Method for preparing perovskite structure layer and light emitting diode

Abstract

The present disclosure relates to the technical field of perovskite light-emitting diode, and particularly relates to a preparation method of perovskite structure layer and a light-emitting diode. The preparation method comprises the following steps: mixing a chlorinated hydrocarbon and a nucleophile to perform a nucleophilic substitution reaction and form an ion exchange solution, the ion exchange solution comprising chloride ions; coating the ion exchange solution on the surface of a perovskite thin film, the chloride ions in the ion exchange solution exchange with bromide ions on the surface of the perovskite thin film, so as to replace part of the bromide ions on the surface of the perovskite thin film with chloride ions, and obtain a perovskite structure layer and a mixed solution formed on the surface of the perovskite structure layer, the mixed solution comprising a brominated hydrocarbon and a nucleophile; the polarity of the chlorinated hydrocarbon and the brominated hydrocarbon is not greater than 4. The present disclosure realizes controllable chlorine doping and halogen exchange through a mild in-situ nucleophilic substitution reaction, and simultaneously optimizes the color purity, light-emitting efficiency and working stability of a deep blue perovskite light-emitting diode under the premise of reducing or avoiding damage to perovskite crystals.

Description

Technical Field

[0001] This disclosure belongs to the field of perovskite light-emitting diode technology, specifically relating to a method for preparing a perovskite structural layer and a light-emitting diode. Background Technology

[0002] Currently, there are generally two methods for preparing high-performance deep blue PeLEDs (Perovskite Light-Emitting Diodes): one is to directly add chloride salts to the perovskite precursor solution, since chloride ions (Cl...) - Its solubility in common solvents is much lower than that of bromide ions (Br). - The precursor solution easily forms localized inhomogeneous regions rich in Br and Cl. Another method involves dissolving chloride salts in isopropyl alcohol (IPA) solution and then spin-coating or impregnating the solution onto the surface of the pre-formed perovskite film. Due to the high polarity of isopropyl alcohol, it easily dissolves or erodes the perovskite grain surface, disrupting the original continuous and dense morphology, leading to pores, cracks, or grain boundary deterioration in the film. This damage introduces new nonradiative recombination centers and disrupts the interfacial contact between the perovskite and the charge transport layer, resulting in decreased carrier injection efficiency and increased leakage current. Summary of the Invention

[0003] The purpose of this disclosure is to provide a method for preparing a perovskite structure layer and a light-emitting diode, which can reduce or avoid damage to the perovskite crystal and improve the color purity, luminous efficiency and working stability of the deep blue perovskite light-emitting diode.

[0004] This disclosure provides a method for preparing a perovskite structure layer, including:

[0005] Provide perovskite thin films; A chlorinated hydrocarbon and a nucleophile are provided, which are mixed to carry out a nucleophilic substitution reaction and form an ion exchange solution comprising a reaction intermediate and chloride ions; The ion exchange solution is coated onto the surface of the perovskite film. Chloride ions in the ion exchange solution exchange with bromide ions on the surface of the perovskite film to replace some of the bromide ions with chloride ions, thereby obtaining the perovskite structural layer and a mixed solution formed on the surface of the perovskite structural layer. The mixed solution includes a brominated hydrocarbon formed by the reaction of the reaction intermediate with the bromide ions and the nucleophile; wherein the polarity of the chlorinated hydrocarbon and the brominated hydrocarbon is not greater than 4. Remove the mixed solution.

[0006] In one exemplary embodiment of this disclosure, the polarity of the chlorinated hydrocarbon and the bromine hydrocarbon ranges from 3.0 to 4.0.

[0007] In one exemplary embodiment of this disclosure, the chlorinated hydrocarbon is a benzyl-type aromatic chlorinated hydrocarbon.

[0008] In one exemplary embodiment of this disclosure, the chlorinated hydrocarbon is benzyl chloride.

[0009] In one exemplary embodiment of this disclosure, the nucleophile is either a trialkylphosphine or a trialkylamine.

[0010] In one exemplary embodiment of this disclosure, the nucleophile is tripropylphosphine.

[0011] In one exemplary embodiment of this disclosure, the nucleophile in the ion exchange solution has a volume fraction of 0.03 vol.

[0012] In one exemplary embodiment of this disclosure, the perovskite film is an all-inorganic three-dimensional perovskite.

[0013] In one exemplary embodiment of this disclosure, the preparation steps of the perovskite thin film include: A perovskite precursor solution is prepared, wherein the solutes in the perovskite precursor solution are weighed according to a molar ratio of tetraphenylphosphonium bromide: cesium bromide: lead bromide: lead chloride of 0.075:1.5:0.37:0.63, and the total mass fraction of the four solid solutes in the perovskite precursor solution is 10 wt.%; the solvent in the perovskite precursor solution is mixed with dimethyl sulfoxide and deionized water at a volume ratio of 920:80; the weighed solid solutes are added to the mixed solvent and stirred until the solutes are completely dissolved to obtain the perovskite precursor solution; A substrate is provided, and the perovskite precursor solution is spin-coated onto the substrate and annealed to form the perovskite thin film.

[0014] This disclosure provides a light-emitting diode comprising, in sequence: an anode, a hole transport layer, a perovskite structure layer as described above, an electron transport layer, an electron injection layer, and a cathode.

[0015] The technical solution provided in this disclosure has at least the following advantages: This disclosure proposes a method for preparing high-performance deep blue PeLEDs based on chlorinated hydrocarbon solvent-assisted halogen exchange. It uses a low-polarity chlorinated hydrocarbon with a polarity not exceeding 4 as the halogen exchange reaction medium, combined with a nucleophilic reagent. Through a mild in-situ nucleophilic substitution reaction, controllable chlorine doping and halogen exchange are achieved. This method simultaneously optimizes the color purity, luminous efficiency, and operational stability of deep blue PeLEDs while minimizing or avoiding damage to the microstructure of the perovskite thin film, effectively overcoming the bottlenecks of traditional technologies.

[0016] Other features and advantages of this disclosure will become apparent from the following detailed description, or may be learned in part from practice of this disclosure.

[0017] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit this disclosure. Attached Figure Description

[0018] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure. It is obvious that the drawings described below are merely some embodiments of this disclosure, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0019] Figure 1 A flowchart illustrating the method for preparing the perovskite structure layer in an embodiment of this disclosure is shown.

[0020] Figure 2 The bond-line structural formula of benzyl chloride in an embodiment of this disclosure is shown.

[0021] Figure 3 The bond-line structural formula of tripropylphosphine in an embodiment of this disclosure is shown.

[0022] Figure 4 The bond-line structural formula of tributylphosphine in an embodiment of this disclosure is shown.

[0023] Figure 5 The bond-line structural formula of tripropylamine in the embodiments of this disclosure is shown.

[0024] Figure 6 A schematic diagram of the nucleophilic substitution reaction of tripropylphosphine with benzyl chloride in an embodiment of this disclosure is shown.

[0025] Figure 7 A schematic diagram illustrating the mechanism of halogen exchange and defect repair of perovskite thin films by the tripropylphosphine-benzyl chloride system in the embodiments of this disclosure is shown.

[0026] Figure 8 The deep blue PeLED electroluminescence spectrum of an embodiment of this disclosure is shown.

[0027] Figure 9 A CIE coordinate diagram of a deep blue PeLED in an embodiment of this disclosure is shown.

[0028] Figure 10 The JV curve and LV curve of the deep blue PeLED in the embodiments of this disclosure are shown.

[0029] Figure 11 The J-EQE curve of a deep blue PeLED in an embodiment of this disclosure is shown.

[0030] Figure 12 The stability test curve of the deep blue PeLED in the embodiment of this disclosure is shown.

[0031] Figure 13 The diagram shows the CIE color coordinate variation curves of the deep blue PeLED under different bias voltages in the embodiments of this disclosure.

[0032] Figure 14 A schematic diagram of the structure of a light-emitting diode in an embodiment of this disclosure is shown.

[0033] Explanation of reference numerals in the attached figures: 1. Anode; 2. Hole transport layer; 3. Perovskite structure layer; 4. Electron transport layer; 5. Electron injection layer; 6. Cathode. Detailed Implementation

[0034] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided so that this disclosure will be more thorough and complete, and will fully convey the concept of the exemplary embodiments to those skilled in the art.

[0035] Furthermore, the described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. Numerous specific details are provided in the following description to give a thorough understanding of embodiments of this disclosure. However, those skilled in the art will recognize that the technical solutions of this disclosure can be practiced without one or more of the specific details, or other methods, components, apparatuses, steps, etc., can be employed. In other instances, well-known methods, apparatuses, implementations, or operations are not shown or described in detail to avoid obscuring various aspects of this disclosure.

[0036] The present disclosure will now be described in further detail with reference to the accompanying drawings and specific embodiments. It should be noted that the technical features involved in the various embodiments of the present disclosure described below can be combined with each other as long as they do not conflict with each other. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present disclosure, and should not be construed as limiting the present disclosure.

[0037] PeLEDs are considered a core contender for next-generation display technology due to their advantages such as high color purity, high brightness, and solution-processability. Currently, the performance of red and green PeLEDs is close to commercial levels, but the development of high-performance deep blue PeLEDs that meet the Rec.2020 standard color coordinates (0.131, 0.046) still faces significant technical bottlenecks. The key to achieving deep blue light emission lies in increasing the chlorine (Cl) content in the perovskite lattice.

[0038] Currently, there are generally two methods for preparing high-performance deep blue PeLEDs: one is high chloride doping, which involves directly increasing the chloride content in the perovskite precursor solution, because Cl... - Its solubility in common solvents is much lower than that of Br. - The precursor solution readily forms localized inhomogeneous regions rich in Br and Cl. During spin-coating and annealing crystallization, the differences in halogen composition in different regions lead to the separation of the Cl-rich and Br-rich phases, forming a non-uniform mixed halide perovskite. This phase separation induces lattice distortion, generating numerous halogen vacancy defects and deep-level trap states. These defects become non-radiative recombination centers, severely reducing the photoluminescence quantum yield and device efficiency of the thin film.

[0039] Another method involves dissolving chloride salts in isopropanol and then spin-coating or impregnating the solution onto the surface of the pre-formed perovskite film. Isopropanol, being highly polar, readily dissolves or erodes the perovskite grain surface, disrupting the original continuous and dense morphology and leading to pores, cracks, or grain boundary deterioration in the film. This damage introduces new non-radiative recombination centers and disrupts the interfacial contact between the perovskite and the charge transport layer, resulting in decreased carrier injection efficiency and increased leakage current.

[0040] Furthermore, to achieve deep blue light emission, the two methods described above introduce high Cl content, typically with a Cl / Br molar ratio >30%. However, high Cl content reduces the tolerance factor of perovskite, causing lattice distortion and decreased crystal structure stability. Simultaneously, Cl-related defects (such as chlorine vacancies and interstitial chlorine) have low formation energies, easily generating in large numbers within the lattice, forming deep-level traps. These traps efficiently trap charge carriers and release energy through non-radiative recombination, leading to a sharp decrease in the PLQE (Photoluminescence Quantum Efficiency) of the perovskite thin film and the EQE (External Quantum Efficiency) of the ultimately fabricated device. Therefore, the two methods described above often fall into the dilemma of "the greater the blue shift, the lower the efficiency," making it difficult to simultaneously meet the Rec.2020 standard and high-performance requirements.

[0041] To address the aforementioned technical problems, this disclosure provides a method for preparing a perovskite structural layer, such as... Figure 1 As shown, the preparation method may include: S1. Provide perovskite thin films; S2. Provide a chlorinated hydrocarbon and a nucleophile, mix them to carry out a nucleophilic substitution reaction, and form an ion exchange solution, which includes the reaction intermediates and chloride ions; S3. An ion exchange solution is coated onto the surface of a perovskite film. Chloride ions in the ion exchange solution exchange with bromide ions on the surface of the perovskite film to replace some of the bromide ions on the surface of the perovskite film with chloride ions, thereby obtaining a perovskite structural layer and a mixed solution formed on the surface of the perovskite structural layer. The mixed solution includes a brominated hydrocarbon formed by the reaction of reaction intermediates with bromide ions and a nucleophile; wherein the polarity of the chlorinated hydrocarbon and the brominated hydrocarbon is not greater than 4. S4. Remove the mixed solution.

[0042] It should be noted that solvent polarity is usually characterized by the polarity parameter (Rohrschneider Polarity Index) proposed by the chromatographic expert Rohrschneider, which is denoted by P'. In this disclosure, the polarity of chlorinated and bromine hydrocarbons is P'≤4.

[0043] This disclosure proposes a method for preparing high-performance deep blue PeLEDs based on chlorinated hydrocarbon solvent-assisted halogen exchange. The method uses low-polarity chlorinated hydrocarbons with a polarity of no more than 4 as the halogen exchange reaction medium, combined with nucleophilic reagents, to achieve controllable chlorine doping and halogen exchange through a mild in-situ nucleophilic substitution reaction. While reducing or avoiding damage to the perovskite thin film crystal, the method simultaneously optimizes the color purity, luminous efficiency, and working stability of deep blue PeLEDs, effectively breaking through the bottlenecks of traditional technologies.

[0044] Specifically, this disclosure abandons the process approach of directly adding chloride salts to the precursor solution, thus improving the halogen phase separation problem in perovskite films. This disclosure first prepares a perovskite film with low chloride content and uniform composition. This film exhibits excellent crystallinity and is free from Cl- and Br-rich component segregation and phase separation defects. Based on this, a mild nucleophilic substitution reaction between chlorinated hydrocarbons and nucleophiles is utilized to controllably and slowly release chloride ions onto the perovskite film surface. These chloride ions then undergo halogen exchange with bromide ions on the perovskite film surface, regulating the surface composition of the perovskite film, achieving a blue shift in the spectrum, and preserving the original uniform crystal composition and single crystalline phase within the film, thereby improving the bulk halogen phase separation problem.

[0045] Meanwhile, compared with highly polar solvents such as isopropanol, this disclosure uses low-polarity chlorinated hydrocarbons as the reaction medium, which reduces or avoids the dissolution and erosion of perovskite grains. In the entire post-processing process, the complete grain morphology, grain boundary structure and overall compactness of the perovskite film can be basically preserved, reducing or avoiding the generation of secondary defects such as pores, cracks and morphology collapse, reducing or avoiding non-radiative recombination loss caused by solvent damage, and improving the preparation yield of high-quality deep blue light perovskite structure layers with low defect density.

[0046] The perovskite structure layer disclosed herein can be used as the light-emitting layer in a light-emitting diode (PED). This disclosure, through a non-destructive and controllable halogen exchange process, largely preserves the integrity of the perovskite lattice, effectively reducing the growth of intrinsic defects such as chloride vacancies and interstitial chloride, significantly suppressing defect-induced halide ion migration and non-radiative recombination effects, and significantly improving carrier transport stability. Simultaneously, the well-preserved thin-film morphology optimizes the interfacial compatibility between the perovskite structure layer and the charge transport layers (such as hole and electron transport layers) in the PeLED, improving the degradation problem of the light-emitting diode caused by interfacial charge accumulation, and effectively enhancing the long-term operational stability of deep blue PeLEDs. The improved stability of the light-emitting diode significantly reduces replacement and maintenance costs in display applications, laying a cost foundation for commercialization.

[0047] In other words, this disclosure achieves efficient chlorine doping of perovskite and meets the Rec.2020 deep blue light color gamut standard through a mild and non-destructive halogen exchange strategy, while maximizing the crystal quality within the perovskite structure layer and the photoelectric performance of the light-emitting diode. This breaks the dilemma of "blue shift and efficiency being mutually exclusive" in traditional processes, and can produce deep blue light PeLEDs with high color purity, high efficiency, and high stability. These PeLEDs are well-suited for perovskite full-color wide color gamut display scenarios and have extremely high application value.

[0048] In some embodiments, the polarity of chlorinated hydrocarbons and bromine hydrocarbons can range from 3.0 to 4.0.

[0049] For example, the polarity of chlorinated and bromine hydrocarbons can be: 3, 3.1, 3.2, 3.4, 3.5, 3.6, 3.8, 4, etc.

[0050] This disclosure improves the problem of excessively high solvent polarity corroding perovskite films by ensuring that the polarity of the chlorinated hydrocarbon is no greater than 4, reducing or preventing the diffusion of chloride ions into the bulk phase of the perovskite film, and ensuring that only surface halogen exchange occurs in the perovskite film. By ensuring that the polarity of the chlorinated hydrocarbon is no less than 3, it ensures that the solvent has sufficient halogen exchange reaction activity, avoiding the inability to trigger the surface halogen exchange reaction due to insufficient polarity, ensuring the smooth progress of chlorine doping, thereby accurately achieving blue shift modulation of the target emission wavelength and meeting the color gamut requirements of deep blue light emission.

[0051] This disclosure improves the problem of excessively high polarity of brominated hydrocarbons eroding the perovskite lattice by ensuring that the polarity of the brominated hydrocarbons generated on the surface of the perovskite structure layer after the halogen reaction is no greater than 4. At the same time, it reduces the adsorption and binding force of brominated hydrocarbons on the film surface, making it easier to remove them later. By ensuring that the polarity of the brominated hydrocarbons is no less than 3, the generated brominated hydrocarbons can be stably dissolved in the mixed solution on the film surface, avoiding the precipitation of particulate impurities on the film surface and preventing the introduction of local non-radiative recombination defects.

[0052] In some embodiments, the chlorinated hydrocarbon is a benzyl-type aromatic chlorinated hydrocarbon, which has both low polarity and high nucleophilic substitution activity.

[0053] Specifically, in benzyl aromatic chloroalkanes, the chlorine atom is bonded to an sp³ hybridized saturated carbon atom, and the halogen atom in the benzyl aromatic chloroalkane is separated from the unsaturated carbon atom of the benzene ring by this saturated carbon atom. During nucleophilic substitution reactions, the empty p orbitals of the carbocation intermediate formed after halogen departure can conjugate and overlap with the large π bond of the benzene ring, delocalizing the positive charge on the intermediate and dispersing it to the ortho and para positions of the benzene ring. This effectively lowers the activation energy, increases the stability of the carbocation intermediate, and facilitates the departure of halide ions, making nucleophilic substitution reactions easier and at a suitable rate. In contrast, ordinary haloalkanes (such as chloroform) dissociate to form alkyl carbocations, which are sp² hybridized. The empty p orbitals lack conjugable adjacent π bonds, and the positive charge is concentrated on a single carbon atom. These intermediates have high energy and poor stability, making nucleophilic substitution reactions difficult to proceed smoothly and hindering the stable and controllable release of halide ions as a halogen source for ion exchange.

[0054] Meanwhile, the low overall solvent polarity of benzyl aromatic chlorinated hydrocarbons can reduce or avoid dissolution and erosion of perovskite films. During post-processing, the perovskite grain morphology, grain boundary structure, and film compactness can be largely preserved, reducing or avoiding porosity, cracks, and secondary defects caused by solvent damage. The halogen exchange reaction occurs on the surface of the perovskite film. The halide ions released by the benzyl aromatic chlorinated hydrocarbons participate in the halogen exchange on the surface of the perovskite film, which basically does not damage the internal crystal structure of the perovskite film. This is beneficial to maintaining the single crystal phase of the perovskite bulk and improving the bulk phase separation problem. The polarity of the brominated byproducts generated by the reaction (i.e., brominated hydrocarbons in the mixed solution) matches the target polarity range (i.e., polarity of 3~4), and can dissolve in the mixed solution on the surface of the perovskite structural layer, which is convenient for subsequent removal and reduces the introduction of non-radiative recombination centers by impurity residues.

[0055] like Figure 2 As shown, further, among the many benzyl-type aromatic chlorinated hydrocarbons, the chlorinated hydrocarbon can be selected as benzyl chloride (BC).

[0056] Compared to other benzyl chloride derivatives with electron-donating, electron-withdrawing, or ortho-substituent groups on the benzene ring, benzyl chloride exhibits no additional electronic effects or steric hindrance. It relies solely on the intrinsic large π bond of the benzene ring for charge delocalization, resulting in a moderate activation energy and high overall nucleophilic substitution reactivity. Only a trace amount of the nucleophile TPP is needed to efficiently release chloride ions, facilitating subsequent halide ion exchange reactions on the perovskite film surface. This fundamentally avoids the corrosion and degradation of subsequent deep blue perovskite films caused by excessive nucleophile introduction. This characteristic allows for precise, slow, and stable chloride ion release, mitigating the problems of instantaneous chloride ion enrichment, interstitial chloride defect surges, and local lattice distortion caused by excessively high reactivity in substituted benzyl chlorides. It also addresses the deficiencies of insufficient chloride source supply and substandard blue shift in the spectrum caused by low reactivity. Meanwhile, benzyl chloride is a commercially available liquid reagent with readily available raw materials, controllable costs, and strong compatibility. It is perfectly suited for spin-coating solution processing technology, with a wide process window and good repeatability, making it more suitable for the large-scale preparation of high-performance deep blue perovskite light-emitting diodes.

[0057] The nucleophile in this disclosure should have strong nucleophilicity. For example, in some embodiments, the nucleophile may be selected from either trialkylphosphine or trialkylamine.

[0058] Trialkylphosphine and trialkylamine have phosphorus and nitrogen atoms as their central atoms, respectively. Both central atoms possess lone pairs of electrons, enabling them to donate electron pairs to carbon atoms in chloroalkyl molecules, thereby initiating nucleophilic substitution reactions and releasing chloride ions. This provides a chlorine source for halogen exchange on the surface of perovskite films. Their alkyl substituents are selected from C1-C6. 10 Alkyl groups, whether straight-chain or branched, are chemically stable and do not readily undergo side reactions. Trialkylphosphine, in particular, has a lower electronegativity and larger atomic radius in its phosphorus atom, resulting in a stronger nucleophilic attack capability. It can efficiently undergo nucleophilic substitution reactions under mild conditions, achieving a stable release of halide ions. Trialkylamines achieve nucleophilicity through the lone pair of electrons on their nitrogen atom and can be used as alternative nucleophiles.

[0059] This disclosure selects trialkylphosphine or trialkylamine as nucleophiles to perform liquid-phase post-treatment on the surface of perovskite thin films. This allows for the controlled release of halide ions via nucleophilic reactions under ambient temperature and pressure, ensuring that bromine-chlorine exchange occurs primarily on the surface of the perovskite film. This improves upon the problem of localized chlorine enrichment caused by the instantaneous release of large amounts of chloride ions, reducing the formation of defects such as interstitial chlorine. It maintains the internal crystal composition and single-phase structure of the perovskite film while suppressing bulk phase separation. The saturated alkyl groups in these reagents are chemically inert and do not introduce additional impurities or defects. Furthermore, these reagents maintain good solubility in benzyl-type aromatic chlorocarbons, facilitating the preparation of ion exchange solutions and adapting to solution processing techniques such as spin coating. All nucleophiles used are conventional organic chemical raw materials, inexpensive and readily available.

[0060] For example, such as Figures 3 to 5 As shown, the nucleophile in this disclosure can be one of tripropylphosphine (TPP), tributylphosphine (TBP), or tripropylamine (TAA).

[0061] Preferably, TPP can be used as the nucleophile in this disclosure. Compared with other nucleophiles of the trialkylamine class, the central phosphorus atom of TPP has a large atomic radius and low electronegativity, resulting in a stronger nucleophilic attack capability. It can efficiently attack the benzylic sp³ carbon atom in BC that is connected to the chlorine atom, causing nucleophilic substitution and releasing chloride ions. The benzylic phosphonium cation intermediate generated by the reaction achieves positive charge delocalization through the conjugation of the benzene ring π bond. The intermediate has high stability, and the reaction can be carried out under mild conditions in the liquid phase at room temperature. The phosphonium salt obtained by the reaction can be distributed in the perovskite grain boundaries, which has a binding effect on interstitial chlorine, inhibits ion migration, reduces non-radiative recombination, and improves device stability. This passivation effect is better than that of the ammonium salt generated by the reaction of trialkylamine.

[0062] Furthermore, the ion exchange solution composed of TPP and BC, compared to the solution of TPP with ordinary haloalkanes, exhibits superior nucleophilic activity. Ordinary haloalkanes, after reaction, generate alkyl carbocations, which lack conjugation effects, have concentrated positive charges, and exhibit high and unstable intermediate energy, making effective nucleophilic substitution difficult and hindering stable chloride ion supply. In contrast, BC, being a benzyl-type aromatic chloroalkane, allows for conjugation delocalization of reaction intermediates, resulting in a low activation energy and controllable chloride ion release. Simultaneously, BC's polarity falls within the target polarity range, preventing corrosion of the perovskite film, and facilitating the removal of reaction byproducts (bromoalkanes). Compared to the solution of trialkylamines with BC, TPP demonstrates higher nucleophilic activity, fully leveraging the structural advantages of BC. The moderate chloride ion generation rate achieves sufficient bromine-chlorine exchange on the perovskite film surface while reducing or avoiding interstitial chloride defects caused by localized chloride enrichment. Furthermore, the phosphonium salt provides superior defect passivation, contributing to the formation of low-defect perovskite structural layers and highly stable light-emitting devices.

[0063] In some embodiments, the nucleophile in the ion exchange solution has a volume fraction of 0.03 vol%.

[0064] For example, when the chlorinated hydrocarbon is BC and the nucleophile is TPP, TPP and BC can be mixed and stirred at room temperature in a glove box for 2 hours to allow the two to fully undergo a nucleophilic reaction, thereby preparing an ion exchange solution in which the volume fraction of the nucleophile in the ion exchange solution is 0.03 vol.

[0065] By limiting the volume fraction of the nucleophile in the ion exchange solution to 0.03 vol%, the total amount of nucleophile available for reaction in the ion exchange solution is very small, thus only a very small amount of Cl can be slowly released per unit time. - It does not instantly generate high concentrations of chloride ions that penetrate into the film, thus enabling surface halogen exchange in perovskite films, reducing or avoiding damage to the internal crystal structure of the film, and effectively reducing or suppressing the occurrence of bulk phase separation.

[0066] Meanwhile, the concentration of the nucleophile directly determines the release rate and total amount of chloride ions. By precisely limiting and adjusting the volume fraction of the nucleophile in the ion exchange solution, the number of chloride ions entering the perovskite lattice can be continuously and linearly controlled, achieving precise linear control of halogen doping. With increasing nucleophile volume fraction, the PL (Photoluminescence) peak of the perovskite film achieves a linear blue shift, gradually shifting the emission peak from sky blue to deep blue, enabling precise and predictable adjustment of the emission wavelength. This solves the problems of low halogen doping control precision, poor perovskite bandgap adjustment precision, and large emission peak position deviation in related technologies. It precisely meets the stringent requirements of the Rec.2020 standard for deep blue color coordinates without the need for complex, multiple process trials. Under this precise and controllable halogen exchange regulation, the final deep blue perovskite LED exhibits higher EQE and better long-term operational stability.

[0067] In some embodiments, the perovskite film is an all-inorganic three-dimensional perovskite.

[0068] Compared to organic-inorganic hybrid perovskites, this disclosure uses an all-inorganic CsPb(Br / Cl)3 perovskite system, which has higher thermal and chemical stability. All-inorganic perovskites have good tolerance to low-polarity haloalkanes solvents and will not undergo side reactions with nucleophiles or reaction intermediates during ion exchange, ensuring the purity and efficiency of nucleophilic substitution reactions.

[0069] After ion exchange, the all-inorganic three-dimensional perovskite retains its single three-dimensional crystal structure, inheriting the intrinsic characteristics of high carrier mobility and excellent carrier transport efficiency, which is beneficial for realizing high-brightness and high-efficiency deep blue light-emitting diodes (LEDs). Halogen exchange is performed based on this all-inorganic three-dimensional perovskite, and deep blue light emission is achieved by controlling the band gap through chloride-bromine ion exchange, while avoiding the insulating ligand effect and Auger recombination problem present in low-dimensional perovskites. When the perovskite structure layer obtained by halogen exchange of the all-inorganic three-dimensional perovskite with an ion exchange solution is applied to an LED, it can achieve balanced carrier injection and efficient recombination, enabling the LED to achieve high brightness at low driving voltage, thus solving the problem of insufficient brightness in deep blue PeLEDs.

[0070] Inorganic Cs + Cations compared to organic cations (MA) + FA + It is not easily decomposed and has strong tolerance to low polarity solvents. It can maintain the integrity of the crystal lattice during ion exchange post-treatment and subsequent annealing, avoiding film collapse and defect surge caused by organic component degradation, and further ensuring film quality and device working stability.

[0071] Compared to the long-chain organic ligands prepared from traditional low-dimensional perovskites, the raw material cost of preparing all-inorganic three-dimensional perovskites disclosed in this invention is significantly reduced.

[0072] In some embodiments, the preparation steps of the perovskite thin film include: preparing a perovskite precursor solution, wherein the solutes in the perovskite precursor solution are weighed according to a molar ratio of tetraphenylphosphonium bromide (TPPB): cesium bromide (CsBr): lead bromide (PbBr2): lead chloride (PbCl2) of 0.075:1.5:0.37:0.63 (Cl / Br=35%), and the total mass fraction of the four solid solutes in the perovskite precursor solution is 10 wt.%; the solvent in the perovskite precursor solution is mixed with dimethyl sulfoxide (DMSO) and deionized water (H2O) at a volume ratio of 920:80; the weighed solid solutes are added to the mixed solvent and stirred until the solutes are completely dissolved to obtain the perovskite precursor solution. Next, a substrate is provided, the perovskite precursor solution is spin-coated onto the substrate, and annealing is performed to form a perovskite thin film.

[0073] For example, the mixed solvent can be heated and stirred at 90°C for 4 hours to obtain a perovskite precursor solution.

[0074] The prepared perovskite precursor solution was uniformly spin-coated onto the substrate surface. The spin-coating parameters could be set to a spin speed of 6000 rpm and a spin-coating time of 45 s. After spin-coating, the substrate was annealed at 130°C for 10 min to remove residual solvent and complete crystallization, thus preparing the perovskite thin film. Subsequently, a pre-prepared ion exchange solution (e.g., TPP / BC ion exchange solution) was uniformly spin-coated onto the surface of the prepared perovskite thin film. The spin-coating parameters could be set to 6000 rpm and a spin-coating time of 45 s. After spin-coating, the substrate was allowed to stand at room temperature for 10 s to allow the ion exchange solution to fully wet the perovskite thin film surface and undergo a mild nucleophilic substitution and halogen exchange reaction, thus completing the surface halogen exchange of the perovskite thin film.

[0075] This disclosure allows for systematic optimization of multiple dimensions, including chlorine content, lattice stability, film quality, and emission wavelength, by limiting the solid solute ratio in the perovskite precursor solution. Compared to the preparation method of directly adding high-concentration chloride salts to the perovskite precursor solution, this disclosure first prepares an all-inorganic perovskite film with low chlorine content. This film has uniform crystallization and no separation of Cl-rich and Br-rich phases, which can reserve space for precise control of subsequent ion exchange.

[0076] Furthermore, this disclosure utilizes a solution spin-coating method throughout the preparation process. This method is simple, requires no sophisticated and expensive equipment, and avoids harsh conditions such as high temperature and high pressure. Material costs are controllable, and it is easily integrated with existing PeLED fabrication processes. It is well-suited for existing display panel mass production processes and possesses excellent potential for large-scale industrial production. Spin-coating relies on centrifugal force to remove excess solution, ultimately forming an ultrathin liquid film on the perovskite film surface. During halogen exchange, chloride ions can only exchange with surface bromide ions and cannot penetrate into the bulk phase, thus inhibiting bulk phase separation at its source.

[0077] Taking BC as a chlorinated hydrocarbon, TPP as a nucleophile, and an all-inorganic three-dimensional perovskite as a perovskite thin film as an example, such as Figures 6 to 7 As shown, the nucleophile TPP attacks the carbon atom (C) bonded to the Cl atom in the chlorinated hydrocarbon BC, while the P atom in the strong nucleophile TPP attacks the Cl atom on BC, forming the tripropylphosphine benzyl carbocation intermediate (C3H7)3P-PhCH2. + and release Cl - This process provides a Cl source for subsequent ion exchange (corresponding to a nucleophilic reaction). In benzyl-type aromatic chloroalkanes, the chlorine atom is separated from the unsaturated carbon atom by an sp³ hybridized saturated carbon atom. The empty p orbital of the central carbon atom conjugates and overlaps with the large π bond of the benzene ring. This causes the positive charge to delocalize and disperse to the ortho and para positions of the benzene ring. The more dispersed the charge, the lower the required activation energy. The intermediate (C3H7)3P-PhCH2 +The more stable the ion, the easier it is for Cl ions to leave, thus accelerating the reaction rate and favoring nucleophilic substitution reactions. - Diffusion into the perovskite lattice, reacting with Br - An exchange occurs. The Br that is exchanged... - It can combine with reaction intermediates to form brominated hydrocarbons (corresponding to halogen exchange reactions). The entire process takes place in a mild haloalkane medium, avoiding film dissolution and achieving non-destructive and controllable chlorine doping.

[0078] When the perovskite structure layer prepared by the above method is applied to a deep blue PeLED, the emission peak of the LED prepared based on the perovskite structure layer obtained by nucleophilic substitution reaction (SN2 reaction) solution treatment is at 464 nm (e.g., Figure 8 As shown), corresponding to the International Commission on Illumination (CIE) coordinates (0.137, 0.045), it fully meets the Rec.2020 blue standard (as shown). Figure 9 (As shown). The light-emitting diode has approximately 1300 cd cm⁻¹ at a low voltage of 5 V. -2 High brightness (such as) Figure 10 (As shown). Furthermore, this LED achieved a peak EQE of 6.1% (as shown). Figure 11 As shown), this light-emitting diode can operate even at 1000 cd / cm². -2 It maintains approximately 5% EQE even at high brightness. Meanwhile, with an initial brightness L0 of 100 cd / cm², it also maintains this level of performance. -2 When the brightness of the LED decays to 50% of its initial brightness, the corresponding operating time T is... 50 Up to 42 minutes (e.g.) Figure 12 As shown). The CIE coordinates of this LED remain essentially unchanged under different bias voltages, demonstrating good color stability (e.g., ...). Figure 13 (As shown).

[0079] This disclosure also provides a light-emitting diode, which may include, in sequence, an anode 1, a hole transport layer 2, a perovskite structure layer 3 as described above, an electron transport layer 4, an electron injection layer 5, and a cathode 6, wherein the perovskite structure layer 3 may serve as the light-emitting layer in the light-emitting diode.

[0080] For example, anode 1 can be made of indium tin oxide (ITO) transparent conductive glass; hole transport layer 2 can be made of poly(3,4-ethylenedioxythiophene):polystyrene sulfonic acid (PEDOT:PSS); electron transport layer 4 can be made of 1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene (TPBi), and the thickness of electron transport layer 4 can be 55 nm; electron injection layer 5 can be made of lithium fluoride (LiF), and the thickness of electron injection layer 5 can be 1.2 nm; cathode 6 can be made of aluminum (Al), and the thickness of cathode 6 can be 100 nm. For details, please refer to [reference needed]. Figure 14 As shown.

[0081] After preparing the perovskite precursor solution, a clean substrate made of ITO is provided to serve as the anode 1 in the light-emitting diode. PEDOT:PSS is spin-coated onto the substrate at 5000 rpm for 45 seconds. After spin-coating, the substrate is annealed at 130 °C for 10 minutes to prepare the hole transport layer 2. Next, the prepared perovskite precursor solution is spin-coated onto the hole transport layer 2 to prepare the perovskite thin film. After preparing the perovskite structure layer 3, it is transferred to a vacuum evaporation chamber to prepare the electron transport layer 4. The evaporation chamber pressure is set to 6 × 10⁻⁶. -7 Torr controlled the evaporation rate at 0.05 nm / s-0.1 nm / s to finally prepare an electron transport layer 4 with a thickness of 55 nm. After the electron transport layer 4 was deposited, the electron injection layer 5 and the cathode 6 were deposited sequentially: when depositing the electron injection layer 5, the evaporation rate was controlled below 0.01 nm / s, and the thickness could be set to 1.2 nm; when depositing the cathode 6, the evaporation rate was maintained at 0.1 nm / s, and the thickness could be set to 100 nm. In this disclosure, the effective area of ​​the light-emitting diode can be 3 mm².

[0082] Under forward bias, holes are injected from anode 1 / hole transport layer 2, and electrons are injected from cathode 6 / electron injection layer 5 / electron transport layer 4. Both recombine in the perovskite structure layer 3 to emit light. By controlling the halogen ratio (Br / Cl) of the perovskite through halogen exchange, the band gap is increased, thus achieving deep blue light emission. After chlorination treatment, defects in the perovskite structure layer 3 are reduced, non-radiative recombination is decreased, and the luminous efficiency, brightness, stability, and color purity of the light-emitting diode are all improved.

[0083] Furthermore, it should be noted that terms such as "upper," "lower," "left," and "right" are used only for distinction and convenience of description, and do not impose any positional limitations on the embodiments of the present invention. For example, "upper" in practice can refer to "lower," "left," or "right." In this disclosure, unless otherwise explicitly specified and limited, terms such as "assembly" and "connection" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in this disclosure can be understood according to the specific circumstances.

[0084] In the description of this specification, references to terms such as "some embodiments," "exemplarily," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this disclosure. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0085] Although embodiments of the present disclosure have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present disclosure. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present disclosure. Therefore, any changes or modifications made in accordance with the claims and description of the present disclosure should fall within the scope of the patent coverage of the present disclosure.

Claims

1. A method for preparing a perovskite structure layer, characterized in that, include: Provide perovskite thin films; A chlorinated hydrocarbon and a nucleophile are provided, which are mixed to carry out a nucleophilic substitution reaction and form an ion exchange solution comprising a reaction intermediate and chloride ions; The ion exchange solution is coated onto the surface of the perovskite film. Chloride ions in the ion exchange solution exchange with bromide ions on the surface of the perovskite film to replace some of the bromide ions with chloride ions, thereby obtaining the perovskite structural layer and a mixed solution formed on the surface of the perovskite structural layer. The mixed solution includes a brominated hydrocarbon formed by the reaction of the reaction intermediate with the bromide ions and the nucleophile; wherein the polarity of the chlorinated hydrocarbon and the brominated hydrocarbon is not greater than 4. Remove the mixed solution.

2. The preparation method according to claim 1, characterized in that, The polarity of the chlorinated hydrocarbon and the bromine hydrocarbon ranges from 3.0 to 4.

0.

3. The preparation method according to claim 1, characterized in that, The chlorinated hydrocarbon is a benzyl-type aromatic chlorinated hydrocarbon.

4. The preparation method according to claim 3, characterized in that, The chlorinated hydrocarbon is benzyl chloride.

5. The preparation method according to claim 1, characterized in that, The nucleophile is either a trialkylphosphine or a trialkylamine.

6. The preparation method according to claim 5, characterized in that, The nucleophile is tripropylphosphine.

7. The preparation method according to claim 1, characterized in that, The nucleophile in the ion exchange solution has a volume fraction of 0.03 vol.

8. The preparation method according to claim 1, characterized in that, The perovskite film is an all-inorganic three-dimensional perovskite.

9. The preparation method according to claim 8, characterized in that, The preparation steps of the perovskite thin film include: A perovskite precursor solution is prepared, wherein the solutes in the perovskite precursor solution are weighed according to a molar ratio of tetraphenylphosphonium bromide: cesium bromide: lead bromide: lead chloride of 0.075:1.5:0.37:0.63, and the total mass fraction of the four solid solutes in the perovskite precursor solution is 10 wt.%; the solvent in the perovskite precursor solution is mixed with dimethyl sulfoxide and deionized water at a volume ratio of 920:80; the weighed solid solutes are added to the mixed solvent and stirred until the solutes are completely dissolved to obtain the perovskite precursor solution; A substrate is provided, and the perovskite precursor solution is spin-coated onto the substrate and annealed to form the perovskite thin film.

10. A light-emitting diode, characterized in that, It comprises, in sequence, an anode, a hole transport layer, a perovskite structure layer as described in any one of claims 1 to 9, an electron transport layer, an electron injection layer, and a cathode.

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