Bromine-doped methyl ammonium iodide perovskite X-ray detector and preparation method thereof

Abstract

The invention discloses a bromine-doped methyl ammonium iodide perovskite X-ray detector and a preparation method thereof, the bromine-doped methyl ammonium iodide perovskite X-ray detector comprises a conductive substrate, a hole transport layer, a bromine-doped methylamino perovskite absorption layer, an electron transport layer, a hole barrier layer and a metal cathode which are sequentially arranged from bottom to top, the bromine-doped methylamino perovskite absorption layer adopts an MAPb (I1-xBrx) 3 material, the hole transport layer is made of a poly [bis (4-phenyl) (2, 4, 6-trimethylphenyl) amine] (PTAA) material, the electron transport layer is made of a C60 material, and the hole blocking layer is made of a 2, 9-dimethyl-4, 7 diphenyl-1, 10-phenanthroline material. A small amount of Br is doped in methyl ammonium iodide, so that the dark current of a device can be effectively reduced, doped perovskite particles are enlarged, the grain boundary defect state density is reduced, relatively long fluorescence lifetime is shown, non-radiative recombination in an absorption layer is reduced, and separation and extraction of photon-generated carriers are increased by designing a matched device structure; the optimized X-ray detector has excellent performance and shows certain advantages in the aspects of device structure and component optimization.

Description

Technical Field

[0001] The present invention relates to the technical field of X-ray detectors, and in particular to a bromine-doped methylammonium iodide perovskite X-ray detector and a preparation method thereof. Background Art

[0002] X-ray detection technology has been widely used in many fields such as medical imaging, industrial flaw detection, and security inspection and control, and is closely related to the national economy and people's livelihood. In the past few years, amorphous selenium (α-Se) has dominated the market of direct X-ray detectors. However, amorphous selenium has low X-ray absorption capacity and poor charge transfer performance. Therefore, alternative materials with high X-ray absorption capacity have been widely studied. In recent years, metal halide perovskites have attracted much attention due to their high radiation absorption coefficient, high carrier mobility, long carrier lifetime, tunable optical band gap, high photoluminescence quantum efficiency, and compatibility with integrated circuits, and have become excellent candidate materials for high-sensitivity X-ray detectors. During this period, people have made a lot of efforts to improve the sensitivity of perovskites for X-ray detectors. However, the high sensitivity will be obtained at the cost of high dark current, resulting in large device noise and interference signals, and increasing the detection limit and medical radiation risk to patients.

[0003] In recent years, researchers have paid much attention to reducing dark current, including quasi-2D perovskites, 2D / 3D double-layer perovskites, perovskite pn homojunctions, 2D / 3D heterojunctions, and inserting insulating polymers between perovskites and electrodes. Although encouraging progress has been made, the high dark current density of perovskite X-ray detectors remains the biggest challenge for their practical application. Due to the excellent X-ray stopping ability and solution processability of perovskites, they have become an unprecedented candidate for planar X-ray detectors. The causes of high dark current include: 1) defects in the perovskite material itself, which can capture and release charge carriers and increase dark current; 2) defects in the perovskite material at the interface, which can also capture and release charge carriers and increase dark current; 3) design of device structure, reasonable design of transport layer and energy level matching, thereby reducing the recombination of charge carriers and reducing dark current.

[0004] The following are relevant studies on the above issues:

[0005] The patent with the publication number CN118019363A discloses a bismuth-doped formamidinium perovskite X-ray detector and its preparation method. By replacing a small amount of lead with the hetero-valent element bismuth to keep it in the black perovskite phase, it belongs to a photoconductive detector. It mainly regulates the lattice stress through doping to improve the stability of the perovskite phase and increase the resistance to reduce the dark current. The patent with the publication number CN113394344A discloses a direct-indirect hybrid perovskite X-ray detector. Its absorption layer is prepared by mixing Cs3Cu2I5 and MAPbI3 to reduce the dark current, and its dark current is 20 microamperes. Summary of the Invention

[0006] The purpose of the present invention is to provide a bromine-doped methylammonium iodide perovskite X-ray detector, which solves the problem of relatively high dark current density in pure perovskite X-ray detectors. The present invention improves the perovskite grain morphology, reduces the defect states of the perovskite material, and reduces the recombination of electron-hole carriers, thereby reducing the dark current density of the perovskite X-ray detector while maintaining high sensitivity.

[0007] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0008] A bromine-doped methylammonium iodide perovskite X-ray detector includes a conductive substrate, a hole transport layer, a bromine-doped methylammonium perovskite absorption layer, an electron transport layer, a hole blocking layer, and a metal cathode arranged in sequence from bottom to top. The bromine-doped methylammonium perovskite absorption layer uses MAPb(I 1-x Br x )3 material. MAPb(I x Br y )3 indicates that bromine replaces part of iodine in the methylammonium iodide perovskite material, 0% < x ≤ 20%. The bromine-doped methylammonium iodide perovskite material is a polycrystalline thin film. The hole transport layer uses poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) material, the electron transport layer uses C60 material, and the hole blocking layer uses 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline material.

[0009] The conductive substrate uses ITO conductive glass, and the metal cathode uses metal materials such as gold and silver.

[0010] A preparation method of a bromine-doped methylammonium iodide perovskite X-ray detector includes the following steps:

[0011] (1) Clean the ITO conductive glass and use it as the conductive substrate;

[0012] (2) The poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] material is dissolved in toluene solvent, heated, stirred, filtered, and then spin-coated on a clean conductive substrate, and then annealed at 130° C. to form a hole transport layer.

[0013] (3) Methylammonium iodide (MAI), PbI2 and PbBr2 are dissolved in a γ-butyrolactone solvent as solutes to obtain a solution with a mass fraction of 78 wt%, followed by a periodic oscillation reaction at 80-100°C, and α-pinene alcohol with a mass fraction of 30%-40% of γ-butyrolactone is added, and the periodic oscillation at 80-100°C is continued for 4-6 hours to finally obtain a perovskite suspension precursor slurry, which is then scraped onto the hole transport layer and then annealed at 120°C to form a bromine-doped methylamino perovskite absorption layer (MAPb(I 1-x Br x )3, the molar ratio of (PbI2+PbBr2):MAI is 1:1, and the molar percentage of PbBr2 in the total amount of PbI2 and PbBr2 is greater than 0% and less than or equal to 20%, preferably 10%-20%, and more preferably 15%. Pinene alcohol can increase the viscosity of the solution, which is conducive to scraping a thicker bromine-doped methylamino perovskite absorption layer on the hole transport layer. The thickness of the bromine-doped methylamino perovskite absorption layer is 400-830nm, preferably 650nm.

[0014] (4) The device prepared in step (3) is placed in a vacuum evaporator, and an electron transport layer C60, a hole blocking layer 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) and a metal cathode are sequentially evaporated.

[0015] (1) The present invention dopes a small amount of Br into methylammonium iodide, thereby increasing the size of the perovskite particles after doping, reducing the density of grain boundary defect states, and reducing the non-radiative recombination in the absorption layer, thereby effectively reducing the dark current of the device.

[0016] (2) The present invention increases the separation and extraction of photogenerated carriers by designing a matching device structure. The optimized X-ray detector has excellent performance and shows certain advantages in device structure and component optimization.

[0017] (3) The present invention prepares a thicker thin film absorption layer by a scraping method, and has certain commercial potential in the preparation of X-ray detectors on a large scale. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the structure of the perovskite X-ray detector.

[0019] Figure 2 This is the SEM image of the MAPbI3 surface, the scale is 50μm.

[0020] Figure 3MAPb(I 0.85 Br 0.15 )3 Surface SEM image.

[0021] Figure 4 Dark current and photocurrent measurement diagrams of 0%, 15%, and 20% Br doped perovskite X-ray detectors.

[0022] Figure 5 Radiation dose rate-sensitivity calculation diagram of 0%, 15%, and 20% Br doped perovskite X-ray detector. DETAILED DESCRIPTION

[0023] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and technical solutions.

[0024] Example 1

[0025] The present embodiment involves a bromine-doped methylammonium iodide perovskite X-ray detector, comprising a conductive substrate (ITO), a hole transport layer (PTAA), a bromine-doped methylamino perovskite absorption layer, an electron transport layer (C60), a hole blocking layer (BCP) and a metal cathode, which are arranged in sequence from bottom to top. The bromine-doped methylammonium iodide perovskite material is composed of bromine replacing part of the iodine in the methylammonium iodide perovskite material. The bromine-doped methylammonium iodide perovskite material is a polycrystalline thin film, and the bromine-doped methylammonium iodide perovskite device structure is a diode.

[0026] A method for preparing a bromine-doped methylammonium iodide perovskite X-ray detector comprises the following steps:

[0027] (1) The conductive substrate (ITO conductive glass) was ultrasonically cleaned with glass cleaning agent, deionized water, acetone, and ethanol for 10 minutes, blown dry with a nitrogen gun, and then treated with a plasma cleaning machine for 15 minutes.

[0028] (2) Poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) material was dissolved in toluene solvent, heated and stirred at 70°C for 6-8h, and the solution was filtered through an organic filter membrane and spin-coated on a clean ITO substrate at 2500 rpm, followed by annealing at 130°C for 35 min to form a hole transport layer.

[0029] (3) 1 mmol of methylammonium iodide MAI, 0.85 mmol of PbI2, and 0.15 mmol of PbBr2 powder were dissolved in 0.1709 g of γ-butyrolactone (GBL) to form a solution with a concentration of 78 wt%. The solution was then oscillated at 90 ° C for 4-6 h, and 30%-40% of α-pinene alcohol relative to the mass of γ-butyrolactone was added. The solution was oscillated at 90 ° C for 4-6 h to finally obtain a perovskite suspension precursor slurry. The perovskite suspension precursor slurry was scraped onto the poly [bis (4-phenyl) (2,4,6-trimethylphenyl) amine] (PTAA) layer, and then annealed at 120 ° C for 2-3 h to form a bromine-doped methylamino perovskite absorption layer MAPb (I 0.85 Br 0.15 )3 (15% Br doping), the thickness of the bromine-doped methylamino perovskite absorber layer ranges from 400 to 830 nm.

[0030] (4) The device prepared in step (3) is placed in a vacuum evaporator, and an electron transport layer C60, a hole blocking layer 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) and a silver electrode are sequentially evaporated.

[0031] Example 2

[0032] The present embodiment involves a method for preparing a bromine-doped methylammonium iodide perovskite X-ray detector, which is the same as that of the first embodiment except for step (3).

[0033] (3) 1 mmol of methylammonium iodide MAI, 0.8 mmol of PbI2, and 0.2 mmol of PbBr2 powder were dissolved in 0.1696 g of γ-butyrolactone (GBL) to form a solution with a concentration of 78 wt%. The solution was then oscillated at 90 ° C for 4-6 h, and 30%-40% of α-pinene alcohol relative to the mass of γ-butyrolactone was added. The solution was oscillated at 90 ° C for 4-6 h to finally obtain a perovskite suspension precursor slurry. The perovskite suspension precursor slurry was scraped onto the poly [bis (4-phenyl) (2,4,6-trimethylphenyl) amine] (PTAA) layer, and then annealed at 120 ° C for 2-3 h to form a bromine-doped methylamino perovskite absorption layer MAPb (I 0.8 Br 0.2 )3(20% Br doping).

[0034] Comparative Example 1

[0035] The preparation method of a methylammonium iodide perovskite X-ray detector involved in this comparative example is the same as that of Example 1 except for step (3).

[0036] (3) Take 1mmol methylammonium iodide MAI and 1mmol PbI2 powder and dissolve them in 0.1736g γ-butyrolactone (GBL) to form a 78wt% concentration solution. Then, after the solution is periodically shaken at 90℃ for 4-6h, 30%-40% of α-pinene alcohol relative to the mass of γ-butyrolactone is added, and the solution is periodically shaken at 90℃ for 4-6h to finally obtain a perovskite suspension precursor slurry. The perovskite suspension precursor slurry is scraped on top of the PTAA layer and then annealed at 120℃ for 2-3h to form a methylamino perovskite absorption layer MAPbI3 (0% Br doping).

[0037] The performance of the perovskite X-ray detectors prepared in Examples 1-2 and Comparative Example 1 was tested. The results are as follows: Figure 2-5 shown. Figure 3 The grain size of the 15%Br-doped thick film is relative to Figure 2 The undoped bromine has increased a little. The larger grain size can reduce the grain boundaries, which helps to reduce the non-radiative recombination of carriers at the grain boundaries, thereby reducing the dark current. Figure 4 It shows that the dark current of the device is reduced by one order of magnitude to 8.01*10 -10 Acm -2 , which is consistent with the characterization results. Figure 5 The sensitivity is highest when the Br doping concentration is 15%, indicating that the dark current of the device is reduced and the sensitivity is improved after Br doping.

Claims

1. A bromine-doped methylammonium iodide perovskite X-ray detector, characterized in that: It includes a conductive substrate, a hole transport layer, a bromine-doped methylammonium perovskite absorption layer, an electron transport layer, a hole blocking layer, and a metal cathode, which are sequentially arranged from bottom to top. The bromine-doped methylammonium perovskite absorption layer uses MAPb(I 1-x Br x )3 material, where 0% < x ≤ 20%. The hole transport layer uses poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) material, the electron transport layer uses C60 material, and the hole blocking layer uses 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline material.

2. The bromine-doped methylammonium iodide perovskite X-ray detector according to claim 1, characterized in that: The bromine-doped methylammonium iodide perovskite material is a polycrystalline thin film.

3. The bromine-doped methylammonium iodide perovskite X-ray detector according to claim 1, characterized in that: The thickness of the bromine-doped methylamino perovskite absorber layer is 405-825nm.

4. The bromine-doped methylammonium iodide perovskite X-ray detector according to claim 1, characterized in that: The conductive substrate is made of ITO conductive glass.

5. The bromine-doped methylammonium iodide perovskite X-ray detector according to claim 1, characterized in that: The metal cathode is gold or silver.

6. A method for preparing the bromine-doped methylammonium iodide perovskite X-ray detector according to claim 1, characterized in that: The steps include: (1) Cleaning the ITO conductive glass as a conductive substrate; (2) dissolving poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] in toluene solvent, heating, stirring, filtering, spin coating on a clean conductive substrate, and then annealing at 130° C. to form a hole transport layer; (3) Methylammonium iodide (MAI), PbI2 and PbBr2 are dissolved in a γ-butyrolactone solvent as solutes to obtain a solution with a mass fraction of 78 wt%, followed by a periodic oscillation reaction at 80-100°C, and α-pinene alcohol with a mass fraction of 30%-40% of γ-butyrolactone is added, and the periodic oscillation at 80-100°C is continued for 4-6 hours to finally obtain a perovskite suspension precursor slurry, which is then scraped onto the hole transport layer and then annealed at 120°C to form a bromine-doped methylamino perovskite absorption layer (MAPb(I 1-x Br x )3, the molar ratio of (PbI2+PbBr2):MAI is 1:1, and the molar percentage of PbBr2 in the total amount of PbI2 and PbBr2 is greater than 0% and less than or equal to 20%; (4) The device prepared in step (3) is placed in a vacuum evaporator, and an electron transport layer C60, a hole blocking layer 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) and a metal cathode are sequentially evaporated.

7. The method for preparing the bromine-doped methylammonium iodide perovskite X-ray detector according to claim 6, characterized in that: The molar percentage of PbBr2 in the total amount of PbI2 and PbBr2 is 10%-20%.

Images