CN111326660A - Highly discrete nanocrystalline light-emitting layer applied to electroluminescent devices and electroluminescent devices based thereon - Google Patents

Abstract

The invention discloses a highly discrete nanocrystalline light-emitting layer applied to an electroluminescent device and an electroluminescent device based thereon. The light-emitting layer is composed of a conjugated organic small molecule as a host material and a nanocrystalline light-emitting body as a guest material. The host-guest composite light-emitting layer; wherein: the conjugated organic small molecule is a P-type semiconductor, and two-dimensional orientation crystal growth in the light-emitting layer; The volume fraction in the layer does not exceed 5%. By reducing the volume fraction of nanocrystals in the light ^- emitting layer, the present invention can increase the hole injection ratio by more than 6 orders of magnitude, and realize electroluminescence with high quantum efficiency. Its fluorescence quantum efficiency can still exceed 80%.

Description

Highly discrete nanocrystalline light-emitting layers for electroluminescent devices and electroluminescent layers based thereon light emitting device

technical field

The invention belongs to the field of electroluminescent devices, and particularly relates to a composite light-emitting layer with a host-guest structure composed of a small molecule organic semiconductor and an inorganic nanocrystalline light-emitting body and an electroluminescent device based thereon.

Background technique

Nanocrystals can be formed into thin films by solution methods, and their emission spectrum has a relatively narrow spectral bandwidth and a tunable wavelength range. In practical applications, nanocrystals need to be repaired by surface ligands to repair surface defect states, thereby reducing the probability of non-radiative recombination and improving the stability of nanocrystals in solvents. However, the currently used surface ligands have poor electrical conductivity, which leads to a large energy loss in electroluminescent devices. The existing technology directly uses nanocrystals as the light-emitting layer, the conductivity of electrons is much higher than that of holes, and the contribution of hole injection to current (hole injection ratio) is as low as 10 ^-8 . contribution can be ignored. Since the carrier injection is extremely unbalanced, a certain thickness of the electron blocking layer must be employed to enforce balanced carrier injection characteristics. The introduction of the barrier layer brings about energy loss to a certain extent, and its thickness is only a few nanometers, which is not easy to precisely control, so it is not conducive to the design of electroluminescent devices with simple structure and reliable performance.

Existing electroluminescent devices based on nanocrystalline light-emitting layers, the light-emitting layers of which are prepared by a solution method, are suitable for use as a surface light source with a planar two-dimensional structure, such as a display backlight. The volume ratio of nanocrystals in the light-emitting layer of such devices is 100%. Due to the low power per unit area, which is in the order of milliwatts, a significant feature of nanocrystal emitters in such devices is the comparison of non-equilibrium carrier concentrations. In this case, the lifetime of carrier radiative recombination is relatively close to that of non-radiative recombination, and the non-radiative recombination process cannot be ignored, so the quantum efficiency of the device in actual operation is significantly lower than that under high power conditions. .

SUMMARY OF THE INVENTION

The present invention is to avoid the above-mentioned deficiencies in the prior art, and provides a highly discrete nanocrystalline light-emitting layer applied to an electroluminescent device and an electroluminescent device based thereon, so as to improve the hole injection ratio and the luminescent nanocrystalline The purpose of the invention is to improve the electroluminescence quantum efficiency of the device or simplify the structure of the device. By rationally setting the structure of the light-emitting layer and reducing the volume ratio occupied by nanocrystals in the light-emitting layer, the quantum efficiency of the device can be improved.

The present invention adopts the following technical scheme to solve the technical problem:

The present invention firstly discloses a highly discrete nanocrystalline light-emitting layer applied to an electroluminescent device, which is characterized in that: the highly discrete nanocrystalline light-emitting layer uses a conjugated organic small molecule as a host material and a nanocrystalline light-emitting body as a guest material A host-guest composite light-emitting layer is formed; wherein: the conjugated organic small molecule is a P-type semiconductor, and the two-dimensional orientation crystal grows in the light-emitting layer, and the in-plane field effect mobility is greater than 0.5cm ² V ^-1 s ^-1 ; the nanocrystal emits light The bulk is distributed in the host material in a sufficiently discrete form, and the volume fraction of nanocrystalline luminophores in the light-emitting layer does not exceed 5%.

The invention can continuously adjust the hole injection ratio of the light-emitting layer by adjusting the volume fraction of the nanocrystalline light-emitting body in the light-emitting layer, and the variable range is not less than 6 orders of magnitude, so as to precisely control the carrier balance and realize high quantum efficiency. Electroluminescence.

In the light-emitting layer of the present invention, the host material has a larger optical band gap than the guest material; the indirect excitation method is adopted, that is, the photon energy (hν) of the excitation light is greater than the optical band gap of the host material, and the photoluminescence quantum of the light-emitting layer is measured. The efficiency is higher than that of electroluminescent devices using pure nanocrystalline materials as the light-emitting layer.

Further, the conjugated organic small molecule is C8-BTBT, and the nanocrystal light-emitting body is a lead-halide perovskite quantum dot. The middle skeleton of the C8-BTBT molecular structure is a π-plane conjugated structure with alkyl chains at both ends or both sides; The ray diffraction has a characteristic peak of (00l) out-of-plane orientation, the π-plane conjugated structure of the molecule self-assembles along the substrate surface direction (in-plane direction), and the carrier mobility in the in-plane direction is greater than that perpendicular to the substrate surface. mobility.

The preparation method of the highly discrete nanocrystal light-emitting layer of the present invention is to uniformly disperse the conjugated organic small molecule and the nanocrystal light-emitting body in an organic solvent, and then form a film by a spin coating method or a solution shearing method. Specifically include the following steps:

First, prepare a precursor solution: according to the mass ratio of the nanocrystal light emitter and the conjugated organic small molecule of 1:3-4, the conjugated organic small molecule and the nanocrystal light emitter are uniformly dispersed in an organic solvent to obtain a precursor solution, wherein The concentration of nanocrystals is 5-15 mg/mL;

Then the precursor solution is formed on the target substrate by spin coating or solution shearing to form a highly discrete nanocrystalline light-emitting layer;

The specific method of the spin coating method is as follows: uniformly coating the precursor solution on the target substrate, and then vacuum drying to form a highly discrete nanocrystalline light-emitting layer;

The solution shearing method is based on the relative directional mechanical movement between the substrate and the solution state precursor to complete the oriented film formation, and the blade coating method or the pulling method can be used. The specific method of the blade coating method is as follows: drop the precursor solution on the target substrate for blade coating, while the temperature of the target substrate is kept at 90° C., the shear rate of the blade is 1 cm/s, the inclination angle of the blade is 45°, and the blade is scraped. After coating, it is naturally dried to form a highly discrete nanocrystalline light-emitting layer; the process parameters of the pulling method are: dipping speed 30mm/min, dipping time 180s, and pulling speed 5mm/min.

The invention also discloses an electroluminescent device based on the highly discrete nanocrystalline light-emitting layer, which is characterized in that: ITO conductive glass is used as a substrate (ITO is used as a cathode of the device), and on the substrate are sequentially arranged ZnO thin film (preferably Mg, Li co-doped ZnO thin film) as electron transport layer, highly discrete nanocrystalline light _- emitting layer, CBP thin film as hole transport layer, MoO3 layer as hole injection layer, and anode as anode the Al layer.

Compared with the prior art, the beneficial effects of the present invention are embodied in:

1. The light-emitting layer of the present invention can inject electrons and holes efficiently, realize a wide adjustment range of injection ratio, especially can greatly improve the injection efficiency of holes, so that the hole injection ratio can be increased from ^10-8 to more than ^10-2 , Compared with the existing electron blocking layer technology, the control precision is higher and the repeatability is better;

2. The volume fraction of nanocrystals in the light-emitting layer of the present invention is less than 5%, which greatly increases the non-equilibrium carrier concentration inside the nanocrystals, thereby increasing the occurrence probability of radiative recombination;

3. Based on the layered morphology of the two-dimensional growth of the host material, the light-emitting layer film of the present invention has a high coverage rate and is conducive to the transport of carriers in the in-plane direction, which is a good carrier transport layer and electroluminescent device. Uniform light emission can be achieved without the need for a carrier transport layer;

4. The preparation process of the light-emitting layer film of the present invention is suitable for substrates of different materials or shapes, and has universality;

5. In the electroluminescent device based on the light-emitting layer of the present invention, by adjusting the volume fraction of the nanocrystalline light-emitting body in the light-emitting layer, the hole injection ratio of the light-emitting layer can be precisely adjusted, and the variable range exceeds 6 orders of magnitude, thereby achieving high quantum efficiency electroluminescence.

6. Under the condition of low power (<1.0mWcm ^-2 ), the fluorescence quantum efficiency of the light-emitting layer of the electroluminescent device of the present invention can still exceed 80%, and the application in low-power electronic products has the advantage of more power saving.

Description of drawings

Fig. 1 is the molecular structure of the typical host material C8-BTBT in the embodiment of the present invention;

Fig. 2 is the molecular arrangement of conjugated organic small molecule C8-BTBT in the embodiment of the present invention;

Figure 3 is a polarizing microscope photo of a highly discrete nanocrystalline light-emitting layer prepared by spin coating;

Fig. 4 is the fluorescence microscope photograph of the highly discrete nanocrystalline light-emitting layer prepared by the blade coating method;

Fig. 5 is the XRD diffraction pattern of CsPbBr ₃ nanocrystals and C8-BTBT composite light-emitting layers with different composite ratios prepared by spin coating on a single crystal silicon substrate;

Fig. 6 is the XRD diffraction pattern of CsPbBr ₃ nanocrystals and C8-BTBT composite light-emitting layers with different composite ratios prepared by solution shearing method on a single crystal silicon substrate;

Figure 7 is a polarizing microscope image of a composite nanocrystal light-emitting layer prepared with a host-guest composite ratio of 1:1;

Figure 8 is a polarizing microscope image of a highly discrete nanocrystalline light-emitting layer prepared with a 3:1 host-guest composite ratio;

Fig. 9 is the fluorescence quantum efficiency (excitation power density is 20μWcm ^-2 ) of composite films with different mass ratios;

10 is a schematic structural diagram of an electroluminescent device using ZnO as an electron injection layer;

Fig. 11 is the voltage and current density curves of single-electron device and single-hole device;

FIG. 12 is a schematic structural diagram of an electroluminescent device capable of achieving balanced carrier injection.

Detailed ways

In order to make the above objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention will be described in detail below with reference to the embodiments. The following contents are only examples and descriptions of the concept of the present invention. Those skilled in the art can make various modifications or supplements to the specific embodiments described or substitute them in a similar manner, as long as they do not deviate from the concept of the invention. Or beyond the scope defined by the claims, all belong to the protection scope of the present invention.

Example 1

In this embodiment, the highly discrete nanocrystal light-emitting layer is a host-guest composite light-emitting layer composed of a conjugated organic small molecule C8-BTBT as a host material and a perovskite _CsPbBr3 nanocrystal light-emitting body as a guest material; wherein: conjugated The organic small molecule C8-BTBT is a P-type semiconductor, which grows in two-dimensional orientation crystals in the light-emitting layer, and the in-plane field effect mobility is greater than 0.5cm ² V ^{- 1} s ^-1 ; the nanocrystalline light-emitting body is distributed in the host in a sufficiently discrete form In the material, and the volume fraction of the nanocrystalline light-emitting body in the light-emitting layer does not exceed 5%.

1 and 2 are the molecular structure and molecular arrangement diagram of the host material C8-BTBT. _The middle skeleton of the molecular structure of C _{8 -BTBT} is a π-plane conjugated structure with alkyl chains at both ends or both sides; - The ray diffraction has a characteristic peak of (00l) out-of-plane orientation, the π-plane conjugated structure of the molecule is arranged parallel to the substrate surface, and the mobility of carriers in the in-plane direction is greater than that perpendicular to the substrate surface.

The preparation method of the highly discrete nanocrystal light-emitting layer is to uniformly disperse the conjugated organic small molecule and the nanocrystal light-emitting body in a solvent, and then form a film by a spin coating method or a solution shearing method. details as follows:

First prepare the precursor solution: according to the mass ratio required by the conjugated organic small molecule C8-BTBT and _CsPbBr3 nanocrystal luminophores, the conjugated organic small molecule and nanocrystals are uniformly dispersed in an organic solvent (the organic solvent used in the spin coating method is Heptane, the organic solvent used in the solution shearing method is toluene solvent) to obtain a precursor solution, wherein the concentration of nanocrystals is 5 mg/mL; then the precursor solution is formed on the target substrate by spin coating method or solution shearing method. film, forming a highly discrete nanocrystalline light-emitting layer;

The solution shearing method in this embodiment can control the thickness and morphology of the light-emitting layer by setting the concentration of the precursor solution, the temperature of the substrate, the shearing speed of the scraper, and the inclination angle of the blade, thereby achieving good repeatability and full coverage. , Oriented crystalline composite light-emitting layer thin film. Specifically, the solution shearing method adopts the blade coating method or the pulling method; the specific method of the blade coating method is as follows: drop the precursor solution on the target substrate for blade coating, while the temperature of the target substrate is kept at 90 ° C, and the shear rate of the blade is The inclination angle of the blade is 1cm/s, the inclination angle of the blade is 45°, and the film is naturally dried after scraping to form a highly discrete nanocrystalline light-emitting layer; the process parameters of the pulling method are: dipping speed 30mm/min, dipping time 180s, pulling Speed 5mm/min.

The specific method of the spin coating method in this embodiment is as follows: the precursor solution is evenly spin-coated on the target substrate (rotation speed is 2500 rpm, time is 60 s), and then vacuum dried (drying at room temperature for 30 min), that is, the formation of highly discrete nanocrystalline luminescence Floor;

In this embodiment, the spin coating method or the solution shearing method adopted for the light-emitting layer have advantages and disadvantages. The spin coating method is relatively mature, and it is easy to obtain a film with a uniform and controllable thickness. However, in this example, since the host material organic small molecule C8-BTBT is easier to align and grow, the in-plane orientation of the host-guest composite film prepared by the spin coating method is relatively weak; the solution shearing method can obtain thicker films , and the crystalline orientation of the film is good, and the nanocrystals in the highly discrete nanocrystal composite light-emitting layer are prone to preferential orientation during the self-assembly process of small molecule orientation, but the thickness uniformity is not as good as that of the film prepared by spin coating.

Fig. 3 is a polarized light microscope photo of the highly discrete nanocrystalline light-emitting layer prepared by spin coating method (the target substrate is ITO glass deposited with ZnO, and the mass ratio of CsPbBr ₃ quantum dots to C8-BTBT is CsPbBr ₃ : C8-BTBT=1: 3), Figure 4 is a fluorescence microscope photo of the highly discrete nanocrystalline light-emitting layer prepared by the blade coating method (the target substrate is ITO glass deposited with ZnO, and the mass ratio of CsPbBr ₃ quantum dots to C8-BTBT is CsPbBr ₃ :C8-BTBT = 1:3). It can be seen that the film prepared by spin coating method has continuous crystal and uniform morphology, but the film prepared by solution shearing method has a certain orientation while obtaining high coverage.

Figure 5 and Figure 6 are the XRD diffraction patterns of the CsPbBr ₃ nanocrystals and the C8-BTBT composite light-emitting layer with different composite ratios prepared by the spin coating method and the pulling method, respectively. It can be seen that the light-emitting layer thin films prepared by spin coating method or solution shearing method have broad diffraction peaks at 15.2° and 30.7°, which are the characteristics of nanocrystal diffraction. In addition, it can be seen that the composite light-emitting layer prepared by the solution shearing method has a strong lattice interaction between the organic small molecules and the nanocrystals. Especially in the highly discrete composite light-emitting layer, the nanocrystals have a significant preferred orientation, which shows that the characteristic diffraction peak at 30.7° is greatly enhanced. It is also demonstrated that by reducing the volume fraction of nanocrystals, their dispersed morphology in the host material undergoes a controllable transformation.

7 and 8 are polarizing microscope images of the composite light-emitting layer prepared by the pulling method. When the mass ratio of CsPbBr ₃ : C8-BTBT is 1:1, the morphology of C8-BTBT presents a one-dimensional linear crystal form, and the high discrete composite luminescence with a mass ratio of CsPbBr ₃ : C8-BTBT of 1:3 layer, the morphology of C8-BTBT showed a two-dimensional planar growth crystal form. According to the XRD diffraction spectrum, the lattice parameters of small molecular crystals and nanocrystals can be obtained (refer to patent PCT/CN2018/083738), and their densities can be calculated to be 0.65gcm ^-3 and 5.15gcm ^-3 respectively, and then different masses can be obtained. ratio of the film to the corresponding nanocrystal integral fraction. For example, in a highly discrete composite light-emitting layer with a mass ratio of 1:3, the volume fraction of nanocrystals is 4%.

FIG. 9 is the fluorescence quantum efficiency of the composite thin films with different mass ratios prepared by the pulling method. The excitation power density used is 20 μWcm ⁻² and the excitation wavelength is 410 nm. For the highly discrete composite light-emitting layer with a mass ratio of CsPbBr ₃ :C8-BTBT of 1:3, the maximum fluorescence quantum efficiency is still higher than 80%. Fluorescence quantum efficiency is an important indicator to measure the photoluminescence properties of the light-emitting layer, and high fluorescence quantum efficiency is also a necessary condition for the preparation of efficient electroluminescence devices. It can be seen that even at low excitation power density, the fluorescence quantum efficiency of the host-guest composite light-emitting layer relative to the pure nanocrystalline light-emitting layer is increased from 66.8% to 80.2%, and the energy conversion efficiency of the host-guest composite light-emitting layer is greatly improved.

The morphology of the host material C8-BTBT of the light-emitting layer in this embodiment has the characteristics of oriented crystallization, two-dimensional growth and high coverage, and has the characteristics of P-type semiconductor, and its in-plane field effect mobility is greater than 0.5cm ² V ^-1 s ^-1 . It has been demonstrated that the growth and morphology features of C8-BTBT are not limited to ZnO substrates, and such features can exist on a variety of substrates, which provides more possibilities for designing and optimizing device structures. This embodiment provides a method for designing and optimizing the structure of an electroluminescent device. This embodiment is based on the ITO/ZnO/CsPbBr ₃ :C8-BTBT/CBP/MoO ₃ /Al shown in FIG. The light-emitting layer increases the hole injection ratio, and then according to the requirements of carrier injection balance, the ZnO layer is further doped to reduce the current density of electron injection until it reaches the same order of magnitude as the current density of hole injection.

The structure of the electroluminescent device based on the highly discrete nanocrystalline light-emitting layer in this embodiment is as follows: an indium tin oxide ITO conductive glass is used as a substrate, and an electron transport layer, a light-emitting layer, a hole transport layer, an electron transport layer, a light-emitting layer, a hole transport layer, a hole injection layer and anode. Among them, as shown in Figure 10, the electron transport layer is a ZnO thin film (70nm thick), the light-emitting layer is a highly discrete nanocrystalline light-emitting layer composed of conjugated organic small molecules C8-BTBT and perovskite _CsPbBr3 nanocrystals, holes The transport layer is a CBP thin film (50 nm in thickness), the hole injection layer is a MoO3 layer ( ₁₀ nm in thickness), and the electrode is an aluminum electrode (100 nm in thickness). Electrons and holes recombine in the light-emitting layer to emit light.

The fabrication method of the electroluminescent device in this embodiment is as follows:

1. Preparation of ZnO thin films as electron transport layers

An ethanolic solution of zinc oxide (30 mg/mL) was coated on ITO glass that had been cleaned and treated with ultraviolet ozone. The spin coating parameters were 1500 rpm and 40 s, and then annealed at 150 °C for 10 min to obtain a ZnO thin film.

2. Preparation of highly discrete nanocrystalline light-emitting layer

The highly discrete nanocrystalline light-emitting layer was prepared according to the above method.

3. Evaporate CBP film (thickness of 50nm), MoO ₃ layer (thickness of 10nm) and aluminum electrode (thickness of 100nm) in turn with a vacuum coating machine.

In order to quantitatively study the effect of the volume fraction of nanocrystals in the composite light-emitting layer on the hole injection ratio, a single-hole device (ITO/PEDOT:PSS/light-emitting layer/CBP/MoO ₃ /Al) and a single-electron device were designed in this example. (ITO/ZnO/light-emitting layer/Ag), and its voltage and current density curves were tested with ITO as the cathode, as shown in FIG. 11 . For pure nanocrystalline light-emitting layers, the electron injection current density is 8 orders of magnitude higher than the hole injection current density, and this unbalanced carrier injection leads to extremely low quantum efficiency of electroluminescent devices. By gradually increasing the composition of the host material in the light-emitting layer, that is, CsPbBr ₃ :C8-BTBT=1:0 to 1:3, the volume fraction of nanocrystals is gradually reduced from 100% to 4%, and the corresponding single-hole device has a The hole injection ability is gradually enhanced, and the hole injection current density can be increased by 6 orders of magnitude, which sharply increases the radiative recombination probability of electrons and holes in the light-emitting layer, so that more efficient electroluminescence can be achieved.

It can be seen from Figure 11 that the electron injection current density is still 2 orders of magnitude higher than the hole injection current density, and the electron injection current density near the turn-on voltage is too large, so the electron injection current density needs to be further reduced. For example, using Mg, Li co-doped ZnO (MLZO) as shown in Figure 12 as the electron injection layer, due to the increase of the band gap and the decrease of the surface exciton quenching density, the electron injection current density and surface non-radiative recombination will be affected by suppression, thereby further improving the external quantum efficiency of the device.

Claims (8)

1. be applied to the high discrete nanocrystalline light-emitting layer of electroluminescent device, it is characterized in that: described high discrete nanocrystalline light-emitting layer is with conjugated organic small molecule as the host material, with the nanocrystal light-emitting body as the host material constituted as the guest material. Guest composite light-emitting layer; Among them: the conjugated organic small molecule is a P-type semiconductor, which grows in two-dimensional orientation in the light-emitting layer, and the in-plane field effect mobility is greater than 0.5cm ² V ^-1 s ^-1 ; the nanocrystalline light-emitting body is distributed in a sufficiently discrete form in In the host material, the volume fraction of the nanocrystalline light-emitting body in the light-emitting layer does not exceed 5%. 2. The highly discrete nanocrystalline light-emitting layer applied to an electroluminescent device according to claim 1, wherein the hole injection of the light-emitting layer can be continuously adjusted by adjusting the volume fraction of the nanocrystalline light-emitting body in the light-emitting layer The variable range is not less than 6 orders of magnitude, so as to precisely control the carrier balance and realize electroluminescence with high quantum efficiency. 3. The highly discrete nanocrystalline light-emitting layer applied to an electroluminescent device according to claim 1, wherein the conjugated organic small molecule is C8-BTBT, and the nanocrystalline light-emitting body is lead-halide perovskite Mine quantum dots. 4. The highly discrete nanocrystalline light-emitting layer applied to an electroluminescent device according to claim 3, wherein the middle skeleton of the C8-BTBT molecular structure is a π plane conjugated structure, and both ends or both sides have alkyl groups chain; in the light-emitting layer film formed by the self-assembly of C8-BTBT and nanocrystals in solution, the X-ray diffraction of C8-BTBT has a characteristic peak of (00l) out-of-plane orientation, and the π-plane conjugated structure of the molecule is along the substrate surface. Directional self-assembly, the carrier mobility in the in-plane direction is greater than that perpendicular to the substrate surface. 5. A method for preparing a highly discrete nanocrystal light-emitting layer according to any one of claims 1 to 4, wherein the conjugated organic small molecule and the nanocrystal light-emitting body are uniformly dispersed in an organic solvent, and then Obtained by spin coating or solution shearing. 6. the preparation method of the highly discrete nanocrystalline light-emitting layer according to claim 5, is characterized in that: First, prepare a precursor solution: according to the mass ratio of the nanocrystal light emitter and the conjugated organic small molecule of 1:3-4, the conjugated organic small molecule and the nanocrystal light emitter are uniformly dispersed in an organic solvent to obtain a precursor solution, wherein The concentration of nanocrystals is 5-15 mg/mL; Then the precursor solution is formed on the target substrate by spin coating or solution shearing to form a highly discrete nanocrystalline light-emitting layer; The specific method of the spin coating method is as follows: using a spin coater to uniformly spin the precursor solution on the target substrate, and then vacuum drying to form a highly discrete nanocrystalline light-emitting layer; The solution shearing method adopts the blade coating method or the pulling method; the specific method of the blade coating method is: drop the precursor solution on the target substrate for blade coating, while the temperature of the target substrate is maintained at 90 ° C, and the blade shear rate is 1cm/s, the inclination angle of the blade is 45°, and the film is naturally dried after scraping to form a highly discrete nanocrystalline light-emitting layer; the process parameters of the pulling method are as follows: dipping speed 30mm/min, dipping time 180s, pulling speed 5mm/min. 7. An electroluminescent device based on the highly discrete nanocrystalline light-emitting layer according to any one of claims 1 to 4, characterized in that: ITO conductive glass is used as a substrate, and arranged on the substrate in sequence There are ZnO thin films as electron transport layers, highly discrete nanocrystalline light emitting layers, CBP thin films as hole transport layers, _MoO3 layers as hole injection layers, and Al layers as anodes. 8 . The electroluminescent device of claim 7 , wherein the ZnO thin film is a Mg and Li co-doped ZnO thin film. 9 .

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