Method for the manipulation of halogen perovskite microstructures with laser and electric field at cryogenic temperatures

Abstract

The application provides a method for regulating halogen perovskite microstructure at a frozen temperature by using a laser and an electric field, and relates to a device, which is a customized TEM in-situ sample rod equipped with a laser optical fiber and a liquid nitrogen Dewar bottle, and a Nd:YAG pulse laser system with a wavelength of 532 nm, adjustable pulse frequency and a pulse duration of 7 ns coupled into a transmission electron microscope through the optical fiber; first, at a frozen temperature, perovskite nanocrystals are etched by controlling the energy, frequency and action time of the pulse laser, then at the frozen temperature, the small crystal nucleus rotation of the perovskite nanocrystals is controlled by using a low-energy pulse laser and applying an electric field, and the perovskite nanocrystals are recrystallized along specific crystal faces, so that perovskite nanocrystals with specific exposed surfaces, reduced microstructure defects and increased radiation resistance are obtained, and the method has great value for large-scale industrial production.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of perovskite materials, and particularly relates to a method for regulating halogen perovskite microstructure by laser and electric field at a frozen temperature. BACKGROUND

[0002] Low-dimensional metal halide perovskite materials such as CsPbBr3, CsPbI3 quantum dots and the like have excellent photoelectric properties, such as high quantum efficiency, wide band gap and small dispersion, and exhibit great potential in the field of optoelectronics, and have been proven to be successfully applied in many research fields such as solar cells, light-emitting diodes, photodetectors and the like. As an important class of semiconductor materials, all-inorganic halide perovskite nanocrystals (CsPbX3, where X is Cl, Br and I) have bright and narrow photoluminescence (PL) performance, and exhibit broad application potential. The synthesis method is simple and the cost is relatively low, and it is easy to realize low-cost mass production, especially the composition and size of the nanocrystals can be adjusted, which can very easily realize the emission from ultraviolet to near-infrared waveband, which can be well applied to the field of display, LED lighting and the like. Halide perovskite nanocrystals are prone to degradation in water, air, ultraviolet radiation and the like, which is one of the main obstacles to further application. In order to improve the stability and photoelectric performance, microstructure and defect regulation methods have been proven to be effective, such as phase transition control, surface defect engineering, exposure surface and size control. Chemical techniques such as theophylline passivation and ligand design, and physical techniques such as heat treatment and laser irradiation have also been developed. Among them, laser irradiation treatment has attracted more and more attention. It has been reported that the size of halide perovskite nanocrystals can be changed by different laser irradiation conditions, and short-time high-energy density laser irradiation (300 mJ / cm 2 , seconds) will cause the phase transition of perovskite nanocubes from cubic phase to orthorhombic phase. However, too strong laser irradiation will cause the degradation of perovskite, resulting in material failure. Under low temperature conditions, the intrinsic properties of halide perovskite nanocrystals and their dynamic changes under external treatment conditions both exhibit different effects from those at normal temperature, and exhibit significant performance enhancement and unexpected characteristics. SUMMARY

[0003] The main purpose of the present application is to provide a method for regulating halogen perovskite microstructure by laser and electric field at a frozen temperature, and a method for regulating halogen perovskite microstructure to obtain perovskite nanocrystals with specific exposure surface and reduced microstructure defects and increased radiation resistance.

[0004] To achieve the above-mentioned purposes, the technical scheme adopted by the present application is as follows:

[0005] The method of controlling halogen perovskite microstructure with laser and electric field at cryogenic temperature is performed in a TEM with a custom TEM in-situ sample holder equipped with a laser fiber (Thorlabs Inc.) and a liquid nitrogen Dewar, which can be connected to a source measurement unit (Keithley Instrument Inc.) from the outside. A pulsed Nd:YAG laser system (Changchun New Industrial Optoelectronic Technology Co., Ltd.) with a wavelength of 532 nm, adjustable pulse frequency (1-100 Hz), and pulse duration of 7 ns is coupled into the transmission electron microscope through an optical fiber, while the sample is maintained at a level close to the liquid nitrogen temperature (-180℃). Before pulsed laser irradiation in the transmission electron microscope, the distance between the sample and the laser fiber tip is fine-tuned to 200 nm (controlled by a piezoelectric drive mechanism with a step size of 100 pm) to obtain the best laser irradiation area, where the effective laser flux ranges from 0.01 mJ / cm2 to 500 mJ / cm2. Controlling the energy, frequency, and action time of the pulsed laser and applying an external electric field at cryogenic temperature controls the recrystallization of perovskite nanocrystals along a specific crystal plane (111), regulates the exposed surface, and reduces the internal defects of the nanocrystals to improve their stability.

[0006] The method specifically comprises the following steps:

[0007] S1, irradiating perovskite nanocrystals with high-energy pulsed laser at cryogenic temperature for a period of time;

[0008] S2, irradiating perovskite nanocrystals with low-energy high-frequency pulsed laser at cryogenic temperature for a short period of time while applying an electric field;

[0009] S3, irradiating perovskite nanocrystals with low-energy high-frequency pulsed laser at cryogenic temperature for a long period of time.

[0010] Further, the high energy in S1 is about 50 mJ / cm 2 , the pulsed laser frequency is 1 Hz, and the period of time is about 5 s.

[0011] Further, the low energy in S2 is about 10 mJ / cm 2 , the high frequency is 20 Hz, and the short period of time is about 1 s.

[0012] Further, the low energy in S3 is about 0.1 mJ / cm 2 , the high frequency is 100 Hz, and the long period of time is more than 90 s.

[0013] Compared with the prior art, the main advantages of the present application include:

[0014] 1. By applying laser and electric field under low temperature conditions, the recrystallization of halide perovskite nanocrystals along a specific crystal plane (111) can be controlled, which is of great value for large-scale industrial production (which requires controllable crystal plane to improve performance).

[0015] 2. Low-temperature laser annealing is used to etch halide perovskite nanocrystals and recrystallize them, which can eliminate some of their original defects and make their crystal form more perfect, which is conducive to obtaining halide perovskite nanocrystals with stronger stability and better performance.

[0016] 3. The method used in this invention applies laser and electric field under low temperature conditions, which can be easily applied to large-scale processing. The conditions are simple and it is easy to realize large-scale industrial production. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the device used in the present invention to regulate the microstructure of haloperovskites.

[0018] Figure 2 This is a schematic diagram of a device for controlling the exposed surface of halide perovskite nanocrystals by applying laser and electric field under low-temperature conditions.

[0019] Figure 3 In-situ HRTEM and corresponding Fast Fourier Transform (FFT) images of the exposed surfaces of halide perovskite nanocrystals under low-temperature conditions controlled by laser and electric field: a) before laser irradiation (initial state); b) during laser irradiation; c) after the entire laser irradiation process is completely finished.

[0020] Figure 4 Laser annealing (0.02 mJ / cm) 2 Cryo-transmission electron microscopy (CTEM) images of haloperovskite nanocrystals before and after 5000 seconds (100 Hz); (a) CTEM image before laser annealing; (b) CTEM image after laser annealing; (c) PL spectra of the samples before and after processing. Detailed Implementation

[0021] The specific technical solutions of the present invention will be described with reference to the embodiments.

[0022] Example 1

[0023] Devices used to regulate the microstructure of halide perovskites, such as Figure 1 As shown, the liquid nitrogen Dewar flask 3 is connected to the sample stage 1 via the sample rod 2. The liquid nitrogen Dewar flask 3 is connected to the control system 5 via the voltage and current detection multi-channel system 4. The liquid nitrogen Dewar flask 3 is also equipped with a vacuum pump 6, and an electron microscope 7 is also provided at the sample stage 1.

[0024] like Figure 2The experiment was performed in a transmission electron microscope 7 using a custom TEM in-situ sample holder 2 equipped with a laser fiber (Thorlabs Inc.) and a liquid nitrogen Dewar 3, which can be externally connected to a source measurement unit (Keithley Instrument Inc.). A Nd:YAG pulsed laser system (Changchun Xin Gongye Guangdian Technology Co., Ltd.) with a wavelength of 532 nm, adjustable pulse frequency (1-100 Hz), and pulse duration of 7 ns was coupled into the transmission electron microscope 7 through a fiber, while the sample was kept at a level close to the liquid nitrogen temperature (-180°C).

[0025] The distance between the sample and the laser fiber tip was fine-tuned to 200 nm (controlled by a piezoelectric driving mechanism with a step size of 100 pm) before pulsed laser irradiation in the transmission electron microscope 7 to obtain the optimal laser irradiation area, where the effective laser flux ranged from 0.01 mJ / cm 2 to 500 mJ / cm 2 .

[0026] At -180°C, CsPbBr3nanocrystals were first irradiated with a pulsed laser at 1 Hz, 50 mJ / cm 2 for 5 s, then irradiated with a pulsed laser at 10 mJ / cm 2 , 20 Hz for 1 s, and finally irradiated with a pulsed laser at 0.1 mJ / cm 2 , 100 Hz for more than 90 s to control the recrystallization of perovskite nanocrystals along a specific crystal plane (111), as shown in Figure 3 The in-situ HRTEM of the exposed surface of halogen perovskite nanocrystals under low temperature conditions and the corresponding fast Fourier transform (FFT) images under the application of laser and electric field.

[0027] Example 2

[0028] The device used to regulate the halogen perovskite microstructure: in the transmission electron microscope 7, a custom TEM in-situ sample holder equipped with a laser fiber (Thorlabs Inc.) and a liquid nitrogen Dewar 3 was used, which can be externally connected to a source measurement unit (Keithley Instrument Inc.). A Nd:YAG pulsed laser system (Changchun Xin Gongye Guangdian Technology Co., Ltd.) with a wavelength of 532 nm, adjustable pulse frequency (1-100 Hz), and pulse duration of 7 ns was coupled into the transmission electron microscope 7 through a fiber, while the sample was kept at a level close to the liquid nitrogen temperature (-180°C).

[0029] The distance between the sample and the laser fiber tip was fine-tuned to 200 nm (controlled by a piezoelectric driving mechanism, with a step size of 100 pm) before pulsed laser irradiation in the transmission electron microscope 7 to obtain the optimal laser irradiation area, in which the effective laser flux ranged from 0.01 mJ / cm 2 to 500 mJ / cm 2 .

[0030] Low-temperature pulsed laser annealing heat treatment was performed on the CsPbBr3 perovskite degradation sample that had appeared Pb precipitation using a pulsed laser with 1 mJ / cm 2 , 1 Hz at -180°C, and the original defects of the nanocrystals were reduced, the crystallization was more perfect, the PL peak intensity was significantly enhanced, and the performance was better, as shown in Figure 4 Freeze transmission electron microscope images of halide perovskite nanocrystals before and after laser annealing (0.02 mJ / cm 2 , 100 Hz) for 5000 seconds.

Claims

1. A method for controlling the microstructure of halide perovskites using lasers and electric fields at freezing temperatures, characterized in that: The procedure was performed using a custom-designed in-situ TEM sample holder equipped with a laser fiber and a liquid nitrogen Dewar flask, which was externally connected to the source measurement unit. A 532 nm wavelength, tunable pulse frequency, and 7 ns pulse duration Nd:YAG pulsed laser system was coupled into the transmission electron microscope (TEM) via fiber optic cable, while the sample was maintained at -180°C. Before pulsed laser irradiation in the TEM, the distance between the sample and the tip of the laser fiber was fine-tuned to 200 nm to obtain the optimal laser irradiation area, with an effective laser flux range of 0.01 mJ / cm². 2 Up to 500mJ / cm 2 By controlling the energy, frequency, and duration of the pulsed laser at freezing temperatures and applying an external electric field, the perovskite nanocrystals are recrystallized along a specific crystal plane (111), thus regulating their exposed surface.

2. The method for controlling the microstructure of halide perovskite using laser and electric field at freezing temperature according to claim 1, characterized in that: Specifically, the following steps are included: S1. Perovskite nanocrystals are irradiated with a high-energy pulsed laser at freezing temperature. S2. At freezing temperature, perovskite nanocrystals are irradiated with a low-energy, high-frequency pulsed laser while a certain electric field is applied. S3. At freezing temperature, perovskite nanocrystals are irradiated with a low-energy, high-frequency pulsed laser.

3. The method for controlling the microstructure of halide perovskite using laser and electric field at freezing temperature according to claim 1, characterized in that: The freezing temperature is less than 245K.

4. The method for controlling the microstructure of halide perovskite using laser and electric field at freezing temperature according to claim 1, characterized in that: The high energy in S1 is 50 mJ / cm. 2 The pulsed laser frequency is 1Hz and the irradiation time is 5s.

5. The method for controlling the microstructure of halide perovskite using laser and electric field at freezing temperature according to claim 1, characterized in that: The low energy level of S2 is 10 mJ / cm². 2 The frequency was 20Hz, the irradiation time was 1s, the applied electric field was 100kV / cm2, and the laser wavelength was 532nm.

6. The method for controlling the microstructure of halide perovskite using laser and electric field at freezing temperature according to claim 1, characterized in that: The low energy of S3 is 0.1 mJ / cm. 2 The high frequency is 100Hz, and the irradiation time is more than 90s.

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