阅读说明：本技术 发光器件及发光器件的制备方法 (Light emitting device and method for manufacturing light emitting device ) 是由 金一政 崔洁圆 刘杨 于 2020-03-31 设计创作，主要内容包括：本发明提供了一种发光器件的制备方法及发光器件,该发光器件的制备方法包括：准备钙钛矿前体液,准备发光器件的功能基板,将钙钛矿前体液覆盖于功能基板的上表面,得到钙钛矿前体液态层,对钙钛矿前体液态层进行加热,从而形成包括纳米片的钙钛矿发光层；钙钛矿前体液包括至少一芳香族化合物,调节该芳香族化合物在钙钛矿前体液中的摩尔比例从而调节钙钛矿发光层中纳米片的平行于功能基板的水平偶极比例,使得水平偶极比例为大于67％。(The invention provides a preparation method of a light-emitting device and the light-emitting device, wherein the preparation method of the light-emitting device comprises the following steps: preparing a perovskite precursor liquid, preparing a functional substrate of a light-emitting device, covering the perovskite precursor liquid on the upper surface of the functional substrate to obtain a perovskite precursor liquid layer, and heating the perovskite precursor liquid layer to form a perovskite light-emitting layer comprising nano sheets; the perovskite precursor liquid comprises at least one aromatic compound, and the molar ratio of the aromatic compound in the perovskite precursor liquid is adjusted so as to adjust the horizontal dipole ratio of the nanosheets in the perovskite light-emitting layer, which is parallel to the functional substrate, so that the horizontal dipole ratio is greater than 67%.)

1. A method of fabricating a light emitting device, the method comprising: preparing a perovskite precursor liquid, preparing a functional substrate of the light-emitting device, covering the perovskite precursor liquid on the upper surface of the functional substrate to obtain a perovskite precursor liquid layer, and heating the perovskite precursor liquid layer to form a perovskite light-emitting layer comprising nano sheets; wherein the preparing a perovskite precursor fluid comprises: dissolving at least one aromatic compound, a first cationic compound and a second cationic compound in a first polar solvent to obtain a first solution, dissolving a lithium ion compound in a second polar solvent to obtain a second solution, mixing the first solution and the second solution according to a certain proportion to obtain a third solution, and diluting or not diluting the third solution to obtain the perovskite precursor liquid; wherein the aromatic compound has a basic structure of benzene or naphthalene, and the aromatic compound has an alkylamine substituent and a halogen substituent; the first cation in the first cationic compound is selected from one or more of cesium ions, methylamine ions and formamidine ions, the second cation in the second cationic compound is selected from one or two of lead ions and tin ions, the molar ratio of the aromatic compound in the perovskite precursor liquid is adjusted so as to adjust the horizontal dipole ratio of the nanosheets in the perovskite light-emitting layer parallel to the functional substrate, so that the horizontal dipole ratio is greater than 67%.

2. The method for producing a light-emitting device according to claim 1, wherein a molar concentration ratio of the aromatic compound, the first cationic compound, the second cationic compound, and the lithium ion compound in the perovskite precursor liquid is (0.5 to 1.5): 1.75: 1.4: 0.25.

3. a method for fabricating a light emitting device according to claim 1, wherein the alkylamine substituent is a methylamino group, a propylamino group, an ethylamino group, or a butylamino group, and preferably the halogen substituent is bromine.

4. The method for preparing the light-emitting device according to claims 1 to 3, wherein the aromatic compound comprises bromobenzamide and bromophenylethylamine, and the molar ratio of the bromobenzamide to the bromophenylethylamine is less than or equal to 3: 1.

5. the method for manufacturing a light-emitting device according to claim 1, wherein anions in the first cationic compound, the second cationic compound, and the lithium ion compound are all halogen ions, and preferably, the halogen ions are bromine.

6. The method for manufacturing a light-emitting device according to claim 1, wherein the heating temperature is in a range of 85 to 130 ℃.

7. The method of manufacturing a light emitting device according to claim 1, wherein the third solution is diluted with the first polar solvent or the second polar solvent, and preferably both the first polar solvent and the second polar solvent are dimethyl sulfoxide.

8. The method for manufacturing a light-emitting device according to claim 1, wherein the process of preparing the functional substrate of the light-emitting device comprises: a substrate including a first electrode layer is prepared, a hole injection layer is provided on the first electrode layer, and a hole transport layer is provided on the hole injection layer.

9. The method for manufacturing a light-emitting device according to claim 8, wherein the method for manufacturing the hole injection layer comprises: and disposing a nickel oxide precursor solution on the first electrode layer, and heating the nickel oxide precursor solution to obtain the hole transport layer, wherein the hole transport layer is preferably made of TFB.

10. The method of manufacturing a light emitting device according to claim 1, further comprising: providing an electron transport layer over the perovskite luminescent layer, a second electrode layer over the electron transport layer; preferably, the material of the electron transport layer is TPBi, and the second electrode layer includes a lithium fluoride electrode layer and an aluminum electrode layer.

11. A light-emitting device comprising a functional substrate and a perovskite light-emitting layer stacked in sequence, characterised in that the perovskite material in the perovskite light-emitting layer comprises a plurality of nanoplates, and a% of the dipoles of the nanoplates are parallel to the functional substrate, a being greater than 67.

12. The light-emitting device according to claim 11, which is produced by the production method according to any one of claims 1 to 10, wherein a is 80 or more and 90 or less.

13. The light-emitting device of claim 11 or 12 having an external quantum efficiency of 23% or greater and a fluorescence quantum yield of 75% or greater for the nanoplatelets; preferably, the transverse dimension of the nano-sheet is 16.6-30.6 nm.

Technical Field

The invention relates to the technical field of LED light-emitting devices, in particular to a light-emitting device and a preparation method thereof.

Background

In the field of LEDs, the External Quantum Efficiency (EQE) of a device is one of the most important indicators for evaluating the quality of the device. The most important factor that currently limits the luminous efficiency of LED devices is the light extraction rate of the devices. The means for improving the light-emitting rate of the device comprises that a microstructure is arranged in the device, so that a part of light originally limited to the internal total reflection (microcavity effect) of the device can be extracted, and the light-emitting rate of the device is improved. In the field of OLEDs, researchers have synthesized small molecules of organic light-emitting layers with a certain orientation, and the dipole arrangement of such small molecules also has orientation. These organic molecules having orientation are aligned horizontally by a thermal vapor deposition method. The formed dipoles of the organic light emitting layer tend to be arranged parallel to the substrate, so that the photon emission ratio in the direction perpendicular to the substrate is increased, and the loss of plasmon polaritons from the electrodes to emitted light is reduced, so that the light extraction rate of the light emitting device is increased, and the light emitting device has good fluorescence emission. In the field of perovskite light emitting diodes (pelds), researchers also research and prepare nanosheets with transition dipole moments arranged parallel to a substrate as a light emitting layer, but the light emitting efficiency is not high.

Disclosure of Invention

The invention aims to provide a light-emitting device and a preparation method thereof, and aims to solve the problem that the dipole is parallel to a substrate and the fluorescence efficiency is high in the prior art.

In order to achieve the above object, according to an aspect of the present invention, there is provided a method of manufacturing a light emitting device, the method comprising: preparing a perovskite precursor liquid, preparing a functional substrate of a light-emitting device, covering the perovskite precursor liquid on the upper surface of the functional substrate to obtain a perovskite precursor liquid layer, and heating the perovskite precursor liquid layer to form a perovskite light-emitting layer comprising nano sheets; wherein preparing the perovskite precursor liquid comprises: dissolving at least one aromatic compound, a first cationic compound and a second cationic compound in a first polar solvent to obtain a first solution, dissolving a lithium ion compound in a second polar solvent to obtain a second solution, mixing the first solution and the second solution according to a certain proportion to obtain a third solution, and diluting or not diluting the third solution to obtain a perovskite precursor liquid; wherein the aromatic compound has a basic structure of benzene or naphthalene, and the aromatic compound has an alkylamine substituent and a halogen substituent; the first cation in the first cationic compound is selected from one or more of cesium ions, methylamine ions and formamidine ions, the second cation in the second cationic compound is selected from one or two of lead ions and tin ions, the molar ratio of the aromatic compound in the perovskite precursor liquid is adjusted, so that the horizontal dipole ratio of the nanosheets in the perovskite light-emitting layer parallel to the functional substrate is adjusted, and the horizontal dipole ratio is greater than 67%.

Further, the molar concentration ratio of the aromatic compound, the first cationic compound, the second cationic compound and the lithium ion compound in the perovskite precursor liquid is (0.5-1.5): 1.75: 1.4: 0.25.

further, the alkylamine substituent is methylamino, propylamino, ethylamino or butylamino, and preferably, the halogen substituent is bromine.

Further, the aromatic compounds comprise bromobenzamide and bromobenzethylamine, and the molar ratio of the bromobenzamide to the bromobenzethylamine is less than or equal to 3: 1.

further, the anions in the first cationic compound, the second cationic compound and the lithium ion compound are all halogen ions, preferably, the halogen ions are bromine.

Further, the heating temperature range is 85-130 ℃. Further, the third solution is diluted with a first polar solvent or a second polar solvent, preferably both the first polar solvent and the second polar solvent are dimethyl sulfoxide.

Further, the process of preparing the functional substrate of the light emitting device includes: a substrate including a first electrode layer is prepared, a hole injection layer is provided on the first electrode layer, and a hole transport layer is provided on the hole injection layer.

Further, the method for preparing the hole injection layer comprises the following steps: the hole transport layer is preferably formed by disposing a nickel oxide precursor solution on the first electrode layer and heating the nickel oxide precursor solution.

Further, the preparation method also comprises the following steps: an electron transport layer is arranged on the perovskite luminescent layer, and a second electrode layer is arranged on the electron transport layer; preferably, the material of the electron transport layer is TPBi, and the second electrode layer includes a lithium fluoride electrode layer and an aluminum electrode layer.

According to an aspect of the present invention, there is provided a light emitting device comprising a functional substrate and a perovskite light emitting layer stacked in sequence, the perovskite material in the perovskite light emitting layer comprising a plurality of nanosheets, and a% of the dipoles of the nanosheets being parallel to the functional substrate, a being greater than 67.

Further, a light-emitting device is manufactured by any one of the above manufacturing methods, and a is 80 or more and 90 or less.

Further, the external quantum efficiency of the light-emitting device is greater than or equal to 23%, and the fluorescence quantum yield of the nanosheet is greater than or equal to 75%; preferably, the transverse dimension of the nano-sheets is 16.6-30.6 nm.

By applying the technical scheme of the application, the preparation method of the perovskite luminescent layer of the luminescent device is an in-situ film forming method, and the nano sheets with orientation arrangement and excellent optical performance can be formed by controlling the proportion of the aromatic compounds, so that dipoles of the nano sheets are arranged in parallel to the substrate, and the light extraction rate of the luminescent device is improved. The method is simple to operate, the perovskite nanocrystalline is not required to be synthesized firstly and then the film is formed, the problem that the optical performance of the perovskite nanocrystalline dispersion liquid is lost in the film forming process is successfully solved, the arrangement orientation of the luminescent material is not required to be further regulated, the method has no influence on the electroluminescent spectrum shape of the perovskite luminescent layer, and the electroluminescent spectrum shape is still approximate to a Gaussian function.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the invention and, together with the description, serve to explain the invention and not to limit the invention. In the drawings:

fig. 1 shows a sectional aberration-corrected scanning transmission electron microscope image of a light-emitting device of example 1;

FIG. 2 shows a graph of the angular distribution PL of the device of example 2;

FIG. 3 shows a focal plane imaging diagram of the device of example 2;

figure 4a shows a high power scanning electron micrograph of a light emitting device nanoplate of example 1 with cross-sectional aberration correction;

fig. 4b shows a high resolution scanning electron micrograph of a luminescent device nanoplate of example 1;

FIG. 5 shows the statistical distribution of the device nanoplatelet size of example 2;

FIG. 6 is a graph showing the relationship between the light-emitting efficiency and the horizontal dipole ratio of a light-emitting device simulated by software;

FIG. 7 is a graph showing an electroluminescence spectrum at a voltage of 6V of the light-emitting device of example 1;

fig. 8 shows External Quantum Efficiency (EQE) variation graphs at different voltages of the light emitting device of example 1;

FIG. 9a shows the thin film absorption and emission spectra of the quartz device prepared in example 2;

FIG. 9b shows PLQY variation at different excitation densities for the quartz device prepared in example 2;

FIG. 10 shows absorption and emission spectra of the thin film of the quartz device prepared in comparative example 1;

FIG. 11 shows absorption and emission spectra of thin films of the quartz device prepared in example 6;

FIG. 12 shows PLQY variation of the quartz devices prepared in example 2 and comparative example 2 at different excitation densities;

FIG. 13 shows PLQY variation at different excitation densities for the quartz devices prepared in comparative example 1 and example 6;

fig. 14 shows the change of the ratio of aromatic compounds and the corresponding ratio of horizontal dipoles in the specific example and the comparative example.

Detailed Description

It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

It is noted that the terms first, second and the like in the description and in the claims of the present application are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order.

The terms "comprises," "comprising," and "having," and any variations thereof, in the description and claims of this application, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus. The term "dipole" in the description and claims of this application is collectively referred to as the transition dipole moment.

In an exemplary embodiment of the present application, there is provided a method of manufacturing a light emitting device, the method including: preparing a perovskite precursor liquid, preparing a functional substrate of a light-emitting device, covering the perovskite precursor liquid on the upper surface of the functional substrate to obtain a perovskite precursor liquid layer, and heating the perovskite precursor liquid layer to form a perovskite light-emitting layer comprising nano sheets; wherein preparing the perovskite precursor liquid comprises: dissolving at least one aromatic compound, a first cationic compound and a second cationic compound in a first polar solvent to obtain a first solution, dissolving a lithium ion compound in a second polar solvent to obtain a second solution, mixing the first solution and the second solution according to a certain proportion to obtain a third solution, and diluting or not diluting the third solution to obtain a perovskite precursor liquid; wherein the aromatic compound has a basic structure of benzene or naphthalene, and the aromatic compound has an alkylamine substituent and a halogen substituent; the first cation in the first cationic compound is selected from one or more of cesium ions, methylamine ions and formamidine ions, the second cation in the second cationic compound is selected from one or two of lead ions and tin ions, the molar ratio of the aromatic compound in the perovskite precursor liquid is adjusted, so that the horizontal dipole ratio of the nanosheets in the perovskite light-emitting layer parallel to the functional substrate is adjusted, and the horizontal dipole ratio is greater than 67%.

The preparation method of the perovskite luminescent layer of the luminescent device is an in-situ film forming method, and can form nanosheets which are arranged in an oriented mode and have excellent optical performance at the same time by controlling the proportion of aromatic compounds, so that dipoles of the nanosheets are arranged in parallel to the substrate, and the light extraction rate of the luminescent device is improved. The preparation method is simple to operate, the perovskite nanocrystalline does not need to be synthesized firstly, the problem of optical property loss of the perovskite nanocrystalline dispersion liquid in the film forming process is avoided, the arrangement orientation of the luminescent material does not need to be further regulated, and the method has no influence on the electroluminescent spectrum shape of the perovskite luminescent layer. The defects of the nanosheets are reduced by using the lithium ion compound, so that non-radiative recombination of the perovskite luminescent layer is reduced, and the fluorescence quantum yield is improved. From theoretical calculation, the dipole can be decomposed into three components of x, y and z in three-dimensional space, if the dipole is randomly distributed, the three directional components of x, y and z respectively account for 1/3, and the x and y are horizontal components accounting for two thirds, so that the theoretical proportion of the horizontal dipole is 67%.

In some embodiments, the molar concentration ratio of the aromatic compound, the first cationic compound, the second cationic compound, and the lithium ion compound in the perovskite precursor liquid is (0.5-1.5): 1.75: 1.4: 0.25. the molar concentrations of the first cationic compound, the second cationic compound, and the lithium ion compound refer to the molar concentrations of the first cation, the second cation, and the lithium ion.

In some embodiments, by controlling the ratio of the substances of the perovskite precursor fluid, the formation of nanosheets of different emission wavelengths can be controlled.

In some embodiments, the molar ratio of the aromatic compound in the perovskite precursor liquid is adjusted to adjust the horizontal dipole ratio of the nanosheets in the perovskite light-emitting layer parallel to the functional substrate such that the horizontal dipole ratio is 70-80%.

In some embodiments, the molar ratio of the aromatic compound in the perovskite precursor liquid is adjusted to adjust the horizontal dipole ratio of the nanosheets in the perovskite light-emitting layer parallel to the functional substrate such that the horizontal dipole ratio is 78-80%.

In some embodiments, the molar ratio of the aromatic compound in the perovskite precursor liquid is adjusted to adjust the horizontal dipole ratio of the nanosheets in the perovskite light-emitting layer parallel to the functional substrate such that the horizontal dipole ratio is 80-90%.

In some embodiments, the molar ratio of the aromatic compound in the perovskite precursor liquid is adjusted to adjust the horizontal dipole ratio of the nanosheets in the perovskite light-emitting layer parallel to the functional substrate such that the horizontal dipole ratio is 80-87%.

In some embodiments, the alkylamine substituent is methylamino, propylamino, ethylamino, or butylamino, and the halogen substituent is bromo, iodo, chloro; preferably, the halogen substituent is bromine.

In some embodiments, the aromatic compound comprises bromobenzamide and bromophenylethylamine, and the molar ratio of bromobenzamide to bromophenylethylamine is less than or equal to 3: 1.

in some embodiments, the anions in the first cationic compound, the second cationic compound, and the lithium ion compound are all halide ions, preferably, the halide ions are bromide.

In some embodiments, the temperature range of heating is 85-130 ℃. Within the temperature range, reactants in the perovskite precursor liquid react and form nanosheets with uniform morphology.

In some embodiments, the perovskite precursor liquid is coated on the upper surface of the functional substrate by any means of spin coating, slot coating, ink jet printing, and the like.

In some embodiments, the third solution is diluted with a first polar solvent or a second polar solvent, preferably both the first polar solvent and the second polar solvent are dimethyl sulfoxide.

In some embodiments, the process of preparing the functional substrate of the light emitting device includes: a substrate including a first electrode layer is prepared, a hole injection layer is provided on the first electrode layer, and a hole transport layer is provided on the hole injection layer.

In some embodiments, a method of preparing a hole injection layer includes: the hole transport layer is preferably formed by disposing a nickel oxide precursor solution on the first electrode layer and heating the nickel oxide precursor solution.

In some embodiments, the method of making further comprises: an electron transport layer is arranged on the perovskite luminescent layer, and a second electrode layer is arranged on the electron transport layer; preferably, the material of the electron transport layer is TPBi, and the second electrode layer includes a lithium fluoride electrode layer and an aluminum electrode layer.

In an exemplary embodiment of the present application, there is provided a light emitting device comprising a functional substrate and a perovskite light emitting layer stacked, the perovskite material in the perovskite light emitting layer comprising a plurality of nanosheets, and a% of the dipoles of the nanosheets being parallel to the functional substrate, a being greater than 67. The light emitting device has a high light extraction rate.

In some embodiments, the functional substrate includes a stacked substrate, a first electrode layer, a hole injection layer, and a hole transport layer.

In some embodiments, the perovskite light emitting layer further comprises an electron transport layer and a second electrode layer stacked in sequence.

In some embodiments, the light emitting device is prepared according to any one of the above light emitting device preparation methods, and a is greater than or equal to 80 and less than or equal to 90.

In some embodiments, the external quantum efficiency of the light emitting device is 23% or greater and the fluorescence quantum yield of the nanoplatelets is 75% or greater. In some embodiments, the nanoplatelets have a lateral dimension of 16.6 to 30.6 nm.

In some embodiments, the light emitting device has a peak emission wavelength in the range of 500 to 550nm, preferably 518 nm.

In some embodiments, the light emitting device is a light emitting diode, or a display panel having a plurality of light emitting diode array structures.

The advantageous effects of the present application will be further described below with reference to examples and comparative examples.

Experimental drugs and reagents: lead bromide (PbBr)₂) 99.999% pure, ultra dry, Sigma-Aldrich; cesium bromide (CsBr), purity 99.999%, Alfa Aesar; phentermine (PBA), purity > 98.0%, Alfa Aesar; dimethyl sulfoxide (DMSO), 99.9% purity, Alfa Aesar; hydrobromic acid (HBr), 48% mass fraction aqueous solution, Alfa Aesar; nickel acetate tetrahydrate with purity of 99%, ultrapure, Acros; ethanolamine, purity 99%, Acros; ethanol, 99.5% purity, ultra-dry, Acros; poly [9, 9-dioctylfluorene-CO-N- (4-butylphenyl) diphenylamine](TFB), American dye; chlorobenzene, 99.8% pure, analytically pure, Acros; poly [ 9-vinylcarbazole](PVK) having an average molecular weight of 25,000 to 50,000 g/mol^-1Sigma-Aldrich; poly [ N, N '-bis (4-butylphenyl) -N, N' -bis (phenyl) -benzidine](ii) a (Poly-TPD), American dye source; 1,3, 5-tris (1-phenyl-1H-benzimidazol-2-yl) benzene (TPBi) with a purity of 98%, J&K; lithium fluoride (LiF) with the purity of 99.999 percent, Zhongnuo new material; metal aluminum particles with the purity of 99.999 percent, Zhongnuo new material; an ITO substrate with the thickness of 100nm, a resistor of 25 omega and Shenzhen Huayu; ethanol, analytical pure (AR), chinese drug; deionized water with a resistivity of 18M omega cm, deionized water machine.

Example 1

Preparation of perovskite precursor liquid

Preparation of bromophenylethylamine, bromophenylamine reference Si, J.et al.Effect and high-color-purity light-emitting diodes based on in situ growth files of CsPbX₃(X ═ Br, I) nanoplates with controlled threads. ACS Nano 11, 11100-.

1) 18.9mg of bromobenzamide, 5.5mg of bromobenzethylamine, 40.8mg of cesium bromide and 56.2mg of lead bromide were weighed on a precision balance, mixed into 1mL of DMSO solvent, heated at 60 ℃ and stirred at 600rpm for more than 2 hours to dissolve to give a first solution.

2) 9.55mg of LiBr was weighed out and dissolved in 1mL of DMSO solution, heated at 60 ℃ and stirred at 600rpm for more than 2 hours to dissolve to obtain a second solution.

3) Mixing the first solution and the second solution according to the ratio of 4: 1, and diluting the mixed solution with DMSO to 70% volume fraction. Obtaining perovskite precursor liquid required by the perovskite luminous layer.

Preparation process of PeLED light-emitting device

1) Cleaning an ITO substrate: the front and back sides of ITO (20 omega, thickness 100nm) glass are lightly wiped by dust-free cloth, then the glass is rubbed and washed by a cotton swab in acetone and ethanol, then ultrasonic treatment is sequentially carried out for 10 minutes according to the sequence of acetone-ethanol-deionized water-ethanol, after the ultrasonic treatment, a nitrogen gun is used for carefully drying the glass, and finally air plasma treatment is carried out for 15 minutes.

2) Preparing a nickel oxide hole injection layer: dropping the nickel oxide precursor solution on an ITO substrate, spin-coating the nickel oxide precursor solution for 45 seconds at the rotating speed of 4000 revolutions per minute, transferring the substrate to a 275 ℃ hot bench for annealing for 30 minutes, cooling the temperature to room temperature, and carrying out ozone treatment for 30 minutes to obtain the nickel oxide film with the thickness of about 7 nm.

3) Preparing a hole transport layer: the nickel oxide hole injection layer was spin-coated with 8mg/mL of TFB (solvent: chlorobenzene) at 2000 rpm for 45 seconds, the wafer was then transferred to a 150 ℃ hot stage and annealed for 30 minutes, after cooling the substrate, the TFB surface was spin-coated with chlorobenzene solvent once to obtain a TFB layer of about 2nm, and finally the TFB layer was spin-coated with 14mg/mL of PVK (solvent: chlorobenzene) and annealed at 150 ℃ for 30 minutes to obtain a PVK layer of about 35 nm.

4) Preparing a perovskite light-emitting layer: the perovskite precursor droplets were spin coated on the hole transport layer at 4000 rpm for 2 minutes. After the spin coating was completed, the substrate was rapidly transferred to a 100 ℃ hot stage and annealed for 25 minutes.

5) Evaporating an electron transport layer: the sample was transferred to a vacuum evaporation apparatus for evaporation of TPBi to a thickness of 48 nm.

6) Evaporating lithium fluoride electrode and aluminum electrode under 2X 10-7 Torr: the thicknesses were 1nm and 100nm, respectively.

Example 2

The perovskite precursor liquid was prepared as in example 1.

Preparation process of quartz device for verification

1) And preparing a quartz substrate and cleaning.

2) 8mg/mL of TFB (solvent: chlorobenzene) was spin-coated on a quartz substrate at 2000 rpm for 45 seconds, then the wafer was transferred to a 150 ℃ hot stage and annealed for 30 minutes, after the substrate was cooled, the surface of TFB was spin-coated once with chlorobenzene solvent to obtain a TFB layer of about 2nm, and finally 14mg/mL of PVK (solvent: chlorobenzene) was spin-coated on the TFB layer and annealed for 30 minutes at 150 ℃.

3) The perovskite precursor droplets were spin coated on the PVK layer at 4000 rpm for 2 minutes. After the spin coating was completed, the substrate was rapidly transferred to a 100 ℃ hot stage and annealed for 25 minutes.

Example 3

The perovskite precursor liquid was prepared in the same manner as in example 1 except that the aromatic compound concentration was changed. The preparation method comprises the following steps:

9.5mg of bromobenzamide, 2.8mg of bromobenzethylamine, 40.8mg of cesium bromide and 56.2mg of lead bromide were weighed on a precision balance, mixed into 1mL of DMSO solvent, heated at 60 ℃ and stirred at 600rpm for more than 2 hours to dissolve to give a first solution.

The procedure for the preparation of the quartz device for verification was the same as in example 2.

Example 4

The perovskite precursor liquid was prepared in the same manner as in example 1 except that the aromatic compound concentration was changed. The preparation method comprises the following steps:

28.4mg of bromobenzamide, 8.3mg of bromobenzethylamine, 40.8mg of cesium bromide and 56.2mg of lead bromide were weighed on a precision balance, mixed into 1mL of DMSO solvent, heated at 60 ℃ and stirred at 600rpm for more than 2 hours to dissolve to give a first solution.

The procedure for the preparation of the quartz device for verification was the same as in example 2.

Example 5

The perovskite precursor liquid was prepared in the same manner as in example 1 except that the aromatic compound concentration was changed. The preparation method comprises the following steps:

37.8mg of bromobenzamide, 11.0mg of bromobenzethylamine, 40.8mg of cesium bromide and 56.2mg of lead bromide were weighed on a precision balance, mixed into 1mL of DMSO solvent, heated at 60 ℃ and stirred at 600rpm for more than 2 hours to dissolve to give a first solution.

The procedure for the preparation of the quartz device for verification was the same as in example 2.

Comparative example 1

Preparation of perovskite precursor liquid

1) 40.8mg of cesium bromide and 56.2mg of lead bromide were weighed out by a precision balance, mixed into 1mL of a DMSO solvent, heated at 60 ℃ and stirred at 600rpm for more than 2 hours to dissolve to obtain a first solution.

2) 9.55mg of LiBr was dissolved in 1mL of DMSO solution, heated at 60 ℃ and stirred at 600rpm for more than 2 hours to dissolve to obtain a second solution.

3) Mixing the first solution and the second solution according to the ratio of 4: 1, and diluting the mixed solution with DMSO to 70% volume fraction. Obtaining perovskite precursor liquid required by the perovskite luminous layer.

The procedure for the preparation of the quartz device for verification was the same as in example 2.

Comparative example 2

Preparation of perovskite precursor liquid

1) 18.9mg of bromobenzamide, 5.5mg of bromobenzethylamine, 40.8mg of cesium bromide and 56.2mg of lead bromide were weighed on a precision balance, mixed into 1mL of DMSO solvent, heated at 60 ℃ and stirred at 600rpm for more than 2 hours to dissolve to give a first solution.

3) The first solution and DMSO solvent were mixed as 4: 1, and diluting the mixed solution with DMSO to 70% volume fraction. Obtaining perovskite precursor liquid required by the perovskite luminous layer.

The procedure for the preparation of the quartz device for verification was the same as in example 2.

The method for testing the external quantum efficiency comprises the following steps:

the current density-voltage curve of the light emitting device was measured using Keithley2400, and the luminance of the light emitting device was measured using an integrating sphere (FOIS-1) in combination with a marine optical spectrometer (QE-pro). And calculating the external quantum efficiency of the light-emitting device according to the measured current density and brightness. The external quantum efficiency represents the ratio of the number of photons emitted by the light-emitting device to the number of electrons injected into the device in the observation direction, and is an important parameter for representing the light-emitting efficiency of the light-emitting device of the device, and the higher the external quantum efficiency is, the higher the light-emitting efficiency of the device is.

The ultraviolet visible absorption spectrum testing equipment is a Carry 5000(Agilent) spectrometer. The PL spectroscopic testing device was an Edinburgh Instruments FLS920 spectrometer. PLQY test methods reference Liu, Y.et al.Effect blue light-emitting diodes based on quantum-defined bromine peroxide catalysts nano structures. Nature Photon.13,760-764 (2019).

The light-emitting device obtained in example 1 was observed by a scanning transmission electron microscope with corrected cross-sectional aberration, and the obtained cross-sectional view is shown in fig. 1, where "Perov" is a perovskite light-emitting layer.

In order to verify whether the dipoles of the nanosheets in example 1 are parallel to the ITO substrate, the quartz device of example 2 was subjected to an angular distribution PL test, the results of which are shown in fig. 2, and a focal plane imaging test, the results of which are shown in fig. 3, respectively, and two dipole distribution test methods were used to verify whether the results are consistent. As can be seen from fig. 2, the proportion (symbol Θ) of horizontal dipoles (aligned parallel to the substrate) in the nanoplatelets of the perovskite light-emitting layer is about 85%; as can be seen from fig. 3, the proportion of horizontal dipoles is 87%, and Θ represents the proportion of dipoles in the horizontal portion to the overall dipoles (horizontal portion + vertical portion). In the abscissa of FIG. 3, k0 represents the photon momentum in air and k// represents the plane photon momentum. The calculation method of the horizontal dipole ratio comprises the following steps: the actual ratio is estimated by comparing the actual measurement curve with three simulation curves (reference standards) with known horizontal dipole ratios. From the above results, it is believed that the horizontal dipole of the nanosheet is dominant in the perovskite light emitting layer. Optical tests showed that the fluorescence quantum yield (PLQY) of the quartz device of example 2 was around 79%.

From a magnified view of the nanoplatelets shown in fig. 1, it can be seen that the nanoplatelets in fig. 4a have sharp high quality lattice edges without distortion or dislocation phenomena. To determine the shape and size distribution of the nanoplatelets, we transferred the perovskite onto a copper mesh for viewing a high resolution electron lens image, resulting in fig. 4 b. FIG. 4b shows a typical perovskite nanosheet morphology, which is approximately square in shape and approximately 23nm in lateral dimension. The perovskite layer of example 2 was observed under low magnification, and it was found that the average transverse dimension of the nanosheets was 23.6. + -. 7.0nm, and the statistical results of the size distribution are shown in FIG. 5.

To investigate the relationship between the horizontal dipole ratio and the light emission ratio (the ratio of the number of photons emitted from the device to the number of all photons emitted from the light-emitting layer), further, the results of fitting the light emission ratio and the horizontal dipole ratio of the light-emitting device were obtained by inputting the data of table 1 to software based on a model (refer to [1] new ts, k.a.relationship of light emission from the thin-film microorganisms.j.opt.soc.am.a 15, 962. 971(1998) [2] Lukosz, W. & Kunz, r.light emission by magnetic and electric dipole close to a plate interface.i.total radial power.j.op.soc.soc.am.67, 1607-1977) as shown in fig. 6: black pentagram represents the corresponding horizontal dipole proportion and light-emitting rate of the perovskite luminescent layer; the black circles represent the corresponding simulated light extraction rates if the dipoles in the perovskite light emitting layer were completely randomly arranged. The bottom left and top right insets in fig. 6 are schematic diagrams of dipole arrangements. As can be seen from fig. 6, the simulated light-emitting efficiency of the light-emitting device prepared by the in-situ growth ordered arrangement of the anisotropic nanostructures can be increased from 23.4% to about 31.3% when the dipoles are randomly arranged, and the increase of the proportion of the horizontal dipoles and the increase of the light-emitting efficiency have a positive correlation. The light emitting device of example 1 has an observed External Quantum Efficiency (EQE) of 23.6% and a PLQY of 75%, and can estimate a light yield of 23.6%/75%, that is, about 31.5%, which is almost identical to the simulated light yield.

TABLE 1

Note: the refractive indices and extinction coefficients of the individual layers were determined by ellipsometry (j.a. woollam, USA).

FIG. 7 is an electroluminescence spectrum at a voltage of 6V of the light-emitting device obtained in example 1, and the emission peak wavelength was 518nm and the half-width was 74emV (about 16 nm). The inset in FIG. 7 is a light emitting device (size 3.24 mm) obtained in example 1²) The photograph of (2). Fig. 8 is a graph showing the change of the EQE of the light emitting device obtained in example 1 under different voltages, and the EQE of the light emitting device can reach up to 23.6% when the voltage is 3.8V.

The thin film absorption and emission spectra of the quartz device prepared in example 2 are shown in fig. 9a, the PLQY changes under different excitation intensities in fig. 9b, and the PLQY at low excitation intensity is about 75%. The absorption and emission spectra of comparative example 1 are shown in FIG. 10, and those of example 6 are shown in FIG. 11. It is known that changing the ratio of the aromatic compound has a significant effect on the structure of the perovskite luminescent thin film. In the figure, the absorption spectrum is a curve close to the left ordinate, and the emission spectrum is a bell curve distant from the left ordinate.

Fig. 12 shows PLQY changes at different excitation densities for the quartz devices prepared in example 2 and comparative example 2, and it can be seen that PLQY is reduced compared to example 2 in the absence of the lithium ion compound in comparative example 2. High PLQY is one of means for improving the efficiency of a light-emitting device, and therefore, a nanosheet prepared with a lithium-ion compound has high PLQY.

Referring to fig. 13, it can be seen that PLQY of comparative example 1 and example 6 also varies significantly. Of these, the quartz device of comparative example 1 had a PLQY of about 8% at low excitation intensity, and the quartz device of example 6 had a PLQY of about 52% at low excitation intensity. Referring to fig. 14, it can be seen that changing the ratio of aromatics has a fundamental effect on the orientation of the nanocrystals, with increasing ratio of aromatics (expressed as y), i.e., y is taken to be 0, 0.5, 1.5, 2, and the ratio of horizontal dipoles (see table 2) increases and then decreases. Whereas the light extraction is largely influenced by the dipole orientation. Therefore, the method is an effective method for further improving the efficiency of the light-emitting device by adjusting the proportion of the aromatic compound to adjust the orientation of the horizontal dipole so as to improve the light-emitting rate. It can be presumed from table 2 that when the value of y is low, it may be difficult to form a nanosheet, and when the value of y is too high, non-platelet-shaped nanoparticles may be formed, resulting in a first increase and then a decrease in the horizontal dipole ratio. The aromatic compound adjusts the morphology, and further adjusts the horizontal dipole ratio. For a particular implementation, the value of y needs to be determined experimentally.

TABLE 2

From the above, according to the technical scheme of the application, the PLQY of the nanosheet is improved by adding the lithium ion compound, and meanwhile, the proportion of the horizontal dipole is improved by regulating and controlling the proportion of the aromatic compound, so that the light-emitting device with high light-emitting efficiency can be obtained.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.