Quantum dot electroluminescent device having light-emitting layer disorder‑gradient and manufacturing method therefor

Abstract

The present invention relates to the field of electroluminescent devices, and particularly relates to a quantum dot electroluminescent device having a light-emitting layer disorder-gradient. 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 which are sequentially arranged. The quantum dot light-emitting layer is formed by stacking a plurality of colloidal nanocrystal single-layer self-assembled films, each single-layer self-assembled film has the same density of electronic states distribution average energy and nanocrystal average size, and the density of electronic states distribution widths and nanocrystal size distribution widths of the highest occupied molecular orbital and the lowest unoccupied molecular orbital of each single-layer self-assembled film decrease monotonically in the normal direction of the substrate with the increase of the distance from a hole transport layer-quantum dot layer interface, and finally tend to be constant values. According to the solution, a breakthrough of the solution of boosting hole injection on the basis of an energy level matching theory is achieved, a hole injection barrier between the hole transport layer and the quantum dot layer is reduced by means of a disorder-gradient gradual change, and the light emitting performance of the device is improved.

Description

A quantum dot electroluminescent device with a luminescent layer disorder gradient and a preparation method thereof Technical Field

[0001] The present invention belongs to the field of electroluminescent devices, and in particular relates to a quantum dot electroluminescent device with a light-emitting layer disorder gradient. Background Art

[0002] Quantum dot materials possess unique properties, including narrow half-width (FWHM), high color purity, particle size-controlled emission wavelength, and compatibility with solution-based methods. Consequently, quantum dot electroluminescent diodes (QLEDs) have demonstrated significant commercial value and application prospects in the display and lighting sectors. With continued in-depth research, the luminous efficiency of QLEDs has significantly improved, approaching that of commercial organic light-emitting diodes (OLEDs). From a long-term perspective, quantum dot electroluminescent displays are poised to become the next generation of mainstream display technology.

[0003] Over the years of development, QLED has gradually formed its current mainstream structure, which includes an anode, a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer, and a cathode. After voltage is applied, electrons and holes are injected from the corresponding electrodes, injected through various functional layers, and transported to the light-emitting layer. In the quantum dots, the carriers generate photons through radiation recombination. In order to achieve high performance of the device, the hole transport layer is generally required to have a high hole mobility, and the highest occupied molecular orbital (HOMO) energy level must match the work function of the hole injection layer and the valence band energy level of the quantum dot light-emitting layer to reduce the hole injection barrier. The electron transport layer needs to have good electron mobility, and the lowest unoccupied molecular orbital (LUMO) energy level must match the conduction band of the light-emitting layer and the electrode work function of 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, current researchers mainly focus on increasing the probability of carrier recombination, such as improving the carrier injection and transmission efficiency, and promoting carrier injection balance.

[0005] For QLED devices, whether the electron-hole injection and transport efficiency can be balanced is an important factor affecting the performance and lifespan of the device itself. The electron transport layer materials selected in mainstream device processes have higher electron mobility, which is usually greater than the hole mobility of common hole transport layer materials. In addition, their LUMO energy level matches the conduction band of QDs (quantum dots), and the electron injection barrier is small. Conversely, the hole injection barrier is larger, which leads to charge imbalance. Unbalanced carrier injection charges the quantum dots, increases the Auger recombination rate, and increases the operating voltage, thereby reducing the luminous efficiency and operating life of the device.

[0006] To address the issue of low hole injection efficiency, researchers in the QLED field have made many attempts. These can be categorized into the following types based on the injection barrier.

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

[0008] (2) Improving the hole injection efficiency between the hole transport layer and the inorganic nanocrystal material can be divided into two schemes: 2-1 constructing a multilayer hole transport layer to form a stepped HOMO energy level to alleviate 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 double-layer hole transport layer; 2-2 by developing a hole transport layer with a deeper HOMO energy level to reduce the barrier between the hole transport layer and the inorganic nanocrystal.

[0009] Summary of the Invention

[0010] In order to solve the problem of low hole injection efficiency in the prior art, many attempts have been made in the hole injection layer and the quantum dot light-emitting layer, but all have certain limitations.

[0011] (1) Of the two solutions for improving the hole injection efficiency between the electrode and the hole transport layer, 1-1 is difficult to obtain and difficult to prepare by solution coating; 1-2 is difficult to obtain by increasing the apparent work function of the electrode material, which helps to reduce the hole injection barrier. However, there is usually a severe Fermi energy pinning effect at the electrode-hole transport layer interface, and the injection barrier between the electrode and the hole transport layer is still very high.

[0012] (2) There are two schemes for improving the hole injection efficiency between the hole transport layer and the inorganic nanocrystalline material. 2-1, constructing a multilayer hole transport layer to form a stepped HOMO energy level, although it alleviates the injection barrier, it is affected by the orthogonal solvent effect and material selection, and this scheme is difficult to be widely applied to device preparation through the solution method; 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 cause a higher injection barrier between the electrode and the hole transport layer, thereby accelerating device degradation and reducing the working life.

[0013] In summary, low hole injection efficiency is the main drawback of existing QLEDs. Furthermore, existing solutions struggle to ensure that hole injection meets device requirements.

[0014] In response to the defects of the current mainstream QLED devices, the main problem solved by the present invention is to improve the efficiency of QLED hole injection into quantum dots, thereby improving device performance.

[0015] In view of the shortcomings of the existing technology 1-1, the present invention aims to solve the technical problem 1-1: the device structure improves hole injection without relying on high work function electrodes, and the device structure is suitable for solution coating preparation.

[0016] In view of the shortcomings of the existing technologies 1-2, the present invention aims to solve the technical problem 1-2: the device structure reduces the hole injection barrier without relying on ultra-thin layer dielectric materials.

[0017] In response to the shortcomings of existing technology 2-1, the present invention aims to solve technical problem 2-1: the device structure improves hole injection without relying on the HOMO gradient structure of the multi-layer hole injection layer, and is generally applicable to various solution coating preparation schemes.

[0018] In response to the shortcomings of existing technology 2-2, the present invention aims to solve technical problem 2-2: the device structure improves hole injection without relying on a deep HOMO energy level hole transport layer, thereby increasing the working life of the QLED.

[0019] In view of the defects of the existing technology, the present 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 effect of improving hole injection efficiency, improving carrier injection balance, and enhancing QLED device performance.

[0020] In order to solve the above-mentioned technical problems, this application provides the following technical solutions:

[0021] The present invention provides a quantum dot electroluminescent device with a gradient of disorder in 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 in sequence;

[0022] The quantum dot light-emitting layer is composed of a stack of multiple colloidal nanocrystal monolayer self-assembled films with a thickness of 10-100 nm;

[0023] 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;

[0024] The electronic state density distribution width of the highest occupied orbital and the lowest unoccupied orbital of each colloidal nanocrystal monolayer self-assembled film and the nanocrystal size distribution width decrease monotonically along the normal direction of the substrate with increasing distance from the interface between the hole transport layer and the quantum dot light-emitting layer and eventually tend to a constant value.

[0025] The quantum dot light-emitting layer is composed of colloidal nanocrystals, and 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-mass quantum dot materials.

[0026] In one embodiment of the present invention, the substrate is made of one or both of glass and polyethylene terephthalate (PET). The substrate has good surface wettability to facilitate solution coating.

[0027] In one embodiment of the present invention, the device anode and cathode are independently made of one or more materials selected from indium tin oxide (ITO), fluorine-doped tin dioxide (FTO), aluminum (Al), and silver (Ag), and each has a thickness of 20-200 nm. The device anode and cathode each have a sheet resistance of less than 50 Ω, enabling low-loss charge transfer.

[0028] In one embodiment of the present invention, the hole injection layer is made of a material selected from one or both of polyethylene polymers and polythiophene polymers, and has a thickness of 10-150 nm.

[0029] Furthermore, the hole injection layer is prepared by solution coating.

[0030] Furthermore, the hole injection layer has a work function of 5.1 eV or more and a conductivity greater than 10 -5 S / cm.

[0031] Furthermore, the polyethylene polymer is selected from poly(thiophene-3-[2-(2-methoxyethoxy)ethoxy]-2,5-diyl)( OC), poly (3,4-ethylenedioxythiophene): polystyrene sulfonic acid (PEDOT:PSS) and one or more of a PEDOT:PSS (a kind of aqueous solution of a high molecular polymer) modified material doped with perfluoroionomer (PEDOT:PSS:PFI); the polythiophene polymer is selected from the polymer polythiophene: poly (perfluoroethylene-perfluoroether sulfonic acid) (PTT:PFFSA).

[0032] In one embodiment of the present invention, the material of the hole transport layer is selected from one or more of triphenylamine-based compounds and polymer derivatives thereof, fluorene-based compounds and polymer derivatives thereof, carbazole-based compounds and polymer derivatives thereof, and spirocyclic compounds.

[0033] Furthermore, the triphenylamine compound and its derivative polymer are selected from one or more of 4,4',4"-tris(carbazol-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).

[0034] Furthermore, the fluorenyl compound and its derivative polymer are selected from one or more of N,N'-iminodiphenyl-4,4'-fluorene, 9,9-bis[4-(di-p-toluylamino)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-octylfluorenyl-2,7-diyl)] (TFB).

[0035] Furthermore, the carbazole-based compound and its derivative polymer are selected from one or more of 4,4'-bis(9-carbazole)biphenyl (CBP), 3',6'-bis(carbazole-9-yl)-bis[9-(2-ethylhexyl)carbazole-3,6-diyl] (G1CBC), and polyvinylcarbazole (PVK).

[0036] Furthermore, the spirocyclic compound is selected from one or more of N,N'-bis(3-methylphenyl)-N,N'-di(phenyl)-2,7-diamino-9,9-spirobifluorene (Spiro-TPD) and 2,2',7,7'-tetrakis(N,N-diphenylamino)-2,7-diamino-9,9-spirophenanthrene (Spiro-TAD).

[0037] The hole transport layer has good film forming properties and hole mobility, and its HOMO energy level is well matched with the work function of the HIL layer and the valence band energy level of the quantum dot light-emitting layer. The thickness of the hole transport layer is 10-150nm.

[0038] In one embodiment of the present invention, the quantum dot light-emitting layer is composed of a plurality of colloidal nanocrystal monolayer self-assembled films with a thickness of 10-100 nm;

[0039] Furthermore, the colloidal nanocrystal monolayer self-assembled film is obtained by coating colloidal nanocrystals and a photosensitive crosslinker 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-mass quantum dot materials.

[0040] Furthermore, 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) or cadmium sulfide (CdS) or cadmium telluride (CdTe), the zinc-based quantum dots are zinc selenide (ZnSe) or zinc sulfide (ZnS) or zinc telluride (ZnTe), and the alloy quantum dots contain at least two of the above II-VI compounds, such as Zn 1-x Cd x Se 1-x S 1-y or ZnTe 1-y Se y ;

[0041] Furthermore, the III-V quantum dot (nanocrystal) 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.

[0042] Furthermore, the single-mass quantum dot material is one or both of carbon quantum dots and silicon quantum dots.

[0043] Furthermore, the perovskite semiconductor material is one or more of cesium bromide, cesium bromide, cesium chloride, methylamine bromide or methylammonium iodide quantum dot materials.

[0044] The photosensitive crosslinker is selected from one or more of a nitrene compound, a carbene compound, a carbonium ion compound, and a free radical compound. Figure 5 shows the structures of several representative photosensitive crosslinkers, namely A, 3,3'-(4,4'-(perfluorobutane-1,4-diyl)bis(4,1-phenylene))bis(3-(trifluoromethyl)-3H-diazoxide, B, ethylene bis(4-azido-2,3,5,6-tetrafluorobenzoate), C, (3E,5E)3,5-bis-(4-azide-2,3,5,6-tetrafluorobenzylidene)-1-methylpiperidin-4-one, and D, (1E,4E)-1,5-bis(4-azido-2,3,5,6-tetrafluorophenyl)penta-1,4-diene-3-one.

[0045] The colloidal nanocrystal monolayer self-assembled film is prepared by solution coating. The colloidal nanocrystals have fluorescent properties; all colloidal nanocrystals in the quantum dot layer have the same chemical composition; the nanocrystal colloidal solution contains a photosensitive component that can cause the nanocrystals to crosslink and solidify after being irradiated with light of a specific wavelength; the electronic state density of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of each monolayer self-assembled film and the size of the nanocrystals are monodispersely distributed; 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; and along the normal direction of the substrate, the electronic state density distribution width (σ) and the nanocrystal size distribution width 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.

[0046] 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, organic metal chelates and compounds containing o-phenanthroline groups, and has a thickness of 10-150 nm.

[0047] Furthermore, the metal oxide is selected from tin oxide (SnO2), zinc oxide (ZnO) and magnesium zinc oxide (Zn 1- x Mg x O) in one or more.

[0048] 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-benzo[d]imidazol-1-yl)benzene (iTPyBIB).

[0049] 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-pyridin-3-ylphenyl)benzene (TpPyPB).

[0050] Furthermore, the pyrimidine compound is selected from one or both of 4,6-bis(3,5-di(3-pyridyl)phenyl)-2-methylpyrimidine (B3PYMPM) and 4,6-bis(3,5-di(4-pyridyl)phenyl)-2-methylpyrimidine (B4PYMPM).

[0051] Furthermore, the anthracene compound is 9,10-bis(6-phenylpyridin-3-yl)anthracene (DPPyA).

[0052] Furthermore, the organic metal chelate is tris(8-hydroxyquinoline)aluminum (Alq3).

[0053] Furthermore, the compound containing an o-phenanthroline group is selected from one or both of 4,7-diphenyl-1,10-phenanthroline (BPhen) and 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP).

[0054] The electron transport layer can be prepared by solution coating.

[0055] 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.

[0056] The present invention also provides a method for preparing the above-mentioned quantum dot electroluminescent device with a light-emitting layer disorder gradient, comprising the following steps: depositing a hole injection layer, a hole transport layer, a quantum dot light-emitting layer, an electron transport layer and a device cathode in sequence on a substrate loaded with a device anode to obtain the quantum dot electroluminescent device.

[0057] The technical solution of the present invention has the following advantages over the prior art:

[0058] 1. This solution breaks through the solution of improving hole injection based on energy level matching theory, and reduces the injection barrier between the hole transport layer and the quantum dot layer by gradually changing the disorder gradient.

[0059] 2. Without changing the band gap of the quantum dot film, it improves the charge balance, reduces the operating voltage of the QLED device, improves the luminous efficiency of the QLED device, and increases the working life of the QLED device. It is suitable for all types of quantum dot electroluminescent devices.

[0060] 3. The preparation process is compatible with the existing solution coating preparation process and can be applied to inkjet printing or large-area quantum dot light-emitting devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] FIG1 is a diagram showing the structure of a quantum dot light-emitting diode device that introduces a quantum dot disorder step layer.

[0062] Figure 2 is a schematic diagram of Gaussian distribution.

[0063] FIG3 is a schematic diagram of an equivalent injection barrier Φ.

[0064] Figure 4 shows the particle size distribution of the QD layer and the LUMO and HOMO electronic state density distribution.

[0065] Figure 5 shows the structures of four representative small molecule photosensitive crosslinkers.

[0066] FIG6 is a comparison diagram of the current-voltage test curves of Example 1 and Comparative Example 1.

[0067] FIG7 is a comparison diagram of external quantum efficiency-brightness test curves of Example 1 and Comparative Example 1.

[0068] FIG8 is a comparison diagram of the brightness-voltage test curves of Example 1 and Comparative Example 1.

[0069] FIG9 is a comparison diagram of the current-voltage test curves of Example 2 and Comparative Example 2.

[0070] FIG10 is a comparison diagram of external quantum efficiency-brightness test curves of Example 2 and Comparative Example 2.

[0071] FIG11 is a comparison diagram of the brightness-voltage test curves of Example 2 and Comparative Example 2.

[0072] FIG12 is a comparison diagram of the current-voltage test curves of Example 3 and Comparative Example 3.

[0073] FIG13 is a comparison diagram of external quantum efficiency-brightness test curves of Example 3 and Comparative Example 3.

[0074] FIG14 is a comparison diagram of the brightness-voltage test curves of Example 3 and Comparative Example 3.

[0075] Explanation of the reference numerals: 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 DESCRIPTION

[0076] 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 the present invention and implement it. However, the embodiments are not intended to limit the present invention.

[0077] In all the above embodiments, the quantum dot layer with a disorder gradient in the light-emitting layer is named disorder-gradient quantum dots (D-QDs). Specifically, in Example 1, the zinc cadmium selenide sulfur quantum dot layer with a disorder gradient in the light-emitting layer is named D-ZnCdSeS-QDs; in Example 2, the cesium lead bromide perovskite quantum dot layer with a disorder gradient in the light-emitting layer is named D-CsPbBr3-QDs; and in Example 3, the indium phosphide quantum dot layer with a disorder gradient in the light-emitting layer is named D-InP / ZnSe / ZnS-QDs.

[0078] Example 1

[0079] A zinc cadmium selenium sulfur quantum dot (D-ZnCdSeS-QDs) light-emitting device with a central wavelength of 466 nm and a light-emitting layer disorder gradient was prepared.

[0080] (1) Material preparation:

[0081] 1-1: Ultrasonic cleaning of an indium tin oxide substrate (substrate 1) with ITO (device anode 2) using glass cleaning solution, deionized water, acetone, and isopropyl alcohol. The cleaned substrate is then pretreated in a UV-ozone cleaning machine for 15 minutes.

[0082] 1-2: Use zinc cadmium selenium sulfur (ZnCdSeS) quantum dot solutions with central wavelengths of 462, 466, and 470 nm (energy interval greater than 0.02 eV) to prepare each single-layer quantum dot light-emitting layer. In addition to the different central wavelengths, the half-maximum width of the fluorescence peak of the three solutions is 20 nm and the concentration is 20 mg / mL.

[0083] Solutions with central wavelengths of 462, 466, and 470 nm were named Q-, Q0, and Q+, respectively. Colloidal solution 1 was prepared using 80% (volume) Q0, 10% Q-, and 10% Q+. A small molecule crosslinker, 3,3'-(4,4'-(perfluorobutane-1,4-diyl)bis(4,1-phenylene))bis(3-(trifluoromethyl)-3H-diazoxide, was added at 5% (volume) relative to colloidal solution 1. The structure of the small molecule crosslinker is shown in A in Figure 5 .

[0084] Colloidal solution 2 was prepared using 90% (volume) Q0, 5% Q-, and 5% Q+, and a small molecule crosslinker was added at 5% (volume) relative to colloidal solution 2; colloidal solution 3 was prepared using 95% (volume) Q0, 2.5% Q-, and 2.5% Q+, and a small molecule crosslinker was added at 5% (volume) relative to colloidal solution 3; Q0 was used as colloidal solution 4;

[0085] (2) Device preparation part:

[0086] 2-1: Use a spin coater to spin-coat PEDOT:PSS onto an ITO substrate (i.e., the device anode 2) at a rate of 5000 rpm, and then anneal at 150°C for 15 minutes to obtain a hole injection layer 3 with a thickness of 25 nm;

[0087] 2-2: The sample formed in step 2-1 was transferred to a glove box with a nitrogen atmosphere. TFB was spin-coated on the sample at a speed of 3000 rpm using a spin coater to a thickness of 30 nm. The sample was then annealed at 150°C for 30 min to obtain a hole transport layer 4.

[0088] 2-3: Spin-coat the colloidal solution 1 onto the sample formed in step 2-2 at a speed of 3000 rpm to a thickness of about 8 nm, and then perform UV exposure treatment with an exposure dose of 150 mJ / cm 2 ;

[0089] 2-4: Spin-coat the colloidal solution 2 onto the sample formed in step 2-3 at a speed of 3000 rpm to a thickness of about 8 nm, and then perform UV exposure treatment with an exposure dose of 150 mJ / cm 2 ;

[0090] 2-5: Spin-coat the colloidal solution 3 onto the sample formed in step 2-4 at a speed of 3000 rpm to a thickness of about 8 nm, and then perform UV exposure treatment with an exposure dose of 150 mJ / cm 2 ;

[0091] 2-6: Spin-coat the colloidal solution 4 on the sample formed in step 2-5 at a rate of 4000 rpm to a thickness of about 20 nm, and anneal at 80° C. for 10 min to obtain a quantum dot light-emitting layer 5;

[0092] 2-7: Spin-coating zinc oxide nanoparticles on the sample formed in step 2-6 at a rate of 3000 rpm to a thickness of 30 nm, and then annealing at 80° C. for 30 min to obtain an electron transport layer 6;

[0093] 2-8: The sample formed in step 2-7 is transferred to a vacuum evaporation device and subjected to physical vapor deposition of 100 nm silver to obtain the device cathode 7.

[0094] The final device structure is ITO / PEDOT:PSS / TFB / D-ZnCdSeS-QDs / ZnO / Ag.

[0095] Example 2

[0096] A cesium lead bromine perovskite quantum dot (D-CsPbBr3-QDs) light-emitting device with a central wavelength of 520nm and a light-emitting layer disorder gradient was prepared.

[0097] (1) Material preparation:

[0098] 1-1 Use glass cleaning solution, deionized water, acetone and isopropyl alcohol to ultrasonically clean the indium tin oxide substrate (substrate 1) with ITO (device anode 2). Then put the cleaned substrate into a UV ozone cleaning machine for 15 minutes of pretreatment.

[0099] 1-2. Cesium lead bromide perovskite quantum dot solutions (energy interval greater than 0.02 eV) with central wavelengths of 515, 520, and 525 nm were used to prepare individual single-layer quantum dot light-emitting layers. In addition to the different central wavelengths, the three solutions all had a fluorescence peak half-width of 20 nm and a concentration of 20 mg / mL. The solutions with central wavelengths of 515, 520, and 525 nm were named Q-, Q0, and Q+, respectively. Colloidal solution 1 was prepared using 80% (volume) Q0, 10% Q-, and 10% Q+, and a small molecule cross-linking agent was added at 5% (volume) relative to the colloidal solution 1; colloidal solution 2 was prepared using 90% (volume) Q0, 5% Q-, and 5% Q+, and a small molecule cross-linking agent was added at 5% (volume) relative to the colloidal solution 2; colloidal solution 3 was prepared using 95% (volume) Q0, 2.5% Q-, and 2.5% Q+, and a small molecule cross-linking agent was added at 5% (volume) relative to the colloidal solution 3; Q0 was used as colloidal solution 4;

[0100] (2) Device preparation part:

[0101] 2-1 Using a spin coater, PTT:PFFSA was spin-coated on an ITO substrate (i.e., the device anode 2) at a rate of 5000 rpm, and then annealed at 150°C for 20 min to obtain a hole injection layer 3 with a thickness of 25 nm;

[0102] 2-2 The sample formed in 2-1 was transferred to a glove box with a nitrogen atmosphere, and a hole transport layer material PVK was spin-coated on it at a rate of 3000 rpm using a spin coater to a thickness of 30 nm. The sample was then annealed at 150°C for 20 min to obtain a hole transport layer 4.

[0103] 2-3 Spin-coat the colloidal solution 1 onto the sample formed in 2-2 at a speed of 3000 rpm to a thickness of about 8 nm, and then perform UV exposure treatment with an exposure dose of 150 mJ / cm 2 ;

[0104] 2-4 Spin-coat the colloidal solution 2 on the sample formed in 2-3 at a speed of 3000 rpm to a thickness of about 8 nm, and then perform UV exposure treatment with an exposure dose of 150 mJ / cm 2 ;

[0105] 2-5 Spin-coat the colloidal solution 3 on the sample formed in 2-4 at a speed of 3000 rpm to a thickness of about 8 nm, and then perform UV exposure treatment with an exposure dose of 150 mJ / cm 2 ;

[0106] 2-6 Spin-coat the colloidal solution 4 on the sample formed in 2-5 at a rate of 4000 rpm to a thickness of about 20 nm, and anneal at 80° C. for 15 min to obtain a quantum dot light-emitting layer 5;

[0107] 2-7 The sample formed in 2-6 was transferred to a vacuum evaporation device and physically vapor deposited with 30 nm of 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene (TPBi) to obtain an electron transport layer 6;

[0108] 2-8 The sample formed in 2-7 is further subjected to vapor deposition of a 1 nm cathode electrode modification layer of lithium fluoride (LiF);

[0109] 2-9 The sample formed in 2-8 is finally subjected to vapor deposition of a 100 nm thick aluminum electrode to obtain a device cathode 7;

[0110] The final device structure is ITO / PTT:PFFSA / PVK / D-CsPbBr3-QDs / TPBi / LiF / Al.

[0111] Example 3

[0112] An indium phosphide quantum dot (D-InP / ZnSe / ZnS-QDs) light-emitting device with a central wavelength of 620 nm and a light-emitting layer disorder gradient was prepared.

[0113] (1) Material preparation:

[0114] 1-1 Use glass cleaning solution, deionized water, acetone and isopropyl alcohol to ultrasonically clean the indium tin oxide substrate (substrate 1) with FTO (device anode 2). Then put the cleaned substrate into a UV ozone cleaning machine for 15 minutes of pretreatment.

[0115] 1-2 Indium phosphide quantum dot solutions with central wavelengths of 614, 620, and 626 nm (energy interval greater than 0.02 eV) were used to prepare individual single-layer quantum dot light-emitting layers. Aside from the different central wavelengths, the three solutions all had a fluorescence peak half-width of 30 nm and a concentration of 20 mg / mL. The solutions with central wavelengths of 614, 620, and 626 nm were named Q-, Q0, and Q+, respectively. Colloidal solution 1 was prepared using 80% (volume) Q0, 10% Q-, and 10% Q+, and a small molecule cross-linking agent was added at 5% (volume) relative to the colloidal solution 1; colloidal solution 2 was prepared using 90% (volume) Q0, 5% Q-, and 5% Q+, and a small molecule cross-linking agent was added at 5% (volume) relative to the colloidal solution 2; colloidal solution 3 was prepared using 95% (volume) Q0, 2.5% Q-, and 2.5% Q+, and a small molecule cross-linking agent was added at 5% (volume) relative to the colloidal solution 3; Q0 was used as colloidal solution 4;

[0116] (2) Device preparation part:

[0117] 2-1 Using a spin coater, PEDOT:PSS was spin-coated on an FTO substrate (i.e., the device anode 2) at a rate of 5000 rpm, and then annealed at 150°C for 15 min to obtain a hole injection layer 3 with a thickness of 25 nm.

[0118] 2-2 The sample formed in 2-1 was transferred to a glove box with a nitrogen atmosphere, and a hole transport layer material, Poly-TPD, was spin-coated thereon at a rate of 3000 rpm using a spin coater to a thickness of 30 nm. The sample was then annealed at 150°C for 15 min to obtain a hole transport layer 4.

[0119] 2-3 Spin-coat the colloidal solution 1 onto the sample formed in 2-2 at a speed of 3000 rpm to a thickness of about 8 nm, and then perform UV exposure treatment with an exposure dose of 150 mJ / cm 2 ;

[0120] 2-4 Spin-coat the colloidal solution 2 on the sample formed in 2-3 at a speed of 3000 rpm to a thickness of about 8 nm, and then perform UV exposure treatment with an exposure dose of 150 mJ / cm 2 ;

[0121] 2-5 Spin-coat the colloidal solution 3 on the sample formed in 2-4 at a speed of 3000 rpm to a thickness of about 8 nm, and then perform UV exposure treatment with an exposure dose of 150 mJ / cm 2 ;

[0122] 2-6 Spin-coat the colloidal solution 4 on the sample formed in 2-5 at a rate of 4000 rpm to a thickness of about 20 nm, and anneal at 80° C. for 10 min to obtain a quantum dot light-emitting layer 5;

[0123] 2-7: Spin-coating zinc magnesium oxide nanoparticles on the sample formed in 2-6 at a rate of 3000 rpm to a thickness of 30 nm, and then annealing at 80° C. for 30 min to obtain an electron transport layer 6;

[0124] 2-8 The sample formed in 2-7 was transferred to a vacuum evaporation device and subjected to physical vapor deposition of 100 nm silver to obtain device cathode 7.

[0125] The final device structure is FTO / PEDOT:PSS / Poly-TPD / D-InP / ZnSe / ZnS-QDs / ZnMgO / Ag.

[0126] Comparative Example 1

[0127] A zinc cadmium selenium sulfur quantum dot (ZnCdSeS-QDs) light-emitting device with a wavelength of 466nm was prepared.

[0128] (1) Material preparation:

[0129] 1-1 Use glass cleaning solution, deionized water, acetone and isopropyl alcohol to ultrasonically clean the indium tin oxide substrate (substrate 1) with ITO (device anode 2). Then put the cleaned substrate into a UV ozone cleaning machine for 15 minutes of pretreatment.

[0130] 1-2 Use cadmium selenide quantum dot solution with a central wavelength of 466nm as the quantum dot light-emitting layer, the half-peak width of the fluorescence peak is 20nm, and the concentration is 20mg / mL

[0131] (2) Device preparation part:

[0132] 2-1 Use a spin coater to spin-coat PEDOT:PSS onto an ITO substrate at a rate of 5000 rpm, and then anneal at 150°C for 15 min to a thickness of 25 nm;

[0133] 2-2 The sample formed in 2-1 was transferred to a glove box with a nitrogen atmosphere, and TFB was spin-coated on it at a speed of 3000 rpm using a spin coater to a thickness of 30 nm, and then annealed at 150° C. for 30 min;

[0134] 2-3 Spin-coat the cadmium selenide quantum dot solution on the sample formed in 2-2 at a rate of 2000 rpm to a thickness of about 35 nm, and anneal at 80° C. for 10 min;

[0135] 2-4. Zinc oxide nanoparticles were spin-coated on the sample formed in 2-3 at a speed of 3000 rpm to a thickness of 30 nm, and then annealed at 80° C. for 30 min.

[0136] 2-5 The sample formed in 2-4 was transferred to a vacuum evaporation device for physical vapor deposition of 100 nm silver.

[0137] The final device structure is ITO / PEDOT:PSS / TFB / ZnCdSeS-QDs / ZnO / Ag.

[0138] Comparative Example 2

[0139] A cesium lead bromine perovskite quantum dot (CsPbBr3-QDs) light-emitting device with a wavelength of 520nm was prepared.

[0140] (1) Material preparation:

[0141] 1-1 Use glass cleaning solution, deionized water, acetone and isopropyl alcohol to ultrasonically clean the indium tin oxide substrate (substrate 1) with ITO (device anode 2). Then put the cleaned substrate into a UV ozone cleaning machine for 15 minutes of pretreatment.

[0142] 1-2 Use cesium lead bromide perovskite quantum dot solution with a central wavelength of 520nm as the quantum dot light-emitting layer, the half-peak width of the fluorescence peak is 20nm, and the concentration is 20mg / mL

[0143] (2) Device preparation part:

[0144] 2-1 Use a spin coater to spin-coat PTT:PFFSA onto an ITO substrate at a rate of 5000 rpm, and then anneal at 150°C for 20 min to a thickness of 25 nm;

[0145] 2-2 The sample formed in 2-1 was transferred to a glove box with a nitrogen atmosphere, and a hole transport layer material PVK was spin-coated on it at a rate of 3000 rpm using a spin coater to a thickness of 30 nm, and then annealed at 150° C. for 20 min;

[0146] 2-3 Spin-coat the cesium lead bromide perovskite quantum dot solution on the sample formed in 2-2 at a rate of 2000 rpm to a thickness of about 20 nm, and anneal at 80° C. for 10 min;

[0147] 2-4 The sample formed in 2-3 was transferred to a vacuum evaporation device and a 30 nm electron transport layer of 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene (TPBi) was physically vapor deposited;

[0148] 2-5 The sample formed in 2-4 is further subjected to vapor deposition of a 1 nm cathode electrode modification layer of lithium fluoride (LiF);

[0149] 2-6 The sample formed in 2-5 is finally vapor-deposited with a 100 nm thick aluminum electrode;

[0150] The final device structure is ITO / PTT:PFFSA / PVK / CsPbBr3-QDs / TPBi / LiF / Al.

[0151] Comparative Example 3

[0152] An indium phosphide quantum dot (InP / ZnSe / ZnS-QDs) light-emitting device with a wavelength of 620 nm was prepared.

[0153] (1) Material preparation:

[0154] 1-1 Use glass cleaning solution, deionized water, acetone and isopropyl alcohol to ultrasonically clean the indium tin oxide substrate (substrate 1) with FTO (device anode 2). Then put the cleaned substrate into a UV ozone cleaning machine for 15 minutes of pretreatment.

[0155] 1-2 uses an indium phosphide quantum dot solution with a wavelength of 620 nm as the quantum dot light-emitting layer, the half-width of its fluorescence peak is 30 nm, and the concentration is 20 mg / mL.

[0156] (2) Device preparation part:

[0157] 2-1 Use a spin coater to spin-coat PEDOT:PSS onto an FTO substrate at a rate of 5000 rpm, and then anneal at 150°C for 15 min to a thickness of 25 nm;

[0158] 2-2 The sample formed in 2-1 was transferred to a glove box with a nitrogen atmosphere, and the hole transport layer material Poly-TPD was spin-coated on it at a rate of 3000 rpm using a spin coater to a thickness of 30 nm, and then annealed at 150°C for 20 min;

[0159] 2-3 Spin-coat the indium phosphide quantum dot solution on the sample formed in 2-2 at a rate of 2000 rpm to a thickness of about 35 nm, and anneal at 80° C. for 10 min;

[0160] 2-4: ZnO-Mg nanoparticles were spin-coated on the sample formed in 2-3 at a speed of 3000 rpm to a thickness of 30 nm, and then annealed at 80° C. for 20 min.

[0161] 2-5 The sample formed in 2-4 was transferred to a vacuum evaporation device for physical vapor deposition of 100 nm silver.

[0162] The final device structure is FTO / PEDOT:PSS / Poly-TPD / InP / ZnSe / ZnS-QDs / ZnMgO / Ag.

[0163] Effect evaluation 1

[0164] (1) The devices in Example 1 and Comparative Example 1 were placed in a test fixture with a silicon tube, respectively. A Keithley 2400 source meter was used to output the voltage and record the current density. A picoammeter Keithley 6485 was used to measure the silicon tube response current, and the corresponding current, external quantum efficiency (EQE) and brightness were calculated. As shown in Figures 6, 7, and 8, the device with a gradient distribution of disorder in the quantum dot light-emitting layer increased the external quantum efficiency by about 10%, the current by about 35%, and the brightness by about 30% compared to the device with a uniform distribution of the quantum dot light-emitting layer. This proves that the gradient distribution of disorder in the quantum dot layer improves the hole injection efficiency, thereby improving the efficiency of the zinc cadmium selenium sulfur quantum dot light-emitting device.

[0165] (2) The devices in Example 2 and Comparative Example 2 were placed in a test fixture with a silicon tube, respectively. The voltage was output and the current density was recorded using a Keithley 2400 source meter. The silicon tube response current was measured using a picoammeter Keithley 6485, and the corresponding current, external quantum efficiency (EQE), and brightness were calculated. As shown in Figures 9, 10, and 11, the current and external quantum efficiency of the device with a gradient distribution of disorder in the quantum dot light-emitting layer have been improved to a certain extent. This proves that the gradient distribution of disorder in the quantum dot layer improves the hole injection efficiency, thereby improving the efficiency of the cesium lead bromine perovskite quantum dot light-emitting device.

[0166] (2) The devices in Example 3 and Comparative Example 3 were placed in a test fixture with a silicon tube, respectively. The voltage was output and the current density was recorded using a Keithley 2400 source meter. The silicon tube response current was measured using a picoammeter Keithley 6485, and the corresponding current, external quantum efficiency (EQE), and brightness were calculated. As shown in Figures 12, 13, and 14, the current and external quantum efficiency of the device with a gradient distribution of disorder in the quantum dot light-emitting layer were improved to a certain extent. This proves that the gradient distribution of disorder in the quantum dot layer improves the hole injection efficiency, thereby improving the efficiency of the indium phosphide quantum dot light-emitting device.

[0167] Effect evaluation 2

[0168] The problem of uneven particle size of quantum dots during the synthesis process cannot be completely avoided. Under the same chemical composition, the HOMO and LUMO energy levels of quantum dots are mainly determined by their particle size. Therefore, the phenomenon of broadening the HOMO and LUMO energy level distribution due to uneven particle size is called energy level disorder of quantum dots. The degree of disorder of energy levels is called disorder, and the size of disorder is described by the width of the electronic state density distribution of HOMO and LUMO. For completely random disordered aggregates, the state density distribution of energy levels is usually described by Gaussian distribution. Among them, the center position of the Gaussian distribution is the maximum value of the state density, which is called HOMO max or LUMOmax The density of states decreases as the distance from the center increases. Energy states with lower state density are called tail states. A schematic diagram of the Gaussian distribution is shown in Figure 2.

[0169] Electrostatic studies have shown that the HOMO energy level difference at the interface between the hole transport layer and the quantum dot layer will decrease as the disorder of the quantum dot layer at the interface increases. Dynamic studies have shown that the highest frequency path in the process of hole transmission from the hole transport layer to the quantum dot layer is from the HOMO of the hole transport layer to the quantum dot layer. max The HOMO tail state (HOMO tail ), so the equivalent injection barrier is Φ=|HOMO max,HTL -HOMO tail,QD |. Therefore, it is possible to max Under the condition that the average energy of the electronic density of states of each monolayer self-assembled film is the same as the average size of the nanocrystal, the hole injection efficiency is improved without changing the central wavelength of the quantum dot emission peak by increasing the width of the quantum dot state density distribution at the interface between the hole transport layer and the quantum dot layer. A schematic diagram of the equivalent injection barrier Φ is shown in Figure 3.

[0170] The particle size distribution of the QD layer and the LUMO and HOMO electronic state density distributions are shown in Figure 4. The disorder of the quantum dots decreases along the substrate normal direction as the distance from the quantum dot light-emitting layer-hole transport layer interface increases.

[0171] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A quantum dot electroluminescent device having a light-emitting layer disorder gradient, characterized in that: It comprises 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) which are arranged in sequence; The quantum dot light-emitting layer (5) is composed of a stack of multiple colloidal nanocrystal monolayer self-assembled films, with a thickness of 10-100 nm; 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; The electronic state density distribution width of the highest occupied state orbital and the lowest unoccupied state orbital of each colloidal nanocrystal monolayer self-assembled film and the nanocrystal size distribution width decrease monotonically along the normal direction of the substrate (1) as the distance from the interface of the hole transport layer (4) and the quantum dot light-emitting layer (5) increases, and eventually tends to a constant value; The quantum dot light-emitting layer is composed of colloidal nanocrystals, and 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-mass quantum dot materials.

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

3. The quantum dot electroluminescent device having a light-emitting layer disorder gradient according to claim 1, characterized in that: The thickness of the device anode (2) and the device cathode (7) are both 20-200 nm.

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

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

6. The quantum dot electroluminescent device having a light-emitting layer disorder gradient according to claim 1, characterized in that: The material of the hole transport layer (4) is selected from one or more of triphenylamine-based compounds and polymer derivatives thereof, fluorene-based compounds and polymer derivatives thereof, carbazole-based compounds and polymer derivatives thereof, and spirocyclic compounds.

7. The quantum dot electroluminescent device having a light-emitting layer disorder gradient according to claim 1, characterized in that: The thickness of the hole transport layer (4) is 10-150 nm.

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

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

10. A method for preparing a quantum dot electroluminescent device having a light-emitting layer disorder gradient according to any one of claims 1 to 9, characterized in that: The method comprises 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) in sequence on a substrate (1) loaded with a device anode (2) to obtain the quantum dot electroluminescent device.

Images