sample dry naturally. As Figure 2 shown, the perovskite nanosheets are uniformly distributed in the prepared fibers and there is a stacking phenomenon, indicating the existence of multi-layer perovskite.

[0047] 2. X-ray diffraction test of samples with different n c values

[0048] After compacting the fiber samples, they were laid flat on the sample stage for testing; as can be seen from Figure 3 it, the (002), (040), and (006) diffractions are the characteristic diffraction peaks of quasi-two-dimensional perovskite, and the (100), (200), (110), and (210) diffractions are the characteristic diffraction peaks of three-dimensional perovskite;

[0049] 3. Absorption and emission spectra tests of samples with different n c values

[0050] As can be seen from Figure 4 a, the characteristic absorption peak of the sample with n c value of 1 is around 390 nm, the characteristic absorption peak of the sample with n c value of 2 is around 425 nm, and the samples with n c value greater than 2 have multiple absorption peaks at 425 nm, 450 nm, and 467 nm; as can be seen from Figure 4 b, the luminescence performance of the sample with n value of 1 is the weakest. When the n c value ranges from 2 to 5, the fluorescence characteristic emission peak of the perovskite composite polymer film redshifts from 440 nm to 475 nm;

[0051] 4. Circular dichroism absorption and circularly polarized fluorescence spectra tests of samples with different n c values

[0052] As can be seen from Figure 5 a, as the n c value increases, the CD intensity of the composite material continuously decreases, indicating that the less the content of chiral molecules, the weaker the circular dichroism of the composite material; as can be seen from Figure 5 b, as the n c value increases, the CPL intensity of the composite material always remains in the same dimension, indicating that the dimension has not much influence on CPL, and the shape of the CPL spectrum is basically the same as that of the PL spectrum;

[0053] 5. SEM and TEM tests of samples with different polymer protections and different B sites

[0054] As can be seen fromFigure 6 It can be seen that for the coaxial electrospinning sample with polystyrene as the shell and polyacrylonitrile as the core, the electrospun fibers are evenly distributed, and the average diameter is about 372 nm; from Figure 6 It can be seen from b that for the coaxial electrospinning sample with polystyrene as the shell and polyacrylonitrile as the core, there is an obvious boundary between polystyrene and polyacrylonitrile, proving the successful synthesis of the core-shell structure; from Figure 7 It can be seen from a that for the sample with FA + as the B site, the electrospun fibers are evenly distributed, and the average diameter is about 342 nm; from Figure 7 It can be seen from b that for the sample with Cs + as the B site, the electrospun fibers are evenly distributed, and the average diameter is about 402 nm; from Figure 8 It can be seen from a that for the sample with polymethyl methacrylate as the electrospinning matrix, the electrospun fibers are evenly distributed, and the average diameter is about 353 nm; from Figure 8 It can be seen from b that for the sample with polyacrylonitrile as the electrospinning matrix, the electrospun fibers are evenly distributed, and the average diameter is about 1250 nm;

[0055] 6. Stability test of samples protected by different polymers

[0056] Figure 9 It can be seen from the results that when using polyacrylonitrile, polystyrene, and polymethyl methacrylate as the electrospinning matrix, the best air stability is shown by polymethyl methacrylate, which can still maintain 73% of the initial fluorescence intensity after being placed in an environment with a humidity of 70% for three days;

[0057] 7. Stability test of coaxial electrospinning samples

[0058] Figure 10 It can be seen that the deep blue circularly polarized luminescent film using the coaxial electrospinning structure has excellent air stability and water stability. It can still maintain 82% of the initial fluorescence intensity after being placed in an environment with a humidity of 70% for 15 days; and it can still maintain 66% of the initial fluorescence intensity after being placed in water for 36 hours;

[0059] Example 2:

[0060] S1. Preparation of a perovskite spinning precursor with deep blue circularly polarized response, steps are as follows: Cesium bromide (CsBr), lead bromide (PbBr2), and methylbenzylammonium bromide (R- / S-MBABr) are precursor salts, and oleic acid (OA) and oleylamine (OAm) are ligands, which are dissolved in N,N-dimethylformamide (DMF). In a typical process, CsBr, PbBr2, and R- / S-MBABr (molar ratio 1:1 / 2:1) are added into a 10 mL vial, then 3 mL of DMF, as well as OA (134 μL) and OAm (40 μL) are added to completely dissolve the precursor salts into DMF.

[0061] S2. Dissolve polyacrylonitrile in S1 (mass ratio of polyacrylonitrile:DMF = 3:20), and stir. After the reaction mixture is stirred at room temperature for 3 h, an electrospinning precursor solution is obtained. Transfer 2 mL of the above transparent solution into a 22G (inner diameter 0.4 mm) syringe with a metal needle. Apply a 20 kV high-voltage power supply to the metal needle, set the pushing speed of the propulsion system to 0.5 mL / h, and collect the electrospun nanofiber film with aluminum foil. The collection distance between the metal needle and the collector is 15 cm.

[0062] Example 3:

[0063] S1. Preparation of a perovskite spinning precursor with deep blue circularly polarized response, steps are as follows: Formamidinium bromide (FABr), lead bromide (PbBr2), and methylbenzylammonium bromide (R- / S-MBABr) are precursor salts, and oleic acid (OA) and oleylamine (OAm) are ligands, which are dissolved in N,N-dimethylformamide (DMF). In a typical process, FABr, PbBr2, and R- / S-MBABr (molar ratio 1:1 / 2:1) are added into a 10 mL vial, then 3 mL of DMF, as well as OA (134 μL) and OAm (40 μL) are added to completely dissolve the precursor salts into DMF.

[0064] S2. Dissolve polyacrylonitrile in S1 (mass ratio of polyacrylonitrile:DMF = 3:20), and stir. After the reaction mixture is stirred at room temperature for 3 h, an electrospinning precursor solution is obtained. Transfer 2 mL of the above transparent solution into a 22G (inner diameter 0.4 mm) syringe with a metal needle. Apply a 20 kV high-voltage power supply to the metal needle, set the pushing speed of the propulsion system to 0.5 mL / h, and collect the electrospun nanofiber film with aluminum foil. The collection distance between the metal needle and the collector is 15 cm.

[0065] Example 4:

[0066] S1. Preparation of a perovskite electrospinning precursor with deep blue circularly polarized response is as follows: Methylammonium bromide (MABr), lead bromide (PbBr2), and methylbenzylammonium bromide (R- / S-MBABr) are precursor salts, and oleic acid (OA) and oleylamine (OAm) are ligands, which are dissolved in N,N-dimethylformamide (DMF). In a typical process, MABr, PbBr2, and R- / S-MBABr (in a ratio of 1:1 / 2:1) are added to a 10 mL vial, then 3 mL of DMF, as well as OA (134 μL) and OAm (40 μL) are added to completely dissolve the precursor salts in DMF.

[0067] S2. Poly(methyl methacrylate) is dissolved in S1 (mass ratio of poly(methyl methacrylate):DMF = 3:20), and stirred. After the reaction mixture is stirred at room temperature for 3 h, an electrospinning precursor solution is obtained. 2 mL of the above transparent solution is transferred to a 22G (inner diameter 0.4 mm) syringe with a metal needle. A 20 kV high-voltage power supply is applied to the metal needle, and the pushing speed of the propulsion system is set at 0.5 mL / h. The electrospun nanofiber film is collected by aluminum foil, and the collection distance between the metal needle and the collector is 15 cm.

[0068] Example 5:

[0069] S1. Preparation of a perovskite electrospinning precursor with deep blue circularly polarized response is as follows: Methylammonium bromide (MABr), lead bromide (PbBr2), and methylbenzylammonium bromide (R- / S-MBABr) are precursor salts, and oleic acid (OA) and oleylamine (OAm) are ligands, which are dissolved in N,N-dimethylformamide (DMF). In a typical process, MABr, PbBr2, and R- / S-MBABr (in a ratio of 1:1 / 2:1) are added to a 10 mL vial, then 3 mL of DMF, as well as OA (134 μL) and OAm (40 μL) are added to completely dissolve the precursor salts in DMF.

[0070] S2. Polystyrene is dissolved in S1 (mass ratio of polystyrene:DMF = 3:20), and stirred. After the reaction mixture is stirred at room temperature for 3 h, an electrospinning precursor solution is obtained. 2 mL of the above transparent solution is transferred to a 22G (inner diameter 0.4 mm) syringe with a metal needle. A 20 kV high-voltage power supply is applied to the metal needle, and the pushing speed of the propulsion system is set at 0.5 mL / h. The electrospun nanofiber film is collected by aluminum foil, and the collection distance between the metal needle and the collector is 15 cm.

[0071] Example 6:

[0072] Device preparation: Cut a 0.5 cm * 0.5 cm thin sheet from the composite material synthesized in Example 1 and attach it to a 375 nm ultraviolet lamp bead. A photoluminescent LED device is obtained.

[0073] Circular polarization performance test of the device

[0074] As Figure 11 shown, the device has excellent deep blue light emission performance and good performance in selectively emitting left-handed and right-handed circularly polarized light;

[0075] The above-disclosed are only the preferred embodiments of the present invention. Of course, the scope of the rights of the present invention cannot be limited thereby. Therefore, equivalent changes made according to the claims of the present invention still fall within the scope covered by the present invention.

Claims

1. A method for preparing a deep blue circularly polarized luminescent film, characterized in that: It includes the following steps: S1: Prepare an electrospun perovskite precursor solution: The molecular formula of the perovskite is A2B nc- 1Pb nc Br 3nc+1 , where A is a chiral aromatic amine cation, B is an alkylamine cation, a formamidine cation or a cesium cation, n c = 1 - 5; In this step, any one of alkylamine salts, formamidine salts or cesium salts, chiral aromatic amine salts and lead halides are used as perovskite precursor salts, oleylamine oleic acid is used as a small molecule ligand, and a polymer is used as a spinning matrix. Using N, N-dimethylformamide as a solvent, a spinning precursor solution is prepared; S2: Place the spinning precursor solution described in step S1 in an electrospinning instrument and equipment for spinning, grow quasi-two-dimensional perovskite in the polymer, and obtain a deep blue circularly polarized luminescent film; The spinning is carried out in a coaxial manner, and the spinning precursor solution is used as the core, and the polymers of the spinning solution and the shell are any one of polyacrylonitrile, polymethyl methacrylate, polystyrene, polyvinylidene fluoride, and polyvinyl alcohol, to obtain a deep blue circularly polarized luminescent film with a coaxial structure.

2. The preparation method of a deep blue circularly polarized luminescence thin film according to claim 1, characterized in that: The chiral aromatic amine salt in the step S1 is R - / S -methylbenzylammonium bromide or R - / S -methylnaphthylmethylamine bromide, the alkylamine salt in the step S1 is methylamine bromide, the cesium salt in the step S1 is cesium bromide, the formamidine salt in the step S1 is formamidine bromide, and the lead halide in the step S1 is lead bromide.

3. The preparation method of a deep blue circularly polarized luminescent thin film according to claim 1, wherein: The polymer in the step S1 is any one of polyacrylonitrile, polymethyl methacrylate, polystyrene, polyvinylidene fluoride or polyvinyl alcohol.

4. The preparation method of a deep blue circularly polarized luminescent thin film according to claim 1, characterized in that: For the described quasi-two-dimensional perovskite n c When = 1 to 5, the molar ratios of methylammonium bromide, lead bromide, and methylbenzylammonium bromide in step S1 are 2:0:1, 1:1 / 2:1, 2 / 3:2 / 3:1, 1 / 2:3 / 4:1, or 2 / 5:4 / 5:1, respectively.

5. The preparation method of a deep blue circularly polarized luminescent thin film according to claim 1, wherein: The mass fraction of the polymer in the spinning precursor solution in the step S1 is 10 wt%-15 wt%.

6. The preparation method of a deep blue circularly polarized luminescence thin film according to claim 1, characterized in that: After the raw materials of the spinning precursor solution in the step S1 are mixed, they are stirred at a speed of 600-800 rpm at 40 °C for 3-5 h.

7. The preparation method of a deep blue circularly polarized luminescent thin film according to claim 1, wherein: In the step S2, electrospinning is carried out using a roller receiver. The rotation speed of the roller is 900~1300 rpm / min, the voltage is 15-20 KV, the distance from the syringe needle to the roller is 15-18 cm, and the feeding speed of the feeding system is 0.10 mL / min. The electrospinning process in the step S2 is carried out under the conditions of an ambient temperature of 25-30 °C and an ambient relative humidity of 40-50%.

8. A deep blue circularly polarized luminescent film prepared by the preparation method according to claim 1.

9. An application of the deep blue circularly polarized luminescent film according to claim 8 as a circularly polarized luminescent active material in a circularly polarized light emitting diode.

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