A flexible blue light perovskite light-emitting diode and a preparation method thereof

Abstract

This invention discloses a flexible blue perovskite light-emitting diode and its fabrication method, belonging to the field of display and lighting technology. The light-emitting diode includes a composite light-emitting film, which is formed by thermally initiated in-situ free radical polymerization of a perovskite precursor and a small molecule monomer of trimethylolpropane triacrylate, simultaneously forming a three-dimensional elastic network during the perovskite film formation process. This network not only achieves grain boundary passivation through the coordination of carbonyl groups with lead ions, improving the blue light radiation recombination efficiency and suppressing ion migration, but its elastic structure can also absorb and disperse the mechanical internal stress generated by repeated bending of the flexible substrate. The fabricated device achieves an external quantum efficiency of 17.7%, a hysteresis index of less than 0.02, and exhibits no redshift in its spectrum after heat treatment at 100℃, providing a new solution for efficient, stable, and flexible blue light devices.

Description

Technical Field

[0001] This invention belongs to the field of display and lighting technology, specifically relating to a flexible blue perovskite light-emitting diode and its fabrication method. Background Technology

[0002] Metal halide perovskite materials, with their advantages of tunable emission spectra, high color purity, and low solution processing costs, have shown great application potential in the field of next-generation ultra-thin, flexible display technology. Currently, significant breakthroughs have been achieved in the external quantum efficiency of red and green perovskite light-emitting diodes (PeLEDs), and device stability has also made considerable progress. However, the development of blue flexible PeLEDs remains significantly lagging, becoming a key bottleneck restricting the industrialization of full-color displays and solid-state lighting.

[0003] Blue light emission from perovskite materials typically employs a strategy of halide ion composition modulation to broaden the light bandgap and achieve blue light emission. However, mixed halogen systems face severe halide ion migration problems: under electric or thermal stress, chloride and bromide ions readily migrate, leading to a redshift in the emission spectrum, significant current-voltage hysteresis, and a sharp decline in device stability. Simultaneously, the perovskite film contains numerous grain boundary defects (such as uncoordinated lead ions and halogen vacancies), which act as non-radiative recombination centers, severely limiting carrier radiative recombination efficiency. These problems are even more pronounced in flexible applications: the mechanical stress generated during repeated bending of the flexible substrate easily induces perovskite lattice distortion and even microcracks, not only degrading the film's crystal quality but also accelerating moisture and oxygen erosion, resulting in a sharp decrease in device performance.

[0004] To overcome these challenges, researchers have attempted to modify perovskite films by introducing polymers or small organic molecule additives. One approach involves physical doping with pre-synthesized high-molecular-weight polymers to passivate defects and alleviate stress. However, pre-synthesized polymers have limited solubility in polar solvents, and their significant steric hindrance makes it difficult for them to penetrate into the gaps between perovskite grains, leading to macroscopic phase separation. Furthermore, simple physical doping cannot establish stable mechanical and chemical bonds at the molecular level, making them prone to failure under applied stress. Another approach involves introducing small molecule additives that can form non-covalent interactions (such as hydrogen bonds) to build a network structure through intermolecular forces, which can suppress ion migration to some extent. However, hydrogen bond networks inherently rely on reversible non-covalent interactions. Under repeated electric, thermal, or mechanical stress, hydrogen bonds are prone to breakage and recombination. Their persistence in suppressing ion migration and their ability to buffer mechanical stress remain insufficient, making it difficult to meet the stringent long-term stability requirements of flexible devices.

[0005] The patent CN121665874A, entitled "A Blue Perovskite Light Emitting Diode Based on a Hydrogen Bond Network and Its Fabrication Method," specifically discloses the addition of 3-(5-fluoropyridin-2-yl)acrylate hydrochloride molecules to a blue perovskite precursor solution. These molecules form hydrogen bonds with halide ions through pyridine nitrogen groups and interact with organic ligands through carboxylic acid groups, synergistically constructing a hydrogen bond network during perovskite crystallization to suppress ion migration and passivate defects. However, the constructed hydrogen bond network relies on non-covalent interactions. Under long-term electric field conditions or thermal stress, the stability of the hydrogen bonds still has room for improvement. Furthermore, this method is insufficient to effectively absorb and disperse the mechanical internal stress generated during repeated bending of flexible devices. Summary of the Invention

[0006] To address the shortcomings of existing blue perovskite light-emitting diodes, such as spectral redshift and hysteresis caused by halide ion migration, nonradiative recombination caused by grain boundary defects, and the tendency for thin films to crack when the flexible substrate is bent, this invention provides a flexible blue perovskite light-emitting diode and its fabrication method to obtain a blue light-emitting device with high external quantum efficiency, low hysteresis index, and excellent flexible mechanical stability.

[0007] To achieve this objective, the following solution is provided: This invention provides a method for preparing a flexible blue perovskite light-emitting diode. The blue perovskite precursor components are crystallized by heat treatment, and trifunctional small molecule monomers are polymerized to form a three-dimensional interpenetrating elastic network interspersed between the grains, constituting a composite light-emitting thin film. On this basis, an electrode functional layer is prepared to obtain a flexible blue perovskite light-emitting diode.

[0008] Furthermore, the method for fabricating the flexible blue perovskite light-emitting diode includes the following steps: S1. Dissolve trimethylolpropane triacrylate monomer and initiator in blue light perovskite precursor solution to obtain composite precursor solution; S2. Form a hole transport layer on a flexible substrate; S3. The composite precursor liquid is coated onto the hole transport layer and subjected to heat treatment, so that the components of the blue light perovskite precursor begin to crystallize in situ as the solvent evaporates. At the same time, the trimethylolpropane triacrylate monomer (TMPTA) is induced to undergo in situ free radical polymerization, and a three-dimensional interpenetrating network structure is constructed at the perovskite grain boundaries and bulk defects. The three-dimensional interpenetrating elastic network is interwoven between the perovskite grains and at the grain boundaries to obtain a composite light-emitting film. S4. An electron transport layer, a cathode modification layer, and a metal electrode are sequentially fabricated on the composite light-emitting thin film to obtain the flexible blue perovskite light-emitting diode.

[0009] Furthermore, in step S1, the blue light perovskite precursor solution is composed of cesium bromide, lead bromide, lead chloride, formamidinium hydrobromide, and p-fluorophenylethylamine bromide dissolved in anhydrous dimethyl sulfoxide in a molar ratio of 1:1:1:0.3.

[0010] Further, in step S1, the initiator is 2,2-azobisisobutyronitrile with a mass concentration of 0.01-0.03 mg / mL; the mass concentration of trimethylolpropane triacrylate monomer is 0.4-1.2 mg / mL.

[0011] Furthermore, in step S2, the flexible substrate is polyethylene naphthalate or polyethylene terephthalate (PEN / ITO).

[0012] Furthermore, in step S2, the hole transport layer is composed of a stack of poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) and poly(9-vinylcarbazole) (PVK).

[0013] Furthermore, in step S3, the heat treatment is an annealing process performed at 80-95°C for 10-30 minutes.

[0014] Furthermore, in step S4, the electron transport layer is 2,4,6-tris[3-(diphenylphosphino)phenyl]-1,3,5-triazine (PO-T2T); the cathode modification layer is lithium fluoride (LiF); and the metal electrode is aluminum.

[0015] The present invention also provides a flexible blue perovskite light-emitting diode.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention uses trimethylolpropane triacrylate (TMT) as a small-molecule monomer as a precursor. Its small molecular weight and high diffusion mobility allow it to spontaneously penetrate into the perovskite precursor solution, polymerizing simultaneously with perovskite crystallization during annealing. This achieves uniform dispersion of the polymer network at the molecular level and close interpenetration with the perovskite grains, avoiding the phase separation problems associated with traditional physical doping. Furthermore, a covalently cross-linked three-dimensional interpenetrating elastic network is simultaneously formed during perovskite crystallization. This network, with stable carbon-carbon covalent bonds as its framework and an irreversible structure, continuously provides physical barrier properties during long-term device operation, significantly improving the persistence of halide ion migration suppression.

[0017] 2. This invention utilizes a three-dimensional interpenetrating network interspersed between perovskite grains to form a continuous physical barrier, directly blocking the migration channels of halide ions. Simultaneously, carbonyl functional groups in the network form coordination bonds with uncoordinated lead ions, stabilizing the perovskite lattice. The synergistic effect of physical barrier and chemical coordination reduces the device hysteresis index from above 0.2 in existing technologies to below 0.02, and the spectrum shows no red shift after heat treatment at 100℃, achieving a significant breakthrough in the spectral stability of blue perovskite light-emitting diodes.

[0018] 3. The three-dimensional interpenetrating elastic network constructed in this invention is interlocked with the perovskite grains. When the flexible substrate is repeatedly bent, the elastic network can actively absorb and disperse the mechanical internal stress, preventing stress concentration at the grain boundaries. Experiments show that the fluidity of the trimethylolpropane triacrylate monomer can effectively fill the grain boundary gaps, and the root mean square roughness of the composite light-emitting film surface is reduced from 1.72 nm to 0.12 nm. The film density and uniformity are significantly improved, fundamentally enhancing the flexible mechanical reliability of the device.

[0019] 4. This invention utilizes an integrated design of "in-situ polymerization of small molecule monomers" and "simultaneous perovskite crystallization" to construct a three-dimensional interpenetrating elastic network within the blue light perovskite film, integrating defect passivation, ion migration suppression, and stress buffering. This network is not a simple superposition of single functions, but rather, through the synergistic effect of chemical coordination, physical barrier, and elastic framework, it simultaneously solves three long-standing technical challenges in mixed halogen blue light perovskites: non-radiative recombination, halogen ion migration, and flexible bending cracking. It is this synergistic effect of integrated "structure-function" that enables the device to achieve an external quantum efficiency as high as 17.7%. This achieves a balance between high efficiency, high spectral stability, and high flexible mechanical reliability, which is difficult to achieve simultaneously with existing technologies. Attached Figure Description

[0020] Figure 1 This is a schematic diagram illustrating the mechanism of in-situ polymerization of trimethylolpropane triacrylate small monomers to form a three-dimensional elastic network in Example 1. Figure 2 The infrared spectrum characterization of the in-situ polymerization process of the composite luminescent thin film in Example 1 is shown below. Figure 3 This is a comparison of the surface morphology of the composite luminescent film and the pure perovskite film in Example 1; Figure 4 This is a comparison of the transient fluorescence lifetime curves of the composite luminescent film and the pure perovskite film in Example 1; Figure 5 This is a comparison chart of the fluorescence quantum yield of the composite luminescent film and the pure perovskite film in Example 1; Figure 6 The temperature-dependent photoluminescence spectra and exciton binding energy fitting diagrams of the composite luminescent film and the pure perovskite film in Example 1 are shown. Figure 7 The two-dimensional pseudo-color spectra of femtosecond transient absorption and the carrier decay kinetic curves of the composite luminescent film and the pure perovskite film in Example 1 are shown. Figure 8 The image shows the spectral stability test results of the composite luminescent film and the pure perovskite film in Example 1 under cyclic treatment from room temperature to high temperature (100°C). Figure 9 The external quantum efficiency curve of the flexible blue light device prepared by the composite light-emitting thin film in Example 1; Figure 10 The image shows a comparison of the current density-voltage characteristic curves and hysteresis index of the flexible blue light-emitting devices prepared by the composite light-emitting thin film and the pure perovskite thin film in Example 1 under forward and reverse scanning. Detailed Implementation

[0021] The present invention will be further described below with reference to preferred embodiments. The endpoints and any values ​​of the ranges disclosed in the present invention are not limited to the precise ranges or values. These ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed herein.

[0022] Unless otherwise specified, the experimental methods in the following embodiments are conventional methods, performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions.

[0023] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0024] Example 1 This embodiment provides a method for fabricating a flexible blue perovskite light-emitting diode, including the following steps: S1. Weigh cesium bromide, lead bromide, lead chloride, and formamidinium hydrobromide in a molar ratio of 1:1:1:0.3 and dissolve them in anhydrous dimethyl sulfoxide to prepare a blue light perovskite precursor solution, wherein the total mass concentration of lead salt is 0.213 M. Subsequently, add the organic ligand p-fluorophenylethylamine bromide as a passivating agent to the solution. Dissolve 0.8 mg of trimethylolpropane triacrylate monomer and 0.02 mg of 2,2-azobisisobutyronitrile initiator in 1 mL of the above blue light perovskite precursor solution, and stir continuously at room temperature for 12 h to ensure that the components are uniformly mixed at the molecular level to obtain a composite precursor solution. S2. Select a clean flexible PEN / ITO substrate and pre-prepare a hole transport layer on its surface. S3. Spin-coat the composite precursor liquid onto the hole transport layer at a spin speed of 4000 rpm. After spin-coating, transfer the flexible PEN / ITO substrate to a hot plate and anneal at 87 °C for 20 min. This induces in-situ free radical polymerization of trimethylolpropane triacrylate monomers during perovskite film formation, constructing a three-dimensional interpenetrating network structure at perovskite grain boundaries and bulk defects. Simultaneously, the blue light perovskite precursor components crystallize in situ, and the three-dimensional interpenetrating elastic network is interwoven between the perovskite grains to obtain a composite light-emitting thin film. S4. On the prepared composite light-emitting film, a 40 nm thick PO-T2T electron transport layer, a 1 nm thick LiF cathode modification layer, and a 100 nm thick aluminum electrode are sequentially deposited by vacuum evaporation to obtain a flexible blue perovskite light-emitting diode.

[0025] The performance of the obtained composite luminescent film was tested. Figure 1 A schematic diagram illustrating the mechanism of in-situ polymerization of trimethylolpropane triacrylate small monomers to form a three-dimensional elastic network; Figure 2 The infrared spectral characterization confirmed the disappearance of the C=C double bond, indicating that the C=C double bond in the TMPTA monomer had opened under thermal initiation conditions and undergone free radical polymerization, forming a three-dimensional polymer network structure. The surface morphology of the composite luminescent film was observed using atomic force microscopy (AFM), and the results are as follows: Figure 3 As shown, the pure perovskite film exhibits obvious grain boundaries, with a root mean square roughness (Rq) of 1.72 nm, indicating a rapid perovskite crystallization process, uneven grain growth, and numerous gaps and defects at grain boundaries, resulting in a rough film surface. In contrast, the composite luminescent film containing an in-situ polymerized three-dimensional interpenetrating network of TMPTA shows significantly improved surface morphology, blurred grain boundaries, and a more compact and smooth overall film, with a reduced RMS roughness to 0.12 nm. This is because the trimethylolpropane triacrylate monomer undergoes in-situ polymerization during annealing, forming a three-dimensional interpenetrating network that effectively fills the gaps and grain boundary defects between perovskite grains, while simultaneously regulating the crystallization growth of the perovskite and inhibiting excessive grain growth and agglomeration. Figure 4 Transient fluorescence lifetime curves and Figure 5 A comparison of fluorescence quantum yields shows that, due to the polymer network's influence on Pb... 2+ Effective passivation of defects eliminated nonradiative recombination centers, resulting in a fluorescence lifetime of 82.1 ns for the pure perovskite film and an extended fluorescence lifetime of 112.3 ns for the TMPTA / perovskite composite film. The photoluminescence quantum yield increased significantly from 45.28% to 77.86%, and consequently, the nonradiative recombination rate increased from 6.67 μs. - ¹Decreased to 1.97 μs -¹; Figure 6 The results show that after modification, the exciton-phonon coupling strength of the film was reduced from 57.7 meV to 42.5 meV, and the exciton binding energy was increased from 82.3 meV to 87.7 meV, which significantly enhanced the thermal stability of excitons at room temperature. Figure 7 The femtosecond transient absorption spectrum shows that the decay model of the modified film changed from triple exponential to double exponential, corresponding to the complete disappearance of the fast component of the rapid defect trapping, which confirms the passivation of the trap state. Figure 8 The results show the spectral stability of the thin film under cyclic treatment from room temperature to high temperature (100°C). The TMPTA / perovskite composite film device can still maintain 78.77% of the initial luminescence intensity after 100°C heat treatment, and the emission peak position is always locked at 486 nm without shift. In contrast, the control group device only retains 47.04% and shows a significant red shift, which proves that the three-dimensional cross-linked network effectively suppresses thermally induced ion migration.

[0026] The performance of the obtained flexible blue perovskite light-emitting diode was tested. Figure 9 The external quantum efficiency curves of flexible blue LED devices based on pure perovskite and TMPTA / perovskite composite films as the emitting layer are shown. The external quantum efficiency of the flexible device based on the TMPTA / perovskite composite film is significantly improved from 8.3% in the control group to 17.7%. Figure 10 The current density-voltage characteristic curves and hysteresis index of the device under forward and reverse scanning are compared. The hysteresis index of the TMPTA / perovskite composite film device decreased from 0.2 in the control group to 0.02, showing excellent electrical stability.

[0027] Example 2 This embodiment provides a method for fabricating a flexible blue perovskite light-emitting diode, including the following steps: S1. Weigh cesium bromide, lead bromide, lead chloride, and formamidinium hydrobromide in a molar ratio of 1:1:1:0.3 and dissolve them in anhydrous dimethyl sulfoxide to prepare a blue light perovskite precursor solution, wherein the total mass concentration of lead salt is 0.213 M. Subsequently, add the organic ligand p-fluorophenylethylamine bromide as a passivating agent to the solution. Dissolve 0.4 mg of trimethylolpropane triacrylate monomer and 0.01 mg of 2,2-azobisisobutyronitrile initiator in 1 mL of the above blue light perovskite precursor solution, and stir continuously at room temperature for 12 h to ensure that the components are uniformly mixed at the molecular level to obtain a composite precursor solution. S2. Select a clean flexible PEN / ITO substrate and pre-prepare a hole transport layer on its surface. S3. Spin-coat the composite precursor liquid onto the hole transport layer at a spin speed of 4000 rpm. After spin-coating, transfer the flexible PEN / ITO substrate to a hot plate and anneal at 95 °C for 10 min. This induces in-situ free radical polymerization of trimethylolpropane triacrylate monomers during perovskite film formation, constructing a three-dimensional interpenetrating network structure at perovskite grain boundaries and bulk defects. Simultaneously, the blue light perovskite precursor components crystallize in situ, and the three-dimensional interpenetrating elastic network is interwoven between the perovskite grains to obtain a composite light-emitting thin film. S4. On the prepared composite light-emitting film, a 40 nm thick PO-T2T electron transport layer, a 1 nm thick LiF cathode modification layer, and a 100 nm thick aluminum electrode are sequentially deposited by vacuum evaporation to obtain a flexible blue perovskite light-emitting diode.

[0028] Example 3 This embodiment provides a method for fabricating a flexible blue perovskite light-emitting diode, including the following steps: S1. Weigh cesium bromide, lead bromide, lead chloride, and formamidinium hydrobromide in a molar ratio of 1:1:1:0.3 and dissolve them in anhydrous dimethyl sulfoxide to prepare a blue light perovskite precursor solution, wherein the total mass concentration of lead salt is 0.213 M. Subsequently, add the organic ligand p-fluorophenylethylamine bromide as a passivating agent to the solution. Dissolve 1.2 mg of trimethylolpropane triacrylate monomer and 0.03 mg of 2,2-azobisisobutyronitrile initiator in 1 mL of the above blue light perovskite precursor solution, and stir continuously at room temperature for 12 h to ensure that the components are uniformly mixed at the molecular level to obtain a composite precursor solution. S2. Select a clean flexible PEN / ITO substrate and pre-prepare a hole transport layer on its surface. S3. Spin-coat the composite precursor liquid onto the hole transport layer at a spin speed of 4000 rpm. After spin-coating, transfer the flexible PEN / ITO substrate to a hot plate and anneal at 80 °C for 30 min. This induces in-situ free radical polymerization of trimethylolpropane triacrylate monomers during perovskite film formation, constructing a three-dimensional interpenetrating network structure at perovskite grain boundaries and bulk defects. Simultaneously, the blue light perovskite precursor components crystallize in situ, and the three-dimensional interpenetrating elastic network is interwoven between the perovskite grains to obtain a composite light-emitting thin film. S4. On the prepared composite light-emitting film, a 40 nm thick PO-T2T electron transport layer, a 1 nm thick LiF cathode modification layer, and a 100 nm thick aluminum electrode are sequentially deposited by vacuum evaporation to obtain a flexible blue perovskite light-emitting diode.

[0029] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing a flexible blue perovskite light-emitting diode, characterized in that, The blue perovskite precursor components are crystallized by heat treatment, and trifunctional small molecule monomers are polymerized to form a three-dimensional interpenetrating elastic network interspersed between the grains, forming a composite light-emitting film. On this basis, an electrode functional layer is prepared to obtain a flexible blue perovskite light-emitting diode.

2. The method for fabricating a flexible blue perovskite light-emitting diode according to claim 1, characterized in that, Includes the following steps: S1. Dissolve trimethylolpropane triacrylate monomer and initiator in blue light perovskite precursor solution to obtain composite precursor solution; S2. Form a hole transport layer on a flexible substrate; S3. The composite precursor liquid is coated onto the hole transport layer and subjected to heat treatment, so that the components of the blue light perovskite precursor begin to crystallize in situ as the solvent evaporates. At the same time, the trimethylolpropane triacrylate monomer is induced to undergo in situ free radical polymerization, and a three-dimensional interpenetrating network structure is constructed at the perovskite grain boundaries and bulk defects. The three-dimensional interpenetrating elastic network is interwoven between the perovskite grains and at the grain boundaries to obtain a composite light-emitting film. S4. An electron transport layer, a cathode modification layer, and a metal electrode are sequentially fabricated on the composite light-emitting thin film to obtain the flexible blue perovskite light-emitting diode.

3. The method for fabricating a flexible blue perovskite light-emitting diode according to claim 2, characterized in that, In step S1, the blue light perovskite precursor solution is composed of cesium bromide, lead bromide, lead chloride, formamidinium hydrobromide, and p-fluorophenylethylamine bromide dissolved in anhydrous dimethyl sulfoxide in a molar ratio of 1:1:1:0.

3.

4. The method for fabricating a flexible blue perovskite light-emitting diode according to claim 2, characterized in that, In step S1, the initiator is 2,2-azobisisobutyronitrile with a mass concentration of 0.01-0.03 mg / mL; the mass concentration of trimethylolpropane triacrylate monomer is 0.4-1.2 mg / mL.

5. The method for fabricating a flexible blue perovskite light-emitting diode according to claim 2, characterized in that, In step S2, the flexible substrate is polyethylene naphthalate or polyethylene terephthalate.

6. The method for fabricating a flexible blue perovskite light-emitting diode according to claim 2, characterized in that, In step S2, the hole transport layer is composed of a poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] and a poly(9-vinylcarbazole) stack.

7. The method for fabricating a flexible blue perovskite light-emitting diode according to claim 2, characterized in that, In step S3, the heat treatment is annealing at 80-95℃ for 10-30 minutes.

8. The method for fabricating a flexible blue perovskite light-emitting diode according to claim 2, characterized in that, In step S4, the electron transport layer is 2,4,6-tris[3-(diphenylphosphino)phenyl]-1,3,5-triazine; the cathode modification layer is lithium fluoride; and the metal electrode is aluminum.

9. A flexible blue perovskite light-emitting diode prepared by the preparation method according to any one of claims 1-8.

Images