Method for preparing blue light film, blue light film and light-emitting device

Abstract

This invention discloses a method for preparing a blue light-emitting thin film, the blue light-emitting thin film, and a light-emitting device. The method involves dissolving a mixture of cesium bromide, lead bromide, lead chloride, and an organic ligand in dimethyl sulfoxide solvent to obtain a precursor solution. An additional ligand is added to the precursor solution to obtain a perovskite precursor solution. An additive is added to the perovskite precursor solution, and the mixture is stirred for a predetermined first time to obtain a homogeneous solution. The homogeneous solution is then spin-coated in a nitrogen-filled glove box, with an antisolvent added during the spin-coating process to obtain a raw thin film. The raw thin film is annealed and then vacuum-dried to obtain a blue light-emitting perovskite thin film. The above method uses amine salts as organic ligands and small-molecule amine salts as additional ligands, ultimately resulting in a significant improvement in the photoluminescence quantum efficiency, maximum external quantum efficiency, and maximum power efficiency of the prepared blue light-emitting perovskite thin film, as well as achieving high maximum brightness and a stable electroluminescence spectrum.

Description

Technical Field

[0001] This invention relates to the field of light-emitting diode technology, and in particular to a method for preparing a blue light-emitting thin film, the blue light-emitting thin film, and a light-emitting device. Background Technology

[0002] PeLEDs (Organometal halide perovskite LEDs) are comparable to commercially available organic light-emitting diodes (OLEDs) and quantum dot LEDs (QLEDs) in the green, red, and near-infrared regions. However, the development of blue PeLEDs has been slow.

[0003] Currently, although the efficiency of blue PeLEDs has been gradually improved, their performance remains unsatisfactory. Firstly, current research mainly focuses on improvements through single-method engineering (e.g., dimensional engineering, synthesis engineering, or stage engineering), while co-engineering has been rarely studied. Since each engineering method has a different impact on device performance, the lack of understanding of co-engineering may limit performance improvements in blue PeLEDs. Secondly, achieving high efficiency (EQE ≥ 9%) and high brightness (≥ 2000 cd / m²) in blue PeLEDs is a challenge. -2 First, it's quite difficult. Currently, the maximum efficiency of blue PeLEDs is typically achieved at low brightness, and since high brightness is crucial for displays and lighting, the low brightness of blue PeLEDs hinders practical applications. Second, the power efficiency (PE) of blue PeLEDs is generally low. Third, stable color is essential for display applications. However, blue PeLEDs typically exhibit poor spectral stability. Summary of the Invention

[0004] This invention aims to at least solve the technical problems existing in the prior art. To this end, the first aspect of this invention proposes a method for preparing a blue light-emitting thin film, the method comprising:

[0005] A mixture of cesium bromide, lead bromide, lead chloride, and an organic ligand was dissolved in dimethyl sulfoxide to obtain a precursor solution; the organic ligand was phenylethylammonium bromide.

[0006] An additional ligand is added to the precursor solution to obtain a perovskite precursor solution; the additional ligand is a mixture of two or more types of small molecule ammonium salts, including: ammonium salts with small-sized ammonium ions, ammonium salts with large-sized ammonium ions, and ammonium salts with diamines.

[0007] Additives are added to the perovskite precursor solution and stirred for a preset first time to obtain a homogeneous solution;

[0008] In a nitrogen-filled glove box, the homogeneous solution is spin-coated, and an anti-solvent is added during the spin-coating process to obtain the original film;

[0009] The original film was annealed and then vacuum dried to obtain a blue perovskite film.

[0010] Optionally, the ammonium salts having small-sized ammonium ions include: formamidinium hydrobromide, methylammonium bromide, and ethylamine hydrobromide; the ammonium salts having large-sized ammonium ions include: isopropylamine hydrobromide, butylamine hydrobromide, and guanidine hydrobromide; the ammonium salts having diamines include: ethylamine thiourea, ethylenediamine dihydrobromide, 1,3-diaminopropane dihydrobromide, N1,N1-dimethylethane-1,2-diamine dihydrobromide, and 2-aminoacetamidine hydrobromide.

[0011] Optionally, the spin coating of the homogeneous solution, and the addition of an antisolvent during the spin coating process, includes:

[0012] The uniform solution was coated by rotating at 4000 rpm, and timing was started.

[0013] An anti-solvent is added at the start of perovskite crystallization during the spin coating process, and the spin coating ends at 90 seconds; the start of perovskite crystallization is at 22 seconds.

[0014] Optionally, the step of annealing the original film and then vacuum drying it includes:

[0015] The original film was annealed at 65°C for 5 minutes and then vacuum dried.

[0016] Optionally, the antisolvent is ethyl acetate.

[0017] Optionally, the additive is 1,4,7,10,13,16-hexaoxane at a concentration of less than or equal to 20%.

[0018] Optionally, the first duration is 12 to 24 hours.

[0019] A second aspect of the present invention provides a blue light thin film prepared by the method described in the first aspect.

[0020] A third aspect of the present invention provides a light-emitting device, comprising a substrate, a cathode, an anode, and a functional layer between the anode and the cathode; the functional layer comprises a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer, and an electron injection layer stacked sequentially, wherein the light-emitting layer is the blue light-emitting thin film described in the second aspect.

[0021] Optionally, the hole transport layer is a mixture of PEDOT:PSS (model 4083) and deionized purified water in a target ratio.

[0022] The embodiments of the present invention have the following beneficial effects:

[0023] The present invention provides a method for preparing a blue light-emitting thin film, a blue light-emitting thin film, and a light-emitting device. The method involves dissolving a mixture of cesium bromide, lead bromide, lead chloride, and an organic ligand in dimethyl sulfoxide solvent to obtain a precursor solution; the organic ligand is phenylethylammonium bromide; an additional ligand is added to the precursor solution to obtain a perovskite precursor solution; the additional ligand is a mixture of two or more types of small-molecule ammonium salts, including: ammonium salts with small-sized ammonium ions, ammonium salts with large-sized ammonium ions, and ammonium salts with diamines; an additive is added to the perovskite precursor solution, and the mixture is stirred for a preset first time to obtain a homogeneous solution; the homogeneous solution is spin-coated in a nitrogen-filled glove box, and an antisolvent is added during the spin-coating process to obtain a raw thin film; the raw thin film is annealed and then vacuum-dried to obtain a blue light-emitting perovskite thin film. The above-mentioned approach employs a synergistic strategy involving ligand, antisolvent, device, and additive engineering. By using sterically hindered ammonium salts as organic ligands and two or more types of small-molecule ammonium salts as additional ligands, it reduces steric hindrance, strengthens coupling between different phases of the perovskite film, and enhances the conductivity of the perovskite film, thereby improving injection efficiency. Ultimately, this results in significant improvements in the photoluminescence quantum efficiency, maximum external quantum efficiency, and maximum power efficiency of the prepared blue perovskite luminescent film. Furthermore, it also achieves high maximum brightness and a stable electroluminescence spectrum. Attached Figure Description

[0024] Figure 1 A flowchart illustrating a method for preparing a blue light-emitting thin film according to an embodiment of the present invention;

[0025] Figure 2 This is a schematic diagram of the structure of a light-emitting device provided in an embodiment of the present invention;

[0026] Figure 3 A performance comparison diagram of a conventional thin film and the optimized thin film of the present invention is provided for an embodiment of the present invention. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Hereinafter, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of embodiments of this disclosure, unless otherwise stated, "a plurality of" means two or more. Furthermore, the use of "based on" or "according to" implies openness and inclusiveness, because processes, steps, calculations, or other actions "based on" or "according to" one or more of the stated conditions or values ​​may in practice be based on additional conditions or beyond the stated values.

[0029] Metal halide perovskite materials possess advantages such as high luminous quantum efficiency, high color purity, high color saturation, high fluorescence quantum yield, solution-processability, and large-area fabrication, making them well-suited to meet the demands of next-generation display and white light illumination technologies. Compared to traditional GaN-based inorganic light-emitting diodes (LEDs), perovskite LEDs (PeLEDs) offer the advantage of achieving emission across the ultraviolet, infrared, and entire visible light regions by adjusting the perovskite bandgap. Compared to organic light-emitting diodes (OLEDs), PeLEDs exhibit a narrower full width at half maximum (FWHM) and higher color purity. Therefore, PeLEDs can effectively complement inorganic LEDs and OLEDs, and hold promise as an ideal light-emitting device for high-performance display technologies.

[0030] Since Saito's group first observed electroluminescence in liquid nitrogen in 1994, and Friend's group fabricated the first room-temperature PeLED in 2014, PeLEDs have gained popularity among researchers due to their excellent photoelectric properties, simple device structure, and low synthesis cost. In just a few years, the EQE of PeLEDs in the green, red, and near-infrared regions has exceeded 20%, and their stability has improved from minutes to thousands of hours. Their efficiency is comparable to commercially available OLEDs and quantum dot light-emitting diodes (QLEDs). Therefore, PeLEDs are expected to become a strong contender for next-generation display technologies.

[0031] However, the development of blue PeLEDs has been slow, suffering from problems such as low luminous efficiency, low brightness, poor spectral stability, and short lifespan. Furthermore, current research on blue PeLEDs mainly focuses on the sky blue light range, while research on pure blue and deep blue light required for displays is even slower. The highest reported EQE (External Efficiency) for blue PeLEDs is currently 13.8%, making further improvement of the photoelectric performance of blue PeLEDs a key factor in perovskite full-color displays. Researchers have reported several methods for realizing blue PeLEDs, such as compositional engineering through Cl- doping and dimensional engineering based on quantum confinement effects. The former involves adding an appropriate amount of Cl- to the green perovskite precursor solution to extend the perovskite's band gap, causing a blue shift in its emission spectrum; this is the most commonly used method for preparing blue PeLEDs. The latter involves introducing long-chain ligands or organic ammonium salts onto a three-dimensional perovskite base to form layered quasi-two-dimensional perovskites or quantum dots, thereby achieving blue light emission. Therefore, it is not difficult to see that understanding the properties of PeLED and mastering PeLED performance optimization methods are crucial to further enhancing the competitiveness of blue PeLED.

[0032] Currently, although the efficiency of blue PeLEDs has been gradually improved, their performance remains unsatisfactory. First, current research mainly focuses on improvements in single-method engineering (e.g., dimensional engineering, synthesis engineering, or stage engineering), while co-engineering is rarely studied. Since each engineering method has a different impact on device performance, the lack of understanding of co-engineering may limit performance improvements in blue PeLEDs. Second, achieving high efficiency (EQE ≥ 9%) and high brightness (≥ 2000 cd m⁻²) for blue PeLEDs is challenging. Currently, the highest efficiency of blue PeLEDs is typically achieved at low brightness, which hinders practical applications since high brightness is crucial for displays and lighting. Third, the power efficiency (PE) of blue PeLEDs is generally low. Fourth, stable color is essential for display applications. However, blue PeLEDs typically exhibit poor spectral stability.

[0033] In this approach, by employing a synergistic strategy of ligand, antisolvent, device, and additive engineering, the optimized perovskite luminescent film achieves a photoluminescent quantum efficiency (PLQY) greater than 80%, one of the best results for blue perovskite films. The corresponding blue PeLED exhibits a light-induced quantum efficiency greater than 100 cd / m². -2 It exhibits a maximum external quantum efficiency (EQE) greater than 10% at high brightness, with a maximum PE greater than 10 lm / W. -1 In addition, a value greater than 3000 cd m was obtained. -2Maximum brightness and stable electroluminescence spectrum.

[0034] To obtain high-performance blue PeLEDs, a perovskite emitting layer with high radiative recombination efficiency is indispensable. Compared with similar products, quasi-two-dimensional (2D) perovskites have great potential for developing high-performance blue PeLEDs because they can not only ensure a stable exciton system during device operation, but also enable efficient charge and energy transfer between different phases.

[0035] Therefore, the preparation of blue light perovskite thin films was carried out first.

[0036] Figure 1 This is a flowchart illustrating a method for preparing a blue light-emitting thin film according to an embodiment of the present invention. Figure 1 As shown, the method may include the following steps:

[0037] Step 101: Dissolve a mixture of cesium bromide, lead bromide, lead chloride and an organic ligand in an organic solvent to obtain a precursor solution; the organic ligand is phenylethylammonium bromide.

[0038] Specifically, a mixture of 0.1 mmol cesium bromide (CsBr), 0.08 mmol lead bromide (PbBr2), 0.02 mmol lead chloride (PbCl2), and 0.1 mmol phenylethyl ammonium bromide (PEABr) was dissolved in 1 mL of dimethyl sulfoxide (DMSO) solvent to obtain a pristine perovskite precursor solution.

[0039] Among them, the organic solvent can be an ammonium salt with large steric hindrance, such as phenylethylammonium bromide (PEABr).

[0040] CsPb(Br / Cl)3, engineered with ligands, was used to generate blue emission, with phenylethylammonium bromide (PEABr) initially introduced as an organic ligand into the precursor. Experimental results showed that as the PEABr ratio in the precursor increased from 0% to high concentrations (e.g., greater than 60%), the photoluminescence spectrum shifted to the blue region. PEABr plays a crucial role in modulating perovskite properties because appropriate amounts of PEABr can passivate defects and promote low-dimensional phases (n≤4), forming quasi-2D perovskites with a blue-shifted peak.

[0041] Step 102: Add an organic ligand and an additional ligand to the precursor solution to obtain a perovskite precursor solution; the additional ligand is a mixture of two or more types of small molecule ammonium salts, including: ammonium salts with small-sized ammonium ions, ammonium salts with large-sized ammonium ions, and ammonium salts with diamines.

[0042] The high steric hindrance of PEA+ restricts charge and energy transfer between quasi-2D phases, which is detrimental to PeLED. Therefore, introducing two or more additional small-molecule ammonium salts as ligands into the PEA-CsPb(Br / Cl)3 precursor solution can reduce the steric hindrance of PEA+, enhance the conductivity of the perovskite film, and strengthen the coupling between different phases of the perovskite, thereby obtaining a blue perovskite film with high PLQY (Photoluminescence Quantum Yield). The PLQY of this blue perovskite film is much higher than that of the PEA-CsPb(Br / Cl)3 film, with a PLQY increase of more than 4 times.

[0043] Among them, small molecule ammonium salts refer to ammonium salts with smaller molecular weights.

[0044] This scheme classifies small molecule ammonium salts into three categories. The first category consists of ammonium salts with small ammonium ions, which can be incorporated into the crystal lattice after doping with perovskites, with the substituted Cs+ becoming A-site cations. The second category consists of ammonium salts with large ammonium ions, which cause lattice splitting after doping to form layered perovskites, with the ligand phenylethylammonium bromide (PEABr) replacing the ions, effectively reducing the steric hindrance caused by the benzene ring in PEA+. The third category consists of ammonium salts with diamines, which not only help to form DJ-phase quasi-two-dimensional perovskites and passivate defects, but also enhance the coupling between different phases.

[0045] In one possible embodiment, the ammonium salt having small-sized ammonium ions includes: formamidinium hydrobromide, methylammonium bromide, and ethylamine hydrobromide; the ammonium salt having large-sized ammonium ions includes: isopropylamine hydrobromide, butylamine hydrobromide, and guanidine hydrobromide; the ammonium salt having diamines includes: ethylamine thiourea, ethylenediamine dihydrobromide, 1,3-diaminopropane dihydrobromide, N1,N1-dimethylethane-1,2-diamine dihydrobromide, and 2-aminoacetamidine hydrobromide.

[0046] Specifically, the molecular formulas and chemical structures of the aforementioned ammonium salts are shown in Table 1.

[0047] Table 1

[0048]

[0049] Step 103: Add additives to the perovskite precursor solution and stir for a preset first time to obtain a homogeneous solution.

[0050] Additive engineering was used to further enhance the performance of blue PeLEDs. Unlike ligands, additives comprise only a small fraction of the perovskite precursor solution.

[0051] After adding the additive, the precursor solution is stirred for a first time. This first time can be preset based on experience. The purpose of stirring the precursor solution is to make the solution more homogeneous and the reaction more complete.

[0052] In one possible implementation, the additive is 1,4,7,10,13,16-hexaoxane at a concentration of less than or equal to 20%.

[0053] Specifically, 1,4,7,10,13,16-hexaoxane (18-crown-6) is selected as the additive here, and the concentration of the additive is less than or equal to 20%.

[0054] In one possible implementation, the first duration is 12 to 24 hours.

[0055] Step 104: In a nitrogen-filled glove box, the uniform solution is spin-coated, and an anti-solvent is added during the spin-coating process to obtain the original film.

[0056] A glove box is a laboratory device that fills a chamber with high-purity inert gas and circulates it to filter out reactive substances. It is also called a vacuum glove box or inert gas protection chamber. Its main function is to remove O2, H2O, and organic gases.

[0057] Spin coating is a commonly used fabrication method for organic light-emitting diodes (OLEDs). The spin coating method includes three steps: ingredient preparation, high-speed spinning, and evaporation to form a film. The film thickness is controlled by adjusting the spin coating time, spin speed, drop volume, and the concentration and viscosity of the solution used.

[0058] The preceding steps used a large amount of insulating ligands to achieve blue emission, which hinders charge injection and energy coupling in the PeLED, resulting in poor device performance. To overcome this bottleneck, this approach employs antisolvent engineering to remove excess ligands from the perovskite film during device fabrication, which is crucial for ensuring high-performance blue PeLEDs.

[0059] To achieve a dissolution process for pinhole-free perovskite films, this approach developed various methods, such as antisolvent engineering, additive-assisted deposition, vacuum treatment, and interface engineering. Among these, antisolvent engineering has proven to be an effective method for improving the efficiency of perovskite LEDs.

[0060] In one possible implementation, the antisolvent is ethyl acetate.

[0061] The inventors investigated the effects of toluene (Tol), chlorobenzene (CB), and ethyl acetate (EA) as antisolvents on blue perovskite LEDs. The polarities of Tol, CB, EA, and DMSO were 2.4, 2.7, 4.3, and 7.2, respectively. The significant polarity difference between Tol and the mixed solvents hindered their dissolution process. As a result, Tol could not effectively and completely extract DMF and DMSO from the perovskite film, leading to a blurred surface. CB has a higher polarity, thus allowing for more effective solvent extraction. However, CB has a high boiling point (132℃), resulting in a large amount of CB remaining in the film after spin coating. The residual CB volatilizes slowly during the 90℃ heat treatment, leading to surface inhomogeneity and increased roughness.

[0062] EA has suitable polarity and a low boiling point (77 °C). After low-temperature (<100 °C) heat treatment, it can effectively extract the solvent and is easily volatile, thus obtaining the optimal morphology. Therefore, this scheme uses EA as the antisolvent.

[0063] In one possible implementation, step 104 includes:

[0064] Step 1041: Coat the homogeneous solution by rotating it at a speed of 4000 rpm and start timing;

[0065] Step 1042: Add antisolvent when perovskite crystallization begins during the spin coating process, and end the spin coating at 90 seconds; the perovskite crystallization begins at 22 seconds.

[0066] In steps 1041-1042, a perovskite film was prepared in a glove box filled with N2 by spinning a homogenized solution at 4000 rpm for 90 seconds. After spin coating began, 300 ml of EA was introduced as an antisolvent at approximately 22 seconds.

[0067] In antisolvent engineering, the timing of antisolvent addition has a significant impact on perovskite thin films. To obtain high-quality films, the dropping time of antisolvent (EA) was investigated, with perovskite films prepared by using different addition times (i.e., before crystallization, after crystallization, and immediately after crystallization).

[0068] Experimental results showed that the optimal time to add EA was at the beginning of perovskite crystallization. This not only dissolves and removes residual ligands but also does not damage the perovskite layer or the underlying polymer layer. If EA is added before crystallization, ligands in the precursor solution may be pre-washed away, affecting the formation of the quasi-2D phase. If EA is added after crystallization, it may damage the ligands incorporated into the perovskite lattice and create defects. Furthermore, EA significantly enhanced the conductivity of the perovskite film with increasing current density. These facts indicate that introducing antisolvent engineering can improve the performance of blue PELEDs.

[0069] Step 105: After annealing the original film, vacuum dry it to obtain a blue perovskite film.

[0070] Vacuum drying involves placing the raw film to be dried in a sealed drying chamber. While the chamber is being evacuated using a vacuum system, the film is being heated continuously and appropriately. This causes the moisture inside the material to diffuse to the surface through pressure or concentration differences. Water molecules gain sufficient kinetic energy on the film surface and, after overcoming intermolecular attraction, escape into the low-pressure air of the vacuum chamber, where they are then removed by a vacuum pump.

[0071] When the moisture in the original film is dried under vacuum, a blue perovskite film is obtained.

[0072] In one possible implementation, step 105 includes:

[0073] The original film was annealed at 65°C for 5 minutes and then vacuum dried.

[0074] Through multiple experiments, this method determined that 65 degrees Celsius should be selected as the annealing temperature.

[0075] In summary, the method for preparing the blue light perovskite thin film provided in this embodiment of the invention involves dissolving a mixture of cesium bromide, lead bromide, lead chloride, and an organic ligand in dimethyl sulfoxide solvent to obtain a precursor solution; the organic ligand is phenylethyl ammonium bromide; an additional ligand is added to the precursor solution to obtain a perovskite precursor solution; the additional ligand is a mixture of two or more types of small molecule ammonium salts, including: ammonium salts with small-sized ammonium ions, ammonium salts with large-sized ammonium ions, and ammonium salts with diamines; an additive is added to the perovskite precursor solution, and the mixture is stirred for a preset first time to obtain a homogeneous solution; the homogeneous solution is spin-coated in a nitrogen-filled glove box, and an antisolvent is added during the spin-coating process to obtain a raw thin film; the raw thin film is annealed and then vacuum-dried to obtain the blue light perovskite thin film. The above-mentioned approach employs a synergistic strategy involving ligand, antisolvent, device, and additive engineering. By using sterically hindered ammonium salts as organic ligands and two or more types of small-molecule ammonium salts as additional ligands, it reduces steric hindrance, strengthens coupling between different phases of the perovskite film, and enhances the conductivity of the perovskite film, thereby improving injection efficiency. Ultimately, this results in significant improvements in the photoluminescence quantum efficiency, maximum external quantum efficiency, and maximum power efficiency of the prepared blue perovskite luminescent film. Furthermore, it also achieves high maximum brightness and a stable electroluminescence spectrum.

[0076] This invention also provides a blue light thin film, made of... Figure 1 The blue light perovskite thin film was prepared using the method described in the paper.

[0077] pass Figure 1 The blue perovskite luminescent film prepared by the method described above has a photoluminescence quantum efficiency (PLQY) greater than 80%, and the blue PeLED has a wavelength greater than 100 cd / m². -2 It exhibits a maximum external quantum efficiency (EQE) greater than 10% and a maximum power efficiency (PE) greater than 10 lm W at high brightness. -1 In addition, a value greater than 3000 cd m was obtained. -2 Maximum brightness and stable electroluminescence spectrum.

[0078] This invention also provides a light-emitting device, including a substrate, a cathode, an anode, and a functional layer between the anode and the cathode; the functional layer includes a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer, and an electron injection layer stacked sequentially, wherein the light-emitting layer is made of... Figure 1 The blue perovskite luminescent thin film obtained by the preparation method described in the article.

[0079] Specifically, the perovskite electroluminescent device is fabricated on a pre-cleaned ITO (indium tin oxide) glass substrate.

[0080] Figure 2 This is a schematic diagram of the structure of a light-emitting device provided in an embodiment of the present invention.

[0081] like Figure 2 As shown, Glass represents the glass substrate, ITO is the anode, PEDOT:PSS is the hole transport layer (HTL), Perovskites is the light-emitting layer, TPBi is the electron transport layer, LiF is the electron injection layer, and Al is the cathode. The light-emitting layer is the blue perovskite light-emitting thin film of this invention.

[0082] To study the optical properties of different perovskite films and optimize the performance of PeLED, we designed different light-emitting layers: the light-emitting layer of device A is the conventional PEA-CsPb(Br / Cl)3, and the light-emitting layer of device B is the optimized blue perovskite light-emitting film of this invention.

[0083] Figure 3 A performance comparison diagram of a conventional thin film and the optimized thin film of the present invention is provided for an embodiment of the present invention.

[0084] like Figure 3 As shown, the dashed line represents the performance curve of the ordinary thin film of device A, and the solid line represents the performance curve of the optimized blue perovskite luminescent thin film of device B.

[0085] Comparative analysis revealed that the optimized perovskite thin film light-emitting layer exhibited a significant improvement in luminescence efficiency (Photoluminescence Quantum Yield, PLQY).

[0086] Furthermore, comparison revealed that device B exhibits significantly improved performance across various aspects due to its optimized blue perovskite luminescent film emissive layer. Table 2 compares the performance parameters of device A and device B.

[0087] Table 2

[0088]

[0089] In one possible implementation, the hole transport layer is a mixture of PEDOT:PSS (model 4083) and deionized purified water in a target ratio.

[0090] The inventors considered that the unbalanced injection of holes and electrons could cause carriers to accumulate at the interface or recombination sites to shift, leading to severe nonradiative recombination and accelerating perovskite decomposition. Therefore, they studied the balance and regulation of carrier injection.

[0091] Balanced carrier injection involves two aspects: band alignment and mobility matching. The inventors used TPBi as the electron transport layer, which has a mobility of 3.3 × 10⁻⁵ cm²V⁻¹s⁻¹.

[0092] The inventors studied the performance of related devices using six hole transport layers or combinations: PEDOT(4083), PEDOT(8000), NiOx / TFB / PVK, poly-TPD, and PEDOT(4083) / PVK (2 mg / mL and 4 mg / mL). By selecting a more suitable hole transport layer and optimizing related parameters, they obtained perovskite LED devices with injection balance.

[0093] Table 3 shows the experimental results comparing the performance of related devices with six different hole transport layers or combinations.

[0094] Table 3

[0095]

[0096] Based on the analysis of band alignment, mobility matching and experimental results, the inventors believe that PEDOT:PSS(4083) is the most ideal hole transport layer for blue perovskite LEDs.

[0097] Furthermore, the inventors discovered through experiments that the vertical distribution of perovskite grains on the PEDOT:PSS layer is not uniform. The concentration of PEDOT:PSS can be adjusted by adding a target proportion of deionized pure water, thereby changing the thickness of the transport layer, achieving the control of hole and electron recombination sites, further balancing carrier injection and improving radiative recombination efficiency.

[0098] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions within the technical scope disclosed in the present invention should be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a blue light-emitting thin film, characterized in that, include: A mixture of cesium bromide, lead bromide, lead chloride, and organic ligands was dissolved in dimethyl sulfoxide to obtain a precursor solution. The organic ligand is brominated phenylethylammonium; An additional ligand is added to the precursor solution to obtain a perovskite precursor solution; The additional ligand is a mixture of two or more types of small molecule ammonium salts, including: ammonium salts with small-sized ammonium ions, ammonium salts with large-sized ammonium ions, and ammonium salts with diamines. Additives are added to the perovskite precursor solution and stirred for a preset first time to obtain a homogeneous solution; In a nitrogen-filled glove box, the homogeneous solution is spin-coated, and an anti-solvent is added during the spin-coating process to obtain the original film; The original film was annealed and then vacuum dried to obtain a blue light perovskite film. The ammonium salts having small-sized ammonium ions include: formamidinium hydrobromide, methylammonium bromide, and ethylamine hydrobromide; the ammonium salts having large-sized ammonium ions include: isopropylamine hydrobromide, butylamine hydrobromide, and guanidine hydrobromide.

2. The method according to claim 1, characterized in that, The ammonium salts containing diamines include: thiourea, ethylenediamine dihydrobromide, 1,3-diaminopropane dihydrobromide, N1,N1-dimethylethane-1,2-diamine dihydrobromide, and 2-aminoacetamidine hydrobromide.

3. The method according to claim 1, characterized in that, The step of spin-coating the homogeneous solution, and adding an anti-solvent during the spin-coating process, includes: The uniform solution was coated by rotating at 4000 rpm, and timing was started. An anti-solvent is added at the start of perovskite crystallization during the spin coating process, and the spin coating ends at 90 seconds; the start of perovskite crystallization is at 22 seconds.

4. The method according to claim 1, characterized in that, The process of vacuum drying the original film after annealing includes: The original film was annealed at 65°C for 5 minutes and then vacuum dried.

5. The method according to claim 1, characterized in that, The antisolvent is ethyl acetate.

6. The method according to claim 1, characterized in that, The additive is 1,4,7,10,13,16-hexaoxane at a concentration of less than or equal to 20%.

7. The method according to claim 1, characterized in that, The first duration is 12 to 24 hours.

8. A blue light-emitting thin film, characterized in that, Prepared by the method described in any one of claims 1-7.

9. A light-emitting device, characterized in that, It includes a substrate, a cathode, an anode, and a functional layer between the anode and the cathode; the functional layer includes a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer, and an electron injection layer stacked in sequence, wherein the light-emitting layer is the blue light thin film as described in claim 8.

10. The device according to claim 9, characterized in that, The hole transport layer is a mixture of PEDOT:PSS (model 4083) and deionized purified water in a target ratio.

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