Preparation method of perovskite direct type X-ray detector and perovskite ink

Abstract

The invention discloses a preparation method of a perovskite direct type X-ray detector and perovskite ink, and belongs to the field of preparation of direct type X-ray detectors. The preparation method comprises the following steps: dissolving perovskite precursor powder in an organic mixed solvent to obtain perovskite ink; cleaning the substrate, and preheating at 75 DEG C; depositing perovskite ink on a substrate in an ultrasonic spraying manner to form a perovskite thin film; carrying out annealing treatment on the perovskite thin film, and then cooling the perovskite thin film to room temperature; coating the surface of the perovskite thin film with a carbon electrode by using a mask plate, and heating and curing to obtain a direct X-ray detector; the organic mixed solvent is prepared from 2-methoxyethanol and a coordination solvent, and the coordination solvent is 1-cyclohexyl-2-pyrrolidone (CHP) or triethylene glycol monomethyl ether (TGME). According to the method, a low-temperature ultrasonic spraying process based on a perovskite intermediate phase is provided, the growth temperature of perovskite is reduced by 50-60 DEG C, and the problem of interface failure caused by interface thermal mismatch is relieved from the source.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of direct X-ray detector preparation, and particularly relates to a preparation method of a perovskite direct X-ray detector and a perovskite ink. BACKGROUND

[0002] X-ray detectors have a wide range of applications in medical imaging, industrial non-destructive testing, security checks, scientific research, radiation protection, etc. According to the working mechanism, X-ray detectors can be divided into indirect and direct types. Among them, the direct type can directly convert X-rays into electrical signals, thereby avoiding the problem of light scattering of the indirect type, and thus has the significant advantages of high spatial resolution and simple structure. Currently, the direct X-ray detector commercially used mainly adopts amorphous selenium as a photoelectric conversion layer, but due to the weak X-ray absorption and poor carrier transport properties of amorphous selenium, its application scenarios are limited to soft X-rays, and it has the disadvantages of high driving voltage and low detection sensitivity. In recent years, perovskite has become the most promising X-ray direct detection material due to its large X-ray absorption coefficient, ideal carrier transport properties and solution processing characteristics. Currently, the sensitivity of the perovskite direct X-ray detector has reached hundreds of times that of the traditional amorphous selenium detector, and the detection limit is also three orders of magnitude lower than that of the amorphous selenium detector, which is expected to bring revolutionary development to the direct X-ray detector.

[0003] It is worth noting that in order for perovskite to achieve full absorption of X-rays, its thickness needs to reach the order of hundreds of microns, which is 3 orders of magnitude different from the thickness of perovskite used in solar cells and photodiodes, which is in the order of hundreds of nanometers. Therefore, traditional perovskite solution processing methods such as spin coating cannot achieve the preparation of perovskite thick films for X-ray detection. Ultrasonic spray method, as a newly emerging method for depositing polycrystalline perovskite thin films, is very suitable for preparing perovskite light absorption layers for direct X-ray detectors, and its main process is as follows: first, the perovskite precursor solution is converted into mist droplets by using an ultrasonic oscillator, the atomized droplets are carried by a carrier gas (such as nitrogen) to a nozzle, and finally deposited on a high-temperature substrate. By adjusting the distance from the nozzle to the substrate, the moving speed of the nozzle and other parameters, the precise coverage of the atomized droplets can be achieved. This method can continuously grow polycrystalline perovskite thin films on the substrate to hundreds of microns by balancing the crystallization-dissolution-re-crystallization process of perovskite to meet the full absorption of X-rays.

[0004] Although depositing polycrystalline perovskite thin films by ultrasonic spray method has many advantages, unfortunately, this method still has a fatal disadvantage - when the perovskite thin film reaches a certain thickness (for example, 50 μm), it will fall off from the substrate during the heat annealing cooling process due to the thermal mismatch at the interface between the perovskite and the substrate (for example, FTO), which will cause the detector to fail. This is mainly due to the mismatch of the thermal expansion coefficients between the perovskite and the substrate (for example, FTO) (αFTO :~10 -6 K -1 ;alpha Perovskite :~10 -5 K -1 ), so that the perovskite will produce considerable tensile stress in the annealing cooling process. The greater the tensile stress, the greater the driving force of the perovskite off the substrate, and when the driving force is greater than the critical fracture energy of the perovskite, the perovskite film will spontaneously fall off the substrate, and the tensile stress of the perovskite and the driving force of the perovskite off the substrate mainly follow the following formula:

[0005]

[0006] Wherein, sigma is the tensile stress, E p is the Young's modulus of the perovskite (10-15GPa), u p is the Poisson's ratio (0.3), alpha is the thermal expansion coefficient, delta T is the temperature difference of the perovskite thermal annealing cooling, z is a dimensionless constant, d is the thickness of the perovskite film, and E' is the Young's modulus under biaxial strain.

[0007] Taking the preparation of MAPbI3 perovskite on FTO conductive glass by ultrasonic spraying technology as an example, generally, a high temperature of 135 DEG C is needed to ensure the volatilization of the solvent and the ordered crystallization of the perovskite. However, in the process of thermal annealing cooling, due to the large temperature difference, a large tensile stress will be generated at the interface between the perovskite and the conductive glass substrate, so that the MAPbI3 perovskite is prone to fall off the substrate when the thickness reaches 50 mu m. It can be seen that the thermal mismatch between the perovskite and the substrate is an important problem restricting the development of the perovskite direct X-ray detector, and therefore the preparation method of the perovskite direct X-ray detector and the perovskite ink are proposed. SUMMARY

[0008] In view of the shortcomings of the prior art, the purpose of the present application is to provide a preparation method of a perovskite direct X-ray detector and a perovskite ink, which solves the problems in the prior art.

[0009] The purpose of the present application can be achieved by the following technical solutions:

[0010] The preparation method of the perovskite direct X-ray detector comprises the following steps:

[0011] Dissolve the perovskite precursor powder in the organic mixed solvent to obtain the perovskite ink;

[0012] After the substrate is cleaned, it is preheated at 75 DEG C;

[0013] The perovskite ink is added to the ultrasonic spraying system and deposited on the substrate in the form of ultrasonic spraying to form a perovskite thin film;

[0014] The perovskite film is subjected to annealing treatment, and then cooled to room temperature;

[0015] The carbon electrode is scraped to the surface of the perovskite film by using a stainless steel mask plate, and the carbon electrode is heated and solidified to obtain a direct type X-ray detector.

[0016] The organic mixed solvent comprises 2-methoxyethanol and a coordination solvent, and the coordination solvent is 1-cyclohexyl-2-pyrrolidone or triethylene glycol monomethyl ether.

[0017] Further, the volume ratio of 2-methoxyethanol and the coordination solvent is 9:1.

[0018] Further, the perovskite precursor powder comprises AX1 and BX2, and the obtained perovskite is ABX3; A is MA, FA or Cs; B is Pb or Bi; and X is Cl, Br, I or SCN.

[0019] Further, the molar ratio of AX1 and BX2 is 1:1.

[0020] Further, the substrate is FTO conductive glass.

[0021] Further, the cleaning process of the substrate comprises the following steps: sequentially performing ultrasonic cleaning on the substrate by using glass cleaning liquid, deionized water, acetone, isopropanol, deionized water and anhydrous ethanol, then placing the substrate in an oven for drying, and then placing the dried substrate in an ultraviolet ozone cleaning instrument for cleaning.

[0022] Further, the ultrasonic spraying system comprises an atomization component, a driving component, a nozzle and a displacement component; the atomization component comprises an ultrasonic oscillator for atomizing the perovskite ink; the driving component injects carrier gas into the atomization component and carries the atomized perovskite ink to the nozzle; and the displacement component drives the nozzle to move under the action of a stepping motor.

[0023] Further, after the annealing treatment, the cooling rate is 1℃ / min -1 .

[0024] Further, the temperature for solidifying the carbon electrode is 80℃.

[0025] A perovskite ink comprises perovskite precursor powder AX1 and BX2, 2-methoxyethanol and a coordination solvent, and the coordination solvent is 1-cyclohexyl-2-pyrrolidone or triethylene glycol monomethyl ether; wherein A is MA, FA or Cs; B is Pb or Bi; and X is Cl, Br, I or SCN.

[0026] The perovskite ink has the following advantages:

[0027] 1. The low-temperature ultrasonic spray method based on the perovskite ink can deposit high-quality polycrystalline perovskite thin films on different substrates at low temperature, and the thickness of the thin film is highly adjustable in the range of several microns to several hundred microns. The traditional ultrasonic spray method will cause the perovskite to peel off the substrate due to thermal mismatch at the interface between the perovskite and the substrate when depositing perovskite films above 50 μm. By special selection of the perovskite precursor solvent, such as 2-methoxyethanol, the nucleation energy barrier of perovskite can be reduced, thereby reducing the crystallization temperature of perovskite. Finally, the tensile stress between the perovskite and the substrate during the annealing cooling process is significantly reduced, thereby significantly improving the fatal defect of the traditional ultrasonic spray method in depositing perovskite thick films. At the same time, in this ink formula, combined with the coordination solvent engineering, such as using 1-cyclohexyl-2-pyrrolidone as a coordination solvent, the balance between nucleation rate and crystal growth can be adjusted by forming an intermediate phase adduct with the precursor solution to maintain good crystallinity.

[0028] 2. The low-temperature ultrasonic spray method based on the perovskite ink formula can deposit high-quality polycrystalline perovskite thick films at low temperature (such as 75℃), which has the advantages of low energy consumption, adaptation to different substrates and easy large-area preparation, and provides a new technical route for the development of future perovskite direct X-ray detectors with high sensitivity, low dark current and high resolution.

[0029] 3. In the solvent system (2-methoxyethanol, CHP or TGME) of the present application, the intermediate phase formed at 65℃ can inhibit uncontrolled rapid nucleation, exhibit the characteristics of controlled crystallization path, and promote more ordered and complete growth to perovskite phase after annealing, thereby enabling the preparation of high-quality perovskite polycrystalline thick films at 75℃. Moreover, the spraying temperature of 75℃ is based on the preferred temperature condition of the solvent system of the present application. When the film is sprayed at 75℃ in the solvent system of the present application, the solvent evaporation rate and the nucleation and growth rate of the perovskite crystal can reach a dynamic balance. Therefore, this temperature condition of 75℃ is special and unique to the present application. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, for those skilled in the art, other drawings can also be obtained without creative labor based on these drawings.

[0031] Figure 1 is a direct X-ray detector and its preparation process schematic diagram of the present application;

[0032] Figure 2 is a scanning electron microscope cross-sectional view of the polycrystalline perovskite thick film prepared in Example 1;

[0033] Figure 3 is a partial enlarged view of Figure 2 ;

[0034] Figure 4 is a cross-sectional view of the polycrystalline perovskite thick film prepared by the comparative example 1 by scanning electron microscopy;

[0035] Figure 5 is a partial enlarged view of Figure 4 ;

[0036] Figure 6 is a cross-sectional view of the polycrystalline perovskite thick film prepared by the comparative example 2 by scanning electron microscopy;

[0037] Figure 7 is an XRD comparison chart of the perovskite thin film in the example 1 prepared at 65℃ and annealed at 75℃;

[0038] Figure 8 is an XRD comparison chart of the perovskite thin film in the example 2 prepared at 65℃ and annealed at 75℃;

[0039] Figure 9 is a light response current analysis chart of the direct type X-ray detector prepared by the example 1 under different dose X-rays;

[0040] Figure 10 is a sensitivity analysis chart of the direct type X-ray detector prepared by the example 1 under different dose X-rays;

[0041] Figure 11 is a normalized stability analysis chart of the direct type X-ray detector prepared by the example 1 under different dose X-rays.

[0042] In the figure: 1-atomizing component, 2-driving component, 3-nozzle, 4-displacement component, 5-perovskite thin film, 6-substrate, 7-constant temperature heating table, 8-carbon electrode. DETAILED DESCRIPTION

[0043] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the 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 skilled in the art without creative labor fall within the protection scope of the present application.

[0044] As shown in Figure 1 , the preparation method of the perovskite direct type X-ray detector comprises the following steps:

[0045] S1, perovskite precursor powder is weighed according to a specific stoichiometric ratio, and is dissolved in an organic mixed solvent to obtain perovskite ink;

[0046] S2, after cleaning the substrate 6 (FTO conductive glass), place it on the constant temperature heating table 7, and preheat at 75℃;

[0047] S3, add the perovskite ink into the ultrasonic spraying system, and deposit it on the substrate 6 by ultrasonic spraying to form the perovskite film 5;

[0048] S4, anneal the obtained perovskite film 5, and then slowly cool it (at a rate of 1℃ / min -1 ) to room temperature;

[0049] S5, after annealing, use a 0.1mm thick stainless steel mask to squeegee the carbon electrode 8 onto the surface of the perovskite film 5, and then heat the perovskite film 5 at 80℃ for 15min to solidify the carbon electrode 8, thereby preparing a direct type X-ray detector.

[0050] Wherein:

[0051] In S1, the organic mixed solvent includes 2-methoxyethanol and a complexing solvent, and the volume ratio of the two is 9:1; and the complexing solvent is 1-cyclohexyl-2-pyrrolidone or triethylene glycol monomethyl ether.

[0052] In S1, the perovskite precursor powder includes AX1 and BX2, and the obtained perovskite is ABX3; wherein A is MA, FA or Cs; B is Pb or Bi; X is Cl, Br, I or SCN, etc. quasi-halogen.

[0053] In S2, the cleaning process of the substrate 6 is as follows:

[0054] Put the substrate 6 (FTO conductive glass) into a beaker, and sequentially ultrasonically clean it with glass cleaning solution, deionized water, acetone, isopropanol, deionized water, and anhydrous ethanol. After cleaning, place it in an oven for drying, and then place the dried substrate 6 (FTO conductive glass) in a UV ozone cleaning instrument for 15min of cleaning to enhance the hydrophilicity of the substrate 6 (FTO conductive glass) and improve the surface contact between the perovskite droplets and the substrate 6 (FTO conductive glass).

[0055] In S3, the ultrasonic spraying system is as shown in (a) of Figure 1 , which includes an atomization component 1, a driving component 2, a nozzle 3, and a displacement component 4; the atomization component 1 includes an ultrasonic oscillator, and the perovskite ink is placed in the atomization component 1 after being prepared, and the ultrasonic oscillator is used to atomize the perovskite ink; the driving component 2 injects carrier gas (nitrogen) into the atomization component 1, and carries the atomized perovskite ink to the nozzle 3; the displacement component 4 is driven by a stepper motor to move the nozzle;

[0056] The process of depositing perovskite film by using the above ultrasonic spray system is specifically as follows:

[0057] S31, turn on the ultrasonic oscillator to atomize the perovskite ink, at this time, the carrier gas (nitrogen) is introduced, and the atomized perovskite ink is carried by the carrier gas to the nozzle 3;

[0058] S32, adjust the height of the nozzle 3 from the substrate 6, turn on the stepper motor to control the movement of the nozzle 3, and the perovskite mist will be sprayed onto the substrate 6 at a constant temperature of 75℃, and then continuously deposit the perovskite film 5 on the substrate 6;

[0059] Wherein, the movement of the nozzle 3 is controlled by pre-setting the built-in program of the stepper motor, such as the starting position, step length and speed; and the thickness of the perovskite film can be controlled by the number of cycles of the stepper motor, and the spraying can be stopped when the thickness reaches the expected requirement.

[0060] In S4, the parameters of the annealing treatment are:

[0061] In example 1, example 2 and comparative example 2, the annealing is at 75℃ for 20min.

[0062] In comparative example 1, the annealing is at 135℃ for 20min.

[0063] The technical scheme of the present application will be illustrated in detail by the following examples and comparative examples;

[0064] Example 1

[0065] In this embodiment, a method for preparing a perovskite direct type X-ray detector on an FTO conductive glass substrate by a low-temperature ultrasonic spray method is provided, which comprises the following steps:

[0066] (1) Put the FTO conductive glass into a beaker, and sequentially perform ultrasonic cleaning with glass cleaning solution, deionized water, acetone, isopropyl alcohol, deionized water, and anhydrous ethanol, then put it into an oven for drying, and then put the dried FTO conductive glass into an ultraviolet ozone cleaning instrument for cleaning for 15min, so as to enhance the hydrophilicity of the FTO glass surface and improve the surface contact between the perovskite droplets and the glass substrate.

[0067] (2) Dissolve lead iodide (PbI2) and methylammonium iodide (MAI) in an organic mixed solvent at a molar ratio of 1:1, stir for more than 8h to obtain a three-dimensional perovskite MAPbI3 ink with a concentration of 0.5mol / L, and the above-mentioned organic mixed solvent is 2-methoxyethanol and 1-cyclohexyl-2-pyrrolidone with a volume ratio of 9:1.

[0068] (3) The perovskite ink is filtered with an organic filter to remove fine impurities in the solution, and then injected into the atomization component 1, while the FTO conductive glass is placed on the constant temperature heating table 7 for constant temperature preheating at 75°C.

[0069] (4) The stepper motor is programmed to set the starting position, step size, and speed parameters.

[0070] (5) Turn on the ultrasonic oscillator in the atomization component 1 to atomize the perovskite ink, and then turn on the driving component 2 to introduce the carrier gas (nitrogen), which will carry the atomized perovskite ink to the nozzle 3.

[0071] (6) Adjust the distance between the nozzle 3 and the FTO conductive glass, then turn on the stepper motor to control the circular movement of the nozzle, start spraying, and the perovskite atomized droplets will immediately form a perovskite thin film when they contact the 75°C FTO glass surface. With the circular movement of the nozzle, the perovskite thin film 5 will continuously deposit on the FTO glass.

[0072] (7) The thickness of the perovskite thin film 5 is controlled by the number of cycles of the stepper motor. In this embodiment, a 50μm thick perovskite film is obtained after 500 cycles, Figure 2 and Figure 3 are the SEM cross-sectional view and SEM cross-sectional local magnification view of the perovskite thick film, respectively. After the film thickness reaches the desired value, the spraying can be stopped, and the obtained perovskite thick film is annealed by slowly cooling (at a rate of 1°C / min -1 ) to room temperature.

[0073] (8) After annealing is completed, the carbon electrode 8 is squeegeed onto the surface of the perovskite thin film 5 using a 0.1mm thick stainless steel mask, and then the perovskite thin film 5 is heated at 80°C for 15min to solidify the carbon electrode 7, thereby preparing a perovskite direct type X-ray detector, and the device structure is shown in Figure 1 (b).

[0074] Example 2

[0075] In this embodiment, a method for preparing a perovskite direct type X-ray detector on an FTO conductive glass substrate using a low-temperature ultrasonic spray method is provided, which includes the following steps:

[0076] (1) Place the FTO conductive glass in a beaker and sequentially ultrasonically clean it with glass cleaning solution, deionized water, acetone, isopropanol, deionized water, and anhydrous ethanol. After cleaning, place the dried FTO conductive glass in an ultraviolet ozone cleaning instrument for 15min of cleaning to enhance the hydrophilicity of the FTO glass surface and improve the surface contact between the perovskite droplets and the glass substrate.

[0077] (2) Lead iodide (PbI2) and methylammonium iodide (MAI) are dissolved in an organic mixed solvent at a molar ratio of 1:1, stirred for more than 8 h, to obtain a three-dimensional perovskite MAPbI3 ink with a concentration of 0.5 mol / L, and the organic mixed solvent is 2-methoxyethanol and triethylene glycol monomethyl ether at a volume ratio of 9:1.

[0078] (3) The perovskite ink is filtered with an organic filter head to remove fine impurities in the solution, and then injected into the atomization component 1, while the FTO conductive glass is placed on the constant temperature heating table 7 for constant temperature preheating at 75°C.

[0079] (4) The stepper motor is programmed and set, and the starting position, step size and speed parameters are set.

[0080] (5) Turn on the ultrasonic oscillator in the atomization component 1, atomize the perovskite ink, and then turn on the driving component 2 to introduce the carrier gas (nitrogen), and the atomized perovskite ink will be carried by the carrier gas to the nozzle 3.

[0081] (6) Adjust the distance between the nozzle 3 and the FTO conductive glass, then turn on the stepper motor to control the circular movement of the nozzle, start spraying, and the perovskite atomized droplets will immediately form a perovskite thin film when they contact the 75°C FTO glass surface. With the circular movement of the nozzle, the perovskite thin film 5 will continuously deposit on the FTO glass.

[0082] (7) The thickness of the perovskite thin film 5 is controlled by the number of cycles of the stepper motor. When the film thickness reaches the desired value, the spraying can be stopped, and the obtained perovskite thick film is annealed by slowly cooling (at a rate of 1°C / min -1 ) to room temperature.

[0083] (8) After annealing is completed, a 0.1 mm thick stainless steel mask is used to squeegee the carbon electrode 8 onto the surface of the perovskite thin film 5, and then the perovskite thin film 5 is heated at 80°C for 15 min to solidify the carbon electrode 7, thereby preparing a perovskite direct type X-ray detector, and the device structure is shown in Figure 1 (b).

[0084] Comparative Example 1

[0085] Comparative Example 1 provides a method for preparing a perovskite direct type X-ray detector on an FTO conductive glass substrate by ultrasonic spraying, which comprises the following steps:

[0086] (1) Place the FTO conductive glass in a beaker and clean it with glass cleaning solution, deionized water, acetone, isopropanol, deionized water and anhydrous ethanol in sequence. After cleaning, place it in an oven to dry. Then place the dried FTO conductive glass in an ultraviolet ozone cleaner for 15 minutes to enhance the hydrophilicity of the FTO glass surface and improve the surface contact between perovskite droplets and the glass substrate.

[0087] (2) Lead iodide (PbI2) and methyl ammonium iodide (MAI) were dissolved in an organic mixed solvent at a molar ratio of 1:1 and stirred for more than 8 hours to obtain a three-dimensional perovskite MAPbI3 ink with a concentration of 0.5 mol / L. The organic mixed solvent was dimethyl sulfoxide and N,N-dimethylformamide in a volume ratio of 1:1.

[0088] (3) After filtering the perovskite ink with an organic filter head to remove fine impurities in the solution, it is injected into the atomizing component 1. At the same time, the FTO conductive glass is placed on the constant temperature heating stage 7 for constant temperature preheating at 135°C.

[0089] (4) Set the program for the stepper motor, including setting the starting position, step length, and speed.

[0090] (5) Turn on the ultrasonic oscillator in the atomizing component 1 to atomize the perovskite ink, and then turn on the driving component 2 to introduce carrier gas (nitrogen). The atomized perovskite ink will be carried to the nozzle 3 by the carrier gas.

[0091] (6) Adjust the distance between the nozzle 3 and the FTO conductive glass, then turn on the stepper motor to control the cyclic movement of the nozzle and start spraying. When the perovskite atomized droplets come into contact with the FTO glass surface at 135°C, a perovskite film will be generated immediately. As the nozzle moves cyclically, a perovskite film 5 will be continuously deposited on the FTO glass.

[0092] (7) The thickness of the perovskite film 5 is controlled by the number of cycles of the stepper motor. For example, a perovskite film with a thickness of 50 μm will be obtained after 500 cycles. Figure 4 and Figure 5 The images show a SEM cross-sectional view and a magnified partial SEM cross-sectional view of the perovskite thick film, respectively. Once the film thickness reaches the desired level, spraying can be stopped, and the resulting perovskite thick film can be annealed by slow cooling (at a rate of 1℃ / min). -1 (Let it cool to room temperature.)

[0093] (8) After annealing, carbon electrode 8 is coated onto the surface of perovskite film 5 using a 0.1 mm thick stainless steel mask. The perovskite film 5 is then heated at 80 °C for 15 min to solidify the carbon electrode 7, thus fabricating a direct-type perovskite X-ray detector. The device structure is as follows: Figure 1 As shown in (b) of the diagram.

[0094] Comparative Example 2

[0095] Comparative Example 2 provides a method for preparing a perovskite direct type X-ray detector on an FTO conductive glass substrate by a low-temperature ultrasonic spray method, comprising the following steps:

[0096] (1) Put the FTO conductive glass into a beaker, and sequentially perform ultrasonic cleaning with glass cleaning solution, deionized water, acetone, isopropanol, deionized water, and anhydrous ethanol. After cleaning, place the FTO conductive glass in an oven for drying, and then place the dried FTO conductive glass in an ultraviolet ozone cleaning instrument for 15 min of cleaning to enhance the hydrophilicity of the FTO glass surface and improve the surface contact of perovskite droplets with the glass substrate.

[0097] (2) Dissolve lead iodide (PbI2) and methylammonium iodide (MAI) in an organic solvent at a molar ratio of 1:1, and stir for more than 8 h to obtain a three-dimensional perovskite MAPbI3 ink with a concentration of 0.5 mol / L. The above-mentioned organic solvent is dimethoxyethanol.

[0098] (3) After filtering the perovskite ink with an organic filter to remove fine impurities in the solution, inject it into the atomization component 1, and at the same time, place the FTO conductive glass on the constant temperature heating table 7 for 75°C constant temperature preheating.

[0099] (4) Program the stepper motor, and set the starting position, step size, and speed parameters.

[0100] (5) Turn on the ultrasonic oscillator in the atomization component 1 to atomize the perovskite ink, and then turn on the driving component 2 to introduce the carrier gas (nitrogen). The atomized perovskite ink will be carried by the carrier gas to the nozzle 3.

[0101] (6) Adjust the distance between the nozzle 3 and the FTO conductive glass, then turn on the stepper motor to control the cyclic movement of the nozzle, start spraying, and the perovskite atomized droplets will immediately form a perovskite thin film when they contact the 75°C FTO glass surface. With the cyclic movement of the nozzle, the perovskite thin film 5 will continuously deposit on the FTO glass.

[0102] (7) The thickness of the perovskite thin film 5 is controlled by the number of cycles of the stepper motor, Figure 6 the SEM cross-sectional view of the perovskite thick film. After the film thickness reaches the expected value, stop spraying, and perform annealing treatment on the obtained perovskite thick film, and slowly cool it to room temperature at a rate of 1°C / min -1 ).

[0103] (8) After annealing, carbon electrode 8 is coated onto the surface of perovskite film 5 using a 0.1 mm thick stainless steel mask. The perovskite film 5 is then heated at 80 °C for 15 min to solidify the carbon electrode 7, thus fabricating a direct-type perovskite X-ray detector. The device structure is as follows: Figure 1 As shown in (b) of the diagram.

[0104] The advantages of the present invention will be explained in more detail and comprehensively below with reference to implementation examples, comparative examples and accompanying drawings. The perovskite precursor solution formulation in Comparative Example 1 is a conventional dimethyl sulfoxide and N,N-dimethylformamide. A scanning electron microscope cross-sectional image of the perovskite thick film prepared using this conventional perovskite ink formulation is observed. Figure 4 ) and its enlarged portion ( Figure 5 It is evident that the perovskite thick film detached from the FTO substrate, which is caused by the tensile stress resulting from the large temperature difference during the cooling process of thermal annealing. Therefore, in Comparative Example 2, 2-methoxyethanol was used instead of the traditional perovskite precursor solution formulation. This is because 2-methoxyethanol can lower the nucleation energy barrier of perovskite, thereby lowering the crystallization temperature of perovskite. This allows for the preparation of polycrystalline perovskite thick films via low-temperature ultrasonic spraying, solving the problem of perovskite film detachment from the substrate during thermal annealing. The scanning electron microscope cross-sectional image of the perovskite thick film prepared in Comparative Example 2 (…) Figure 6 From the perspective of [the study], although using 2-methoxyethanol as a precursor solvent for perovskite can solve the subsequent problem of film removal from the substrate, it cannot continuously form a dense perovskite film perpendicular to the substrate, and the film quality is very poor. This is due to the uncontrolled crystal growth caused by the excessively rapid nucleation rate of perovskite. Therefore, in Examples 1 and 2, coordination solvents such as 1-cyclohexyl-2-pyrrolidone and triethylene glycol monomethyl ether were added, respectively. The XRD comparison images of the perovskite films prepared at 65°C and annealed at 75°C in Examples 1 and 2 are shown below. Figure 7 and Figure 8 From this, we can see that these coordination solvents can form mesophase adducts with the perovskite precursor solvent at 65°C, and these mesophase adducts dominate at 65°C. In Examples 1 and 2, after annealing at 75°C, the mesophase disappears, and the normal crystal orientation of the perovskite polycrystalline film (110 and 220 are dominant) is transformed. It is precisely because of the presence of this mesophase adduct that uncontrolled rapid nucleation is suppressed, exhibiting the characteristics of a controlled crystallization path, and promoting more ordered and complete growth of the perovskite phase after annealing. Finally, high-quality polycrystalline perovskite thick films can be deposited at a low temperature of 75°C using ultrasonic spraying. From the scanning electron microscope cross-sectional image of the perovskite thick film prepared in Example 1 (…), we can see… Figure 2 ) and a magnified view of a section of the scanning electron microscope (SEM) Figure 3According to the preferred perovskite ink formulation of this invention, the perovskite thick film prepared by low-temperature ultrasonic spraying grows perpendicular to the substrate, is dense, and does not detach from the substrate.

[0105] Finally, the direct-type X-ray detector prepared based on the perovskite ink formulation of the preferred embodiment of the present invention also exhibited excellent performance. The test process and test results are as follows:

[0106] The device under test (DUT) is placed in a specific fixture, with electrode outlets connected to carbon and FTO electrodes, respectively. A Mini-X2 X-ray tube serves as the X-ray source above the fixture, and the X-ray dose rate is changed by adjusting the current in the X-ray tube. During testing, a certain bias voltage is applied across the electrodes of the device.

[0107] When a bias voltage of 1.5V was applied, the photoresponse of the direct-type X-ray detector prepared by the perovskite ink formulation of Example 1 was tested under different doses of X-rays. The results showed that the device had a low dark current. Figure 9 ), and at the same time by Figure 9 Fitting 4344μC Gyair -1 cm -2 higher sensitivity ( Figure 10 Finally, the device's stability was tested at a bias voltage of 1.5V and different dose rates, and the results showed that the device has good stability. Figure 11 ).

[0108] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0109] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A method for fabricating a perovskite direct-type X-ray detector, characterized in that, Includes the following steps: Perovskite precursor powder is dissolved in an organic mixed solvent to obtain perovskite ink; After cleaning the substrate, preheat it to 75°C; Perovskite ink is added to an ultrasonic spraying system and deposited onto a substrate using ultrasonic spraying to form a perovskite film. The perovskite film was annealed and then cooled to room temperature. A carbon electrode is coated onto the surface of a perovskite thin film using a stainless steel mask, and then the carbon electrode is cured by heating to obtain a direct-type X-ray detector. The organic mixed solvent includes 2-methoxyethanol and a coordination solvent, wherein the coordination solvent is 1-cyclohexyl-2-pyrrolidone or triethylene glycol monomethyl ether.

2. The method for fabricating a perovskite direct-type X-ray detector according to claim 1, characterized in that, The volume ratio of 2-methoxyethanol to the coordinating solvent is 9:

1.

3. The method for fabricating a perovskite direct-type X-ray detector according to claim 1, characterized in that, The perovskite precursor powder includes: AX1 and BX2, and the resulting perovskite is ABX3; A is MA, FA or Cs; B is Pb or Bi; X is Cl, Br, I or SCN.

4. The method for fabricating a perovskite direct-type X-ray detector according to claim 1, characterized in that, The molar ratio of AX1 to BX2 is 1:

1.

5. The method for fabricating a perovskite direct-type X-ray detector according to claim 1, characterized in that, The substrate is FTO conductive glass.

6. The method for fabricating a perovskite direct-type X-ray detector according to claim 1 or 5, characterized in that, The cleaning process of the substrate is as follows: the substrate is ultrasonically cleaned in sequence with glass cleaning solution, deionized water, acetone, isopropanol, deionized water and anhydrous ethanol, then placed in an oven to dry, and then the dried substrate is placed in an ultraviolet ozone cleaner for cleaning.

7. The method for fabricating a perovskite direct-type X-ray detector according to claim 1, characterized in that, The ultrasonic spraying system includes: an atomizing component, a driving component, a nozzle, and a displacement component; the atomizing component includes an ultrasonic oscillator for atomizing perovskite ink; the driving component injects carrier gas into the atomizing component and carries the atomized perovskite ink to the nozzle; the displacement component drives the nozzle to move under the action of a stepper motor.

8. The method for fabricating a perovskite direct-type X-ray detector according to claim 1, characterized in that, After annealing, the cooling rate is: 1℃ / min. -1 .

9. The method for fabricating a perovskite direct-type X-ray detector according to claim 1, characterized in that, The temperature for curing the carbon electrode is 80℃.

10. A perovskite ink, characterized in that, include: The perovskite precursor powders AX1 and BX2, 2-methoxyethanol, and a coordination solvent, wherein the coordination solvent is 1-cyclohexyl-2-pyrrolidone or triethylene glycol monomethyl ether; wherein A is MA, FA, or Cs; B is Pb or Bi; and X is Cl, Br, I, or SCN.

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