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

Abstract

The present application relates to the field of blue perovskite light-emitting diodes, in particular to a blue perovskite light-emitting diode and a preparation method and application thereof.The present application aims at the problem that the organic ligand in quasi-two-dimensional perovskite is prone to deprotonation in a polar solvent and a thermal annealing process, leading to ligand loss and stability degradation, and proposes a method for inhibiting ligand degradation by introducing 2-phosphonic acid propionic acid, which can stabilize the organic ammonium ligand during film formation and annealing process, reduce its conversion to neutral amine, thereby improving the ligand coverage and enhancing the surface passivation effect.The perovskite film prepared by the method has a more optimal phase distribution, the low n phase is effectively inhibited, and the defect state density is significantly reduced.The blue perovskite light-emitting diode constructed based on this has significantly improved device stability while maintaining high luminous efficiency, and the electroluminescent lifetime is improved by nearly an order of magnitude, providing an effective way to realize high-efficiency and stable blue perovskite light-emitting devices.

Description

Technical Field

[0001] This invention relates to the field of blue perovskite light-emitting diodes, and in particular to a blue perovskite light-emitting diode, its fabrication method, and its application. Background Technology

[0002] Metal halide perovskites, due to their tunable spectrum, high color purity, solution-processability, and excellent charge transport properties, show broad application prospects in fields such as light-emitting diodes (LEDs). Compared to organic LEDs, perovskite LEDs can achieve a color gamut of up to 140% of the NTSC standard, making them more likely to meet the BT.2020 standard and a strong competitor for next-generation displays. The external quantum efficiency of red and green perovskite LEDs has exceeded theoretical limits, and their operational stability is comparable to mature display technologies. However, the development of blue perovskite LEDs lags behind, due to their increased bandgap leading to high defect state density and poor crystal quality. Currently, adding organic ligands to the precursor to form two-dimensional passivation helps blue devices achieve an external quantum efficiency exceeding 20%, but their operational stability remains significantly insufficient, becoming a key issue limiting their application. Summary of the Invention

[0003] Therefore, this invention targets the main defect passivators in perovskites. Organic ammonium ligands are prone to deprotonation, disrupting the interaction between the organic ligand and the perovskite, leading to the re-exposure of deep-level defects and increased nonradiative recombination losses. Different phosphate carboxylic acid molecules significantly influence the deprotonation behavior of organic ammonium ligands through their acid dissociation constants and molecular structure differences. This invention proposes using molecules with stronger acidity and shorter chain lengths to provide higher local proton concentrations, suppressing the conversion of organic ammonium to neutral amines, thereby improving operational stability. This provides a feasible approach for achieving efficient and stable blue perovskite light-emitting devices.

[0004] To address the aforementioned technical problems, this invention provides a method for fabricating a blue perovskite light-emitting diode, comprising the following steps: S11: Prepare a hole transport layer on the substrate; S12: Coat the surface of the hole transport layer with a perovskite precursor solution and anneal to form a perovskite luminescent layer; the solute in the perovskite precursor solution includes metal halides, organic long-chain ligands and molecules with high acid dissociation constants, wherein the molecules with high acid dissociation constants are selected from one or more of 2-phosphoacetic acid, 3-phosphopropionic acid and 4-phosphobutyric acid. S13: An electron transport layer, an electrode modification layer, and an electrode are sequentially fabricated on the surface of the perovskite light-emitting layer to obtain the blue perovskite light-emitting diode.

[0005] The substrate is an indium tin oxide (ITO) substrate, which is prepared by ultrasonically cleaning the etched conductive ITO substrate for 20 minutes using Decon cleaning solution, ultrapure water, ethanol, and isopropanol. The cleaned conductive ITO substrate is then dried in an oven at 100°C and treated with an ozone generator.

[0006] Preferably, in step S11, the material of the hole transport layer is one or more of PEDOT:PSS (polyethylenedioxythiophene-polystyrene sulfonate, CAS No. 155090-83-8, molecular weight range 100000-500000 g / mol), PVK (polyvinylcarbazole, CAS No. 25067-59-8, molecular weight range 50000-1000000 g / mol) and Poly-TPD (poly[bis(4-phenyl)(4-butylphenyl)amine], CAS No. 472960-35-3, molecular weight range 20000-100000 g / mol).

[0007] Preferably, in step S11, the hole transport layer is prepared by spin coating followed by annealing; the spin coating speed is 3500-4500 r / min, the time is 35-45 s, the annealing temperature is 135-450℃, and the time is 12-18 min.

[0008] Preferably, the metal halide is one or more of CsBr, PbBr2, PbCl2 and CsCl.

[0009] Preferably, the perovskite luminescent layer is coated under nitrogen conditions; the coating speed is 3500-4500 rpm and the coating time is 50-70 s.

[0010] Preferably, the organic long-chain ligand is one or more of pF-PEABr, pF-PEACl, PEABr, and PEACl. Specifically, pF-PEABr is 4-fluorophenylethyl ammonium bromide (CAS number 1807536-06-6); pF-PEACl is 4-fluorophenylethyl ammonium chloride (CAS number 459-19-8); PEABr is phenylethylamine bromide (CAS number 53916-94-2); and PEACl is phenylethylamine chloride (CAS number 156-28-5).

[0011] Preferably, in the perovskite precursor solution, the mass ratio of metal halide, organic long-chain ligand, and high-acid dissociation constant molecule is 60-64:17-21:2. The high-acid dissociation constant molecule can suppress ligand loss during high-temperature crystallization, protect the ligand's defect passivation and resistance to water and oxygen, and enhance the operational stability of the blue perovskite light-emitting diode.

[0012] Preferably, the solvent in the perovskite precursor solution is dimethyl sulfoxide, and the concentration of the metal halide in dimethyl sulfoxide is 60-64 mg / mL.

[0013] Preferably, in step S12, the annealing temperature is 65-75℃ and the time is 5-10 min.

[0014] Preferably, in step S13, the electron transport layer, electrode modification layer, and electrode are prepared by vapor deposition using a vacuum coating machine.

[0015] Furthermore, the electron transport layer is made of one or more of the following materials: 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene (TPBi), 1,3,5-tris[(3-pyridyl)-3-phenyl]benzene (TmPyPB), 2,4,6-tris(3-cyanobiphenyl-3'-yl)-1,3,5-triazine (CN-T2T), 2,4,6-tris[3-(diphenylphosphoxy)phenyl]-1,3,5-triazine (PO-T2T), 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), and 4,6-bis(3,5-di(3-pyridyl)phenyl)-2-methylpyrimidine (B3PYMPM). The electrode modification layer is made of LiF or CsF, and the electrode is made of Al or Ag.

[0016] The present invention also provides a blue perovskite light-emitting diode prepared by the above-described method. The modified perovskite light-emitting diode achieves a device lifetime of 480 min.

[0017] Preferably, the thickness ratio of the perovskite light-emitting layer, the electron transport layer, the electrode modification layer, and the electrode is 15-25:30-50:1:90-110.

[0018] The present invention also provides a display device, including the above-described blue perovskite light-emitting diode.

[0019] This invention addresses the problem of deprotonation of organic ligands in quasi-two-dimensional perovskites during polar solvents and thermal annealing, leading to ligand loss and stability degradation. It proposes a method to inhibit ligand degradation by introducing 2-phosphopropionic acid. Compared to 6-phosphopropionic acid, 2-phosphopropionic acid has a higher acid dissociation constant, which can stabilize organic ammonium ligands during film formation and annealing, reducing their conversion to neutral amines, thereby improving ligand coverage and enhancing surface passivation. The perovskite film prepared using this method exhibits a better phase distribution, with effective suppression of the low-n phase and a significant reduction in defect state density. The blue perovskite light-emitting diode constructed based on this method maintains high luminous efficiency while significantly improving device stability and increasing electroluminescence lifetime by nearly an order of magnitude. This invention provides an effective approach to achieving efficient and stable blue perovskite light-emitting devices.

[0020] Compared with the prior art, the above-described technical solution of the present invention has the following advantages: This invention utilizes 2-phosphopropionic acid, a molecule with a high acid dissociation constant, as an additive to suppress ligand dissociation and reduce non-radiative recombination losses, thereby increasing the stability of blue perovskite light-emitting diodes (LEDs). The sky-blue perovskite LED prepared by this invention significantly improves the electroluminescence characteristics of perovskite light-emitting devices, achieving a device lifetime of 480 min at 484 nm and realizing stable sky-blue light emission. Attached Figure Description

[0021] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0022] Figure 1 This is a graph showing the change in N content relative to Pb content in the original example and Example 1 of this invention; Figure 2 These are the X-ray photoelectron spectroscopy (XPS) spectra of the original example and Example 1 of this invention; Figure 3 These are the N 1s electron signal change graphs of the original example and Example 1 of XPS-oriented content analysis according to the present invention; Figure 4 These are the photoluminescence spectra of the original example and Example 1 of this invention; Figure 5 These are the ultraviolet-visible absorption spectra of the original example and Example 1 of this invention; Figure 6 This is a time-effect graph showing the electroluminescence brightness decay of the original example and Example 1 of this invention. Detailed Implementation

[0023] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0024] This invention proposes a method for improving the stability of blue perovskite light-emitting diodes and its fabrication, comprising the following steps: sequentially fabricating a hole transport layer, a perovskite light-emitting layer, an electron transport layer, an electrode modification layer, and a cathode layer on a patterned transparent indium tin oxide (ITO) substrate. Except for the different precursor solution used to prepare the perovskite layer, the other raw materials and steps involved are conventional techniques.

[0025] Example 1:

[0026] In this embodiment, a device structure for improving the stability of a blue perovskite light-emitting diode is: ITO / PEDOT:PSS / Perovskite / TPBi / LiF / Al.

[0027] Preparation of the perovskite precursor solution in this embodiment: Prepare the perovskite precursor solution: Dissolve 30 mg of CsBr, 16 mg of PbCl2, 16 mg of PbBr2, 9.5 mg of pF-PEABr and 1 mg of 2-phosphopropionic acid in 1 mL of dimethyl sulfoxide (DMSO), stir overnight at 40 °C, and let stand for 2 hours before use.

[0028] Fabrication of the blue perovskite light-emitting diode device in this embodiment: Step 1: Clean the patterned transparent electrode ITO substrate sequentially with cleaning solution, ultrapure water, ethanol and isopropanol, and then clean it with an ultrasonic cleaner for 20 min.

[0029] Step 2: Place the cleaned ITO substrate (100 nm) in a 100°C oven for 2 hours to completely remove solvent and moisture.

[0030] Step 3: Treat the ITO substrate with ozone using an ozone generator for 30 min, and spin-coat the hole transport layer PEDOT:PSS in the air. Use a 0.45 μm filter head, adjust the spin coater speed to 4000 r / min, and the time to 40 s, so that PEDOT:PSS forms a 30 nm thick anode interface layer on the surface of the patterned transparent anode layer. Place it on a hot stage at 140℃ and heat it for annealing for 15 min. Step 4: Take 80 μL of the modified perovskite precursor solution and spin-coat it onto the hole transport layer. Adjust the spin coater speed to 4000 r / min and the time to 60 s. Then heat and anneal at 70℃ for 7 min to form a 20 nm thick perovskite luminescent layer.

[0031] Step 5: Place the perovskite luminescent layer obtained in Step 4 into a vacuum coating machine and evacuate it until the vacuum level reaches 4×10⁻⁶. -4 At Pa, a 40 nm thick TPBi electron transport layer, a 1 nm thick LiF cathode interface modification layer, and a 100 nm thick Al cathode layer are sequentially evaporated.

[0032] Example 2:

[0033] The preparation method in this embodiment is the same as in Example 1, except that 2-phosphoacetic acid is used instead of 2-phosphopropionic acid.

[0034] Example 3:

[0035] The preparation method in this embodiment is the same as in Example 1, except that 4-butyric acid is used instead of 2-propionic acid.

[0036] Example 4:

[0037] The preparation method in this embodiment is the same as in Example 1, except that the annealing temperature is 65°C and the time is 5 min.

[0038] Example 5:

[0039] The preparation method in this embodiment is the same as in Example 1, except that the annealing temperature is 75°C and the time is 10 min.

[0040] Original example (comparative example): The perovskite light-emitting diode device structure used in this original example is: ITO / PEDOT:PSS / Perovskite / TPBi / LiF / Al.

[0041] Preparation of the perovskite precursor solution in this original example: Prepare the perovskite precursor solution: Dissolve 30 mg of CsBr, 16 mg of PbCl2, 16 mg of PbBr2, and 9.5 mg of pF-PEABr in 1 mL of DMSO, stir overnight at 40 °C, and let stand for 2 hours before use.

[0042] Fabrication of the blue perovskite light-emitting diode device in this original example: Step 1: Clean the patterned transparent electrode ITO substrate sequentially with cleaning solution, ultrapure water, ethanol and isopropanol, and then clean it with an ultrasonic cleaner for 20 min. Step 2: Place the cleaned ITO substrate in a 100℃ oven for 2 hours to completely remove solvent and moisture; Step 3: Treat the ITO substrate with ozone using an ozone generator for 30 min, and spin-coat the hole transport layer PEDOT:PSS in air. Use a 0.45 μm filter head, adjust the spin coater speed to 4000 r / min, and the time to 40 s, so that PEDOT:PSS forms a 30 nm thick anode interface layer on the surface of the patterned transparent anode layer. Place it on a hot stage at 140℃ and heat it for annealing for 15 min. Step 4: Take 80 μL of the modified perovskite precursor solution and spin-coat it onto the hole transport layer. Adjust the spin coater speed to 4000 r / min and the time to 60 s. Then heat and anneal at 70℃ for 7 min to form a 20 nm thick perovskite luminescent layer. Step 5: Place the perovskite luminescent layer obtained in Step 4 into a vacuum coating machine and evacuate it until the vacuum level reaches 4×10⁻⁶. -4At Pa, a 40 nm thick TPBi electron transport layer, a 1 nm thick LiF cathode interface modification layer, and a 100 nm thick Al cathode layer are sequentially evaporated.

[0043] Effect evaluation: Figure 1 The XPS spectra differences in the N 1s orbital between the annealed example and the original example are clearly demonstrated. Compared with the original film, the signal intensity of Example 1 is significantly enhanced, and accurate quantitative analysis of the nitrogen content in the film is achieved. The results show that after the introduction of 2-phosphopropionic acid, the N / Pb atomic ratio of the perovskite film is significantly increased from 0.31 in the original sample to 0.41, indicating that the organic ligand content is effectively retained.

[0044] High-resolution XPS analysis further revealed changes in the chemical state of nitrogen. Figure 2 The N 1s spectrum of the original thin film exhibits a typical bimodal characteristic: the main peak located at a high binding energy (approximately 401.5 eV) is attributed to protonated ammonium (–NH4+). 3+ The shoulder peak at the low binding energy (approximately 399.4 eV) corresponds to the deprotonated neutral amine group (–NH2). This result indicates a significant ligand deprotonation process, i.e., ligand degradation, in the original example. In contrast, the –NH2-related signal was significantly weakened after the introduction of 2-phosphopropionic acid, and the NH2-related signal was significantly reduced. 3+ The / NH2 peak area ratio increased significantly from 3.382 to 6.734, indicating that the ligand deprotonation process was effectively suppressed. Combined with elemental analysis, it can be confirmed that high-temperature annealing exacerbates the deprotonation and loss of organic ligands, while the introduction of 2-phosphopropionic acid stabilizes the ligand structure during annealing, significantly increasing the ligand retention in the final film, thereby ensuring sufficient surface coverage and defect passivation.

[0045] With ligand degradation effectively inhibited, the effect of 2-phosphopropionic acid on optical properties was further investigated. For example... Figure 4 As shown, the photoluminescence intensity of the embodiment is significantly enhanced, indicating a marked reduction in defect state density and effective suppression of nonradiative recombination processes. Steady-state absorption spectrum ( Figure 5 The results show that, compared with the original sample, the absorption characteristics of the low-n phase in Example 1 are significantly weakened, indicating that the method effectively regulates the phase distribution of the quasi-two-dimensional perovskite and suppresses the exciton-phonon coupling process associated with the low-n phase, thereby facilitating energy transfer to the high-n phase and improving luminescence efficiency.

[0046] Electroluminescence lifetime test results ( Figure 6 This indicates that, at an initial brightness of 100 cd / m², -2Under the given conditions, the brightness decay of the device in the example reached 50% (T50) in 480 minutes, while the original device only lasted 50 minutes, representing a nearly one-order-of-magnitude improvement in lifetime. These results clearly demonstrate that by suppressing ligand degradation and optimizing phase structure distribution, non-radiative losses and performance degradation during device operation can be significantly reduced, thereby effectively improving the stability of blue perovskite light-emitting diodes.

[0047] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a blue perovskite light-emitting diode, characterized in that, Includes the following steps: S11: Prepare a hole transport layer on the substrate; S12: Coat the surface of the hole transport layer with a perovskite precursor solution and anneal to form a perovskite luminescent layer; the solute in the perovskite precursor solution includes metal halides, organic long-chain ligands and molecules with high acid dissociation constants, wherein the molecules with high acid dissociation constants are selected from one or more of 2-phosphoacetic acid, 3-phosphopropionic acid and 4-phosphobutyric acid. S13: An electron transport layer, an electrode modification layer, and an electrode are sequentially fabricated on the surface of the perovskite light-emitting layer to obtain the blue perovskite light-emitting diode.

2. The preparation method according to claim 1, characterized in that: The metal halide is one or more of CsBr, PbBr2, PbCl2 and CsCl.

3. The preparation method according to claim 1, characterized in that: The organic long-chain ligand is one or more of pF-PEABr, pF-PEACl, PEABr, and PEACl.

4. The preparation method according to claim 1, characterized in that: In the perovskite precursor solution, the mass ratio of metal halide, organic long-chain ligand, and molecules with high acid dissociation constant is 60-64:17-21:

2.

5. The preparation method according to claim 1, characterized in that: The solvent in the perovskite precursor solution is dimethyl sulfoxide, and the concentration of the metal halide in dimethyl sulfoxide is 60-64 mg / mL.

6. The preparation method according to claim 1, characterized in that: In step S12, the annealing temperature is 65-75℃ and the time is 5-10 min.

7. The preparation method according to claim 1, characterized in that: In step S13, the electron transport layer, electrode modification layer, and electrode are prepared by vapor deposition using a vacuum coating machine.

8. A blue perovskite light-emitting diode prepared by the preparation method according to any one of claims 1-7.

9. The blue perovskite light-emitting diode according to claim 8, characterized in that: In the blue perovskite light-emitting diode, the thickness ratio of the perovskite light-emitting layer, the electron transport layer, the electrode modification layer, and the electrode is 15-25:30-50:1:90-110.

10. A display device, characterized in that, Including the blue perovskite light-emitting diode as described in claim 8 or 9.

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