Oxalic acid assisted growth of fpea2sni4-fpea2pbi4 single crystal heterojunction x-ray detector and preparation

Abstract

Oxalic acid assisted growth FPEA2SnI4-FPEA2PbI4 single crystal heterojunction X-ray detector and preparation, belong to X-ray detection technical field.The application uses oxalic acid reducing agent to assist in preparing FPEA2SnI4 single crystal, so that its quality and stability have been significantly improved, and the defect density has been reduced by an order of magnitude.The FPEA2SnI4-FPEA2PbI4 single crystal heterojunction X-ray detector provided by the application can be used for 80kV X-ray detection.Because of the energy level matching between FPEA2PbI4 and FPEA2SnI4, the X-ray detector combines the good charge transport performance of tin perovskite and the relative stability of lead perovskite, so that the sensitivity of the single crystal heterojunction X-ray detector is improved to 1.7x10 5 μC·Gy ‑1 ·cm ‑2 The new X-ray detector combines the advantages of tin perovskite and lead perovskite, and provides new opportunities and challenges for the next generation of products.

Description

Technical Field

[0001] This invention belongs to the field of X-ray detection technology, specifically relating to an FPEA2SnI4 single-crystal optoelectronic device grown with oxalic acid reducing agent, an FPEA2SnI4-FPEA2PbI4 single-crystal heterojunction X-ray detector and its preparation method. Background Technology

[0002] Perovskite halide single crystals have shown great potential in X-ray detection applications due to their tunable band gap, strong energy blocking ability, large carrier mobility-lifetime product, small exciton binding energy, bipolar transport capability, and high defect tolerance. However, lead ions in perovskites pose a serious biotoxicity risk and hinder their commercialization. Therefore, extensive research has been conducted to find environmentally friendly metal ions to replace lead. Tin and lead belong to the same group and have similar electronic structures. 2+ ionic radius With Pb 2+ The very close proximity of tin perovskites allows them to inherit many excellent optoelectronic properties. Furthermore, tin perovskites typically have a low band gap, thus lowering the electron-hole pair formation energy and generating more charge under X-ray excitation. The excellent conductivity of tin perovskites further promotes efficient charge transport, improving charge collection efficiency and sensitivity. However, due to the long growth time required at room temperature, the quality of solution-grown tin perovskite single crystals remains a major issue. In this process, Sn... 2+ It is easily oxidized to Sn 4 + Ultimately, this affects the performance and stability of the corresponding devices.

[0003] The main problems with tin perovskites include easy oxidation, heterogeneous crystallization rate, and high trap density. To address the Sn in the precursor solution... 2+ The stability issue is addressed by traditional methods using halo acids (HX, X = Cl) at high temperatures. - ,Br - I - Phosphorous acid (H3PO2) is added to the solution as a reducing agent. However, the H3PO2 solution contains a large amount of water and is limited to complex acid solutions containing multiple ionic environments, increasing the possibility of ions entering the perovskite lattice or grain boundaries. Furthermore, HI, as an intermediate, can promote the formation of Sn in tin-iodine perovskites. 2+The oxidation process is involved. Therefore, crystals grown using this method often have high defect densities, making it difficult to obtain high-quality single crystals with good reproducibility. Organic solvents are less corrosive than complex acid solutions and have higher solubility for perovskite raw materials, thus requiring milder reaction conditions (such as lower temperatures). Furthermore, the ionization of perovskite in organic solvents is relatively weak, resulting in a simpler and more stable crystal growth environment. Some high-quality tin perovskite single crystals are typically grown in organic solutions under an inert atmosphere or in a glove box, which significantly increases the complexity of the process and production costs. However, currently there is no suitable reducing agent for use in organic solvents that allows for growth in air. Therefore, there is an urgent need to develop a reducing agent suitable for growing tin perovskite in organic systems. Summary of the Invention

[0004] The primary objective of this invention is to provide a high-quality tin perovskite FPEA2SnI4 single-crystal optoelectronic device grown with oxalic acid reducing agent assistance. The addition of oxalic acid significantly improves the quality and stability of the FPEA2SnI4 single crystal in air, reducing the defect density by an order of magnitude. Furthermore, to mitigate the oxidation of tin perovskite devices in ambient air, we grew bandgap-matched FPEA2PbI4 single crystals on top of the FPEA2SnI4 single crystal, obtaining an FPEA2SnI4-FPEA2PbI4 single-crystal heterojunction X-ray detector. The sensitivity of this single-crystal heterojunction X-ray detector is increased to 1.7 × 10⁻⁶. 5 μC·Gy -1 ·cm -2 It is superior to the FPEA2PbI4 single crystal detector.

[0005] The method for growing high-quality tin perovskite FPEA2SnI4 single crystals in air with oxalic acid assistance and the method for fabricating optoelectronic devices based on these single crystals, as described in this invention, comprises the following steps:

[0006] (a) Dissolve p-fluorophenylethylamine iodide (FPEAI), SnI2 and H2C2O4 in methanol (CH3OH) at a molar ratio of 2:1:0.5 and stir at 60-70°C until a clear yellow solution is obtained. Then, quickly heat filter the solution using a 0.45 μm polytetrafluoroethylene (PTFE) filter and allow the filtered solution to stand at this temperature for 20-40 min to stabilize.

[0007] (b) Cool the solution prepared in step (a) rapidly at a rate of 1-2 °C / h. After small crystals begin to precipitate on the surface, remove some small crystals with tweezers and wipe them dry with lint-free paper to use as seed crystals.

[0008] (c) Heat the solution from step (b) until all the small crystals dissolve and the solution becomes clear. Stabilize it for 20-40 minutes. Then start cooling at a rate of 0.2-0.5℃ / h. After the solution is saturated, put in the seed crystal obtained in step (b) and continue cooling and growth. After 20-30 hours, a hexagonal FPEA2SnI4 single crystal with flat upper and lower surfaces is obtained. Remove it from the solution with tweezers, wipe the solution off the surface of the single crystal quickly with lint-free paper, and store it in a glove box.

[0009] (d) The upper and lower surfaces of the FPEA2SnI4 single crystal obtained in step (c) are polished with 2000 grit, 8000 grit and 10000 grit sandpaper respectively, and finally polished on both sides with polishing paper.

[0010] (e) A Cr electrode with a thickness of 15-20 nm is deposited on one side of the FPEA2SnI4 single crystal obtained in step (d);

[0011] (f) An electron transport layer C is deposited on the other side of the FPEA2SnI4 single crystal obtained in step (e). 60 The thickness is 20-30 nm;

[0012] (g) The electron transport layer C obtained in step (f) 60 A hole blocking layer (BCP) with a thickness of 8–10 nm is deposited on top.

[0013] (h) A cathode Au with a thickness of 20-30 nm is deposited on the hole blocking layer BCP obtained in step (g) to obtain an optoelectronic device based on FPEA2SnI4 single crystal.

[0014] This invention also provides a method for growing an FPEA2SnI4-FPEA2PbI4 single-crystal heterojunction and a method for fabricating a perovskite X-ray detector based on this single-crystal heterojunction. From bottom to top, the structure consists of an anode (Cr), an FPEA2SnI4-FPEA2PbI4 single-crystal heterojunction X-ray detector material, and an electron transport layer (C). 60 The structure consists of a hole-blocking layer (BCP) and a cathode (Au); the FPEA2SnI4-FPEA2PbI4 single-crystal heterojunction X-ray detector material is the active layer for absorbing X-ray photons, and the growth method and device fabrication method are as follows:

[0015] (a) First, PbI2, FPEAI and H2C2O4 in a molar ratio of 1:2:0.5 were dissolved in γ-valerol (GVL) and stirred at 70-90°C to form a yellow transparent solution. Then, the solution was rapidly heat filtered through a 0.45 μm polytetrafluoroethylene (PTFE) filter. After standing for 20-40 min to stabilize, the solution was cooled to 55-65°C to obtain FPEA2PbI4 solution.

[0016] (b) Place the hexagonal FPEA2SnI4 single crystal with flat upper and lower surfaces obtained in step c of the previous method into the FPEA2PbI4 solution in step (a). Control the evaporation of the solvent by controlling the size of the opening above the container where the solution is located by adding a glass cover. FPEA2PbI4 grows slowly on the surface of the FPEA2SnI4 single crystal through the organic molecular layer shared with FPEA2SnI4. After 10-20 hours, an FPEA2SnI4-FPEA2PbI4 single crystal heterojunction is obtained. After removing it from the solution with tweezers, quickly wipe the solution on the surface of the single crystal with lint-free paper and store it in a glove box.

[0017] (c) The upper and lower surfaces of the single-crystal heterojunction obtained in step (b) are polished with 600-grit, 2000-grit, 8000-grit, and 10000-grit sandpaper respectively, and finally polished with polishing paper.

[0018] (d) Cr electrode is deposited on the surface of the single-crystal heterojunction FPEA2SnI4 obtained in step (c) with a thickness of 30-50 nm.

[0019] (e) Evaporate an electron transport layer C on the surface of the single-crystal heterostructure obtained in step (d) using FPEA2PbI4. 60 The thickness is 20-30 nm;

[0020] (f) The electron transport layer C obtained in step (e) 60 A hole blocking layer (BCP) is deposited on the surface with a thickness of 8–10 nm.

[0021] (g) A cathode Au is deposited on the hole blocking layer BCP obtained in step (f) with a thickness of 30-50 nm, thereby obtaining a perovskite X-ray detector based on the FPEA2SnI4-FPEA2PbI4 single crystal heterojunction, with a total thickness of 0.8-1.0 mm.

[0022] In this invention, the Chinese name of FPEA is 4-fluorophenylethylamine, and the Chinese name of BCP is 2,9-dimethyl-4,7-biphenyl-1,10-o-diazaphenanthroline. Both of these reagents are commercially available and do not require further purification. Their structural formulas are as follows:

[0023]

[0024] Compared with existing technologies, the present invention has the following advantages:

[0025] This invention utilizes oxalic acid, a residue-free reducing agent for growing high-quality tin perovskite single crystals in an organic solvent system and air environment, significantly improving the quality and stability of FPEA2SnI4 single crystals in air, and reducing the defect density by an order of magnitude. This invention also provides a high-sensitivity, low-dose-rate detection FPEA2SnI4-FPEA2PbI4 single-crystal heterojunction X-ray detector for 80kV X-ray detection. Due to the energy level matching between FPEA2PbI4 and FPEA2SnI4, this X-ray detector combines the excellent charge transport properties of tin perovskite with the relative stability of lead perovskite, increasing the sensitivity of the single-crystal heterojunction X-ray detector to 1.7 × 10⁻⁶. 5 μC·Gy -1 ·cm -2 This detector outperforms the FPEA2PbI4 single-crystal detector. Furthermore, the inclusion of an outer layer of FPEA2PbI4 not only suppresses the damage to the internal FPEA2SnI4 from oxygen and water in the air, but also reduces the dark current of the heterojunction detector due to the high resistivity of FPEA2PbI4, exhibiting good stability under high electric field strength, high X-ray dose, and total dose, as well as over extended periods. This detector is inexpensive to manufacture, exhibits good stability, and is sensitive to 80kV X-rays. This novel X-ray detector combines the advantages of tin perovskite and lead perovskite, offering new opportunities and challenges for next-generation products. Attached Figure Description

[0026] Figure 1 This is a comparison diagram of the reduction potentials of the eight reducing agents described in this invention; the reducing agents include H3PO2, H2C2O4, Sn, H2, H2SO3, and I. - Fe 2+ HNO2; the figure also shows oxides O2 and Sn. 4+ The standard electrode potential; the vials in the illustration, from left to right, are solutions of tin perovskite precursor containing hypophosphoric acid, solutions containing oxalic acid reducing agent, and solutions of tin perovskite precursor without reducing agent; the horizontal axis represents the reducing agent, the products are in parentheses, and the vertical axis represents the standard redox potential.

[0027] Figure 2 The graph shows the color changes of perovskite precursor solutions with added oxalic acid (w, right side) and perovskite precursor solutions without added oxalic acid (w / o, left side) after being exposed to air for different times.

[0028] Figure 3 This is a schematic diagram illustrating the process of growing FPEA2SnI4 perovskite single crystals with oxalic acid assistance.

[0029] Figure 4The image shows the powder XRD pattern of FPEA2SnI4 perovskite single crystals, which were grown from methanol solution containing oxalic acid (top curve) and hydroiodic acid solution containing hypophosphoric acid (bottom curve), respectively. The star symbol represents the diffraction peak of the oxidation product SnI4.

[0030] Figure 5 The curve shows the defect density as a function of depletion layer depth, measured by excitation level capacitance analysis (DLCP). The device structure is ITO / PEDOT:PSS / tin perovskite thin film / C 60 / BCP / Cu.

[0031] Figure 6 The images show the surface (top) and cross-section (bottom) of the FPEA2SnI4-FPEA2PbI4 single-crystal heterojunction under indoor light (left) and the surface and cross-section of the single-crystal heterojunction under 365nm ultraviolet light (right).

[0032] Figure 7 This is a device structure diagram of an FPEA2SnI4-FPEA2PbI4 single-crystal heterojunction X-ray detector, where Au is the cathode, BCP is the hole blocking layer, and C... 60 The electron transport layer is a single crystal heterojunction (FSI and FPI, representing FPEA2SnI4 and FPEA2PbI4 respectively) which is the active layer for absorbing X-ray photons, and Cr is the anode.

[0033] Figure 8 The graph shows the current density as a function of electric field strength for three single-crystal devices: FPEA2SnI4(FSI), FPEA2PbI4(FPI), and FPEA2SnI4-FPEA2PbI4(FPI-FSI).

[0034] Figure 9 The graph shows the current density relationship of FPEA2PbI4 (FPI) single crystal and FPEA2SnI4-FPEA2PbI4 (FPI-FSI) single crystal heterojunction X-ray detectors at different X-ray dose rates. The sensitivity of each detector can be calculated from the slope.

[0035] Figure 10 The graph shows the photocurrent stability of the X-ray response of the fabricated FPEA2SnI4-FPEA2PbI4 (FPI-FSI) single-crystal heterojunction X-ray detector. The horizontal axis represents the value of the X-ray response when a continuous 350 V·mm² voltage is applied to the device. -1 Field strength and 6.5 mGy·s -1 The dose rate is measured over time, with the X-ray photocurrent of the device represented on the vertical axis.

[0036] Figure 1The redox potentials of some ions / molecules that may be used as reducing agents are summarized. Considering Sn... 2+ / Sn 4+ The redox potential is 0.154V (dashed line). A more negative redox potential indicates stronger reducing power. We selected four reducing agents (solid dots and stars below the dashed line): H3PO2, H2C2O4, Sn, and H2. Hydrogen requires high temperature and high pressure (HPHT) reaction conditions, making it unsuitable for solution growth. Sn metal is insoluble in organic solvents and acts as a nucleation site in solution, easily forming polycrystalline or twinned crystals. H3PO2 solution contains a large amount of water, which can damage the perovskite structure. Notably, H2C2O4 has higher solubility in organic solvents, facilitating single-crystal growth under environmental conditions. Furthermore, the reduction product of H2C2O4 as a reducing agent is gaseous CO2, making it an ideal additive to avoid introducing additional impurities. The small bottles in the top left image, from left to right, represent the following: when H3PO2 solution is added to the perovskite precursor solution, yellow powder precipitates out; when H2C2O4 is added to the precursor solution, the solution remains a pale yellow color in its unoxidized state; and the precursor solution without a reducing agent quickly changes from pale yellow to black.

[0037] Figure 2 A color comparison of the perovskite precursor solution (w / o) and the perovskite precursor solution (w) with 50% mol H₂C₂O₄ added after a period of time. Both solutions were sealed in vials and placed in air. The perovskite precursor solution (w / o) showed a significant color change after 5 hours of storage, changing from pale yellow to black. This change can be attributed to Sn. 2+ It is oxidized to Sn by oxygen in the atmosphere. 4+ This subsequently promoted I - The conversion to elemental iodine (I₂). In contrast, the perovskite precursor solution containing H₂C₂O₄ maintained a relatively unchanged color during the 24-hour observation period, demonstrating its stability. 2+ The effect of ions.

[0038] Figure 3 This diagram illustrates the process of growing FPEA2SnI4 perovskite single crystals with oxalic acid assistance. The presence of H2C2O4, acting as a bidentate ligand, forms an unstable six-coordinate intermediate with tin iodide (SnI2) in the precursor solution, effectively preventing the intrusion of oxygen from the ambient air. As the temperature decreases, the coordinated oxygen atoms are gradually replaced by the more coordinating I2O4. - Ion substitution promotes a more stable metallic octahedron [SnI6]. 4- The octahedral layer combines with the organic large cation layer to construct a two-dimensional layered structure, forming a high-quality and stable tin perovskite FPEA2SnI4.

[0039] Figure 4 The images show the powder XRD patterns of FPEA2SnI4 perovskite single crystals, grown from a methanol solution containing H2C2O4 (top curve) and from a hydroiodic acid solution containing hypophosphoric acid (bottom curve), respectively. The asterisks represent the diffraction peaks of the oxidation product SnI4. The results indicate that the FPEA2SnI4 perovskite single crystals grown in the H3PO2 / HI system are of poor quality, having been oxidized by air, with the oxidation product SnI4 appearing on the surface. In contrast, the FPEA2SnI4 perovskite single crystals grown in the H2C2O4 / CH3OH system are of better quality and more stable.

[0040] Figure 5 The curves showing the defect density as a function of depletion layer depth, measured by excited level capacitance analysis (DLCP), indicate that defects are mainly concentrated at the interface, while the tin-containing perovskite film / C 60 The defect density at the interface is significantly higher than that on the other side; the defect density of the tin-containing perovskite thin film device without H2C2O4 (control group) is an order of magnitude higher than that with H2C2O4, which verifies the important role of H2C2O4 as a reducing agent.

[0041] Figure 6 The images show photographs of the surface and cross-section of the FPEA2SnI4-FPEA2PbI4 single-crystal heterojunction under indoor light (left) and under 365nm ultraviolet light (right). The results demonstrate that the outer orange-yellow FPEA2PbI4 single crystal successfully grew onto the black FPEA2SnI4 single crystal surface. Under 365nm light, the outer single crystal exhibits green fluorescence, while the inner black crystal shows red fluorescence, consistent with the fluorescence results of different parts of the single-crystal heterojunction.

[0042] Figure 7 This is a device structure diagram of an FPEA2SnI4-FPEA2PbI4 single-crystal heterojunction X-ray detector, where Au is the cathode, BCP is the hole blocking layer, C60 is the electron transport layer, the single-crystal heterojunction is the active layer for absorbing X-ray photons, and Cr is the anode. The energy level diagram shows that the energy levels of FPEA2SnI4 and FPEA2PbI4 are well-matched, which is beneficial for carrier transport.

[0043] Figure 8 The figures show the current density versus electric field intensity for three single-crystal devices: FPEA2SnI4 (FSI), FPEA2PbI4 (FPI), and FPEA2SnI4-FPEA2PbI4 (FPI-FSI). The results indicate that the heterojunction formed by combining the low-resistivity FPEA2SnI4 with the high-resistivity FPEA2PbI4 has a resistivity between the two, and is also relatively high, basically meeting the requirements for X-ray detection.

[0044] Figure 9 The graphs show the current density relationships of FPEA2PbI4 (FPI) single-crystal and FPEA2SnI4-FPEA2PbI4 (FPI-FSI) single-crystal heterojunction X-ray detectors at different X-ray dose rates. The sensitivities of each detector can be calculated from the slopes. The results show that this single-crystal heterojunction device maintains relative stability in air while combining the excellent carrier transport capabilities of FPEA2SnI4, resulting in a significantly higher sensitivity than a pure FPEA2PbI4 single-crystal device. This provides insights for the design of subsequent novel X-ray detectors.

[0045] Figure 10 The photocurrent stability curves of the fabricated FPEA2SnI4-FPEA2PbI4 (FPI-FSI) single-crystal heterojunction X-ray detector in response to X are shown. The results indicate that the device maintains stable X-ray current at 350 V·mm⁻¹. -1 The electric field strength and 6.5 mGy·s -1 At the dose rate, after working for one hour without encapsulation air and being subjected to a total dose of 23.4 Gy of radiation, the device still maintained its original photocurrent signal to 80 kV X-rays without signal loss, indicating that the device has good operational stability. Detailed Implementation

[0046] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the present invention is not limited to the following embodiments. Unless otherwise specified, all components in the preparation method described in this invention are commercially available products well known to those skilled in the art.

[0047] Example 1:

[0048] The present invention describes a method for selecting a residue-free reducing agent for growing high-quality tin perovskite single crystals in an organic solvent system and in an air environment. The steps are as follows:

[0049] (a) Consult the literature (Analytical Chemistry, edited by Su Xingguang, Tian Yuan, et al., Higher Education Press, 2015; The Influence of Low Molecular Weight Organic Acids on Mercury Redox Reactions, Zhao Shibao et al., Environmental Science, 2014, 35(06)) to identify the organic and inorganic reducing agents frequently used in the experiment. For example, organic reducing agents include: oxalic acid (H2C2O4), ascorbic acid, citric acid, glucose, tartaric acid (all five are solid reducing agents, easily soluble in organic solvents, with oxalic acid having the strongest reducing power), acetic acid, and organic reducing agents with excessive reactivity; inorganic reducing agents include hydrogen (H2), hypophosphorous acid (H3PO2), nitrous acid (HNO2), sulfurous acid (H2SO3), Fe 2+ I - And various reactive metals, etc.

[0050] (b) Considering that the reducing agent needs to have the following characteristics: it should not react with the unoxidized perovskite precursor solution, i.e., its reducing power should not be too strong; it should have good solubility in organic solvents; it should not introduce ions that easily enter the perovskite lattice, i.e., the reduction product should leave no residue; and its reducing power should be sufficient to reduce Sn... 4+ Restore to Sn 2+ Based on their capabilities and other characteristics, we selected the following eight reducing agents: H3PO2, H2C2O4, Sn, H2, H2SO3, I - Fe 2+ Compare HNO2 and H2O;

[0051] (c) Consulting reference materials (Analytical Chemistry, edited by Su Xingguang, Tian Yuan, et al., Higher Education Press, 2015), Sn 4+ Reduced to Sn 2+ The standard electrode potential is 0.154V. Based on the characteristic that the more negative the standard electrode potential, the stronger the reducing power, the standard electrode potential of the selected reducing agent must be less than 0.154V. There are four reducing agents that meet the requirements: H3PO2, H2C2O4, Sn, and H2. Among them, H2 requires high temperature and high pressure for reaction, which is not suitable for solution reaction; the introduction of insoluble Sn metal will increase nucleation sites, leading to the growth of polycrystalline and twinned crystals; while H3PO2 solution contains a large amount of water, which will destroy the perovskite structure. In summary, we selected H2C2O4 as the reducing agent, which meets all the requirements of this system.

[0052] Example 2

[0053] The method for growing high-quality tin perovskite FPEA2SnI4 single crystals in air with oxalic acid assistance and the method for fabricating optoelectronic devices based on these single crystals, as described in this invention, comprises the following steps:

[0054] (a) Dissolve p-fluorophenylethylamine iodide (FPEAI), SnI2 and H2C2O4 in methanol (CH3OH) at a molar ratio of 2:1:0.5 and stir at 65°C until a clear yellow solution is obtained. Then immediately filter the solution rapidly with a preheated 0.45 μm polytetrafluoroethylene (PTFE) filter and stabilize the filtered solution at this temperature for half an hour.

[0055] (b) Cool the solution prepared in step (a) rapidly at a rate of 1°C / h. After small crystals begin to precipitate on the surface, remove some small crystals with tweezers and wipe them dry with lint-free paper as seed crystals for later use.

[0056] (c) Heat the solution prepared in step (b) until all the small crystals dissolve and the solution becomes clear. After stabilizing for 30 minutes, start cooling at a rate of about 0.3℃ / h. After confirming that the solution is saturated, put in the seed crystal obtained in step (b) and continue cooling and growth. After 25 hours, a hexagonal FPEA2SnI4 single crystal with flat upper and lower surfaces is obtained. Remove it from the solution with tweezers, wipe the solution on the surface of the single crystal with lint-free paper, and store it in a glove box.

[0057] (d) The upper and lower surfaces of the FPEA2SnI4 single crystal from step (c) are polished with 2000-grit, 8000-grit, and 10000-grit sandpaper respectively, and then polished with polishing paper.

[0058] (e) Place the single crystal obtained in step (d) on a glass slide, and then perform vapor deposition on one side surface of the single crystal at a rate of 0.03 nm / s (the vapor deposition equipment is a Shenyang Kecheng single-source six-chamber resistive coating equipment, and the vapor deposition is all within a range of less than 5 × 10⁻⁶ nm / s). -4 The process was carried out under vacuum conditions of Pa, with a Cr electrode having a thickness of 15 nm.

[0059] (f) Remove the single crystal from the glass slide in step (e), flip it over to the other side, and place it back on the glass slide. Then, deposit an electron transport layer C on the surface of that side at a rate of 0.03 nm / s. 60 The thickness is 30nm;

[0060] (g) The electron transport layer C in step (f) 60 A hole blocking layer (BCP) with a thickness of 10 nm was deposited by evaporation at a rate of 0.02 nm / s.

[0061] (h) A cathode Au with a thickness of 30 nm is deposited on the hole blocking layer BCP in step (g) at a rate of 0.03 nm / s to obtain an optoelectronic device based on FPEA2SnI4 single crystal.

[0062] Comparative Example 1

[0063] This invention provides a method for fabricating FPEA2SnI4 single crystals and their devices, comprising the following steps:

[0064] (a) FPEAI, SnI2 and H3PO2 were dissolved in HI at a molar ratio of 2:1:0.5 and dissolved in HI under heating at 110°C until a clear yellow solution was obtained. The solution was then immediately filtered rapidly with a preheated 0.45 μm polytetrafluoroethylene (PTFE) filter and the solution was heated at 110°C for half an hour to stabilize it.

[0065] (b) Cool the solution prepared in step (a) to 95°C at a cooling rate of 1°C / h, and then slowly cool it at a cooling rate of 0.2°C / h until thin sheet-like single crystals precipitate. Remove them from the solution with tweezers, quickly wipe the solution off the surface of the single crystals with lint-free paper, and store them in a glove box.

[0066] (c) The upper and lower surfaces of the FPEA2SnI4 single crystal from step (b) are polished with 2000-grit, 8000-grit, and 10000-grit sandpaper respectively, and then polished with polishing paper.

[0067] (d) Place the single crystal obtained in step (c) on a glass slide, and then perform vapor deposition on one side surface of the single crystal at a rate of 0.03 nm / s (the vapor deposition equipment is a Shenyang Kecheng single-source six-chamber resistive coating equipment, and the vapor deposition is all within 5 × 10⁻⁶ nm / s). -4 The process was carried out under vacuum conditions of Pa, with a Cr electrode having a thickness of 15 nm.

[0068] (e) Remove the single crystal from the glass slide in step (d), flip it over to the other side, and place it back on the glass slide. Then, deposit an electron transport layer C on the surface of that side at a rate of 0.03 nm / s. 60 The thickness is 30nm;

[0069] (f) The electron transport layer C in step (e) 60 A hole blocking layer (BCP) with a thickness of 10 nm was deposited by evaporation at a rate of 0.02 nm / s.

[0070] (g) A cathode Au with a thickness of 30 nm is deposited on the hole blocking layer BCP in step (f) at a rate of 0.03 nm / s, thereby obtaining an optoelectronic device based on FPEA2SnI4 single crystal.

[0071] Example 3

[0072] This invention also provides a method for growing an FPEA2SnI4-FPEA2PbI4 single-crystal heterojunction and a method for fabricating a perovskite X-ray detector based on this single-crystal heterojunction. From bottom to top, the structure consists of an anode (Cr), an FPEA2SnI4-FPEA2PbI4 single-crystal heterojunction X-ray detector material, and an electron transport layer (C). 60 The structure consists of a hole-blocking layer (BCP) and a cathode (Au); the FPEA2SnI4-FPEA2PbI4 single-crystal heterojunction X-ray detector material is the active layer for absorbing X-ray photons, and the growth method and device fabrication method are as follows:

[0073] (a) First, PbI2, FPEAI and H2C2O4 in a molar ratio of 1:2:0.5 were dissolved in γ-valerol (GVL) and stirred at 80°C to form a yellow transparent solution. Then, the solution was immediately rapidly filtered through a preheated 0.45μm polytetrafluoroethylene (PTFE) filter. After standing for half an hour to stabilize, the solution was cooled to 60°C to obtain FPEA2PbI4 solution.

[0074] (b) The hexagonal FPEA2SnI4 single crystal with flat upper and lower surfaces obtained in step c of Example 2 was placed in the FPEA2PbI4 solution in step (a). The evaporation of the solvent was controlled by controlling the size of the opening above the container where the solution was placed by adding a glass cover. FPEA2PbI4 slowly grew on the surface of the FPEA2SnI4 single crystal through the organic molecular layer shared with FPEA2SnI4. After 12 hours, an FPEA2SnI4-FPEA2PbI4 single crystal heterojunction was obtained. After removing it from the solution with tweezers, the solution on the surface of the single crystal was quickly wiped dry with lint-free paper.

[0075] (c) The upper and lower surfaces of the single-crystal heterojunction in step (b) are polished with 600-grit, 2000-grit, 8000-grit, and 10000-grit sandpaper respectively, and finally polished with polishing paper.

[0076] (d) Place the polished single-crystal heterojunction from step (c) onto a glass plate, and then deposit a Cr electrode with a thickness of 40 nm onto one side of the FPEA2SnI4 surface.

[0077] (e) Remove the single crystal from the glass slide in step (d), flip it over to the other side of FPEA2PbI4, and place it back on the glass slide. Then, deposit an electron transport layer C on the surface of that side. 60 The thickness is 30nm;

[0078] (f) The electron transport layer C in step (e) 60 A hole blocking layer (BCP) with a thickness of 10 nm is deposited on top.

[0079] (g) A cathode Au with a thickness of 30 nm is deposited on the hole blocking layer BCP in step (f) to obtain the FPEA2SnI4-FPEA2PbI4 single crystal heterojunction perovskite X-ray detector.

[0080] Comparative Example 2

[0081] This invention provides a method for fabricating FPEA2PbI4 single crystal and a single crystal X-ray detector, comprising the following steps:

[0082] (a) First, PbI2 and FPEAI in a molar ratio of 1:2 were dissolved in γ-valerol (GVL) and stirred at 80°C to form a yellow transparent solution. Then, the solution was quickly filtered through a preheated 0.45 μm polytetrafluoroethylene (PTFE) filter. After standing for half an hour to stabilize, the solution was cooled to 60°C to obtain FPEA2PbI4 solution.

[0083] (b) Cool the solution prepared in step (a) rapidly at a rate of 1°C / h. After small crystals begin to precipitate on the surface, remove some small crystals with tweezers and wipe them dry with lint-free paper to use as seed crystals.

[0084] (c) Heat the solution from step (b) until all the small crystals dissolve and the solution becomes clear. Stabilize for 30 minutes. Then start cooling at a rate of 0.3℃ / h. After the solution is saturated, put in the seed crystal obtained in step (b) and continue cooling to grow. Cool to 50℃ at a rate of 1℃ / h, and then slowly cool at a rate of 0.2℃ / h until plate-like single crystals precipitate. Continue cooling until the crystal grows. Remove it from the solution with tweezers and quickly wipe the solution off the surface of the single crystal with lint-free paper and store it.

[0085] (d) The upper and lower surfaces of the FPEA2PbI4 single crystal from step (c) are polished with 2000-grit, 8000-grit, and 10000-grit sandpaper respectively, and then polished with polishing paper.

[0086] (e) Place the polished single-crystal heterojunction from step (d) onto a glass plate, and then deposit a Cr electrode with a thickness of 40 nm.

[0087] (f) Remove the single crystal from the glass slide in step (e), flip it over and place it back on the glass slide, then deposit an electron transport layer C on the surface of that side. 60 The thickness is 30nm;

[0088] (g) The electron transport layer C in step (f) 60 A hole blocking layer (BCP) with a thickness of 10 nm is deposited on top.

[0089] (h) A cathode Au with a thickness of 30 nm is deposited on the hole blocking layer BCP in step (g) to obtain an FPEA2PbI4 single crystal X-ray detector.

Claims

1. A method for fabricating an FPEA2SnI4 single-crystal optoelectronic device grown with oxalic acid reducing agent, comprising the following steps: (a) Dissolve FPEAI, SnI2 and H2C2O4 in methanol at a molar ratio of 2:1:0.5, and heat at 60~70°C. o Dissolved under temperature C by stirring until a clear yellow solution is obtained, then rapidly heat-filtered using a 0.22µm polytetrafluoroethylene filter. The filtered solution is then cooled to 60-70°C. o Let it stand at room temperature for 20-40 minutes to stabilize; (b) Cool the solution prepared in step (a) rapidly. After small crystals begin to precipitate on the surface, use tweezers to remove some small crystals and wipe them dry with lint-free paper to use as seed crystals. (c) Heat the solution from step (b) until all the small crystals dissolve and the solution becomes clear. Stabilize it for 20-40 minutes. Then start cooling. After the solution is saturated, put in the seed crystal obtained in step (b) and continue cooling to grow. After 20-30 hours, a hexagonal FPEA2SnI4 single crystal with flat upper and lower surfaces is obtained. Remove it from the solution with tweezers and quickly wipe the solution off the surface of the single crystal with lint-free paper. Store it in a glove box. (d) Grind the upper and lower surfaces of the FPEA2SnI4 single crystal obtained in step (c) respectively, and finally polish both sides. (e) A Cr electrode with a thickness of 15~20 nm is deposited on one side of the FPEA2SnI4 single crystal obtained in step (d); (f) An electron transport layer C is deposited on the other side of the FPEA2SnI4 single crystal obtained in step (e). 60 The thickness is 20~30nm; (g) The electron transport layer C obtained in step (f) 60 A hole blocking layer (BCP) with a thickness of 8-10 nm is deposited on top. (h) A cathode Au with a thickness of 20~30nm is deposited on the hole blocking layer BCP obtained in step (g) to obtain an optoelectronic device based on FPEA2SnI4 single crystal.

2. The method for fabricating an FPEA2SnI4 single-crystal optoelectronic device assisted by oxalic acid reducing agent growth as described in claim 1, characterized in that: The cooling rate in step (b) is 1~2℃ / h, and the cooling rate in step (c) is 0.2~0.5℃ / h.

3. The method for fabricating an FPEA2SnI4 single-crystal optoelectronic device assisted by oxalic acid reducing agent growth as described in claim 1, characterized in that: In step (d), sanding is performed using 2000 grit, 8000 grit, and 10000 grit sandpaper respectively, and finally double-sided polishing is performed using polishing paper.

4. A single-crystal optoelectronic device of FPEA2SnI4 grown with oxalic acid reducing agent, characterized in that: It is prepared by the method described in claim 1, 2 or 3.

5. A method for preparing an FPEA2SnI4-FPEA2PbI4 single-crystal heterojunction X-ray detector grown with oxalic acid reducing agent, the steps of which are as follows: (a) First, PbI2, FPEAI and H2C2O4 in a molar ratio of 1:2:0.5 were dissolved in γ-valerol and stirred at 70~90℃ to form a yellow transparent solution. Then, the solution was rapidly heat filtered through a 0.22µm polytetrafluoroethylene filter. After standing for 20~40 min to stabilize, the solution was cooled to 55~65℃ to obtain FPEA2PbI4 solution. (b) The hexagonal FPEA2SnI4 single crystal with flat upper and lower surfaces obtained in step (c) of claim 1 is placed in the FPEA2PbI4 solution in step (a). The evaporation of the solvent is controlled. FPEA2PbI4 grows slowly on the surface of the FPEA2SnI4 single crystal through the organic molecular layer shared with FPEA2SnI4. After 10-20 hours, an FPEA2SnI4-FPEA2PbI4 single crystal heterojunction is obtained. After removing it from the solution with tweezers, the solution on the surface of the single crystal is quickly wiped dry with lint-free paper. (c) Grind the upper and lower surfaces of the single-crystal heterojunction obtained in step (b) respectively, and finally polish both sides. (d) Cr electrode is deposited on the surface of the single-crystal heterojunction FPEA2SnI4 obtained in step (c) with a thickness of 30~50nm; (e) An electron transport layer C is deposited on the surface of the single-crystal heterojunction FPEA2PbI4 obtained in step (d). 60 The thickness is 20~30nm; (f) The electron transport layer C obtained in step (e) 60 A hole blocking layer (BCP) is deposited on the surface with a thickness of 8~10nm; (g) A cathode Au with a thickness of 30~50nm is deposited on the surface of the hole blocking layer BCP obtained in step (f) to obtain a perovskite X-ray detector device of FPEA2SnI4-FPEA2PbI4 single crystal heterojunction.

6. The method for preparing an oxalic acid-reducing agent-assisted growth FPEA2SnI4-FPEA2PbI4 single-crystal heterojunction X-ray detector as described in claim 5, characterized in that: In step (d), sanding is performed using 2000 grit, 8000 grit, and 10000 grit sandpaper respectively, and finally double-sided polishing is performed using polishing paper.

7. An FPEA2SnI4-FPEA2PbI4 single-crystal heterojunction X-ray detector grown with oxalic acid reducing agent, characterized in that: It is prepared by the method described in claim 5 or 6.

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