A bromine-doped methylammonium iodide perovskite X-ray detector and its fabrication method

Abstract

This invention discloses a bromine-doped ammonium methyl iodide perovskite X-ray detector and its fabrication method, comprising, from bottom to top, a conductive substrate, a hole transport layer, a bromine-doped ammonium methyl iodide perovskite absorption layer, an electron transport layer, a hole blocking layer, and a metal cathode. The bromine-doped ammonium methyl iodide perovskite absorption layer uses MAPb(I) 1‑x Br x The X-ray detector utilizes three materials: a hole transport layer made of poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA), an electron transport layer made of C60, and a hole blocking layer made of 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline. By doping a small amount of Br into ammonium methyl iodide, the dark current of the device can be effectively reduced. The doped perovskite particles become larger, the density of grain boundary defect states decreases, resulting in a longer fluorescence lifetime. Non-radiative recombination within the absorption layer is reduced. Through the design of a matched device structure, the separation and extraction of photogenerated carriers are enhanced. The optimized X-ray detector exhibits excellent performance, demonstrating certain advantages in device structure and composition optimization.

Description

Technical Field

[0001] This invention relates to the field of X-ray detector technology, and in particular to a bromine-doped methylammonium iodide perovskite X-ray detector and its preparation method. Background Technology

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

[0003] In recent years, researchers have focused on reducing dark current, including quasi-2D perovskites, 2D / 3D bilayer perovskites, perovskite pn homojunctions, 2D / 3D heterojunctions, and inserting insulating polymers between the perovskite and the electrodes. While 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 blocking 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 trap and release charge carriers, increasing dark current; 2) defects at the interface of the perovskite material, which can also trap and release charge carriers, increasing dark current; 3) device structure design, including the rational design of the transport layer and energy level matching, thereby reducing charge carrier recombination and lowering dark current.

[0004] The following are relevant studies addressing 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 lead with a small amount of 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 increases 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 object of the present invention is to provide a bromine-doped methylammonium iodide perovskite X-ray detector, which solves the problem of the relatively high dark current density of 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] To achieve the above object, 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 the MAPb(I 1-x Br x )3 material. MAPb(I x Br y )3 means 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) Dissolve poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] in toluene solvent, heat and stir, filter, spin coat onto a clean conductive substrate, and then anneal at 130°C to form a hole transport layer.

[0013] (3) Methylammonium iodide (MAI), PbI2, and PbBr2 were dissolved in γ-butyrolactone solvent to obtain a solution with a mass fraction of 78 wt%. The solution was then subjected to periodic shaking at 80-100 °C. α-terpineol (30%-40% by mass of γ-butyrolactone) was added, and the mixture was shaken periodically at 80-100 °C for 4-6 hours to obtain a perovskite suspension precursor slurry. This perovskite suspension precursor slurry was coated onto the hole transport layer and then annealed at 120 °C to form a bromine-doped methylamino perovskite absorber layer MAPb(I 1-x Br x 3. The molar ratio of (PbI2 + PbBr2):MAI is 1:1. 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%. Terpineol increases the solution viscosity, which is beneficial for creating a thicker bromine-doped methylamino perovskite absorber layer on the hole transport layer. The thickness of the bromine-doped methylamino perovskite absorber layer is 400-830 µm, preferably 650 µm.

[0014] (4) Place the device prepared in step (3) into a vacuum evaporation machine and deposit the electron transport layer C60, the hole blocking layer 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) and the metal cathode in sequence.

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

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

[0017] (3) The present invention prepares a thicker thin film absorption layer by the scraping method, which has certain commercial potential in the large-area preparation of X-ray detectors. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of a perovskite X-ray detector.

[0019] Figure 2 The image shows a SEM image of the MAPbI3 surface, with a scale bar of 50 μm.

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

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

[0022] Figure 5 Radiation dose rate-sensitivity calculation graphs for 0%, 15%, and 20% Br-doped perovskite X-ray detectors. Detailed Implementation

[0023] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and technical solutions.

[0024] Example 1

[0025] This embodiment relates to a bromine-doped methylammonium iodide perovskite X-ray detector, comprising, from bottom to top, a conductive substrate (ITO), a hole transport layer (PTAA), a bromine-doped methylammonium perovskite absorber layer, an electron transport layer (C60), a hole blocking layer (BCP), and a metal cathode. 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 fabricating a bromine-doped methylammonium iodide perovskite X-ray detector includes the following steps:

[0027] (1) The conductive substrate (ITO conductive glass) was ultrasonically cleaned for 10 minutes in sequence with glass cleaner, deionized water, acetone and ethanol, then dried with a nitrogen gun, and then treated with a plasma cleaner for 15 minutes.

[0028] (2) Dissolve poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) in toluene solvent, heat and stir at 70°C for 6-8 hours, filter the solution through an organic filter membrane, spin coat it onto a clean ITO substrate at 2500 rpm, and then anneal at 130°C for 35 minutes to form a hole transport layer.

[0029] (3) Dissolve 1 mmol of methylammonium iodide (MAI), 0.85 mmol of PbI2, and 0.15 mmol of PbBr2 powder in 0.1709 g of γ-butyrolactone (GBL) to form a 78 wt% solution. After the solution is periodically shaken at 90°C for 4-6 h, add 30%-40% α-terpineol relative to the mass of γ-butyrolactone and continue to periodically shake at 90°C for 4-6 h to finally obtain a perovskite suspension precursor slurry. Coat the perovskite suspension precursor slurry on top of a poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) layer, and then anneal at 120°C for 2-3 h to form a bromine-doped methylamino perovskite absorber layer MAPb(I 0.85 Br 0.15 )3 (15% Br doped), the thickness of the bromine-doped methylamino perovskite absorber layer ranges from 400 to 830 µm.

[0030] (4) Place the device prepared in step (3) into a vacuum evaporation machine and deposit the electron transport layer C60, the hole blocking layer 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) and the silver electrode in sequence.

[0031] Example 2

[0032] The preparation method of the bromine-doped methylammonium iodide perovskite X-ray detector involved in this embodiment is the same as that in Example 1, except for step (3).

[0033] (3) Dissolve 1 mmol of methylammonium iodide (MAI), 0.8 mmol of PbI2, and 0.2 mmol of PbBr2 powder in 0.1696 g of γ-butyrolactone (GBL) to form a 78 wt% solution. After cyclically shaking the solution at 90 °C for 4-6 h, add 30%-40% α-terpineol relative to the mass of γ-butyrolactone and continue cyclically shaking at 90 °C for 4-6 h to finally obtain a perovskite suspension precursor slurry. Coat the perovskite suspension precursor slurry onto a poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) layer, and then anneal at 120 °C for 2-3 h to form a bromine-doped methylamino perovskite absorber layer MAPb(I 0.8 Br 0.2 )3 (20% Br doping).

[0034] Comparative Example 1

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

[0036] (3) Take 1 mmol of methyl ammonium iodide (MAI) and 1 mmol of PbI2 powder and dissolve them in 0.1736 g of γ-butyrolactone (GBL) to form a solution with a concentration of 78 wt%. After the solution is periodically shaken at 90 °C for 4-6 h, add 30%-40% of α-terpineol relative to the mass of γ-butyrolactone and continue to shake at 90 °C for 4-6 h to finally obtain a perovskite suspension precursor slurry. Coat the perovskite suspension precursor slurry on top of the PTAA layer and then anneal at 120 °C for 2-3 h to form a methylamino perovskite absorber layer MAPbI3 (0% Br doped).

[0037] The performance of the perovskite X-ray detectors prepared in Examples 1-2 and Comparative Example 1 was tested, and the results are as follows: Figure 2-5 As shown. Figure 3 The grain size of a 15% Br-doped thick film relative to Figure 2 The undoped bromine increases in size, and the larger grain size can reduce grain boundaries, which helps to reduce the nonradiative recombination of charge carriers at the grain boundaries, thereby reducing the dark current. Figure 4 This indicates that the dark current of the device decreases by an order of magnitude to 8.01 × 10⁻⁶ when the Br doping concentration is 15%. -10 A cm -2 This is consistent with the characterization results. Figure 5 The highest sensitivity was observed at a 15% Br doping concentration, indicating that Br doping reduces the dark current of the device while also improving its sensitivity.

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; the bromine-doped methylammonium iodide perovskite material is a polycrystalline thin film; The method for fabricating the bromine-doped methylammonium iodide perovskite X-ray detector is characterized by comprising the following steps: (1) The ITO conductive glass is cleaned and used as a conductive substrate; (2) Dissolve poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] in toluene solvent, heat and stir, filter, spin coat onto a clean conductive substrate, and then anneal at 130°C to form a hole transport layer; (3) Methylammonium iodide (MAI), PbI2, and PbBr2 were dissolved in γ-butyrolactone solvent to obtain a solution with a mass fraction of 78 wt%. The solution was then subjected to periodic shaking at 80-100 °C. α-terpineol (30%-40% by mass of γ-butyrolactone) was added, and the mixture was shaken periodically at 80-100 °C for 4-6 hours to obtain a perovskite suspension precursor slurry. This perovskite suspension precursor slurry was coated onto the hole transport layer and then annealed at 120 °C to form a bromine-doped methylamino perovskite absorber 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) Place the device prepared in step (3) into a vacuum evaporation machine and deposit the electron transport layer C60, the hole blocking layer 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) and the metal cathode in sequence. The thickness of the bromine-doped methylamino perovskite absorber layer is 405-825µm.

2. 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.

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

4. The method for preparing a bromine-doped methylammonium iodide perovskite X-ray detector according to claim 3, characterized in that, The molar percentage of PbBr2 in the total amount of PbI2 and PbBr2 is 10%-20%.

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