Method for preparing high-stability cellulose acetate perovskite quantum dot material by one-step method

Abstract

The invention relates to the technical field of semiconductor materials, and provides a method for preparing a high-stability cellulose acetate perovskite quantum dot material by a one-step method, cellulose acetate (CA) is used as an inorganic matrix, CsPbBr3PQDs are generated and packaged in one step by an improved ligand-assisted precipitation method, and a CA-CsPbBr3PQDs composite film with a cicada pupa-shaped gap network structure is formed. According to the composite film, high-quality PQDs (the uniform size is 5.7 nm, the narrow FWHM is equal to 20.6 nm and the long quantum life is 16.9 ns) are prepared, the environmental stability of the composite film is remarkably enhanced, the optical performance of the composite film is not obviously reduced after 60-day water immersion and 100-day UV-resistant experiments, and the composite film has excellent extreme environment adaptability.

Description

Technical Field

[0001] This invention patent relates to the technical field of quantum dot materials, and particularly to a method for preparing highly stable cellulose acetate perovskite quantum dot materials by a one-step method. Background Art

[0002] Quantum dots are tiny semiconductor particles with sizes in the order of a few nanometers. They exhibit unique electronic and optical properties different from those of bulk semiconductor materials, and their electron wave functions are similar to the discrete electron states of real atoms. Therefore, they are often referred to as artificial atoms. Quantum dots have been applied in various modern technologies, including solar cells, photodetectors, field-effect transistors, biomedicine, and light-emitting diodes. Perovskite quantum dots (PQDs) are a new type of optoelectronic nanomaterial developed in recent years. Among them, oil-soluble inorganic perovskite CsPbX3 (X = Cl, Br, I) has the characteristics of being inexpensive, color-tunable, narrow full width at half maximum (FWHM < 40 nm), cadmium-free, and high photoluminescence quantum yield (PLQY > 95%). In the prior art, the preparation methods of perovskite quantum dots generally include porous structure template synthesis method, hot injection method (HI), ligand-assisted precipitation method (LARP), ultrasonic synthesis method, microwave radiation synthesis method, ball milling method, and laser-assisted in-situ synthesis method, etc. These methods effectively prepare PQDs with uniform distribution, stronger luminescence intensity, and better stability. Currently, the mainstream PODs preparation methods mainly rely on the hot injection method and ligand-assisted reprecipitation.

[0003] Compared with traditional quantum dots and rare earth fluorescent materials, perovskite quantum dots exhibit excellent optical properties, and the preparation method is simple and the cost is low. However, whether it is metal-organic hybrid perovskite quantum dots or all-inorganic perovskite quantum dots, the problem of poor stability is still significant, which limits their application in complex environments. Due to its ionic compound characteristics, perovskite is prone to ion migration in natural environments, continuous irradiation, and polar solvents such as water. Ion exchange makes the spectral tuning of perovskite easy, but it also leads to the instability of the structure of mixed halogen perovskite itself. In the prior art, ligands such as alkanes with different chain lengths, conjugated structures, silanes, and inorganic ligands are used to solve problems such as crystal defects, stability, optical regulation, charge transport, and film formation during growth. However, the addition of ligands often introduces complex synthesis steps and chemical environments, increasing the difficulty and cost of the synthesis process, and may also affect the optical properties and subsequent processing applications of quantum dots. Against this background, synthesizing high-quality quantum dots using a simplified synthesis method has become an important research direction.

[0004] A large number of research results have been achieved in the application of cellulose and its derivatives in perovskite materials, mainly reflected in being used as a substrate membrane, reinforcing material, and auxiliary role in the crystal growth process. In the prior art, cellulose nanocrystal (CNC) colloidal materials can effectively mix with CH3NH3PbBr3 precursors and spontaneously form perovskite crystals during the film-forming process. The film has a light absorption efficiency of 91% and strong green light emission (518 nm).

[0005] Cellulose Acetate (CA), as a natural polymer material with good biodegradability and film-forming properties, has been widely used in perovskite solar cells in recent years due to its moisture resistance, heat resistance, good optical transparency, and ultraviolet shielding potential. However, there is no report on the technology of directly using cellulose acetate and perovskite quantum dots to prepare perovskite quantum dots by a one-step film-forming method to improve the stability of perovskite quantum dots. Summary of the Invention

[0006] In order to solve the problems of non-renewable raw materials and high synthesis costs caused by the cumbersome synthesis conditions due to treating surface defects to enhance the stability of PQDs by organic ligand design, polymer, and molecular organic framework (MOF) coating encapsulation in the prior art, the purpose of the present invention is to provide a method for preparing a highly stable cellulose acetate perovskite quantum dot material by a one-step method. Using cellulose acetate (CA) as an inorganic matrix, CsPbBr3 PQDs are generated and encapsulated in one step by improving the ligand-assisted precipitation method, forming a CA-CsPbBr3 PQDs composite film with a cicada pupa-like void network structure. The composite film not only prepares high-quality PQDs (uniform size of 5.7 nm, narrow FWHM = 20.6 nm, and high quantum lifetime of 16.9 ns), but also significantly enhances its environmental stability. After 60 days of water immersion and 100 days of UV resistance experiments, its optical performance does not significantly decline, showing excellent extreme environmental adaptability.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] The present invention provides a method for preparing a highly stable cellulose acetate perovskite quantum dot material by a one-step method, comprising the following steps:

[0009] (1) Synthesis of the precursor solution: Dissolve CsBr and PbBr2 in DMF, stir magnetically at room temperature until the solution is completely transparent, and seal for later use;

[0010] (2) Preparation of the CA solution: Dissolve cellulose acetate powder in DMF and seal for later use;

[0011] (3) Preparation of CA-CsPbBr3-PQDs composite film: Add the precursor solution in step (1) to the CA solution in step (2), stir magnetically at room temperature, perform vacuum filtration, and then conduct vacuum drying to obtain the CA-CsPbBr3-PQDs composite film.

[0012] The synthesis schematic diagram of the method for preparing high-stability cellulose acetate perovskite quantum dot materials by the one-step method of the present invention is as Figure 1 shown.

[0013] Furthermore, the molar ratio of CsBr to PbBr2 in step (1) is 1:1.

[0014] Furthermore, the solid-liquid ratio of the precursor solution in step (1) is 14 - 15 g / L.

[0015] Furthermore, the rotation speed of the magnetic stirring in step (1) is 600 rpm, and the time of the magnetic stirring is 3 h.

[0016] Furthermore, the concentration of the CA solution in step (2) is 2 wt%.

[0017] Furthermore, the volume ratio of the precursor solution to the CA solution in step (3) is (1 - 5):10.

[0018] Even further, the volume ratio of the precursor solution to the CA solution in step (3) is 2.5:10.

[0019] Furthermore, the rotation speed of the magnetic stirring in step (3) is 600 rpm, and the time of the magnetic stirring is 3 h.

[0020] Furthermore, the time of the vacuum filtration in step (3) is 24 h.

[0021] Furthermore, the vacuum degree of the vacuum drying in step (3) is 0.1 atmospheres.

[0022] Furthermore, the temperature of the vacuum drying in step (3) is 45 °C, and the time of the vacuum drying is 24 h.

[0023] Furthermore, the size of the cellulose acetate perovskite quantum dots is 5 - 6.5 nm.

[0024] Even further, the size of the cellulose acetate perovskite quantum dots is 5.7 nm.

[0025] The beneficial effects that can be produced by this application are as follows:

[0026] (1) The present invention prepares a CA-CsPbBr3-PQDs film with excellent luminescence performance through a one-step method. By simplifying the ligand-assisted precipitation method, the precursor solution without addition is mixed in the CA solution, and PQDs are generated and encapsulated inside the CA in one step, thus preparing a CA-CsPbBr3-PQDs composite film with excellent luminescence performance.

[0027] (2) The CA-CsPbBr3-PQDs film has excellent optical properties and stability. The composite film has a long quantum lifetime (τ ave = 16.895 ns), a narrow FWHM (20.6 nm), and a relatively uniform quantum dot size (5.7 nm). It has good ability to maintain the crystal structure at low temperature (E b = 80.74 meV, and the FWHM peak position remains unchanged).

[0028] (3) It shows excellent stability in the stability tests of humid and ultraviolet environments. The PL intensity does not decrease after being immersed in water for 60 days, and the PL performance is still 86.2% of the original after being irradiated by 16W ultraviolet light for 100 days, greatly reducing the susceptibility of PODs to extreme environments such as water and ultraviolet light. Description of the Drawings

[0029] Figure 1 It is a schematic diagram of the synthesis method for preparing a highly stable cellulose acetate perovskite quantum dot material by the one-step method of the present invention.

[0030] Figure 2 It is an X-ray diffraction spectrogram of the CA-CsPbBr3-PQDs composite film prepared in Example 1. The left inset is a photo excited by 365 nm ultraviolet light, and the right is its high-resolution TEM photo.

[0031] Figure 3 It is an optical property analysis diagram of the CA-CsPbBr3-PQDs composite film prepared in Example 1. (a-c) show the TEM images of CA-CsPbBr3-PQDs, and the inset is a statistical chart of the quantum dot size distribution under a 20 nm TEM image; (d-e) are the environmental conditions and POM photos of the prepared CA-CsPbBr3-PQDs quantum dot film, and (f-g) are the photos taken under 360 nm ultraviolet light and POM in the UV mode.

[0032] Figure 4Temperature-dependent test chart of the CA-CsPbBr3-PQDs composite film prepared in Example 1, where (a) is the PL spectrum of CA-CsPbBr3-PQDs varying with temperature in the range of 80 - 300 K; (b) is the calculation of the exciton binding energy: the function of 1 / PL and 1 / T of CA-CsPbBr3-PQDs, and the solid line best fits a model assuming the existence of free excitons and self-trapped excitons; (c) is the temperature dependence of the emission peak energy; (d) is the FWHM of the steady-state PL spectrum as a function of temperature.

[0033] Figure 5 Cross-sectional SEM photos of the CA-CsPbBr3-PQDs composite film prepared in Example 5 and the CA film prepared in Comparative Example 2, where (a-c) show the scanning electron microscope photos of the cross-section of the pure CA film formed in Comparative Example 2; (d-f) show the scanning electron microscope photos of the cross-section of the CA-CsPbBr3-PQDs composite film prepared in Example 5.

[0034] Figure 6 PL spectra of the CA-CsPbBr3-PQDs composite films prepared in Examples 1 - 10, where (a) shows the photoluminescence spectra of CA-CsPbBr3-PQDs with different doping volumes in the form of a three-dimensional map; (b) the dependence of the PL peak intensity of CA-CsPbBr3-PQDs and (c) the position of the emission peak on the doping volume.

[0035] Figure 7 PL spectrogram of the CA-CsPbBr3-PQDs composite film prepared in Example 1 and CsPbBr3PQDs prepared in Comparative Example 1 under 360 nm ultraviolet light excitation.

[0036] Figure 8 PL spectrogram of the CA-CsPbBr3-PQDs composite film prepared in Example 1 immersed in pure water, and the inset shows its contact angle test, natural light and 360 nm ultraviolet photos.

[0037] Figure 9UV tolerance test charts of the CA-CsPbBr3-PQDs composite film prepared in Example 1 and the CsPbBr3 PQDs prepared in Comparative Example 1, where (a) is the PL spectrum of the CsPbBr3 PQDs prepared in Comparative Example 1 under continuous 16W UV, (b) shows the changes in the PL intensity and emission peak position of the CsPbBr3 PQDs prepared in Comparative Example 1 over time; (c) is the PL spectrum of the CA-CsPbBr3-PQDs composite film prepared in Example 1 under continuous 16W UV, (d) shows the changes in the PL intensity and emission peak position of the CA-CsPbBr3-PQDs composite film prepared in Example 1 over time. Detailed implementation manners

[0038] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.

[0039] In the following examples and comparative examples, the cellulose acetate powder was purchased from Shanghai Macklin Biochemical Technology and contained 9.8 wt% acetyl group and 3.5 wt% hydroxyl group.

[0040] Example 1

[0041] A method for preparing a highly stable cellulose acetate perovskite quantum dot material by a one-step method, comprising the following steps:

[0042] (1) Synthesis of the precursor solution: Dissolve 0.5 mmol CsBr and 0.5 mmol PbBr2 in 20 mL of DMF respectively, set the magnetic stirrer to 600 rpm, stir at room temperature for 3 hours until the solution is completely transparent, and store it sealed in a sample bottle for subsequent use;

[0043] (2) Preparation of the CA solution: Dissolve the cellulose acetate powder in DMF at room temperature to prepare a CA solution with a concentration of 2 wt%, and seal the prepared CA solution with a sealant for later use;

[0044] (3) Preparation of the CA-CsPbBr3-PQDs composite film: Take 2.5 mL of the precursor solution in step (1) and add it to 10 mL of the CA solution in step (2), stir magnetically at 600 rpm at room temperature for 3 hours, vacuum filter for 24 hours, and then dry in a vacuum drying oven at 45 °C under 0.1 atmospheric pressure for 24 hours to obtain the CA-CsPbBr3-PQDs composite film.

[0045] The X-ray diffraction spectrogram of the CA-CsPbBr3-PQDs composite film prepared in this example is as follows Figure 2 shown. The left inset is a photo under 365 nm ultraviolet light excitation, and the right one is its high-resolution TEM photo; the quantum dot liquid in the cuvette emits bright green light, and this strong luminescence performance proves the successful preparation of PQDs. The characteristic peaks 15.21°, 21.50°, 30.70°, 34.20°, 37.60°, 43.69° in the XRD pattern correspond to the (100), (110), (200), (210), (211), (202) crystal planes of the perovskite structure cubic crystal image, corresponding to the pdf card of cesium lead bromide perovskite. The TEM photo on the right further confirms the formation of CsPbBr3 PQDs.

[0046] The optical property analysis diagram of the CA-CsPbBr3-PQDs composite film prepared in this example is as follows Figure 3 shown. (a-c) show the TEM images of CA-CsPbBr3-PQDs, and the inset is the statistical chart of the quantum dot size distribution under the 20 nm TEM image; (d-e) show the CA-CsPbBr3-PQDs quantum dot film under environmental conditions and POM photos, and (f-g) are the photos taken under 360 nm ultraviolet light and POM in the UV mode. (a) shows that PQDs are evenly dispersed on the surface of CA. The average size of the generated quantum dots is statistically obtained as 5.7 nm, mainly concentrated in the range of 5 nm and 6.5 nm. The synthesized PQDs have a narrow size distribution and uniform size. Figure (c) shows the structure and lattice spacing of single PQDs as 0.205 nm, corresponding to the (200) plane, which is consistent with the lattice parameters of CsPbBr3 PQDs reported previously. (d-e) show that the CA-CsPbBr3-PQDs film presents a light yellow color as a whole under natural light. The surface of CA observed by POM is not a smooth surface. When the surface solvent volatilizes and water molecules precipitate, the CA molecular chains are prone to contract and attract each other, and at the same time, it also provides a strong coating and spatial confinement effect for the formation of PQDs. (f) shows that under 360 nm ultraviolet light excitation, the film exhibits bright pure green fluorescence. When observing the CA-G-PQDs film using POM under ultraviolet excitation, the result is as shown in (g). The luminescence uniformity of the surface PQDs of the film at the microscale shows that there are no local quenching or strong absorption regions in the film, indicating that the quantum dots are evenly dispersed in the film.

[0047] The temperature dependence test diagram of the CA-CsPbBr3-PQDs composite film prepared in this example is as follows Figure 4As shown, where (a) is the PL spectrum of CA-CsPbBr3-PQDs as a function of temperature in the range of 80 - 300 K; (b) is the calculation of the exciton binding energy: 1 / PL of CA-CsPbBr3-PQDs as a function of 1 / T, and the solid line best fits a model assuming the existence of free excitons and self-trapped excitons; (c) is the temperature dependence of the emission peak energy; (d) is the FWHM of the steady-state PL spectrum as a function of temperature. The PL intensity of CA-CsPbBr3-PQDs in (a) gradually increases from 80 K to 140 K and then continuously decreases after 140 K. After calculation, the exciton binding energy E b = 80.74 meV was obtained; it can be seen from (c) that under the coordination and spatial confinement chelation, the PQDs with the assisted growth of CA have a stable lattice structure. When the temperature changes, the energy change caused by the electron-phonon interaction is small, which means that the PQDs can maintain relatively stable optoelectronic properties at different temperatures. It can be seen from (d) that when the temperature rises from 80 K to 140 K, the FWHM of CA-CsPbBr3-PQDs decreases from 55.35 meV to 44.46 meV. The reason is that the increase in the exciton binding energy at low temperature means that electrons and holes are more tightly bound together, reducing the interaction with the lattice and thus reducing the phonon-induced scattering events.

[0048] Example 2

[0049] A method for preparing highly stable cellulose acetate perovskite quantum dot materials by a one-step method, comprising the following steps:

[0050] (1) Synthesis of the precursor solution: Dissolve 0.5 mmol of CsBr and 0.5 mmol of PbBr2 in 20 mL of DMF respectively, set the magnetic stirrer to 600 rpm, stir at room temperature for 3 hours until the solution is completely transparent, and store it sealed in a sample bottle for subsequent use;

[0051] (2) Preparation of the CA solution: Dissolve cellulose acetate powder in DMF at room temperature to prepare a 2 wt% CA solution, and seal the prepared CA solution with a sealant for standby;

[0052] (3) Preparation of the CA-CsPbBr3-PQDs composite film: Take 0.5 mL of the precursor solution in step (1) and add it to 10 mL of the CA solution in step (2), stir magnetically at 600 rpm at room temperature for 3 hours, vacuum filter for 24 hours, and then dry in a vacuum drying oven at 45 °C under 0.1 atmospheric pressure for 24 hours to obtain the CA-CsPbBr3-PQDs composite film.

[0053] Example 3

[0054] A method for preparing highly stable cellulose acetate perovskite quantum dot materials by a one-step method, comprising the following steps:

[0055] (1) Synthesis of precursor solution: Dissolve 0.5 mmol of CsBr and 0.5 mmol of PbBr2 in 20 mL of DMF respectively, set the magnetic stirrer to 600 rpm, stir at room temperature for 3 hours until the solution is completely transparent, and store it sealed in a sample bottle for subsequent use;

[0056] (2) Preparation of CA solution: Dissolve cellulose acetate powder in DMF under normal temperature conditions to prepare a CA solution with a concentration of 2 wt%, and seal the prepared CA solution with a sealant for standby;

[0057] (3) Preparation of CA-CsPbBr3-PQDs composite film: Take 1 mL of the precursor solution in step (1) and add it to 10 mL of the CA solution in step (2), stir magnetically at 600 rpm at room temperature for 3 hours, vacuum filter for 24 hours, and then dry in a vacuum drying oven at 45 °C under a vacuum of 0.1 atmosphere for 24 hours to obtain a CA-CsPbBr3-PQDs composite film.

[0058] Example 4

[0059] A method for preparing highly stable cellulose acetate perovskite quantum dot materials by a one-step method, comprising the following steps:

[0060] (1) Synthesis of precursor solution: Dissolve 0.5 mmol of CsBr and 0.5 mmol of PbBr2 in 20 mL of DMF respectively, set the magnetic stirrer to 600 rpm, stir at room temperature for 3 hours until the solution is completely transparent, and store it sealed in a sample bottle for subsequent use;

[0061] (2) Preparation of CA solution: Dissolve cellulose acetate powder in DMF under normal temperature conditions to prepare a CA solution with a concentration of 2 wt%, and seal the prepared CA solution with a sealant for standby;

[0062] (3) Preparation of CA-CsPbBr3-PQDs composite film: Take 1.5 mL of the precursor solution in step (1) and add it to 10 mL of the CA solution in step (2), stir magnetically at 600 rpm at room temperature for 3 hours, vacuum filter for 24 hours, and then dry in a vacuum drying oven at 45 °C under a vacuum of 0.1 atmosphere for 24 hours to obtain a CA-CsPbBr3-PQDs composite film.

[0063] Example 5

[0064] A method for preparing highly stable cellulose acetate perovskite quantum dot materials by a one-step method, comprising the following steps:

[0065] (1) Synthesis of precursor solution: Dissolve 0.5 mmol of CsBr and 0.5 mmol of PbBr2 separately in 20 mL of DMF. Set the magnetic stirrer to 600 rpm and stir at room temperature for 3 hours until the solution becomes completely transparent. Seal it and store it in a sample bottle for subsequent use;

[0066] (2) Preparation of CA solution: Dissolve cellulose acetate powder in DMF at room temperature to prepare a CA solution with a concentration of 2 wt%. Seal the prepared CA solution with a sealant for later use;

[0067] (3) Preparation of CA-CsPbBr3-PQDs composite film: Take 2 mL of the precursor solution from step (1) and add it to 10 mL of the CA solution from step (2). Stir magnetically at 600 rpm at room temperature for 3 hours, then perform vacuum filtration for 24 hours and dry in a vacuum drying oven at 45 °C under a vacuum of 0.1 atm for 24 hours to obtain the CA-CsPbBr3-PQDs composite film.

[0068] Example 6

[0069] A method for preparing highly stable cellulose acetate perovskite quantum dot materials by a one-step method, comprising the following steps:

[0070] (1) Synthesis of precursor solution: Dissolve 0.5 mmol of CsBr and 0.5 mmol of PbBr2 separately in 20 mL of DMF. Set the magnetic stirrer to 600 rpm and stir at room temperature for 3 hours until the solution becomes completely transparent. Seal it and store it in a sample bottle for subsequent use;

[0071] (2) Preparation of CA solution: Dissolve cellulose acetate powder in DMF at room temperature to prepare a CA solution with a concentration of 2 wt%. Seal the prepared CA solution with a sealant for later use;

[0072] (3) Preparation of CA-CsPbBr3-PQDs composite film: Take 3 mL of the precursor solution from step (1) and add it to 10 mL of the CA solution from step (2). Stir magnetically at 600 rpm at room temperature for 3 hours, then perform vacuum filtration for 24 hours and dry in a vacuum drying oven at 45 °C under a vacuum of 0.1 atm for 24 hours to obtain the CA-CsPbBr3-PQDs composite film.

[0073] Example 7

[0074] A method for preparing highly stable cellulose acetate perovskite quantum dot materials by a one-step method, comprising the following steps:

[0075] (1) Synthesis of precursor solution: Dissolve 0.5 mmol of CsBr and 0.5 mmol of PbBr2 in 20 mL of DMF respectively. Set the magnetic stirrer to 600 rpm and stir at room temperature for 3 hours until the solution becomes completely transparent. Seal it and store it in a sample bottle for subsequent use;

[0076] (2) Preparation of CA solution: Dissolve cellulose acetate powder in DMF at room temperature to prepare a CA solution with a concentration of 2 wt%. Seal the prepared CA solution with a sealant for standby;

[0077] (3) Preparation of CA-CsPbBr3-PQDs composite film: Take 3.5 mL of the precursor solution in step (1) and add it to 10 mL of the CA solution in step (2). Stir magnetically at 600 rpm at room temperature for 3 hours, perform vacuum filtration for 24 hours, and then dry it in a vacuum drying oven at 45 °C under 0.1 atmospheric pressure for 24 hours to obtain the CA-CsPbBr3-PQDs composite film.

[0078] Example 8

[0079] A method for preparing highly stable cellulose acetate perovskite quantum dot materials by a one-step method, comprising the following steps:

[0080] (1) Synthesis of precursor solution: Dissolve 0.5 mmol of CsBr and 0.5 mmol of PbBr2 in 20 mL of DMF respectively. Set the magnetic stirrer to 600 rpm and stir at room temperature for 3 hours until the solution becomes completely transparent. Seal it and store it in a sample bottle for subsequent use;

[0081] (2) Preparation of CA solution: Dissolve cellulose acetate powder in DMF at room temperature to prepare a CA solution with a concentration of 2 wt%. Seal the prepared CA solution with a sealant for standby;

[0082] (3) Preparation of CA-CsPbBr3-PQDs composite film: Take 4 mL of the precursor solution in step (1) and add it to 10 mL of the CA solution in step (2). Stir magnetically at 600 rpm at room temperature for 3 hours, perform vacuum filtration for 24 hours, and then dry it in a vacuum drying oven at 45 °C under 0.1 atmospheric pressure for 24 hours to obtain the CA-CsPbBr3-PQDs composite film.

[0083] Example 9

[0084] A method for preparing highly stable cellulose acetate perovskite quantum dot materials by a one-step method, comprising the following steps:

[0085] (1) Synthesis of precursor solution: Dissolve 0.5 mmol of CsBr and 0.5 mmol of PbBr2 in 20 mL of DMF respectively. Set the magnetic stirrer to 600 rpm and stir at room temperature for 3 hours until the solution becomes completely transparent. Seal it and store it in a sample bottle for subsequent use;

[0086] (2) Preparation of CA solution: Dissolve cellulose acetate powder in DMF under normal temperature conditions to prepare a CA solution with a concentration of 2 wt%. Seal the prepared CA solution with a sealant for later use;

[0087] (3) Preparation of CA-CsPbBr3-PQDs composite film: Take 4.5 mL of the precursor solution in step (1) and add it to 10 mL of the CA solution in step (2). Stir magnetically at 600 rpm at room temperature for 3 hours, perform vacuum filtration for 24 hours, and then dry it at 45 °C in a vacuum drying oven under 0.1 atmospheric pressure for 24 hours to obtain the CA-CsPbBr3-PQDs composite film.

[0088] Example 10

[0089] A method for preparing highly stable cellulose acetate perovskite quantum dot materials by a one-step method, comprising the following steps:

[0090] (1) Synthesis of precursor solution: Dissolve 0.5 mmol of CsBr and 0.5 mmol of PbBr2 in 20 mL of DMF respectively. Set the magnetic stirrer to 600 rpm and stir at room temperature for 3 hours until the solution becomes completely transparent. Seal it and store it in a sample bottle for subsequent use;

[0091] (2) Preparation of CA solution: Dissolve cellulose acetate powder in DMF under normal temperature conditions to prepare a CA solution with a concentration of 2 wt%. Seal the prepared CA solution with a sealant for later use;

[0092] (3) Preparation of CA-CsPbBr3-PQDs composite film: Take 4.5 mL of the precursor solution in step (1) and add it to 10 mL of the CA solution in step (2). Stir magnetically at 600 rpm at room temperature for 3 hours, perform vacuum filtration for 24 hours, and then dry it at 45 °C in a vacuum drying oven under 0.1 atmospheric pressure for 24 hours to obtain the CA-CsPbBr3-PQDs composite film.

[0093] Comparative Example 1

[0094] A method for preparing CsPbBr3 PQDs by a ligand-assisted precipitation method, comprising the following steps:

[0095] 1) Synthesis of precursor solution: Dissolve 0.5 mmol of CsBr and 0.5 mmol of PbBr2 in 20 mL of DMF respectively. Set the magnetic stirrer to 600 rpm and stir at room temperature for 3 hours until the solution becomes completely transparent. Seal it and store it in a sample bottle for subsequent use;

[0096] (2) Preparation of PQDs colloidal solution using ligand-assisted precipitation method (LARP): Take 5 mL of the precursor solution in a beaker, add 200 μL of oleic acid (OA) and 70 μL of oleylamine (OLA), and stir for 3 minutes under magnetic stirring to ensure complete dissolution of the ligands. Subsequently, quickly add the above 200 μL of solution dropwise to 10 mL of toluene, and continue stirring for 5 minutes to promote the reaction. After the reaction, separate the coarse particles by high-speed centrifugation (7000 rpm, 5 minutes), collect the supernatant and store it at room temperature for subsequent use;

[0097] (3) Preparation of CsPbBr3 PQDs: Vacuum filter the supernatant in step (2) for 24 hours and then dry it in a vacuum drying oven at 45 °C under 0.1 atm for 24 hours to obtain CsPbBr3 PQDs.

[0098] Comparative Example 2

[0099] A method for preparing a CA membrane, comprising the following steps:

[0100] Under normal temperature conditions, dissolve cellulose acetate powder in DMF to prepare a CA solution with a concentration of 2 wt%. Vacuum filter it for 24 hours and then dry it in a vacuum drying oven at 45 °C under 0.1 atm for 24 hours to obtain a CA membrane.

[0101] The cross-sectional SEM photos of the CA-CsPbBr3-PQDs composite membrane prepared in Example 5 and the CA membrane prepared in Comparative Example 2 are as shown in Figure 5As shown, where (a-c) show the scanning electron microscope photos of the cross-section of the pure CA film prepared in Comparative Example 2; (d-f) show the scanning electron microscope photos of the cross-section of the CA-CsPbBr3-PQDs composite film prepared in Example 5; the cross-section in (b) shows a very obvious hierarchical structure. The formation of this layered structure is related not only to the uneven solvent evaporation and the interaction between CA molecules, but also to the interaction between the solvent and water. Especially during the suction filtration process, since the upper layer of the film is exposed to the environment, it inevitably contacts with the moisture in the air and undergoes phase separation. An obvious porous structure appears in the upper layer. Further magnification shows the details in (c), where "cicada pupa-shaped" large particles are produced, and the opening is a network structure combined by small particles. The reason for this phenomenon is that water enters the surface of the film, especially the upper layer, and interacts with the molecules in the CA solution, promoting the formation of a gel-like structure in the upper layer and accelerating the phase separation of the upper layer. The formation of the gel makes the upper layer structure looser and more porous, which is consistent with the porosity characteristics caused by the relatively fast solvent evaporation rate. The lower layer in (a), due to less water contact, slower solvent evaporation, molecular packing and heat conduction effects, forms a relatively dense film layer. The formation of this layered structure reflects the self-assembly process of the film, the difference in solvent evaporation rate, and the deposition and solidification characteristics of substances.

[0102] Due to the growth of PQDs in the film, there are obvious differences from pure CA: (d) shows a more rough and irregular surface. This is because the addition of perovskite quantum dots triggers new self-assembly behavior on the surface of the film, resulting in the formation of a relatively loose network-like structure. The perovskite quantum dots themselves are small in size and easily dispersed in the matrix material. The network structure provides a growth environment for PQDs and is conducive to the uniform formation of PQDs to a certain extent. In (f), the quantum dots are wrapped in "cicada pupa-shaped" particles. PQDs can be relatively evenly distributed in the CA film. The CA matrix provides support and attachment scenarios for the growth of quantum dots through its spatial structure, preventing excessive aggregation or crystallization, and thus maintaining the optical activity of the quantum dots. This stability explains the retention of the photoluminescence intensity. Even without ligands, the chemical and physical environment of the matrix itself may play a partial stabilizing role, enabling the quantum dots to maintain their optical properties.

[0103] The PL spectra of the CA-CsPbBr3-PQDs composite films prepared in Examples 1-10 are as Figure 6As shown, where (a) shows the photoluminescence spectra of CA-CsPbBr3-PQDs with different doping volumes in the form of a three-dimensional spectrum; (b) the dependence of the PL peak intensity of CA-CsPbBr3-PQDs and (c) the luminescence peak position on the doping volume; it can be seen that the luminescence peaks of the prepared CA-CsPbBr3-PQDs composite films with different doping volumes are mainly located between 510 and 525 nm, showing green fluorescence emission characteristics. At the same time, with the increase of the precursor volume, the intensity and position of the PL peak change.

[0104] The average carrier lifetimes of the CA-CsPbBr3-PQDs composite films in Examples 1-10 were fitted using the TRPL decay exponential function, and the results are shown in Table 1 below.

[0105] Table 1

[0106]

[0107] From the data in Table 1, it can be seen that the average lifetime of the quantum dots in the CA-CsPbBr3-PQDs composite film of the present invention can reach up to 16.895 ns at most. It is twice that of CsPbBr3 QDs (τ ave = 7-8 ns) synthesized by the oleic acid / oleylamine ligand-assisted precipitation method in the prior art.

[0108] The PL spectra of the CA-CsPbBr3-PQDs composite film prepared in Example 1 and the CsPbBr3 PQDs prepared in Comparative Example 1 under 360 nm ultraviolet light excitation are as Figure 7 shown. It can be seen that under the same excitation test conditions, CA-CsPbBr3-PQDs can still maintain a green light emission intensity similar to that of CsPbBr3 PQDs. At the same time, CA-CsPbBr3-PQDs has a narrow FWHM = 20.6 nm (close to 19.6 nm of CsPbBr3 PQDs), which means better monochromaticity and higher color purity.

[0109] Stability test

[0110] The CA-CsPbBr3-PQDs composite film prepared in Example 1 was immersed in pure water, and the obtained PL spectrum is as Figure 8As shown, the illustration shows its contact angle test, natural light and 360 nm ultraviolet photos. Over time, the emission wavelength of the quantum dots did not change significantly (black data in the figure), remaining at approximately 527 nm. Such a change usually indicates that the optical bandgap of the quantum dots has not changed significantly. The reason is that CA has good water resistance and non-swelling properties. The hydroxyl groups (-OH) in cellulose in the CA molecule are replaced by acetate groups (-OCOCH3), and the overall performance is hydrophobic (contact angle is 94.3°). This characteristic enables the CA-CsPbBr3-PQDs composite film not to swell in water and maintain a good basic morphology (shown in the lower right inset). At the same time, the cicada pupa-shaped protective layer and dense pores formed by CA can prevent water and water-soluble impurities from directly contacting the quantum dots. The water molecules on the surface of CA make the film flatter through hydrogen bonds, which also explains that the PL intensity (yellow-green data in the figure) fluctuates over time and even generally shows an increasing trend. It means that CA-G-PQDs has strong water stability.

[0111] The CA-CsPbBr3-PQDs composite film prepared in Example 1 and the CsPbBr3PQDs prepared in Comparative Example 1 were continuously subjected to UV (RH = 60%, RT, 16W UV) tolerance tests under the conditions of relative environmental humidity of 60% and room temperature. The test results are shown in Figure 9As shown, where (a) is the PL spectrum of CsPbBr3 PQDs prepared in Comparative Example 1 under continuous 16W UV, (b) is the variation of the PL intensity and emission peak position of CsPbBr3 PQDs prepared in Comparative Example 1 with time; (c) is the PL spectrum of the CA-CsPbBr3-PQDs composite film prepared in Example 1 under continuous 16W UV, (d) is the variation of the PL intensity and emission peak position of the CA-CsPbBr3-PQDs composite film prepared in Example 1 with time. It can be seen that under UV irradiation for up to 100 days, the PL intensity of the CA-CsPbBr3-PQDs composite film only decreased by 13.8%, showing stronger UV stability than CsPbBr3 PQDs. With the increase of time (from 1 to 8 days) in the emission spectrum of CsPbBr3 PQDs, the intensity of the emission peak gradually weakened and reached zero on the eighth day, and the peak position also showed a red shift. For the CA-CsPbBr3-PQDs composite film, there was a small increase in the first 20 days and then a stable decrease. The reason for the increase may be that at the initial stage of UV irradiation, electrons and holes in the quantum dots are rapidly generated, and the photo-generated carriers may redistribute on the surface or inside of the quantum dots, resulting in a small increase in the PL intensity. This process is usually related to the accumulation of photo-generated carriers in local areas. At the same time, the passivation effect on the surface of PQDs may gradually increase. With the continuous radiation exposure, the molecular chains in cellulose acetate may interact more effectively with the photo-generated carriers, reducing the generation of defect states, thereby temporarily improving the exciton recombination efficiency and increasing the PL intensity. The reason for the decrease may be that with the increase of UV irradiation time, UV light may trigger more surface defects or lattice damage, leading to the degradation of the optical properties of the material. Some exciton recombination paths are converted into non-radiative recombination paths, and these defect states will consume photo-generated carriers, resulting in a decrease in the luminescence efficiency and ultimately a decrease in the PL intensity. In addition, CA also has the ability to absorb UV, which can greatly alleviate the process of PL intensity weakening and improve the stability of PQDs under UV.

[0112] The above is a specific description of the preferred embodiments of the present invention, but the present invention is not limited to the described embodiments. Those skilled in the art can make various equivalent deformations or substitutions without departing from the spirit of the present invention, and these equivalent deformations or substitutions are all included within the scope defined by the claims of this application.

Claims

1. A one-step method for preparing high-stability cellulose acetate perovskite quantum dot material, characterized in that: The following steps are involved: (1) Synthesis of precursor solution: CsBr and PbBr2 were dissolved in DMF, magnetically stirred at room temperature until the solution was completely transparent, and sealed for later use; (2) Preparation of CA solution: dissolve cellulose acetate powder in DMF and seal for later use; (3) Preparation of CA-CsPbBr3-PQDs composite film: The precursor solution in step (1) was added to the CA solution in step (2), magnetically stirred at room temperature, vacuum filtered and then vacuum dried to obtain a CA-CsPbBr3-PQDs composite film.

2. The method for preparing a high-stability cellulose acetate perovskite quantum dot material in one step according to claim 1, characterized in that: The molar ratio of CsBr to PbBr2 in step (1) is 1:

1.

3. The method for preparing a high-stability cellulose acetate perovskite quantum dot material in one step according to claim 1, characterized in that: The solid-liquid ratio of the precursor solution in step (1) is 14-15 g / L.

4. The method for preparing a high-stability cellulose acetate perovskite quantum dot material in one step according to claim 1, characterized in that: The rotation speed of the magnetic stirring in step (1) is 600 rpm, and the time of the magnetic stirring is 3 h.

5. The method for preparing a high-stability cellulose acetate perovskite quantum dot material in one step according to claim 1, characterized in that: The concentration of the CA solution in step (2) is 2 wt %.

6. The method for preparing a high-stability cellulose acetate perovskite quantum dot material in one step according to claim 1, characterized in that: The volume ratio of the precursor solution to the CA solution in step (3) is (1-5):

10.

7. The method for preparing a high-stability cellulose acetate perovskite quantum dot material in one step according to claim 1, characterized in that: The rotation speed of the magnetic stirring in step (3) is 600 rpm, and the time of the magnetic stirring is 3 h.

8. The method for preparing a high-stability cellulose acetate perovskite quantum dot material in one step according to claim 1, characterized in that: The vacuum filtration time in step (3) is 24 hours.

9. The method for preparing a high-stability cellulose acetate perovskite quantum dot material in one step according to claim 1, characterized in that: The vacuum degree of the vacuum drying in step (3) is 0.1 atmosphere.

10. The method for preparing high-stability cellulose acetate perovskite quantum dot material in one step according to claim 1, characterized in that: The vacuum drying temperature in step (3) is 45° C., and the vacuum drying time is 24 h.

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