A polishing method for improving the surface properties of large-size perovskite crystals

Abstract

A polishing method for improving the surface performance of a perovskite single crystal is provided, comprising polishing the upper and lower surfaces of the crystal using a novel polishing liquid while chemically passivating the surface. The present invention uses a chemical polishing liquid to mechanically polish the surface of the perovskite single crystal while passivating the surface, thereby achieving the effects of reducing surface roughness, reducing surface defects, and improving crystal transmittance and electrical stability. The surface roughness and defects of the polished crystal are significantly reduced, and the transmittance and electrical stability are significantly improved. Therefore, the improved method proposed by the present invention is a feasible means of improving the surface performance of the crystal.

Description

Technical Field

[0001] The invention relates to the field of single crystal perovskite defect elimination and post-processing, and in particular to a polishing method for improving the surface performance of single crystal perovskite crystals. Background Art

[0002] Single crystal perovskites are widely used in solar cells and photodiodes because of their high carrier mobility and migration lifetime product (μτ). In addition, due to their efficient absorption of high-energy rays, perovskite single crystals are also considered to be a new generation of high-energy radiation detection materials. Considering that photogenerated carriers can be collected more efficiently by electrodes, the thickness of perovskite single crystals should be optimized. In addition, in order to achieve commercial applications, it is crucial to prepare large-size, high-quality perovskites. Currently, the growth methods used to grow perovskite single crystals include solution method and melt method. However, the shape and thickness of large-size single crystals often cannot meet the needs of preparing detectors. Polishing, as a top-down processing method, is widely used to optimize the shape and thickness of single crystals. (Chinese patents with patent application numbers 200610013980.4 and 201611059072.9) Although the traditional polishing method reduces the surface roughness, defects are often introduced during the polishing process because the polishing liquid used can dissolve the perovskite single crystal. (Chinese patents with patent application numbers 202110212877.7, 202210600516.4, 201910113597.3, and 201711083278.X) These defects provide a path for ion migration in perovskites, accelerate the degradation of perovskite single crystals, and affect the long-term stability of the device. The long-term stability of perovskite single crystal devices is not reported in these patents. Finding a suitable new polishing solution that can improve the surface roughness of single crystals, reduce defect density, and improve the long-term stability of devices is crucial for the commercial application of perovskite single crystal detectors. Summary of the invention

[0003] In order to overcome the deficiencies of the above-mentioned prior art, the present invention provides a polishing method for improving the surface performance of single crystal perovskite crystals, using a polishing liquid mixed with PEABr, CeO2, cyclohexane and tert-amyl alcohol to achieve physical mechanical grinding and chemical passivation at the same time, improve crystal transmittance and surface roughness, reduce the degree of crystal surface defects, and improve the electrical stability of perovskite single crystal devices. The single crystal surface roughness and defect density are effectively reduced, the crystal transmittance is improved, and the method has the characteristics of strong repeatability, simple operation, and low requirements on the working environment.

[0004] The technical solution provided by the present invention is as follows:

[0005] A method for improving the surface properties of a crystal based on chemical polishing, wherein the chemical polishing comprises at least: a workbench, a polishing liquid and a polishing crystal, characterized in that it comprises the following steps:

[0006] Step 1: Use sandpaper to grind the upper and lower surfaces of the perovskite crystal to be polished so that the parallelism tolerance of the upper and lower surfaces is less than 0.5 mm; Step 2: Prepare a polishing solution by preparing a mixed solvent of cyclohexane: tert-amyl alcohol in a volume ratio of 4:1, and add PEABr and CeO2 powder to prepare a polishing solution; Step 3: Place the perovskite crystal to be polished on the platform of the polishing device, and polish it with the polishing solution, so that the polishing solution undergoes a passivation reaction on the surface of the perovskite crystal to be polished, thereby reducing the surface defect density and improving the electrical stability of the crystal.

[0007] The polishing method for improving the surface performance of single crystal perovskite crystal is characterized in that the sandpaper is 1000, 1200, 1500, 2000 mesh silicon carbide sandpaper.

[0008] The polishing method for improving the surface performance of single crystal perovskite crystals is characterized in that the particle size of the CeO2 powder is 0.5 μm and the concentration of the PEABr applied is 0.1-0.2 mg / ml.

[0009] The method for improving the surface properties of a crystal based on chemical polishing is characterized in that the relative rotation speed between the crystal and the workbench is 50 RPM, and when the crystal contacts the workbench, the force applied to the crystal is 0.1 to 0.4 MPa.

[0010] The method for improving crystal surface properties based on chemical polishing is characterized in that the material used in the polishing liquid is a mixed solution prepared by adding PEABr with a concentration of 0.1 g / mL to a mixed solvent of cyclohexane: tert-amyl alcohol with a volume ratio of 4:1, the polishing powder used is CeO2 powder with a particle size of 0.5 μm, and the dosage of the polishing liquid dripped on the workbench during the cycle is 1 to 3 ml.

[0011] The method for improving crystal surface properties based on chemical polishing is characterized in that the crystal is a MAPbBr3 perovskite single crystal.

[0012] The method for improving crystal surface properties based on chemical polishing is characterized in that when the perovskite crystal contacts the polishing device platform, the force applied to the perovskite crystal is 0.1-0.4 MPa.

[0013] The polishing method for improving the surface performance of single crystal perovskite crystals is characterized in that: in the step three, the surface morphology of the perovskite crystal is observed using an optical microscope and an atomic force microscope, and polishing is repeated multiple times until the upper and lower surface roughness is reduced to 1 to 5 nm.

[0014] The method for improving crystal surface properties based on chemical polishing is characterized in that during the cycle, the dosage of the polishing liquid dripped onto the workbench is 1 to 3 ml.

[0015] The method for improving crystal surface properties based on chemical polishing is characterized in that when the perovskite crystal contacts the polishing device platform, the rotation speed of the polishing device platform relative to the perovskite crystal is 50 rpm.

[0016] The working principle of the present invention is:

[0017] In the polishing liquid, 4:1 cyclohexane:tert-amyl alcohol can corrode the defects on the surface of perovskite single crystals at a suitable rate, and PEABr can fill a large number of Br vacancies on the surface of perovskite single crystals, thereby passivating the surface defects of perovskite single crystals. CeO2 assists in grinding the surface of perovskite single crystals while chemically corroding and passivating, further reducing the surface roughness.

[0018] The beneficial effects of the present invention are as follows:

[0019] 1. The present invention is a method for improving the surface properties of crystals based on chemical polishing. While reducing the surface roughness by mechanical grinding, the defect density of the crystal surface is further reduced by chemical corrosion passivation to improve the electrical stability of the crystal.

[0020] 2. The processing method of the present invention can provide perovskite single crystals for preparing optoelectronic devices such as solar cells, LEDs and high-energy radiation detectors.

[0021] 3. Although the present invention is implemented based on lead halide perovskite materials, it can be easily extended to a wider range of perovskite single crystals.

[0022] 4. There is no precedent in the prior art for using a mixed solution of PEABr, CeO2, cyclohexane and tert-amyl alcohol as a polishing liquid. The present application creatively uses a mixed solution of PEABr, CeO2, cyclohexane and tert-amyl alcohol as a polishing liquid for polishing. During the polishing process, the surface of the crystal sample will not react with the polishing liquid, which reduces the possibility of secondary scratches on the perovskite crystal and improves its surface roughness. At the same time, the polishing liquid also has the effect of passivating the surface, reducing surface defects and improving the long-term stability of the perovskite crystal. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 A schematic diagram of a device for improving crystal surface properties based on chemical polishing according to the present invention;

[0024] Among them: 1 is the workbench, 2 is the polishing liquid

[0025] Figure 2 The surface morphology of the single crystal under an optical microscope before and after the improvement of the present invention;

[0026] Figure 3 The surface morphology of the single crystal under an atomic force microscope before and after the improvement of the present invention;

[0027] Figure 4 The improved single crystal permeability of the present invention;

[0028] Figure 5 The figure shows the comparison of the single crystal ultraviolet visible light transmittance spectra before and after the improvement of the present invention.

[0029] Figure 6 The figure shows the comparison of electrical stability and defect density of single crystal before and after the improvement of the present invention. DETAILED DESCRIPTION

[0030] A method of improving the surface properties of a crystal by mechanical grinding accompanied by chemical passivation polishing.

[0031] Wherein, the chemical polishing device is as follows Figure 1 As shown in the figure, it can be seen that it at least includes: a workbench 1 and a polishing liquid 2, characterized in that it includes the following steps: step 1, using sandpaper to grind the upper and lower surfaces of the crystal to a level; step 2, using the chemical polishing to reduce the roughness of the upper and lower surfaces of the crystal. The workbench 1 is a four-axis grinding and polishing machine with a silk polishing cloth, and the rotation speed is ~50RPM. The material used in the polishing liquid 2 is a mixed solution prepared by adding 0.1mg / mL PEABr and an appropriate amount of CeO2 powder to a mixed solvent of cyclohexane: tert-amyl alcohol with a volume ratio of 4:1. The polishing liquid has the effect of passivating surface Br vacancies.

[0032] Example 1 The crystal to be polished is a perovskite crystal MAPbBr3

[0033] 1. The workbench substrate is made of silk velvet with a roughness of ~20nm.

[0034] 2. Add 0.1 g / mL PEABr and an appropriate amount of CeO2 powder to a mixed solvent of cyclohexane: tert-amyl alcohol in a volume ratio of 4:1 to prepare a mixed solution as a polishing solution;

[0035] 3. The perovskite crystal MAPbBr3 to be polished is continuously polished with 1000, 1200, 1500, and 2000 grit sandpaper until the horizontal tolerance of the upper and lower surfaces is 0.1 to 0.5 mm;

[0036] 4. Add 3 ml of polishing liquid onto the workbench;

[0037] 5. Place the polished perovskite crystal MAPbBr3 on the workbench where the polishing liquid is added, and fix the crystal with a mechanical arm. The force applied by the mechanical arm on the crystal is 0.1 to 0.4

[0038] MPa;

[0039] 6. Set the workbench speed to 50RPM, turn on the workbench, remove it 10 minutes after polishing, and observe whether it meets the roughness standard under an optical microscope and an atomic force microscope. Otherwise, repeat steps 4 to 6;

[0040] 7. After the surface roughness of the perovskite crystal MAPbBr3 meets the requirements, the workbench is turned off and the speed finally drops to 0RPM;

[0041] 8. Use optical microscope and atomic force microscope to analyze the surface roughness of samples;

[0042] 9. Use UV-visible transmittance spectrum to analyze sample transmittance.

[0043] like Figure 2 As shown in the figure, after polishing, the surface defects and cracks of the sample disappeared and the holes were reduced.

[0044] like Figure 3 As shown in the figure, the surface roughness of the sample is reduced after polishing, and the surface is smoother.

[0045] like Figure 4 As shown, the permeability of the sample is significantly improved after polishing, and the words on the paper are clearly visible through the crystal. The permeability of multiple samples has been significantly improved, and the surface experiment is reliable and repeatable.

[0046] like Figure 5 As shown, the UV-visible transmittance spectrum of the polished sample shows that the transmittance is also greatly improved, increasing from the original ~30% to 70%, indicating that the surface performance of the crystal is improved.

[0047] like Figure 6 As shown in the figure, the defect density obtained from the voltage-current scanning curve of the polished sample is reduced by one order of magnitude compared with that before polishing. After polishing, the resistivity can reach 10 8 The dark current of the polished sample changed with time when it was continuously powered on for 10 hours at a bias voltage of 0.5 V. This showed that the electrical stability of the device based on the polished single crystal was significantly improved. The current drift dropped from 30 nA before polishing to 4 nA, indicating that the surface defects of the crystal were reduced and the device performance was improved.

[0048] The difference between Example 2 and Example 1 is that the crystal to be polished is CsPbBr3.

[0049] Example 3 is different from Example 1 in that the concentration of PEABr added to the polishing liquid is 0.2 mg / mL

[0050] The difference between Example 4 and Example 1 is that the crystal to be polished is FAPbBr3

[0051] The difference between Example 5 and Example 1 is that the polishing liquid content added each time during the polishing process is 1 ml.

[0052] The above descriptions are merely embodiments of the present application and are not intended to limit the patent scope of the present application. Any equivalent structural or equivalent process transformations made using the contents of the specification and drawings of the present application, such as the mutual combination of technical features between the embodiments, or direct or indirect application in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A polishing method for improving the surface performance of a perovskite single crystal, characterized in that: The steps include: Step 1: using sandpaper to grind the upper and lower surfaces of the perovskite crystal (3) to be polished, so that the parallelism tolerance of the upper and lower surfaces is less than 0.5 mm; Step 2, preparing a polishing liquid (2), preparing a mixed solvent of cyclohexane: tert-amyl alcohol in a volume ratio of 4:1, and adding PEABr and CeO2 powder to prepare a polishing liquid; Step 3: placing the perovskite crystal to be polished (3) on the polishing device platform (1), and polishing it with a polishing liquid, so that the polishing liquid undergoes a passivation reaction on the surface of the perovskite crystal to be polished (3), thereby reducing the surface defect density and improving the electrical stability of the crystal; The perovskite crystal (3) to be polished is MAPbBr 3、 CsPbBr3 or FAPbBr3.

2. The polishing method for improving the surface properties of a perovskite single crystal according to claim 1, characterized in that: The sandpaper in step 1 is silicon carbide sandpaper with mesh numbers of 1000, 1200, 1500, and 2000, and the crystal is polished in order from low to high mesh numbers.

3. The polishing method for improving the surface properties of a perovskite single crystal according to claim 1, characterized in that: In the step 2, the particle size of the CeO2 powder is 0.5 μm, and the concentration of the PEABr applied is 0.1-0.2 mg / ml.

4. The polishing method for improving the surface properties of a perovskite single crystal according to claim 1, characterized in that: When the perovskite crystal (3) contacts the polishing device platform (1) in step three, the force applied to the perovskite crystal is 0.1-0.4 MPa.

5. The polishing method for improving the surface properties of a perovskite single crystal according to claim 1, characterized in that: In the step three, the surface morphology of the perovskite crystal (3) is observed using an optical microscope and an atomic force microscope, and polishing is repeated multiple times until the roughness of the upper and lower surfaces is reduced to 1 to 5 nm.

6. The polishing method for improving the surface properties of a perovskite single crystal according to claim 5, characterized in that: During the cycle, the dosage of the polishing liquid (2) dripped onto the polishing device platform (1) is 1 to 3 ml.

7. The polishing method for improving the surface properties of a perovskite single crystal according to claim 1, characterized in that: When the perovskite crystal (3) contacts the polishing device platform (1), the rotation speed of the polishing device platform (1) relative to the perovskite crystal (3) is 50 rpm.

Images