Quantum dot electroluminescent device with a gradient of disorder in the light emitting layer and method of manufacturing the same

Abstract

The application belongs to the field of electroluminescent devices, and particularly relates to a quantum dot electroluminescent device with a gradient of disorder degree of a light-emitting layer. The device comprises a substrate, a device anode, a hole injection layer, a hole transport layer, a quantum dot light-emitting layer, an electron transport layer and a device cathode arranged in sequence. The quantum dot light-emitting layer is stacked by a plurality of colloidal nanocrystal monolayer self-assembled films. The average energy of the electronic state density distribution and the average size of nanocrystals of each monolayer self-assembled film are the same. The width of the electronic state density distribution of the highest occupied state orbital and the lowest unoccupied state orbital and the width of the nanocrystal size distribution of each monolayer self-assembled film monotonically decrease along the normal direction of the substrate with the increase of the distance from the hole transport layer-quantum dot layer interface, and finally tend to a constant. The scheme breaks through the scheme of improving hole injection based on the energy level matching theory, reduces the hole injection barrier between the hole transport layer and the quantum dot layer through the gradient change of the disorder degree, and improves the light-emitting performance of the device.

Description

Technical Field

[0001] This invention belongs to the field of electroluminescent devices, specifically relating to a quantum dot electroluminescent device with a disorder gradient in the light-emitting layer. Background Technology

[0002] Quantum dot materials possess unique properties, including narrow full width at half maximum (FWHM), high color purity, controllable emission wavelength based on particle size, and compatibility with solution-based methods. Therefore, quantum dot electroluminescent semiconductors (QLEDs) demonstrate immense commercial value and application prospects in the display and lighting fields. With continued research, the luminous efficiency of QLEDs has been significantly improved, approaching that of commercially available organic light-emitting diodes (OLEDs). From the long-term development perspective of display technology, quantum dot electroluminescent displays are expected to become the next generation of mainstream display technology.

[0003] Over the years, QLEDs have gradually evolved into their current mainstream structure, consisting of an anode, hole injection layer, hole transport layer, light-emitting layer, electron transport layer, and cathode. When a voltage is applied, electrons and holes are injected from their respective electrodes, transported through the functional layers to the light-emitting layer, and then recombine with the carriers in the quantum dot to generate photons. To achieve high device performance, the hole transport layer generally requires high hole mobility, and the highest occupied molecular orbital (HOMO) level must match the work function of the hole injection layer and the valence band level of the quantum dot's light-emitting layer to reduce the hole injection barrier. The electron transport layer needs good electron mobility, and the lowest unoccupied molecular orbital (LUMO) level must match the work function of the conduction band of the light-emitting layer and the cathode to reduce the electron injection barrier.

[0004] There are many factors that affect the performance of QLED. In order to improve the performance of QLED devices, researchers currently focus on increasing the probability of carrier recombination, such as improving carrier injection transport efficiency and promoting carrier injection balance.

[0005] For QLED devices, the balance between electron and hole injection transport efficiency is a crucial factor affecting device performance and lifetime. Mainstream device fabrication processes utilize electron transport layer materials with higher electron mobility than common hole transport layer materials, and their LUMO level matches the conduction band of QDs (quantum dots), resulting in a low electron injection barrier. Conversely, a higher hole injection barrier leads to charge imbalance. This unbalanced carrier injection charges the quantum dots, increasing the Auger recombination rate and raising the operating voltage, thereby reducing the device's luminous efficiency and lifetime.

[0006] To address the problem of low hole injection efficiency, researchers in the QLED field have made many attempts. These can be categorized based on the different injection barriers.

[0007] (1) There are two schemes to improve the hole injection efficiency between the electrode and the hole transport layer: 1-1 select an electrode material with a higher work function to match the deep HOMO energy level of the hole transport material; 1-2 use an ultra-thin dielectric material to improve the apparent work function of the electrode material, such as using MoO3 to greatly increase the apparent work function of ITO.

[0008] (2) There are two approaches to improve the hole injection efficiency between the hole transport layer and the inorganic nanocrystal material: 2-1 Constructing a multilayer hole transport layer to form a stepped HOMO energy level and ease the injection barrier. For example, poly[(N,N'-(4-n-butylphenyl)-N,N'-diphenyl-1,4-phenylenediamine)-co-(9,9-di-n-octylfluorenyl-2,7-diyl)](TFB) and polyvinylcarbazole (PVK) are used to form a bilayer hole transport layer; 2-2 The potential barrier between the hole transport layer and the inorganic nanocrystal is reduced by developing a hole transport layer with a deeper HOMO energy level. Summary of the Invention

[0009] In order to solve the problem of low hole injection efficiency, many attempts have been made in the hole injection layer and quantum dot light-emitting layer in the existing technology, but they all have certain limitations.

[0010] (1) Of the two schemes to improve the hole injection efficiency between the electrode and the hole transport layer, 1-1 electrodes with high work function are usually difficult to obtain and difficult to be compatible with solution coating preparation; 1-2 although improving the apparent work function of the electrode material helps to reduce the hole injection barrier, the electrode-hole transport layer interface usually has a serious Fermi pinning effect, and the injection barrier between the electrode and the hole transport layer is still very high.

[0011] (2) Among the two schemes to improve the hole injection efficiency between the hole transport layer and the inorganic nanocrystalline material, 2-1, constructing a multi-layer hole transport layer to form a stepped HOMO energy level, although it eases the injection barrier, it is difficult to be widely applied to device fabrication by solution method due to the influence of orthogonal solvent effect and material selection; 2-2, selecting a hole transport layer with a deeper HOMO energy level, although this scheme reduces the barrier between the hole transport layer and the light-emitting layer, it is easy to create a high injection barrier between the electrode and the hole transport layer, thereby accelerating device decay and reducing working life.

[0012] In summary, low hole injection efficiency is the main drawback of existing QLEDs. Furthermore, known solutions are all insufficient to meet device requirements for hole injection.

[0013] In view of the shortcomings of current mainstream QLED devices, the main problem solved by this invention is to improve the efficiency of hole injection into quantum dots in QLEDs, thereby improving device performance.

[0014] In view of the shortcomings of the existing technology 1-1, the technical problem to be solved by the present invention 1-1 is that the device structure improves hole injection without relying on high work function electrodes, and the device structure is suitable for solution coating preparation.

[0015] In view of the shortcomings of existing technologies 1-2, the technical problem to be solved by the present invention 1-2 is: the device structure reduces the hole injection barrier without relying on ultrathin dielectric material.

[0016] In view of the shortcomings of the existing technology 2-1, the technical problem 2-1 to be solved by the present invention is: the device structure improves hole injection without relying on the multilayer hole injection layer HOMO gradient structure, and is universally applicable to various solution coating preparation schemes.

[0017] In view of the shortcomings of the existing technology 2-2, the technical problem 2-2 that this invention aims to solve is: to improve hole injection and increase the working life of QLED without relying on the deep HOMO level hole transport layer.

[0018] In view of the shortcomings of existing technologies, this invention proposes a new scheme for hole injection efficiency in QLED devices based on disorder gradient engineering. This scheme is compatible with the device solution coating preparation process. By increasing the disorder of the light-emitting layer adjacent to the hole transport layer, the hole transport barrier is reduced, ultimately achieving the effects of improving hole injection efficiency, improving carrier injection balance, and enhancing QLED device performance.

[0019] To address the aforementioned technical problems, this application provides the following technical solution:

[0020] The present invention provides a quantum dot electroluminescent device with a disorder gradient of the light-emitting layer, comprising a substrate, a device anode, a hole injection layer (HIL), a hole transport layer (HTL), a quantum dot light-emitting layer, an electron transport layer (ETL), and a device cathode arranged sequentially.

[0021] The quantum dot light-emitting layer is composed of multiple colloidal nanocrystal monolayer self-assembled films stacked together, with a thickness of 10-100 nm.

[0022] The average energy of the electronic state density distribution of each colloidal nanocrystal monolayer self-assembled film is the same as the average size of the nanocrystals.

[0023] The electronic state density distribution width and nanocrystal size distribution width of the highest occupied state orbital and the lowest unoccupied state orbital of each colloidal nanocrystal monolayer self-assembled film decrease monotonically along the normal direction of the substrate as the distance from the interface between the hole transport layer and the quantum dot light-emitting layer increases, and eventually tend to a constant value.

[0024] The quantum dot luminescent layer is composed of colloidal nanocrystals, which are selected from one or more of II-VI quantum dot (nanocrystal) materials, III-V quantum dot (nanocrystal) materials, perovskite quantum dot materials, and single-mass quantum dot materials.

[0025] In one embodiment of the present invention, the substrate material is selected from one or both of glass and polyethylene terephthalate (PET). The substrate has good surface wetting properties, facilitating solution coating.

[0026] In one embodiment of the present invention, the materials of the anode and cathode of the device are independently selected from one or more of indium tin oxide (ITO), fluorine-doped tin dioxide (FTO), aluminum (Al), and silver (Ag), and each has a thickness of 20-200 nm. The sheet resistance of the anode and cathode of the device is less than 50 Ω, enabling low-loss charge transfer.

[0027] In one embodiment of the present invention, the material of the hole injection layer is selected from one or two of polyethylene polymers and polythiophene polymers, and the thickness is 10-150 nm.

[0028] Furthermore, the hole injection layer is prepared by solution coating.

[0029] Furthermore, the work function of the hole injection layer is above 5.1 eV, and the conductivity is greater than 10. -5 S / cm.

[0030] Further, the polyethylene polymer is selected from poly(thiophene-3-[2-(2-methoxyethoxy)ethoxy]-2,5-dimethyl) OC), poly(3,4-ethylenedioxythiophene):polystyrene sulfonic acid (PEDOT:PSS) and PEDOT:PSS (an aqueous solution of a polymer) modified material (PEDOT:PSS:PFI) doped with perfluorinated ionomers; wherein the polythiophene polymer is selected from the polymer polythiophene:poly(perfluoroethylene-perfluoroether sulfonic acid) (PTT:PFFSA).

[0031] In one embodiment of the present invention, the material of the hole transport layer is selected from one or more of triphenylamine compounds and their derivative polymers, fluorene compounds and their derivative polymers, carbazole compounds and their derivative polymers, and spirocyclic compounds.

[0032] Furthermore, the triphenylamine compound and its derived polymers are selected from one or more of 4,4',4”-tris(carbazole-9-yl)triphenylamine (TCTA), N,N'-diphenyl-N,N'-di(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD), 4,4,4”-tris[(2,3,4,5-tetraphenyl)phenyl]aniline (TTPPPA), poly(N,N'-bis-4-butylphenyl-N,N'-bisphenyl)benzidine Poly-TPD, and poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine (PTAA).

[0033] Furthermore, the fluorene compound and its derived polymers are selected from one or more of N,N'-iminodiphenyl-4,4'-fluorene, 9,9-bis[4-(di-p-toluidine)phenyl]-2,7-bis-(2-naphthylphenylamino)fluorene, and poly[(N,N'-(4-n-butylphenyl)-N,N'-diphenyl-1,4-phenylenediamine)-co-(9,9-di-n-octylfluorene-2,7-diyl)](TFB).

[0034] Furthermore, the carbazolium compound and its derivative polymers are selected from one or more of 4,4'-bis(9-carbazolyl)biphenyl (CBP), 3',6'-bis(carbazol-9-yl)-bis[9-(2-ethylhexyl)carbazol-3,6-diyl] (G1CBC), and polyvinylcarbazole (PVK).

[0035] Further, the spirocyclic compound is selected from one or more of N,N'-bis(3-methylphenyl)-N,N'-di(phenyl)-2,7-diamino-9,9-spirodifluorene (Spiro-TPD) and 2,2',7,7'-tetra(N,N-diphenylamino)-2,7-diamino-9,9-spirophenanthrene (Spiro-TAD).

[0036] The hole transport layer exhibits good film-forming properties and hole mobility, while its HOMO energy level and HIL layer work function are well matched with the valence band energy level of the quantum dot luminescent layer. The thickness of the hole transport layer is 10-150 nm.

[0037] In one embodiment of the present invention, the quantum dot light-emitting layer is composed of several colloidal nanocrystal monolayer self-assembled films with a thickness of 10-100 nm.

[0038] Furthermore, the colloidal nanocrystal monolayer self-assembled film is obtained by coating colloidal nanocrystals and a photosensitive crosslinking agent and then subjecting them to ultraviolet exposure treatment; the colloidal nanocrystals are selected from one or more of II-VI quantum dot (nanocrystal) materials, III-V quantum dot (nanocrystal) materials, perovskite quantum dot materials and single quantum dot materials.

[0039] Further, the II-VI quantum dot (nanocrystalline) material is one or more of cadmium-based quantum dots, zinc-based quantum dots, and alloy quantum dots; the cadmium-based quantum dots are cadmium selenide (CdSe), cadmium sulfide (CdS), or cadmium telluride (CdTe); the zinc-based quantum dots are zinc selenide (ZnSe), zinc sulfide (ZnS), or zinc telluride (ZnTe); and the alloy quantum dots contain at least two of the above-mentioned II-VI compounds simultaneously, such as Zn 1-x Cd x Se 1-x S 1-y or ZnTe 1-y Se y ;

[0040] Furthermore, the III-V quantum dot (nanocrystalline) material is one or more of indium-based quantum dots, gallium-based quantum dots, and alloy quantum dots; the indium-based quantum dots are indium phosphide (InP) or indium arsenide (InAs); the gallium-based quantum dots are gallium nitride (GaN) or gallium arsenide (GaAs); the alloy quantum dots contain at least one of the above-mentioned III-V compounds and one II-VI compound, such as InP / ZnSe / ZnS.

[0041] Furthermore, the single quantum dot material is one or both of carbon quantum dots and silicon quantum dots.

[0042] Furthermore, the perovskite semiconductor material is one or more of cesium bromide, cesium bromide, cesium chloride, methylamino bromide, or formamidinium iodide quantum dot materials.

[0043] The photosensitive crosslinking agent is selected from one or more of nitrogen benzylidene compounds, carbenzylidene compounds, carbocation compounds, and free radical compounds. Figure 5 The structures of several representative photosensitive crosslinking agents are given, namely A, 3,3'-(4,4'-(perfluorobutane-1,4-diyl)bis(4,1-phenylene))bis(3-(trifluoromethyl)-3H-diazine, B, ethylene bis(4-azono-2,3,5,6-tetrafluorobenzoate), C, (3E,5E)3,5-bis-(4-azido-2,3,5,6-tetrafluorobenzyl)-1-methylpiperidin-4-one, and D, (1E,4E)-1,5-bis(4-azido-2,3,5,6-tetrafluorophenyl)penta-1,4-dien-3-one.

[0044] The colloidal nanocrystal monolayer self-assembled film is prepared by solution coating. The colloidal nanocrystals exhibit fluorescence properties; all colloidal nanocrystals in the quantum dot layer have the same chemical composition; the nanocrystal colloidal solution contains additional photosensitive components, which allow the nanocrystals to crosslink and solidify after being exposed to light of a specific wavelength; the electronic state density of the highest occupied orbital (HOMO) and the lowest unoccupied orbital (LUMO) of each monolayer self-assembled film, as well as the nanocrystal size, exhibit a monodisperse distribution; the average energy of the electronic state density distribution and the average size of the nanocrystals are the same for each monolayer self-assembled film; along the normal direction of the substrate, the width of the electronic state density distribution (σ) and the width of the nanocrystal size distribution of each monolayer self-assembled film monotonically decrease with increasing distance from the hole transport layer-quantum dot layer interface and eventually tend to a constant value.

[0045] In one embodiment of the present invention, the material of the electron transport layer is selected from one or more of metal oxides, imidazole compounds, pyridine compounds, pyrimidine compounds, anthracene compounds, organometallic chelates and compounds containing o-phenanthroline groups, and the thickness is 10-150 nm.

[0046] Furthermore, the metal oxide is selected from tin oxide (SnO2), zinc oxide (ZnO), and zinc magnesium oxide (ZnO). 1- x Mg x One or more of (O).

[0047] Furthermore, the imidazole compound is selected from one or both of 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene (TPBi) and 1,3,5-tris(2-(pyridin-2-yl)-1H-benzimidazol-1-yl)benzene (iTPyBIB).

[0048] Furthermore, the pyridine compound is selected from one or both of 1,3,5-tris[(3-pyridyl)-3-phenyl]benzene (TmPyPB) and 1,3,5-tris(4-pyridyl-3-ylphenyl)benzene (TpPyPB).

[0049] Furthermore, the pyrimidine compound is selected from one or both of 4,6-bis(3,5-di(3-pyridinylphenyl)-2-methylpyrimidine (B3PYMPM) and 4,6-bis(3,5-di(4-pyridinylphenyl)-2-methylpyrimidine (B4PYMPM).

[0050] Further, the anthracene compound is 9,10-bis(6-phenylpyridin-3-yl)anthracene (DPPyA).

[0051] Furthermore, the organometallic chelate is tris(8-hydroxyquinoline)aluminum (Alq3).

[0052] Furthermore, the compound containing the o-phenanthroline group is selected from one or both of 4,7-diphenyl-1,10-o-phenanthroline (BPhen) and 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP).

[0053] The electron transport layer can be prepared by solution coating.

[0054] The electron transport layer has good electron mobility and electron injection performance, and the LUMO energy level is well matched with the conduction band energy level of the light-emitting layer and the electrode work function of the cathode.

[0055] The present invention also provides a method for fabricating the above-mentioned quantum dot electroluminescent device with disorder gradient of the light-emitting layer, comprising the following steps: sequentially depositing a hole injection layer, a hole transport layer, a quantum dot light-emitting layer, an electron transport layer and a device cathode on a substrate on which a device anode has been loaded, to obtain the quantum dot electroluminescent device.

[0056] The technical solution of the present invention has the following advantages compared with the prior art:

[0057] 1. This scheme breaks through the previous approach of improving hole injection based on energy level matching theory. It reduces the injection barrier between the hole transport layer and the quantum dot layer by gradually changing the disorder gradient.

[0058] 2. Without changing the band gap of the quantum dot film, it improves the charge balance, reduces the operating voltage of QLED devices, increases the luminous efficiency of QLED devices, and extends the operating life of QLED devices. It is applicable to various quantum dot electroluminescent devices.

[0059] 3. The preparation process is compatible with existing solution coating processes and can be applied to inkjet printing or large-area quantum dot light-emitting devices. Attached Figure Description

[0060] Figure 1 A structural diagram of a quantum dot light-emitting diode device with an introduced quantum dot disorder ladder layer.

[0061] Figure 2 This is a schematic diagram of a Gaussian distribution.

[0062] Figure 3 A schematic diagram of the equivalent injection barrier Φ.

[0063] Figure 4 The diagram shows the particle size distribution of the QD layer and the electronic state density distributions of LUMO and HOMO.

[0064] Figure 5 The diagram shows the structures of four representative small-molecule photosensitive crosslinking agents.

[0065] Figure 6This is a comparison graph of the current-voltage test curves of Example 1 and Comparative Example 1.

[0066] Figure 7 This is a comparison chart of the external quantum efficiency-brightness test curves of Example 1 and Comparative Example 1.

[0067] Figure 8 This is a comparison chart of the brightness-voltage test curves of Example 1 and Comparative Example 1.

[0068] Figure 9 This is a comparison graph of the current-voltage test curves of Example 2 and Comparative Example 2.

[0069] Figure 10 This is a comparison chart of the external quantum efficiency-brightness test curves for Example 2 and Comparative Example 2.

[0070] Figure 11 This is a comparison chart of the brightness-voltage test curves of Example 2 and Comparative Example 2.

[0071] Figure 12 This is a comparison graph of the current-voltage test curves of Example 3 and Comparative Example 3.

[0072] Figure 13 This is a comparison chart of the external quantum efficiency-brightness test curves of Example 3 and Comparative Example 3.

[0073] Figure 14 This is a comparison chart of the brightness-voltage test curves of Example 3 and Comparative Example 3.

[0074] Explanation of reference numerals in the attached figures: 1-substrate, 2-device anode, 3-hole injection layer, 4-hole transport layer, 5-quantum dot light-emitting layer, 6-electron transport layer, 7-device cathode. Detailed Implementation

[0075] 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.

[0076] In all embodiments, quantum dot layers with a disorder gradient in the luminescent layer are named disorder-gradient quantum dots (D-QDs). Specifically, in Example 1, a zinc-cadmium-selenium-sulfur quantum dot layer with a disorder gradient in the luminescent layer is named D-ZnCdSeS-QDs; in Example 2, a cesium-lead-bromine-perovskite quantum dot layer with a disorder gradient in the luminescent layer is named D-CsPbBr3-QDs; and in Example 3, an indium phosphide quantum dot layer with a disorder gradient in the luminescent layer is named D-InP / ZnSe / ZnS-QDs.

[0077] Example 1

[0078] A zinc-cadmium-selenium-sulfur quantum dot (D-ZnCdSeS-QDs) light-emitting device with a disorder gradient in the light-emitting layer and a center wavelength of 466 nm was fabricated.

[0079] (1) Materials preparation:

[0080] 1-1: The indium tin oxide substrate (substrate 1) with ITO (device anode 2) was ultrasonically cleaned successively using glass cleaning solution, deionized water, acetone and isopropanol. Then the cleaned substrate was placed in an ultraviolet ozone cleaner for 15 minutes of pretreatment.

[0081] 1-2: Zinc cadmium selenide sulfur (ZnCdSeS) quantum dot solutions with center wavelengths of 462, 466, and 470 nm (energy intervals higher than 0.02 eV) were used to prepare monolayer quantum dot emitting layers. Except for the different center wavelengths, the fluorescence peak half widths of the three solutions were all 20 nm, and the concentrations were all 20 mg / mL.

[0082] Solutions with center wavelengths of 462, 466, and 470 nm were named solutions Q-, Q0, and Q+, respectively. Colloidal solution 1 was prepared using 80% (volume) Q0, 10% Q-, and 10% Q+, and 5% (volume) of the small molecule crosslinking agent 3,3'-(4,4'-(perfluorobutane-1,4-diyl)bis(4,1-phenylene))bis(3-(trifluoromethyl)-3H-diazine) was added relative to colloidal solution 1. The structure of the small molecule crosslinking agent is as follows: Figure 5 As shown in A;

[0083] Colloidal solution 2 was prepared using 90% (volume) Q0, 5% Q-, and 5% Q+, and a small molecule crosslinking agent was added relative to 5% (volume) of colloidal solution 2; colloidal solution 3 was prepared using 95% (volume) Q0, 2.5% Q-, and 2.5% Q+, and a small molecule crosslinking agent was added relative to 5% (volume) of colloidal solution 3; Q0 was used as colloidal solution 4;

[0084] (2) Device fabrication section:

[0085] 2-1: PEDOT:PSS was spin-coated onto the ITO substrate, i.e. the device anode 2, at a speed of 5000 rpm using a spin coater, and then annealed at 150°C for 15 min to obtain a hole injection layer 3 with a thickness of 25 nm.

[0086] 2-2: The sample formed in step 2-1 was transferred to a glove box under a nitrogen atmosphere. TFB was spin-coated onto the sample at a rate of 3000 rpm to a thickness of 30 nm using a spin coater. The sample was then annealed at 150 °C for 30 min to obtain hole transport layer 4.

[0087] 2-3: Spin-coat colloidal solution 1 onto the sample formed in step 2-2 at a speed of 3000 rpm, to a thickness of approximately 8 nm, followed by UV exposure treatment at an exposure dose of 150 mJ / cm². 2 ;

[0088] 2-4: Spin-coat colloidal solution 2 onto the sample formed in step 2-3 at a speed of 3000 rpm, to a thickness of approximately 8 nm, followed by UV exposure treatment at an exposure dose of 150 mJ / cm². 2 ;

[0089] 2-5: Spin-coat colloidal solution 3 onto the sample formed in step 2-4 at a speed of 3000 rpm, to a thickness of approximately 8 nm, followed by UV exposure treatment at an exposure dose of 150 mJ / cm². 2 ;

[0090] 2-6: Spin-coat colloidal solution 4 onto the sample formed in step 2-5 at a rate of 4000 rpm, with a thickness of about 20 nm, and anneal at 80 °C for 10 min to obtain quantum dot luminescent layer 5;

[0091] 2-7: Zinc oxide nanoparticles were spin-coated onto the sample formed in step 2-6 at a rate of 3000 rpm, with a thickness of 30 nm, and then annealed at 80 °C for 30 min to obtain electron transport layer 6.

[0092] 2-8: The sample formed in step 2-7 is transferred to a vacuum evaporation apparatus to deposit 100 nm of silver using physical vapor deposition, thus obtaining the device cathode 7.

[0093] The final device structure is ITO / PEDOT:PSS / TFB / D-ZnCdSeS-QDs / ZnO / Ag.

[0094] Example 2

[0095] A cesium lead bromide perovskite quantum dot (D-CsPbBr3-QDs) light-emitting device with a disorder gradient in the emitting layer and a center wavelength of 520 nm was fabricated.

[0096] (1) Materials preparation:

[0097] 1-1 The indium tin oxide substrate (substrate 1) with ITO (device anode 2) was ultrasonically cleaned in sequence using glass cleaning solution, deionized water, acetone and isopropanol. Then the cleaned substrate was placed in an ultraviolet ozone cleaner for 15 minutes of pretreatment.

[0098] 1-2 Cesium lead bromide perovskite quantum dot solutions (energy intervals higher than 0.02 eV) with center wavelengths of 515, 520, and 525 nm were used to prepare monolayer quantum dot emitting layers. Except for the different center wavelengths, the three solutions all had a full width at half maximum (FWHM) of 20 nm and a concentration of 20 mg / mL. The solutions with center wavelengths of 515, 520, and 525 nm were named solutions Q-, Q0, and Q+, respectively. Colloidal solution 1 was prepared using 80% (volume) Q0, 10% Q-, and 10% Q+, and 5% (volume) of a small molecule crosslinking agent was added relative to colloidal solution 1; colloidal solution 2 was prepared using 90% (volume) Q0, 5% Q-, and 5% Q+, and 5% (volume) of a small molecule crosslinking agent was added relative to colloidal solution 2; colloidal solution 3 was prepared using 95% (volume) Q0, 2.5% Q-, and 2.5% Q+, and 5% (volume) of a small molecule crosslinking agent was added relative to colloidal solution 3; Q0 was used as colloidal solution 4;

[0099] (2) Device fabrication section:

[0100] 2-1 PTT:PFFSA was spin-coated onto the ITO substrate, i.e. the device anode 2, at a speed of 5000 rpm using a spin coater, and then annealed at 150°C for 20 min to obtain a hole injection layer 3 with a thickness of 25 nm.

[0101] 2-2 The sample formed in 2-1 was transferred to a glove box under a nitrogen atmosphere. Hole transport layer material PVK was spin-coated onto it at a rate of 3000 rpm with a thickness of 30 nm using a spin coater. Then, it was annealed at 150 °C for 20 min to obtain hole transport layer 4.

[0102] 2-3. Colloidal solution 1 was spin-coated onto the sample formed in 2-2 at a speed of 3000 rpm, to a thickness of approximately 8 nm. Following this, UV exposure was performed at a dose of 150 mJ / cm². 2 ;

[0103] 2-4 Colloidal solution 2 was spin-coated onto the sample formed in 2-3 at a speed of 3000 rpm, to a thickness of approximately 8 nm, followed by UV exposure treatment at an exposure dose of 150 mJ / cm². 2 ;

[0104] 2-5. Colloidal solution 3 was spin-coated onto the sample formed in 2-4 at a speed of 3000 rpm, to a thickness of approximately 8 nm. Following this, UV exposure was performed at a dose of 150 mJ / cm². 2 ;

[0105] 2-6 The colloidal solution 4 was spin-coated onto the sample formed in 2-5 at a rate of 4000 rpm, with a thickness of about 20 nm, and then annealed at 80 °C for 15 min to obtain the quantum dot luminescent layer 5.

[0106] 2-7 The sample formed in 2-6 was transferred to a vacuum evaporation apparatus to physically vapor deposit 30 nm of 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene (TPBi) to obtain electron transport layer 6;

[0107] 2-8 The sample formed in 2-7 will be further vapor-deposited with a 1 nm cathode electrode modification layer of lithium fluoride (LiF);

[0108] 2-9 The sample formed in 2-8 is finally vapor-deposited with a 100nm aluminum electrode to obtain the device cathode 7;

[0109] The final device structure is ITO / PTT:PFFSA / PVK / D-CsPbBr3-QDs / TPBi / LiF / Al.

[0110] Example 3

[0111] A light-emitting device with indium phosphide quantum dot (D-InP / ZnSe / ZnS-QDs) and disorder gradient of the light-emitting layer with a center wavelength of 620 nm was fabricated.

[0112] (1) Materials preparation:

[0113] 1-1 The indium tin oxide substrate (substrate 1) with FTO (device anode 2) was ultrasonically cleaned sequentially using glass cleaning solution, deionized water, acetone and isopropanol. After that, the cleaned substrate was placed in an ultraviolet ozone cleaner for 15 minutes of pretreatment.

[0114] 1-2 Indium phosphide quantum dot solutions (energy intervals higher than 0.02 eV) with center wavelengths of 614, 620, and 626 nm were used to prepare monolayer quantum dot emitting layers. Except for the different center wavelengths, the three solutions all had a full width at half maximum (FWHM) of 30 nm and a concentration of 20 mg / mL. The solutions with center wavelengths of 614, 620, and 626 nm were named solutions Q-, Q0, and Q+, respectively. Colloidal solution 1 was prepared using 80% (volume) Q0, 10% Q-, and 10% Q+, and 5% (volume) of a small molecule crosslinking agent was added relative to colloidal solution 1; colloidal solution 2 was prepared using 90% (volume) Q0, 5% Q-, and 5% Q+, and 5% (volume) of a small molecule crosslinking agent was added relative to colloidal solution 2; colloidal solution 3 was prepared using 95% (volume) Q0, 2.5% Q-, and 2.5% Q+, and 5% (volume) of a small molecule crosslinking agent was added relative to colloidal solution 3; Q0 was used as colloidal solution 4;

[0115] (2) Device fabrication section:

[0116] 2-1 PEDOT:PSS was spin-coated onto the FTO substrate, i.e. the anode 2 of the device, at a speed of 5000 rpm using a spin coater, and then annealed at 150°C for 15 min to obtain a hole injection layer 3 with a thickness of 25 nm.

[0117] 2-2 The sample formed in 2-1 was transferred to a glove box under a nitrogen atmosphere. The hole transport layer material Poly-TPD was spin-coated onto it at a rate of 3000 rpm using a spin coater, with a thickness of 30 nm. Then, it was annealed at 150 °C for 15 min to obtain hole transport layer 4.

[0118] 2-3. Colloidal solution 1 was spin-coated onto the sample formed in 2-2 at a speed of 3000 rpm, to a thickness of approximately 8 nm. Following this, UV exposure was performed at a dose of 150 mJ / cm². 2 ;

[0119] 2-4 Colloidal solution 2 was spin-coated onto the sample formed in 2-3 at a speed of 3000 rpm, to a thickness of approximately 8 nm, followed by UV exposure treatment at an exposure dose of 150 mJ / cm². 2 ;

[0120] 2-5. Colloidal solution 3 was spin-coated onto the sample formed in 2-4 at a speed of 3000 rpm, to a thickness of approximately 8 nm. Following this, UV exposure was performed at a dose of 150 mJ / cm². 2 ;

[0121] 2-6 The colloidal solution 4 was spin-coated onto the sample formed in 2-5 at a rate of 4000 rpm, with a thickness of about 20 nm, and then annealed at 80 °C for 10 min to obtain the quantum dot luminescent layer 5.

[0122] 2-7 Zinc oxide magnesium nanoparticles were spin-coated onto the sample formed in 2-6 at a rate of 3000 rpm, with a thickness of 30 nm. Then, the sample was annealed at 80 °C for 30 min to obtain electron transport layer 6.

[0123] 2-8 The sample formed in 2-7 is transferred to a vacuum evaporation apparatus to deposit 100 nm of silver by physical vapor deposition, thus obtaining the device cathode 7.

[0124] The final device structure is FTO / PEDOT:PSS / Poly-TPD / D-InP / ZnSe / ZnS-QDs / ZnMgO / Ag.

[0125] Comparative Example 1

[0126] A zinc cadmium selenide sulfur quantum dot (ZnCdSeS-QDs) light-emitting device with a wavelength of 466 nm was fabricated.

[0127] (1) Materials preparation:

[0128] 1-1 The indium tin oxide substrate (substrate 1) with ITO (device anode 2) was ultrasonically cleaned in sequence using glass cleaning solution, deionized water, acetone and isopropanol. Then the cleaned substrate was placed in an ultraviolet ozone cleaner for 15 minutes of pretreatment.

[0129] 1-2 A cadmium selenide quantum dot solution with a center wavelength of 466 nm was used as the quantum dot emitting layer, with a full width at half maximum (FWHM) of 20 nm and a concentration of 20 mg / mL.

[0130] (2) Device fabrication section:

[0131] 2-1 PEDOT:PSS was spin-coated onto an ITO substrate at a rate of 5000 rpm using a spin coater, and then annealed at 150°C for 15 min to a thickness of 25 nm.

[0132] 2-2 The sample formed in 2-1 was transferred to a glove box under a nitrogen atmosphere. TFB was spin-coated onto the sample at a rate of 3000 rpm to a thickness of 30 nm using a spin coater. The sample was then annealed at 150 °C for 30 min.

[0133] 2-3 The cadmium selenide quantum dot solution was spin-coated onto the sample formed in 2-2 at a rate of 2000 rpm, with a thickness of about 35 nm, and then annealed at 80 °C for 10 min.

[0134] 2-4 Zinc oxide nanoparticles were spin-coated onto the sample formed in 2-3 at a rate of 3000 rpm to a thickness of 30 nm, and then annealed at 80 °C for 30 min.

[0135] 2-5 The sample formed in 2-4 is transferred to a vacuum evaporation apparatus for physical vapor deposition of 100 nm silver.

[0136] The final device structure is ITO / PEDOT:PSS / TFB / ZnCdSeS-QDs / ZnO / Ag.

[0137] Comparative Example 2

[0138] A cesium lead bromide perovskite quantum dot (CsPbBr3-QDs) light-emitting device with a wavelength of 520 nm was fabricated.

[0139] (1) Materials preparation:

[0140] 1-1 The indium tin oxide substrate (substrate 1) with ITO (device anode 2) was ultrasonically cleaned in sequence using glass cleaning solution, deionized water, acetone and isopropanol. Then the cleaned substrate was placed in an ultraviolet ozone cleaner for 15 minutes of pretreatment.

[0141] 1-2 A cesium lead bromide perovskite quantum dot solution with a center wavelength of 520 nm was used as the quantum dot emitting layer, with a full width at half maximum (FWHM) of 20 nm and a concentration of 20 mg / mL.

[0142] (2) Device fabrication section:

[0143] 2-1 PTT:PFFSA was spin-coated onto an ITO substrate at a rate of 5000 rpm using a spin coater, and then annealed at 150°C for 20 min to a thickness of 25 nm.

[0144] 2-2 The sample formed in 2-1 was transferred to a glove box under a nitrogen atmosphere. Hole transport layer material PVK was spin-coated onto it at a rate of 3000 rpm to a thickness of 30 nm using a spin coater. Then it was annealed at 150 °C for 20 min.

[0145] 2-3 A cesium lead bromide perovskite quantum dot solution was spin-coated onto the sample formed in 2-2 at a rate of 2000 rpm, with a thickness of about 20 nm, and then annealed at 80 °C for 10 min.

[0146] 2-4 The sample formed in 2-3 is transferred to a vacuum evaporation apparatus to physically vapor deposit a 30 nm electron transport layer of 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene (TPBi);

[0147] 2-5 The sample formed in 2-4 will be further vapor-deposited with a 1 nm cathode electrode modification layer of lithium fluoride (LiF);

[0148] 2-6 The sample formed in 2-5 will be vapor-deposited with a 100nm aluminum electrode;

[0149] The final device structure is ITO / PTT:PFFSA / PVK / CsPbBr3-QDs / TPBi / LiF / Al.

[0150] Comparative Example 3

[0151] Indium phosphide quantum dot (InP / ZnSe / ZnS-QDs) light-emitting devices with a wavelength of 620 nm were fabricated.

[0152] (1) Materials preparation:

[0153] 1-1 The indium tin oxide substrate (substrate 1) with FTO (device anode 2) was ultrasonically cleaned sequentially using glass cleaning solution, deionized water, acetone and isopropanol. After that, the cleaned substrate was placed in an ultraviolet ozone cleaner for 15 minutes of pretreatment.

[0154] 1-2 Indium phosphide quantum dot solution with a wavelength of 620 nm was used as the quantum dot luminescent layer, with a full width at half maximum (FWHM) of 30 nm and a concentration of 20 mg / mL.

[0155] (2) Device fabrication section:

[0156] 2-1 PEDOT:PSS was spin-coated onto an FTO substrate at a rate of 5000 rpm using a spin coater, and then annealed at 150°C for 15 min to a thickness of 25 nm.

[0157] 2-2 The sample formed in 2-1 was transferred to a glove box under a nitrogen atmosphere. Hole transport layer material Poly-TPD was spin-coated onto it at a rate of 3000 rpm to a thickness of 30 nm using a spin coater. Then it was annealed at 150 °C for 20 min.

[0158] 2-3 Indium phosphide quantum dot solution was spin-coated onto the sample formed in 2-2 at a rate of 2000 rpm, with a thickness of about 35 nm, and then annealed at 80 °C for 10 min.

[0159] 2-4 Zinc oxide magnesium nanoparticles were spin-coated onto the sample formed in 2-3 at a rate of 3000 rpm to a thickness of 30 nm, and then annealed at 80 °C for 20 min.

[0160] 2-5 The sample formed in 2-4 is transferred to a vacuum evaporation apparatus for physical vapor deposition of 100 nm silver.

[0161] The final device structure is FTO / PEDOT:PSS / Poly-TPD / InP / ZnSe / ZnS-QDs / ZnMgO / Ag.

[0162] Effect Evaluation 1

[0163] (1) The devices in Example 1 and Comparative Example 1 were placed in test fixtures with silicon diodes, respectively. A Keithley 2400 source meter was used to output the voltage and record the current density. A Keithley 6485 picoammeter was used to measure the silicon diode response current, and the corresponding current, external quantum efficiency (EQE), and brightness were calculated. Figure 6 , Figure 7 , Figure 8As shown in Figure 1, devices with a gradually varying disordered gradient distribution of the quantum dot emitting layer exhibit approximately 10% higher external quantum efficiency, 35% higher current, and 30% higher brightness compared to devices with a uniformly distributed quantum dot emitting layer. This demonstrates that the disordered gradient distribution of the quantum dot layer enhances hole injection efficiency, thereby improving the efficiency of zinc-cadmium-selenium-sulfur quantum dot light-emitting devices.

[0164] (2) The devices in Example 2 and Comparative Example 2 were placed in test fixtures with silicon diodes, respectively. A Keithley 2400 source meter was used to output the voltage and record the current density. A Keithley 6485 picoammeter was used to measure the silicon diode response current, and the corresponding current, external quantum efficiency (EQE), and brightness were calculated. Figure 9 , Figure 10 , Figure 11 As shown, the current and external quantum efficiency of devices with a gradually varying disorder gradient distribution in the quantum dot emitting layer are improved. This demonstrates that the disorder gradient distribution of the quantum dot layer enhances hole injection efficiency, thereby improving the efficiency of cesium lead bromide perovskite quantum dot emitting devices.

[0165] (2) The devices in Example 3 and Comparative Example 3 were placed in test fixtures with silicon diodes, respectively. A Keithley 2400 source meter was used to output the voltage and record the current density. A Keithley 6485 picoammeter was used to measure the silicon diode response current, and the corresponding current, external quantum efficiency (EQE), and brightness were calculated. Figure 12 , Figure 13 , Figure 14 As shown, the current and external quantum efficiency of devices with a gradually varying disorder gradient distribution in the quantum dot light-emitting layer are improved. This demonstrates that the disorder gradient distribution of the quantum dot layer enhances hole injection efficiency, thereby improving the efficiency of indium phosphide quantum dot light-emitting devices.

[0166] Effect Evaluation 2

[0167] The problem of non-uniform particle size in quantum dots during synthesis cannot be completely avoided. With identical chemical compositions, the HOMO and LUMO energy levels of quantum dots are primarily determined by their particle size. Therefore, the broadening of the HOMO and LUMO energy level distributions due to particle size inhomogeneity is called energy level disorder in quantum dots. The degree of disorder is called the disorder level, and its magnitude is described by the width of the electronic density of states distribution in the HOMO and LUMO. For a completely random disordered aggregate, the density of states distribution is usually described by a Gaussian distribution. The center of the Gaussian distribution represents the maximum value of the density of states, which is called the HOMO. max Or LUMO max The density of states decreases with increasing distance from the center; states with lower density of states are called tail states. A schematic diagram of a Gaussian distribution is shown below. Figure 2 As shown.

[0168] Electrostatic studies show that the HOMO energy level difference at the interface between the hole transport layer and the quantum dot layer decreases due to the increased disorder of the quantum dot layer at the interface. Dynamical studies indicate that the highest frequency path during hole transport from the hole transport layer to the quantum dot layer is the HOMO energy level from the hole transport layer. max HOMO tail states that jump to the quantum dot layer nearby tail Therefore, the equivalent injection barrier is Φ = |HOMO|. max,HTL -HOMO tail,QD Therefore, it is possible to achieve quantum dot HOMO without changing the quantum dot HOMO. max In the case where (in terms of process, the average energy of the electronic state density distribution of each monolayer self-assembled film is the same as the average size of the nanocrystals), the width of the quantum dot state density distribution at the hole transport layer-quantum dot layer interface is increased. This achieves the goal of improving hole injection efficiency without changing the center wavelength of the quantum dot emission peak. A schematic diagram of the equivalent injection barrier Φ is shown below. Figure 3 As shown.

[0169] QD layer particle size distribution and LUMO and HOMO electronic state density distribution, such as Figure 4 As shown, the disorder of the quantum dot along the substrate normal decreases with increasing distance from the quantum dot emitting layer-hole transport layer interface.

[0170] 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 quantum dot electroluminescent device with a disorder gradient in the light-emitting layer, characterized in that, The device includes a substrate (1), a device anode (2), a hole injection layer (3), a hole transport layer (4), a quantum dot light-emitting layer (5), an electron transport layer (6), and a device cathode (7) arranged sequentially. The quantum dot light-emitting layer (5) is composed of multiple colloidal nanocrystal monolayer self-assembled films stacked together, with a thickness of 10-100 nm; the colloidal nanocrystal monolayer self-assembled film is obtained by coating colloidal nanocrystals and photosensitive crosslinking agents and then crosslinking them. The average energy of the electronic state density distribution of each of the colloidal nanocrystal monolayer self-assembled films is the same as the average size of the nanocrystals. The electronic state density distribution width and nanocrystal size distribution width of the highest occupied state orbit and the lowest unoccupied state orbit of each of the colloidal nanocrystal monolayer self-assembled films decrease monotonically along the normal direction of the substrate (1) as the distance from the interface with the hole transport layer (4) and the quantum dot light-emitting layer (5) increases and eventually tends to a constant value. The quantum dot luminescent layer is composed of colloidal nanocrystals, which are selected from one or more of II-VI quantum dot nanocrystal materials, III-V quantum dot nanocrystal materials, perovskite quantum dot materials, and single-mass quantum dot materials.

2. The quantum dot electroluminescent device with a disorder gradient in the light-emitting layer as described in claim 1, characterized in that, The materials of the anode (2) and cathode (7) of the device are independently selected from one or more of indium tin oxide, fluorine-doped tin dioxide, aluminum, and silver.

3. The quantum dot electroluminescent device with a disorder gradient in the light-emitting layer as described in claim 1, characterized in that, The thickness of the anode (2) and cathode (7) of the device is 20-200 nm.

4. The quantum dot electroluminescent device with a disorder gradient in the light-emitting layer as described in claim 1, characterized in that, The material of the hole injection layer (3) is selected from one or two of polyethylene polymers and polythiophene polymers.

5. The quantum dot electroluminescent device with a disorder gradient in the light-emitting layer as described in claim 1, characterized in that, The thickness of the hole injection layer (3) is 10-150 nm.

6. The quantum dot electroluminescent device with a disorder gradient in the light-emitting layer as described in claim 1, characterized in that, The material of the hole transport layer (4) is selected from one or more of triphenylamine compounds and their derivative polymers, fluorenyl compounds and their derivative polymers, carbazole compounds and their derivative polymers, and spirocyclic compounds.

7. The quantum dot electroluminescent device with a disorder gradient in the light-emitting layer as described in claim 1, characterized in that, The hole transport layer (4) has a thickness of 10-150 nm.

8. The quantum dot electroluminescent device with a disorder gradient in the light-emitting layer as described in claim 1, characterized in that, The material of the electron transport layer (6) is selected from one or more of the following: metal oxides, imidazole compounds, pyridine compounds, pyrimidine compounds, anthracene compounds, organometallic chelates, and compounds containing o-phenanthroline groups.

9. The quantum dot electroluminescent device with a disorder gradient in the light-emitting layer as described in claim 1, characterized in that, The thickness of the electron transport layer (6) is 10-150 nm.

10. A method for fabricating a quantum dot electroluminescent device with a disorder gradient of the emitting layer as described in any one of claims 1-9, characterized in that, The process includes the following steps: depositing a hole injection layer (3), a hole transport layer (4), a quantum dot light-emitting layer (5), an electron transport layer (6), and a device cathode (7) sequentially on a substrate (1) on which the device anode (2) has been loaded, to obtain the quantum dot electroluminescent device.

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