Light-emitting device, preparation method thereof and display device

Abstract

The invention discloses a light-emitting device and a preparation method thereof and a display device, the light-emitting device comprises an anode, a light-emitting function layer and a cathode which are stacked, the light-emitting function layer comprises N light-emitting sub-layers which are stacked, and N is an integer greater than or equal to 2; in the direction from the cathode to the anode, the absolute value of the conduction band energy level and the absolute value of the valence band energy level of the N light-emitting sub-layers are gradually increased. According to the technical scheme, the design of a plurality of light-emitting sub-layers is adopted, the light-emitting sub-layers with different conduction band energy levels and valence band energy levels are utilized to construct the energy level gradient of carrier transmission, a carrier function layer can be replaced to a certain extent, the selection difficulty of a film layer material is reduced, and the preparation cost of the device is reduced.

Description

Technical Field

[0001] The present application relates to the technical field of semiconductor devices, and particularly to a light-emitting device, a manufacturing method thereof, and a display device. Background Art

[0002] Light-emitting devices emit light by the recombination of electrons and holes, and are widely used in the technical fields such as display and lighting. Existing light-emitting devices are usually based on a "sandwich" structure, which is composed of an electrode layer, a light-emitting sub-layer, and a carrier functional layer located between the electrode layer and the light-emitting sub-layer. The carrier functional layer includes, but is not limited to, a hole injection layer, a hole transport layer, an electron injection layer, an electron transport layer, etc.

[0003] The increase of the carrier functional layer brings problems such as the difficulty in material selection, the complexity of the manufacturing process, and the high manufacturing cost, which restricts the development of light-emitting devices. Summary of the Invention

[0004] In view of this, the present application provides a light-emitting device, a manufacturing method thereof, and a display device.

[0005] The embodiments of the present application are implemented as follows:

[0006] In a first aspect, an embodiment of the present application provides a light-emitting device, which includes a stacked anode, a light-emitting functional layer, and a cathode. The light-emitting functional layer includes N stacked light-emitting sub-layers, where N is an integer greater than or equal to 2;

[0007] In the direction from the cathode to the anode, the absolute values of the conduction band energy levels and the absolute values of the valence band energy levels of the N light-emitting sub-layers gradually increase.

[0008] In a second aspect, an embodiment of the present application provides a manufacturing method of a light-emitting device, including the following steps:

[0009] Providing a first electrode;

[0010] Successively preparing a plurality of unit film layers on one side of the first electrode to obtain a light-emitting functional layer;

[0011] Preparing a second electrode on the side of the light-emitting functional layer away from the first electrode;

[0012] Wherein, the first electrode is selected from one of the anode and the cathode, the second electrode is selected from the other of the anode and the cathode, the plurality of unit film layers include N light-emitting sub-layers, and in the direction from the cathode to the anode, the absolute values of the conduction band energy levels and the absolute values of the valence band energy levels of the N light-emitting sub-layers gradually increase, where N is an integer greater than or equal to 2.

[0013] In a third aspect, the present application provides a display device, including the light-emitting device described above, or including a light-emitting device prepared by the preparation method described above.

[0014] The light-emitting device provided by the technical solution of the present application adopts a design of multiple light-emitting sub-layers, and constructs an energy level gradient for carrier transfer by using light-emitting sub-layers with different conduction band energy levels and valence band energy levels. To a certain extent, it can replace the carrier functional layer, reduce the difficulty of selecting film layer materials, and reduce the manufacturing cost of the device. Description of the Drawings

[0015] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present application. For those skilled in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0016] Figure 1 is a schematic structural diagram of an embodiment of a light-emitting device provided by the present application;

[0017] Figure 2 is a schematic structural diagram of another embodiment of a light-emitting device provided by the present application;

[0018] Figure 3 is Figure 2 a schematic diagram of the energy band gap energy levels of the light-emitting functional layer in

[0019] Reference numerals: light-emitting device 100; anode 10; cathode 20; light-emitting functional layer 30; first light-emitting sub-layer 31; second light-emitting sub-layer 32; third light-emitting sub-layer 33; first ohmic contact layer 34; second ohmic contact layer 35. Detailed Embodiments

[0020] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative efforts belong to the scope of protection of the present application. In addition, it should be understood that the specific implementation manners described herein are only used to illustrate and explain the present application, and are not used to limit the present application. In the present application, unless otherwise stated, the orientation terms such as "upper" and "lower" specifically refer to the drawing directions in the drawings. In addition, in the description of the present application, the term "comprising" means "including but not limited to". The various embodiments of the present application may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be construed as a rigid limitation on the scope of the present application; therefore, it should be considered that the description of the range has specifically disclosed all possible sub-ranges and individual values within that range. For example, it should be considered that the description of the 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., and individual numbers within that range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. In addition, whenever a numerical range is indicated herein, it means including any cited number (fraction or integer) within the indicated range.

[0021] In the present application, "and / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B may represent: A exists alone, A and B exist simultaneously, or B exists alone. Wherein A and B may be singular or plural.

[0022] In the present application, "at least one" means one or more, and "a plurality" means two or more. "At least one kind", "at least one of the following items (pieces)" or similar expressions refer to any combination of these items, including any combination of single items (pieces) or plural items (pieces). For example, "at least one of a, b, or c", or, "at least one of a, b, and c" can both represent: a, b, c, a - b (i.e., a and b), a - c, b - c, or a - b - c, where a, b, and c can be single or multiple respectively.

[0023] In a first aspect, an embodiment of the present application provides a light-emitting device 100, including but not limited to an organic light-emitting diode (OLED), a quantum dot light-emitting diode (QLED), such as Figure 1 and Figure 2As shown, the light-emitting device 100 includes a stacked anode 10, a light-emitting functional layer 30, and a cathode 20. The light-emitting functional layer 30 includes N stacked light-emitting sub-layers; in the direction from the cathode 20 to the anode 10, the absolute value of the conduction band energy level and the absolute value of the valence band energy level of the N light-emitting sub-layers gradually increase, where N is an integer greater than or equal to 2.

[0024] The light-emitting device 100 provided by the technical solution of this application adopts the design of multiple light-emitting sub-layers, and constructs an energy level gradient for carrier transfer by using light-emitting sub-layers with different conduction band energy levels and valence band energy levels. To a certain extent, it can replace the carrier functional layer, simplify the film layer types of the light-emitting device 100, and no longer require a carrier functional layer with high cost and difficult material selection, thereby effectively reducing the difficulty of selecting film layer materials and reducing the device manufacturing cost.

[0025] In the light-emitting device 100, the direction from the cathode 20 to the anode 10 is defined as the first direction. Please refer to Figure 3 , in the light-emitting functional layer 30 of the light-emitting device 100 provided by the embodiment of this application, the absolute value of the conduction band energy level of the multiple light-emitting sub-layers gradually increases in the first direction, and the absolute value of the valence band energy level of the multiple light-emitting sub-layers gradually increases in the first direction, thereby constructing a gradient energy level between the cathode 20 and the anode 10 to promote carrier transport. Specifically, in some embodiments, the light-emitting device 100 may include an anode 10, a light-emitting functional layer 30, and a cathode 20 stacked in sequence from bottom to top. The absolute value of the conduction band energy level of the multiple light-emitting sub-layers included in the light-emitting functional layer 30 gradually decreases in the bottom-to-top direction, and the absolute value of the valence band energy level of the multiple light-emitting sub-layers gradually decreases in the bottom-to-top direction; in other embodiments, the light-emitting device 100 may include a cathode 20, a light-emitting functional layer 30, and an anode 10 stacked in sequence from bottom to top. The absolute value of the conduction band energy level of the multiple light-emitting sub-layers included in the light-emitting functional layer 30 gradually increases in the bottom-to-top direction, and the absolute value of the valence band energy level of the multiple light-emitting sub-layers gradually increases in the bottom-to-top direction.

[0026] In the light-emitting functional layer 30, two light-emitting sub-layers may be provided, or three light-emitting sub-layers, four light-emitting sub-layers, or more than four light-emitting sub-layers may be provided. In some embodiments, in the light-emitting functional layer 30, the number of the light-emitting sub-layers is 2 to 5, such as 2, 3, 4, or 5; in other embodiments, in the light-emitting functional layer 30, the number of the light-emitting sub-layers is 2 or 3.

[0027] It can be understood that the gradually increasing described in this article means that the absolute values of the conduction band energy levels / valence band energy levels of multiple light-emitting sub-layers generally show an increasing trend as a whole. The specific implementation form is as follows: the absolute value of the conduction band energy level / valence band energy level of the light-emitting sub-layer closest to the anode among the multiple light-emitting sub-layers must be greater than the absolute value of the conduction band energy level / valence band energy level of the light-emitting sub-layer closest to the cathode among the multiple light-emitting sub-layers, and among any two adjacent light-emitting sub-layers, the absolute value of the conduction band energy level / valence band energy level of the light-emitting sub-layer closer to the anode is greater than or equal to the absolute value of the conduction band energy level / valence band energy level of the light-emitting sub-layer closer to the cathode.

[0028] Please refer to Figure 1 In an embodiment, the light-emitting device 100 includes an anode 10, a first light-emitting sub-layer 31, a second light-emitting sub-layer 32, a third light-emitting sub-layer 33, and a cathode 20 that are sequentially stacked. The absolute value of the conduction band energy level of the first light-emitting sub-layer 31, the absolute value of the conduction band energy level of the second light-emitting sub-layer 32, and the absolute value of the conduction band energy level of the third light-emitting sub-layer 33 gradually decrease; the absolute value of the valence band energy level of the first light-emitting sub-layer 31, the absolute value of the valence band energy level of the second light-emitting sub-layer 32, and the absolute value of the valence band energy level of the third light-emitting sub-layer 33 gradually decrease; specifically, the three light-emitting sub-layers can be designed in the following manner (only taking the conduction band energy level as an example for illustration): it can be designed that the absolute value of the conduction band energy level of the first light-emitting sub-layer 31 is greater than the absolute value of the conduction band energy level of the second light-emitting sub-layer 32, and the absolute value of the conduction band energy level of the second light-emitting sub-layer 32 is greater than the absolute value of the conduction band energy level of the third light-emitting sub-layer 33; it can also be designed that the absolute value of the conduction band energy level of the first light-emitting sub-layer 31 is equal to the absolute value of the conduction band energy level of the second light-emitting sub-layer 32, and the absolute value of the conduction band energy level of the second light-emitting sub-layer 32 is greater than the absolute value of the conduction band energy level of the third light-emitting sub-layer 33; it can also be designed that the absolute value of the conduction band energy level of the first light-emitting sub-layer 31 is greater than the absolute value of the conduction band energy level of the second light-emitting sub-layer 32, and the absolute value of the conduction band energy level of the second light-emitting sub-layer 32 is equal to the absolute value of the conduction band energy level of the third light-emitting sub-layer 33.

[0029] In another embodiment, the light-emitting device 100 includes an anode 10, a first light-emitting sub-layer 31, a second light-emitting sub-layer 32, and a cathode 20 that are sequentially stacked. The absolute value of the conduction band energy level of the first light-emitting sub-layer 31 is greater than the absolute value of the conduction band energy level of the second light-emitting sub-layer 32, and the absolute value of the valence band energy level of the first light-emitting sub-layer 31 is greater than the absolute value of the valence band energy level of the second light-emitting sub-layer 32.

[0030] In some embodiments, the thickness of the light-emitting sub-layer is 10 to 20 nm; for example, it can be 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, 16 nm, 17 nm, 18 nm, 19 nm, 20 nm, and values between any two of the above values.

[0031] In some embodiments, among any two adjacent light-emitting sub-layers, the absolute value of the conduction band energy level / valence band energy level of the light-emitting sub-layer closer to the anode is greater than the absolute value of the conduction band energy level / valence band energy level of the light-emitting sub-layer closer to the cathode.

[0032] In some embodiments, the absolute value of the conduction band energy level difference between any two adjacent light-emitting sub-layers is 0.2 to 0.4 eV; for example, it can be 0.2 eV, 0.22 eV, 0.25 eV, 0.27 eV, 0.29 eV, 0.3 eV, 0.31 eV, 0.32 eV, 0.34 eV, 0.35 eV, 0.38 eV, 0.4 eV, and values between any two of the above values. Controlling the conduction band energy level difference within this range helps for better matching between the light-emitting sub-layers and constructing a better gradient.

[0033] In some embodiments, the absolute value of the valence band energy level difference between any two adjacent light-emitting sub-layers is 0.2 to 0.4 eV; for example, it can be 0.2 eV, 0.22 eV, 0.25 eV, 0.27 eV, 0.29 eV, 0.3 eV, 0.31 eV, 0.32 eV, 0.34 eV, 0.35 eV, 0.38 eV, 0.4 eV, and values between any two of the above values. Controlling the valence band energy level difference within this range helps for better matching between the light-emitting sub-layers and constructing a better gradient.

[0034] In some embodiments, the absolute value of the band gap energy level difference between any two adjacent light-emitting sub-layers is 0 to 0.2 eV; for example, it can be 0 eV, 0.01 eV, 0.03 eV, 0.05 eV, 0.08 eV, 0.1 eV, 0.12 eV, 0.14 eV, 0.15 eV, 0.17 eV, 0.19 eV, 0.2 eV, and values between any two of the above values. Controlling the band gap energy level difference within this range helps for better matching between the light-emitting sub-layers, helps to regulate interface stress, defects, and lattice growth conditions, and improves the performance of the light-emitting functional layer 30.

[0035] In the light-emitting functional layer 30, the materials of each light-emitting sub-layer independently include a quantum dot light-emitting material, and the quantum dot light-emitting material is selected from at least one of a single-structure quantum dot, a core-shell structure quantum dot, and a perovskite semiconductor material. The single-structure quantum dot is selected from at least one of II-VI group compounds, IV-VI group compounds, III-V group compounds, and I-III-VI group compounds. The II-VI group compounds are 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 IV-VI group compounds are selected from at least one of SnS, SnSe, SnTe, PbS, PbSe, PbTe, SnSeS, SnSeTe, SnSTe, PbSeS, PbSeTe, PbSTe, SnPbS, SnPbSe, SnPbTe, SnPbSSe, SnPbSeTe, and SnPbSTe. The III-V group compounds are selected from at least one of 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 I-III-VI group compounds are selected from at least one of CuInS, CuInSe, and AgInS. The core of the core-shell structure quantum dot is selected from any one of the above single-structure quantum dots. The shell layer of the core-shell structure quantum dot includes one or more layers, and any shell layer material of the core-shell structure quantum dot is independently selected from at least one of CdS, CdTe, CdSeTe, CdZnSe, CdZnS, CdSeS, ZnSe, ZnSeS, and ZnS.

[0036] As an example, the quantum dots of the core-shell structure can be selected from but not limited to at least one of CdZnSe / CdZnSe / ZnSe / CdZnS / ZnS, CdZnSe / CdZnSe / CdZnS / ZnSCdSe / CdSeS / CdS, InP / ZnSeS / ZnS, CdZnSe / ZnSe / ZnS, CdSeS / ZnSeS / ZnS, CdSe / ZnS, CdSe / ZnSe / ZnS, ZnSe / ZnS, ZnSeTe / ZnS, CdSe / CdZnSeS / ZnS, and InP / ZnSe / ZnS.

[0037] It should be noted that for the materials of the aforementioned single-structure quantum dots, or the core materials of the core-shell structure quantum dots, or the shell materials of the core-shell structure quantum dots, the provided chemical formulas only indicate the elemental composition and do not indicate the content of each element. For example, CdZnSe only represents being composed of three elements, Cd, Zn, and Se. If the content of each element is to be represented, it corresponds to Cd x Zn 1-x Se, where 0 < x < 1.

[0038] The perovskite semiconductor material is selected from doped or undoped inorganic perovskite semiconductors, or organic-inorganic hybrid perovskite semiconductors; the general structural formula of the inorganic perovskite semiconductor is AMX 3 , where A is Cs + ion, M is a divalent metal cation selected from at least one of Pb 2+ , Sn 2+ , Cu 2+ , Ni 2+ , Cd 2+ , Cr 2+ , Mn 2+ , Co 2+ , Fe 2+ , Ge 2+ , Yb 2+ , Eu 2+ , and X is a halogen anion selected from at least one of Cl - , Br - , I - ; the general structural formula of the organic-inorganic hybrid perovskite semiconductor is BMX 3 , where B is an organic amine cation selected from CH 3 (CH 2 ) n-2 NH 3 + or [NH 3 (CH 2 ) n NH 3 ​2+ , where n ≥ 2, M is a divalent metal cation selected from Pb 2+ , Sn 2+ , Cu 2+ , Ni 2+ , Cd 2+ , Cr 2+ , Mn 2+ , Co 2+ , Fe 2+ , Ge 2+ , Yb 2+ , Eu 2+ and at least one of the following, X is a halogen anion selected from Cl - , Br - , I - and at least one of the following.

[0039] The materials of multiple light-emitting sub-layers can be the same or different.

[0040] The conduction band energy level, valence band energy level and band gap energy level of the light-emitting sub-layer are affected by various factors, including but not limited to the type, size, surface defect state of the quantum dot light-emitting material, and parameters in the preparation process. In practical applications, quantum dot light-emitting materials with different conduction band energy levels, valence band energy levels or band gap energy levels can be directly selected on the market to fabricate the light-emitting sub-layer, or the quantum dot synthesis methods and energy level regulation methods commonly used in the art can be referred to, and by regulating the above influencing factors, the required quantum dot light-emitting materials can be prepared.

[0041] In some specific embodiments, the following binary quantum dot light-emitting materials are proposed. CdSe quantum dots have the following energy information: the band gap energy level range is about 1.7 - 2.8 eV, the conduction band energy level is about -4.2 eV, and the valence band energy level is about -6.0 eV; CdS quantum dots have the following energy information: the band gap energy level range is about 2.2 - 3.0 eV, the conduction band energy level is about -3.8 eV, and the valence band energy level is about -6.0 eV; CdTe quantum dots have the following energy information: the band gap energy level range is about 1.45 - 2.3 eV, the conduction band energy level is about -3.5 eV, and the valence band energy level is about -5.5 eV.

[0042] Among them, the band gap energy level value can be finely adjusted by controlling the particle size. Specifically, it can be adjusted by controlling the reaction temperature and time during the synthesis of quantum dots. In some embodiments, the synthesis methods of the above three kinds of quantum dots can be as follows: Mix a cadmium precursor solution and an anion precursor solution (Se precursor, S precursor or Te precursor), and react at a temperature of 220°C - 300°C for 30 s - 10 min to obtain a quantum dot luminescent material. If it is desired to increase the band gap energy level, the reaction temperature and reaction time can be increased within the above temperature range, and the wavelength of the quantum dots can be measured in real time. When the wavelength reaches the desired wavelength or band gap energy level, the reaction is stopped, and the quantum dots with the desired band gap energy level can be obtained. It can be understood that the above cadmium precursor and anion precursor are common precursors in the art. For example, the cadmium precursor solution can be obtained by dissolving cadmium oxide in oleic acid, and the Se precursor solution can be obtained by dispersing selenium powder in trioctylphosphine.

[0043] In some specific embodiments, the following ternary quantum dot luminescent materials are proposed. CdZnSe has the following energy information: the band gap energy level range is about 1.7 - 2.8 eV, the conduction band energy level is about -4.2 eV to -3.8 eV, and the valence band energy level is about -6.0 eV;.CdZnS has the following energy information: the band gap energy level range is about 2.2 - 3.0 eV, the conduction band energy level is about -4.2 eV to -3.8 eV, and the valence band energy level is about -6.0 eV. In this embodiment, the band gap energy level value can be finely adjusted by controlling the content of Zn and the particle size. Specifically, during the synthesis process, it can be adjusted by controlling the feeding amount of the zinc source, as well as the reaction temperature and time. While adjusting the parameters, monitor the wavelength of the quantum dots. When the wavelength reaches the desired wavelength or band gap energy level, the reaction is stopped, and the quantum dots with the desired band gap energy level can be obtained.

[0044] In some specific embodiments, quantum dots with a core-shell structure are also proposed, such as CdSe / ZnS, CdSe / CdS, CdTe / CdS, etc. The quantum dots in this embodiment can also be prepared by referring to the above method. Specifically, in some embodiments, the preparation steps of CdSe / ZnS can be as follows: Mix the cadmium precursor solution and the Se precursor solution, react at a temperature of 250 °C for 1 min, then add the zinc precursor solution and the sulfur precursor solution, and react at 230 °C for 50 s to obtain CdSe / ZnS. The valence band energy level of CdSe / ZnS is about -5.74 eV, the conduction band energy level is about -3.80 eV, and the band gap energy level is about 1.94 eV; in some other embodiments, the preparation steps of CdSe / CdS can be as follows: Mix the cadmium precursor solution and the Se precursor solution, react at a temperature of 250 °C for 1 min, then add the zinc precursor solution and the sulfur precursor solution, and react at 255 °C for 90 s to obtain CdSe / CdS. The valence band energy level of CdSe / CdS is about -5.70 eV, the conduction band energy level is about -3.71 eV, and the band gap energy level is about 1.99 eV; in still some other embodiments, the preparation steps of CdTe / CdS can be as follows: Mix the cadmium precursor solution and the Se precursor solution, react at a temperature of 280 °C for 90 s, then add the zinc precursor solution and the sulfur precursor solution, and react at 260 °C for 190 s to obtain CdTe / CdS. The valence band energy level of CdTe / CdS is about -5.64 eV, the conduction band energy level is about -3.59 eV, and the band gap energy level is about 2.05 eV.

[0045] In some embodiments, the light-emitting functional layer 30 further includes N - 1 ohmic contact layers. The N light-emitting sub-layers and the N - 1 ohmic contact layers are stacked alternately, and one of the ohmic contact layers is provided between any two adjacent light-emitting sub-layers. By providing an ohmic contact layer between two adjacent light-emitting sub-layers, an ohmic contact is formed between the light-emitting sub-layers, which helps to enhance the mobility of carriers between the light-emitting sub-layers, improve the interfacial compatibility between the light-emitting sub-layers, thereby reducing the accumulation of carriers at the interface and reducing the damage of the accumulated carriers to the light-emitting sub-layer material.

[0046] In the light-emitting device 100 proposed in the embodiments of the present application, the light-emitting functional layer 30 is composed of a plurality of light-emitting sub-layers and at least one ohmic contact layer stacked alternately. An energy level gradient for carrier transfer is constructed through the light-emitting sub-layers with different bandgaps. The ohmic contact layer promotes carrier transfer, avoids carrier accumulation, helps enhance exciton recombination, improves the utilization rate of carriers, reduces the adverse effects of accumulated carriers, and thus can still have good luminous efficiency and service life without the need to additionally introduce a carrier functional layer. Compared with the light-emitting device 100 with a traditional structure (having a carrier functional layer), the energy level gradient constructed by the device proposed in the embodiments of the present application allows carriers to be transmitted in a tunneling manner through the self-built electric field without having to cross the energy level barrier, and there is no problem of carrier imbalance, greatly reducing the accumulated carriers, improving the carrier mobility and utilization rate, and effectively improving the device efficiency and life.

[0047] In some embodiments, the light-emitting device 100 is composed of the anode 10, the light-emitting functional layer 30, and the cathode 20, and the light-emitting functional layer 30 is composed of the plurality of light-emitting sub-layers and the at least one ohmic contact layer. The carrier functional layers such as the hole functional layer and the electron functional layer are omitted in the device of this embodiment, simplifying the types of the film layers of the light-emitting device 100. In this way, it is no longer necessary to use carrier functional layer materials with high costs and high screening difficulties, thus greatly reducing the device manufacturing cost and difficulty and being suitable for large-scale production.

[0048] To enhance the migration of carriers between the light-emitting sub-layers, the material of the ohmic contact layer can be a material with high conductivity. In some embodiments, the conductivity of the material of the ohmic contact layer is greater than or equal to 10 3 S / m; in this way, it is easier to form an ohmic contact between the light-emitting sub-layers. It can be understood that the "conductivity" in the present application refers to the conductivity value of the material at 25 ± 2°C.

[0049] In some embodiments, the light transmittance of the ohmic contact layer is greater than or equal to 90%; the ohmic contact layer has high light transmittance, which is beneficial to light emission.

[0050] Under the condition that the conductivity is greater than or equal to 10 3 S / m and the light transmittance is greater than or equal to 90%, any commonly used conductive material in the art can be used for the ohmic contact layer. In some embodiments, the material of the ohmic contact layer is a carbon material. In other embodiments, the material of the ohmic contact layer can be solution-treated.

[0051] In some specific embodiments, the material of the ohmic contact layer includes carbon materials, and the carbon materials include one or both of carbon nanotubes and graphene; the above materials not only have high conductivity and high light transmittance, but are not easily oxidized, have better stability, are not affected by external interference, and also have a graphene structure, and have high adhesion and high compatibility with the substrate material for optical properties. In addition, these materials can be solution-processed and are applicable to solution processes such as spin coating, printing, inkjet, etc., and are applicable to the standard preparation process of the light-emitting device 100.

[0052] It can be understood that when multiple ohmic contact layers are provided, the materials of the multiple ohmic contact layers can be the same or different.

[0053] To better promote carrier transfer, in some embodiments, the thickness of the ohmic contact layer is 3 to 8 nm, for example, it can be 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, and values between any two of the above; controlling the thickness of the ohmic contact layer within this range helps to improve the interfacial compatibility between the light-emitting sublayers while enabling better carrier transfer. In addition, it also helps to improve the light transmittance of the ohmic contact layer. In other embodiments, the thickness of the ohmic contact layer is 3 to 5 nm. It can be understood that when multiple ohmic contact layers are provided, the thicknesses of the multiple ohmic contact layers can be the same or different.

[0054] In the light-emitting functional layer 30, one ohmic contact layer can be provided, or two or more ohmic contact layers can be provided. Specifically, if the number of light-emitting sublayers in the light-emitting functional layer 30 is N (N is an integer greater than or equal to 2), then the number of ohmic contact layers is N - 1. In some embodiments, in the light-emitting functional layer 30, the number of ohmic contact layers is 1 to 4, such as 1, 2, 3, or 4; in other embodiments, in the light-emitting functional layer 30, the number of ohmic contact layers is 1 or 2.

[0055] Please refer to Figure 1, in one embodiment, the light-emitting functional layer 30 includes a first light-emitting sub-layer 31, a first ohmic contact layer 34, a second light-emitting sub-layer 32, a second ohmic contact layer 35, and a third light-emitting sub-layer 33 that are sequentially stacked in the direction from the anode 10 to the cathode 20. The absolute value of the conduction band energy level of the first light-emitting sub-layer 31, the absolute value of the conduction band energy level of the second light-emitting sub-layer 32, and the absolute value of the conduction band energy level of the third light-emitting sub-layer 33 gradually decrease; the absolute value of the valence band energy level of the first light-emitting sub-layer 31, the absolute value of the valence band energy level of the second light-emitting sub-layer 32, and the absolute value of the valence band energy level of the third light-emitting sub-layer 33 gradually decrease; in another embodiment, the light-emitting device 100 includes an anode 10, a first light-emitting sub-layer 31, a first ohmic contact layer 34, a second light-emitting sub-layer 32, and a cathode 20 that are sequentially stacked. The absolute value of the conduction band energy level of the first light-emitting sub-layer 31 is greater than the absolute value of the conduction band energy level of the second light-emitting sub-layer 32, and the absolute value of the valence band energy level of the first light-emitting sub-layer 31 is greater than the absolute value of the valence band energy level of the second light-emitting sub-layer 32.

[0056] In addition, the anode 10 and the cathode 20 are each independently selected from metal electrodes, carbon electrodes, doped or undoped metal oxide electrodes, and composite electrodes; wherein, the material of the metal electrode is selected from at least one of Al, Ag, Cu, Mo, Au, Ba, Ca, Ni, Ir, and Mg; the material of the carbon electrode is selected from at least one of graphite, carbon nanotubes, graphene, and carbon fibers; the material of the doped or undoped metal oxide electrode is selected from at least one of ITO, FTO, ATO, AZO, GZO, IZO, MZO, ITZO, ICO, AMO, SnO 2 , In 2 O 3 , Cd:ZnO, Ga:SnO 2 ; the material of the composite electrode is selected from one of 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, and ZnS / Al / ZnS. Among them, " / " represents a stacked structure. For example, the composite electrode AZO / Ag / AZO represents an electrode with a three-layer stacked composite structure composed of an AZO layer, an Ag layer, and an AZO layer.

[0057] It can be understood that, in addition to the above-mentioned functional layers, the light-emitting device 100 may further be provided with some functional layers that are commonly used in the light-emitting device 100 and are helpful for improving the performance of the light-emitting device 100, such as an electron blocking layer, an electron injection layer, a hole blocking layer, and / or an interface modification layer, etc.

[0058] It can be understood that the materials and thicknesses of the respective layers of the light-emitting device 100 may be correspondingly set and adjusted according to the light-emitting requirements of the light-emitting device 100.

[0059] In some embodiments, the light-emitting device 100 further includes a substrate (not shown in the figure), and the substrate may also be referred to as a substrate, and the above-mentioned film layer structure is disposed on one side of the substrate. The substrate may be a rigid substrate or a flexible substrate. The rigid substrate may be a ceramic material or various glass materials, etc. The flexible substrate may be formed of a substrate made of a polyimide film (PI) and its derivatives, polyethylene naphthalate (PEN), phosphoenolpyruvate (PEP), or a polyphenylene ether resin, etc. In one embodiment, the material of the substrate includes one or more combinations of glass, silicon wafer, polycarbonate, polymethyl methacrylate, polyethylene terephthalate, polyethylene naphthalate, polyamide, and polyethersulfone.

[0060] It can be understood that the light-emitting device 100 may be a top-emitting light-emitting device or an inverted light-emitting device. When the light-emitting device 100 is a top-emitting device, the substrate is bonded to the side of the anode 10 away from the light-emitting functional layer 30. When the light-emitting device 100 is an inverted device, the substrate is bonded to the side of the cathode 20 away from the light-emitting functional layer 30.

[0061] It can be understood that the light-emitting device 100 may further include a packaging layer (not shown in the figure) to isolate water and oxygen (for example, to make the concentrations of oxygen and water lower than 0.1 ppm) and improve the performance stability of the light-emitting device 100. Specifically, the packaging material used to form the packaging layer may be selected from at least one of UV glue, metal thin film, and glass glue, etc. In a specific embodiment, the packaging material may be an acrylic resin or an epoxy resin.

[0062] The embodiment of the present application further provides a method for manufacturing a light-emitting device 100, including the following steps:

[0063] S10, providing a first electrode;

[0064] S20, preparing a light-emitting functional layer 30 on one side of the first electrode;

[0065] S30, preparing a second electrode on the side of the light-emitting functional layer 30 facing away from the first electrode;

[0066] Wherein, the first electrode is selected from one of the anode 10 and the cathode 20, and the second electrode is selected from the other of the anode 10 and the cathode 20;

[0067] The preparation of the light-emitting functional layer 30 includes: sequentially laminating and preparing N light-emitting sub-layers on one side of the first electrode to obtain the light-emitting functional layer, and in the direction from the cathode 20 to the anode 10, the absolute value of the conduction band energy level and the absolute value of the valence band energy level of the N light-emitting sub-layers gradually increase, where N is an integer greater than or equal to 2.

[0068] Briefly, the preparation method of the light-emitting device 100 can be: according to the film layer lamination sequence of the light-emitting device 100 described above, prepare multiple film layers in sequence from bottom to top, and then obtain the light-emitting device 100. Among them, the multiple film layers refer to the anode 10, the cathode 20, and the light-emitting functional layer 30. The film layer lamination sequence can be the anode 10, the light-emitting functional layer 30, and the cathode 20 laminated in sequence from bottom to top, or the cathode 20, the light-emitting functional layer 30, and the anode 10 laminated in sequence from bottom to top.

[0069] When the light-emitting device 100 is an inverted device, the first electrode is the cathode 20. Thus, the lamination sequence of the multiple light-emitting sub-layers in the light-emitting functional layer 30 should be that the absolute value of the conduction band energy level and the absolute value of the valence band energy level of the materials of the multiple light-emitting sub-layers gradually increase from bottom to top. Correspondingly, the preparation of the N light-emitting sub-layers includes:

[0070] S1a, providing the first quantum dot light-emitting material to the Nth quantum dot light-emitting material, and the absolute value of the conduction band energy level and the absolute value of the valence band energy level of the first quantum dot light-emitting material to the Nth quantum dot light-emitting material increase in sequence;

[0071] S2a, sequentially depositing the first quantum dot light-emitting material to the Nth quantum dot light-emitting material to obtain the first light-emitting sub-layer 31 to the Nth light-emitting sub-layer.

[0072] When the light-emitting device 100 is a normal device, the first electrode is the anode 10. Thus, the lamination sequence of the multiple light-emitting sub-layers in the light-emitting functional layer 30 should be that the absolute value of the conduction band energy level and the absolute value of the valence band energy level of the materials of the multiple light-emitting sub-layers gradually decrease from bottom to top. Correspondingly, the preparation of the N light-emitting sub-layers includes:

[0073] S1b, providing the first quantum dot light-emitting material to the Nth quantum dot light-emitting material, and the absolute value of the conduction band energy level and the absolute value of the valence band energy level of the first quantum dot light-emitting material to the Nth quantum dot light-emitting material increase in sequence;

[0074] S2b, sequentially depositing the Nth quantum dot light-emitting material to the first quantum dot light-emitting material to obtain the first light-emitting sub-layer 31 to the Nth light-emitting sub-layer.

[0075] by Figure 1 Taking the upright device shown as an example, the preparation of its light-emitting functional layer 30 includes: providing a first quantum dot light-emitting material to a third quantum dot light-emitting material, the absolute values ​​of the conduction band energy levels and the absolute values ​​of the valence band energy levels of the first quantum dot light-emitting material to the third quantum dot light-emitting material increase successively; depositing the third quantum dot light-emitting material on the cathode 20 to obtain a first light-emitting sublayer 31, depositing the second quantum dot light-emitting material on the first light-emitting sublayer 31 to obtain a second light-emitting sublayer 32, and depositing the first quantum dot light-emitting material on the second light-emitting sublayer 32 to obtain a third light-emitting sublayer 33.

[0076] Furthermore, in some embodiments, the light-emitting functional layer 30 further includes N-1 ohmic contact layers. In any two adjacent light-emitting sublayers, the light-emitting sublayer close to the first electrode is defined as a lower light-emitting sublayer, and the light-emitting sublayer close to the second electrode is defined as an upper light-emitting sublayer; accordingly, the preparation of the light-emitting functional layer 30 further includes: providing a conductive material, arranging the conductive material on the side of the lower light-emitting sublayer away from the first electrode to obtain an ohmic contact layer, and the side of the ohmic contact layer away from the lower light-emitting sublayer is used to prepare the upper light-emitting sublayer.

[0077] Still Figure 1 Taking the upright device shown as an example, the preparation of its light-emitting functional layer 30 includes: providing a first quantum dot light-emitting material, a second quantum dot light-emitting material, a third quantum dot light-emitting material, a first conductive material and a second conductive material, wherein the absolute values ​​of the conduction band energy levels and the absolute values ​​of the valence band energy levels of the first quantum dot light-emitting material to the third quantum dot light-emitting material increase in sequence; depositing the third quantum dot light-emitting material on the cathode 20 to obtain a first light-emitting sublayer 31; depositing the first conductive material on the first light-emitting sublayer 31 to obtain a first ohmic contact layer 34; depositing the second quantum dot light-emitting material on the first ohmic contact layer 34 to obtain a second light-emitting sublayer 32; depositing the second conductive material on the second light-emitting sublayer 32 to obtain a second ohmic contact layer 35; depositing the first quantum dot light-emitting material on the second ohmic contact layer 35 to obtain a third light-emitting sublayer 33.

[0078] It can be understood that the preparation methods of the respective film layers in the light-emitting device 100 provided in the present application, including the anode 10, the cathode 20, the light-emitting sublayer, the ohmic contact layer, and other film layers, can be realized by conventional techniques in the art, such as chemical methods or physical methods. Among them, the chemical methods include chemical vapor deposition, sequential ionic layer adsorption and reaction, anodic oxidation, electrodeposition, and coprecipitation. The physical methods include physical coating methods and solution methods. Among them, the physical coating methods include: thermal evaporation coating, electron beam evaporation coating, magnetron sputtering, multi-arc ion coating, physical vapor deposition, atomic layer deposition, pulsed laser deposition, etc.; the solution method can be spin coating, printing, inkjet printing, blade coating, printing, dip coating, immersion, spraying, roll coating, casting, slot die coating, and bar coating, etc.

[0079] In some embodiments, the light-emitting sublayer is prepared by a solution method. Correspondingly, the preparation of each light-emitting sublayer includes: dispersing the corresponding quantum dot light-emitting material (i.e., the quantum dot light-emitting material used to prepare this light-emitting sublayer) in a first solvent to form a first solution, depositing the first solution on the previous film layer to obtain a light-emitting liquid film, and then performing heat treatment on the light-emitting liquid film to obtain the light-emitting sublayer. It can be understood that the previous film layer mentioned herein refers to a film layer located below and adjacent to the currently fabricated film layer in the light-emitting device 100.

[0080] Among them, the first solution can be one or more of non-polar alkane solvents with 5 to 9 carbon atoms and non-polar cycloalkane solvents with 5 to 8 ring atoms. For example, it can include but is not limited to one or more of pentane, hexane, heptane, cyclopentane, cyclohexane, and cycloheptane.

[0081] Among them, in the first solution, the concentration of the quantum dot light-emitting material can be 10 to 15 mg / mL. For example, it can be 10 mg / mL, 11 mg / mL, 12 mg / mL, 13 mg / mL, 14 mg / mL, 15 mg / mL, and values between any two of these values.

[0082] Among them, the heat treatment can adopt a conventional heating treatment method or a flash lamp sintering treatment method. Using the flash lamp sintering method to perform heat treatment on the light-emitting liquid film can accurately control the heat treatment depth and temperature, and while ensuring effective heat treatment of the light-emitting sublayer, avoid the influence of high temperature on the film layer below this film layer. Specifically, the preparation of the light-emitting sublayer further includes: after depositing the corresponding quantum dot light-emitting material to obtain the light-emitting liquid film, performing a first flash lamp sintering treatment on the light-emitting liquid film to obtain the light-emitting sublayer.

[0083] To simultaneously ensure the improvement of the treatment effect and the reduction of the adverse impact on the underlying film layer, the depth of the first flash lamp sintering treatment is 20 to 30 nm; for example, it can be 20 nm, 21 nm, 22 nm, 23 nm, 24 nm, 25 nm, 26 nm, 27 nm, 28 nm, 29 nm, 30 nm, and values between any two of these values.

[0084] In some embodiments, the maximum illuminance is greater than 5 J / cm 2 ; for example, it can be 5 J / cm 2 , 6 J / cm 2 , 7 J / cm 2 , 8 J / cm 2 , 9 J / cm 2 , 10 J / cm 2 , 11 J / cm 2 , 12 J / cm 2 , 13 J / cm 2 , 14 J / cm 2 , 15 J / cm 2 , 16 J / cm 2 , 17 J / cm 2 , 18 J / cm 2 , 19 J / cm 2 , 20 J / cm 2 , 22 J / cm 2 , 25 J / cm 2 , 30 J / cm 2 , 30 J / cm 2 and values above, as well as values between any two of these values. Controlling the illuminance within this range can effectively achieve the heat treatment temperature and depth, while reducing the impact on the material. In some embodiments, the maximum illuminance is 5 to 20 J / cm 2 .

[0085] In some embodiments, the pulse width range of the pulsed light is 1100 to 1900 μs; for example, it can be 1100 μs, 1200 μs, 1300 μs, 1400 μs, 1500 μs, 1600 μs, 1700 μs, 1800 μs, 1900 μs, and values between any two of these values. The pulse width refers to the duration for which the pulsed light reaches the required illuminance. Controlling it within this range can ensure that the energy of the pulsed light hits the sample continuously and uniformly at a fixed frequency, which helps to better adjust the depth and effect of the heat treatment and reduce the impact on the material.

[0086] In some embodiments, the minimum pulse interval is 100 to 105 μs; for example, it can be 100 μs, 101 μs, 102 μs, 103 μs, 104 μs, 105 μs, and values between any two of these values.

[0087] In some embodiments, the wavelength range of the pulsed light is 780 - 1100 nm. For example, it can be 780 nm, 800 nm, 850 nm, 900 nm, 950 nm, 1000 nm, 1100 nm, and values between any two of these. By outputting pulsed light within the above range, the influence on the material can be reduced while effectively achieving the heat treatment temperature and depth.

[0088] The temperature of the light-emitting sublayer under the first flash lamp sintering treatment is 80 - 100 °C; for example, it can be 80 °C, 85 °C, 90 °C, 95 °C, 100 °C, and values between any two of these. By adjusting the parameter conditions of the flash lamp sintering, the temperature of the light-emitting sublayer under the first flash lamp sintering treatment can be adjusted. Controlling its temperature within the above range can effectively achieve the heat treatment of the light-emitting liquid film and produce a light-emitting sublayer with excellent performance.

[0089] In some embodiments, the ohmic contact layer is prepared by a solution method. Correspondingly, the preparation of each ohmic contact layer includes: dispersing the corresponding conductive material (i.e., the conductive material used to prepare this ohmic contact layer) in a second solvent to form a second solution, depositing the second solution on the previous film layer to obtain a conductive liquid film, and then performing heat treatment on the conductive liquid film to obtain the ohmic contact layer.

[0090] Among them, the second solution can be one or more of polar solvents, including but not limited to one or more of acetone, methanol, ethanol, isopropanol, chloroform, dichloromethane, acetonitrile, ethyl acetate, and ether.

[0091] Among them, in the second solution, the concentration of the conductive material can be 2.5 - 5 mg / mL. For example, it can be 2.5 mg / mL, 3 mg / mL, 3.5 mg / mL, 4 mg / mL, 4.5 mg / mL, 5 mg / mL, and values between any two of these.

[0092] Among them, the heat treatment can adopt a conventional heating treatment method or a flash lamp sintering treatment method. Using the flash lamp sintering method to perform heat treatment on the conductive liquid film can accurately control the heat treatment depth and temperature, and while ensuring the effective heat treatment of the ohmic contact layer, avoid the influence of high temperature on the film layer below this film layer. Specifically, the preparation of the ohmic contact layer further includes: after depositing the corresponding conductive material to obtain a conductive liquid film, performing a second flash lamp sintering treatment on the conductive liquid film to obtain the ohmic contact layer.

[0093] To simultaneously ensure the improvement of the processing effect and the reduction of the adverse effects on the underlying film layer, the depth of the second flash lamp sintering treatment is 3 to 8 nm; for example, it can be 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, and values between any two of these values.

[0094] In some embodiments, the maximum illuminance is greater than 5 J / cm 2 ; for example, it can be 5 J / cm 2 , 6 J / cm 2 , 7 J / cm 2 , 8 J / cm 2 , 9 J / cm 2 , 10 J / cm 2 , 11 J / cm 2 , 12 J / cm 2 , 13 J / cm 2 , 14 J / cm 2 , 15 J / cm 2 , 16 J / cm 2 , 17 J / cm 2 , 18 J / cm 2 , 19 J / cm 2 , 20 J / cm 2 , 22 J / cm 2 , 25 J / cm 2 , 30 J / cm 2 , 30 J / cm 2 The above values and values between any two of these values. Controlling the illuminance within this range can effectively achieve the heat treatment temperature and depth while reducing the impact on the material. In some embodiments, the maximum illuminance is 5 to 20 J / cm 2 .

[0095] In some embodiments, the pulse width range of the pulsed light is 100 to 1100 μs; for example, it can be 100 μs, 200 μs, 300 μs, 400 μs, 500 μs, 600 μs, 700 μs, 800 μs, 900 μs, 1000 μs, 1100 μs, and values between any two of these values. Controlling it within this range can ensure that the energy of the pulsed light hits the sample at a fixed frequency, continuously and evenly, which helps to better adjust the depth and effect of the heat treatment and reduce the impact on the material.

[0096] In some embodiments, the minimum pulse interval is 100 to 105 μs; for example, it can be 100 μs, 101 μs, 102 μs, 103 μs, 104 μs, 105 μs, and values between any two of these values.

[0097] In some embodiments, the wavelength range of the pulsed light is 320 - 780 nm. For example, it can be 320 nm, 340 nm, 350 nm, 380 nm, 400 nm, 420 nm, 450 nm, 480 nm, 500 nm, 550 nm, 600 nm, 650 nm, 700 nm, 750 nm, 780 nm, and values between any two of these values. By outputting pulsed light within the above range, the influence on the material can be reduced while effectively reaching the heat treatment temperature and depth.

[0098] Under the second flash lamp sintering treatment, the temperature of the ohmic contact layer is 150 - 200 °C; for example, it can be 150 °C, 160 °C, 170 °C, 180 °C, 190 °C, 200 °C, and values between any two of these values. By adjusting the parameter conditions of the flash lamp sintering, the temperature of the ohmic contact layer under the second flash lamp sintering treatment can be adjusted. Controlling its temperature within the above range can effectively achieve the heat treatment of the conductive liquid film and produce an ohmic contact layer with excellent performance.

[0099] During the above flash lamp sintering treatment, the flash lamp sintering equipment used can be purchased on the market. In some embodiments, the number of lamp tubes of the flash lamp sintering equipment can be 1 or 2; the discharge mode of the flash lamp sintering equipment can be a single pulse mode or a multi - pulse mode.

[0100] This application also relates to a display device, and the display device includes the light - emitting device 100 provided by this application. The display device can be any electronic product with a display function. The electronic products include but are not limited to smartphones, tablet computers, laptop computers, digital cameras, digital video cameras, smart wearable devices, smart weighing electronic scales, in - vehicle displays, televisions, or e - book readers. Among them, the smart wearable devices can be, for example, smart bracelets, smart watches, virtual reality (VR) helmets, etc.

[0101] The following specifically describes this application through specific embodiments. The following embodiments are only partial embodiments of this application and do not limit this application. The raw materials used in the following embodiments are all commercially available products unless otherwise specified.

[0102] Example 1

[0103] This embodiment provides a quantum dot light - emitting diode and its preparation method, which specifically includes the following steps.

[0104] Step 1: After cleaning and drying the ITO substrate (with a thickness of 200 nm), it is treated in an ultraviolet ozone cleaner for 15 min.

[0105] Step 2: Disperse the first luminescent sublayer material CdSe / ZnS in n - hexane to obtain a first luminescent sublayer material solution (in the solution, the concentration of the first luminescent sublayer material CdSe / ZnS is 12 mg / ml). Spin - coat the first luminescent sublayer material solution on the ITO substrate at a speed of 1500 rpm. After forming a liquid film with a thickness of 25 nm, perform heat treatment through a flash lamp sintering device to obtain the first luminescent sublayer. Among them, the parameters of the flash lamp sintering device are: the number of pulse lamp tubes is 2, the illumination range is 10 J / cm 2 , the discharge mode is single - pulse mode, the minimum pulse interval is set to 100 μs, the pulse light wavelength range is 1000 nm, the pulse width is 1500 μs, the pulse time is 30 s, and the heat treatment depth is 23 - 25 nm.

[0106] Step 3: Disperse graphene in ethanol to prepare a first graphene solution with a graphene concentration of 3 mg / ml. Spin - coat the first graphene solution on the first luminescent sublayer at a speed of 6000 rpm. After forming a liquid film with a thickness of 8 nm, perform heat treatment through a flash lamp sintering device to obtain the first ohmic contact layer. The conductivity of the first ohmic contact layer is 2×10 3 S / m, and the transmittance is 95%. Among them, the parameters of the flash lamp sintering device are basically the same as those in Step 2, except that the pulse light wavelength range is 400 nm, the pulse width is 800 μs, the pulse time is 15 s, and the heat treatment depth is 5 - 8 nm.

[0107] Step 4: Disperse the second luminescent sublayer material CdSe / CdS in n - hexane to obtain a second luminescent sublayer material solution (in the solution, the concentration of the second luminescent sublayer material CdSe / CdS is 12 mg / ml). Spin - coat the second luminescent sublayer material solution on the first ohmic contact layer at a speed of 1500 rpm. After forming a liquid film with a thickness of 25 nm, perform heat treatment through a flash lamp sintering device to obtain the second luminescent sublayer. Among them, the parameters of the flash lamp sintering device are basically the same as those in Step 2, except that the pulse light wavelength range is 900 nm, the pulse width is 1600 μs, the pulse time is 40 s, and the heat treatment depth is 23 - 25 nm;

[0108] Step 5: Disperse graphene in ethanol to prepare a second graphene solution with a graphene concentration of 3 mg / ml. Spin - coat the second graphene solution on the second luminescent sublayer at a speed of 6000 rpm. After forming a liquid film with a thickness of 8 nm, perform heat treatment through a flash lamp sintering device to obtain the second ohmic contact layer. The conductivity of the second ohmic contact layer is 2×10 3S / m, with a light transmittance of 95%. Among them, the parameters of the flash lamp sintering equipment are basically the same as those in Step 2, except that the pulse light wavelength range is 400 nm, the pulse width is 800 μs, the pulse time is 15 s, and the heat treatment depth is 5 - 8 nm.

[0109] Step 6: Disperse the third light-emitting sublayer material CdTe / CdS in n-hexane to obtain a third light-emitting sublayer material solution (in the solution, the concentration of the third light-emitting sublayer material CdTe / CdS is 12 mg / ml). Spin-coat the third light-emitting sublayer material solution on the second ohmic contact layer at a rotation speed of 1500 rpm. After forming a liquid film with a thickness of 25 nm, perform heat treatment through a flash lamp sintering equipment to obtain the third light-emitting sublayer. Among them, the parameters of the flash lamp sintering equipment are basically the same as those in Step 2, except that the pulse light wavelength range is 800 nm, the pulse light power is 1800 μs, the pulse time is 50 s, and the heat treatment depth is 23 - 25 nm.

[0110] Step 7: Vacuum deposit an Rb-cathode with a thickness of 100 nm on the third light-emitting sublayer; then seal the device with epoxy resin to obtain a QLED device.

[0111] The performance data of the light-emitting sublayer materials in the device of this embodiment are shown in Table 1-1.

[0112] Table 1-1

[0113]

[0114] Example 2

[0115] This embodiment is basically the same as Example 1, except that in this embodiment, the materials of the first light-emitting sublayer, the second light-emitting sublayer, and the third light-emitting sublayer are shown in Table 1-2. Correspondingly, when performing flash lamp sintering on the first light-emitting sublayer, the second light-emitting sublayer, and the third light-emitting sublayer, the flash lamp sintering parameters are shown in Table 1-2. Except for this, other parameters and steps remain unchanged.

[0116] Table 1-2

[0117]

[0118]

[0119] Example 3

[0120] This embodiment is basically the same as Embodiment 1, except that in this embodiment, the materials of the first light-emitting sub-layer, the second light-emitting sub-layer, and the third light-emitting sub-layer are as shown in Table 1-3. Correspondingly, when flash lamp sintering the first light-emitting sub-layer, the second light-emitting sub-layer, and the third light-emitting sub-layer, the flash lamp sintering parameters are as shown in Table 1-3. Except for this, other parameters and steps remain unchanged.

[0121] Table 1-3

[0122]

[0123] Embodiment 4

[0124] This embodiment is basically the same as Embodiment 1, except that in this embodiment, the materials of the first light-emitting sub-layer, the second light-emitting sub-layer, and the third light-emitting sub-layer are as shown in Table 1-4. Correspondingly, when flash lamp sintering the first light-emitting sub-layer, the second light-emitting sub-layer, and the third light-emitting sub-layer, the flash lamp sintering parameters are as shown in Table 1-4. Except for this, other parameters and steps remain unchanged.

[0125] Table 1-4

[0126]

[0127]

[0128] Embodiment 5

[0129] This embodiment is basically the same as Embodiment 1, except that in this embodiment, the light-emitting functional layer is composed of a first light-emitting sub-layer, a first ohmic contact layer, and a second light-emitting sub-layer. Correspondingly, in the preparation steps, Steps 5 and 6 are omitted, and in Step 7, Rb is directly evaporated on the second light-emitting sub-layer. Except for this, other parameters and steps remain unchanged.

[0130] Embodiment 6

[0131] This embodiment is basically the same as Embodiment 1, except that in this embodiment, the materials of the first ohmic contact layer and the second ohmic contact layer are changed from graphene to carbon nanotubes. Correspondingly, the conductivity of the first ohmic contact layer becomes 1.5×10 3 S / m, and the light transmittance becomes 91%. Except for this, other parameters and steps remain unchanged.

[0132] Embodiment 7

[0133] This embodiment is basically the same as Embodiment 1, except that in this embodiment, the heat treatment of the third light-emitting sub-layer adopts a heating treatment method. Correspondingly, the heat treatment of the third light-emitting sub-layer is changed to heating to 80°C for 30 minutes. Except for this, other parameters and steps remain unchanged.

[0134] Example 8

[0135] This example is basically the same as Example 1, except that in this example, the light-emitting functional layer is composed of a first light-emitting sub-layer, a second light-emitting sub-layer, and a third light-emitting sub-layer. Correspondingly, in the preparation steps, steps 3 and 5 are omitted. In step 4, the second light-emitting sub-layer is directly prepared on the first light-emitting sub-layer, and in step 6, the third light-emitting sub-layer is directly prepared on the second light-emitting sub-layer. Except for this, other parameters and steps remain unchanged.

[0136] Comparative Example 1

[0137] This comparative example is basically the same as Example 1, except that the structure of the device in this comparative example is anode / first light-emitting sub-layer / cathode. Correspondingly, in the preparation steps, steps 3 to 6 are omitted. In step 7, Rb is directly evaporated on the first light-emitting sub-layer. Except for this, other parameters and steps remain unchanged.

[0138] Comparative Example 2

[0139] This comparative example is basically the same as Comparative Example 1, except that the device in this comparative example further has a hole transport layer, a hole injection layer, and an electron transport layer. Correspondingly, the preparation method of the device in this comparative example is as follows:

[0140] Step 1: After cleaning and drying an ITO substrate (with a thickness of 200 nm), it is treated in an ultraviolet ozone cleaner for 15 min.

[0141] Step 2: Spin-coat a PEDOT:PSS solution on the ITO substrate to obtain a hole injection layer with a thickness of 30 nm.

[0142] Step 3: Spin-coat a chlorobenzene solution of TFB (with a concentration of 6.5 mg / ml) on the hole injection layer to obtain a hole transport layer with a thickness of 40 nm.

[0143] Step 4: Disperse the light-emitting sub-layer material CdSe / ZnS in n-hexane to obtain a light-emitting sub-layer material solution (in the solution, the concentration of the light-emitting sub-layer material CdSe / ZnS is 12 mg / ml). Spin-coat the light-emitting sub-layer material solution on the hole transport layer at a rotation speed of 1500 rpm. After forming a liquid film with a thickness of 25 nm, it is then heat-treated through a flash lamp sintering device to obtain the light-emitting sub-layer. Among them, the parameters of the flash lamp sintering device are: the number of pulse lamp tubes is 2, the illumination range is 10 J / cm 2 , the discharge mode is single pulse mode, the minimum pulse interval is set to 100 μs, the pulse light wavelength range is 1000 nm, the pulse width is 1500 μs, the pulse time is 30 s, and the heat treatment depth is 23 - 25 nm.

[0144] Step 5: Spin-coat an ethanol solution of ZnO (30 mg / ml) on the light-emitting sublayer to obtain an electron transport layer with a thickness of 38 nm;

[0145] Step 6: Vacuum-evaporate an Rb-cathode with a thickness of 100 nm on the electron transport layer; then seal the device with epoxy resin to obtain a QLED device.

[0146] Experimental Example

[0147] Perform performance tests on the quantum dot light-emitting diodes of the examples and comparative examples, and the test results are shown in Table 2.

[0148] (1) The test method for the external quantum efficiency EQE is as follows:

[0149] The ratio of the number of electron-hole pairs injected into the quantum dots converted into the number of emitted photons, with the unit of %, is an important parameter to measure the quality of an electroluminescent device and can be obtained by measuring with an EQE optical test instrument. The specific calculation formula is as follows:

[0150]

[0151] Among them, ηe is the optical output coupling efficiency, ηr is the ratio of the number of recombined carriers to the number of injected carriers, χ is the ratio of the number of excitons generating photons to the total number of excitons, K R is the radiation process rate, and K NR is the non-radiation process rate.

[0152] Test conditions: Conducted at room temperature with an air humidity of 30 - 60%.

[0153] (2) The test method for the lifetime T95@1000nit is as follows:

[0154] The time required for the device to reduce the brightness to a certain proportion of the maximum brightness under a constant current or voltage drive. The time when the brightness drops to 95% of the maximum brightness is defined as T95, and this lifetime is the measured lifetime. To shorten the test cycle, the device lifetime test is usually carried out at high brightness by accelerating the device aging and is obtained by fitting with an extended exponential decay brightness decay fitting formula. For example, the lifetime at 1000 nit is denoted as T95@1000nit. The specific calculation formula is as follows:

[0155]

[0156] Among them, T95 L is the lifetime at low brightness, T95 H is the measured lifetime at high brightness, L H is the device accelerated to the maximum brightness, L LIt is 1000 nit. A is the acceleration factor. In this experiment, the value of A is obtained as 1.7 by measuring the lifetimes of several groups of red QLED devices at the rated brightness.

[0157] Table 2

[0158]

[0159]

[0160] As can be seen from the above table, the devices of each embodiment all have a certain EQE and T95@1000 nit, indicating that the devices of this application can fabricate light-emitting devices with the photoelectric effect by constructing gradient energy levels with light-emitting sublayers of different conduction band energy levels / valence band energy levels, demonstrating the feasibility of the device with this structural design.

[0161] Furthermore, by comparing Examples 1 to 7 and Comparative Examples 1 and 2, it can be seen that Examples 1 to 7 have significantly higher EQE and T95@1000 nit. Obviously, compared with the device of Comparative Example 1 that only has one layer of light-emitting sublayer and no carrier functional layer and the device of Comparative Example 2 that adopts the traditional device structure (carrier functional layer + light-emitting sublayer), the light-emitting devices proposed in the embodiments of this application have higher luminous efficiency and longer lifetime. This shows that the light-emitting devices proposed in this application can not only achieve luminescence without additionally introducing a carrier functional layer, but also greatly improve the luminous efficiency and service life of the devices. This may be because in the device of Comparative Example 1, an internal built-in electric field cannot be formed between the film layers, and the injection of carriers between the electrode and the light-emitting sublayer is difficult, affecting the luminous efficiency and lifetime of the device. In the device of Comparative Example 2, due to the existence of the carrier functional layer, there are certain energy level barriers and carrier transport imbalance problems in the device, affecting the luminous efficiency and lifetime of the device.

[0162] Furthermore, by comparing Example 1 and Example 8, it can be seen that Example 1 has significantly higher EQE and T95@1000 nit, indicating that setting an ohmic contact layer between adjacent light-emitting sublayers helps to improve the interfacial compatibility between the light-emitting sublayers, enhance the mobility of carriers between the light-emitting sublayers, and thus greatly improve the luminous efficiency and lifetime of the device.

[0163] In addition, Example 1 has better EQE and T95@1000 nit than Example 7, indicating that using the method of flash lamp sintering to heat-treat the film layer can well control the treatment depth, avoid affecting the underlying materials, and further avoid affecting the efficiency and lifetime of the light-emitting device.

[0164] The above has introduced in detail the technical solutions provided by the embodiments of the present application. Specific examples are used herein to elaborate on the principle and implementation manner of the present application. The description of the above embodiments is only used to help understand the method and its core idea of the present application; at the same time, for those skilled in the art, according to the idea of the present application, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present application.

Claims

1. A light-emitting device, characterized in that, the light-emitting device includes an anode, a light-emitting functional layer, and a cathode that are stacked, and the light-emitting functional layer includes N light-emitting sub-layers stacked, where N is an integer greater than or equal to 2; in the direction from the cathode to the anode, the absolute value of the conduction band energy level and the absolute value of the valence band energy level of the N light-emitting sub-layers gradually increase.

2. The light-emitting device according to claim 1, characterized in that, the light-emitting functional layer further includes N - 1 ohmic contact layers, and one of the ohmic contact layers is provided between any two adjacent light-emitting sub-layers.

3. The light-emitting device according to claim 2, characterized in that, The conductivity of the material of the ohmic contact layer is greater than or equal to 10 3 S / m; and / or, the light transmittance of the ohmic contact layer is greater than or equal to 90%; and / or, the material of the ohmic contact layer includes a carbon material; and / or, the thickness of the ohmic contact layer is 3 - 8 nm; and / or, in the light-emitting functional layer, the number of the ohmic contact layers is 1 - 4.

4. The light-emitting device according to claim 3, characterized in that, the carbon material includes one or both of carbon nanotubes and graphene.

5. The light-emitting device according to any one of claims 1 to 4, characterized in that, the absolute value of the conduction band energy level difference between any two adjacent light-emitting sub-layers is 0.2 - 0.4 eV; and / or, the absolute value of the valence band energy level difference between any two adjacent light-emitting sub-layers is 0.2 - 0.4 eV.

6. The light-emitting device according to any one of claims 1 to 4, characterized in that, the absolute value of the band gap energy level difference between any two adjacent light-emitting sub-layers is 0 - 0.2 eV.

7. The light-emitting device according to any one of claims 1 to 4, characterized in that, the thickness of the light-emitting sub-layer is 10 - 20 nm; and / or, in the light-emitting functional layer, the number of the light-emitting sub-layers is 2 - 5; and / or, The material of the light-emitting sublayer includes quantum dot light-emitting materials, and the quantum dot light-emitting materials are selected from at least one of single-structure quantum dots, core-shell structure quantum dots, and perovskite semiconductor materials. The single-structure quantum dots are selected from at least one of II-VI group compounds, IV-VI group compounds, III-V group compounds, and I-III-VI group compounds. The II-VI group compounds are 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 IV-VI group compounds are selected from at least one of SnS, SnSe, SnTe, PbS, PbSe, PbTe, SnSeS, SnSeTe, SnSTe, PbSeS, PbSeTe, PbSTe, SnPbS, SnPbSe, SnPbTe, SnPbSSe, SnPbSeTe, and SnPbSTe. The III-V group compounds are selected from at least one of 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 I-III-VI group compounds are selected from at least one of CuInS, CuInSe, and AgInS. The core of the core-shell structure quantum dots is selected from any one of the above single-structure quantum dots. The shell layer of the core-shell structure quantum dots includes one or more layers. Any shell layer material of the core-shell structure quantum dots is independently selected from at least one of CdS, CdTe, CdSeTe, CdZnSe, CdZnS, CdSeS, ZnSe, ZnSeS, and ZnS.The perovskite semiconductor material is selected from doped or undoped inorganic perovskite semiconductors, or organic-inorganic hybrid perovskite semiconductors; the structural general formula of the inorganic perovskite semiconductor is AMX; 3 , where A is a Cs + ion, M is a divalent metal cation selected from Pb 2 + , Sn 2+ , Cu 2+ , Ni 2+ , Cd 2+ , Cr 2+ , Mn 2+ , Co 2+ , Fe 2+ , Ge 2+ , Yb 2+ , Eu 2+ and at least one of them, X is a halogen anion selected from at least one of Cl-, Br - , I-; the structural general formula of the organic-inorganic hybrid perovskite semiconductor is BMX 3 , where B is an organic amine cation selected from CH 3 (CH 2 ) n-2 NH 3 + or [NH 3 (CH 2 ) n NH 3 2+ , where n≥2, M is a divalent metal cation selected from Pb 2+ , Sn 2+ , Cu 2+ , Ni 2+ , Cd 2+ , Cr 2+ , Mn 2+ , Co 2+ , Fe 2+ , Ge 2+ , Yb 2+ , Eu 2+ and at least one of them, X is a halogen anion selected from at least one of Cl - , Br - , I - and at least one of them; and / or,​ The anode and the cathode are each independently selected from a metal electrode, a carbon electrode, a doped or undoped metal oxide electrode, and a composite electrode; wherein, the material of the metal electrode is selected from at least one of Al, Ag, Cu, Mo, Au, Ba, Ca, Ni, Ir, and Mg; the material of the carbon electrode is selected from at least one of graphite, carbon nanotubes, graphene, and carbon fiber; the material of the doped or undoped metal oxide electrode is selected from at least one of ITO, FTO, ATO, AZO, GZO, IZO, MZO, ITZO, ICO, AMO, SnO 2 , In 2 O 3 , Cd:ZnO, Ga:SnO 2 ; the material of the composite electrode is selected from one of 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, and ZnS / Al / ZnS.

8. The light-emitting device according to claim 2, characterized in that, the light-emitting functional layer includes a first light-emitting sub-layer, a first ohmic contact layer, a second light-emitting sub-layer, a second ohmic contact layer, and a third light-emitting sub-layer that are stacked in sequence along the direction from the anode to the cathode; the absolute value of the conduction band energy level of the first light-emitting sub-layer, the absolute value of the conduction band energy level of the second light-emitting sub-layer, and the absolute value of the conduction band energy level of the third light-emitting sub-layer gradually decrease; the absolute value of the valence band energy level of the first light-emitting sub-layer, the absolute value of the valence band energy level of the second light-emitting sub-layer, and the absolute value of the valence band energy level of the third light-emitting sub-layer gradually decrease.

9. The light-emitting device according to claim 2, characterized in that, the light-emitting device is composed of the anode, the light-emitting functional layer, and the cathode, and the light-emitting functional layer is composed of the plurality of light-emitting sub-layers and the at least one ohmic contact layer.

10. A method for manufacturing a light-emitting device, characterized in that, comprises the following steps: providing a first electrode; preparing a light-emitting functional layer on one side of the first electrode; preparing a second electrode on the side of the light-emitting functional layer away from the first electrode; wherein, the first electrode is selected from one of the anode and the cathode, and the second electrode is selected from the other of the anode and the cathode; The preparation of the light-emitting functional layer includes: preparing N light-emitting sublayers by stacking them in sequence on one side of the first electrode to obtain a light-emitting functional layer, and in the direction from the cathode to the anode, the absolute values ​​of the conduction band energy levels and the absolute values ​​of the valence band energy levels of the N light-emitting sublayers gradually increase, wherein N is an integer greater than or equal to 2.

11. The preparation method according to claim 10, It is characterized in that When the first electrode is a cathode, the preparation of the N light-emitting sublayers includes: Providing a first quantum dot light-emitting material to an Nth quantum dot light-emitting material, wherein the absolute values ​​of the conduction band energy levels and the absolute values ​​of the valence band energy levels of the first quantum dot light-emitting material to the Nth quantum dot light-emitting material increase in sequence; Depositing the first quantum dot luminescent material to the Nth quantum dot luminescent material in sequence to obtain the first luminescent sublayer to the Nth luminescent sublayer; Alternatively, when the first electrode is an anode, the preparation of the N light-emitting sublayers includes: Providing a first quantum dot light-emitting material to an Nth quantum dot light-emitting material, wherein the absolute values ​​of the conduction band energy levels and the absolute values ​​of the valence band energy levels of the first quantum dot light-emitting material to the Nth quantum dot light-emitting material increase in sequence; The Nth quantum dot light-emitting material is sequentially deposited onto the first quantum dot light-emitting material to obtain the first light-emitting sublayer to the Nth light-emitting sublayer.

12. The preparation method according to claim 11, It is characterized in that The preparation of the luminescent sublayer further comprises: after depositing the corresponding quantum dot luminescent material to obtain a luminescent liquid film, performing a first flash lamp sintering process on the luminescent liquid film to obtain the luminescent sublayer.

13. The preparation method according to claim 12, It is characterized in that The conditions of the first flash lamp sintering process are: The depth of the first flash lamp sintering process is 20 to 30 nm; and / or, The temperature of the light-emitting sublayer in the first flash lamp sintering process is 80-100° C.; and / or, The pulse width of the pulse light ranges from 1100 to 1900 μs; and / or, The maximum illuminance is greater than 5 J / cm 2 ; and / or, The minimum pulse interval is 100 to 105 μs; and / or, The wavelength of the pulse light is in the range of 780 to 1100 nm.

14. The preparation method according to claim 11, It is characterized in that The light-emitting functional layer further includes N-1 ohmic contact layers, and in any two adjacent light-emitting sublayers, the light-emitting sublayer close to the first electrode is defined as a lower light-emitting sublayer, and the light-emitting sublayer close to the second electrode is defined as an upper light-emitting sublayer; The preparation of the light-emitting functional layer also includes: providing a conductive material, arranging the conductive material on the side of the lower light-emitting sublayer away from the first electrode to obtain an ohmic contact layer, and the side of the ohmic contact layer away from the lower light-emitting sublayer is used to prepare the upper light-emitting sublayer.

15. The preparation method according to claim 14, It is characterized in that The preparation of the ohmic contact layer further includes: after depositing corresponding conductive materials to obtain a conductive liquid film, performing a second flash lamp sintering process on the conductive liquid film to obtain the ohmic contact layer.

16. The preparation method according to claim 15, It is characterized in that The conditions of the second flash lamp sintering process are: The depth of the second flash lamp sintering process is 3 to 8 nm; and / or, The temperature of the ohmic contact layer under the second flash lamp sintering treatment is 150 to 200 °C; and / or, The pulse width range of the pulsed light is 100 to 1100 μs; and / or, The maximum illuminance is greater than 5 J / cm 2 ; and / or, The minimum pulse interval is 100 to 105 μs; and / or, The wavelength range of the pulsed light is 320 to 780 nm.

17. A display device, Characterized in that, It includes the light-emitting device according to any one of claims 1 to 9, or includes the light-emitting device prepared by the preparation method according to any one of claims 10 to 16.

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