Ink, composite material, light emitting device, method for manufacturing the same, and light emitting apparatus

Abstract

This application relates to the field of display technology, specifically to an ink, a composite material, a light-emitting device, a method for preparing the same, and a light-emitting apparatus. It addresses the problem that solution-based light-emitting devices in related technologies are only suitable for inverted light-emitting devices, and that these devices suffer from poor stability and performance. An ink comprises: transition metal oxide nanoparticles, an N-heterocyclic carbene precursor, and a solvent; the N-heterocyclic carbene precursor comprises one or more compounds represented by the following structural formulas (i), (ii), and (iii): in formulas (i), (ii), and (iii), R1 and R2 are each independently selected from hydrogen, deuterium, unsubstituted or substituted C1-C... 20 Alkyl, unsubstituted or substituted C6-C 20 aryl and unsubstituted or substituted C1-C 20 Any of the heteroaryl groups, wherein the heteroaryl group includes at least one heteroatom selected from at least one of N, P, O, and S, and the substituent is selected from halogen, cyano, C1-C20 alkyl, C1-C20 alkoxy, and C1-C20 alkylthio.

Description

Technical Field

[0001] This application relates to the field of display technology, and in particular to an ink, a composite material, a light-emitting device, a method for preparing the same, and a light-emitting apparatus. Background Technology

[0002] Solution-based light-emitting devices have low-cost manufacturing processes and offer significant advantages for large-area and diverse terminal displays.

[0003] However, the doping materials currently used for electron transport layers (such as n-type dopants) are unstable in solution, which means there are currently no ideal solution-based organic electron transport materials for use in light-emitting devices. Therefore, many current electron transport layers are still prepared using vapor deposition. While solution-based transition metal oxide nanoparticles (such as zinc oxide) have advantages such as solution-based preparation and high electron mobility, the electron transport layers used in solution-based processes have deep conduction band positions, making electron injection into the light-emitting layer difficult and resulting in suboptimal device performance.

[0004] Currently, the most common method is to modify the surface of zinc oxide with aliphatic amines (such as PEI (polyethylene tetraamine)). This method utilizes the dipole interaction between the amine groups and the zinc oxide surface to change the electron injection barrier to the light-emitting layer. However, this method is only suitable for inverted light-emitting devices (such as those that first deposit zinc oxide and then treat the zinc oxide surface). Furthermore, as the light-emitting device is used, aliphatic amines are prone to absorbing water, and their own insulating properties lead to charge accumulation in the device. This makes it easy for the electron injection barrier between the aliphatic amine and zinc oxide to change, resulting in poor stability of the light-emitting device. Summary of the Invention

[0005] Based on this, this application provides an ink, a composite material, a light-emitting device, a method for preparing the same, and a light-emitting apparatus, to solve the problem that light-emitting devices prepared by solution methods in related technologies are only applicable to inverted light-emitting devices, and that the stability and performance of the light-emitting devices are poor.

[0006] In a first aspect, an ink is provided, comprising transition metal oxide nanoparticles, an N-heterocyclic carbene precursor, and a solvent.

[0007] Optionally, the N-heterocyclic carbene precursor includes one or more compounds represented by the following structural formulas (i), (ii), and (iii):

[0008]

[0009] In equations (i), (ii), and (iii), R1 and R2 are each independently selected from hydrogen, deuterium, and...

[0010] Unsubstituted or substituted C1-C 20Alkyl, unsubstituted or substituted C6-C 20 Aryl and unsubstituted or substituted C1-C 20 Any of the heteroaryl groups, wherein the heteroaryl group includes at least one heteroatom selected from at least one of N, P, O, and S, and the substituent is selected from halogen, cyano, C1-C20 alkyl, C1-C20 alkoxy, and C1-C20 alkylthio.

[0011] Furthermore, in equation (I), the number of R2 is 1 to 2; in equation (II), the number of R2 is 1 to 3; and in equation (III), the number of R2 is 1 to 4.

[0012] Optionally, R1 is selected from C1-C6 alkyl groups that are unsubstituted or substituted with C1-C6 alkyl groups, C1-C6 cycloalkyl groups that are unsubstituted or substituted with C1-C6 alkyl groups, and C6-C6 alkyl groups that are unsubstituted or substituted with C1-C6 alkyl groups. 10 The aryl group and any one of the C1-C6 heteroaryl groups that are unsubstituted or substituted with C1-C6 alkyl groups, wherein the heteroaryl group includes an N atom;

[0013] R2 is selected from any one of C1-C6 alkyl groups that are unsubstituted or substituted with C1-C6 alkyl groups and C1-C6 alkoxy groups that are unsubstituted or substituted with C1-C6 alkyl groups.

[0014] Optionally, R1 can be selected from any of the following structural formulas:

[0015]

[0016] In the above structural formula, the dashed line represents the connection bond between R1 and N in the N-heterocyclic carbene precursor.

[0017] Optionally, the transition metal oxide nanoparticles are doped or undoped transition metal oxide nanoparticles. The undoped transition metal oxide nanoparticles include one or more of ZnO, SnO2, TiO2, ZrO2, Ga2O3, SiO2, Al2O3, CaO, and HfO2. The doping element in the doped transition metal oxide nanoparticles is selected from at least one of Al, Mg, Li, In, Ga, Sr, and Ba.

[0018] And / or, the mass ratio of transition metal oxide nanoparticles to N-heterocyclic carbene precursor is 20:1 to 1:1;

[0019] And / or, the solvent is specifically selected from one or more of methanol, ethanol, isopropanol, n-butanol, n-hexanol, acetonitrile, and cyclohexanone.

[0020] In a second aspect, a composite material is provided, which is a metal carbene composite material, wherein the metal carbene composite material comprises transition metal oxide nanoparticles and N-heterocyclic carbene ligands.

[0021] Optionally, the N-heterocyclic carbene ligand includes one or more compounds represented by the following structural formulas (I), (II), and (III):

[0022]

[0023] In formulas (I), (II), and (III), R1 and R2 are each independently selected from hydrogen, deuterium, unsubstituted or substituted C1-C. 20 Alkyl, unsubstituted or substituted C6-C 20 Aryl and unsubstituted or substituted C1-C 20 Any of the heteroaryl groups, wherein the heteroaryl group includes at least one heteroatom selected from at least one of N, P, O, and S, and * represents a coordinating atom in the N-heterocyclic carbene ligand that coordinates with the transition metal oxide nanoparticle;

[0024] Furthermore, in equation (I), the number of R2 is 1 to 2; in equation (II), the number of R2 is 1 to 3; and in equation (III), the number of R2 is 1 to 4.

[0025] Optionally, the N-heterocyclic carbene ligand includes one or more of the following structural formulas:

[0026]

[0027] In the above structural formula, the definition of * is the same as the definition of * above.

[0028] Thirdly, a light-emitting device is provided, comprising:

[0029] First electrode;

[0030] The second electrode is stacked on top of the first electrode;

[0031] A light-emitting layer is located between the first electrode and the second electrode;

[0032] An electron transport layer is located between the first electrode and the light-emitting layer;

[0033] The material of the electron transport layer is prepared from the electron transport ink described in the first aspect or is composed of the composite material described in the second aspect.

[0034] Optionally, the thickness of the electron transport layer is 5–50 nm; and / or, the first electrode and the second electrode are independently selected from one or more of Al, Ag, Cu, Mo, Au, Ba, Ca, Yb, Mg, graphite, carbon nanotubes, graphene, carbon fiber, ITO, FTO, ATO, AZO, GZO, IZO, MZO, AMO, AZO / Ag / AZO, AZO / Al / AZO, ITO / Ag / ITO, ITO / Al / ITO, ZnO / Ag / ZnO, ZnO / Al / ZnO, ZnS / Ag / ZnS, ZnS / Al / ZnS, TiO2 / Ag / TiO2, and TiO2 / Al / TiO2;

[0035] And / or, the material of the light-emitting layer includes F8BT.

[0036] Fourthly, a method for fabricating a light-emitting device is provided, comprising:

[0037] Form the first electrode;

[0038] An electron transport layer is formed on the first electrode;

[0039] A light-emitting chamber is formed on the electron transport layer;

[0040] A second electrode is formed in the light-emitting layer;

[0041] or,

[0042] Form the first electrode;

[0043] A light-emitting layer is formed on the first electrode;

[0044] An electron transport layer is formed on the light-emitting layer;

[0045] A second electrode is formed in the electron transport layer;

[0046] The electron transport layer is made of a metal carbene composite material, which includes transition metal oxide nanoparticles and N-heterocyclic carbene ligands coordinated with the transition metal oxide nanoparticles. The transition metal oxide nanoparticles have electron transport functionality.

[0047] Optionally, an electron transport layer is formed on the first electrode, including:

[0048] The precursors of transition metal oxide nanoparticles and N-heterocyclic carbene precursors were prepared into solutions;

[0049] A liquid film containing a precursor of transition metal oxide nanoparticles and the N-heterocyclic carbene precursor is formed on the first electrode;

[0050] The first electrode on which the liquid film is formed is annealed to allow the N-heterocyclic carbene precursor and the precursor of transition metal oxide nanoparticles to react and prepare an electron transport layer.

[0051] Alternatively, an electron transport layer may be formed on the light-emitting layer, including:

[0052] Transition metal oxide nanoparticles and N-heterocyclic carbene precursors were prepared into solutions;

[0053] A liquid film containing precursors of transition metal oxide nanoparticles and N-heterocyclic carbene precursors is formed on the luminescent layer;

[0054] An electron transport layer is prepared by annealing the liquid film to react the N-heterocyclic carbene precursor and the transition metal oxide nanoparticle precursor.

[0055] Optionally, the annealing atmosphere is an inert gas atmosphere, the annealing temperature is 140℃~180℃, and the annealing time is 5~120min.

[0056] Fifthly, a light-emitting device is provided, comprising:

[0057] The light-emitting device as described in the third aspect or the light-emitting device prepared by the method described in the fourth aspect.

[0058] Compared with the prior art, this application has the following beneficial effects:

[0059] Since this ink comprises transition metal oxide nanoparticles and an N-heterocyclic carbene precursor, a composite material of transition metal oxide nanoparticles and N-heterocyclic carbene ligands can be obtained when preparing the electron transport layer using a solvent method. This results in a stable dipole layer (at the interface between the N-heterocyclic carbene ligand and the transition metal oxide nanoparticles), altering the electron injection barrier to the light-emitting layer. Compared to related techniques that use aliphatic amines to surface-modify zinc oxide and utilize the dipole interaction between the amine groups and the transition metal oxide nanoparticles to change the electron injection barrier, this metal carbene composite material is applicable to both inverted and upright light-emitting devices, without being limited by the device's structure. Furthermore, the N-heterocyclic carbene ligand and transition metal oxide nanoparticles can form a relatively stable dipole layer, resulting in better device stability. Moreover, experimental comparisons show that the device performance of the resulting light-emitting device, such as luminous efficiency and lifetime, is effectively improved, and the driving voltage of the device can be reduced, indicating that the electron transport layer can effectively enhance the electron injection capability into the light-emitting layer. Attached Figure Description

[0060] Figure 1This is a cross-sectional structural schematic diagram of a light-emitting device provided in an embodiment of this application;

[0061] Figure 2 A cross-sectional view of another light-emitting device provided in an embodiment of this application;

[0062] Figure 3 A cross-sectional view of another light-emitting device provided in an embodiment of this application;

[0063] Figure 4 This is a cross-sectional structural schematic diagram of another light-emitting device provided in an embodiment of this application. Detailed Implementation

[0064] The present application will be further described in detail below with reference to specific embodiments. The present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this application.

[0065] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0066] Based on the above technical problems, some embodiments of this application provide an ink comprising transition metal oxide nanoparticles, an N-heterocyclic carbene precursor, and a solvent.

[0067] Carbene, also known as carbene or carbene alkene, is an electrically neutral compound containing a divalent carbon atom. A carbene is formed by a carbon atom covalently bonded to two other groups, and the carbon atom also has two free electrons. N-heterocyclic carbene (NHC) is a relatively new class of carbene, also called stable carbene, possessing exceptional stability; some can be stored indefinitely. In typical N-heterocyclic carbenes, the divalent carbon atom is located on an imidazole, thiazole, 1,2,4-triazine ring, or on a carbon atom bonded to two substituted amino groups.

[0068] In the electron transport ink provided in this application embodiment, since the ink includes transition metal oxide nanoparticles and an N-heterocyclic carbene precursor, a composite material of transition metal oxide nanoparticles and N-heterocyclic carbene ligands can be obtained when the electron transport layer is prepared using a solvent method. This results in a stable dipole layer (between the N-heterocyclic carbene ligand and the transition metal oxide nanoparticle interface), changing the electron injection barrier to the light-emitting layer. Compared with related technologies that use aliphatic amines to surface-modify zinc oxide and utilize the dipole interaction between the amine groups and the transition metal oxide nanoparticles to change the electron injection barrier to the light-emitting layer, this metal carbene composite material is suitable not only for inverted light-emitting devices but also for upright light-emitting devices, and is not limited by the structure of the light-emitting device. Furthermore, the N-heterocyclic carbene ligand and the transition metal oxide nanoparticles can form a relatively stable dipole layer, resulting in better device stability. On the other hand, experimental comparisons revealed that the device performance of the resulting light-emitting device, such as luminous efficiency and lifetime, was effectively improved, and the driving voltage of the light-emitting device could be reduced, indicating that the electron transport layer can effectively enhance the injection capability of electrons into the light-emitting layer.

[0069] In some embodiments, the particle size of the transition metal oxide nanoparticles can be 3–10 nm.

[0070] In some embodiments, the above-mentioned N-heterocyclic carbene precursor comprises one or more compounds represented by the following structural formulas (i), (ii), and (iii):

[0071]

[0072] In equations (i), (ii), and (iii), R1 and R2 are each independently selected from hydrogen, deuterium, unsubstituted or substituted C1-C. 20 Alkyl, unsubstituted or substituted C6-C 20 Aryl and unsubstituted or substituted C1-C 20 Any of the heteroaryl groups, wherein the heteroaryl group includes at least one heteroatom selected from at least one of N, P, O, and S, and the substituent is selected from halogen, cyano, C1-C20 alkyl, C1-C20 alkoxy, and C1-C20 alkylthio.

[0073] Furthermore, in equation (I), the number of R2 is 1 to 2; in equation (II), the number of R2 is 1 to 3; and in equation (III), the number of R2 is 1 to 4.

[0074] In these embodiments, the main structure of the N-heterocyclic carbene precursor is an imidazole (or dihydroimidazole), tetrahydropyrimidine, or benzimidazole ring, thus making the N-heterocyclic carbene precursor readily available. Furthermore, the N-heterocyclic carbene precursor is a thermally activated precursor. During the reaction, the C-C bond between the two nitrogen atoms in the N-heterocyclic carbene precursor breaks at high temperature, releasing CO2 to form a carbene intermediate. The carbon atom of this carbene intermediate acts as a strong σ-electron donor, coordinating with transition metal oxide nanoparticles to obtain a stable dipole layer.

[0075] Optionally, R1 is selected from C1-C6 alkyl groups that are unsubstituted or substituted with C1-C6 alkyl groups, C1-C6 cycloalkyl groups that are unsubstituted or substituted with C1-C6 alkyl groups, and C6-C6 alkyl groups that are unsubstituted or substituted with C1-C6 alkyl groups. 10 The aryl group and any one of the C1-C6 heteroaryl groups that are unsubstituted or substituted with C1-C6 alkyl groups, wherein the heteroaryl group includes an N atom;

[0076] R2 is selected from any one of C1-C6 alkyl groups that are unsubstituted or substituted with C1-C6 alkyl groups and C1-C6 alkoxy groups that are unsubstituted or substituted with C1-C6 alkyl groups.

[0077] Optionally, R1 can be selected from any of the following structural formulas:

[0078]

[0079] In the above structural formula, the dashed line represents the connection bond between R1 and N in the N-heterocyclic carbene precursor.

[0080] In some embodiments, the above-mentioned N-heterocyclic carbene precursor includes one or more of the following structural formulas:

[0081]

[0082] In some embodiments, the transition metal oxide nanoparticles are doped or undoped transition metal oxide nanoparticles. Undoped transition metal oxide nanoparticles include one or more of zinc oxide, tin oxide, titanium oxide, ZrO2, Ga2O3, SiO2, Al2O3, CaO, and HfO2. The doping element in the doped transition metal oxide nanoparticles is selected from at least one of Al, Mg, Li, In, Ga, Sr, and Ba. And / or, the mass ratio of transition metal oxide nanoparticles to N-heterocyclic carbene precursor is 20:1 to 1:1. And / or, the solvent is specifically selected from one or more of methanol, ethanol, isopropanol, n-butanol, n-hexanol, acetonitrile, and cyclohexanone.

[0083] In these embodiments, the electron injection capability of the light-emitting device 10 can be maximized by controlling the mass ratio of transition metal oxide nanoparticles to N-heterocyclic carbene precursor within the above-mentioned range.

[0084] In some embodiments, the mass ratio of transition metal oxide nanoparticles to N-heterocyclic carbene precursor is 5:1.

[0085] Experiments revealed that excessive N-heterocyclic carbene precursors tend to form byproducts with poor conductivity after the reaction, which is detrimental to improving the efficiency of electron injection into the light-emitting layer 32.

[0086] Some embodiments of this application provide a composite material, which is a metal carbene composite material comprising transition metal oxide nanoparticles and N-heterocyclic carbene ligands.

[0087] N-heterocyclic carbene ligands are highly reactive reaction intermediates. They possess excellent metal-bonding capabilities, as well as more flexible and varied steric hindrance and electronic effects, resulting in diverse structural types and ease of preparation. N-heterocyclic carbene ligands are strong σ-electron donors, increasing the electron density of the central metal. Simultaneously, the central metal exerts a certain back-bonding effect on the C atom, ensuring the stability of the carbene metal complex.

[0088] This composite material is an electron transport material with a stable dipole layer (between the N-heterocyclic carbene ligand and the transition metal oxide nanoparticles). This alters the electron injection barrier into the emitting layer. Compared to related techniques that use aliphatic amines to surface-modify zinc oxide and utilize the dipole interaction between the amine groups and the transition metal oxide nanoparticles to change the electron injection barrier, this metal carbene composite material is suitable for both inverted and upright emitting devices, regardless of the device's structure. Furthermore, the N-heterocyclic carbene ligand and the transition metal oxide nanoparticles can form a relatively stable dipole layer, resulting in better device stability. Moreover, experimental comparisons show that the resulting emitting device exhibits significantly improved performance, such as luminous efficiency and lifetime, and a reduced driving voltage, indicating that the electron transport material effectively enhances the electron injection capability into the emitting layer.

[0089] In some embodiments, the N-heterocyclic carbene ligand comprises one or more compounds represented by the following structural formulas (I), (II), and (III):

[0090]

[0091] In formulas (I), (II), and (III), R1 and R2 are each independently selected from hydrogen, deuterium, unsubstituted or substituted C1-C. 20 Alkyl, unsubstituted or substituted C6-C 20 Aryl and unsubstituted or substituted C1-C 20 Any of the heteroaryl groups, wherein the heteroaryl group includes at least one heteroatom selected from at least one of N, P, O, and S, and * represents a coordinating atom in the N-heterocyclic carbene ligand that coordinates with the transition metal oxide nanoparticle;

[0092] Furthermore, in equation (I), the number of R2 is 1 to 2; in equation (II), the number of R2 is 1 to 3; and in equation (III), the number of R2 is 1 to 4.

[0093] In formula (I) above, the dashed line indicates that the main structure of the N-heterocyclic carbene ligand can be imidazole or dihydroimidazole. In formula (I) above, when there is one R2, R2 can be attached to any one carbon of the imidazole or dihydroimidazole ring, and a hydrogen atom is attached to the other carbon, indicating that only one carbon of the imidazole or dihydroimidazole is substituted with hydrogen. When there are two R2s, R2 can be attached to both carbons of the imidazole or dihydroimidazole ring, indicating that both carbons of the imidazole or dihydroimidazole are substituted with hydrogen. In formula (II) above, when there is one R2, R2 can be attached to any one carbon of the tetrahydropyrimidine ring, and hydrogen atoms are attached to the other two carbons, indicating that the tetrahydropyrimidine... In equation (III), only one carbon atom on the ring is substituted with hydrogen; when there are two R2 atoms, R2 can be attached to any two carbons of the tetrahydropyrimidine ring, and a hydrogen atom is attached to the other carbon, indicating that two carbons on the tetrahydropyrimidine ring are substituted with hydrogen; when there are three R2 atoms, R2 can be attached to all three carbons of the tetrahydropyrimidine ring, indicating that all three carbons on the tetrahydropyrimidine ring are substituted with hydrogen; in equation (III) above, the number of R2 atoms can be 1 to 4, and for specific representation, please refer to the description of equations (I) and (II) above, which will not be repeated here.

[0094] In these embodiments, the host structure of the N-heterocyclic carbene ligand can be an imidazole (or dihydroimidazole), tetrahydropyrimidine, or benzimidazole ring. The resulting N-heterocyclic carbene ligands exhibit good stability, facilitating the preparation of the desired precursor materials. Furthermore, these N-heterocyclic carbene ligands can form stable dipole layers with transition metal oxide nanoparticles, thus improving the performance of light-emitting devices.

[0095] In some embodiments, R1 is selected from any of the following structural formulas:

[0096]

[0097] In the above structural formula, the dashed line represents the connection bond between R1 and N in the N-heterocyclic carbene.

[0098] In some embodiments, N-heterocyclic carbene ligands include one or more of the following structural formulas:

[0099]

[0100] In the above structural formula, the definition of * is the same as the definition of * above.

[0101] Some embodiments of this application provide a light-emitting device 10, such as... Figure 1 and Figure 2 As shown, it includes: a first electrode 1 and a second electrode 2 stacked together, a light-emitting layer disposed between the first electrode 1 and the second electrode 2, and an electron transport layer 31 disposed between the first electrode and the light-emitting layer. The electron transport layer 31 is made of the electron transport ink described above or composed of the composite material described above.

[0102] The light-emitting device 10 can be an inverted light-emitting device or a normal light-emitting device.

[0103] Taking the arrangement of the first electrode 1, the light-emitting layer, the electron transport layer, and the second electrode 2 in the light-emitting device 10 from bottom to top as an example, when the light-emitting device 10 is a positively positioned light-emitting device, as follows: Figure 1 As shown, the first electrode 1 is the anode, and the second electrode 2 is the cathode. In this case, the light-emitting layer 32 of the first light-emitting unit 3 is located below the electron transport layer 31. The electron transport layer 31 can be entirely composed of the aforementioned metal carbene composite material. That is, a liquid film containing transition metal oxide nanoparticles and N-heterocyclic carbene precursors can be directly formed on the side of the light-emitting layer 32 away from the first electrode 1 using a solution method. Then, by heating, the transition metal oxide nanoparticles and N-heterocyclic carbene precursors react to generate the metal carbene composite material, thereby forming a stable dipole layer above the light-emitting layer 32, reducing the electron injection barrier to the light-emitting layer 32, and thus improving device performance. However, in the case where the light-emitting device 10 is an inverted light-emitting device, as... Figure 2As shown, the first electrode 1 is the cathode and the second electrode 2 is the anode. At this time, the electron transport layer 31 is located below the light-emitting layer 32. In this case, similar to the above, a whole layer of metal carbene composite material can be formed on the first electrode 1 to form a stable dipole layer. Alternatively, transition metal oxide nanoparticles (such as zinc oxide) can be formed on the first electrode 1 first, and then an N-heterocyclic carbene precursor can be formed on the surface of zinc oxide away from the first electrode 1. By heating, the transition metal oxide nanoparticles and the N-heterocyclic carbene precursor react to generate a metal carbene composite material. In this case, the metal carbene composite material is only formed on the surface of the transition metal oxide nanoparticles near the light-emitting layer 32, which can also form a stable dipole layer and reduce the injection barrier of electrons into the light-emitting layer 32, thereby improving the performance of the light-emitting device 10.

[0104] In the light-emitting device provided in this application, a stable dipole layer (between the N-heterocyclic carbene ligand and the transition metal oxide nanoparticles) can be obtained by coordinating N-heterocyclic carbene ligands and transition metal oxide nanoparticles, thereby changing the electron injection barrier to the light-emitting layer 32. Compared with related technologies that use aliphatic amines to modify the surface of zinc oxide and utilize the dipole interaction between the amine groups and zinc oxide to change the electron injection barrier to the light-emitting layer 32, this metal carbene composite material is applicable not only to inverted light-emitting devices but also to upright light-emitting devices, and is not limited by the structure of the light-emitting device 10. Furthermore, the N-heterocyclic carbene ligand and the transition metal oxide nanoparticles can form a relatively stable dipole layer, resulting in better device stability. Moreover, experimental comparisons show that the device performance of the light-emitting device 10 obtained in this way, such as luminous efficiency and lifetime, is effectively improved, and the driving voltage of the light-emitting device 10 can be reduced, indicating that the electron transport layer 31 can effectively enhance the electron injection capability to the light-emitting layer.

[0105] In some embodiments, the thickness of the electron transport layer is 5–50 nm; and / or, the first electrode and the second electrode are independently selected from one or more of Al, Ag, Cu, Mo, Au, Ba, Ca, Yb, Mg, graphite, carbon nanotubes, graphene, carbon fiber, ITO, FTO, ATO, AZO, GZO, IZO, MZO, AMO, AZO / Ag / AZO, AZO / Al / AZO, ITO / Ag / ITO, ITO / Al / ITO, ZnO / Ag / ZnO, ZnO / Al / ZnO, ZnS / Ag / ZnS, ZnS / Al / ZnS, TiO2 / Ag / TiO2, and TiO2 / Al / TiO2; and / or, the material of the light-emitting layer includes F8BT.

[0106] In these embodiments, the thickness of the electron transport layer is controlled within the above-mentioned range, which can achieve the function of electron transport and injection without significantly affecting the thickness of the device.

[0107] The above describes the case where the light-emitting device 10 includes only one light-emitting unit, namely the first light-emitting unit 3. Those skilled in the art will understand that, in addition to the light-emitting layer 32 and the electron transport layer 31, the first light-emitting unit 3 may also include at least one functional layer selected from the following: a hole transport layer 33, a hole injection layer 34, an electron injection layer, an electron blocking layer, and a hole blocking layer. These functional layers are stacked between the first electrode 1 and the second electrode 2.

[0108] In some embodiments, such as Figure 3 and Figure 4 As shown, the light-emitting device 10 may further include a second light-emitting unit 4. The second light-emitting unit 4 is connected in series with the first light-emitting unit 3 between the first electrode 1 and the second electrode 2. The second light-emitting unit 4 includes an electron transport layer 41, which is disposed on the side of the light-emitting layer 32 of the first light-emitting unit 3 away from the electron transport layer 31.

[0109] In these embodiments, the second light-emitting unit 4 and the first light-emitting unit 3 are connected in series, which can effectively improve the luminous brightness and luminous efficiency, and also achieve high brightness under low current density, thereby effectively improving the service life of the light-emitting device.

[0110] The material of the electron transport layer 41 may be the same as or different from the material of the electron transport layer 31, and no specific limitation is made here.

[0111] In some embodiments, the material of electron transport layer 41 is the same as that of electron transport layer 31. That is, the material of electron transport layer 41 includes the aforementioned metal carbene composite material. The preparation method of electron transport layer 41 can be found in the above description of the preparation method of electron transport layer 31, and will not be repeated here.

[0112] In some embodiments, such as Figure 3 As shown, the second light-emitting unit 4 is the light-emitting unit closest to the cathode in the light-emitting device 10. The second light-emitting unit 4 also includes an electron injection layer, which is disposed between the electron transport layer 41 and the cathode, or the electron transport layer 41 is replaced by the electron injection layer described above.

[0113] In these embodiments, the electron injection efficiency can be further improved by providing an electron injection layer, thereby further improving the device performance of the light-emitting device 10. By replacing the electron transport layer 41 with an electron injection layer, the fabrication of the electron transport layer 41 can be eliminated, and the higher injection efficiency of the electron injection layer can be used to effectively improve the device performance of the light-emitting device 10.

[0114] Here, it should be noted that, similar to the first light-emitting unit 3 mentioned above, as... Figure 3 and Figure 4 As shown, in addition to the light-emitting layer 42 and the electron transport layer 41, the second light-emitting unit 4 may also include at least one of the following functional layers: hole transport layer 43, hole injection layer 44, electron injection layer, electron blocking layer and hole blocking layer. Unlike the light-emitting device 10, which only includes one light-emitting unit, the functional layers included in the second light-emitting unit 4 and the first light-emitting unit 3 are stacked between the first electrode 1 and the second electrode 2, and the functional layers included in both are arranged in the same order in the vertical direction, together forming an upright light-emitting device or an inverted light-emitting device.

[0115] In some embodiments, the light-emitting device 10 may be an OLED (Organic Light-Emitting Diode) light-emitting device or a QLED (Quantum Dot Light Emitting Diode) light-emitting device.

[0116] When the light-emitting device 10 is an OLED light-emitting device, compared with the doping material (n-type dopant) used in the electron transport layer in related technologies, which is unstable in solution, a stable electron transport material in solution can be provided. This reduces the manufacturing cost and effectively lowers the injection barrier of electrons into the light-emitting layer, thereby improving the device performance of the light-emitting device.

[0117] Some embodiments of this application provide a method for fabricating a light-emitting device, including:

[0118] S1, Form the first electrode 1.

[0119] S2. An electron transport layer 31 of the first light-emitting unit 3 is formed on the first electrode 1;

[0120] S3. Form the light-emitting layer 32 on the light-emitting layer 32;

[0121] S4. Form a second electrode in the light-emitting layer;

[0122] or,

[0123] S1, Form the first electrode 1;

[0124] S2. A light-emitting layer 32 of the first light-emitting unit 3 is formed on the first electrode 1;

[0125] S3. An electron transport layer 31 is formed on the light-emitting layer 32;

[0126] S4. A second electrode is formed in the electron transport layer.

[0127] In some embodiments, a first electrode 1 may be formed on a substrate layer, which may be a substrate of glass or other materials.

[0128] The first electrode 1 can be an anode or a cathode. When the first electrode 1 is an anode, the light-emitting device 10 is a positive light-emitting device. When the first electrode 1 is a cathode, the light-emitting device 10 is an inverted light-emitting device.

[0129] In some embodiments, when the first electrode 1 is an anode, the first electrode 1 can be a material with a high work function, such as ITO; when the first electrode 1 is a cathode, the first electrode 1 can be a material with a low work function, such as metal.

[0130] Taking ITO as an example for the first electrode 1, after the first electrode 1 is prepared, it can also be treated with ITO under UV conditions for 15 minutes, which can increase its work function and wettability.

[0131] The electron transport layer 31 is made of a metal carbene composite material, which includes transition metal oxide nanoparticles and N-heterocyclic carbene ligands coordinated with the transition metal oxide nanoparticles. The transition metal oxide nanoparticles have electron transport function.

[0132] N-heterocyclic carbene ligands are a relatively new class of carbenes, also known as stable carbenes, possessing exceptional stability; some can be preserved indefinitely. In typical N-heterocyclic carbenes, the divalent carbon is located on an imidazole, thiazole, 1,2,4-triazine ring, or a carbon bonded to two substituted amino groups. As a reaction intermediate, N-heterocyclic carbene ligands exhibit very high reactivity. They possess excellent metal-bonding capabilities, as well as more flexible and varied steric hindrance and electronic effects, resulting in diverse structural types and ease of preparation. N-heterocyclic carbene ligands are strong σ-electron donors, increasing the electron density of the central metal. Simultaneously, the central metal exerts a certain back-bonding effect on the carbon atom, ensuring the stability of the carbene metal complex.

[0133] In some embodiments, the light-emitting layer 32 can be prepared by vapor deposition or solution method (such as spin coating).

[0134] Of course, in some embodiments, the first light-emitting unit 3 may include, in addition to the light-emitting layer 32 and the electron transport layer 31, at least one of the following: hole transport layer 33, hole injection layer 34, electron injection layer, electron blocking layer and hole blocking layer.

[0135] In some embodiments, when the light-emitting device 10 is a positively oriented light-emitting device, the hole transport layer 33, the hole injection layer 34, and the electron blocking layer are all located below the light-emitting layer 32, and the electron injection layer and the hole blocking layer are all located above the light-emitting layer 32. When the light-emitting device 10 is an inverted light-emitting device, the hole transport layer 33, the hole injection layer 34, and the electron blocking layer are all located above the light-emitting layer 32, and the electron injection layer and the hole blocking layer are all located below the light-emitting layer 32.

[0136] The hole transport layer 33, hole injection layer 34, electron injection layer, electron blocking layer and hole blocking layer mentioned above can also be prepared by vapor deposition or solution method (spin coating).

[0137] In some embodiments, an electron transport layer 31 is formed on the first electrode 1, including:

[0138] Transition metal oxide nanoparticles and N-heterocyclic carbene precursors were prepared into solutions;

[0139] A liquid film containing transition metal oxide nanoparticles and N-heterocyclic carbene precursors is formed on the first electrode 1;

[0140] The first electrode 1, on which the liquid film is formed, is annealed to allow the N-heterocyclic carbene precursor and the precursor of transition metal oxide nanoparticles to react, thereby preparing the electron transport layer 31.

[0141] An electron transport layer is formed on the light-emitting layer, including:

[0142] Transition metal oxide nanoparticles and N-heterocyclic carbene precursors were prepared into solutions;

[0143] A liquid film containing the precursor of the transition metal oxide nanoparticles and the N-heterocyclic carbene precursor is formed on the light-emitting layer;

[0144] An electron transport layer is prepared by annealing the liquid film to react the N-heterocyclic carbene precursor and the transition metal oxide nanoparticle precursor.

[0145] In these embodiments, the aforementioned metal carbene composite material can be prepared via a solution method to obtain a stable dipole layer (between the transition metal oxide nanoparticles and the N-heterocyclic carbene interface). This metal carbene composite material comprises transition metal oxide nanoparticles and N-heterocyclic carbene ligands coordinated with the transition metal oxide nanoparticles. Experiments have shown that the preparation of this metal carbene composite material is applicable not only to inverted light-emitting devices but also to upright light-emitting devices, and is not limited by the structure of the light-emitting device. Furthermore, compared with the structure of zinc oxide surface modification with aliphatic amines in related technologies, this metal carbene composite material can obtain a more stable dipole layer, thereby improving the stability of the light-emitting device. Moreover, experiments have shown that compared with the structure of zinc oxide surface modification with aliphatic amines, it can effectively reduce the driving voltage of the light-emitting device, improve the luminous efficiency and lifetime of the light-emitting device, and thus improve the overall performance of the light-emitting device.

[0146] In summary, the aforementioned metal carbene composite material can effectively enhance the electron injection capability into the light-emitting layer and improve device stability.

[0147] The N-heterocyclic carbene precursor mentioned above can be found in the description of the N-heterocyclic carbene precursor in the above-mentioned electronic transmission ink, and will not be repeated here.

[0148] In some embodiments, the annealing atmosphere is an inert gas atmosphere, the annealing temperature is 140°C to 180°C, and the annealing time is 5 to 120 minutes.

[0149] In these embodiments, setting the annealing atmosphere to an inert gas atmosphere effectively protects the carbene intermediate, thereby enabling the carbene intermediate to undergo a coordination reaction with the transition metal oxide nanoparticles. Meanwhile, excessively low annealing temperatures lead to incomplete decomposition of the N-heterocyclic carbene precursor, hindering the reaction, while excessively high annealing temperatures can easily cause wire cracks to appear in the transition metal oxide nanoparticles under stress.

[0150] In some embodiments, the inert gas is argon and / or nitrogen.

[0151] In some embodiments, the solvent used to prepare the solution may be a highly polar solvent. For example, the highly polar solvent may include one or more of methanol, ethanol, isopropanol, n-butanol, n-hexanol, acetonitrile, and cyclohexanone.

[0152] It should be noted that regardless of whether the light-emitting device 10 is a forward-facing or inverted light-emitting device, the electron transport layer 31 can be prepared using the above method. When the light-emitting device 10 is an inverted light-emitting device, since the electron transport layer 31 is located below the light-emitting layer 32, a metal oxide electron transport layer can be formed first, followed by the formation of a liquid film of an N-heterocyclic carbene precursor on the surface of the metal oxide electron transport layer. Through the aforementioned annealing process, the N-heterocyclic carbene precursor and the metal oxide nanoparticles can react. The difference is that the metal carbene composite material formed in this way is only formed on the surface of the electron transport layer 31. Furthermore, by forming a stable dipole layer on the surface of the electron transport layer 31, the injection barrier of electrons into the light-emitting layer 32 can be reduced, thereby improving the device performance of the light-emitting device 10.

[0153] Some embodiments of this application provide a light-emitting device, including: a light-emitting device as described above or a light-emitting device prepared by the method described above.

[0154] The technical effects of the light-emitting device provided in the embodiments of this application are the same as those of the light-emitting device provided in the embodiments of this application, and will not be repeated here.

[0155] In the following examples and comparative examples, all raw materials were commercially available, and to maintain the reliability of the experiments, the raw materials used in the following examples and comparative examples had the same physical and chemical parameters or underwent the same treatment.

[0156] Example 1

[0157] Step 1) Solution preparation: Disperse ZnO nanoparticles with a size of about 5 nm in acetonitrile at a concentration of 15 mg / mL; at the same time, dissolve the NHC precursor DMImC in acetonitrile at a concentration of 3 mg / mL. Then mix the two solutions at a volume ratio of 1:1 to obtain a solution with a mass ratio of ZnO nanoparticles to DMImC of 5:1.

[0158] Step 2) Device fabrication: The ITO anode substrate was cleaned and then treated under UV conditions for 15 min to increase its work function and wettability. A 30 nm thick PEDOT:PSS layer was then spin-coated onto the treated ITO substrate and baked at 150 °C for 20 min in air. TFB was then spin-coated onto the PEDOT:PSS substrate as a 30 nm thick hole transport layer and baked at 180 °C for 60 min in nitrogen. A 60 nm thick polymer light-emitting layer F8BT was then spin-coated onto the substrate and baked at 150 °C for 10 min. A 10 nm thick composite electron transport layer liquid film was then spin-coated and annealed at 160 °C for 30 min. A 100 nm thick Ag layer was then vacuum-deposited, and finally, the substrate was encapsulated and annealed at 80 °C for 30 min.

[0159] Example 2

[0160] In Example 2, the mass ratio of ZnO NPs to DMImC in the solution was 15:1, and the other preparation methods were the same as in Example 1.

[0161] Example 3

[0162] In Example 3, the mass ratio of ZnO NPs to DMImC in the solution was 1.5:1, and the other preparation methods were the same as in Example 1.

[0163] Example 4

[0164] In Example 4, the annealing temperature of the liquid film was 120°C, and the other preparation methods were the same as in Example 1.

[0165] Example 5

[0166] In Example 5, DMImC in the solution was replaced with DPImC, and the other preparation methods were the same as in Example 1.

[0167] Example 6

[0168] In Example 6, the mass ratio of ZnO NPs to DMImC in the solution was 30:1, and the other preparation methods were the same as in Example 1.

[0169] Example 7

[0170] In Example 7, the mass ratio of ZnO NPs to DMImC in the solution was 1:2, and the other preparation methods were the same as in Example 1.

[0171] Comparative Example 1

[0172] In Comparative Example 1, no NHC precursor was added to the solution, and the other preparation methods were the same as in Example 1.

[0173] The devices prepared in the above embodiments and comparative examples were tested for performance using an IVL device, and the lifetime of each device was measured using a lifetime aging device. The results are shown in Table 1 below.

[0174] Table 1

[0175]

[0176]

[0177] As shown in Table 1, the composite electron transport layer prepared by adding NHC precursor to ZnO has a significantly reduced driving voltage and improved lifetime and efficiency, indicating that the ability of electrons to be injected into the light-emitting layer is improved.

[0178] Examples 1, 2, 3, 6, and 7 show that when the ratio of zinc oxide to NHC precursor is greater than 20:1 or less than 1:1, both device efficiency and device lifetime decrease to some extent, while the driving voltage increases slightly. A comparison between Examples 1 and 4 shows that as the annealing temperature decreases, both device efficiency and device lifetime decrease to some extent, while the driving voltage increases.

[0179] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0180] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. An ink, characterized in that, The mixture comprises transition metal oxide nanoparticles, an N-heterocyclic carbene precursor, and a solvent; the mass ratio of the transition metal oxide nanoparticles to the N-heterocyclic carbene precursor is 20:1 to 1:1; wherein the N-heterocyclic carbene precursor comprises one or more compounds represented by the following structural formulas (i), (ii), and (iii): In equations (i), (ii), and (iii), R1 and R2 are each independently selected from hydrogen, deuterium, unsubstituted or substituted C1-C. 20 Alkyl, unsubstituted or substituted C6-C 20 Aryl and unsubstituted or substituted C1-C 20 Any of the heteroaryl groups, wherein the heteroaryl group comprises at least one heteroatom selected from at least one of N, P, O, and S, and the substituent is selected from halogen, cyano, C1-C. 20 Alkyl, C1-C 20 Alkoxy, C1-C 20 Alkylthio; Furthermore, in equation (i), the number of R2 is 1 to 2; in equation (ii), the number of R2 is 1 to 3; and in equation (iii), the number of R2 is 1 to 4. The transition metal oxide nanoparticles are doped or undoped transition metal oxide nanoparticles. The undoped transition metal oxide nanoparticles include one or more of ZnO, SnO2, TiO2, ZrO2, Ga2O3, SiO2, Al2O3, CaO, and HfO2. The doping element in the doped transition metal oxide nanoparticles is selected from at least one of Al, Mg, Li, In, Ga, Sr, and Ba.

2. The ink according to claim 1, characterized in that, R1 is selected from C1-C6 alkyl groups that are unsubstituted or substituted with C1-C6 alkyl groups, C1-C6 cycloalkyl groups that are unsubstituted or substituted with C1-C6 alkyl groups, and C6-C6 alkyl groups that are unsubstituted or substituted with C1-C6 alkyl groups. 10 The aryl group and any one of the C1-C6 heteroaryl groups that are unsubstituted or substituted with C1-C6 alkyl groups, wherein the heteroaryl group includes an N atom; R2 is selected from any one of C1-C6 alkyl groups that are unsubstituted or substituted with C1-C6 alkyl groups and C1-C6 alkoxy groups that are unsubstituted or substituted with C1-C6 alkyl groups.

3. The ink according to claim 1 or 2, characterized in that, R1 is selected from any of the following structural formulas: In the above structural formula, the dashed line represents the connection bond between R1 and N in the N-heterocyclic carbene precursor.

4. The ink according to claim 1 or 2, characterized in that, The solvent is specifically selected from one or more of methanol, ethanol, isopropanol, n-butanol, n-hexanol, acetonitrile, and cyclohexanone.

5. A light-emitting device, characterized in that, include: First electrode; The second electrode is stacked on top of the first electrode; A light-emitting layer is located between the first electrode and the second electrode; An electron transport layer is located between the first electrode and the light-emitting layer; The material of the electron transport layer is prepared from the electron transport ink according to any one of claims 1-4.

6. The light-emitting device according to claim 5, characterized in that, The thickness of the electron transport layer is 5~50 nm; And / or, the first electrode and the second electrode are each independently selected from one or more of Al, Ag, Cu, Mo, Au, Ba, Ca, Yb, Mg, graphite, carbon nanotubes, graphene, carbon fiber, ITO, FTO, ATO, AZO, GZO, IZO, MZO, AMO, AZO / Ag / AZO, AZO / Al / AZO, ITO / Ag / ITO, ITO / Al / ITO, ZnO / Ag / ZnO, ZnO / Al / ZnO, ZnS / Ag / ZnS, ZnS / Al / ZnS, TiO2 / Ag / TiO2, and TiO2 / Al / TiO2; And / or, the material of the light-emitting layer includes F8BT.

7. A method for fabricating a light-emitting device, characterized in that, include: Form the first electrode; An electron transport layer is formed on the first electrode; A light-emitting layer is formed on the electron transport layer. A second electrode is formed in the light-emitting layer; or, Form the first electrode; A light-emitting layer is formed on the first electrode; An electron transport layer is formed on the light-emitting layer. A second electrode is formed in the electron transport layer; The electron transport layer is made of a metal carbene composite material, which comprises transition metal oxide nanoparticles and N-heterocyclic carbene ligands coordinated with the transition metal oxide nanoparticles. The transition metal oxide nanoparticles have electron transport functionality. An electron transport layer is formed on the first electrode, comprising: The transition metal oxide nanoparticles and N-heterocyclic carbene precursor were prepared into a solution; A liquid film comprising the precursor of the transition metal oxide nanoparticles and the N-heterocyclic carbene precursor is formed on the first electrode; The first electrode on which the liquid film is formed is annealed to react the N-heterocyclic carbene precursor and the precursor of the transition metal oxide nanoparticles to prepare the electron transport layer. Alternatively, an electron transport layer may be formed on the light-emitting layer, comprising: The transition metal oxide nanoparticles and N-heterocyclic carbene precursor were prepared into a solution; A liquid film containing the precursor of the transition metal oxide nanoparticles and the N-heterocyclic carbene precursor is formed on the light-emitting layer; The liquid film is annealed to react the N-heterocyclic carbene precursor and the transition metal oxide nanoparticle precursor to prepare the electron transport layer.

8. The method according to claim 7, characterized in that, The annealing process is performed in an inert gas atmosphere, the annealing temperature is 140℃~180℃, and the annealing time is 5~120min.

9. A light-emitting device, characterized in that, include: The light-emitting device as described in any one of claims 5 to 6 or the light-emitting device prepared by the method as described in any one of claims 7 to 8.

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