Method for realizing anisotropic carrier transport of lead-free perovskite Cs2AgBiBr6 single crystal
By treating Cs2AgBiBr6 single crystals under high voltage and controlling their crystal structure, anisotropic carrier transport of lead-free perovskite Cs2AgBiBr6 was achieved, solving the problems of low carrier mobility and large band gap, and improving photoelectric performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- DALIAN INSTITUTE OF CHEMICAL PHYSICS CHINESE ACADEMY OF SCIENCES
- Filing Date
- 2024-11-20
- Publication Date
- 2026-05-22
AI Technical Summary
Existing lead-free perovskite Cs2AgBiBr6 materials have low carrier mobility and large band gap in optoelectronic devices, resulting in poor absorption performance and limiting the improvement of their optoelectronic performance.
By treating Cs2AgBiBr6 single crystals under high pressure, the crystal structure changes were controlled by pressure to achieve anisotropic carrier transport. The specific steps included applying pressure to a diamond anvil cell, using silicone oil as the pressure transmission medium, performing two rounds of pressurization and maintaining the pressure for a certain period of time before depressurizing to atmospheric pressure, and testing the diffusion coefficient under different pressures.
Anisotropic carrier transport was successfully achieved in lead-free perovskite Cs2AgBiBr6 single crystals, improving the carrier migration performance of the material and enhancing its optoelectronic properties.
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Figure CN122071817A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of material carrier transport, specifically relating to a method for realizing anisotropic carrier transport in lead-free perovskite Cs2AgBiBr6 single crystals. Background Technology
[0002] In recent years, lead-containing perovskite metal halide materials ABX3[A=CH3NH3] have been used in research. + (H2N)2CH + B = Pb2 + X = Cl - ,Br - or I - Lead-free perovskite materials have achieved great success in fields such as solar cells, photodetectors, and light-emitting diodes due to their advantages such as high carrier mobility, high light absorption coefficient, and low defect state density. However, their instability and lead pollution still hinder industrialization. Therefore, developing environmentally friendly, high-performance, and stable lead-free perovskite materials will become a key research focus.
[0003] Slavney et al. proposed using Cs + Substituted organic cations (MA) + FA + (etc.), Ag + and Bi 3+ Replacement of Pb 2+ A strategy was employed to successfully synthesize three-dimensional lead-free double perovskite Cs₂AgBiBr₆. Lead-free double perovskite Cs₂AgBiBr₆ is considered a promising new optoelectronic functional material due to its excellent properties such as low toxicity, strong thermal stability, and high absorption coefficient. Research on optoelectronic devices based on Cs₂AgBiBr₆ single crystals has also made some progress. In 2017, Tang's research group fabricated a planar photodetector based on Cs₂AgBiBr₆ single crystals. The fabricated photodetector achieved a 15AW absorption rate under 530nm illumination and an external bias voltage of 1V. -1 The responsivity exhibits excellent photoelectric performance. In 2019, Niu's group reported the quantitative growth of high-quality Cs₂AgBiBr₆ single crystals based on solubility and supersolubility, which were used in high-performance photodetectors and X-ray detectors. In 2022, Huang's group grew a crystal with a trap state density of 1.37 × 10⁻⁶ using a low-temperature solution crystallization method. 10 cm -3This study discovered Cs₂AgBiBr₆ single crystals and, for the first time, fabricated a self-powered photodetector with an Au / Ag asymmetric electrode structure using this material. As a novel all-inorganic lead-free double perovskite material, Cs₂AgBiBr₆ single crystals solve the problems of toxicity and environmental instability associated with organic-inorganic hybrid lead halide perovskite single crystals, making it a promising candidate for photodetection. While some breakthroughs have been achieved with Cs₂AgBiBr₆ in optoelectronic devices, its performance remains unsatisfactory due to factors such as low carrier transport capacity and a large band gap (>2 eV) leading to poor absorption. Therefore, improving the carrier transport performance and reducing the band gap of lead-free double perovskites to enhance their photoelectric performance remains a critical challenge.
[0004] Pressure, as an important thermodynamic parameter, can alter the photophysical properties of materials. On the one hand, pressure can effectively shorten interatomic spacing and enhance the coupling of adjacent electron orbitals, profoundly affecting the structure and properties of materials and playing a crucial role in discovering new phenomena, properties, and elucidating new mechanisms. In recent years, studies on the structural and optical property changes of lead-bearing perovskites under high pressure have become increasingly common. The unique soft lattice of two-dimensional lead-bearing perovskites makes them more sensitive to mechanical compression; related research includes pressure-induced PL modulation processes, bandgap redshift mechanisms, changes in electronic band structure, and the relationship between structure and optical properties. Research on the structural and property changes of three-dimensional lead-bearing perovskites under high pressure has also made some progress, including pressure-induced electronic and crystal structure phase transitions, amorphization, metallization, bandgap modulation, and increased conductivity. Currently, research on Cs₂AgBiBr₆ is limited to the effects of pressure on its structure, bandgap, and optical properties. Li et al. achieved significant bandgap tuning of Cs₂AgBiBr₆ perovskite single crystals through pressure engineering. At a pressure of 15 GPa, the bandgap of Cs₂AgBiBr₆ was comparable to that of MAPbI₃, and after decompression, the bandgap was 8.2% smaller than that under constant pressure. Fu et al., in their study of Cs₂AgBiBr₆ nanocrystals, also found that pressure could significantly reduce the bandgap of Cs₂AgBiBr₆ and systematically studied the changes in the optical properties of Cs₂AgBiBr₆ under different pressures. Lv et al. reported a broad fluorescence emission spectrum (520-1000 nm) of Cs₂AgBiBr₆ thin films induced by pressure. Carrier transport properties are one of the key factors affecting the performance of perovskite optoelectronic devices; however, how pressure affects carrier transport in Cs₂AgBiBr₆ remains unreported. Optimizing the carrier transport properties of Cs2AgBiBr6 material using pressure methods is of great scientific significance for its application in the optoelectronic field.
[0005] On the other hand, studies on high-pressure-induced structural changes in Cs₂AgBiBr₆ have revealed that at pressures around 3 GPa, Cs₂AgBiBr₆ undergoes a transformation from a cubic to a tetragonal phase. In the cubic phase, all cell parameters are identical (a = b = c), while in the tetragonal phase, a = b ≠ c. Furthermore, due to the different shrinkage rates of the cell parameters, the ratio of a = b / c increases with increasing pressure, leading to a gradual decrease in crystal symmetry. Different transport directions of charge carriers exhibit different scattering effects with the lattice, which could potentially result in anisotropic charge carrier transport properties. Summary of the Invention
[0006] Compared to high pressure, the anisotropic carrier transport of Cs₂AgBiBr₆ under ambient pressure is more practically significant. However, perovskite lattices have a certain degree of elasticity, and a few studies have been able to retain the superior performance under high pressure to ambient pressure. Studies on depressurizing Cs₂AgBiBr₆ have found that cubic and tetragonal phases coexist after high-pressure treatment, indicating that the tetragonal phase can be partially retained at ambient pressure. This provides a possibility for achieving anisotropic carrier transport in Cs₂AgBiBr₆ under ambient pressure through pressure treatment. Simultaneously, pressure treatment causes a redshift in the absorption of Cs₂AgBiBr₆, i.e., increased light absorption. This demonstrates the feasibility and practical significance of using pressure to modulate the optoelectronic properties of Cs₂AgBiBr₆, providing theoretical and experimental guidance for developing anisotropic optoelectronic properties of lead-free perovskite optoelectronic devices and offering a new approach to constructing high-efficiency perovskite semiconductor optoelectronic devices.
[0007] The main implementation scheme of this invention is as follows: A lead-free perovskite Cs₂AgBiBr₆ single crystal is transferred to a diamond anvil cell of a high-pressure press using a needle-picking method. A stainless steel ring-shaped gasket is placed on the diamond anvil cell, and silicone oil is dripped into the gasket as a pressure-transmitting medium, subjecting the sample to quasi-hydrostatic pressure. The high-pressure press containing the sample is placed on a self-built fluorescence scanning imaging microscopy system and a fluorescence collection system of a spectrometer in the laboratory to test the diffusion coefficient under different pressures. The experiment shows that as the pressure increases, the diffusion coefficient of the Cs₂AgBiBr₆ single crystal first increases and then shows an inflection point at 2.0 GPa. By applying a certain pressure, applying pressure twice, maintaining the pressure for a certain time, and then depressurizing to atmospheric pressure, anisotropic carrier transport of the lead-free perovskite Cs₂AgBiBr₆ single crystal is successfully achieved.
[0008] The objective of this invention is achieved through the following solution.
[0009] A method for achieving anisotropic carrier transport in lead-free perovskite Cs2AgBiBr6 single crystals, the specific steps of which are as follows:
[0010] (1) Preparation of lead-free perovskite Cs2AgBiBr6 single crystals: CsBr, AgBr, and BiBr3 were dissolved in HBr solution and stirred for a certain time until dissolved. The solution was then slowly cooled to room temperature to precipitate crystals, and finally subjected to heat treatment.
[0011] (2) Transfer of lead-free perovskite Cs2AgBiBr6 single crystal to diamond anvil cell: The sample synthesized in (1) was selected under a microscope by using a needle and transferred to the diamond anvil cell of a high-pressure press. Stainless steel was placed on the diamond anvil cell as a gasket, and silicone oil was dripped into the gasket. The silicone oil was used as a pressure transmission medium to subject the sample to quasi-hydrostatic pressure.
[0012] (3) Diffusion coefficient test of lead-free perovskite Cs2AgBiBr6 single crystal under different pressures: The sample (2) mounted on the high pressure press was placed on the fluorescence scanning imaging microscopy system to test the diffusion coefficient under different pressures.
[0013] (4) Anisotropic carrier transport of lead-free perovskite Cs2AgBiBr6 single crystal after pressure treatment: The sample (2) mounted on the high-pressure press was placed on the fluorescence scanning imaging microscopy system, and the anisotropic carrier transport of lead-free perovskite Cs2AgBiBr6 single crystal after pressure treatment was measured by a. applying a certain pressure, b. applying pressure twice, and c. maintaining a certain pressure for a certain time and then depressurizing to normal pressure.
[0014] Preferably, the raw materials for synthesis in step (1) are 1-3 mmol CsBr, 0.5-2 mmol AgBr, and 0.5-2 mmol BiBr3. The heating and stirring temperature is 120-160℃. The cooling rate is 2-10℃ / h. The drying temperature after washing the single crystal is 40-100℃.
[0015] Preferably, in step (2), the lead-free perovskite Cs2AgBiBr6 single crystal has a length of 100-400 μm, a width of 100-400 μm, and a thickness of 100-400 μm.
[0016] Preferably, in step (3), a) the applied pressure is 6GPa-10GPa; b) the applied pressure in the second pressurization is 2.5GPa-6GPa; c) the applied pressure maintained for a certain time under a certain pressure is 2.5GPa-4GPa, and the maintenance time is 8h-20h.
[0017] This invention enables the testing of the diffusion coefficient of lead-free perovskite Cs₂AgBiBr₆ single crystals under different pressures. It was found that the diffusion coefficient of Cs₂AgBiBr₆ single crystals initially increases with increasing pressure, then reaches an inflection point at 2.8 GPa. By applying a certain pressure, applying pressure twice, maintaining the pressure for a certain time, and then depressurizing to atmospheric pressure, anisotropic carrier transport in lead-free perovskite Cs₂AgBiBr₆ single crystals was successfully achieved.
[0018] Compared with the prior art, the beneficial effects of the present invention are:
[0019] (1) The method of realizing anisotropic carrier transport in lead-free perovskite Cs2AgBiBr6 single crystal of the present invention produces lead-free perovskite Cs2AgBiBr6 single crystal with few defects.
[0020] (2) A method for realizing anisotropic carrier transport in lead-free perovskite Cs2AgBiBr6 single crystals according to the present invention, thereby obtaining the change in diffusion coefficient of lead-free perovskite Cs2AgBiBr6 single crystals under different pressures.
[0021] (3) The present invention provides a method for realizing anisotropic carrier transport in lead-free perovskite Cs2AgBiBr6 single crystals by applying a certain pressure, applying pressure twice, maintaining the pressure for a certain time, and then depressurizing to normal pressure. Attached Figure Description
[0022] Figure 1 The image shows a single crystal of lead-free perovskite Cs2AgBiBr6 prepared in Example 1.
[0023] Figure 2 The diffusion coefficient D of the lead-free perovskite Cs2AgBiBr6 single crystal prepared in Example 1 under different pressures.
[0024] Figure 3 The diffusion coefficients of the lead-free perovskite Cs2AgBiBr6 single crystal prepared in Example 1 at different angles before pressure treatment.
[0025] Figure 4 The diffusion coefficients at different angles were obtained after the lead-free perovskite Cs2AgBiBr6 single crystal prepared in Example 1 was subjected to a certain pressure and then depressurized to normal pressure.
[0026] Figure 5 The diffusion coefficients of the lead-free perovskite Cs2AgBiBr6 single crystal prepared in Example 1 at different angles after two rounds of pressurization and depressurization to normal pressure.
[0027] Figure 6The diffusion coefficients of the lead-free perovskite Cs2AgBiBr6 single crystal prepared in Example 1 were measured at different angles after being maintained under a certain pressure for a certain period of time and then depressurized to atmospheric pressure. Detailed Implementation
[0028] The present invention will be further described in detail below with reference to embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto. All reagents used in the embodiments are commercially available.
[0029] Lead-free perovskite Cs2AgBiBr6 single crystals were transferred to the diamond anvil cell of a high-pressure press (diamond anvil cell press) using a needle-picking method. A stainless steel ring-shaped gasket was placed on the diamond anvil cell, with silicone oil dripped into the gasket as the pressure-transmitting medium, subjecting the sample to quasi-hydrostatic pressure. Ruby balls were used for pressure calibration. The high-pressure press containing the sample was then placed on a fluorescence scanning imaging microscopy system (refer to ACS Energy Lett. 7, 154-161 (2022)) and a fluorescence collection system of a spectrometer to test and calculate the carrier diffusion coefficient of the Cs2AgBiBr6 single crystals under different pressures. The diffusion coefficient was calculated using the method described in J. Phys. Chem. Lett. 11, 6956-6963 (2020); Nat. Commun. 6, 7471 (2015). With increasing pressure, the diffusion coefficient of Cs₂AgBiBr₆ single crystal initially increased and then reached an inflection point at 2.8 GPa. Anisotropic carrier transport in lead-free perovskite Cs₂AgBiBr₆ single crystals was successfully achieved by applying a certain pressure, applying pressure twice, maintaining the pressure for a certain time, and then depressurizing to atmospheric pressure.
[0030] Example 1
[0031] A method for intercepting the high diffusion coefficient of perovskite thin films under high pressure to atmospheric pressure includes the following steps: (1) Accurately weigh 426 mg of CsBr and 448 mg of BiBr3 and dissolve them in 16 ml of HBr. Stir and heat at 140 °C until dissolved. Add 188 mg of AgBr and continue stirring until dissolved. Keep warm for two hours. Then cool down to room temperature at a rate of 2 °C / h. Wash the solid sample with isopropanol solution until clear. Dry the sample at 80 °C to obtain a polygonal lead-free perovskite Cs2AgBiBr6 single crystal with a length of 100-400 μm, a width of 100-400 μm (when measured along two mutually perpendicular directions of length and width), and a thickness of 100-400 μm.
[0032] (2) The diffusion of lead-free perovskite Cs2AgBiBr6 single crystals was measured at 0.0 GPa (normal pressure), 0.2, 0.5, 0.7, 1.1, 2.0 and 2.6 GPa respectively, and the diffusion coefficient D was calculated.
[0033] (3) After applying a pressure of 6.4 GPa to the single crystal sample, the pressure was released, the diffusion after the pressure treatment was measured, and the diffusion coefficient D was calculated.
[0034] (4) Apply 6.4 GPa pressure to the single crystal sample in step (3) and then depressurize it to normal pressure. Apply 2.6 GPa pressure again and depressurize it to normal pressure. Continue to apply pressure to 2.7 GPa and then depressurize it to normal pressure. Measure the diffusion after pressure treatment and calculate the diffusion coefficient D.
[0035] (5) After applying a pressure of 2.6 GPa to the single crystal sample in step (4) and depressurizing it to normal pressure, apply a pressure of 2.6 GPa again and maintain it for 10 hours before depressurizing. Measure the diffusion after pressure treatment and calculate the diffusion coefficient D.
[0036] The lead-free perovskite Cs2AgBiBr6 single crystal prepared in this embodiment is as follows: Figure 1 As shown, the prepared lead-free perovskite Cs2AgBiBr6 single crystals have a regular morphology and few surface defects.
[0037] The diffusion coefficient of lead-free perovskite Cs2AgBiBr6 single crystals prepared in Example 1 under different pressures was tested as follows: Figure 2 As shown in step (2)). It was found that as the pressure increases, the diffusion coefficient of lead-free perovskite Cs2AgBiBr6 single crystal first increases and then shows an inflection point at 2.0 GPa.
[0038] The diffusion coefficients of lead-free perovskite Cs2AgBiBr6 single crystals prepared in Example 1 at different angles before pressure treatment are shown below. Figure 3 As shown, it can be clearly seen that the diffusion coefficient of Cs2AgBiBr6 single crystal is almost the same in different directions, indicating that the carrier transport of lead-free perovskite Cs2AgBiBr6 single crystal without pressure treatment is isotropic.
[0039] The diffusion coefficient of the lead-free perovskite Cs2AgBiBr6 single crystal prepared in Example 1, after being pressurized to 6.4 GPa and then depressurized, is as follows: Figure 4 As shown in step (3)). It can be clearly seen that the diffusion coefficient of Cs2AgBiBr6 single crystal exhibits a periodic variation trend in different directions, indicating that the pressure treatment method of applying pressure of 6.4 GPa and then depressurizing has achieved anisotropic carrier transport of lead-free perovskite Cs2AgBiBr6 single crystal.
[0040] The diffusion coefficient of the lead-free perovskite Cs₂AgBiBr₆ single crystal prepared in Example 1, after being pressurized to 2.6 GPa and then depressurized to atmospheric pressure, and then further pressurized to 2.7 GPa and depressurized, is as follows: Figure 5As shown in step (4)). It can be clearly seen that the diffusion coefficient of Cs2AgBiBr6 single crystal exhibits a periodic variation trend in different directions, indicating that the pressure treatment method of applying a pressure of 2.6 GPa and then depressurizing to atmospheric pressure, and then applying pressure to 2.7 GPa and then depressurizing to atmospheric pressure, achieves anisotropic carrier transport of lead-free perovskite Cs2AgBiBr6 single crystal.
[0041] The diffusion coefficient of the lead-free perovskite Cs2AgBiBr6 single crystal prepared in Example 1, after being pressurized at 2.6 GPa for 10 hours and then depressurized, is as follows: Figure 6 As shown in step (5)). It can be clearly seen that the diffusion coefficient of Cs2AgBiBr6 single crystal in different directions exhibits a periodic variation trend, indicating that the pressure treatment method of maintaining a pressure of 2.6 GPa for 10 hours and then depressurizing to atmospheric pressure has achieved anisotropic carrier transport of lead-free perovskite Cs2AgBiBr6 single crystal.
[0042] The above examples are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the specific examples described above. Any changes, modifications, simplifications, combinations, substitutions, or other substitutions made without departing from the spirit and principle of the present invention are within the protection scope of the present invention.
Claims
1. A method for achieving anisotropic carrier transport in lead-free perovskite Cs₂AgBiBr₆ single crystals, characterized in that, Includes the following steps: (1) Take a lead-free perovskite Cs2AgBiBr6 single crystal and select a polygonal lead-free perovskite Cs2AgBiBr6 single crystal with a length of 100-400μm, a width of 100-400μm (when measured along two mutually perpendicular length and width directions) and a thickness of 100-400μm by needle picking. (2) Method for achieving anisotropic carrier transport in lead-free perovskite Cs2AgBiBr6 single crystals under normal pressure: a: Apply a certain pressure to the Cs2AgBiBr6 single crystal and then depressurize it to normal pressure; b: After the second pressurization, the pressure is released to normal pressure; c: Method of maintaining a certain pressure for a certain period of time and then depressurizing to atmospheric pressure; Anisotropic carrier transport was achieved in lead-free perovskite Cs2AgBiBr6 single crystals.
2. The method according to claim 1, characterized in that, The pressure applied in step (2)a is 6GPa-10GPa.
3. The method according to claim 1, characterized in that, The pressure applied in the second round of pressurization in step (2)b is 2.5GPa-6GPa.
4. The method according to claim 1, characterized in that, The applied pressure, which is maintained at a certain pressure for a certain period of time under step (2)c, is 2.5 GPa-4 GPa, and the maintenance time is 8h-20h.
5. The method according to any one of claims 1-4, characterized in that, As the pressure increases, the diffusion coefficient of Cs2AgBiBr6 single crystal first increases and then reaches an inflection point at 2.0 GPa. By applying a certain pressure, applying pressure twice, maintaining the pressure for a certain period of time, and then depressurizing to atmospheric pressure, anisotropic carrier transport of lead-free perovskite Cs2AgBiBr6 single crystal was successfully achieved.