Hole transport layer for quantum dot electroluminescent device and preparation method and application thereof

Abstract

This invention discloses a hole transport layer for quantum dot electroluminescent devices, its preparation method, and its applications. The hole transport layer comprises a non-conjugated polymer with high mobility and deep HOMO energy levels containing rigid planar groups. By combining it with a conjugated polymer with high hole mobility and shallow HOMO energy levels, the injection of holes from the hole injection layer to the quantum dot emitting layer can be significantly improved, resulting in a more balanced carrier injection into the quantum dot emitting layer. Simultaneously, the carrier recombination region of the device can be confined within the quantum dot emitting layer, reducing exciton non-radiative convergence and thus significantly improving the device efficiency.

Description

Technical Field

[0001] This invention relates to a hole transport material, specifically to a hole transport layer for quantum dot electroluminescent devices, its preparation method, and its application, belonging to the field of quantum dot electroluminescent display technology. Background Technology

[0002] Quantum dot light-emitting diodes (QLEDs) possess advantages such as high color saturation, tunable color, high quantum yield, and simple manufacturing processes, making them a highly competitive candidate for next-generation display technology. However, compared to red and green QLEDs, blue QLEDs still lag behind in efficiency and lifespan, necessitating the resolution of a series of issues.

[0003] Currently, conjugated polymers (HTLs) have made significant progress in the field of QLEDs due to their high hole mobility and other properties. However, the increase in π-conjugation length within the molecular structure of conjugated polymers leads to the stretching of HOMO and LUMO orbitals, resulting in a decrease in the HOMO-LUMO band gap. Therefore, conjugated polymer HTLs (such as TFB, PoLy-TPD, PF8CZ, etc.) often exhibit shallower HOMO levels (approximately -5.4 eV). Compared to quantum dots with deep valence band tops (VBMs), especially for blue quantum dots, this creates a large hole injection barrier at the HTL / QD interface, hindering hole injection.

[0004] Compared to conjugated polymer HTL materials, non-conjugated polymer HTL materials, due to their monomer polymer linkages employing non-conjugated chain structures, break the conjugated structure between functional groups within the molecule. Through molecular design and functional group optimization, HTL materials with deep HOMO energy levels can be easily obtained. Among them, the non-conjugated polymer PVK, with its deep HOMO energy level (-5.8 eV), is widely used in QLEDs to enhance hole injection into the quantum dot layer. Although PVK-based QLED devices can achieve high performance, its hole mobility is extremely low (approximately 10^- ... -6 cm 2 V -1 s -1 This severely affects the hole propagation rate. Furthermore, considering that the energy barrier between the hole injection layer (HIL) and the quantum dot is typically greater than 1 eV, the deep HOMO level HTL introduces an injection barrier problem with the HIL (such as PEDOT:PSS), thus reducing the ability of holes to be injected from the HIL to the HTL.

[0005] In summary, current technologies still rely on PVK as a deep HOMO energy level HTL material. However, because PVK's repeating unit only has a single carbazole group, its hole mobility is too low to meet the requirements of QLEDs. Therefore, it is necessary to develop and explore more polymer HTLs with high mobility and deep HOMO energy levels to further improve the performance of blue QLEDs. Summary of the Invention

[0006] The main objective of this invention is to provide a hole transport layer for quantum dot electroluminescent devices and a method for preparing the same, in order to overcome the shortcomings of the prior art.

[0007] Another object of the present invention is to provide the application of the hole transport layer in quantum dot electroluminescent devices.

[0008] To achieve the aforementioned objectives, the technical solution adopted by this invention includes:

[0009] This invention provides a hole transport layer for quantum dot electroluminescent devices, comprising a non-conjugated polymer with high hole mobility and a deep HOMO energy level containing rigid planar groups, and used in combination with a conjugated polymer with high hole mobility and a shallow HOMO energy level; wherein, a shallow HOMO energy level refers to a HOMO energy level of -5.2 eV to -5.6 eV, a deep HOMO energy level refers to an energy level of -5.7 eV to -6.4 eV, and high hole mobility refers to a hole mobility greater than or equal to 10. - 4 cm 2 V -1 S -1 The non-conjugated polymer with high hole mobility and deep HOMO energy levels comprises the structures shown in formulas (I) to (V) below:

[0010]

[0011] In this system, the nitrogen element is covalently bonded to the adjacent benzene ring at any position, R1 to R5 are selected from hydrogen or alkyl groups containing C1 to C2, R6 is selected from oxygen or cyclohexane, and n = 5 to 100.

[0012] In some embodiments, the hole transport material has a bilayer structure, wherein the hole transport layer comprises a stacked first conjugated polymer layer (also referred to as the first hole transport layer) having high hole mobility and shallow HOMO energy level and a second non-conjugated polymer layer (also referred to as the second hole transport layer) having high hole mobility and deep HOMO energy level.

[0013] This invention also provides a method for fabricating a hole transport layer for a quantum dot electroluminescent device, comprising:

[0014] A first conjugated polymer layer is formed by depositing a conjugated polymer with high hole mobility and shallow HOMO energy level.

[0015] A second non-conjugated polymer layer is formed by applying a non-conjugated polymer with high hole mobility and deep HOMO energy level onto the first conjugated polymer layer, thus obtaining a hole transport layer with a bilayer structure.

[0016] This invention also provides a method for preparing a hole transport layer for a quantum dot electroluminescent device, comprising: mixing a conjugated polymer with high hole mobility and shallow HOMO energy level and a non-conjugated polymer with high hole mobility and deep HOMO energy level and forming a film together to obtain a hybrid hole transport layer with a monolayer structure.

[0017] This invention also provides the application of the hole transport layer for quantum dot electroluminescent devices in quantum dot electroluminescent devices.

[0018] Furthermore, embodiments of the present invention also provide a quantum dot electroluminescent device, which includes the aforementioned hole transport layer.

[0019] Compared with the prior art, the present invention has at least the following beneficial effects:

[0020] The hole transport material for quantum dot electroluminescent devices provided by this invention has high mobility and deep HOMO energy levels, which can significantly improve the injection of holes from the hole injection layer to the quantum dot emitting layer, making the carrier injection into the quantum dot emitting layer more balanced; at the same time, it can confine the carrier recombination region of the device in the quantum dot emitting layer, reduce the nonradiative convergence of excitons, and thus significantly improve the efficiency of the device. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of the energy levels used in a blue quantum dot electroluminescent device according to a typical embodiment of the present invention. Detailed Implementation

[0023] In view of the deficiencies of existing technologies, the inventors of this invention, through long-term research and extensive practice, have proposed the technical solution of this invention. The main focus is to provide a class of non-conjugated polymer hole transport materials with high hole mobility and deep HOMO energy levels. In the molecular design of the material, carbazole groups are used to provide deep HOMO energy levels. Furthermore, by extending the conjugated chain length of the polymer monomers, the π-π transport channels between molecules are increased, thereby improving hole transport capability. Simultaneously, it is further combined with conjugated polymers with high hole mobility and shallow HOMO energy levels to achieve high hole transport and injection capabilities, improving the hole and electron injection balance in QLED devices.

[0024] The following terms require explanation:

[0025] QLED: Quantum Dot Electroluminescent Device; QD: Quantum Dot; ZnO: Zinc Oxide; ETL: Electron Transport Layer; HTL: Hole Transport Layer; HIL: Hole Injection Layer; VBM: Valence Band Top; HOMO: Highest Occupied Molecular Orbital; LUMO: Lowest Unoccupied Molecular Orbital.

[0026] To facilitate understanding of this application, it will be described in more detail below. However, it should be understood that the invention can be implemented in many different forms and is not limited to the embodiments or examples described herein. Rather, these embodiments or examples are provided to provide a thorough and complete understanding of the disclosure of this invention.

[0027] Specifically, as one aspect of the technical solution of the present invention, the hole transport layer for a quantum dot electroluminescent device includes a non-conjugated polymer with high hole mobility and deep HOMO energy level containing rigid planar groups and a conjugated polymer with high hole mobility and shallow HOMO energy level.

[0028] Wherein, the shallow HOMO level refers to a HOMO level of -5.2 eV to -5.6 eV, the deep HOMO level refers to a level of -5.7 eV to -6.4 eV, and the high hole mobility refers to a hole mobility greater than or equal to 10. -4 cm 2 V -1 S -1 .

[0029] In some embodiments, the non-conjugated polymer with high hole mobility and deep HOMO energy levels comprises the structures shown in formulas (I) to (V):

[0030]

[0031] In this carbazole group, the nitrogen element is covalently bonded to the adjacent benzene ring at any position, R1 to R5 are selected from hydrogen or alkyl groups containing C1 to C2, R6 is selected from oxygen or cyclohexane, and n = 5 to 100.

[0032] In some more specific embodiments, the non-conjugated polymer with high hole mobility and deep HOMO energy levels comprises the structures shown in formulas (1) to (9) below:

[0033]

[0034]

[0035] Where n = 5 to 100.

[0036] Among the above materials, the carbazole group provides a deep HOMO energy level. Furthermore, by extending the π-conjugated chain length of the polymer monomers, the intermolecular π-π transport channels are increased, thereby enhancing hole transport capability and exhibiting high mobility and a deep HOMO energy level. Simultaneously, further combination with conjugated polymers with high hole mobility and shallow HOMO energy levels achieves high hole transport and injection capabilities, improving the hole and electron injection balance in QLED devices.

[0037] In some embodiments, the present invention combines the aforementioned non-conjugated polymers with high hole mobility and deep HOMO energy levels with conjugated polymers with shallow HOMO and high mobility to form a hole transport material with gradient HOMO energy levels. The two types of polymers can be stacked to form a bilayer hole transport layer (HTL), or they can be mixed into a single layer, i.e., a single-layer HTL blend.

[0038] In some specific embodiments, the hole transport material has a bilayer structure. Specifically, the hole transport material includes a first conjugated polymer layer (also referred to as the first hole transport layer) with high hole mobility and shallow HOMO energy level, and a second non-conjugated polymer layer (also referred to as the second hole transport layer) with high hole mobility and deep HOMO energy level.

[0039] Furthermore, the thickness of the first conjugated polymer layer is 5–15 nm.

[0040] Furthermore, the thickness of the second non-conjugated polymer layer is 5–15 nm.

[0041] In some specific embodiments, the conjugated polymer with high hole mobility and shallow HOMO energy level may include, but is not limited to, at least one of TFB, Poly-TPD, PF8CZ, PTAA, etc.

[0042]

[0043] In some other embodiments, the hole transport layer comprises a mixture of a non-conjugated polymer having high hole mobility and a deep HOMO energy level and a conjugated polymer having high hole mobility and a shallow HOMO energy level.

[0044] Furthermore, the molar ratio of the non-conjugated polymer with high hole mobility and deep HOMO energy level to the conjugated polymer with high hole mobility and shallow HOMO energy level is 5:1 to 1:5.

[0045] In summary, the hole transport layer for quantum dot electroluminescent devices provided by this invention has high mobility and a deep HOMO energy level. When used in combination with hole transport materials that have high mobility and a shallow HOMO energy level, it can significantly improve hole injection from the hole injection layer to the quantum dot emitting layer, making carrier injection into the quantum dot emitting layer more balanced. At the same time, it can confine the carrier recombination region of the device within the quantum dot emitting layer, reducing nonradiative convergence of excitons, thereby significantly improving the efficiency of the device.

[0046] As another aspect of the technical solution of the present invention, a method for preparing a hole transport layer for a quantum dot electroluminescent device includes:

[0047] A first conjugated polymer layer with high hole mobility and shallow HOMO energy level is formed by depositing a conjugated polymer film.

[0048] A non-conjugated polymer with high hole mobility and deep HOMO energy level is applied to the first conjugated polymer layer to form a second non-conjugated polymer layer with high hole mobility and deep HOMO energy level, thereby obtaining the hole transport layer for quantum dot electroluminescent devices.

[0049] In some specific embodiments, the preparation method includes: mixing a conjugated polymer with high hole mobility and shallow HOMO energy level with a first organic solvent to form a first solution, spin-coating and then annealing to obtain the first conjugated polymer layer.

[0050] Furthermore, the first organic solvent includes any one or a combination of two or more of chlorobenzene, dichlorobenzene, toluene, xylene, etc., but is not limited to this.

[0051] Furthermore, when preparing the first conjugated polymer layer, the spin coating is performed at a speed of 2000–4000 rpm for 10–60 seconds. The annealing temperature is 100–180°C for 5–30 minutes.

[0052] In some specific embodiments, the preparation method includes: mixing a non-conjugated polymer with high hole mobility and deep HOMO energy level with a second organic solvent to form a second solution, spin-coating it onto the first conjugated polymer layer, and then annealing it to obtain the second non-conjugated polymer layer.

[0053] Furthermore, the second organic solvent includes at least one of toluene, xylene, etc., but is not limited to this.

[0054] In preparing the second non-conjugated polymer layer, the spin coating is performed at a speed of 2000–4000 rpm for 10–60 seconds. The annealing temperature is 100–180°C for 5–30 minutes.

[0055] In some other specific embodiments, the preparation method further includes: mixing a conjugated polymer with high hole mobility and shallow HOMO energy level and a non-conjugated polymer with high hole mobility and deep HOMO energy level with a third organic solvent to form a third solution, spin-coating and then annealing to obtain a mixed hole transport layer with a single-layer structure.

[0056] Furthermore, the third organic solvent includes, but is not limited to, xylene.

[0057] Furthermore, the spin coating is performed at a speed of 2000–4000 rpm for 10–60 seconds, and the annealing temperature is 100–180°C for 5–30 minutes.

[0058] As another aspect of the technical solution of the present invention, it also relates to the application of the aforementioned hole transport layer for quantum dot electroluminescent devices in quantum dot electroluminescent devices.

[0059] Furthermore, another aspect of the present invention relates to a quantum dot electroluminescent device comprising the aforementioned hole transport layer.

[0060] For some preferred embodiments, please refer to Figure 1 As shown, the quantum dot electroluminescent device includes an anode, a hole injection layer (HIL), a hole transport layer (HTL), a quantum dot light-emitting layer, an electron transport layer (ETL), and a cathode arranged sequentially along a set direction.

[0061] In some preferred embodiments, the quantum dot emitting layer contains any one of blue quantum dots, red quantum dots, and green quantum dots, preferably blue quantum dots, but not limited thereto. That is, the present invention is not limited to blue QLEDs, but is also applicable to red and green QLEDs.

[0062] Furthermore, the quantum dot can be any one of CdSe, CdS, CdZnSe, ZnSe, InP, perovskite, etc., but is not limited to this.

[0063] Furthermore, the quantum dot electroluminescent device includes, but is not limited to, upright devices or inverted devices.

[0064] The present invention is further illustrated by the following embodiments: The present invention can be better understood from the following embodiments. However, those skilled in the art will readily understand that the specific material ratios, process conditions, and results described in the embodiments are for illustrative purposes only and should not, and will not, limit the present invention as described in detail in the claims.

[0065] Unless otherwise specified, the various raw materials, reaction equipment, testing equipment and testing methods used in the following embodiments are all known in the art.

[0066] Example 1

[0067] I. The synthesis of intermediate a1, the reaction equation is as follows:

[0068]

[0069] 4-(bis(4-iodophenyl)amino)benzamide (4.25 g, 8.1 mmol), carbazole (1.35 g, 8.1 mmol), cuprous iodide (0.23 g, 1.215 mmol), lithium chloride (0.34 g, 8.1 mmol), and cesium carbonate (3.16 g, 9.72 mmol) were mixed and added to a 50 mL three-necked flask. Then, 25 mL of N,N-dimethylformamide was added, and the mixture was purged under nitrogen three times to ensure an oxygen-free atmosphere. The mixture was heated to 170 °C under nitrogen and refluxed overnight. The reaction was stopped, cooled to room temperature, and a large amount of water was added. The mixture was extracted three times with dichloromethane, and the organic phases were combined and dried over anhydrous sodium sulfate. The mixture was then concentrated by rotary evaporation, and the crude product was finally separated by silica gel column chromatography using hexane / ethyl acetate (3:1 v / v). 2.93 g of a pale yellow solid was obtained, with a yield of 60%.

[0070] The NMR data of the product are as follows: 1 H NMR (400MHz, CDCl3) δppm: 9.92 (s, 1H), 8.17 (d, J = 7.7Hz, 4H), 7.88-7.82 (m, 2H), 7.65-7.58 (m, 4H), 7.54-7.42 (m, 12H), 7.35-7.28 (m, 6H).

[0071] II. The synthesis of intermediate b1, the reaction equation is as follows:

[0072]

[0073] Under nitrogen protection, a solution of intermediate a1 (2.90 g, 4.8 mmol) in tetrahydrofuran (50 mL) was added to n-butyllithium (5 mL, 8 mmol). After stirring at room temperature for 2 h, methyltriphenylphosphine bromide (2.9 g, 8.1 mmol, dissolved in 15 mL of tetrahydrofuran) was added dropwise. The reaction mixture was stirred at room temperature overnight and then quenched with water. The organic layer was washed three times with brine, dried over anhydrous sodium sulfate, filtered, and concentrated by rotary evaporation. The crude product was purified by silica gel column chromatography using n-hexane / ethyl acetate (1:1 v / v) as eluent to give the target compound b1 as a white solid (2.45 g, 85% yield).

[0074] The NMR data of the product are as follows:

[0075] 1 H NMR (400MHz, DMSO-d6) δppm: 8.25 (d, J=7.7Hz, 4H), 7.64-7.58 (m, 4H), 7.58-7.53 (m, 2H), 7.51-7.39 (m, 12H), 7 .29 (ddt, J=8.6, 6.0, 2.9Hz, 6H), 6.76 (dd, J=17.6, 10.9Hz, 1H), 5.80 (d, J=17.6Hz, 1H), 5.24 (d, J=11.0Hz, 1H).

[0076] 13 C NMR (400MHz, CDCl3) δppm: 146.85, 146.53, 141.04, 136.11, 133.32, 132.39, 128 .11, 127.56, 125.95, 124.95, 124.88, 123.34, 120.37, 119.91, 113.10, 109.85.

[0077] HRMS: Calcd.forC 44 H 31 N3, 602.2596[M+1]; Found: 602.2599.

[0078] III. The synthesis of the compound shown in formula (1) is carried out by the following reaction equation:

[0079]

[0080] Intermediate b1 (2.4 g, 4 mmol) and N,N-azobisisobutyronitrile (32 mg, 0.2 mmol) were added to a 50 mL Shulenk tube in a glove box under a nitrogen atmosphere and dissolved in 20 mL of anhydrous tetrahydrofuran solution. The reaction was carried out in the glove box at 50 °C for 60 h. The resulting solution was cooled to room temperature and placed under atmospheric pressure. The mixture was poured into methanol, and the precipitate was collected by filtration. The crude product was washed successively with methanol and n-hexane for 24 h each in a Soxhlet extractor. Finally, the residue was extracted with dichloromethane, and the residue was filtered through a 0.45 μm polytetrafluoroethylene filter. The polymer was dried under vacuum at 80 °C for 30 h, with a yield of 76% (1.82 g).

[0081] The NMR data of the product are as follows:

[0082] 1 ¹H NMR (400MHz, CDCl₃) δppm: 8.22-7.60 (aromatic region), 7.60-6.00 (aromatic region), 1.30, 0.92 (alkyl chain).

[0083] GPC (tetrahydrofuran): Mw = 1.1 kDa, PDI = 3.0.

[0084] Example 2

[0085] I. The synthesis of intermediate a3, the reaction equation is as follows:

[0086]

[0087] 3,5-diiodobenzaldehyde (2.9 g, 8.1 mmol), carbazole (1.35 g, 8.1 mmol), cuprous iodide (0.23 g, 1.215 mmol), lithium chloride (0.34 g, 8.1 mmol), and cesium carbonate (3.16 g, 9.72 mmol) were mixed and added to a 50 mL three-necked flask. Then, 25 mL of N,N-dimethylformamide was added. The mixture was kept under nitrogen atmosphere and purged three times under vacuum to ensure an oxygen-free atmosphere. The mixture was heated to 170 °C under nitrogen atmosphere and refluxed overnight. The reaction was stopped, cooled to room temperature, and a large amount of water was added. The mixture was extracted three times with dichloromethane. The organic phases were combined and dried over anhydrous sodium sulfate. The mixture was then concentrated by rotary evaporation, and the crude product was finally separated by silica gel column chromatography using hexane / ethyl acetate (3:1 v / v). 1.94 g of a pale yellow solid was obtained, with a yield of 55%.

[0088] The NMR data of the product are as follows: 1H NMR (400MHz, CDCl3) δppm: 10.21 (s, 1H), 8.22 (d, J = 1.9Hz, 2H), 8.16 (d, J = 7.8Hz, 4 H), 8.13-8.10 (m, 1H), 7.54 (d, J=8.2Hz, 4H), 7.49-7.43 (m, 4H), 7.37-7.31 (m, 4H).

[0089] II. The synthesis of intermediate b3, the reaction equation is as follows:

[0090]

[0091] Under nitrogen protection, a solution of intermediate a3 (1.90 g, 4.3 mmol) in tetrahydrofuran (50 mL) was added to n-butyllithium (5 mL, 8 mmol). After stirring at room temperature for 2 h, methyltriphenylphosphine bromide (2.9 g, 8.1 mmol, dissolved in 15 mL of tetrahydrofuran) was added dropwise. The reaction mixture was stirred at room temperature overnight and then quenched with water. The organic layer was washed three times with brine, dried over anhydrous sodium sulfate, filtered, and concentrated by rotary evaporation. The crude product was purified by silica gel column chromatography using n-hexane / ethyl acetate (1:1 v / v) as eluent to give the target compound b3 as a white solid (1.49 g, 80% yield).

[0092] The NMR data of the product are as follows:

[0093] 1 H NMR (400MHz, DMSO-d6) δppm: 8.27 (d, J=7.9Hz, 4H), 7.95 (d, J=2.4Hz, 2H), 7.73 (t, 1H), 7.57 (d, J=8.2Hz, 4H) , 7.52-7.45 (m, 4H), 7.36-7.28 (m, 4H), 7.02 (dd, J=17.9, 11.1Hz, 1H), 6.18-6.11 (m, 1H), 5.52-5.45 (m, 1H).

[0094] 13 C NMR (400MHz, CDCl3) δppm: 141.17, 140.58, 139.57, 135.36, 126.19, 124.44, 123.59, 123.55, 120.48, 120.35, 116.65, 109.71.

[0095] HRMS: Calcd.forC 32 H 22 N2, 435.1861[M+1]; Found: 435.1862.

[0096] III. The synthesis of the compound shown in formula (3) is carried out by the following reaction equation:

[0097]

[0098] In a nitrogen-atmospheric glove box, b3 (1.4 g, 3.2 mmol) and N,N-azobisisobutyronitrile (32 mg, 0.2 mmol) were added to a 50 mL Shulenk tube and dissolved in 20 mL of anhydrous tetrahydrofuran solution and sealed. The reaction was carried out in the glove box at 50 °C for 60 h. The resulting solution was cooled to room temperature and placed under atmospheric pressure. The mixture was poured into methanol, and the precipitate was collected by filtration. The crude product was washed successively with methanol and n-hexane for 24 h each in a Soxhlet extractor. Finally, the residue was extracted with dichloromethane, and the residue was filtered through a 0.45 μm polytetrafluoroethylene filter. The polymer was dried under vacuum at 80 °C for 30 h, yielding 65% (0.91 g).

[0099] The NMR data of the product are as follows:

[0100] 1 ¹H NMR (400MHz, CDCl₃) δppm: 8.60-4.00 (aromatic region), 1.30, 0.92 (alkyl chain).

[0101] GPC (tetrahydrofuran): Mw = 0.4 kDa, PDI = 2.7.

[0102] Example 3

[0103] I. The synthesis of intermediate a4, the reaction equation is as follows:

[0104]

[0105] CBP (5 g, 10.3 mmol) was dissolved in a mixture of 50 mL chloroform and 15 mL N,N-dimethylformamide, and phosphorus oxychloride (1.58 g, 10.3 mmol, dissolved in 10 mL dichloromethane) was added dropwise at 0 °C. The reaction mixture was then stirred at 80 °C for 12 h and the reaction was terminated by pouring it into an ice-water mixture. After neutralization with sodium bicarbonate, the mixture was extracted with dichloromethane. The organic phases were combined and dried over anhydrous sodium sulfate. The mixture was then concentrated by rotary evaporation, and the crude product was finally separated by silica gel column chromatography using dichloromethane / ethyl acetate (100:1 v / v). 3.48 g of a white solid was obtained, with a yield of 66%.

[0106] The NMR data of the product are as follows: 1H NMR (400MHz, CDCl3) δppm: 10.15 (s, 1H), 8.71 (d, J=1.6Hz, 1H), 8.24 (dd, J=7.8, 1.0Hz, 1H), 8.18 ( dt, J=7.9, 1.1Hz, 2H), 8.02-7.90 (m, 5H), 7.75-7.69 (m, 4H), 7.57-7.42 (m, 8H), 7.35-7.31 (m, 2H).

[0107] II. The synthesis of intermediate b4, the reaction equation is as follows:

[0108]

[0109] Under nitrogen protection, a solution of intermediate a4 (2.46 g, 4.8 mmol) in tetrahydrofuran (50 mL) was added to n-butyllithium (5 mL, 8 mmol). After stirring at room temperature for 2 h, methyltriphenylphosphine bromide (2.9 g, 8.1 mmol, dissolved in 15 mL of tetrahydrofuran) was added dropwise. The reaction mixture was stirred at room temperature overnight and then quenched with water. The organic layer was washed three times with brine, dried over anhydrous sodium sulfate, filtered, and concentrated by rotary evaporation. The crude product was purified by silica gel column chromatography using n-hexane / ethyl acetate (1:1 v / v) as eluent to give the target compound b4 as a white solid (2 g, 82% yield).

[0110] The NMR data of the product are as follows:

[0111] 1 H NMR (400MHz, Benzene-d6) δppm: 8.21 (d, J=1.6Hz, 1H), 8.10 (dd, J=9.5, 8.1Hz, 3H), 7.54 (dd, J=8.5, 1.7Hz, 1H), 7.52-7.46 (m, 4H), 7.41 ( t, J=8.6Hz, 3H), 7.35 (ddt, J=9.3, 5.5, 3.2Hz, 4H), 7.32-7.24 (m, 7H), 7.00-6.90 (m, 1H), 5.81 (d, J=17.5Hz, 1H), 5.22 (d, J=10.9Hz, 1H).

[0112] 13C NMR (400MHz, CDCl3) δppm: 141.21, 140.81, 140.59, 139.33, 139.27, 139.23, 137.34, 137.27, 137.24, 137.12, 132.80, 130.15, 128.54 , 128.52, 127.49, 127.38, 126.19, 126.04, 124.38, 123.72, 123.55, 123.50, 120.41, 120.27, 120.10, 118.40, 111.63, 109.98, 109.84.

[0113] HRMS: Calcd.forC 38 H 26 N2, 511.2174[M+1]; Found: 511.2177.

[0114] III. The synthesis of the compound shown in formula (4) is carried out by the following reaction equation:

[0115]

[0116] In a nitrogen-atmospheric glove box, b4 (2 g, 4 mmol) and N,N-azobisisobutyronitrile (32 mg, 0.2 mmol) were added to a 50 mL Shulenk tube and dissolved in 20 mL of anhydrous tetrahydrofuran solution and sealed. The reaction was carried out in the glove box at 50 °C for 60 h. The resulting solution was cooled to room temperature and placed under atmospheric pressure. The mixture was poured into methanol, and the precipitate was collected by filtration. The crude product was washed successively with methanol and n-hexane for 24 h each in a Soxhlet extractor. Finally, the residue was extracted with dichloromethane, and the residue was filtered through a 0.45 μm polytetrafluoroethylene filter. The polymer was dried under vacuum at 80 °C for 30 h, yielding 82% (1.64 g).

[0117] The NMR data of the product are as follows:

[0118] 1 ¹H NMR (400MHz, CDCl₃) δppm: 8.30-7.85 (aromatic region), 7.85-6.00 (aromatic region), 1.30, 0.92 (alkyl chain).

[0119] GPC (tetrahydrofuran): Mw = 2.8 kDa, PDI = 2.5.

[0120] Example 4

[0121] I. The synthesis of intermediate a5, the reaction equation is as follows:

[0122]

[0123] BCBP (5 g, 10.3 mmol) was dissolved in a mixture of 50 mL chloroform and 15 mL N,N-dimethylformamide, and phosphorus oxychloride (1.58 g, 10.3 mmol, dissolved in 10 mL dichloromethane) was added dropwise at 0 °C. The reaction mixture was then stirred at 80 °C for 12 h and the reaction was terminated by pouring it into an ice-water mixture. After neutralization with sodium bicarbonate, the mixture was extracted with dichloromethane. The organic phases were combined and dried over anhydrous sodium sulfate. The mixture was then concentrated by rotary evaporation, and the crude product was finally separated by silica gel column chromatography using dichloromethane / ethyl acetate (100:1 v / v). 3.12 g of a white solid was obtained, with a yield of 59.2%.

[0124] Elemental analysis: C, 89.49%; H, 4.87%; N, 5.63% (measured); C, 86.69%; H, 4.72%; N, 5.46%; O, 3.12% (C 37 H 24 (Theoretical value of N2O).

[0125] II. The synthesis of intermediate b5, the reaction equation is as follows:

[0126]

[0127] Under nitrogen protection, a solution of intermediate a5 (2.46 g, 4.8 mmol) in tetrahydrofuran (50 mL) was added to n-butyllithium (5 mL, 8 mmol). After stirring at room temperature for 2 h, methyltriphenylphosphine bromide (2.9 g, 8.1 mmol, dissolved in 15 mL of tetrahydrofuran) was added dropwise. The reaction mixture was stirred at room temperature overnight and then quenched with water. The organic layer was washed three times with brine, dried over anhydrous sodium sulfate, filtered, and concentrated by rotary evaporation. The crude product was purified by silica gel column chromatography using n-hexane / ethyl acetate (1:1 v / v) as eluent to give the target compound b5 as a white solid (1.9 g, 77% yield).

[0128] Elemental analysis: C, 89.28%; H, 5.20%; N, 5.51% (measured); C, 89.38%; H, 5.13%; N, 5.49% (C 38 H 26 (Theoretical value of N2).

[0129] III. The synthesis of the compound shown in formula (5) is carried out by the following reaction equation:

[0130]

[0131] In a nitrogen-atmospheric glove box, b5 (2 g, 4 mmol) and N,N-azobisisobutyronitrile (32 mg, 0.2 mmol) were added to a 50 mL Shulenk tube and dissolved in 20 mL of anhydrous tetrahydrofuran solution and sealed. The reaction was carried out in the glove box at 50 °C for 60 h. The resulting solution was cooled to room temperature and placed under atmospheric pressure. The mixture was poured into methanol, and the precipitate was collected by filtration. The crude product was washed successively with methanol and n-hexane for 24 h each in a Soxhlet extractor. Finally, the residue was extracted with dichloromethane, and the residue was filtered through a 0.45 μm polytetrafluoroethylene filter. The polymer was dried under vacuum at 80 °C for 30 h, yielding 86% (1.72 g).

[0132] Example 5

[0133] I. The synthesis of intermediate a7, the reaction equation is as follows:

[0134]

[0135] CDBP (5.28 g, 10.3 mmol) was dissolved in a mixture of 50 mL chloroform and 15 mL N,N-dimethylformamide, and phosphorus oxychloride (1.58 g, 10.3 mmol, dissolved in 10 mL dichloromethane) was added dropwise at 0 °C. The reaction mixture was then stirred at 80 °C for 12 h and the reaction was terminated by pouring it into an ice-water mixture. After neutralization with sodium bicarbonate, the mixture was extracted with dichloromethane. The organic phases were combined and dried over anhydrous sodium sulfate. The mixture was then concentrated by rotary evaporation, and the crude product was finally separated by silica gel column chromatography using dichloromethane / ethyl acetate (100:1 v / v). 3.95 g of a white solid was obtained, with a yield of 71%.

[0136] Elemental analysis: C, 89.29%; H, 5.38%; N, 5.33% (measured); C, 86.64%; H, 5.22%; N, 5.18%; O, 2.96% (C 39 H 28 (Theoretical value of N2O).

[0137] II. The synthesis of intermediate b7, the reaction equation is as follows:

[0138]

[0139] Under nitrogen protection, a solution of intermediate a7 (2.6 g, 4.8 mmol) in tetrahydrofuran (50 mL) was added to n-butyllithium (5 mL, 8 mmol). After stirring at room temperature for 2 h, methyltriphenylphosphine bromide (2.9 g, 8.1 mmol, dissolved in 15 mL of tetrahydrofuran) was added dropwise. The reaction mixture was stirred at room temperature overnight and then quenched with water. The organic layer was washed three times with brine, dried over anhydrous sodium sulfate, filtered, and concentrated by rotary evaporation. The crude product was purified by silica gel column chromatography using n-hexane / ethyl acetate (1:1 v / v) as eluent to give the target compound b7 as a white solid (2.07 g, 80% yield).

[0140] Elemental analysis: C, 89.16%; H, 5.65%; N, 5.18% (measured); C, 89.19%; H, 5.61%; N, 5.20% (C 40 H 30 (Theoretical value of N2).

[0141] III. The synthesis of the compound shown in formula (7) is carried out by the following reaction equation:

[0142]

[0143] In a nitrogen-atmospheric glove box, b7 (2.15 g, 4 mmol) and N,N-azobisisobutyronitrile (32 mg, 0.2 mmol) were added to a 50 mL Shulenk tube and dissolved in 20 mL of anhydrous tetrahydrofuran solution and sealed. The reaction was carried out in the glove box at 50 °C for 60 h. The resulting solution was cooled to room temperature and placed under atmospheric pressure. The mixture was poured into methanol, and the precipitate was collected by filtration. The crude product was washed successively with methanol and n-hexane in a Soxhlet extractor for 24 h each. Finally, the residue was extracted with dichloromethane, and the residue was filtered through a 0.45 μm polytetrafluoroethylene filter. The polymer was dried under vacuum at 80 °C for 30 h, with a yield of 80% (1.72 g).

[0144] Example 6

[0145] I. The synthesis of intermediate a8, the reaction equation is as follows:

[0146]

[0147] O-CBP (5.15 g, 10.3 mmol) was dissolved in a mixture of 50 mL chloroform and 15 mL N,N-dimethylformamide, and phosphorus oxychloride (1.58 g, 10.3 mmol, dissolved in 10 mL dichloromethane) was added dropwise at 0 °C. The reaction mixture was then stirred at 80 °C for 12 h and the reaction was terminated by pouring it into an ice-water mixture. After neutralization with sodium bicarbonate, the mixture was extracted with dichloromethane. The organic phases were combined and dried over anhydrous sodium sulfate. The mixture was then concentrated by rotary evaporation, and the crude product was finally separated by silica gel column chromatography using dichloromethane / ethyl acetate (100:1 v / v). 3.76 g of a white solid was obtained, with a yield of 69%.

[0148] Elemental analysis: C, 89.48%; H, 4.87%; N, 5.64% (measured); C, 84.07%; H, 4.58%; N, 5.30%; O, 6.05% (C 37 H 24 (Theoretical value of N2O2).

[0149] II. The synthesis of intermediate b8, the reaction equation is as follows:

[0150]

[0151] Under nitrogen protection, a solution of intermediate a8 (2.54 g, 4.8 mmol) in tetrahydrofuran (50 mL) was added to n-butyllithium (5 mL, 8 mmol). After stirring at room temperature for 2 h, methyltriphenylphosphine bromide (2.9 g, 8.1 mmol, dissolved in 15 mL of tetrahydrofuran) was added dropwise. The reaction mixture was stirred at room temperature overnight and then quenched with water. The organic layer was washed three times with brine, dried over anhydrous sodium sulfate, filtered, and concentrated by rotary evaporation. The crude product was purified by silica gel column chromatography using n-hexane / ethyl acetate (1:1 v / v) as eluent to give the target compound b8 as a white solid (2.15 g, 85% yield).

[0152] Elemental analysis: C, 89.38%; H, 5.14%; N, 5.48% (measured); C, 86.67%; H, 4.98%; N, 5.32%; O, 3.04% (C 38 H 26 (Theoretical value of N2O).

[0153] III. The synthesis of the compound shown in formula (8) is carried out by the following reaction equation:

[0154]

[0155] In a nitrogen-atmospheric glove box, b8 (2.1 g, 4 mmol) and N,N-azobisisobutyronitrile (32 mg, 0.2 mmol) were added to a 50 mL Shulenk tube and dissolved in 20 mL of anhydrous tetrahydrofuran solution and sealed. The reaction was carried out in the glove box at 50 °C for 60 h. The resulting solution was cooled to room temperature and placed under atmospheric pressure. The mixture was poured into methanol, and the precipitate was collected by filtration. The crude product was washed successively with methanol and n-hexane in a Soxhlet extractor for 24 h each. Finally, the residue was extracted with dichloromethane, and the residue was filtered through a 0.45 μm polytetrafluoroethylene filter. The polymer was dried under vacuum at 80 °C for 30 h. Yield: 84% (1.76 g).

[0156] Test examples (HOMO levels of compounds 1, 3-5, and 7-8)

[0157] Table 1 shows the highest occupied orbital (HOMO) energy levels of compounds 1, 3-5, and 7-8 calculated using ultraviolet photoelectron spectroscopy (UPS). Detailed results are summarized in Table 1. The HOMO energy levels of compounds 1, 3-5, and 7-8 are -5.7 eV, -6.1 eV, -6.0 eV, -6.0 eV, -6.0 eV, and -6.0 eV, respectively. Compounds 3-5 and 7-8 both possess deep HOMO energy levels, which are more conducive to improving the hole injection capability from the HTL to the quantum dot layer.

[0158] Table 1. Summary of the energy levels of the lowest unoccupied orbitals (LUMO) of compounds 1-3 and 7-8

[0159] Material Compound 1 Compound 3 Compound 4 Compound 5 Compound 7 Compound 8 HOMO -5.7eV -6.1eV -6.0eV -6.0eV -6.0eV -6.0eV

[0160] Application Example 1 (Blue Quantum Dot Electroluminescent Device Based on Dual HTL)

[0161] Figure 1 A schematic diagram of the energy levels for a blue quantum dot electroluminescent device according to an application example of the present invention is shown.

[0162] The following method was used to fabricate a blue quantum dot electroluminescent device based on dual HTLs:

[0163] (1) Cleaning: Clean the surface of the ITO glass substrate with detergent, sonicate with ethanol and acetone to remove organic contaminants, rinse three times with ultrapure water, dry with nitrogen, and then treat with oxygen plasma (O-plasma) for 3 minutes to obtain a cleaned ITO glass substrate.

[0164] (2) Preparation of PEDOT:PSS HIL layer: On the ITO glass substrate cleaned in step (1), PEDOT:PSS solution is spin-coated onto the treated ITO glass substrate (4000 rpm, 30 s), and annealed at 130°C for 15 min in an atmospheric atmosphere, and then transferred to a nitrogen glove box (O2<1ppm, H2O<1ppm).

[0165] (3) Preparation of HTL-1 layer: A chlorobenzene solution of HTL-1 material is spin-coated onto the HIL layer obtained in step (2) at a speed of 3000 rpm for 30 seconds, followed by annealing at 130°C for 15 minutes. HTL-1 is a conjugated polymer HTL material with shallow HOMO energy levels and high mobility, which can be any of TFB, Poly-TPD, or PF8CZ. The thickness is prepared to be x nm, where x is in the range of 0-20 nm.

[0166] (4) Preparation of HTL-2 layer: A xylene solution of HTL-2 material is spin-coated onto the HTL-1 layer obtained in step (3) at a speed of 3000 rpm for 30 seconds, followed by annealing at 130°C for 15 min. HTL-2 is any one of PVK, compound 1, 3-5, and 7-8. The thickness is prepared to be 20-x nm, where x is in the range of 0-30 nm.

[0167] (5) Preparation of quantum dot luminescent layer: Spin-coat the HTL-2 obtained in step (4) with an octane-dispersed blue quantum dot solution, and then anneal at 100°C for 2 minutes. The quantum dots can be any of CdSe, CdS, CdZnSe, ZnSe, etc.

[0168] (6) Preparation of ETL layer: Spin-coating Zn onto the QD obtained in step (5). 0.85 Mg 0.15 O nanocrystals (dispersed in ethanol, 25 mg / mL) were spin-coated at 3000 rpm for 30 seconds and then baked at 90°C for 15 minutes.

[0169] (7) The wafer is placed in a vacuum evaporation chamber and a 100nm aluminum electrode (Al) is vacuum evaporated to obtain a quantum dot electroluminescent device.

[0170] Taking compounds 1, 3-5, and 7-8 from the above embodiments of the present invention as HTL-2 and TFB as HTL-1 as an example, the structure of the QLED device is as follows: ITO (thickness approximately 110 nm) / PEDOT:PSS (thickness approximately 28 nm) / TFB (thickness 10 nm) / PVK, compounds 1, 3-5, and 7-8 (thickness 10 nm) / QDs (thickness approximately 20 nm) / Zn0.85MgO. 15O (approximately 50 nm thick) / Al (approximately 100 nm thick). The test data for the QLED device using CdSe blue quantum dots as the emitting layer are shown in Table 2.

[0171] Table 2 Summary of performance of blue QLED devices incorporating different HTL-2 materials

[0172]

[0173] Start-up voltage: at 1 cd·m- 2 At that brightness.

[0174] As shown in Table 2, after using compounds 1, 3-5, and 7-8, the maximum external quantum efficiency (EQE) of the blue QLED device reached 12.9%, 11.2%, 13.5%, 14.0%, 13.8%, and 13.0%, respectively, successfully realizing a high-performance blue QLED device. Compared with the PVK reference device (maximum EQE 7.4%), the performance was improved by 1.74, 1.51, 1.82, 1.89, 1.86, and 1.75 times, respectively. This proves that the introduction of HTL material with high mobility and deep HOMO energy level greatly improves the electron and hole injection balance of the device, indicating that the polymer material of the above embodiments of the present invention can effectively improve the performance of blue QLED devices.

[0175] In addition, the inventors of this case also conducted experiments with other raw materials, process operations, and process conditions described in this specification, referring to the aforementioned embodiments, and obtained relatively ideal results in all cases.

[0176] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A hole transport layer for quantum dot electroluminescent devices, characterized in that, The hole transport layer comprises a non-conjugated polymer with high hole mobility and deep HOMO energy levels containing rigid planar groups, and a conjugated polymer with high hole mobility and shallow HOMO energy levels. The shallow HOMO energy level refers to a HOMO energy level of -5.2 eV to -5.6 eV, the deep HOMO energy level refers to an energy level of -5.7 eV to -6.4 eV, and the high hole mobility refers to a hole mobility greater than or equal to 10. -4 cm 2 V -1 S -1 The non-conjugated polymer with high hole mobility and deep HOMO energy levels comprises the structures shown in formulas (I) to (V) below: In this system, the nitrogen element is covalently bonded to the adjacent benzene ring at any position, R1 to R5 are selected from hydrogen or alkyl groups containing C1 to C2, R6 is selected from oxygen or cyclohexane, and n = 5 to 100.

2. The hole transport layer for quantum dot electroluminescent devices according to claim 1, characterized in that: The hole transport layer has a two-layer structure, comprising a first conjugated polymer layer with high hole mobility and shallow HOMO energy level and a second non-conjugated polymer layer with high hole mobility and deep HOMO energy level. Preferably, the thickness of the first conjugated polymer layer is 5-15 nm; preferably, the thickness of the second non-conjugated polymer layer is 5-15 nm. Alternatively, the hole transport layer may be a single-layer structure, comprising a mixture of a non-conjugated polymer with high hole mobility and deep HOMO energy level and a conjugated polymer with high hole mobility and shallow HOMO energy level. Preferably, the molar ratio of the non-conjugated polymer with high hole mobility and deep HOMO energy level to the conjugated polymer with high hole mobility and shallow HOMO energy level is 5:1 to 1:

5.

3. The hole transport layer for quantum dot electroluminescent devices according to claim 1, characterized in that: The non-conjugated polymer with high hole mobility and deep HOMO energy level includes the structures shown in formulas (1) to (9): Where n = 5100.

4. The hole transport material for quantum dot electroluminescent devices according to claim 1, characterized in that: The conjugated polymer with high hole mobility and shallow HOMO energy level includes any one or a combination of two or more of the compounds shown below.

5. The method for preparing a hole transport layer for a quantum dot electroluminescent device as described in any one of claims 1-4, characterized in that, include: A first conjugated polymer layer is formed by depositing a conjugated polymer with high hole mobility and shallow HOMO energy level. A second non-conjugated polymer layer is formed by applying a non-conjugated polymer with high hole mobility and deep HOMO energy level onto the first conjugated polymer layer, thus obtaining a hole transport layer with a bilayer structure. Alternatively, a hybrid hole transport layer with a monolayer structure can be prepared by mixing a conjugated polymer with high hole mobility and shallow HOMO energy level and a non-conjugated polymer with high hole mobility and deep HOMO energy level and forming a film together.

6. The preparation method according to claim 5, characterized in that, include: A first organic solvent is mixed with a conjugated polymer having high hole mobility and shallow HOMO energy level to form a first solution, which is then spin-coated and annealed to obtain a first conjugated polymer layer. Preferably, the first organic solvent includes any one or a combination of two or more of chlorobenzene, dichlorobenzene, toluene, and xylene; preferably, when preparing the first conjugated polymer layer, the spin coating is performed at a speed of 2000-4000 rpm for 10-60 seconds; preferably, the annealing temperature is 100-180°C for 5-30 minutes.

7. The preparation method according to claim 5, characterized in that, include: A non-conjugated polymer with high hole mobility and deep HOMO energy level is mixed with a second organic solvent to form a second solution. After spin coating and annealing, a second non-conjugated polymer layer is obtained, thus obtaining a hole transport layer with a bilayer structure. Preferably, the second organic solvent includes any one or a combination of two of toluene and xylene; preferably, when preparing the second non-conjugated polymer layer, the spin coating is performed at a rotation speed of 2000-4000 rpm and a spin coating time of 10-60 seconds; preferably, the annealing temperature is 100-180°C and the annealing time is 5-30 min.

8. The preparation method according to claim 5, characterized in that, include: A third organic solvent is mixed with a conjugated polymer with high hole mobility and shallow HOMO energy level and a non-conjugated polymer with high hole mobility and deep HOMO energy level to form a third solution. The solution is then spin-coated and annealed to obtain a mixed hole transport layer with a single-layer structure. Preferably, the third organic solvent includes xylene; preferably, when preparing the mixed hole transport layer, the spin coating is performed at a speed of 2000-4000 rpm and the spin coating time is 10-60 seconds; preferably, the annealing temperature is 100-180℃ and the annealing time is 5-30 min.

9. The use of the hole transport layer for quantum dot electroluminescent devices as described in any one of claims 1-4 in quantum dot electroluminescent devices.

10. A quantum dot electroluminescent device, characterized in that, Includes the hole transport layer for quantum dot electroluminescent devices as described in any one of claims 1-4; Preferably, the quantum dot electroluminescent device includes an anode, a hole injection layer, a hole transport layer, a quantum dot light-emitting layer, an electron transport layer, and a cathode arranged sequentially along a set direction; Preferably, the quantum dots contained in the quantum dot emitting layer include any one of blue quantum dots, red quantum dots, and green quantum dots, with blue quantum dots being the most preferred. Preferably, the quantum dots include any one of CdSe, CdS, CdZnSe, ZnSe, InP, and perovskite quantum dots; Preferably, the quantum dot electroluminescent device includes an upright device or an inverted device.

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