Black-phase all-inorganic perovskite flexible thick film stable at room temperature as well as preparation method and application of black-phase all-inorganic perovskite flexible thick film

Abstract

The invention relates to a black-phase all-inorganic perovskite flexible thick film stable at room temperature and a preparation method and application thereof, and the preparation method comprises the following steps: uniformly mixing PbI2, CsI and an organic ammonium salt in an organic solvent to obtain a perovskite precursor solution; filling a polymer filter membrane with the perovskite precursor solution through a vacuum filtration method to obtain a wet flexible thick membrane; the polymer filter membrane is cleaned, and the thickness is 50 microns or above; and carrying out gradient annealing on the wet flexible thick film to obtain the black-phase all-inorganic perovskite flexible thick film which is stable at room temperature. According to the invention, low-dimensional perovskite induced lattice distortion is formed by adding A-site cations, and the flexible thick film which is thermodynamically stable and uniform at room temperature is obtained based on a solvent suction filtration method by regulating and controlling the addition amount of organic ammonium salt and gradient annealing and regulating and controlling the proportion of residual organic ammonium salt of lattices, and is applied to an X-ray detector. High [mu] [tau] product and high sensitivity are realized, and good flexible detection performance is shown.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of X-ray detection, in particular to a room temperature stable black phase all-inorganic perovskite flexible thick film and a preparation method and application thereof. BACKGROUND

[0002] X-ray detectors have wide and important applications in medical imaging, non-destructive testing and national defense and military industry, and direct detection has higher theoretical spatial resolution, which is the future development direction of X-ray low dose imaging. All-inorganic CsPbI3 perovskite material has high atomic number, large ray absorption cross section and weak ion migration, and is considered as an excellent direct detection material. However, the black phase (alpha, beta and gamma) of all-inorganic perovskite CsPbI3 is thermodynamically unstable at room temperature, and will spontaneously transform into non-photoluminescent yellow phase delta-CsPbI3. The essence of the phase transition is that the atomic radius of Cs (1.81 Å) is not large enough, and the PbI6 octahedron has poor accommodation. It is difficult to stably support the three-dimensional framework composed of PbI6 octahedron. This ion size mismatch causes significant lattice strain, and the thermodynamic stability of the photoluminescent black phase CsPbI3 is extremely poor under external thermal stress or humidity conditions, and will spontaneously transform into non-perovskite yellow phase (delta-CsPbI3). Therefore, the previous work in X-ray detection focuses on the yellow phase delta-CsPbI3 material, but the low mu tau product of the yellow phase structure limits the sensitivity, and it is difficult to meet the demand of direct detection high resolution imaging. +

[0003] In order to solve the phase instability, there are two directions: improving the lattice symmetry and reducing the lattice strain, which is mainly realized by introducing long-chain alkylamine into the perovskite precursor solution, but in order to ensure the purity of the obtained three-dimensional perovskite material, the long-chain alkylamine introduced in the perovskite precursor solution usually needs to be completely removed.

[0004] In order to ensure the X-ray detection effect, the CsPbI3 perovskite film used usually is a thick film (mainly more than one hundred microns), but it is usually difficult to form a uniform thick film structure by scraping, and the method for preparing a uniform thick film structure needs to be further optimized. SUMMARY

[0005] The present application aims to overcome the above technical deficiencies, and provides a room temperature stable black phase all-inorganic perovskite flexible thick film and a preparation method and application thereof, which solves the technical problems of poor phase stability of CsPbI3 perovskite material used in X-ray detector and difficulty in forming a uniform thick film material in the prior art.

[0006] To achieve the above technical purpose, the technical scheme provided by the present application is: ​In a first aspect, the present application provides a method for preparing a room-temperature stable black-phase all-inorganic perovskite flexible thick film, comprising the following steps: S1, uniformly mixing PbI2, CsI and an organic ammonium salt in an organic solvent to obtain a perovskite precursor solution; the molar ratio of PbI2, CsI and the organic ammonium salt is 1:1:(1.2-1.8); S2, filling the perovskite precursor solution into a polymer filter membrane by vacuum filtration to obtain a wet flexible thick film; the polymer filter membrane is cleaned and has a thickness of more than 50 μm; S3, gradient annealing the wet flexible thick film to obtain a room-temperature stable black-phase all-inorganic perovskite flexible thick film.

[0007] In a second aspect, the present application provides a room-temperature stable black-phase all-inorganic perovskite flexible thick film prepared by the above method.

[0008] In a third aspect, the present application provides an electrode / black-phase all-inorganic perovskite flexible thick film, which is prepared by coating electrodes on both sides of the black-phase all-inorganic perovskite flexible thick film.

[0009] In a fourth aspect, the present application provides an application of the above black-phase all-inorganic perovskite flexible thick film or the electrode / black-phase all-inorganic perovskite flexible thick film in an X-ray detector.

[0010] Compared with the prior art, the present application has the following beneficial effects: The present application starts from the root of crystal stability, forms low-dimensional perovskite by adding A-site cations to induce lattice distortion, reduces lattice strain to stabilize CsPbI3; in order to ensure the controllable addition of A-site cations, the present application adjusts the addition amount of organic ammonium salt and precise gradient annealing to control the proportion of residual organic ammonium salt in the lattice, and based on the vacuum filtration method, a room-temperature thermodynamically stable and uniform black-phase all-inorganic perovskite flexible thick film is obtained. The present application first applies DMAI to the flexible thick film X-ray detector with phase change structure, realizes high μτ product and high sensitivity, and has good bending stability, and can still maintain 81.6% of the initial performance after bending 200 times. BRIEF DESCRIPTION OF DRAWINGS

[0011] Figure 1 is a physical map of the flexible thick film obtained in Example 1 and Comparative Examples 2-5 of the present application; Figure 2 is a graph showing the relationship between the X-ray absorption efficiency of the flexible CsPbI3 perovskite thick film with different thicknesses according to the present application; Figure 3 is a thermogravimetric analysis graph of the wet flexible thick film in the preparation process of Example 1 of the present application; Figure 4 is an X-ray diffraction graph of the D-1.5@120 μm flexible thick film prepared in Example 1 of the present application; Figure 5are SEM images of the flexible thick film prepared in Example 1 and Comparative Example 1 of the present application; wherein (a) is Example 1, (b) is Comparative Example 1; Figure 6 are EDS spectroscopy analysis images of the D-1.5@120μm flexible thick film prepared in Example 1 of the present application; Figure 7 are UV-Vis analysis images of the flexible thick films prepared in Example 1 and Comparative Example 5 of the present application; Figure 8 are the mass attenuation coefficient and photon energy curve comparisons of the flexible thick film of Example 1 of the present application with Si and FAPbI3; Figure 9 are the photocurrent-voltage curves of the carbon electrode / D-1.5@120μm flexible thick film prepared in Example 2 of the present application; Figure 10 are the sensitivity curves of the carbon electrode / D-1.5@120μm flexible thick film prepared in Example 2 of the present application at different voltages; Figure 11 are the X-ray dose rate-device response photocurrent curves of the carbon electrode / D-1.5@120μm flexible thick film prepared in Example 2 of the present application and the carbon electrode / D-2.5@120μm flexible thick film prepared in Comparative Example 6; wherein (a) is Example 2, (b) is Comparative Example 6; Figure 12 are the bending test results of the carbon electrode / D-1.5@120μm flexible thick film prepared in Example 2 of the present application; Figure 13 is a process schematic diagram of the flexible thick film prepared in Example 1 of the present application; Figure 14 is a schematic diagram of the principle of forming a black-phase CsPbI3 perovskite flexible thick film by two-dimensional DMAPbI3 according to the present application. DETAILED DESCRIPTION

[0012] In order to make the purpose, technical scheme and advantages of the present application clearer and more apparent, the present application will be further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application.

[0013] In order to solve the phase instability, there are two directions: improving the lattice symmetry and reducing the lattice strain, which is mainly achieved by introducing long-chain alkylamine into the perovskite precursor solution.

[0014] In order to ensure the X-ray detection effect, the CsPbI3 perovskite film used is usually a thick film (mainly more than one hundred microns), but it is usually difficult to form a uniform film material by scraping.

[0015] In view of the defects that the CsPbI3 perovskite material used in the X-ray detector in the prior art has poor phase stability and is difficult to form a uniform thick film material, the additive engineering is adopted in the present application to add RP type A site organic cations in the perovskite precursor solution PbI2 and CsI, for example, by adding DMAI, through regulating the nucleation and growth process of CsPbI3, the larger ion radius of DMAI can improve the strain in the crystal lattice and inhibit the lattice collapse and inhibit the phase transition. The key is that in the hundred micron flexible thick film (especially the thickness is greater than or equal to 120 μm), by controlling the film thickness and gradient precise annealing process parameters and other conditions, the residual DMAI in the crystal lattice after annealing cannot be completely volatilized, and the residual DMA + form a low-dimensional perovskite DMAPbI3 with PbI6, construct a low-dimensional / three-dimensional blend structure with three-dimensional CsPbI3, release the lattice mismatch strain, and finally obtain a room-temperature thermodynamically stable coexistence state of gamma-CsPbI3 / DMAPbI3. By accurately regulating the amount of DMAI added, the proportion of residual DMAI in the crystal lattice after annealing is obtained, and a room-temperature thermodynamically stable black-phase CsPbI3 perovskite and DMAPbI3 coexistence structure is obtained, which can be maintained at room temperature for a long time.

[0016] In order to ensure the purity of the obtained three-dimensional perovskite material, the long-chain alkylamine introduced in the perovskite precursor solution in the prior art usually needs to be completely removed. Therefore, even if long-chain alkylamine is introduced, whether the organic cation such as DMA exists in the crystal lattice, how many DMA cations are in the crystal lattice, the properties of the DMA / Cs mixed perovskite phase, and the phase evolution process during heat treatment are rarely concerned. Based on this, the present application is established.

[0017] In a first aspect, the present application provides a preparation method of a room-temperature stable black-phase all-inorganic perovskite flexible thick film, comprising the following steps: S1, uniformly mixing PbI2, CsI and an organic ammonium salt in an organic solvent to obtain a perovskite precursor solution; the molar ratio of PbI2, CsI and the organic ammonium salt is 1:1:(1.2-1.8); S2, filling the perovskite precursor solution into a polymer filter membrane by vacuum suction filtration to obtain a wet flexible thick film; wherein the polymer filter membrane is washed and the thickness is greater than 50 μm; S3, gradient annealing the wet flexible thick film to obtain a room-temperature stable black-phase all-inorganic perovskite flexible thick film.

[0018] The application starts from the root of crystal stability, forms low-dimensional perovskite by adding A-site cations to induce lattice distortion, reduces lattice strain to stabilize CsPbI3, in order to ensure the controllable addition of A-site cations, the application adjusts the residual organic ammonium salt proportion of the lattice by adjusting the amount of organic ammonium salt and precise gradient annealing, and obtains a thermodynamically stable and uniform black-phase CsPbI3 structure at room temperature based on a solvent filtration method.

[0019] Specifically, the molar ratio of PbI2, CsI and organic ammonium salt includes but is not limited to 1:1:1.2, 1:1:1.3, 1:1:1.4, 1:1:1.5, 1:1:1.6, 1:1:1.7, 1:1:1.8, etc.

[0020] Preferably, in step S1, the general formula of the organic ammonium salt is R-NH3X, XH3N-R-NH3X or R1R2-NH2X, wherein X=I, Br or Cl; R, R1 and R2 are each independently selected from C1-C6 alkyl, including but not limited to methyl, ethyl, propyl or isopropyl; C3-C6 cycloalkyl, including but not limited to cyclopropyl or cyclopentyl; heteroatom-containing C4-C6 cyclic amine group, including but not limited to pyrrolidinyl or piperidinyl; phenyl or substituted phenyl derivative, including but not limited to phenethyl or fluorophenethyl.

[0021] Preferably, in step S1, the radius of the organic cation in the organic ammonium salt is in the range of >Cs + The radius (1.81 Å); the organic cation in the organic ammonium salt of the application is coordinated with the PbI6 octahedron to form a low-dimensional perovskite, and the CsPbI3 lattice is stabilized by low-dimensional / three-dimensional blending.

[0022] Further preferably, the organic ammonium salt includes at least one of dimethylamine iodide (DMAI), ethylamine iodide (EAI), isopropylamine iodide (IPAI), N,N-dimethyl-1,3-propanediamine (DMePDAI2) and phenethylamine iodide (PEAI).

[0023] Preferably, in step S1, the organic solvent includes at least one of N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), etc.

[0024] Preferably, in step S1, the concentration of PbI2 in the perovskite precursor solution is 1-2 mol / L, and specifically the concentration includes but is not limited to 1 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.8 mol / L, 1.9 mol / L, 2.0 mol / L, etc.

[0025] Preferably, in step S1, the PbI2, CsI and organic ammonium salt are mixed uniformly in the organic solvent by adding the PbI2, CsI and organic ammonium salt into the organic solvent, stirring at room temperature for 8-12 h. Specifically, the stirring time includes but is not limited to 8 h, 9 h, 10 h, 11 h, 12 h, etc.

[0026] Preferably, in step S2, the polymer filter film includes a nylon filter film.

[0027] Preferably, in step S2, the polymer filter film has a pore size of less than 5 μm and a thickness of 50-150 μm. Specifically, the thickness includes but is not limited to 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 105 μm, 110 μm, 115 μm, 120 μm, 125 μm, 130 μm, 140 μm, 150 μm, etc.

[0028] Further preferably, the polymer filter film has a thickness of 100-120 μm.

[0029] The present application uses a flexible 100-μm-thick film as a substrate, precisely controls the thickness of the substrate to obtain a stable gamma black phase structure while maintaining a high thickness of the flexible thick film.

[0030] Preferably, in step S2, the polymer filter film cleaning process includes: immersing the polymer filter film in anhydrous ethanol and ultrasonic treatment for 15-30 min; then immersing in ultrapure water, ultrasonic treatment for 15-30 min, and then drying to complete the cleaning of the polymer filter film.

[0031] The present application removes organic residues and grease by immersing the nylon filter film in anhydrous ethanol and ultrasonic treatment.

[0032] Further preferably, the drying is performed in a vacuum drying oven at 80-100 °C for 2-5 h.

[0033] Preferably, in step S2, the vacuum filtration method specifically includes the following steps: placing the polymer filter film on a Buchner funnel, adding the perovskite precursor solution dropwise, and performing filtration under a vacuum degree of less than 1 mbar until the polymer filter film is completely wet.

[0034] It can be understood that, in order to maximize the filling of the perovskite precursor solution in the nylon filter film, vacuum filtration is performed multiple times. The complete wetting of the polymer filter film means that the surface of the polymer filter film absorbs the perovskite precursor solution until saturation, i.e., the internal voids and intermolecular gaps of the filter film are completely filled with the perovskite precursor solution and reach a dynamic equilibrium. The vacuum filtration method can sufficiently ensure the uniformity of the flexible thick film.

[0035] Preferably, in step S3, the gradient annealing is first annealed at 80-100℃ for 1-2h, and then annealed at 100℃-140℃ for 8-10h. Specifically, the low-temperature annealing temperature includes but is not limited to 80℃, 85℃, 90℃, 95℃, 100℃, etc., and the low-temperature annealing time includes but is not limited to 1h, 1.5h, 2h, etc.; the high-temperature annealing temperature includes but is not limited to 100℃, 105℃, 110℃, 120℃, 130℃, 140℃, etc., and the high-temperature annealing time includes but is not limited to 8h, 8.5h, 9h, 9.5h, 10h, etc.

[0036] The present application adopts the gradient annealing method, first performs short-time annealing treatment at low temperature to ensure solvent volatilization, and then performs annealing treatment at a relatively high temperature to prolong the reaction time of DMAPbI3 and inhibit the decomposition of DMAI, so that the DMAPbI3 in the film layer improves the lattice strain of the CsPbI3 perovskite to realize a stable gamma black phase structure.

[0037] In the second aspect, the present application provides a room-temperature-stable black-phase all-inorganic perovskite flexible thick film prepared by the above preparation method.

[0038] In the third aspect, the present application provides an electrode / black-phase all-inorganic perovskite flexible thick film, which is prepared by coating electrodes on both sides of the black-phase all-inorganic perovskite flexible thick film.

[0039] Preferably, the coating thickness of the electrode is 10-12μm, and the area of the carbon electrode is 0.09cm 2 .

[0040] Preferably, the electrode includes a carbon electrode, a silver electrode or a gold electrode.

[0041] In the fourth aspect, the present application provides an application of the above black-phase all-inorganic perovskite flexible thick film or the electrode / black-phase all-inorganic perovskite flexible thick film in an X-ray detector.

[0042] Next, taking dimethylamine iodide (DMAI) as a typical organic ammonium salt as an example, the mechanism of the present application is further described in detail: By adding dimethylamine iodide (DMAI) at the A site of the macromolecule, a two-dimensional perovskite (DMAPbI3) is formed as a "lattice support framework", and the DMA +large radius filling A-site vacancies, reducing the distortion of PbI6 octahedron, and inhibiting the phase transition of CsPbI3 from the root, successfully realizing the room-temperature thermodynamically stable gamma-CsPbI3 black phase. Based on the solvent extraction method, the perovskite precursor solution containing the DAI additive is gradually infiltrated into the porous polymer filter membrane substrate, and finally a room-temperature stable gamma-CsPbI3 flexible thick film is successfully prepared. A high-quality and high-density flexible thick film structure is obtained, and the DMAPbI3 in the film layer significantly improves the lattice strain of the CsPbI3 perovskite to realize the high room-temperature stable gamma black phase structure.

[0043] The black phase all-inorganic perovskite flexible thick film with a room-temperature stable flexible gamma phase structure exhibits excellent X-ray detection performance, and when used in an X-ray detector, the product of mu and tau of the device reaches 1.16*10 -4 cm 2 ·V -1 , which is much higher than the reported yellow phase structure, and the sensitivity is 209 muC·Gy air -1 ·cm -2 . After 200 bending times, the device still maintains the excellent performance of 81.6% of the initial performance, which shows the potential value of all-inorganic perovskite in the application of flexible perovskite X-ray detection and imaging with large area, high sensitivity and high stability, and is expected to provide a new solution for low-dose imaging, portable detection equipment and radiation monitoring in complex environments.

[0044] The application will be further described in detail below through specific examples. To avoid redundancy, the additive DJ macromolecule A site is taken as an example of DMAI, and the process of reducing lattice strain and the phase evolution process and performance characterization in the heat treatment process are mainly introduced. The polymer filter membrane is a nylon filter membrane, and the cleaning process is as follows: the nylon filter membrane is soaked in anhydrous ethanol, ultrasonic treatment for 30 min, and the organic residues and oil are removed. Then, it is soaked in ultrapure water, ultrasonic treatment for 30 min, and finally the nylon filter membrane is placed in a vacuum drying box and dried at 80 DEG C for 2 h.

[0045] Example 1 A preparation method of a room-temperature stable black phase all-inorganic perovskite flexible thick film, comprising the following steps: (1) 5.532g PbI2, 3.118g CsI and 3.114g DMAI and 10mL DMF are mixed, stirred at room temperature for 8h, and configured into a perovskite precursor solution of 1.2mol / L, wherein the molar ratio of PbI2, CsI and DMAI is 1:1:1.5; the following D-1.5 represents the corresponding DMAI addition molar ratio code.

[0046] (2) The cleaned nylon filter membrane (pore size about 5 pm, thickness 120 pm) was placed on a Buchner funnel, and vacuum filtration was performed using a vacuum filtration machine, with the vacuum degree controlled at 1 mbar. The perovskite precursor solution was continuously added dropwise above the nylon filter membrane, and vacuum filtration was performed to fill the perovskite precursor solution in the nylon filter membrane, to obtain a wet flexible thick film; (3) The wet flexible thick film was subjected to gradient annealing, specifically annealing at 80 °C for 2 h, and then annealing at 120 °C for 8 h, to obtain a room-temperature-stable black-phase all-inorganic perovskite flexible thick film g-CPI (D-1.5@120 pm).

[0047] Example 2 A carbon electrode / black-phase all-inorganic perovskite flexible thick film: 10 pm-thick carbon electrodes were respectively coated on both sides of the black-phase all-inorganic perovskite flexible thick film obtained in Example 1, with the electrode area being 0.09 cm 2 , to obtain a carbon electrode / D-1.5@120 pm flexible thick film.

[0048] Comparative Example 1 The difference from Example 1 is only that the amount of DMAI is adjusted to 0 g, and other steps and conditions are the same as those in Example 1, to obtain a D-0@120 pm flexible thick film.

[0049] Comparative Example 2 The difference from Example 1 is only that the amount of DMAI is adjusted to 1.038 g, and other steps and conditions are the same as those in Example 1, to obtain a D-0.5@120 pm flexible thick film.

[0050] Comparative Example 3 The difference from Example 1 is only that the amount of DMAI is adjusted to 5.19 g, and other steps and conditions are the same as those in Example 1, to obtain a D-2.5@120 pm flexible thick film.

[0051] Comparative Example 4 The difference from Example 1 is only that the thickness of the nylon filter membrane is 50 pm, and other steps and conditions are the same as those in Example 1, to obtain a D-1.5@50 pm flexible thick film.

[0052] Comparative Example 5 The difference from Example 1 is only that the thickness of the nylon filter membrane is 200 pm, and other steps and conditions are the same as those in Example 1, to obtain a D-1.5@200 pm flexible thick film.

[0053] Comparative Example 6 The difference from Example 2 is only that the carbon electrode / D-2.5@120 pm flexible thick film is prepared using the D-2.5@120 pm flexible thick film of Comparative Example 3, and other steps and conditions are the same as those in Example 2.

[0054] Performance test (1) The actual image of the flexible thick film obtained in Example 1 and Comparative Examples 2-5 is shown in Figure 1 .

[0055] It can be seen from Figure 1 that the experimental results of different concentrations of DMAI formed in Example 1 and Comparative Examples 2-3 show that when DMAI is added too much (D-2.5) and too little (D-0.5), a large amount of yellow phase doping (yellow phase black phase blending, γ-CPI / δ-CPI) occurs, and D-2.5 is obviously phase-separated. When the flexible thick film is D-1.5, no yellow phase doping occurs, and it is a stable black phase γ-CPI.

[0056] This is mainly due to: when the volatile additive DMAI is added too little (D-0.5), DMAPbI3 generated in the bulk phase is not enough to stabilize the entire system to form a room-temperature stable black phase structure. At the same time, DMAPbI3 decomposes to form volatile DMAI gas during the transformation, which aggravates the generation of yellow phase structure, and at this time the film layer state is δ-CsPbI3 yellow phase, γ-CsPbI3 black phase and DMAPbI3 coexistence state; as the amount of DMAI additive increases to (D-1.5), the DMAPbI3 generated in the bulk phase can well adjust the lattice strain and stabilize the black phase structure, and the film layer state is γ-CsPbI3 black phase and DMAPbI3 coexistence, which can be thermodynamically stable at room temperature for a long time; when the additive is too much (D-2.5), excessive lattice distortion is not conducive to the generation of black phase, and DMAI competes with PbI2 to inhibit the generation of CsPbI3 perovskite structure, at this time the film layer is yellow phase, black phase and DMAPbI3 coexistence.

[0057] The thickness gradient experimental results formed in Example 1 and Comparative Examples 4-5 show that the film thickness is 50 μm and 120 μm, both of which are black phase, and when the film thickness is too thick, 200 μm, due to incomplete diffusion of DMAI in the film layer, the DMAPbI3 generated in the bulk phase is not enough to stabilize the entire system to form a room-temperature stable black phase structure, and at this time the film layer state is δ-CsPbI3 yellow phase, γ-CsPbI3 black phase and DMAPbI3 coexistence state.

[0058] (2) Only the film thickness is changed, and different thicknesses of CsPbI3 perovskite flexible thick film are prepared according to the method of Example 1, and the relationship diagram of X-ray absorption efficiency is shown in Figure 2 . It can be seen from Figure 2 that within 0-0.5 mm, the X-ray absorption efficiency of the film layer increases significantly with the increase of thickness, in order to ensure the photoelectric performance of the device, the film layer needs to be thick enough (preferably the thickness is more than 50 μm, further preferably more than 100 μm, and more preferably 100-120 μm in combination with the above test), and a room-temperature stable black phase structure is formed.

[0059] like Figure 3 As shown, thermogravimetric analysis (TGA) of the wetted flexible thick film in Example 1 revealed the following: The 0–90°C range is the solvent evaporation region, where DMF in the thick film begins to evaporate; the 90–140°C range is the reaction region, where DMAPbI3 begins to form; the temperature above 160°C is the decomposition region, where DMAPbI3 decomposes to form volatile DMAI gas; and above 180°C, the film layer is destroyed. Precise gradient annealing based on the TGA diagram ensures the formation of a stable black phase structure of DMAPbI3 in the thick film.

[0060] like Figure 4 As shown, the D-1.5@120μm flexible thick film prepared in Example 1 was characterized by X-ray diffraction (XRD) and compared with the XRD standard cards of γ-CsPbI3 black phase (γ-CPI) and DMAPbI3, as shown in the spectrum: The room temperature stable black phase flexible thick film D-1.5 exhibits a coexistence of DMAPbI3 phase (characteristic diffraction peak at 11.6° of DMAPbI3 in the figure) and γ-CsPbI3 black phase (characteristic diffraction peaks at 14.3° and 28.5° of γ-CsPbI3 in the figure). The room temperature black phase CsPbI3 is stabilized by low-dimensional / three-dimensional blended perovskite. The DMAPbI3 generated in the bulk phase can effectively adjust the lattice strain and stabilize the black phase structure. The film state is the coexistence of γ-CsPbI3 black phase and DMAPbI3. This state can maintain thermodynamic stability at room temperature for a long time. The system transition state is: PbI2+ CsI + DMAI→ γ-CsPbI3+ DMAPbI3 like Figure 5 As shown, the flexible thick films prepared in Example 1 and Comparative Example 1 were characterized by cross-sectional scanning electron microscopy (SEM). Figure 5 The flexible thick film (D-1.5@120μm) of Example 1 shown in (a) exhibits a three-dimensional grain structure with dense packing, and the grain size is between 5-8μm. CsPbI3 perovskite fully fills the pores in the nylon film, and it shows good stability under SEM electron beam irradiation. Figure 5 As shown in Figure (b), the flexible thick film (D-0@120 μm, δ-CsPbI3 perovskite film) of Comparative Example 1 exhibits a densely stacked rod-like structure with a size of approximately 100 μm. This is because, without the addition of DMAI additive, the three-dimensional orthorhombic crystal structure collapses during the cooling process, resulting in an orthorhombic crystal structure. The above characterization demonstrates that DMAI additive engineering can effectively improve the lattice stability of CsPbI3 perovskite, enabling the acquisition of a room-temperature thermodynamically stable black phase structure on a flexible nylon substrate, and offering the advantage of large-area fabrication.

[0061] like Figure 6EDS spectrum analysis was performed on the D-1.5@120 μm flexible thick film in Example 1 to study the element distribution in the CsPbI3 perovskite component: the results showed that the Cs, Pb and I elements were uniformly distributed in the flexible film layer, with good permeability, and the atomic percentages of Cs / Pb / I were 19.52 %:17.45 %:63.03 %, the atomic ratio of Cs and Pb ≈1 was consistent with the true ratio, and the additional 10.68 % of I element content in the film layer indicated that after the volatilization of DMAI, there was still an appropriate amount of DMAPbI3 in the film layer to stabilize the black phase, which was consistent with the above XRD conclusion. The density of the filled perovskite flexible thick film was calculated to be 3.66 g / cm 3 , the density of CsPbI3 perovskite was 4.54 g / cm 3 , and the interstitial rate of the perovskite as a whole was 80.6 %.

[0062] As shown in Figure 7 , UV-Vis analysis was performed on the flexible thick films prepared in Example 1 and Comparative Example 5. In Comparative Example 5, when the film thickness was 200 μm, the final film layer was a mixture of yellow phase and black phase (γ-CPI / δ-CPI), the band gap increased and the band edge overall blue shifted by about 50 nm compared with the black phase structure (γ-CPI) in Example 1 D-1.5@120 μm, and the light absorption response also significantly decreased, which meant that the yellow phase structure would significantly reduce the photoelectric performance of the perovskite to X-ray absorption.

[0063] As shown in Figure 8 , the mass attenuation coefficient and photon energy curve of the CsPbI3 flexible thick film obtained in Example 1 and the existing X-ray absorption common materials FAPbI3 and Si were calculated by NIST database, and the results showed that the CsPbI3 perovskite material exhibited excellent X-ray absorption performance and was a potential new X-ray detection material.

[0064] (3) The photocurrent-voltage test was performed on the carbon electrode / D-1.5@120 μm flexible thick film prepared in Example 2, and the obtained curve is shown in Figure 9 .

[0065] Figure 9 It can be seen from the results that the μτ product of the carbon electrode / D-1.5@120 μm flexible thick film prepared in Example 2 was tested by fitting the Hecht equation to characterize the carrier transport characteristics, and the results showed that the μτ product of the device was 1.16×10 -4 cm 2 ·V -1 , which was close to the results reported in the literature for three-dimensional perovskite devices, indicating that the flexible black phase structure could effectively improve the diffusion length of the carriers and help the device to obtain high sensitivity.

[0066] The sensitivity test of the carbon electrode / D-1.5@120 μm flexible thick film prepared in Example 2 was carried out under different voltages, and the obtained curve diagram is shown in Figure 10 .

[0067] Figure 10 It can be seen from the results that the sensitivity of the carbon electrode / D-1.5@120 μm flexible thick film prepared in Example 2 reaches 209 μC·Gy air -1 ·cm -2 , which is close to the reported flexible detector, and embodies excellent detection performance.

[0068] The relationship test between the X-ray dose rate and the device response of the carbon electrode / D-1.5@120 μm flexible thick film prepared in Example 2 and the carbon electrode / D-2.5@120 μm flexible thick film prepared in Comparative Example 6 was carried out, the results of the test were processed, and the X-ray dose rate-device response photocurrent curve was obtained, and the results are shown in Figure 11 .

[0069] Figure 11 It can be seen from the results in (a) that the response of the carbon electrode / D-1.5@120 μm flexible thick film prepared in Example 2 to X-rays of different dose rates has good linearity, and the black phase structure (δ-CPI) exhibits excellent X-ray detection performance; and the sensitivity of the device of Example 2 reaches 209 μC·Gy air -1 ·cm -2 , which is 1.79 times higher than the sensitivity of the mixture (γ-CPI / δ-CPI) of yellow phase and black phase in Comparative Example 6, which is 112 μC·Gy air -1 ·cm -2 , and the X-ray detector device performance of the present application is improved by 1.79 times, which also proves that it has excellent X-ray detection performance.

[0070] The bending experiment of the carbon electrode / D-1.5@120 μm flexible thick film prepared in Example 2 was carried out, and the relationship between the bending times and the sensitivity was tested, and the flexible thick film device with bending times change diagram was obtained by processing the test results, and the results are shown in Figure 12 .

[0071] Figure 12 It can be seen from the results that the carbon electrode / D-1.5@120 μm flexible thick film prepared in Example 2 has excellent bending stability, and can still maintain 81.6% of the initial performance after being bent for 200 times.

[0072] As Figure 13As shown, the process of preparing the flexible thick film prepared in Example 1 is demonstrated, and the perovskite precursor solution containing the DMAI additive is gradually infiltrated into the porous nylon film based on the solvent filtration method, and the gradient annealing treatment is performed, and the room temperature stable black phase all-inorganic perovskite flexible thick film is successfully prepared.

[0073] As shown, Figure 14 As shown, the principle of forming the black phase CsPbI3 perovskite flexible thick film by two-dimensional DMAPbI3 in Example 1 of the present application is analyzed, and in the crystallization process of the flexible thick film, part of the residual low-dimensional DMAPbI3 is wrapped around the three-dimensional CsPbI3 perovskite, thereby forming a perovskite film with good crystallization and stability.

[0074] The specific embodiments of the application described above do not constitute a limitation on the protection scope of the application. Any various other corresponding changes and modifications made according to the technical concept of the application shall be included in the protection scope of the claims of the application.

Claims

1. A process for the preparation of room temperature stable black phase all- inorganic perovskite flexible thick films, characterized by, The method comprises the following steps: S1, mixing PbI2, CsI and an organic ammonium salt in an organic solvent to obtain a perovskite precursor solution; The molar ratio of PbI2, CsI and the organic ammonium salt is 1:1:(1.2-1.8); S2, filling the perovskite precursor solution into a polymer filter membrane by vacuum filtration to obtain a wet flexible thick film; the polymer filter membrane is cleaned and has a thickness of more than 50 μm; S3, gradient annealing the wet flexible thick film to obtain a room-temperature-stable black-phase all-inorganic perovskite flexible thick film.

2. The process for the preparation of room temperature stable black phase all- inorganic perovskite flexible thick films as claimed in claim 1 wherein, In step S1, the general formula of the organic ammonium salt is R-NH3X, XH3N-R-NH3X or R1R2-NH2X, wherein X=I, Br or Cl; R, R1 and R2 are each independently selected from C1-C6 alkyl, C3-C6 cycloalkyl, heteroatom-containing C4-C6 cyclic amine group, phenyl or substituted phenyl derivative; The radius of the organic cation in the organic ammonium salt ranges > Cs + radius of Cs.

3. The process for the preparation of room temperature stable black phase all- inorganic perovskite flexible thick film as claimed in claim 1 wherein, In step S1, the organic ammonium salt comprises at least one of dimethylamine iodide, ethylamine iodide, isopropylamine iodide, N,N-dimethyl-1,3-propanediamine and phenethylamine iodide.

4. The process for the preparation of room temperature stable black phase all- inorganic perovskite flexible thick film as claimed in claim 1 wherein, In step S1, the organic solvent comprises at least one of N,N-dimethylformamide and dimethyl sulfoxide; and / or, The concentration of PbI2 in the perovskite precursor solution is 1-2 mol / L; and / or, The PbI2, CsI and the organic ammonium salt are mixed in the organic solvent by adding the PbI2, CsI and the organic ammonium salt into the organic solvent and stirring at room temperature for 8-12 h.

5. The process for the preparation of room temperature stable black phase all- inorganic perovskite flexible thick films as claimed in claim 1 wherein, In step S2, the polymer filter membrane comprises a nylon filter membrane; and / or, The pore size of the polymer filter membrane is less than 5 μm and the thickness is 50-150 μm; And / or, The cleaning of the polymer filter membrane comprises the following steps: soaking the polymer filter membrane in anhydrous ethanol and ultrasonic treatment for 15-30 min; then soaking in ultrapure water and ultrasonic treatment for 15-30 min, and then drying to complete the cleaning of the polymer filter membrane.

6. The process for the preparation of room temperature stable black phase all- inorganic perovskite flexible thick films as claimed in claim 1 wherein, In step S2, the vacuum filtration method comprises the following steps: placing the polymer filter membrane on a Buchner funnel, adding the perovskite precursor solution dropwise, and performing filtration under a vacuum degree of less than 1 mbar until the polymer filter membrane is completely wet.

7. The process for the preparation of room temperature stable black phase all- inorganic perovskite flexible thick films as claimed in claim 1 wherein, In step S3, the gradient annealing is first annealing at 80-100 ℃ for 1-2 h, and then annealing at 100 ℃-140 ℃ for 8-10 h.

8. The room-temperature-stable black-phase all-inorganic perovskite flexible thick film prepared by the preparation method of any one of claims 1-7.

9. An electrode / black phase all-inorganic perovskite flexible thick film, characterized in that, The electrode is prepared by coating on both sides of the black-phase all-inorganic perovskite flexible thick film of claim 8.

10. Application of the black-phase all-inorganic perovskite flexible thick film of claim 8 or the electrode / black-phase all-inorganic perovskite flexible thick film of claim 9 in an X-ray detector.

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