CN116156919A - Light-emitting device, preparation method thereof and display device - Google Patents
Light-emitting device, preparation method thereof and display device Download PDFInfo
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- CN116156919A CN116156919A CN202111360401.4A CN202111360401A CN116156919A CN 116156919 A CN116156919 A CN 116156919A CN 202111360401 A CN202111360401 A CN 202111360401A CN 116156919 A CN116156919 A CN 116156919A
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- C—CHEMISTRY; METALLURGY
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- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
- C09K11/02—Use of particular materials as binders, particle coatings or suspension media therefor
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y20/00—Nanooptics, e.g. quantum optics or photonic crystals
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- C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
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- C09K11/88—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing selenium, tellurium or unspecified chalcogen elements
- C09K11/881—Chalcogenides
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Abstract
The application discloses a light-emitting device, a preparation method thereof and a display device, wherein the light-emitting device comprises an anode and a cathode which are oppositely arranged, and a light-emitting layer arranged between the anode and the cathode, the light-emitting layer is arranged between the anode and the cathode, the material of the light-emitting layer comprises first quantum dots and second quantum dots, the surface of the first quantum dots is provided with first ligands, the surface of the second quantum dots is provided with second ligands, the first ligands contain aryl or heteroaryl, and the second ligands do not contain aryl or heteroaryl; the content of the first quantum dots is gradually increased, and the content of the second quantum dots is gradually decreased along the direction of the cathode towards the anode in the light-emitting layer. Therefore, the carrier mobility of the light-emitting layer near the anode is higher than the carrier mobility of the light-emitting layer near the cathode along the direction of the cathode towards the anode, so that the electron-hole transmission balance of the light-emitting device is promoted, and the light-emitting efficiency and the service life of the light-emitting device are further improved.
Description
Technical Field
The application relates to the technical field of photoelectricity, in particular to a light-emitting device, a preparation method thereof and a display device.
Background
Light Emitting devices include, but are not limited to, organic Light-Emitting Diode (OLED) and quantum dot Light Emitting Diode (Quantum Dot Light Emitting Diodes, QLED), the Light Emitting principle of the Light Emitting device is: electrons are injected into the light-emitting area from the cathode of the device, holes are injected into the light-emitting area from the anode of the device, the electrons and the holes are combined in the light-emitting area to form excitons, and photons are released from the combined excitons in a radiation transition mode, so that light is emitted. The QLED is a light-emitting device based on Quantum Dot (QD) as a light-emitting material, and the QLED becomes a novel light-emitting device with the current most potential due to the characteristics of narrow half-width of a light-emitting spectrum, high color purity, good light stability, wide excitation spectrum, controllable emission spectrum and the like.
In the QLED, since the quantum dot is an N-type semiconductor, the conductivity to electrons is far stronger than that to holes, so that the hole injection level of the QLED is lower than that of the electron injection level, resulting in the problem of unbalanced electron-hole transport of the QLED, and affecting the photoelectric performance and the service life of the QLED.
Therefore, the problem of how to improve the electron-hole transport imbalance of the QLED is of great significance to the application and development of the QLED.
Disclosure of Invention
The present application provides a light emitting device and a display apparatus that promote electron-hole transport balance of the light emitting device by optimizing a light emitting layer of the light emitting device.
The technical scheme of the application is as follows:
in a first aspect, the present application provides a light emitting device comprising:
an anode and a cathode disposed opposite each other;
a light emitting layer disposed between the anode and the cathode, the material of the light emitting layer comprising a first quantum dot having a first ligand on a surface thereof and a second quantum dot having a second ligand on a surface thereof, the first ligand containing an aryl or heteroaryl group, the second ligand not containing an aryl or heteroaryl group;
the content of the first quantum dots is gradually increased, and the content of the second quantum dots is gradually decreased along the direction of the cathode towards the anode in the light-emitting layer.
Further, the first quantum dot is the same as the second quantum dot.
Further, the first quantum dot and the second quantum dot are independently selected from at least one of group II-VI compound, group III-V compound, group IV-VI compound and group I-III-VI compound;
Wherein the II-VI compound is selected from at least one of CdS, cdSe, cdTe, znS, znSe, znTe, znO, hgS, hgSe, hgTe, cdSeS, cdSeTe, cdSTe, znSeS, znSeTe, znSTe, hgSeS, hgSeTe, hgSTe, cdZnS, cdZnSe, cdZnTe, cdHgS, cdHgSe, cdHgTe, hgZnS, hgZnSe, hgZnTe, cdZnSeS, cdZnSeTe, cdZnSTe, cdHgSeS, cdHgSeTe, cdHgSTe, hgZnSeS, hgZnSeTe and HgZnSte;
the III-V compound is at least one selected from GaN, gaP, gaAs, gaSb, alN, alP, alAs, alSb, inN, inP, inAs, inSb, gaNP, gaNAs, gaNSb, gaPAs, gaPSb, alNP, alNAs, alNSb, alPAs, alPSb, inNP, inNAs, inNSb, inPAs, inPSb, gaAlNP, gaAlNAs, gaAlNSb, gaAlPAs, gaAlPSb, gaInNP, gaInNAs, gaInNSb, gaInPAs, gaInPSb, inAlNP, inAlNAs, inAlNSb, inAlPAs and InAlPSb;
the IV-VI compound is at least one selected from SnS, snSe, snTe, pbS, pbSe, pbTe, snSeS, snSeTe, snSTe, pbSeS, pbSeTe, pbSTe, snPbS, snPbSe, snPbTe, snPbSSe, snPbSeTe and SnPbSTe;
the I-III-VI compound is selected from CuInS 2 、CuInSe 2 And AgInS 2 At least one of them.
Further, the first ligand is selected from at least one of an amine ligand having an aryl group and a carbon number of not less than 8, an amine ligand having a heteroaryl group and a carbon number of not less than 8, a carboxylic acid ligand having an aryl group and a carbon number of not less than 8, a carboxylic acid ligand having a heteroaryl group and a carbon number of not less than 8, a thiol ligand having an aryl group and a carbon number of not less than 8, and a thiol ligand having a heteroaryl group and a carbon number of not less than 8.
Further, the first ligand is selected from at least one of 3-phenyl-2-propen-1-amine, 2-phenethyl mercaptan, and 3-phenylpropionic acid.
Further, the second ligand is selected from at least one of amine ligands having a carbon chain length of not less than 8 and not containing an aryl group, amine ligands having a carbon chain length of not less than 8 and not containing a heteroaryl group, carboxylic acid ligands having a carbon chain length of not less than 8 and not containing an aryl group, carboxylic acid ligands having a carbon chain length of not less than 8 and not containing a heteroaryl group, thiol ligands having a carbon chain length of not less than 8 and not containing a heteroaryl group, phosphoric acid ligands having a carbon chain length of not less than 8 and not containing an aryl group, and phosphoric acid ligands having a carbon chain length of not less than 8 and not containing a heteroaryl group.
Further, the second ligand is selected from at least one of oleylamine, octadecene, tri-n-octylphosphine oxide, and octadecylamine.
Further, the first ligand is 3-phenyl-2-propen-1-amine and the second ligand is oleic acid;
alternatively, the first ligand is 3-phenylpropionic acid and the second ligand is octadecene;
alternatively, the first ligand is 2-phenethyl mercaptan and the second ligand is tri-n-octylphosphine oxide.
Further, the light emitting layer includes:
a first light emitting layer disposed between the anode and the cathode; and
a second light-emitting layer disposed between the first light-emitting layer and the cathode;
the material of the first light-emitting layer is a first quantum dot, and the material of the second light-emitting layer is a second quantum dot.
Further, the ratio of the thickness of the second light emitting layer to the thickness of the first light emitting layer is 1: (0.8-1).
Further, the carrier mobility of the first light-emitting layer is 4.6+ -0.55 cm 2 The carrier mobility of the second light-emitting layer is 0.15+ -0.27 cm 2 /V·s。
Further, the light emitting device further includes:
a hole transport layer disposed between the anode and the first light emitting layer, wherein the hole transport layer is made of a material selected from poly (9, 9-dioctylfluorene-CO-N- (4-butylphenyl) diphenylamine), 3-hexyl-substituted polythiophene, poly (9-vinylcarbazole), poly [ bis (4-phenyl) (4-butylphenyl) amine ]Poly (N, N '-bis (4-butylphenyl) -N, N' -diphenyl-1, 4-phenylenediamine-CO-9, 9-dioctylfluorene), 4',4 "-tris (carbazol-9-yl) triphenylamine, 4' -bis (9-carbazol) biphenyl, N '-diphenyl-N, N' -bis (3-methylphenyl) -1,1 '-biphenyl-4, 4' -diamine, N '-diphenyl-N, N' - (1-naphthyl) -1,1 '-biphenyl-4, 4' -diamine, niO, WO 3 、MoO 3 And at least one of CuO; and/or
An electron transport layer arranged between the cathode and the second luminescent layer, wherein the electron transport layer comprises a nano metal oxide selected from ZnO and TiO 2 、SnO 2 、Ta 2 O 3 、ZrO 2 At least one of TiLiO, znGaO, znAlO, znMgO, znSnO, znLiO, inSnO and AlZnO.
In a second aspect, the present application provides a method for manufacturing a light emitting device, including the steps of:
providing a bottom electrode, and preparing and forming a light-emitting layer on one side of the bottom electrode; and
preparing a top electrode on one side of the light-emitting layer far away from the bottom electrode;
wherein one of the bottom electrode and the top electrode is an anode, and the other is a cathode; the light-emitting layer comprises first quantum dots and second quantum dots, wherein the surfaces of the first quantum dots are provided with first ligands, the surfaces of the second quantum dots are provided with second ligands, the first ligands contain aryl or heteroaryl groups, the second ligands do not contain aryl or heteroaryl groups, the light-emitting layer is provided with the cathode facing the anode, the content of the first quantum dots is gradually increased, and the content of the second quantum dots is gradually reduced.
Further, the preparation method comprises the following steps:
providing a bottom electrode serving as an anode, and preparing and forming a first light-emitting layer on one side of the anode;
preparing and forming a second light-emitting layer on one side of the first light-emitting layer far away from the anode;
preparing a top electrode serving as a cathode on one side of the second light-emitting layer away from the first light-emitting layer;
or,
providing a bottom electrode serving as a cathode, and preparing and forming a second light-emitting layer on one side of the cathode;
preparing and forming a first light-emitting layer on one side of the second light-emitting layer far away from the cathode;
preparing a top electrode serving as an anode on one side of the first light-emitting layer away from the second light-emitting layer;
the material of the first light-emitting layer is a first quantum dot, and the material of the second light-emitting layer is a second quantum dot.
Further, after the step of forming a first light emitting layer on one side of the anode, and before the step of forming a second light emitting layer on one side of the first light emitting layer away from the anode, the method further comprises the steps of: applying a passivation material on a side of the first light emitting layer away from the anode, and performing heat treatment;
Alternatively, after the step of forming the second light emitting layer on the side of the cathode and before the step of forming the first light emitting layer on the side of the second light emitting layer away from the cathode, the method further comprises the steps of: applying a passivation material on a side of the second light emitting layer away from the cathode, and performing heat treatment;
wherein the passivation material is selected from at least one of N, N-dimethylformamide, 1, 7-diaminoheptane and diphenyl [4- (triphenylsilyl) phenyl ] phosphine oxide.
In a third aspect, the present application provides a display apparatus comprising a light emitting device as described in any one of the first aspects or comprising a light emitting device manufactured by the manufacturing method described above.
The application provides a light emitting device, a preparation method of the light emitting device and a display device, and the preparation method has the following technical effects:
the light-emitting device comprises an anode, a cathode and a light-emitting layer, wherein the anode and the cathode are oppositely arranged, the light-emitting layer is arranged between the anode and the cathode, the carrier mobility in the light-emitting layer is gradually increased along the direction of the cathode towards the anode, so that the carrier mobility of the light-emitting layer close to one side of the anode is higher than that of the light-emitting layer close to one side of the cathode, the electron injection is reduced, the hole injection is improved, the electron-hole transmission balance of the light-emitting device is promoted, the recombination efficiency of electrons and holes in the light-emitting layer is improved, and the light-emitting efficiency and the service life of the light-emitting device are further improved.
The preparation method of the light-emitting device has the advantages of being simple in operation and suitable for industrial production.
The light-emitting device is applied to the display device, and is beneficial to improving the display effect and prolonging the service life of the display device.
Drawings
Technical solutions and other advantageous effects of the present application will be made apparent from the following detailed description of specific embodiments of the present application with reference to the accompanying drawings.
Fig. 1 is a schematic structural view of a first light emitting device provided in an embodiment of the present application.
Fig. 2 is a schematic structural view of a second light emitting device provided in an embodiment of the present application.
Fig. 3 is a schematic structural view of a third light emitting device provided in an embodiment of the present application.
Fig. 4 is a schematic structural view of a fourth light emitting device provided in an embodiment of the present application.
Fig. 5 is a schematic structural view of a fifth light emitting device provided in an embodiment of the present application.
Fig. 6 is an external quantum efficiency-current density characteristic diagram of the light emitting devices of examples 1 to 7 and comparative examples in experimental examples of the present application.
Reference numerals illustrate:
1: a light emitting device; 11: an anode; 12: a cathode; 13-1: a first light emitting layer; 13-2: a second light emitting layer; 14: a passivation layer; 15: a hole transport layer; 16: an electron transport layer; 17: and a hole injection layer.
Detailed Description
The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. It will be apparent that the described embodiments are only some, but not all, of the embodiments of the present application. All other embodiments, which can be made by those skilled in the art based on the embodiments herein without making any inventive effort, are intended to be within the scope of the present application.
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. In addition, any methods and materials similar or equivalent to those described herein can be used in the present invention. The preferred methods and materials described herein are illustrative only and should not be construed as limiting the scope of the present application.
The following description of the embodiments is not intended to limit the preferred embodiments. In addition, in the description of the present application, the term "comprising" means "including but not limited to". Various embodiments of the present application may exist in a range of forms; it should be understood that the description in a range format is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of the invention; it is therefore to be understood that the range description has specifically disclosed all possible sub-ranges and individual values within that range. For example, it should be considered that a description of a range from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the ranges, such as 1, 2, 3, 4, 5, and 6, wherever applicable. In addition, whenever a numerical range is referred to herein, it is meant to include any reference number (fractional or integer) within the indicated range.
The embodiment of the application provides a light emitting device, as shown in fig. 1, the light emitting device 1 includes an anode 11, a cathode 12 and a light emitting layer 13, wherein the anode 11 and the cathode 12 are oppositely disposed, the light emitting layer 13 is disposed between the anode 11 and the cathode 12, the material of the light emitting layer 13 includes a first quantum dot and a second quantum dot, the surface of the first quantum dot has a first ligand, the surface of the second quantum dot has a second ligand, the first ligand contains aryl or heteroaryl, the second ligand does not contain aryl or heteroaryl, the content of the first quantum dot gradually increases and the content of the second quantum dot gradually decreases along the direction of the cathode 12 towards the anode 11 in the light emitting layer 13.
As used herein, "gradually increasing" and "gradually decreasing" should be understood in a broad sense, that is, the content of the first quantum dot or the content of the second quantum dot may gradually increase or decrease stepwise in the light emitting layer 13 in the direction of the cathode 12 toward the anode 11, or may gradually increase or decrease continuously, and it is only required to satisfy the condition that the content of the first quantum dot on the side close to the anode 11 is greater than the content of the first quantum dot on the side close to the cathode 12, and the content of the second quantum dot on the side close to the anode 11 is smaller than the content of the second quantum dot on the side close to the cathode 12, and since the conductivity of the first ligand is stronger than the conductivity of the second ligand in the direction of the cathode 12 toward the anode 11 in the light emitting layer 13, the carrier mobility of the light emitting layer 13 is gradually increased in the direction of the cathode 12 toward the anode 11, so that the carrier mobility of the light emitting layer 13 on the side close to the anode 11 is higher than the carrier mobility of the light emitting layer 13 on the side close to the cathode 12, thereby achieving the purpose of reducing electron injection and improving the electron-hole transport balance of the light emitting device 1.
In the present embodiment, the materials of the anode 11 and the cathode 12 may be materials common in the art, for example: the materials of the anode 11 and the cathode 12 are independently selected from one or more of metal, carbon material and metal oxide, and the metal is selected from Al, ag, cu, mo, AAt least one of u, ba, ca and Mg; the carbon material is at least one selected from graphite, carbon nano tube, graphene and carbon fiber; the metal oxide may be a doped or undoped metal oxide selected from at least one of ITO, FTO, ATO, AZO, GZO, IZO, MZO and AMO. The anode 11 or cathode 12 may also be independently selected from a composite electrode of doped or undoped transparent metal oxide sandwiching a metal, including but not limited to AZO/Ag/AZO, AZO/Al/AZO, ITO/Ag/ITO, ITO/Al/ITO, znO/Ag/ZnO, znO/Al/ZnO, tiO 2 /Ag/TiO 2 、TiO 2 /Al/TiO 2 、ZnS/Ag/ZnS、ZnS/Al/ZnS、TiO 2 /Ag/TiO 2 TiO 2 /Al/TiO 2 At least one of them. In some embodiments of the present application, the anode 11 has a thickness of 40nm to 160nm and the cathode 12 has a thickness of 20nm to 120nm.
In some embodiments of the present application, the first quantum dot and the second quantum dot are the same, which is favorable for controlling the difference between the first quantum dot and the second quantum dot, and the peak position difference and the peak width difference between the first quantum dot and the second quantum dot should be controlled within a range not higher than 0.5% respectively, so as to ensure that the light emitting peak position and the peak width index of the light emitting device are qualified.
In some embodiments of the present application, the first quantum dot and the second quantum dot are selected from at least one of group II-VI compound, group III-V compound, group IV-VI compound, and group I-III-VI compound, wherein the group II-VI compound is selected from at least one of CdS, cdSe, cdTe, znS, znSe, znTe, znO, hgS, hgSe, hgTe, cdSeS, cdSeTe, cdSTe, znSeS, znSeTe, znSTe, hgSeS, hgSeTe, hgSTe, cdZnS, cdZnSe, cdZnTe, cdHgS, cdHgSe, cdHgTe, hgZnS, hgZnSe, hgZnTe, cdZnSeS, cdZnSeTe, cdZnSTe, cdHgSeS, cdHgSeTe, cdHgSTe, hgZnSeS, hgZnSeTe and HgZnSTe, and the group III-V compound is selected from GaN, gaP, gaAs, gaSb, alN, alP, alAs, alSb, inN, inP, inAs, inSb, gaNP, gaNAs, gaNSb, gaPAs, gaPSb, alNP, alNAs, alNSb, alPAs, alPSb, inNP, inNAs, inNSb, inPAs, inPSb, gaAlNP, gaAlNAs, gaAlNSb, gaAlPAs, gaAlPSb, gaInNP, gaInNAs, gaInNSb, gaInPAs,GaInPSb, inAlNP, inAlNAs, inAlNSb, inAlPAs and InAlPSb, and IV-VI compound is selected from SnS, snSe, snTe, pbS, pbSe, pbTe, snSeS, snSeTe, snSTe, pbSeS, pbSeTe, pbSTe, snPbS, snPbSe, snPbTe, snPbSSe, snPbSeTe and SnPbSTe, and I-III-VI compound is selected from CuInS 2 、CuInSe 2 And AgInS 2 At least one of them. The first quantum dot and the second quantum dot are at least one of red quantum dot, green quantum dot, and blue quantum dot, independently of each other. Further, the first quantum dot and the second quantum dot are blue quantum dots independently of each other. Therefore, the problem of unbalance of electron-hole transmission is avoided, and the performance of the display device formed by the blue quantum dots is improved.
In some embodiments of the present application, the first ligand is selected from at least one of an amine ligand comprising an aryl group and having no less than 8 carbon atoms, an amine ligand comprising a heteroaryl group and having no less than 8 carbon atoms, a carboxylic acid ligand comprising an aryl group and having no less than 8 carbon atoms, a carboxylic acid ligand comprising a heteroaryl group and having no less than 8 carbon atoms, a thiol ligand comprising an aryl group and having no less than 8 carbon atoms, and a thiol ligand comprising a heteroaryl group and having no less than 8 carbon atoms.
As used herein, "aryl" refers to an aromatic carbocyclic group, an aryl group may have a single ring or multiple condensed rings, for example an aryl group having 6 to 20 carbon atoms, another example an aryl group having 6 to 14 carbon atoms, and another example an aryl group having 6 to 10 carbon atoms. In some embodiments of the present application, the aryl group may be unsubstituted. In other embodiments of the present application, the hydrogen atom or atoms on the aryl group are optionally substituted with other groups, such as alkyl, halogen, etc., allowing multiple degrees of substitution to occur. The aryl group may be, for example, phenyl, naphthyl, or the like.
As used herein, "heteroaryl" refers to an aromatic carbocyclyl in which one or more carbon atoms are independently replaced by one or more heteroatoms (e.g., N, O, P and/or S). For example, heteroaryl groups have 3 to 20 carbon atoms, and for example, heteroaryl groups have 5 to 15 carbon atoms, and for example, heteroaryl groups have 5 to 9 carbon atoms. In some embodiments of the present application, heteroaryl groups may be unsubstituted. In other embodiments of the present application, the hydrogen atom or atoms on the heteroaryl group are optionally substituted with other groups, which may be, for example, alkyl, halogen, etc., allowing multiple degrees of substitution to occur. Heteroaryl groups may be, for example, pyrrolyl, pyridyl, and the like.
It can be understood that the first ligand can form a planar conjugated structure by itself, and can also form a planar conjugated structure with benzene rings carried in the material of the hole transport layer, so as to effectively improve carrier mobility of the first light emitting layer, and further enhance hole injection level of the light emitting device.
In some embodiments of the present application, the first ligand is selected from at least one of 3-phenyl-2-propen-1-amine, 2-phenethylmercaptan (CAS number 4410-99-5), and 3-phenylpropionic acid (CAS number 501-52-0), wherein the structural formula of the 3-phenyl-2-propen-1-amine is shown in formula (I) below:
In some embodiments of the present application, the second ligand is selected from at least one of an amine ligand having a carbon chain length of no less than 8 and containing no aryl groups, an amine ligand having a carbon chain length of no less than 8 and containing no heteroaryl groups, a carboxylic acid ligand having a carbon chain length of no less than 8 and containing no heteroaryl groups, a thiol ligand having a carbon chain length of no less than 8 and containing no aryl groups, a thiol ligand having a carbon chain length of no less than 8 and containing no heteroaryl groups, a phosphoric acid ligand having a carbon chain length of no less than 8 and containing no aryl groups, and a phosphoric acid ligand having a carbon chain length of no less than 8 and containing no heteroaryl groups.
In some embodiments of the present application, the second ligand is selected from at least one of oleylamine, octadecene, tri-n-octylphosphinate, and octadecylamine.
In one example of the present application, the first ligand is 3-phenyl-2-propen-1-amine and the second ligand is oleic acid.
In another example of the present application, the first ligand is 3-phenylpropionic acid and the second ligand is octadecene.
In another example of the present application, the first ligand is 2-phenethyl mercaptan and the second ligand is tri-n-octylphosphine oxide.
In some embodiments of the present application, as shown in fig. 2, the light emitting device 1 includes an anode 11, a cathode 12, a first light emitting layer 13-1, and a second light emitting layer 13-2, the anode 11 being disposed opposite the cathode 12; the first light emitting layer 13-1 is disposed between the anode 11 and the cathode 12, and the second light emitting layer 13-2 is disposed between the first light emitting layer 13-1 and the cathode 12; the material of the first light emitting layer 13-1 is a first quantum dot, and the material of the second light emitting layer 13-2 is a second quantum dot.
In the embodiment of the present application, the carrier mobility of the first light emitting layer 13-1 is higher than the carrier mobility of the second light emitting layer 13-2, and the difference between the carrier mobilities of the first light emitting layer 13-1 and the second light emitting layer 13-2 is used to balance the electron injection and the hole injection of the light emitting device 1, so as to improve the problem of unbalance of electron-hole transport, that is, the carrier mobility of the first light emitting layer 13-1 near the anode 11 is higher, so that holes are easier to inject into the first light emitting layer 13-1, and the carrier mobility of the second light emitting layer 13-2 near the cathode 12 is lower, thereby effectively reducing the electron injection into the second light emitting layer 13-2.
In some embodiments of the present application, the thickness of the first light emitting layer 13-1: the thickness of the second light-emitting layer 13-2 is (0.8 to 1): 1. the effect of promoting the electron-hole transport balance is not obvious when the thickness of the first light emitting layer 13-1 is too thick or too thin, and if the thickness of the first light emitting layer 13-1 is too thick, a phenomenon that hole injection is stronger than electron injection may occur; if the thickness of the second light emitting layer 13-2 is too small, the degree of promotion of electron injection is limited. The total thickness of the first light emitting layer 13-1 and the second light emitting layer 13-2 may be, for example, 20nm to 40nm.
The light-emitting layer may have a structure with two or more layers, and the specific number of layers is not particularly limited, and the light-emitting layer may be provided with a condition that the content of the first quantum dot gradually increases and the content of the second quantum dot gradually decreases along the direction of the cathode toward the anode, where the "gradually increasing" or "gradually decreasing" may be a stepwise gradually increasing or gradually decreasing, or may be a continuous gradually increasing or gradually decreasing.
In some embodiments of the present application, the light emitting device further includes a hole transport layer disposed between the anode and the first light emitting layer, the hole transport layer having a material selected from the group consisting of poly (9, 9-dioctylfluorene-CO-N- (4-butylphenyl) diphenylamine) (abbreviated as TFB, CAS No. 220797-16-0), 3-hexyl-substituted polythiophene (CAS No. 104934-50-1), poly (9-vinylcarbazole) (abbreviated as PVK, CAS No. 25067-59-8), poly [ bis (4-phenyl) (4-butylphenyl) amine](abbreviated as Poly-TPD, CAS number 472960-35-3), poly (N, N '-bis (4-butylphenyl) -N, N' -diphenyl-1, 4-phenylenediamine-CO-9, 9-dioctylfluorene) (abbreviated as PFB, CAS number 223569-28-6), 4 '-tris (carbazol-9-yl) triphenylamine (abbreviated as TCTA, CAS number 139092-78-7), 4' -bis (9-carbazol) biphenyl (abbreviated as CBP, CAS number 58328-31-7), N '-diphenyl-N, at least one of N' -bis (3-methylphenyl) -1,1 '-biphenyl-4, 4' -diamine (abbreviated as TPD, CAS No. 65181-78-4) and N, N '-diphenyl-N, N' - (1-naphthyl) -1,1 '-biphenyl-4, 4' -diamine (abbreviated as NPB, CAS No. 123847-85-8), and the material of the hole transporting layer may be selected from inorganic materials having hole transporting ability, including but not limited to NiO, WO 3 、MoO 3 And at least one of CuO. The light-emitting device further comprises an electron transport layer arranged between the cathode and the second light-emitting layer, wherein the electron transport layer comprises a nano metal oxide, which can be undoped nano metal oxide or doped nano metal oxide, and the nano metal oxide is selected from ZnO and TiO 2 、SnO 2 、Ta 2 O 3 、ZrO 2 At least one of TiLiO, znGaO, znAlO, znMgO, znSnO, znLiO, inSnO and AlZnO.
In an example of the present application, as shown in fig. 3, the light emitting device 1 further includes a hole transport layer 15 on the basis of the light emitting device 1 shown in fig. 2, the hole transport layer 15 being disposed between the anode 11 and the first light emitting layer 13-1. The thickness of the hole transport layer 15 may be, for example, 10nm to 50nm.
In another example of the present application, as shown in fig. 4, the light emitting device 1 further includes an electron transport layer 16 on the basis of the light emitting device 1 shown in fig. 3, the electron transport layer 16 being disposed between the cathode 12 and the second light emitting layer 13-2. The thickness of the electron transport layer 16 may be, for example, 10nm to 60nm.
In some embodiments of the present application, the carrier mobility of the first light emitting layer 13-1 is at least 20 times that of the second light emitting layer 13-2 to further reduce the difference between electron injection and hole injection in the light emitting device 1, thereby further promoting electron-hole transport balance.
In some embodiments of the present application, the carrier mobility of the first light emitting layer is 4.6.+ -. 0.55cm 2 The carrier mobility of the second light-emitting layer is 0.15+ -0.27 cm 2 /V·s。
It should be noted that, the light emitting device according to the embodiments of the present application may further include other layer structures, for example, the light emitting device may further include an electron injection layer disposed between the electron transport layer and the cathode, and the material of the electron injection layer includes, but is not limited to, at least one of an alkali metal halide including, but not limited to, liF, an alkali metal organic complex including, but not limited to, lithium 8-hydroxyquinoline, and an organic phosphine compound including, but not limited to, one or more of an organic phosphorus oxide, an organic thiophosphine compound, and an organic selenophosphine compound.
It is understood that the light emitting device according to the embodiments of the present application may further include other layer structures, for example, the light emitting device may further include a hole injection layer, where the hole injection layer is disposed between the hole transport layer and the anode, and the material of the hole injection layer includes, but is not limited to, poly (3, 4-ethylenedioxythiophene): one or more of poly (styrenesulfonic acid) (CAS No. 155090-83-8), copper phthalocyanine (abbreviated as CuPc, CAS No. 147-14-8), 2,3,5, 6-tetrafluoro-7, 7', 8' -tetracyanodimethyl-p-benzoquinone (abbreviated as F4-TCNQ, CAS No. 29261-33-4), 2,3,6,7,10, 11-hexacyano-1, 4,5,8,9, 12-hexaazabenzophenanthrene (abbreviated as HATCN, CAS No. 105598-27-4), transition metal oxide, and transition metal chalcogenide, wherein the transition metal oxide may be Is NiO x 、MoO x 、WO x 、CrO x And one or more of CuO, the metal chalcogenide may be MoS x 、MoSe x 、WS x 、WSe x And one or more of CuS, the hole injection layer may have a thickness of, for example, 10nm to 120nm.
The embodiment of the application also provides a preparation method of the light-emitting device, which comprises the following steps:
b1, providing a bottom electrode, and preparing and forming a light-emitting layer on one side of the bottom electrode;
b2, preparing and forming a top electrode on one side of the light-emitting layer far away from the bottom electrode;
in the above preparation method, one of the bottom electrode and the top electrode is an anode, and the other is a cathode; the light-emitting layer comprises first quantum dots and second quantum dots, wherein the surfaces of the first quantum dots are provided with first ligands, the surfaces of the second quantum dots are provided with second ligands, the first ligands contain aryl or heteroaryl groups, the second ligands do not contain aryl or heteroaryl groups, the content of the first quantum dots is gradually increased along the direction of a cathode towards an anode in the light-emitting layer, and the content of the second quantum dots is gradually reduced.
In some embodiments of the present application, the method of preparation comprises the steps of:
s1, providing a bottom electrode serving as an anode, and preparing and forming a first light-emitting layer on one side of the anode;
s2, preparing and forming a second light-emitting layer on one side of the first light-emitting layer far away from the anode;
And S3, preparing and forming a top electrode serving as a cathode on one side of the second light-emitting layer away from the first light-emitting layer.
Or alternatively
S1', providing a bottom electrode serving as a cathode, and preparing and forming a second light-emitting layer on one side of the cathode;
s2', preparing and forming a first light-emitting layer on one side of the second light-emitting layer far away from the cathode;
and S3', preparing and forming a top electrode serving as an anode on one side of the first light-emitting layer away from the second light-emitting layer.
The material of the first light-emitting layer is a first quantum dot, and the material of the second light-emitting layer is a second quantum dot.
It should be noted that, in the above preparation method, steps S1 to S3 are mainly applicable to preparing a light emitting device having a front structure, and steps S1 'to S3' are mainly applicable to preparing a light emitting device having an inverted structure. The preparation methods of the anode, the first light-emitting layer, the second light-emitting layer and the cathode include, but are not limited to, a solution method and a deposition method, wherein the solution method comprises, but is not limited to, spin coating, ink-jet printing, knife coating, dip-coating, dipping, spraying, roll coating or casting; the deposition method includes a chemical method including, but not limited to, a chemical vapor deposition method, a continuous ion layer adsorption and reaction method, an anodic oxidation method, an electrolytic deposition method, or a coprecipitation method, and a physical method including, but not limited to, a thermal evaporation plating method, an electron beam evaporation plating method, a magnetron sputtering method, a multi-arc ion plating method, a physical vapor deposition method, an atomic layer deposition method, or a pulsed laser deposition method. In addition, a drying process is added after the wet film is prepared by the solution method, and the drying process comprises all operations capable of enabling the wet film to obtain higher energy and be converted into a dry film, and the drying process comprises, but is not limited to, heat treatment, standing, natural drying and the like, wherein the heat treatment can be constant-temperature heat treatment or non-constant-temperature heat treatment (for example, the temperature is changed in a gradient manner). It is understood that the method of manufacturing a light emitting device further comprises the step of manufacturing other film layers, such as a hole functional layer between the first light emitting layer and the anode and/or an electron functional layer between the second light emitting layer and the cathode, the hole functional layer comprising a hole transporting layer and/or a hole injecting layer, the electron functional layer comprising an electron transporting layer and/or an electron injecting layer.
In some embodiments of the present application, between step S1 and step S2, further steps are included: applying a passivation material on one side of the first light-emitting layer away from the anode, and performing heat treatment; alternatively, the steps between step S1 'and step S2' are further included: applying a passivation material on one side of the second light-emitting layer away from the cathode, and performing heat treatment; wherein the passivation material is selected from at least one of N, N-dimethylformamide, 1, 7-diaminoheptane and diphenyl [4- (triphenylsilyl) phenyl ] phosphine oxide. The "passivation material application" includes, but is not limited to, a solution method including, but not limited to, spin coating, ink jet printing, knife coating, dip-coating, dipping, spray coating, roll coating, or casting, wherein the passivation material is applied over the entire surface to passivate the interface defects between the first light emitting layer and the second light emitting layer, so that the interface defects between the first light emitting layer and the second light emitting layer are reduced, thereby improving the probability of radiative recombination of electrons and holes. In some embodiments of the present application, the temperature of the heat treatment is less than the boiling point of the passivation material, so that most of the passivation material volatilizes, and a small amount of non-volatilized passivation material forms a flowing liquid passivation layer, for example, the thickness may be 0.1nm to 0.5nm, and the liquid passivation layer may be completely volatilized in the subsequent functional film preparation process, so that even if the liquid passivation layer is not volatilized subsequently, the residual amount is very small, and the property of the subsequent functional film is not negatively affected.
In one example of the present application, the passivation material is N, N-dimethylformamide, and N, N-dimethylformamide is spin-coated on a side of the first light emitting layer away from the anode or a side of the second light emitting layer away from the cathode, and is subjected to constant temperature heat treatment at 70 ℃ for 10min.
The embodiment of the application also provides a display device, which comprises the light-emitting device or the light-emitting device manufactured by the manufacturing method. The display device may be any electronic product with a display function, including but not limited to a smart phone, a tablet computer, a notebook computer, a digital camera, a digital video camera, a smart wearable device, a smart weighing electronic scale, a vehicle-mounted display, a television set or an electronic book reader, wherein the smart wearable device may be, for example, a smart bracelet, a smart watch, a Virtual Reality (VR) helmet, etc.
The technical solutions and technical effects of the present application are described in detail below by means of specific examples, comparative examples and experimental examples, and the following examples are only some examples of the present application and are not intended to limit the present application in any way.
Example 1
The embodiment provides a light emitting device and a manufacturing method thereof, wherein the light emitting device is a quantum dot light emitting diode with a front-mounted structure, and as shown in fig. 5, in a bottom-up direction, the light emitting device 1 includes a substrate 10, an anode 11, a hole injection layer 17, a hole transport layer 15, a first light emitting layer 13-1, a second light emitting layer 13-2, an electron transport layer 16, and a cathode 12, which are sequentially arranged.
The materials and thicknesses of the layers in the light emitting device 1 are respectively:
the material of the substrate 10 is glass with the thickness of 1mm;
the anode 11 is made of ITO and has a thickness of 80nm;
the cathode 12 is made of Ag and has a thickness of 100nm;
the material of the hole injection layer 17 is PEDOT: PSS, wherein the molar ratio of PEDOT to PSS is 1:1, the thickness of the hole injection layer 17 is 20nm;
the hole transport layer 15 is made of TFB and has a thickness of 25nm;
the material of the first light-emitting layer 13-1 is ZnCdSe quantum dot with 3-phenyl-2-propen-1-amine ligand connected on the surface, the light-emitting wavelength is 470nm, the peak width is 20nm, and the thickness is 12nm;
the material of the second luminescent layer 13-2 is ZnCdSe quantum dot with oleic acid ligand connected on the surface, the luminescent wavelength is 470nm, the peak width is 20nm, and the thickness is 13nm;
the material of the electron transport layer 16 was nano ZnO with a particle size of 5nm and a thickness of 30nm.
The preparation method of the light-emitting device in the embodiment comprises the following steps:
s1.1, providing a substrate, evaporating ITO on one side of the substrate to obtain an ITO layer, then sequentially ultrasonically cleaning the substrate containing the ITO by using acetone for 15min, a cleaning agent for 15min, deionized water for 15min and isopropanol for 15min, and performing surface treatment by using ultraviolet-ozone for 5min after drying to obtain the substrate containing an anode;
S1.2, spin coating PEDOT on one side of the anode far away from the substrate in an air environment at normal temperature and normal pressure: PSS aqueous solution (CAS number 155090-83-8), then heat-treating at 150deg.C for 30min to obtain hole injection layer;
s1.3, spin-coating TFB (CAS number 223569-31-1) -chlorobenzene solution on one side of the hole injection layer far away from the anode in the step S1.2 under the nitrogen environment of normal temperature and normal pressure, and then performing constant temperature heat treatment for 30min at 150 ℃ to obtain a hole transport layer;
s1.4, spin-coating a ZnCdSe quantum dot (with a 3-phenyl-2-propylene-1-amine ligand connected to the surface) solution on one side of the hole transport layer far away from the hole injection layer in the step S1.3 in a nitrogen environment at normal temperature and normal pressure, and then placing the solution at 100 ℃ for heat treatment for 10min to obtain a first luminescent layer, wherein the preparation method of the ZnCdSe quantum dot (with the 3-phenyl-2-propylene-1-amine ligand connected to the surface) solution comprises the following steps: 1mmol of cadmium oxide (CdO) and 9mmol of zinc acetate (Zn (Ac) 2 ) Mixing, then adding 15mL of Octadecene (ODE) and 9mL of 3-phenyl-2-propen-1-amine to obtain a mixture, quickly injecting 2mL of Se-ODE and 2mL of S-ODE into the mixture at 300 ℃, reacting for 10min, then dropwise adding 10mL of S-ODE into the mixture, continuing to react for 30min, cooling to room temperature, adding chloroform and excessive acetone into a reaction product to purify the quantum dots, dispersing the purified quantum dots into n-octane to obtain ZnCdSe quantum dots (the surface of which is connected with 3-phenyl-2-propen-1-amine ligand) -n-octane solution;
S1.5, spin-coating a ZnCdSe quantum dot (the surface of which is connected with an oleic acid ligand) -n-octane solution on one side of the first luminescent layer far away from the hole transport layer in the step S1.4 under a nitrogen environment at normal temperature and normal pressure, and then placing the solution in a 100 ℃ heat treatment for 10min to obtain a second luminescent layer, wherein the preparation method of the ZnCdSe quantum dot (the surface of which is connected with the oleic acid ligand) -n-octane solution comprises the following steps: 1mmol of cadmium oxide (CdO) and 9mmol of zinc acetate (Zn (Ac) 2 ) Mixing, adding 15mL of Octadecene (ODE) and 7mL of oleic acid to obtain a mixture, rapidly injecting 2mL of Se-ODE and 2mL of S-ODE into the mixture at 300 ℃, reacting for 10min, then dropwise adding 10mL of S-ODE into the mixture, continuing reacting for 30min, cooling to room temperature, adding chloroform and excessive acetone into a reaction product to purify quantum dots, dispersing the purified quantum dots in n-octane to obtain ZnCdSe quantum dots (with oleic acid ligand connected to the surface) -n-octane solution;
s1.6, spin-coating a nano ZnO-ethanol solution on one side of the second luminescent layer far away from the first luminescent layer in the step S1.5, and then placing the nano ZnO-ethanol solution at 80 ℃ for heat treatment for 30min to obtain an electron transport layer;
s1.7, evaporating Ag on one side of the electron transport layer far away from the light-emitting layer in the step S1.6 to obtain a cathode, and packaging to obtain the light-emitting device.
Example 2
The present embodiment provides a light emitting device and a method of manufacturing the same, and the structural composition of the light emitting device of the present embodiment is the same as that of embodiment 1.
The preparation method of this example differs from that of example 1 only in that: and adding a step 'in a nitrogen environment at normal temperature and normal pressure' between the step S1.4 and the step S1.5, spin-coating N, N-dimethylformamide on one side of the first luminescent layer far away from the hole transport layer in the step S1.4, and then placing the substrate at 70 ℃ for heat treatment for 10 min.
Example 3
The present embodiment provides a light emitting device and a method for manufacturing the same, which differ from the light emitting device of embodiment 1 only in that: the material of the first luminescent layer is replaced by ' ZnCdSe quantum dot with 3-phenylpropionic acid ligand connected to the surface ', the luminescent wavelength is 470nm, the peak width is 20nm ', and the material of the second luminescent layer is replaced by ' ZnCdSe quantum dot with octadecene ligand connected to the surface, the luminescent wavelength is 470nm, and the peak width is 20nm '.
The preparation method of this example differs from that of example 1 only in that: "3-phenyl-2-propen-1-amine" in step S1.4 was replaced with "3-phenylpropionic acid (CAS No. 501-52-0)", and "oleic acid" in step S1.5 was replaced with "octadecene".
Example 4
The present embodiment provides a light emitting device and a method for manufacturing the same, which differ from the light emitting device of embodiment 1 only in that: the material of the first luminescent layer is replaced by ' ZnCdSe quantum dot with 3-phenylpropionic acid ligand connected to the surface ', the luminescent wavelength is 470nm, the peak width is 20nm ', and the material of the second luminescent layer is replaced by ' ZnCdSe quantum dot with octadecene ligand connected to the surface, the luminescent wavelength is 470nm, and the peak width is 20nm '.
The preparation method of this example differs from that of example 1 only in that: the "3-phenyl-2-propen-1-amine" in step S1.4 was replaced with "3-phenylpropionic acid (CAS No. 501-52-0)", the "oleic acid" in step S1.5 was replaced with "octadecene", and the step "spin-coating N, N-dimethylformamide on the side of the first light-emitting layer of step S1.4 remote from the hole-transporting layer under nitrogen atmosphere at normal temperature and pressure" was added between step S1.4 and step S1.5, followed by heat treatment at 70℃for 10 min.
Example 5
The present embodiment provides a light emitting device and a method for manufacturing the same, which differ from the light emitting device of embodiment 1 only in that: the material of the first luminescent layer is replaced by ' ZnCdSe quantum dot with 3-phenylpropionic acid ligand connected to the surface ', the luminescent wavelength is 470nm, the peak width is 20nm ', and the material of the second luminescent layer is replaced by ' ZnCdSe quantum dot with tri-n-octylphosphinate ligand connected to the surface, the luminescent wavelength is 470nm, and the peak width is 20nm '.
The preparation method of this example differs from that of example 1 only in that: "3-phenyl-2-propen-1-amine" in step S1.4 was replaced with "2-phenethyl mercaptan (CAS No. 4410-99-5)", and "oleic acid" in step S1.5 was replaced with "tri-n-octylphosphino".
Example 6
The present embodiment provides a light emitting device and a method for manufacturing the same, which differ from the light emitting device of embodiment 1 only in that: the material of the first luminescent layer is replaced by ' ZnCdSe quantum dot with 3-phenylpropionic acid ligand connected to the surface ', the luminescent wavelength is 470nm, the peak width is 20nm ', and the material of the second luminescent layer is replaced by ' ZnCdSe quantum dot with tri-n-octylphosphinate ligand connected to the surface, the luminescent wavelength is 470nm, and the peak width is 20nm '.
The preparation method of this example differs from that of example 1 only in that: the "3-phenyl-2-propen-1-amine" in step S1.4 was replaced with "2-phenethyl mercaptan (CAS No. 4410-99-5)", the "oleic acid" in step S1.5 was replaced with "tri-N-octylphosphino", and step "spin-coating N, N-dimethylformamide on the side of the first light-emitting layer of step S1.4 remote from the hole-transporting layer under nitrogen atmosphere at normal temperature and pressure" was added between step S1.4 and step S1.5, followed by heat treatment at 70℃for 10 min.
Example 7
The present embodiment provides a light emitting device and a method for manufacturing the same, which differ from the light emitting device of embodiment 1 only in that: the light emitting device of the embodiment further includes a third light emitting layer and a fourth light emitting layer, wherein the third light emitting layer is disposed between the first light emitting layer and the second light emitting layer, and the fourth light emitting layer is disposed between the third light emitting layer and the second light emitting layer, that is, in a direction in which the anode faces the cathode, the first light emitting layer, the third light emitting layer, the fourth light emitting layer and the second light emitting layer are sequentially disposed; the material of the third luminescent layer is ZnCdSe quantum dot with 3-phenyl-2-propylene-1-amine ligand connected on the surface, the thickness of the third luminescent layer is 12nm, and the content of the 3-phenyl-2-propylene-1-amine ligand in the third luminescent layer is smaller than that of the 3-phenyl-2-propylene-1-amine ligand in the first luminescent layer; the material of the fourth luminescent layer is ZnCdSe quantum dot with oleic acid ligand connected to the surface, the thickness of the fourth luminescent layer is 13nm, and the content of oleic acid ligand in the fourth luminescent layer is smaller than that in the second luminescent layer.
The preparation method of the embodiment comprises the following steps:
s7.1, refer to S1.1;
s7.2, refer to S1.2;
S7.3, refer to S1.3;
s7.4, refer to S1.4;
s7.5, spin-coating ZnCdSe quantum dot (with 3-phenyl-2-propylene-1-amine ligand connected with the surface) on one side of the first luminescent layer far away from the hole transport layer in the step S7.3 in a nitrogen environment at normal temperature and normal pressure, and then placing the solution in a 100 ℃ for heat treatment for 10min to obtain a third luminescent layer, wherein the ZnCdSe quantum dot (with 3-phenyl-2-propylene-1-amine ligand connected with the surface) is coated with n-octaneThe preparation method of the solution comprises the following steps: 1mmol of cadmium oxide (CdO) and 9mmol of zinc acetate (Zn (Ac) 2 ) Mixing, then adding 15mL of Octadecene (ODE) and 7mL of 3-phenyl-2-propen-1-amine to obtain a mixture, quickly injecting 2mL of Se-ODE and 2mL of S-ODE into the mixture at 300 ℃, reacting for 10min, then dropwise adding 10mL of S-ODE into the mixture, continuing to react for 30min, cooling to room temperature, adding chloroform and excessive acetone into a reaction product to purify the quantum dots, dispersing the purified quantum dots into n-octane to obtain ZnCdSe quantum dots (the surface of which is connected with 3-phenyl-2-propen-1-amine ligand) -n-octane solution;
s7.6, spin-coating a ZnCdSe quantum dot (the surface of which is connected with an oleic acid ligand) -n-octane solution on one side of the third luminescent layer far away from the first luminescent layer in the step S7.5 under the nitrogen environment at normal temperature and normal pressure, and then placing the solution in a 100 ℃ heat treatment for 10min to obtain a second luminescent layer, wherein the preparation method of the ZnCdSe quantum dot (the surface of which is connected with the oleic acid ligand) -n-octane solution comprises the following steps: 1mmol of cadmium oxide (CdO) and 9mmol of zinc acetate (Zn (Ac) 2 ) Mixing, adding 15mL of Octadecene (ODE) and 5mL of oleic acid to obtain a mixture, rapidly injecting 2mL of Se-ODE and 2mL of S-ODE into the mixture at 300 ℃, reacting for 10min, then dropwise adding 10mL of S-ODE into the mixture, continuing reacting for 30min, cooling to room temperature, adding chloroform and excessive acetone into a reaction product to purify quantum dots, dispersing the purified quantum dots in n-octane to obtain ZnCdSe quantum dots (with oleic acid ligand connected to the surface) -n-octane solution;
s7.7, refer to S1.5;
s7.8, refer to S1.6;
s7.9, refer to S1.7.
Comparative example
The present comparative example provides a light emitting device and a method of manufacturing the same, which differs from the light emitting device of example 1 only in that: the first light-emitting layer is omitted, the second light-emitting layer is the light-emitting layer of the light-emitting device, and the thickness of the light-emitting layer is 25nm.
The preparation method of this comparative example differs from that of example 1 only in that: step S1.4 is omitted.
Experimental example
Performance tests were performed on the light emitting devices of examples 1 to 7 and comparative examples using a friedel-crafts FPD optical property measuring apparatus, which is an efficiency test system constructed by LabView control QE-PRO spectrometer, keithley 2400, and Keithley 6485, capable of measuring parameters such as voltage, current, luminance, light emission spectrum, etc. of the obtained light emitting devices, and obtaining key parameters such as external quantum dot efficiency, power efficiency, etc. by calculation, and testing the service lives of the above-described respective light emitting devices using a life test apparatus, the external quantum efficiency-current density characteristic curves of the respective light emitting devices being as shown in fig. 6, the maximum external quantum efficiency (EQE max Data of time required for luminance to decay from 100% to 95% (T95, h) and time required for luminance to decay from 100% to 95% at a luminance of 1000nit (T95-1 k, h) are detailed in table 1 below:
table 1 results of performance tests of light emitting devices of examples 1 to 7 and comparative examples
As can be seen from table 1 and fig. 6, the light emitting devices of examples 1 to 7 have a significantly better overall performance than the light emitting device of the comparative example, showing that configuring the light emitting layer of the light emitting device to include a first light emitting layer near the anode and a second light emitting layer near the cathode, and the carrier mobility of the first light emitting layer is higher than that of the second light emitting layer, can promote electron-hole transport balance of the light emitting device, thereby effectively improving light emitting efficiency and service life of the light emitting device. Taking example 7 as an example, the EQEmax of the light emitting device of example 7 is 1.4 times that of the light emitting device of comparative example, T95 of the light emitting device of example 7 is 1.5 times that of the light emitting device of comparative example, and T95-1K of the light emitting device of example 6 is 1.4 times that of the light emitting device of comparative example.
With continued reference to FIG. 6, when the current density is at not higher than 10mA/cm 2 Within (1) along withThe rise in current density, the external quantum efficiency of the light emitting devices of examples 1 to 7 and the comparative example increased with the rise, but the rise in external quantum efficiency of the light emitting devices of examples 1 to 7 was significantly higher than that of the light emitting device of the comparative example, wherein the rise in external quantum efficiency of the light emitting device of example 7 was the largest.
As can be seen from examples 1 and 2, examples 3 and 4, and examples 5 and 6, the passivation material is used to treat the interface of the first light emitting layer near the second light emitting layer, so that the interface defect between the first light emitting layer and the second light emitting layer can be reduced, the probability of recombination of electrons and holes due to radiation can be improved, and the light emitting efficiency and the service life of the light emitting device can be further improved.
The light emitting device, the method for manufacturing the light emitting device and the display device provided in the embodiments of the present application are described in detail above. The principles and embodiments of the present application are described herein with reference to specific examples, the description of which is only for aiding in understanding the technical solution of the present application and its core ideas; those of ordinary skill in the art will appreciate that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the scope of the corresponding technical solutions of the embodiments of the present application.
Claims (16)
1. A light emitting device, comprising:
an anode and a cathode disposed opposite each other;
A light emitting layer disposed between the anode and the cathode, the material of the light emitting layer comprising a first quantum dot having a first ligand on a surface thereof and a second quantum dot having a second ligand on a surface thereof, the first ligand containing an aryl or heteroaryl group, the second ligand not containing an aryl or heteroaryl group;
the content of the first quantum dots is gradually increased, and the content of the second quantum dots is gradually decreased along the direction of the cathode towards the anode in the light-emitting layer.
2. The light emitting device of claim 1, wherein the first quantum dot is the same as the second quantum dot.
3. The light-emitting device according to claim 1, wherein the first quantum dot and the second quantum dot are independently selected from at least one of a group II-VI compound, a group III-V compound, a group IV-VI compound, and a group I-III-VI compound;
wherein the II-VI compound is selected from at least one of CdS, cdSe, cdTe, znS, znSe, znTe, znO, hgS, hgSe, hgTe, cdSeS, cdSeTe, cdSTe, znSeS, znSeTe, znSTe, hgSeS, hgSeTe, hgSTe, cdZnS, cdZnSe, cdZnTe, cdHgS, cdHgSe, cdHgTe, hgZnS, hgZnSe, hgZnTe, cdZnSeS, cdZnSeTe, cdZnSTe, cdHgSeS, cdHgSeTe, cdHgSTe, hgZnSeS, hgZnSeTe and HgZnSte;
The III-V compound is at least one selected from GaN, gaP, gaAs, gaSb, alN, alP, alAs, alSb, inN, inP, inAs, inSb, gaNP, gaNAs, gaNSb, gaPAs, gaPSb, alNP, alNAs, alNSb, alPAs, alPSb, inNP, inNAs, inNSb, inPAs, inPSb, gaAlNP, gaAlNAs, gaAlNSb, gaAlPAs, gaAlPSb, gaInNP, gaInNAs, gaInNSb, gaInPAs, gaInPSb, inAlNP, inAlNAs, inAlNSb, inAlPAs and InAlPSb;
the IV-VI compound is at least one selected from SnS, snSe, snTe, pbS, pbSe, pbTe, snSeS, snSeTe, snSTe, pbSeS, pbSeTe, pbSTe, snPbS, snPbSe, snPbTe, snPbSSe, snPbSeTe and SnPbSTe;
the I-III-VI compound is selected from CuInS 2 、CuInSe 2 And AgInS 2 At least one of them.
4. The light-emitting device according to claim 1, wherein the first ligand is at least one selected from an amine ligand having an aryl group and a carbon number of not less than 8, an amine ligand having a heteroaryl group and a carbon number of not less than 8, a carboxylic acid ligand having an aryl group and a carbon number of not less than 8, a carboxylic acid ligand having a heteroaryl group and a carbon number of not less than 8, a thiol ligand having an aryl group and a carbon number of not less than 8, and a thiol ligand having a heteroaryl group and a carbon number of not less than 8.
5. The light-emitting device according to claim 4, wherein the first ligand is at least one selected from the group consisting of 3-phenyl-2-propen-1-amine, 2-phenethyl mercaptan, and 3-phenylpropionic acid.
6. The light-emitting device according to claim 1, wherein the second ligand is at least one selected from an amine ligand having a carbon chain length of not less than 8 and containing no aryl groups, an amine ligand having a carbon chain length of not less than 8 and containing no heteroaryl groups, a carboxylic acid ligand having a carbon chain length of not less than 8 and containing no heteroaryl groups, a thiol ligand having a carbon chain length of not less than 8 and containing no aryl groups, a thiol ligand having a carbon chain length of not less than 8 and containing no heteroaryl groups, a phosphoric acid ligand having a carbon chain length of not less than 8 and containing no aryl groups, and a phosphoric acid ligand having a carbon chain length of not less than 8 and containing no heteroaryl groups.
7. The light-emitting device according to claim 6, wherein the second ligand is at least one selected from the group consisting of oleylamine, octadecene, tri-n-octylphosphinate, and octadecylamine.
8. The light-emitting device according to claim 1, wherein the first ligand is 3-phenyl-2-propen-1-amine and the second ligand is oleic acid;
Alternatively, the first ligand is 3-phenylpropionic acid and the second ligand is octadecene;
alternatively, the first ligand is 2-phenethyl mercaptan and the second ligand is tri-n-octylphosphine oxide.
9. The light-emitting device according to any one of claims 1 to 8, wherein the light-emitting layer comprises:
a first light emitting layer disposed between the anode and the cathode; and
a second light-emitting layer disposed between the first light-emitting layer and the cathode;
the material of the first light-emitting layer is a first quantum dot, and the material of the second light-emitting layer is a second quantum dot.
10. The light-emitting device according to claim 9, wherein a ratio of a thickness of the second light-emitting layer to a thickness of the first light-emitting layer is 1: (0.8-1).
11. The light-emitting device according to claim 9, wherein carrier mobility of the first light-emitting layer is 4.6±0.55cm 2 The carrier mobility of the second light-emitting layer is 0.15+ -0.27 cm 2 /V·s。
12. A light-emitting device according to any one of claims 1 to 8, further comprising:
a hole transport layer disposed between the anode and the first light emitting layer, wherein the hole transport layer is made of a material selected from poly (9, 9-dioctylfluorene-CO-N- (4-butylphenyl) diphenylamine), 3-hexyl-substituted polythiophene, poly (9-vinylcarbazole), poly [ bis (4-phenyl) (4-butylphenyl) amine ]Poly (N, N '-bis (4-butylphenyl) -N, N' -diphenyl-1, 4-phenylenediamine-CO-9, 9-dioctylfluorene), 4',4 "-tris (carbazol-9-yl) triphenylamine, 4' -bis (9-carbazol) biphenyl, N '-diphenyl-N, N' -bis (3-methylphenyl) -1,1 '-biphenyl-4, 4' -diamine, N '-diphenyl-N, N' - (1-naphthyl) -1,1 '-biphenyl-4, 4' -diamine, niO, WO 3 、MoO 3 And at least one of CuO; and/or
An electron transport layer arranged between the cathode and the second luminescent layer, wherein the electron transport layer comprises a nano metal oxide selected from ZnO and TiO 2 、SnO 2 、Ta 2 O 3 、ZrO 2 At least one of TiLiO, znGaO, znAlO, znMgO, znSnO, znLiO, inSnO and AlZnO.
13. A method of manufacturing a light emitting device, comprising the steps of:
providing a bottom electrode, and preparing and forming a light-emitting layer on one side of the bottom electrode; and
preparing a top electrode on one side of the light-emitting layer far away from the bottom electrode;
wherein one of the bottom electrode and the top electrode is an anode, and the other is a cathode; the light-emitting layer comprises first quantum dots and second quantum dots, wherein the surfaces of the first quantum dots are provided with first ligands, the surfaces of the second quantum dots are provided with second ligands, the first ligands contain aryl or heteroaryl groups, the second ligands do not contain aryl or heteroaryl groups, the light-emitting layer is provided with the cathode facing the anode, the content of the first quantum dots is gradually increased, and the content of the second quantum dots is gradually reduced.
14. The method of manufacturing according to claim 13, comprising the steps of:
providing a bottom electrode serving as an anode, and preparing and forming a first light-emitting layer on one side of the anode;
preparing and forming a second light-emitting layer on one side of the first light-emitting layer far away from the anode;
preparing a top electrode serving as a cathode on one side of the second light-emitting layer away from the first light-emitting layer;
or,
providing a bottom electrode serving as a cathode, and preparing and forming a second light-emitting layer on one side of the cathode;
preparing and forming a first light-emitting layer on one side of the second light-emitting layer far away from the cathode;
preparing a top electrode serving as an anode on one side of the first light-emitting layer away from the second light-emitting layer;
the material of the first light-emitting layer is a first quantum dot, and the material of the second light-emitting layer is a second quantum dot.
15. The method of manufacturing according to claim 14, wherein after the step of manufacturing a first light-emitting layer on a side of the anode and before the step of manufacturing a second light-emitting layer on a side of the first light-emitting layer away from the anode, further comprising the steps of: applying a passivation material on a side of the first light emitting layer away from the anode, and performing heat treatment;
Alternatively, after the step of forming the second light emitting layer on the side of the cathode and before the step of forming the first light emitting layer on the side of the second light emitting layer away from the cathode, the method further comprises the steps of: applying a passivation material on a side of the second light emitting layer away from the cathode, and performing heat treatment;
wherein the passivation material is selected from at least one of N, N-dimethylformamide, 1, 7-diaminoheptane and diphenyl [4- (triphenylsilyl) phenyl ] phosphine oxide.
16. A display device characterized in that it comprises the light-emitting device according to any one of claims 1 to 12 or the light-emitting device produced by the production method according to any one of claims 13 to 15.
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