Bromine-chlorine mixed blue light perovskite thin film, preparation method and perovskite LED device

Abstract

The application belongs to the field of perovskite devices, and specifically discloses a bromine-chlorine mixed blue light perovskite film, a preparation method thereof and a perovskite LED device. The preparation raw materials of the bromine-chlorine mixed blue light perovskite film include cesium halide, lead bromide, lead chloride and an alkaline earth metal bromide; the alkaline earth metal bromide includes at least one of calcium bromide, strontium bromide and barium bromide; and the ratio of the mole number of the alkaline earth metal bromide to the total mole number of Pb in the lead bromide and the lead chloride is not greater than 0.5. The alkaline earth metal bromide with a perovskite phase of low solubility is used to dope the bromine-chlorine mixed blue light perovskite, and the mole ratio of the doping amount of the alkaline earth metal bromide is not higher than 0.5, so that the uneven distribution of bromine and chlorine in the blue light perovskite film during the film forming process is improved, the halogen separation under the electric field is inhibited, and the spectral stability is improved; the doping is directly performed in the precursor, the preparation process is simple, and the method is suitable for large-scale industrial production.

Description

Technical Field

[0001] This invention relates to the field of perovskite devices, and particularly to a bromine-chlorine mixed blue light perovskite thin film and its preparation method, as well as a perovskite LED device. Background Technology

[0002] Perovskite materials possess excellent properties such as high carrier mobility, high luminescent quantum yield, and tunable bandgap, demonstrating enormous application potential in the field of light-emitting diodes (LEDs). Among them, blue perovskite materials, as an important component of tri-color luminescent materials, directly determine the quality of display and lighting devices.

[0003] Currently, the preparation of blue light perovskite materials mostly adopts a bromine-chlorine mixed halide system (such as CsPbBr). 3-x Cl x Blue light emission can be achieved by adjusting the band gap through controlling the doping ratio of Cl. However, existing bromine-chlorine mixed blue light perovskite thin films generally suffer from poor spectral stability: during electroluminescence, halide ion migration and phase separation easily occur inside the film, leading to emission peak shift, broadening of the full width at half maximum (FWHM), and even multi-peak emission, which seriously affects the lifespan and performance stability of the device.

[0004] To improve the stability of blue perovskite, existing technologies often employ strategies such as interface modification or organic ligand engineering. For example, introducing long-chain organic ligands increases the steric hindrance for halide ion migration; however, the introduction of organic ligands may disrupt the crystal structure of the perovskite, making it sensitive to water and oxygen and affecting its stability. Annealing and recrystallization techniques are also used to improve the uniformity of bromine and chloride distribution and enhance spectral stability. However, this technique requires an additional annealing step on top of the conventional preparation process, which not only significantly prolongs the overall process time but also increases process complexity and energy consumption, making it unsuitable for large-scale production. Summary of the Invention

[0005] The present invention aims to improve at least one technical problem in the prior art.

[0006] The first aspect of this invention provides a bromine-chlorine mixed blue light perovskite thin film, the raw materials for which include: cesium halide, lead bromide, lead chloride, alkaline earth metal bromide and organic ligand;

[0007] The perovskite phase corresponding to the alkaline earth metal bromide has a lower solubility in polar organic solvents than CsPbBr3.

[0008] The alkaline earth metal bromides include at least one of calcium bromide, strontium bromide, and barium bromide;

[0009] The ratio of the number of moles of alkaline earth metal bromide to the total number of moles of Pb in lead bromide and lead chloride is not greater than 0.5.

[0010] In existing technologies, the solubility (in polar organic solvents) of the bromide-perovskite phase (CsPbBr3) and the chloride-perovskite phase (CsPbCl3) in bromine-chloride mixed blue light perovskites differs, with the bromide-perovskite phase having a higher solubility than the chloride-perovskite phase. This leads to a situation where, during the crystallization process of perovskite films prepared by solution methods, the chloride-perovskite phase reaches saturation solubility first as the solvent evaporates, resulting in perovskite with a high chloride content. Conversely, the bromide-perovskite phase, due to its higher solubility, reaches saturation solubility later, resulting in perovskite with a high bromine content. Ultimately, the formed perovskite film consists of both chloride-rich and bromine-rich phases, resulting in an uneven distribution of bromine and chloride. This unevenness lowers the migration barrier of bromide and chloride ions, accelerating their migration and separation under the influence of an electric field. If the uneven distribution of bromine and chloride can be suppressed and its uniformity improved, the migration of bromide and chloride ions can be effectively inhibited, enhancing spectral stability.

[0011] This technical solution introduces alkaline earth metal bromide salts into the bromine-chlorine mixed blue light perovskite precursor for the first time. By using alkaline earth metal bromides with low-solubility perovskite phases (CsXBr3, where X represents an alkaline earth metal) to dope the bromine-chlorine mixed blue light perovskite, the solubility of the perovskite phase corresponding to the alkaline earth metal bromide in polar organic solvents is lower than that of CsPbBr3. Furthermore, the molar ratio of alkaline earth metal bromide doping is no greater than 0.5. This allows the bromine-perovskite system to crystallize earlier during the perovskite crystallization process, suppressing phase separation between the bromine-perovskite and chloride-perovskite phases at the crystal structure level. This improves the uneven distribution of bromine and chloride during the film formation process of the bromine-chlorine mixed blue light perovskite film, suppresses halogen separation under an electric field, and enhances its spectral stability. The preparation process is simple, requiring no additional annealing or other processes, and is suitable for large-scale industrial production.

[0012] The molar ratio of alkaline earth metal bromide doping should not exceed 0.5. A value higher than 0.5 will lead to lattice distortion, damage to the integrity of the perovskite phase, and increase in defects, thereby impairing the optoelectronic performance of perovskite devices.

[0013] When magnesium bromide is used for doping, the perovskite structure collapses.

[0014] Introducing organic ligands can passivate perovskite defects and improve the luminous efficiency of perovskite light-emitting diode devices.

[0015] Preferably, the organic ligand includes at least one selected from formamidinium bromide, phenethylamine bromide, p-fluorophenethylamine bromide, and butylamine bromide.

[0016] Preferably, the alkaline earth metal bromide is barium bromide, and the ratio of the number of moles of barium bromide to the total number of moles of Pb in lead bromide and lead chloride is 0.1.

[0017] Preferably, the ratio of the total moles of lead bromide and lead chloride to the moles of cesium halide is 1:1.

[0018] A second aspect of the present invention provides a method for preparing the bromine-chlorine mixed blue light perovskite thin film as described above, comprising the following steps:

[0019] Cesium halide, lead bromide, lead chloride, alkaline earth metal bromide, and organic ligand are dissolved in a polar organic solvent and mixed evenly to obtain a precursor solution.

[0020] The precursor solution was spin-coated onto the substrate and annealed to obtain the bromine-chlorine mixed blue light perovskite film.

[0021] Preferably, the annealing temperature is 90℃-300℃ and the annealing time is 5min-50min.

[0022] Preferably, when spin-coating the precursor solution, the spin-coating speed is 800 rpm to 5000 rpm and the spin-coating time is 5 s to 80 s.

[0023] Preferably, the spin coating time is 20s-80s, and an antisolvent is dropped onto the substrate surface 10s-15s after the spin coating begins. The volume of the antisolvent is 1 / 3-1 / 2 of the volume of the precursor solution.

[0024] Preferably, the antisolvent includes at least one of chlorobenzene and toluene.

[0025] Optionally, the polar organic solvent includes at least one of dimethyl sulfoxide and N,N-dimethylformamide.

[0026] Preferably, the polar organic solvent comprises dimethyl sulfoxide and N,N-dimethylformamide in a volume ratio of 1:(0.5-2).

[0027] A high proportion of DMSO enhances coordination regulation and slows down nucleation; a high proportion of DMF accelerates solvent evaporation and promotes ordered crystallization. By controlling the coordination strength ratio and evaporation rate gradient of the two solvents, a dynamic balance is achieved between precursor dissolution, nucleation-growth kinetics, and film crystallization quality, resulting in perovskite films with high crystallinity, low defects, and uniform morphology.

[0028] Optionally, the antisolvent includes at least one of chlorobenzene and toluene.

[0029] A third aspect of the present invention provides a perovskite LED device comprising the aforementioned bromine-chlorine mixed blue light perovskite thin film, wherein the perovskite LED device comprises, from bottom to top, an ITO substrate, a hole transport layer, the aforementioned bromine-chlorine mixed blue light perovskite thin film, an electron transport layer, an electron injection layer, and an electrode layer.

[0030] Optional fabrication methods for perovskite LED devices:

[0031] (1) Preparation of hole transport layer:

[0032] The process is carried out in an air atmosphere. Take 30-50 μL of PEDOT:PSS solution (Clevios P ​​Al 4083) and drop it evenly onto the center of the plasma-treated ITO substrate. Spin coat the substrate using a spin coater at 500-4000 rpm for 5-30 seconds. After spin coating, immediately transfer the substrate to a preheated hot plate and anneal it at 120-300℃ for 15-20 minutes. After annealing, cool the substrate to room temperature and return it to the glove box for later use.

[0033] (2) Preparation of bromine-chlorine mixed blue light perovskite thin films:

[0034] According to the above-described method for preparing bromine-chlorine mixed blue light perovskite thin films, bromine-chlorine mixed blue light perovskite thin films are prepared on hole transport layers.

[0035] (3) Preparation of other layers:

[0036] The substrate is transferred to a vacuum evaporation chamber, where TPBi / LiF / Al electrodes are deposited sequentially, corresponding to the electron transport layer, electron injection layer, and electrode layer, respectively. The thickness of the TPBi layer is 5-30 nm, the thickness of the LiF layer is 0.5-5 nm, and the thickness of the Al electrode is 100-150 nm. The evaporation rate is controlled at 0.1-5 nm / s to ensure electrode uniformity and conductivity. After evaporation, a perovskite LED device is obtained.

[0037] The beneficial effects of this invention are as follows: This invention uses alkaline earth metal bromides with low solubility perovskite phases to dope bromine-chlorine mixed blue perovskite, and the molar ratio of alkaline earth metal bromides doping is not higher than 0.5. This improves the uneven distribution of bromine and chlorine in the blue perovskite film during the film formation process, suppresses halogen separation under an electric field, and enhances its spectral stability. By directly doping in the precursor, the preparation process is simple and suitable for large-scale industrial production. Attached Figure Description

[0038] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0039] Figure 1 The results are the performance test results of Embodiment 4 and Comparative Example 1 of the present invention. Detailed Implementation

[0040] The following will provide a clear and complete description of the concept and technical effects of this application in conjunction with embodiments and accompanying drawings, so as to fully understand the purpose, solution and effects of this application. It should be understood that these embodiments are only for illustrating this application and not for limiting this application. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. The term "at least one" as used herein refers to any combination of one or more, and is not limited to a specific number. The terms "comprising" or "including" do not exclude the existence of other components or steps not explicitly listed.

[0041] Example 1

[0042] A bromine-chlorine mixed blue light perovskite thin film is prepared by means of: cesium bromide, lead bromide, lead chloride, calcium bromide, and p-fluorophenylethylamine bromide in a molar ratio of 1:0.5:0.5:0.1:0.4, which fixes Pb. 2+ The total concentration is 0.15 M (molar concentration).

[0043] Its preparation method is as follows:

[0044] Cesium bromide, lead bromide, lead chloride, calcium bromide, and p-fluorophenylethylamine bromine were dissolved in a 1:1 mixture of DMF and DMSO solvents and mixed thoroughly (using a magnetic stirrer at room temperature for 12 h at a stirring speed of 600 rpm until the solution was completely clear and transparent, with no visible particles or turbidity). The solution was filtered through a 0.22 μm polytetrafluoroethylene filter membrane (pre-wetted with the mixed solvent) to remove undissolved micro-impurities and agglomerated particles. The filtrate was stored in a sample vial to obtain the precursor solution.

[0045] On an ITO substrate with a pre-deposited hole transport layer, 40 μL of filtered precursor solution was dropped onto the center of the hole transport layer. The precursor solution was then spin-coated at 4000 rpm for 80 s. 15 s after the spin-coating began, 20 μL of chlorobenzene was dropped onto the substrate surface. The substrate was then annealed at 150 °C for 15 min to obtain a bromine-chlorine mixed blue perovskite film.

[0046] Example 2

[0047] A bromine-chlorine mixed blue light perovskite thin film is prepared by means of: cesium bromide, lead bromide, lead chloride, strontium bromide, and p-fluorophenylethylamine bromide in a molar ratio of 1:0.5:0.5:0.1:0.4, which fixes Pb. 2+ The total concentration is 0.15 M (molar concentration).

[0048] Its preparation method is as follows:

[0049] Cesium bromide, lead bromide, lead chloride, strontium bromide, and p-fluorophenylethylamine bromine were dissolved in a 1:1 mixture of DMF and DMSO and mixed thoroughly (using a magnetic stirrer at room temperature for 12 h at a stirring speed of 600 rpm until the solution was completely clear and transparent, with no visible particles or turbidity). The solution was filtered through a 0.22 μm polytetrafluoroethylene filter membrane (pre-wetted with the mixed solvent) to remove undissolved micro-impurities and agglomerated particles. The filtrate was stored in a sample vial to obtain the precursor solution.

[0050] On an ITO substrate with a pre-deposited hole transport layer, 40 μL of filtered precursor solution was dropped onto the center of the hole transport layer. The precursor solution was then spin-coated at 4000 rpm for 80 s. 15 s after the spin-coating began, 20 μL of chlorobenzene was dropped onto the substrate surface. The substrate was then annealed at 150 °C for 15 min to obtain a bromine-chlorine mixed blue perovskite film.

[0051] Example 3

[0052] A bromine-chlorine mixed blue light perovskite thin film is prepared by means of: cesium bromide, lead bromide, lead chloride, barium bromide, and p-fluorophenylethylamine bromide in a molar ratio of 1:0.5:0.5:0.1:0.4, which fixes Pb. 2+ The total concentration is 0.15 M (molar concentration).

[0053] Its preparation method is as follows:

[0054] Cesium bromide, lead bromide, lead chloride, barium bromide, and p-fluorophenylethylamine bromine were dissolved in a 1:1 mixture of DMF and DMSO solvents and mixed thoroughly (using a magnetic stirrer at room temperature for 12 h at a stirring speed of 600 rpm until the solution was completely clear and transparent, with no visible particles or turbidity). The solution was filtered through a 0.22 μm polytetrafluoroethylene filter membrane (pre-wetted with the mixed solvent) to remove undissolved micro-impurities and agglomerated particles. The filtrate was stored in a sample vial to obtain the precursor solution.

[0055] On an ITO substrate with a pre-deposited hole transport layer, 40 μL of filtered precursor solution was dropped onto the center of the hole transport layer. The precursor solution was then spin-coated at 4000 rpm for 80 s. 15 s after the spin-coating began, 20 μL of chlorobenzene was dropped onto the substrate surface. The substrate was then annealed at 150 °C for 15 min to obtain a bromine-chlorine mixed blue perovskite film.

[0056] Example 4

[0057] A perovskite LED device comprises, from bottom to top, an ITO substrate, a hole transport layer, a bromine-chlorine mixed blue light perovskite thin film, an electron transport layer, an electron injection layer, and an electrode layer.

[0058] The preparation method is as follows:

[0059] (1) Preparation of hole transport layer:

[0060] The process was carried out in an air atmosphere. 50 μL of PEDOT:PSS solution (Clevios P ​​Al 4083) was evenly dropped onto the center of the plasma-treated ITO substrate and spin-coated at 3000 rpm for 30 s. After spin-coating, the substrate was immediately transferred to a preheated hot stage and annealed at 250 °C for 20 min. After annealing, the substrate was cooled to room temperature and returned to the glove box for later use.

[0061] (3) Preparation of bromine-chlorine mixed blue light perovskite thin films:

[0062] Using the preparation method of Example 1, the bromine-chlorine mixed blue light perovskite thin film of Example 1 was prepared on the hole transport layer.

[0063] (3) Preparation of other layers:

[0064] The substrate was transferred to a vacuum evaporation chamber, and TPBi / LiF / Al electrodes were deposited sequentially, corresponding to the electron transport layer, electron injection layer, and electrode layer, respectively. The thickness of TPBi was 25 nm, the thickness of the LiF layer was 2 nm, and the thickness of the Al electrode was 150 nm. The evaporation rate was controlled at 1 nm / s to ensure electrode uniformity and conductivity. After the evaporation was completed, a perovskite LED device was obtained.

[0065] According to the preparation method of this embodiment, bromine-chlorine mixed blue light perovskite thin films were prepared as perovskite LED devices in Examples 2 and 3, respectively, and the performance of the perovskite LED devices was tested in a glove box.

[0066] Comparative Example 1

[0067] A perovskite LED device differs from Example 4 in that the raw materials for preparing the bromine-chlorine mixed blue light perovskite thin film do not contain alkaline earth metal bromides. The performance of the perovskite LED device was tested inside a glove box.

[0068] Performance test results

[0069] The perovskite LED devices prepared in Example 4 and Comparative Example 1 were tested, and the results are as follows: Figure 1As shown. Comparative Example 1 corresponds to the perovskite LED device prepared in Comparative Example 1; 10% CaBr2 corresponds to the LED device prepared in Example 4 with a bromine-chlorine mixed blue light perovskite film doped with 10% CaBr2, which uses the bromine-chlorine mixed blue light perovskite film of Example 1; 10% SrBr2 corresponds to the LED device prepared in Example 4 with a bromine-chlorine mixed blue light perovskite film doped with 10% SrBr2, which uses the bromine-chlorine mixed blue light perovskite film of Example 2; 10% BaBr2 corresponds to the LED device prepared in Example 4 with a bromine-chlorine mixed blue light perovskite film doped with 10% BaBr2, which uses the bromine-chlorine mixed blue light perovskite film of Example 3.

[0070] Depend on Figure 1 As can be seen, compared with Comparative Example 1, the perovskite LED device with a bromine-chlorine mixed blue perovskite film obtained by doping with alkaline earth metal bromides in Example 4 showed a significant reduction in spectral redshift and full width at half maximum (FWHM), resulting in a significant improvement in spectral stability. This is because doping the bromine-chlorine mixed blue perovskite with alkaline earth metal bromides (CsXBr3, where X represents an alkaline earth metal) results in lower solubility of the perovskite phase in polar organic solvents compared to CsPbBr3. This leads to earlier crystallization of the bromine-perovskite system during perovskite crystallization, suppressing phase separation between the bromine-perovskite and chloride-perovskite phases at the crystal structure level. This improves the uneven distribution of bromine and chloride in the bromine-chlorine mixed blue perovskite film during film formation, suppresses halogen separation under an electric field, and enhances its spectral stability. Among these, the perovskite LED device doped with 10% BaBr2 showed the best performance, exhibiting the greatest reduction in spectral redshift and FWHM, and the best improvement in spectral stability.

[0071] The preferred embodiments of the present invention have been described in detail above, but this disclosure is not limited to the described embodiments. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention, and these equivalent modifications or substitutions are all included within the scope defined by the claims of this disclosure. The parameter ranges given in this invention are reasonable ranges determined by those skilled in the art based on a comprehensive consideration of material properties, process stability, and device reliability. Equivalent adjustments within this range can achieve the technical effects of the present invention and should be understood as falling within the protection scope of the present invention.

Claims

1. A method for preparing a bromine-chlorine mixed blue light perovskite thin film, characterized in that, Includes the following steps: Cesium halide, lead bromide, lead chloride, alkaline earth metal bromide, and organic ligand are dissolved in a polar organic solvent and mixed evenly to obtain a precursor solution. The precursor solution was spin-coated onto the substrate and annealed to obtain the bromine-chlorine mixed blue light perovskite film. The perovskite phase corresponding to the alkaline earth metal bromide has a lower solubility in polar organic solvents than CsPbBr3. The alkaline earth metal bromides include at least one of calcium bromide, strontium bromide, and barium bromide; The ratio of the number of moles of alkaline earth metal bromide to the total number of moles of Pb in lead bromide and lead chloride is not greater than 0.

5.

2. The method for preparing the bromine-chlorine mixed blue light perovskite thin film according to claim 1, characterized in that: The organic ligand includes at least one of formamidinium bromide, phenethylamine bromide, p-fluorophenethylamine bromide, and butylamine bromide.

3. The method for preparing a bromine-chlorine mixed blue light perovskite thin film according to claim 1, characterized in that: The alkaline earth metal bromide is barium bromide, and the ratio of the number of moles of barium bromide to the total number of moles of Pb in lead bromide and lead chloride is 0.

1.

4. The method for preparing the bromine-chlorine mixed blue light perovskite thin film according to claim 1, characterized in that: The ratio of the total moles of lead bromide and lead chloride to the moles of cesium halide is 1:

1.

5. The method for preparing a bromine-chlorine mixed blue light perovskite thin film according to claim 1, characterized in that, When spin-coating the precursor solution, the spin-coating speed is 800rpm-5000rpm and the spin-coating time is 5s-80s.

6. The method for preparing a bromine-chlorine mixed blue light perovskite thin film according to claim 5, characterized in that, The spin coating time is 20s-80s. 10s-15s after the spin coating begins, an anti-solvent is dropped onto the substrate surface. The volume of the anti-solvent is 1 / 3-1 / 2 of the volume of the precursor solution.

7. The method for preparing a bromine-chlorine mixed blue light perovskite thin film according to claim 1, characterized in that: The polar organic solvent includes at least one of dimethyl sulfoxide and N,N-dimethylformamide.

8. The method for preparing a bromine-chlorine mixed blue light perovskite thin film according to claim 7, characterized in that: The polar organic solvent comprises dimethyl sulfoxide and N,N-dimethylformamide in a volume ratio of 1:(0.5-2).

9. A bromine-chlorine mixed blue light perovskite thin film, characterized in that, The bromine-chlorine mixed blue light perovskite thin film is prepared by the preparation method of the bromine-chlorine mixed blue light perovskite thin film according to any one of claims 1-8.

10. A perovskite LED device, characterized in that, The perovskite LED device comprises, from bottom to top, an ITO substrate, a hole transport layer, the bromine-chlorine mixed blue light perovskite thin film as described in claim 9, an electron transport layer, an electron injection layer, and an electrode layer.

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