CN117683393A - Ink, composite material, light-emitting device, preparation method of light-emitting device and light-emitting device - Google Patents
Ink, composite material, light-emitting device, preparation method of light-emitting device and light-emitting device Download PDFInfo
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Abstract
The application relates to the technical field of display, in particular to ink, a composite material, a light-emitting device, a preparation method of the light-emitting device and a light-emitting device. The method solves the problems that the light-emitting device prepared by the solution method in the related art is only suitable for an inverted light-emitting device, and the stability and the performance of the light-emitting device are poor. An ink, comprising: a transition metal oxide nanoparticle, an N-heterocyclic carbene precursor, and a solvent; the N-heterocyclic carbene precursor comprises: the following structural formulas (i), (ii)And (iii) one or more of the compounds represented by:in the formula (i), the formula (ii) and the formula (iii), R 1 、R 2 Each independently selected from hydrogen, deuterium, unsubstituted or substituted C 1 ‑C 20 Alkyl, unsubstituted or substituted C 6 ‑C 20 Aryl and unsubstituted or substituted C 1 ‑C 20 Heteroaryl, including at least one heteroatom, selected from at least one of N, P, O, S, and substituents selected from halogen, cyano, C1-C20 alkyl, C1-C20 alkoxy, and C1-C20 alkylthio.
Description
Technical Field
The application relates to the technical field of display, in particular to ink, a composite material, a light-emitting device, a preparation method of the light-emitting device and a light-emitting device.
Background
The light-emitting device prepared based on the solution method has the advantages of low-cost manufacturing process and prominent advantages on a terminal display screen with large area and rich morphology.
However, the doping materials (such as n-type dopants) currently used for the electron transport layer are unstable in solution, which makes no ideal organic electron transport material for the light emitting device in solution, and thus many electron transport layers currently are still prepared by vapor deposition. While the transition metal oxide nano particles (such as zinc oxide) based on the solution method have the advantages of being prepared by the solution method, high in electron mobility and the like, the electron transport layer used for the solution method process has a deeper conduction band position, so that the injection of electrons into the light-emitting layer is difficult, and the device performance is not ideal.
At present, the conventional method is mainly to modify the surface of zinc oxide (such as PEI (polyethylene tetramine)) by fatty amine, and change the injection barrier of electrons to a light-emitting layer by utilizing the dipole action of amine groups and the surface of zinc oxide, but the method is only suitable for an inverted light-emitting device (such as depositing zinc oxide first and then treating the surface of zinc oxide), and along with the use of the light-emitting device, the fatty amine is easy to absorb water and the insulativity of the fatty amine itself causes charge accumulation in the device, so that the electron injection barrier of the fatty amine and the zinc oxide is easy to change, and the stability of the light-emitting device is poor.
Disclosure of Invention
Based on the above, the application provides an ink, a composite material, a light-emitting device, a preparation method thereof and a light-emitting device, which are used for solving the problems that the light-emitting device prepared by a solution method in the related art is only suitable for an inverted light-emitting device, and the stability and the performance of the light-emitting device are poor.
In a first aspect, an ink is provided that includes transition metal oxide nanoparticles, an N-heterocyclic carbene precursor, and a solvent.
Optionally, the N-heterocyclic carbene precursor comprises: one or more of the compounds represented by the following structural formulas (i), (ii) and (iii):
in formula (i), formula (ii) and formula (iii), R 1 、R 2 Each independently selected from hydrogen, deuterium,
Unsubstituted or substituted C 1 -C 20 Alkyl, unsubstituted or substituted C 6 -C 20 Aryl and unsubstituted or substituted C 1 -C 20 Any one of heteroaryl, wherein the heteroaryl comprises at least one heteroatom, the heteroatom is selected from at least one of N, P, O, S, and the substituent is selected from halogen, cyano, C1-C20 alkyl, C1-C20 alkoxy and C1-C20 alkylthio;
and, in formula (I), R 2 The number of (C) is 1-2, R in the formula (II) 2 The number of (C) is 1-3, R in the formula (III) 2 The number of (2) is 1-4.
Alternatively, R1 is selected from unsubstituted or C 1 ～C 6 Alkyl substituted C 1 -C 6 Alkyl, unsubstituted or C 1 ～C 6 Alkyl substituted C 1 -C 6 Cycloalkyl, unsubstituted or C 1 ～C 6 Alkyl substituted C 6 -C 10 Aryl and unsubstituted or C 1 ～C 6 Alkyl substituted C 1 -C 6 Any one of heteroaryl groups including an N atom therein;
R 2 selected from unsubstituted or C 1 ～C 6 Alkyl substituted C 1 -C 6 Alkyl and unsubstituted or substitutedQuilt C 1 ～C 6 Alkyl substituted C 1 -C 6 Any one of the alkoxy groups.
Alternatively, R 1 Selected from any one of the following structural formulas:
wherein the broken line in the above structural formula represents R 1 And a bond with N in the N-heterocyclic carbene precursor.
Alternatively, the transition metal oxide nanoparticles are doped or undoped transition metal oxide nanoparticles comprising ZnO, snO 2 、TiO 2 、ZrO 2 、Ga 2 O 3 、SiO 2 、Al 2 O 3 、CaO、HfO 2 The doping element in the doped transition metal oxide nano particles is at least one selected from Al, mg, li, in, ga, sr and Ba;
and/or the mass ratio of the transition metal oxide nano particles to the N-heterocyclic carbene precursor is 20:1-1:1;
and/or the solvent is selected from one or more of methanol, ethanol, isopropanol, n-butanol, n-hexanol, acetonitrile and cyclohexanone.
In a second aspect, a composite is provided, the composite being a metal carbene composite comprising transition metal oxide nanoparticles and N-heterocyclic carbene ligands.
Alternatively, the N-heterocyclic carbene ligands include: one or more of the compounds represented by the following structural formulas (I), (II) and (III):
in the formula (I), the formula (II) and the formula (III), R 1 、R 2 Each independently selected from hydrogen, deuterium, unsubstitutedOr substituted C 1 -C 20 Alkyl, unsubstituted or substituted C 6 -C 20 Aryl and unsubstituted or substituted C 1 -C 20 Any one of heteroaryl groups, wherein the heteroaryl group comprises at least one heteroatom, and the heteroatom is selected from at least one of N, P, O, S, and represents a coordination atom coordinated with a transition metal oxide nanoparticle in an N-heterocyclic carbene ligand;
and, in formula (I), R 2 The number of (C) is 1-2, R in the formula (II) 2 The number of (C) is 1-3, R in the formula (III) 2 The number of (2) is 1-4.
Optionally, the N-heterocyclic carbene ligand comprises one or more of the following structural formulas:
wherein, in the above structural formula, the definition of x is the same as the definition of x.
In a third aspect, there is provided a light emitting device comprising:
a first electrode;
A second electrode laminated with the first electrode;
a light emitting layer between the first electrode and the second electrode;
an electron transport layer 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 the first aspect or is composed of the composite material according to the second aspect.
Optionally, the thickness of the electron transport layer is 5-50 nm; and/or the first electrode and the second electrode are respectively and independently selected from one or more of Al, ag, cu, mo, au, ba, ca, yb, mg, graphite, carbon nano tube, 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/TiO 2;
and/or, the material of the light emitting layer includes F8BT.
In a fourth aspect, there is provided a method of manufacturing a light emitting device, comprising:
forming a first electrode;
forming an electron transport layer on the first electrode;
forming a light-emitting bin on the electron transport layer;
forming a second electrode on the light emitting layer;
or alternatively, the first and second heat exchangers may be,
forming a first electrode;
forming a light emitting layer on the first electrode;
Forming an electron transport layer on the light emitting layer;
forming a second electrode on the electron transport layer;
the material of the electron transport layer comprises a metal carbene composite material, the metal carbene composite material comprises transition metal oxide nano particles and N-heterocyclic carbene ligands coordinated with the transition metal oxide nano particles, and the transition metal oxide nano particles have an electron transport function.
Optionally, forming an electron transport layer on the first electrode includes:
preparing a precursor of the transition metal oxide nano particles and an N-heterocyclic carbene precursor into a solution;
forming a liquid film comprising a precursor of a transition metal oxide nanoparticle and the N-heterocyclic carbene precursor on a first electrode;
annealing the first electrode with the liquid film to react the N-heterocyclic carbene precursor with the precursor of the transition metal oxide nano particle to prepare an electron transport layer;
or, forming an electron transport layer on the light emitting layer, comprising:
preparing a solution from the transition metal oxide nanoparticles and the N-heterocyclic carbene precursor;
forming a liquid film comprising a precursor of the transition metal oxide nanoparticles and an N-heterocyclic carbene precursor on the light-emitting layer;
And (3) annealing the liquid film to enable the N-heterocyclic carbene precursor to react with the precursor of the transition metal oxide nano particles so as to prepare the electron transport layer.
Optionally, the atmosphere of the annealing treatment is inert gas atmosphere, the temperature of the annealing treatment is 140-180 ℃, and the time of the annealing treatment is 5-120 min.
In a fifth aspect, there is provided a light emitting device including:
the light-emitting device according to the third aspect or the light-emitting device manufactured by the method according to the fourth aspect.
Compared with the prior art, the application has the following beneficial effects:
since the ink comprises: the transition metal oxide nanoparticle and the N-heterocyclic carbene precursor are prepared by a solvent method, so that a composite material of the transition metal oxide nanoparticle and the N-heterocyclic carbene ligand can be obtained when the electron transport layer is prepared by the solvent method, a stable dipole layer (between the N-heterocyclic carbene ligand and the transition metal oxide nanoparticle interface) can be obtained, the injection barrier of electrons to the light-emitting layer is changed, compared with the prior art that the zinc oxide is subjected to surface modification by adopting fatty amine, and the injection barrier of electrons to the light-emitting layer is changed by utilizing the dipole effect of an amino group and the transition metal oxide nanoparticle, on one hand, the metal carbene composite material is not only suitable for an inverted light-emitting device, but also suitable for a normal light-emitting device without being limited by the structure of the light-emitting device. On the other hand, the N-heterocyclic carbene ligand and the transition metal oxide nano particles can form a stable dipole layer, so that the stability of the device is better. On the other hand, through experimental comparison, the device performance, such as luminous efficiency and service life, of the light-emitting device obtained by the method are effectively improved, the driving voltage of the light-emitting device can be reduced, and the electron transport layer can effectively enhance the injection capability of electrons to the light-emitting layer.
Drawings
Fig. 1 is a schematic cross-sectional view of a light emitting device according to an embodiment of the present application;
fig. 2 is a schematic cross-sectional structure of another light emitting device according to an embodiment of the present application;
fig. 3 is a schematic cross-sectional structure of another light emitting device according to an embodiment of the present application;
fig. 4 is a schematic cross-sectional structure of still another light emitting device according to an embodiment of the present application.
Detailed Description
The present application is described in further detail below in connection with specific embodiments. This application may be embodied in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.
Unless defined otherwise, 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 in the description of the application 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.
Based on the above technical problems, some embodiments of the present application provide an ink including transition metal oxide nanoparticles, an N-heterocyclic carbene precursor, and a solvent.
Carbenes (carbnes), also known as carbenes, are electrically neutral compounds containing divalent carbon. Carbenes are formed by covalent bonding of one carbon with two other groups, two free electrons being present on the carbon. N-heterocyclic carbenes (N-heterocyclic carbene, NHC) are a relatively novel class of carbenes, also known as stable carbenes, which have particular stability and some can be stored indefinitely. In a typical N-heterocyclic carbene, the carbyl group of the carbene is located on an imidazole, thiazole, 1,2, 4-triazine ring system or carbon attached to two substituted amino groups.
In the electron transport ink provided in the embodiments of the present application, since the ink includes: the transition metal oxide nanoparticle and the N-heterocyclic carbene precursor are prepared by a solvent method, so that a composite material of the transition metal oxide nanoparticle and the N-heterocyclic carbene ligand can be obtained when the electron transport layer is prepared by the solvent method, a stable dipole layer (between the N-heterocyclic carbene ligand and the transition metal oxide nanoparticle interface) can be obtained, the injection barrier of electrons to the light-emitting layer is changed, compared with the prior art that the zinc oxide is subjected to surface modification by adopting fatty amine, and the injection barrier of electrons to the light-emitting layer is changed by utilizing the dipole effect of an amino group and the transition metal oxide nanoparticle, on one hand, the metal carbene composite material is not only suitable for an inverted light-emitting device, but also suitable for a normal light-emitting device without being limited by the structure of the light-emitting device. On the other hand, the N-heterocyclic carbene ligand and the transition metal oxide nano particles can form a stable dipole layer, so that the stability of the device is better. On the other hand, through experimental comparison, the device performance, such as luminous efficiency and service life, of the light-emitting device obtained by the method are effectively improved, the driving voltage of the light-emitting device can be reduced, and the electron transport layer can effectively enhance the injection capability of electrons to the light-emitting layer.
In some embodiments, the transition metal oxide nanoparticles may have a particle size of 3 to 10nm.
In some embodiments, the N-heterocyclic carbene precursor comprises: one or more of the compounds represented by the following structural formulas (i), (ii) and (iii):
in formula (i), formula (ii) and formula (iii), R 1 、R 2 Each independently selected from hydrogen, deuterium, unsubstituted or substituted C 1 -C 20 Alkyl, unsubstituted or substituted C 6 -C 20 Aryl and unsubstituted or substituted C 1 -C 20 Any one of heteroaryl, wherein the heteroaryl comprises at least one heteroatom, the heteroatom is selected from at least one of N, P, O, S, and the substituent is selected from halogen, cyano, C1-C20 alkyl, C1-C20 alkoxy and C1-C20 alkylthio;
and, in formula (I), R 2 The number of (C) is 1-2, R in the formula (II) 2 The number of the components is 1 to 3, in the formulaIn III), R 2 The number of (2) is 1-4.
In these embodiments, the host structure of the N-heterocyclic carbene precursor is an imidazole (or dihydroimidazole), tetrahydropyrimidine, or benzimidazole ring, and thus the N-heterocyclic carbene precursor is readily available. In addition, the N-heterocyclic carbene precursor is a heat-activated precursor, and in the reaction process, C between two nitrogen atoms in the N-heterocyclic carbene precursor is subjected to C-C bond cleavage at high temperature to remove CO 2 A carbene intermediate is formed, and a carbon atom of the carbene intermediate serves as a strong sigma electron donor and coordinates with the transition metal oxide nanoparticles, so that a stable dipole layer can be obtained.
Alternatively, R 1 Selected from unsubstituted or C 1 ～C 6 Alkyl substituted C 1 -C 6 Alkyl, unsubstituted or C 1 ～C 6 Alkyl substituted C 1 -C 6 Cycloalkyl, unsubstituted or C 1 ～C 6 Alkyl substituted C 6 -C 10 Aryl and unsubstituted or C 1 ～C 6 Alkyl substituted C 1 -C 6 Any one of heteroaryl groups including an N atom therein;
R 2 selected from unsubstituted or C 1 ～C 6 Alkyl substituted C 1 -C 6 Alkyl and unsubstituted or C 1 ～C 6 Alkyl substituted C 1 -C 6 Any one of the alkoxy groups.
Alternatively, R 1 Selected from any one of the following structural formulas:
wherein the broken line in the above structural formula represents R 1 And a bond with N in the N-heterocyclic carbene precursor.
In some embodiments, the N-heterocyclic carbene precursor comprises one or more of the following structural formulas:
in some embodiments, the transition metal oxide nanoparticles are doped or undoped transition metal oxide nanoparticles, and the undoped transition metal oxide nanoparticles include zinc oxide, tin oxide, titanium oxide, zrO 2 、Ga 2 O 3 、SiO 2 、Al 2 O 3 、CaO、HfO 2 The doping element in the doped transition metal oxide nano particles is at least one selected from Al, mg, li, in, ga, sr and Ba; and/or the mass ratio of the transition metal oxide nano particles to the N-heterocyclic carbene precursor is 20:1-1:1; and/or the solvent is selected from one or more of methanol, ethanol, isopropanol, n-butanol, n-hexanol, acetonitrile and cyclohexanone.
In these embodiments, the electron injection capability of the light emitting device 10 may be maximized by controlling the mass ratio of the transition metal oxide nanoparticles to the N-heterocyclic carbene precursor within the above-described range.
In some embodiments, the mass ratio of transition metal oxide nanoparticles to N-heterocyclic carbene precursor is 5:1.
Experiments have found that excessive N-heterocyclic carbene precursors tend to form less conductive byproducts after reaction, which are detrimental to the improvement of the efficiency of electron injection into the light emitting layer 32.
Some embodiments of the present application provide a composite material that is a metal carbene composite material that includes transition metal oxide nanoparticles and N-heterocyclic carbene ligands.
The N-heterocyclic carbene ligand is used as a reaction intermediate, has very high reactivity, has very good metal bonding capability, more flexible and changeable steric hindrance and electronic effect, diversified structure types and easy preparation. The N-heterocyclic carbene ligand is a strong sigma electron donor, so that the electron density of the central metal can be increased, and meanwhile, the central metal has a certain feedback pi bond effect on C atoms, so that the carbene metal complex can exist stably.
The composite material is an electron transport material, the electron transport material is provided with a stable dipole layer (between an N-heterocyclic carbene ligand and a transition metal oxide nanoparticle interface), the injection barrier of electrons to a luminescent layer is changed, and compared with the prior art that fatty amine is adopted to carry out surface modification on zinc oxide and the dipole action of amine groups and transition metal oxide nanoparticles is utilized to change the injection barrier of electrons to the luminescent layer, on one hand, the metal carbene composite material is not only suitable for an inverted luminescent device, but also suitable for a positive luminescent device, and is not limited by the structure of the luminescent device. On the other hand, the N-heterocyclic carbene ligand and the transition metal oxide nano particles can form a stable dipole layer, so that the stability of the device is better. On the other hand, through experimental comparison, the device performance, such as luminous efficiency and service life, of the light-emitting device obtained by the method are effectively improved, the driving voltage of the light-emitting device can be reduced, and the electron transport material can effectively enhance the injection capability of electrons to the light-emitting layer.
In some embodiments, the N-heterocyclic carbene ligand comprises: one or more of the compounds represented by the following structural formulas (I), (II) and (III):
In the formula (I), the formula (II) and the formula (III), R 1 、R 2 Each independently selected from hydrogen, deuterium, unsubstituted or substituted C 1 -C 20 Alkyl, unsubstituted or substituted C 6 -C 20 Aryl and unsubstituted or substituted C 1 -C 20 Any one of heteroaryl groups, wherein the heteroaryl group comprises at least one heteroatom, and the heteroatom is selected from at least one of N, P, O, S, and represents a coordination atom coordinated with a transition metal oxide nanoparticle in an N-heterocyclic carbene ligand;
and, in formula (I), R 2 The number of (C) is 1-2, R in the formula (II) 2 The number of (2) is 1-3,in formula (III), R 2 The number of (2) is 1-4.
Wherein, in the above formula (I), the dotted line indicates that the main structure of the N-heterocyclic carbene ligand may be imidazole or dihydroimidazole. In the above formula (I), R 2 When the number of (2) is one, R 2 Can be attached to either carbon of the imidazole or dihydroimidazole ring, the other carbon being attached to a hydrogen atom, meaning that only one carbon of the imidazole or dihydroimidazole is substituted with hydrogen; r is R 2 When the number of (2) is two, R 2 Can be attached to both carbons of imidazole or dihydroimidazole, meaning that the hydrogens on both carbons of imidazole or dihydroimidazole are substituted; in the above formula (II), R 2 When the number of (2) is one, R 2 Can be attached to any one carbon of the ring of the tetrahydropyrimidine, and the other two carbons are attached to a hydrogen atom, meaning that only one carbon of the ring of the tetrahydropyrimidine is substituted; r is R 2 When the number of (2) is two, R 2 Can be connected to any two carbons of the ring of the tetrahydropyrimidine, and the other carbon is connected with a hydrogen atom, which means that the hydrogen on the two carbons of the ring of the tetrahydropyrimidine is replaced; r is R 2 When the number of (3) is three, R 2 May be attached to three carbons of the ring of the tetrahydropyrimidine, meaning that all three carbons of the ring of the tetrahydropyrimidine are substituted; in the above formula (III), R 2 The number of (a) may be 1 to 4, and specific representation may be found in the above description of the formula (I) and the formula (II), and will not be described here again.
In these embodiments, the host structure of the N-heterocyclic carbene ligand may be an imidazole (or dihydroimidazole), tetrahydropyrimidine, or benzimidazole ring, and the resulting N-heterocyclic carbene ligand has good stability, facilitating the preparation of the desired precursor material. And the N-heterocyclic carbene ligands can form a stable dipole layer with the transition metal oxide nano particles, so that the performance of the light-emitting device is improved.
In some embodiments, R 1 Selected from any one of the following structural formulas:
Wherein the broken line in the above structural formula represents R 1 And a linkage to N in the N-heterocyclic carbene.
In some embodiments, the N-heterocyclic carbene ligand comprises one or more of the following structural formulas:
wherein, in the above structural formula, the definition of x is the same as the definition of x.
Some embodiments of the present application provide a light emitting device 10, as shown in fig. 1 and 2, comprising: the first electrode 1 and the second electrode 2 are stacked, and a light-emitting layer provided between the first electrode 1 and the second electrode 2, and an electron transport layer 31 provided between the first electrode and the light-emitting layer. The material of the electron transport layer 31 is prepared from the electron transport ink described above or is composed of the composite material described above.
The light emitting device 10 may be an inverted light emitting device or a front light emitting device.
Taking the example that the first electrode 1, the light emitting layer, the electron transporting layer and the second electrode 2 are sequentially arranged from bottom to top in the light emitting device 10, when the light emitting device 10 is a front-mounted light emitting device, as shown in fig. 1, the first electrode 1 is an anode, and the second electrode 2 is a cathode, at this time, the light emitting layer 32 of the first light emitting unit 3 is located below the electron transporting layer 31, at this time, the material of the whole layer of the electron transporting layer 31 may include the metal carbene composite material, that is, a liquid film containing transition metal oxide nanoparticles and N-heterocyclic carbene precursor may be formed directly on the side of the light emitting layer 32 far from the first electrode 1 by a solution method, and then the transition metal oxide nanoparticles and the N-heterocyclic carbene precursor react by heating to generate the metal carbene composite material, so that a stable dipole layer may be formed above the light emitting layer 32, the injection barrier of electrons into the light emitting layer 32 may be reduced, and the device performance may be improved. In the case where the light emitting device 10 is an inverted light emitting device, as shown in fig. 2, the first electrode 1 is a cathode, and the second electrode 2 is an anode, and at this time, the electron transport layer 31 is located under the light emitting layer 32, and at this time, a whole layer of the metal carbene composite material may be formed on the first electrode 1, similarly to the above, so that a stable dipole layer may be formed; or, first, a transition metal oxide nanoparticle (such as zinc oxide) is formed on the first electrode 1, then an N-heterocyclic carbene precursor is formed on the surface of the zinc oxide away from the first electrode 1, and the transition metal oxide nanoparticle and the N-heterocyclic carbene precursor react to generate a metal carbene composite material through heating, at this time, the metal carbene composite material is formed only on the surface of the transition metal oxide nanoparticle close to the light emitting layer 32, and a stable dipole layer can be formed, so that the effect of reducing the injection barrier of electrons into the light emitting layer 32 is achieved, and the performance of the light emitting device 10 can be improved.
In the light emitting device provided by the application, the N-heterocyclic carbene ligand and the transition metal oxide nanoparticle are coordinated, so that a stable dipole layer (between the N-heterocyclic carbene ligand and the transition metal oxide nanoparticle interface) can be obtained, the injection barrier of electrons to the light emitting layer 32 is changed, compared with the prior art that the aliphatic amine is adopted to carry out surface modification on zinc oxide, and the dipole effect of the amine group and the zinc oxide is utilized to change the injection barrier of electrons to the light emitting layer 32, on one hand, the metal carbene composite material is not only suitable for an inverted light emitting device, but also suitable for a right-placed light emitting device, and is not limited by the structure of the light emitting device 10. On the other hand, the N-heterocyclic carbene ligand and the transition metal oxide nano particles can form a stable dipole layer, so that the stability of the device is better. On the other hand, it was found through experimental comparison that the device performance such as the light emitting efficiency and the lifetime of the light emitting device 10 thus obtained were effectively improved, and the driving voltage of the light emitting device 10 could be reduced, indicating that the electron transport layer 31 could effectively enhance the electron injection capability into the light emitting layer.
In some embodiments, the electron transport layer has a thickness of 5 to 50nm; and/or the first electrode and the second electrode are respectively and independently selected from one or more of Al, ag, cu, mo, au, ba, ca, yb, mg, graphite, carbon nano tube, 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/TiO 2; and/or, the material of the light emitting layer includes F8BT.
In these embodiments, the thickness of the electron transport layer is controlled within the above range, so that the electron transport and injection can be performed without significantly affecting the thickness of the device.
In the above, the case where the light emitting device 10 includes only one light emitting unit, i.e., the first light emitting unit 3, was described. As will be appreciated by those skilled in the art, the above-described first light emitting unit 3 may include at least one functional layer of a hole transport layer 33, a hole injection layer 34, an electron injection layer, an electron blocking layer, and a hole blocking layer, in addition to the light emitting layer 32 and the electron transport layer 31, which are stacked between the first electrode 1 and the second electrode 2.
In some embodiments, as shown in fig. 3 and 4, the light emitting device 10 may further include: the 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, and the electron transport layer 41 is disposed on a side of the light emitting layer 31 of the first light emitting unit 3 away from the electron transport layer 31.
In these embodiments, the second light emitting unit 4 and the first light emitting unit 3 are connected in series, so that the light emitting brightness and the light emitting efficiency can be effectively improved, and the high brightness at a low current density can be realized, thereby effectively improving the service life of the light emitting device.
The material of the electron transport layer 41 may be the same as or different from that of the electron transport layer 31, and is not particularly limited herein.
In some embodiments, the material of electron transport layer 41 is the same as the material of electron transport layer 31. That is, the material of the electron transport layer 41 includes the metal carbene composite material, and the preparation method of the electron transport layer 41 can be referred to the above description of the preparation method of the electron transport layer 31, which is not repeated herein.
In some embodiments, as shown in fig. 3, 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 further includes: an electron injection layer disposed between the electron transport layer 41 and the cathode, or the electron transport layer 41 is replaced with the above electron injection layer.
In these embodiments, the electron injection efficiency may be further improved by providing an electron injection layer, and the device performance of the light emitting device 10 may be further improved. By replacing the electron transport layer 41 with an electron injection layer, the manufacture of the electron transport layer 41 can be omitted, and the device performance of the light emitting device 10 can be effectively improved by utilizing the higher injection efficiency of the electron injection layer.
Here, similarly to the first light emitting unit 3 described above, as shown in fig. 3 and 4, the second light emitting unit 4 may include, in addition to the light emitting layer 42 and the electron transport layer 41: at least one functional layer among the hole transport layer 43, the hole injection layer 44, the electron injection layer, the electron blocking layer, and the hole blocking layer, unlike the light emitting device 10 described above which includes only one light emitting unit, the functional layers included in the second light emitting unit 4 and the first light emitting unit 3 are each disposed between the first electrode 1 and the second electrode 2 in a stacked manner, and the functional layers included in both are in the same order in the vertical direction, together constituting a positive light emitting device or an inverted light emitting device.
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 Diodes, quantum dot Light Emitting Diode) Light Emitting device.
In the case where the light emitting device 10 is an OLED light emitting device, compared with the case where a doping material (n-type dopant) using an electron transport layer in the related art is unstable in a solution, the electron transport material stable in the solution can be provided, the manufacturing cost can be reduced, and at the same time, the injection barrier of electrons to the light emitting layer can be effectively reduced, and the device performance of the light emitting device can be improved.
Some embodiments of the present application provide a method for manufacturing a light emitting device, including:
s1, forming a first electrode 1.
S2, forming an electron transport layer 31 of the first light emitting unit 3 on the first electrode 1;
s3, forming a light-emitting layer 32 on the light-emitting layer 32;
s4, forming a second electrode on the light-emitting layer;
or alternatively, the first and second heat exchangers may be,
s1, forming a first electrode 1;
s2, forming a light-emitting layer 32 of the first light-emitting unit 3 on the first electrode 1;
s3, forming an electron transport layer 31 on the light emitting layer 32;
s4, forming a second electrode on the electron transport layer.
In some embodiments, the first electrode 1 may be formed on a substrate layer, which may be a substrate of glass or other material.
The first electrode 1 may be an anode or a cathode, and the light emitting device 10 is a positive light emitting device in the case where the first electrode 1 is an anode, and the light emitting device 10 is an inverted light emitting device in the case where the first electrode 1 is a cathode.
In some embodiments, in the case where the first electrode 1 is an anode, the first electrode 1 may be a material having a higher work function such as ITO, and in the case where the first electrode 1 is a cathode, the first electrode 1 may be a material having a lower work function such as metal.
Taking the first electrode 1 as ITO here as an example, after the first electrode 1 is prepared, the treatment of ITO under UV conditions for 15min may be further included, so that the work function and wettability thereof may be increased.
The material of the electron transport layer 31 includes a metal carbene composite material, the metal carbene composite material includes transition metal oxide nanoparticles and N-heterocyclic carbene ligands coordinated with the transition metal oxide nanoparticles, and the transition metal oxide nanoparticles have an electron transport function.
N-heterocyclic carbene ligands are a relatively novel class of carbenes, also known as stable carbenes, which have a particular stability and can be stored for some time without limitation. In a typical N-heterocyclic carbene, the carbyl group of the carbene is located on an imidazole, thiazole, 1,2, 4-triazine ring system or carbon attached to two substituted amino groups. The N-heterocyclic carbene ligand is used as a reaction intermediate, has very high reactivity, has very good metal bonding capability, more flexible and changeable steric hindrance and electronic effect, diversified structure types and easy preparation. The N-heterocyclic carbene ligand is a strong sigma electron donor, so that the electron density of the central metal can be increased, and meanwhile, the central metal has a certain feedback pi bond effect on C atoms, so that the carbene metal complex can exist stably.
In some embodiments, the light emitting layer 32 may be prepared by evaporation or solution (e.g., spin coating).
Of course, in some embodiments, the first light emitting unit 3 may include, in addition to the light emitting layer 32 and the electron transporting layer 31: at least one of the hole transport layer 33, the hole injection layer 34, the electron injection layer, the electron blocking layer, and the hole blocking layer.
In some embodiments, in the case where light emitting device 10 is a front-mounted light emitting device, hole transport layer 33, hole injection layer 34, and electron blocking layer are all located below light emitting layer 32, and both the electron injection layer and the hole blocking layer are located above light emitting layer 32. In the case where 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.
The hole transport layer 33, the hole injection layer 34, the electron injection layer, the electron blocking layer, and the hole blocking layer may be prepared by vapor deposition or a solution method (spin coating method).
In some embodiments, forming the electron transport layer 31 on the first electrode 1 includes:
Preparing a solution from the transition metal oxide nanoparticles and the N-heterocyclic carbene precursor;
forming a liquid film containing transition metal oxide nanoparticles and an N-heterocyclic carbene precursor on the first electrode 1;
the first electrode 1 having the liquid film formed thereon is subjected to an annealing treatment to react the N-heterocyclic carbene precursor with the precursor of the transition metal oxide nanoparticle, thereby preparing the electron transport layer 31.
Forming an electron transport layer on the light emitting layer, comprising:
preparing a solution from the transition metal oxide nanoparticles and the N-heterocyclic carbene precursor;
forming a liquid film comprising a precursor of the transition metal oxide nanoparticle and an N-heterocyclic carbene precursor on the light-emitting layer;
and (3) annealing the liquid film to enable the N-heterocyclic carbene precursor to react with the precursor of the transition metal oxide nano particles so as to prepare the electron transport layer.
In these examples, the metal carbene composites described above may be prepared by solution processes, resulting in a stable dipole layer (between the transition metal oxide nanoparticles and the N-heterocyclic carbene interface). The metal carbene composite material comprises transition metal oxide nano particles and N-heterocyclic carbene ligands coordinated with the transition metal oxide nano particles, and experiments show that the preparation of the metal carbene composite material is not only suitable for inverted light-emitting devices, but also suitable for upright light-emitting devices, and is not limited by the structure of the light-emitting devices. On the other hand, compared with the structure of the fatty amine for carrying out surface modification on zinc oxide in the related technology, the metal carbene composite material can obtain a more stable dipole layer, so that the stability of the light-emitting device can be improved. On the other hand, experiments show that compared with the structure of surface modification of zinc oxide by fatty amine, the driving voltage of the light-emitting device can be effectively reduced, the light-emitting efficiency and the service life of the light-emitting device can be improved, and the performance of the light-emitting device can be improved as a whole.
In conclusion, the metal carbene composite material can effectively enhance the injection capability of electrons to the light-emitting layer and improve the stability of the device.
The N-heterocyclic carbene precursor may be referred to the description of the N-heterocyclic carbene precursor in the electron transfer ink, and will not be described herein.
In some embodiments, the annealing atmosphere is inert gas atmosphere, the annealing temperature is 140-180 ℃, and the annealing time is 5-120 min.
In these embodiments, the carbene intermediate can be effectively protected by setting the annealing atmosphere to an inert gas atmosphere, so that the carbene intermediate and the transition metal oxide nanoparticles can undergo a coordination reaction. Meanwhile, the annealing temperature is too low, so that the N-heterocyclic carbene precursor is not completely decomposed, the reaction is not facilitated, and the transition metal oxide nanoparticles are easy to be cracked when the annealing temperature is too high.
In some embodiments, the inert gas is argon and/or nitrogen.
In some embodiments, the solvent used to prepare the solution described above may be a highly polar solvent. By way of example, the highly polar solvent may include one or more of methanol, ethanol, isopropanol, n-butanol, n-hexanol, acetonitrile, cyclohexanone.
Here, the electron transport layer 31 may be prepared by the above-described method, regardless of whether the light emitting device 10 is a front light emitting device or an inverted light emitting device. In the case of the light emitting device 10 being 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 may be formed first, then a liquid film of an N-heterocyclic carbene precursor may be formed on the surface of the metal oxide electron transport layer, and through the annealing process described above, the N-heterocyclic carbene precursor and the metal oxide nanoparticles may be reacted as well, except that the metal carbene composite thus formed is formed only on the surface of the electron transport layer 31, and by forming a stable dipole layer on the surface of the electron transport layer 31, the effect of reducing the injection barrier of electrons into the light emitting layer 32 and improving the device performance of the light emitting device 10 may be also achieved.
Some embodiments of the present application provide a light emitting device, comprising: a light emitting device as described above or a light emitting device prepared by the method as described above.
The technical effects of the light emitting device provided in the embodiment of the present application are the same as those of the light emitting device provided in the embodiment of the present application, and are not described herein again.
In the following examples and comparative examples, all the raw materials were purchased commercially and, in order to maintain the reliability of the experiment, the raw materials used in the following examples and comparative examples all had the same physical and chemical parameters or were subjected to the same treatment.
Example 1
Step 1), solution configuration: znO nano particles with the size of about 5nm are dispersed in acetonitrile, and the concentration is 15mg/mL; and simultaneously, dissolving a NHC precursor DMImC in acetonitrile with the concentration of 3mg/mL, and then mixing the two solutions in a volume ratio of 1:1 to obtain a solution with the mass ratio of ZnO nano particles to DMImC of 5:1.
Step 2), device preparation: cleaning an ITO anode substrate, and then treating the substrate for 15min under the UV condition to increase the work function and wettability of the substrate; spin-coating PEDOT with the thickness of 30nm to PSS on the treated ITO substrate and baking for 20min at 150 ℃ in an air atmosphere; spin-coating TFB as a hole transport layer on a PEDOT-PSS substrate with a thickness of 30nm, and then baking at 180 ℃ for 60min in a nitrogen environment; then spin-coating a 60nm thick polymer light-emitting layer F8BT on the substrate, baking at 150 ℃ for 10min, spin-coating a 10nm thick composite electron transport layer liquid film, annealing at 160 ℃ for 30min, vacuum evaporating 100nm thick Ag, and finally packaging and annealing at 80 ℃ for 30min.
Example 2
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.
Example 3
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.
Example 4
In example 4, the annealing temperature of the liquid film was 120℃and the other preparation methods were the same as in example 1.
Example 5
In example 5, DMImC in solution was replaced with DPImC and the other preparation method was the same as in example 1.
Example 6
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.
Example 7
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.
Comparative example 1
In comparative example 1, the NHC precursor was not added to the solution, and the other preparation methods were the same as in example 1.
The devices prepared in the above examples and comparative examples were tested for performance using an IVL apparatus, and the life of each device was measured using a life aging apparatus, and the results are shown in table 1 below.
TABLE 1
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As shown in table 1, the driving voltage of the device of the composite electron transport layer prepared by adding NHC precursor into ZnO is significantly reduced, the lifetime and efficiency are enhanced, and the injection capability of electrons into the light emitting layer is improved.
As can be seen from examples 1, 2, 3, 6 and 7, as the zinc oxide and NHC precursors are greater than 20:1 or less than 1:1, the device efficiency and the device lifetime are reduced to some extent, and the driving voltage is slightly increased. As can be seen from comparison of example 1 and example 4, as the annealing temperature decreases, the device efficiency and the device lifetime decrease to some extent, and the driving voltage increases.
The technical features of the above-described embodiments may be arbitrarily combined, and all possible combinations of the technical features in the above-described embodiments are not described for brevity of description, however, as long as there is no contradiction between the combinations of the technical features, they should be considered as the scope of the description.
The above examples only represent a few embodiments of the present application, which are described in more detail and are not to be construed as limiting the scope of the claims. It should be noted that it would be apparent to those skilled in the art that various modifications and improvements could be made without departing from the spirit of the present application, which would be within the scope of the present application. Accordingly, the scope of protection of the present application is to be determined by the claims appended hereto.
Claims (13)
1. An ink, comprising transition metal oxide nanoparticles, an N-heterocyclic carbene precursor, and a solvent; wherein the N-heterocyclic carbene precursor comprises: one or more of the compounds represented by the following structural formulas (i), (ii) and (iii):
in formula (i), formula (ii) and formula (iii), R 1 、R 2 Each independently selected from hydrogen, deuterium, unsubstituted or substituted C 1 -C 20 Alkyl, unsubstituted or substituted C 6 -C 20 Aryl and unsubstituted or substituted C 1 -C 20 Any one of heteroaryl, wherein the heteroaryl comprises at least one heteroatom, the heteroatom is selected from at least one of N, P, O, S, and the substituent is selected from halogen, cyano, C1-C20 alkyl, C1-C20 alkoxy and C1-C20 alkylthio;
and, in formula (I), R 2 The number of (C) is 1-2, R in the formula (II) 2 The number of (C) is 1-3, R in the formula (III) 2 The number of (2) is 1-4.
2. The ink of claim 1, wherein R1 is selected from unsubstituted or C 1 ～C 6 Alkyl substituted C 1 -C 6 Alkyl, unsubstituted or C 1 ～C 6 Alkyl substituted C 1 -C 6 Cycloalkyl, unsubstituted or C 1 ～C 6 Alkyl substituted C 6 -C 10 Aryl and unsubstituted or C 1 ～C 6 Alkyl substituted C 1 -C 6 Any one of heteroaryl groups including an N atom therein;
R 2 Selected from unsubstituted or C 1 ～C 6 Alkyl substituted C 1 -C 6 Alkyl and unsubstituted or C 1 ～C 6 Alkyl substituted C 1 -C 6 Any one of the alkoxy groups.
3. The ink according to claim 1 or 2, wherein R is 1 Selected from any one of the following structural formulas:
-----CH3
wherein the broken line in the above structural formula represents R 1 And a bond with N in the N-heterocyclic carbene precursor.
4. The ink according to claim 1 or 2, wherein the transition metal oxide nanoparticles are doped or undoped transition metal oxide nanoparticles comprising ZnO, snO 2 、TiO 2 、ZrO 2 、Ga 2 O 3 、SiO 2 、Al 2 O 3 、CaO、HfO 2 The doping element in the doped transition metal oxide nano particles is at least one selected from Al, mg, li, in, ga, sr and Ba;
and/or the mass ratio of the transition metal oxide nano particles to the N-heterocyclic carbene precursor is 20:1-1:1;
and/or the solvent is selected from one or more of methanol, ethanol, isopropanol, n-butanol, n-hexanol, acetonitrile and cyclohexanone.
5. A composite material, wherein the composite material is a metal carbene composite material comprising transition metal oxide nanoparticles and N-heterocyclic carbene ligands.
6. The composite material of claim 5, wherein the N-heterocyclic carbene ligand comprises: one or more of the compounds represented by the following structural formulas (I), (II) and (III):
in the formula (I), the formula (II) and the formula (III), R 1 、R 2 Each independently selected from hydrogen, deuterium, unsubstituted or substituted C 1 -C 20 Alkyl, unsubstituted or substituted C 6 -C 20 Aryl and unsubstituted or substituted C 1 -C 20 Any one of heteroaryl groups, wherein the heteroaryl group comprises at least one heteroatom, and the heteroatom is selected from at least one of N, P, O, S, and represents a coordination atom coordinated with a transition metal oxide nanoparticle in an N-heterocyclic carbene ligand;
and, in formula (I), R 2 The number of (C) is 1-2, R in the formula (II) 2 The number of (C) is 1-3, R in the formula (III) 2 The number of (2) is 1-4.
7. The composite material of claim 6, wherein the composite material comprises,
the N-heterocyclic carbene ligands include one or more of the following structural formulas:
wherein, in the above structural formula, the definition is the same as that of claim 6.
8. A light emitting device, comprising:
a first electrode;
a second electrode arranged in a stacked manner with the first electrode;
A light emitting layer between the first electrode and the second electrode;
an electron transport layer 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 to 4 or is composed of the composite material according to any one of claims 5 to 7.
9. A light-emitting device according to claim 8, wherein,
the thickness of the electron transport layer is 5-50 nm;
and/or the first electrode and the second electrode are respectively and independently selected from one or more of Al, ag, cu, mo, au, ba, ca, yb, mg, graphite, carbon nano tube, 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/TiO 2;
and/or, the material of the light emitting layer includes F8BT.
10. A method of manufacturing a light emitting device, comprising:
forming a first electrode;
forming an electron transport layer on the first electrode;
a light emitting layer is formed on the electron transport layer,
forming a second electrode on the light emitting layer;
Or alternatively, the first and second heat exchangers may be,
forming a first electrode;
forming a light emitting layer on the first electrode;
an electron transport layer is formed on the light emitting layer,
forming a second electrode on the electron transport layer;
the material of the electron transport layer comprises a metal carbene composite material, the metal carbene composite material comprises transition metal oxide nanoparticles and N-heterocyclic carbene ligands coordinated with the transition metal oxide nanoparticles, and the transition metal oxide nanoparticles have an electron transport function.
11. The method of claim 10, wherein forming an electron transport layer on the first electrode comprises:
preparing the transition metal oxide nanoparticles and the N-heterocyclic carbene precursor into a solution;
forming a liquid film comprising a precursor of the transition metal oxide nanoparticle and the N-heterocyclic carbene precursor on the first electrode;
annealing the first electrode with the liquid film formed, so that the N-heterocyclic carbene precursor and the precursor of the transition metal oxide nano particle react to prepare the electron transport layer;
or, forming an electron transport layer on the light emitting layer, including:
Preparing the transition metal oxide nanoparticles and the N-heterocyclic carbene precursor into a solution;
forming a liquid film comprising a precursor of the transition metal oxide nanoparticle and the N-heterocyclic carbene precursor on the light-emitting layer;
and (3) annealing the liquid film to enable the N-heterocyclic carbene precursor and the precursor of the transition metal oxide nano particle to react, so as to prepare the electron transport layer.
12. The method of claim 11, wherein the step of determining the position of the probe is performed,
the atmosphere of the annealing treatment is inert gas atmosphere, the temperature of the annealing treatment is 140-180 ℃, and the time of the annealing treatment is 5-120 min.
13. A light emitting device, comprising:
a light emitting device according to any one of claims 8 to 9 or a light emitting device prepared by a method according to any one of claims 10 to 12.
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