WO2022143558A1

WO2022143558A1 - Method for preparing quantum dot light-emitting diode

Info

Publication number: WO2022143558A1
Application number: PCT/CN2021/141748
Authority: WO
Inventors: 周礼宽; 杨一行
Original assignee: Tcl科技集团股份有限公司
Priority date: 2020-12-31
Filing date: 2021-12-27
Publication date: 2022-07-07
Also published as: CN114695716A

Abstract

Disclosed in the present application is a method for preparing a quantum dot light-emitting diode. The method comprises the following steps: providing a bottom electrode substrate, and preparing a first functional layer on the bottom electrode substrate; forming a quantum dot material having a surface bonded with an organic ligand on the first functional layer to prepare a quantum dot light-emitting layer, the number of carbon atoms of the organic ligand being 4-12; preparing a second functional layer on the quantum dot light-emitting layer; and preparing a top electrode on the second functional layer to prepare a quantum dot light-emitting diode, and heating the device. According to the present application, a device containing an organic ligand-modified quantum dot light-emitting layer having 4-12 carbon atoms is heated, such that the flatness of the film layer can be increased, and the interface barrier between the quantum dot and the adjacent functional layer is optimized.

Description

Preparation method of quantum dot light-emitting diode

This application claims the priority of the Chinese patent application with the application number 202011636497.8 and the invention titled "Method for the Preparation of Quantum Dot Light Emitting Diodes", filed with the China Patent Office on December 31, 2020, the entire contents of which are incorporated by reference in in this application.

technical field

The present application relates to the field of display technology, and in particular, to a method for preparing a quantum dot light-emitting diode.

Background technique

Quantum Dot Light Emitting Diodes, QLED) has received extensive attention and research in the field of lighting and display in recent years due to its high brightness, low power consumption, wide color gamut, and easy processing. QLED is considered to be the development trend of next-generation display and lighting because of its ability to realize self-luminous, low-power full-color display and solid-state lighting. After more than 20 years of rapid development, QLED has obtained better performance parameters.

Existing QLEDs achieve normal operation of the device by stacking functional layers. High-quality thin films are conducive to the injection and transport of electrons and holes, reducing the probability of non-radiative recombination and improving the efficiency and stability of QLEDs. Poor film-forming quality in QLED will lead to interfacial barrier, and Joule heat generated during device operation will increase the temperature of the device and further accelerate the aging of the device. At the same time, the accumulated heat will affect the formation of excitons, thereby affecting the device’s performance. Luminous efficiency and life; in addition, the uneven interface between the film layer and the film layer can easily lead to contact separation, resulting in device failure.

technical problem

One of the purposes of the embodiments of the present application is to provide a method for preparing a quantum dot light-emitting diode.

technical solutions

The technical scheme adopted in the embodiment of the present application is:

A preparation method of a quantum dot light-emitting diode, comprising the following steps:

providing a bottom electrode substrate, and preparing a first functional layer on the bottom electrode substrate;

forming a quantum dot material with organic ligands bound on the surface on the first functional layer to prepare a quantum dot light-emitting layer, and the number of carbon atoms of the organic ligand is 4-12;

preparing a second functional layer on the quantum dot light-emitting layer, preparing a top electrode on the second functional layer, and preparing a quantum dot light-emitting diode;

heat treatment of the device;

Wherein, the bottom electrode substrate is an anode substrate, the first functional layer is a hole functional layer, the second functional layer is an electron functional layer, and the top electrode is a cathode; or

The bottom electrode substrate is a cathode substrate, the first functional layer is an electron functional layer, the second functional layer is a hole functional layer, and the top electrode is an anode.

In some embodiments, the temperature of the heating treatment is 60°C to 150°C, and the heating time is 1 to 120 min.

In some embodiments, in the quantum dot material, the mass percentage of the organic ligand is 5% to 20%.

In some embodiments, the thickness of the quantum dot light-emitting layer is 8-30 nm, the temperature of the heating treatment is 80°C-140°C, and the heating time is 1-30 minutes.

In some embodiments, the quantum dot light-emitting layer is a red light quantum dot light-emitting layer, and the particle size of the red light quantum dots in the red light quantum dot light-emitting layer is 10-16 nm.

In some embodiments, the quantum dot light-emitting layer is a green light quantum dot light-emitting layer, and the particle size of the green light quantum dots in the green light quantum dot light-emitting layer is 8-12 nm.

In some embodiments, the quantum dot light-emitting layer is a blue quantum dot light-emitting layer, and the particle size of the blue quantum dots in the blue-light quantum dot light-emitting layer is 5-10 nm.

In some embodiments, the quantum dot light-emitting layer is a red light quantum dot light-emitting layer, and the particle size of the red light quantum dots in the red light quantum dot light-emitting layer is 10-16 nm; the quantum dot light-emitting layer is green light quantum dots A light-emitting layer, and the particle size of the green quantum dots in the green quantum dot light-emitting layer is 8-12 nm; the quantum dot light-emitting layer is a blue-light quantum dot light-emitting layer, and the blue quantum dots in the blue-light quantum dot light-emitting layer are The particle size of the dots is 5-10 nm.

In some embodiments, the heat treatment occurs after preparing the quantum dot light-emitting layer or before preparing the second functional layer.

In some embodiments, the heat treatment occurs after the preparation of the second functional layer or before the preparation of the top electrode.

In some embodiments, the heat treatment occurs after preparing the top electrode.

In some embodiments, the organic ligand is selected from ligands containing carboxyl, amine, sulfhydryl and phosphine groups.

In some embodiments, the quantum dot material is CdxZn1-xSe/ZnSe1-ySy/ZnS, wherein the values of x and y satisfy: 0≤x≤1, 0≤y≤1.

In some embodiments, the preparation method further includes encapsulating the prepared quantum dot light emitting diode, and the heating treatment occurs after the encapsulation of the quantum dot light emitting diode.

In some embodiments, the heating treatment method is hot plate heating, oven heating or infrared heating.

In some embodiments, the electron functional layer includes at least one of an electron injection layer, an electron transport layer, and a hole blocking layer.

In some embodiments, the hole functional layer includes at least one of a hole injection layer, a hole transport layer, and an electron blocking layer.

In some embodiments, the quantum dot material includes an inorganic nanoparticle body and an organic ligand bound on the surface of the inorganic nanoparticle body.

In some embodiments, the anode is selected from one or more of indium tin oxide, fluorine-doped tin oxide, indium zinc oxide, graphene, and carbon nanotubes.

In some embodiments, the material of the hole injection layer is PEDOT: one or more of PSS, nickel oxide, molybdenum oxide, tungsten oxide, vanadium oxide, molybdenum sulfide, tungsten sulfide, and copper oxide.

In some embodiments, the material of the hole transport layer is selected from one or more of PVK, Poly-TPD, CBP, TCTA and TFB.

In some embodiments, the material of the electron transport layer is one or more of n-type ZnO, TiO2, SnO, Ta2O3, AlZnO, ZnSnO, InSnO, Alq3, Ca, Ba, CsF, LiF, and CsCO3.

In some embodiments, the cathode is selected from one or more of Al, Ca, Ba, Ag.

beneficial effect

The beneficial effect of the method for preparing a quantum dot light-emitting diode provided by the embodiments of the present application is that: through heat treatment, the organic ligands stacked on the surface of the quantum dots and the adjacent functional layers are fused with each other at the interface, which can shorten the length of the quantum dot light-emitting layer. The distance between the quantum dots and the quantum dots, between the light-emitting layer and the adjacent functional layer, effectively increases the transport efficiency of carriers in the quantum dot light-emitting layer and the interface, reduces the internal equivalent resistance of the device, and improves the device's working state. Stability and reliability. In addition, a buffer layer is formed at the interface between the quantum dot light-emitting layer and the adjacent functional layers on both sides, which can flatten the interface barrier existing between the light-emitting layer and the adjacent functional layers on both sides, which is beneficial to improve the efficiency of carrier injection and improve the device optoelectronic properties.

Description of drawings

In order to illustrate the technical solutions in the embodiments of the present application more clearly, the following briefly introduces the accompanying drawings that need to be used in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only for the present application. In some embodiments, for those of ordinary skill in the art, other drawings can also be obtained according to these drawings without any creative effort.

Fig. 1 is the preparation process flow chart of the quantum dot light-emitting diode provided by the embodiment of the present application;

2 is a schematic diagram of the stacking of quantum dots in the light-emitting layer before heat treatment provided in Application Example 1;

FIG. 3 is a schematic diagram of the fusion of the interface between the light-emitting layer and the adjacent transport layer after heating provided in Example 1 of this application.

Embodiments of the present invention

In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application more clear, the present application will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application, but not to limit the present application.

In the claims and specific embodiments of the present application, the term "and/or" describes the association relationship of associated objects, indicating that there can be three kinds of relationships. For example, A and/or B can represent three cases where A exists alone, A and B exist simultaneously, and B exists alone. where A and B can be singular or plural. The character "/" generally indicates that the associated objects are an "or" relationship.

In this application, "at least one" means one or more, and "plurality" means two or more. "At least one item(s) below" or similar expressions refer to any combination of these items, including any combination of single item(s) or plural items(s). For example, "at least one (one) of a, b, or c", or "at least one (one) of a, b, and c", can mean: a, b, c, a-b ( That is, a and b), a-c, b-c, or a-b-c, where a, b, and c can be single or multiple respectively.

It should be understood that, in various embodiments of the present application, the size of the sequence numbers of the above-mentioned processes does not imply the sequence of execution, some or all of the steps may be executed in parallel or sequentially, and the execution sequence of each process should be based on its functions and It is determined by the internal logic and should not constitute any limitation on the implementation process of the embodiments of the present application.

The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. As used in the embodiments of this application and the appended claims, the singular forms "a," "the," and "the" are intended to include the plural forms as well, unless the context clearly dictates otherwise.

The terms "first" and "second" are used for descriptive purposes only, to distinguish objects such as substances, interfaces, messages, requests and terminals from each other, and should not be understood as indicating or implying relative importance or implying that the number of technical characteristics. For example, without departing from the scope of the embodiments of the present application, the first XX may also be referred to as the second XX, and similarly, the second XX may also be referred to as the first XX. Thus, a feature defined as "first" or "second" may expressly or implicitly include one or more of that feature.

The weight of the relevant components mentioned in the description of the examples of this application can not only refer to the specific content of each component, but also can represent the proportional relationship between the weights of the components. It is within the scope disclosed in the description of the embodiments of the present application that the content of the ingredients is scaled up or down. Specifically, the mass described in the description of the embodiments of the present application may be a mass unit known in the chemical field, such as μg, mg, g, and kg.

In quantum dot light-emitting diodes, the length of the surface ligand affects the spacing between quantum dots in the quantum dot light-emitting layer.

In the preparation process of quantum dot light-emitting diode devices, the material selection of each functional layer and the properties of the functional layer interface have a great influence on the film formation and conductivity of the device. For example, the existing film formation processes include spin coating, solution pulling, transfer Printing, inkjet printing and atomic layer deposition, etc., have problems such as poor film formation flatness and poor interface contact. The quantum dot light-emitting layer is composed of inorganic nanoparticles and surface organic ligands. The structural composition of quantum dots and the selection and content of surface organics have a great impact on the properties of the device such as charge injection and exciton recombination. In addition, factors such as different properties of quantum dot luminescent materials and interface contact are closely related to the optoelectronic properties and lifetime of the device. In view of this, the embodiments of the present application provide a method for preparing a quantum dot light-emitting diode, so as to solve the problems of poor film formation flatness and poor interface contact in the process of preparing the quantum dot light-emitting diode.

As shown in FIG. 1, the preparation method of the quantum dot light-emitting diode provided by the present application includes the following steps:

S01. providing a bottom electrode substrate, and preparing a first functional layer on the bottom electrode substrate;

S02. on the first functional layer, a quantum dot material with an organic ligand is formed on the surface to prepare a quantum dot light-emitting layer, and the number of carbon atoms of the organic ligand is 4 to 12;

S03. Prepare a second functional layer on the quantum dot light-emitting layer, prepare a top electrode on the second functional layer, and prepare a quantum dot light-emitting diode;

Heat the device.

In the preparation method of the quantum dot light-emitting diode provided in the embodiment of the present application, the organic ligands stacked on the surface of the quantum dots and the adjacent functional layers are fused with each other at the interface through heat treatment, which can shorten the time between the quantum dots and the quantum dots in the light-emitting layer of the quantum dots. The distance between the dots, the light-emitting layer and the adjacent functional layer can effectively increase the transport efficiency of carriers in the quantum dot light-emitting layer and the interface, reduce the internal equivalent resistance of the device, and improve the stability and reliability of the device under working conditions. sex. In addition, a buffer layer is formed at the interface between the quantum dot light-emitting layer and the adjacent functional layers on both sides, which can flatten the interface barrier existing between the light-emitting layer and the adjacent functional layers on both sides, which is beneficial to improve the efficiency of carrier injection and improve the device optoelectronic properties.

In the embodiment of the present application, the bottom electrode substrate and the cathode are electrodes opposite to each other, and both are one of a cathode or an anode. The same first functional layer and the second functional layer are opposite functional layers, and both are electrons. One of the functional layer or the hole functional layer. The electron functional layer includes at least one of an electron injection layer, an electron transport layer and a hole blocking layer; the hole functional layer includes at least one of a hole injection layer, a hole transport layer and an electron blocking layer.

In some embodiments, the anode is selected from one or more of indium tin oxide, fluorine-doped tin oxide, indium zinc oxide, graphene, and carbon nanotubes; in some embodiments, the material of the hole injection layer is is PEDOT: one or more of PSS, nickel oxide, molybdenum oxide, tungsten oxide, vanadium oxide, molybdenum sulfide, tungsten sulfide, copper oxide; in some embodiments, the material of the hole transport layer is selected from hole transport The material of the layer is one or more of PVK, Poly-TPD, CBP, TCTA and TFB; in some embodiments, the material of the electron transport layer is n-type ZnO, TiO ₂ , SnO, Ta ₂ O ₃ , AlZnO One or more of , ZnSnO, InSnO, Alq ₃ , Ca, Ba, CsF, LiF, CsCO ₃ ; in some embodiments, the cathode is selected from one or more of Al, Ca, Ba, Ag. In a specific embodiment, the anode is selected from indium tin oxide (ITO), the hole injection layer is PEDOT:PSS, the hole transport layer is TFB, the electron transport layer is ZnO, and the cathode is Ag.

In some embodiments, the bottom electrode substrate is an anode substrate, the first functional layer is a hole functional layer, the second functional layer is an electron functional layer, and the top electrode is a cathode; in some embodiments, the bottom electrode substrate is a cathode substrate, The first functional layer is an electron functional layer, the second functional layer is a hole functional layer, and the top electrode is an anode.

In quantum dot light-emitting diode devices with different quantum dot structures and surface ligands, by introducing the process of device heat treatment, the quantum dot light-emitting layer and the transport layer on the adjacent two sides form an interface fusion layer at the interface, which is flattened. The interface potential barrier existing between the light-emitting layer and the adjacent two-side transport layers is beneficial to the enhancement of the carrier injection efficiency and the improvement of the optoelectronic performance of the device.

In the above step S01, the first functional layer is prepared on the bottom electrode substrate, which can be realized by using a conventional method. In some embodiments, the first functional layer is prepared on the bottom electrode substrate by a solution method. Exemplarily, inkjet printing, spin coating or blade coating of a solution of the first functional material on the bottom electrode substrate, and drying treatment is performed to obtain the first functional layer. When the first functional layer includes a plurality of thin film layers, each thin film layer is sequentially prepared on the bottom electrode.

In some embodiments, the bottom electrode substrate is an anode substrate, the first functional layer is a hole functional layer, and the hole functional layer includes a hole injection layer and a hole transport layer. In this case, preparing the first functional layer on the bottom electrode substrate includes: forming a hole injection material on the anode substrate to prepare a hole injection layer; forming a hole transport material on the hole injection layer to prepare holes transport layer.

In some embodiments, the bottom electrode substrate is a cathode substrate, the first functional layer is an electronic functional layer, and the electronic functional layer is an electron transport layer. In this case, preparing the first functional layer on the bottom electrode substrate includes: forming an electron transport material on the cathode substrate, and preparing the electron transport layer.

In some embodiments, the bottom electrode substrate is a cathode substrate, the first functional layer is an electronic functional layer, and the electronic functional layer includes an electron injection layer and an electron transport layer. In this case, preparing the first functional layer on the bottom electrode substrate includes: forming an electron injection material on the cathode substrate to prepare an electron injection layer; forming an electron transport material on the electron injection layer to prepare an electron transport layer.

In the above step S02, a quantum dot material is formed on the first functional layer to prepare a quantum dot light-emitting layer, and reference may be made to a conventional method for preparing a quantum dot light-emitting layer. In some embodiments, the quantum dot light-emitting layer is prepared using a solution method. Exemplarily, a solution film of quantum dot material is ink-jet printed, spin-coated or blade-coated on the first functional layer, and after removing the solvent, a quantum dot light-emitting layer is obtained.

In the embodiment of the present application, the quantum dot material includes an inorganic nanoparticle body and an organic ligand bound on the surface of the inorganic nanoparticle body, wherein, in the process of preparing the quantum dot solution, the organic ligand is beneficial to the quantum dot material in the solvent. Dispersion, suitable organic ligands are beneficial to improve the dispersibility and stability of quantum dot materials. In the solid-state film of the light-emitting layer formed by using the above quantum dot materials, the quantum dots are isolated from the quantum dots by organic ligands, which can reduce the loss of energy resonance transfer. distance to avoid the quenching of the luminescent properties of the quantum dots by the adjacent transport layer material.

In the examples of the present application, the number of carbon atoms of the organic ligand is 4-12. When the number of carbon atoms of the organic ligand is less than 4, the dispersibility of quantum dots in the solvent drops sharply, and the quantum dot spacing in the obtained quantum dot solid-state film is too small, resulting in energy resonance transfer, fluorescence quenching and other problems. Longer carbon chains and larger steric hindrance are beneficial to increase the dispersibility of quantum dots in organic solvents. When the chain length of the ligand is selected to be greater than 12, the interface barrier after fusion is improved, but the quantum dots emit light. The distance between the layer and the adjacent functional layer is large, and there is still a certain strength of insulation, which is not conducive to the injection and transport of carriers. In addition, after the quantum dot solid film is formed, the distance between the quantum dots will increase, resulting in the distance between the quantum dots being greater than 2 nm. The increase in the distance between the light-emitting hosts leads to an increase in the internal equivalent resistance of the device, which consumes a part of the energy and converts it into Joule heat. and so on to promote the rapid aging of the optoelectronic properties of the device.

In some embodiments, the organic ligand is selected from ligands containing carboxyl, amine, sulfhydryl and phosphine groups, but the selection of reactive groups in the organic ligand is not limited thereto. In this case, active groups such as carboxyl, amine, sulfhydryl and phosphine groups on the surface organic ligands are linked with the surface cations of the quantum dots in the form of coordination bonds. In some embodiments, organic ligands may be selected to include, but are not limited to, oleic acid, amines, n-octyl esters.

In some embodiments, the ligands on the surface of the quantum dots can connect the organic ligands with the surface of the quantum dots by adding a coordinating solvent during the synthesis process, or the original initial ligands on the surface of the quantum dots can be exchanged by ligands. The ligand is replaced by the selected organic ligand.

In the above step S03, the second functional layer is prepared on the quantum dot light-emitting layer, which can be realized by using a conventional method. In some embodiments, the second functional layer is prepared on the quantum dot light-emitting layer by a solution method. Exemplarily, inkjet printing, spin coating or blade coating of a solution of the second functional material on the quantum dot light-emitting layer, and drying treatment to obtain the second functional layer. When the second functional layer includes a plurality of thin film layers, each thin film layer is sequentially prepared on the quantum dot light-emitting layer.

In some embodiments, the bottom electrode substrate is an anode substrate, the second functional layer is an electronic functional layer, and the electronic functional layer is an electron transport layer. In this case, preparing the second functional layer on the quantum dot light-emitting layer includes: forming an electron transport material on the quantum dot light-emitting layer, and preparing the electron transport layer.

In some embodiments, the bottom electrode substrate is an anode substrate, the second functional layer is an electronic functional layer, and the electronic functional layer includes an electron injection layer and an electron transport layer. In this case, preparing the second functional layer on the quantum dot light-emitting layer includes: forming an electron injection material on the quantum dot light-emitting layer to prepare an electron injection layer; forming an electron transport material on the electron injection layer to prepare an electron transport layer .

In some embodiments, the bottom electrode substrate is a cathode substrate, the second functional layer is a hole functional layer, and the hole functional layer includes a hole injection layer and a hole transport layer. In this case, preparing the second functional layer on the quantum dot light-emitting layer includes: forming a hole injection material on the quantum dot light-emitting layer to prepare a hole injection layer; forming a hole transport material on the hole injection layer, A hole transport layer is prepared.

The top electrode is prepared on the second functional layer, and can be prepared by conventional methods, such as evaporation.

In the quantum dot light-emitting device of the stacked structure, the carriers are injected into the light-emitting layer through the cathode and the anode through the transport layer for composite light emission. The material of the light-emitting layer is composed of inorganic nanoparticles and surface organic ligands with a core-shell structure. The holes need to cross the interface barriers of the electron transport layer/light-emitting layer and the hole transport layer/light-emitting layer, respectively. After passing through the organic ligands on the surface of the quantum dots, they are injected into the core of the quantum dots through the shell layer for composite light emission. The carrier needs to overcome the interface barrier, surface organic ligands and shell resistance, and the number of carriers effectively injected into the light-emitting core is proportional to the performance of the quantum dot light-emitting diode device.

The thin film morphology of quantum dot light-emitting diode devices and the performance of quantum dot light-emitting diodes are greatly affected by organic ligands in the light-emitting layer of quantum dots. In particular, since organic ligands are insulating and non-conductive substances, longer organic ligands will reduce Efficiency of charge injection and transport in quantum dot light-emitting diode devices. In view of this, in the process of preparing the quantum dot light-emitting diode device in the examples of the present application, the formation of quantum dots with longer organic ligands with 4-12 carbon atoms on the surface is improved by performing heat treatment during or after the device preparation process performance of the light-emitting layer. Specifically, on the one hand, through heat treatment, the quantum dots in the light-emitting layer, the organic ligands of the light-emitting layer and the adjacent functional layers on the upper and lower sides can be partially fused at the interface, which effectively optimizes the quantum dots and their functions. On the other hand, heat treatment shortens the distance between the functional layer and the light-emitting host, reduces the insulation of organic ligands, improves the efficiency of carrier injection and transmission, and reduces the internal equivalent resistance of the device. Improve the stability and reliability of the device in the working state; at the same time, the quantum dots distributed in the light-emitting layer can more uniformly fill the existing space vacancies under thermal induction, increasing the flatness of the quantum dot light-emitting layer, which can effectively avoid The electrons and holes are directly recombined through the quantum dot film layer, thereby improving the device performance.

In some embodiments, the temperature of the heating treatment is 60°C to 150°C, and the heating time is 1 to 120 min. Although the thickness of the functional layer ranges from nanometers to micrometers, the loss in the heat transfer process makes the effect of fusion of the upper and lower interfaces of the quantum dots different. Therefore, the heating temperature and time need to be changed according to the thickness of the quantum dot light-emitting layer. Specifically, in a quantum dot light-emitting diode device, the thickness of the light-emitting layer affects the exciton concentration in the light-emitting recombination region and the film formation quality between the light-emitting layer and the interface. Different thicknesses of the light-emitting layer are introduced into the heat treatment process. And the quality of the light-emitting layer and the interface film formation are optimized and improved.

When the thickness of the quantum dot light-emitting layer is thick, the interface between the light-emitting layer and the upper and lower functional layers requires a relatively higher heating plate temperature and a longer processing time, resulting in poor device performance. At the same time, it may cause light emission at high temperatures Layer quantum dots and functional layer materials on the upper and lower sides are destroyed. When the thickness of the quantum dot light-emitting layer is reduced, the temperature difference between the interface of the upper transport layer and the interface of the lower transport layer is gradually reduced, and the heat loss between the quantum dot stack layers is reduced, and the required heating temperature and time are reduced. Therefore, in some embodiments, the thickness of the quantum dot light-emitting layer is 8-30 nm, the temperature of the heating treatment is 80-140° C., and the heating time is 1-30 min. The spacing of the quantum dots stacked in the light-emitting layer is determined by the length of the surface ligands, and the light-emitting layer and the adjacent upper and lower transport layers are also separated by the surface ligands. When the thickness of the quantum dot light-emitting layer is within the above range, the heating can be effectively improved. effect achieved. At this time, driven by the heat transferred from the outside, the transport layer adjacent to the light-emitting layer is partially fused through the surface organic ligands.

It should be noted that, in a quantum dot light-emitting device with a stacked structure, since the light-emitting layer in the device structure uses red, green, and blue quantum dot materials with different particle sizes, the interface generated by the difference in the energy level structure of the light-emitting layer material is The potential barriers are different, resulting in different carrier injection efficiencies and large differences in the level of excitons for effective recombination inside the light-emitting layer. In the embodiment of the present application, the exciton concentration in the light-emitting region is adjusted by optimizing the thickness of the light-emitting layer, and a heat treatment process is introduced to improve the spatial arrangement of the stacked quantum dots and the interface morphology between the light-emitting layer and the adjacent transmission layer, and further improve the quantum dots. Point light-emitting diode optoelectronic properties. In some embodiments, the quantum dot light-emitting layer is a red light quantum dot light-emitting layer, and the particle size of the red light quantum dots is 10-16 nm; in some embodiments, the quantum dot light-emitting layer is a green light quantum dot light-emitting layer, and the green light quantum dots The particle size is 8-12 nm; in some embodiments, the quantum dot light-emitting layer is a blue quantum dot light-emitting layer, and the particle size of the blue quantum dots is 5-10 nm. On this basis, the thickness of the light-emitting layer of the quantum dot light-emitting diode device is based on the particle size of the quantum dots used.

During the research, the inventors found that growing a gradient wide-bandgap shell on the outer layer of the selected quantum dot core helps to confine the excitons of the quantum dot core while reducing the potential barrier of charge injection into the light-emitting core. The outer layer of the crystal core is selected from the shell layer material with suitable lattice matching degree and gradient band gap width, which can avoid defects caused by lattice stress and reduce the loss of non-radiative recombination energy. Therefore, in some embodiments, the quantum dot material is Cd _x Zn _1-x Se/ZnSe _1-y S _y /ZnS, wherein the values of x and y satisfy: 0≤x≤1, 0≤y≤1 . By adjusting the values of x and y, the wavelength interval can be set between 450-650nm. In one implementation, the quantum dot light-emitting core Cd _x Zn _1-x Se, when x=0.2, the wavelength is about 465nm; when x=0.35, the wavelength is about 530nm; when x=0.6, the wavelength is about 620nm; is the red, green and blue quantum dot light-emitting cores used in the examples of the present application. In the outer layer of the luminescent core of the quantum dot, a ZnSe _1-y S _y alloy shell layer with gradient changes is grown. At the beginning, y=0, that is, the ZnSe shell layer close to the crystal nucleus has a high lattice matching degree with the CdZnSe core. Growth, with y values ranging from 0 to 1, gradually increases the ZnS composition in the shell until a thinner ZnS shell grows in the outermost layer. The resulting quantum dot structure, through the coating of the shell layer, realizes the confinement of the excitons of the crystal nucleus, and at the same time, it also reduces the resistance of the wide band gap barrier of the shell layer to the charge injection into the crystal nucleus as much as possible, which can effectively realize the shell layer. The effect of the layer on the protection of the crystal nucleus will not have a great influence on the charge injection.

In the examples of the present application, the content of ligands on the surface of the quantum dots has a great influence on the selection of the heat treatment process. The higher the content of surface ligands, the greater the steric hindrance of the quantum dots, and the more difficult it is to produce a significant fusion effect at the interface. In some embodiments, in the quantum dot material, the mass percentage content of organic ligands is 5% to 20%. If the mass percentage of organic ligands exceeds 20%, the density of organic ligands wrapped in the outer layer of the quantum dots is too large, and the fusion process of the interface between the light-emitting layer and the adjacent functional layer such as the transport layer is difficult to occur, and it is impossible to improve the interface potential. In addition, the existence of excess surface organic ligands between quantum dots and quantum dots will increase the difficulty of charge transfer between quantum dots, resulting in high device operating voltage and poor optoelectronic performance. When the mass percentage of the ligand is less than 5%, the dispersibility of the quantum dots in the solvent will also decrease sharply.

In the embodiments of the present application, by heating the device prepared with the quantum dot light-emitting layer, the distance between the functional layers can be shortened, and the efficiency of carrier injection and transmission can be improved. At the same time, the quantum dots distributed in the quantum dot light-emitting layer can more uniformly fill the existing space vacancies under thermal induction, increase the flatness of the quantum dot light-emitting layer, and effectively prevent electrons and holes from tunneling through the quantum dot film layer directly. recombination, thereby improving device performance. It should be understood that the device to be subjected to heat treatment in the embodiments of the present application refers to a device prepared with a quantum dot light-emitting layer, which may be a device after the quantum dot light-emitting layer is prepared, or a device after the second functional layer is prepared on the quantum dot light-emitting layer. The device can also be prepared with a bottom electrode, a first functional layer, a quantum dot light-emitting layer, a second functional layer and a top electrode.

In the embodiment of the present application, there may be multiple options for the time node of the heating process. In some embodiments, the heat treatment may be performed after the quantum dot light-emitting layer is prepared on the first functional layer, that is, the heat treatment occurs after the quantum dot light-emitting layer is prepared or before the top electrode is prepared. In some embodiments, the quantum dot light-emitting layer may be prepared on the first functional layer, and heating treatment may be performed after the second functional layer is prepared on the quantum dot light-emitting layer, that is, the heating treatment occurs after preparing the second functional layer or preparing before the top electrode. In some embodiments, the quantum dot light-emitting layer may be prepared on the first functional layer, the second functional layer may be prepared on the quantum dot light-emitting layer, and the top electrode may be prepared on the second functional layer, followed by heat treatment, that is, heat treatment occurs after the preparation of the top electrode. In some embodiments, after preparing the top electrode and before encapsulating the quantum dot light emitting diodes, the resulting device is subjected to heat treatment; in some embodiments, after preparing the top electrode and encapsulating the quantum dot light emitting diodes, the resulting device is subjected to heat treatment. The device is heat treated.

In the embodiment of the present application, the heating method of the heating treatment may be an additive method such as hot plate heating, oven heating, and infrared heating. The hot plate heating has a uniform and stable heating system. In some embodiments, the heating process is performed by means of hot plate heating, so as to reduce the heat difference obtained within the quantum dot light-emitting layer and the adjacent upper and lower interfaces. In some embodiments, when the quantum dot light-emitting diode is a positive bottom-emitting device, it sequentially includes a laminated glass substrate, an ITO anode, a hole injection layer, a hole transport layer, a quantum dot light-emitting layer, an electron transport layer and a cathode, And when the quantum dot light-emitting layer is prepared and heated with a hot plate, the hot plate is used as a heating tool, the glass substrate is placed on the heating surface of the hot plate, and the heat is transmitted through the glass substrate, the ITO anode, the hole injection layer and the hole. layer, transfer to the hole transport layer/light-emitting layer interface, and then reach the light-emitting layer/electron transport layer interface through the interior of the light-emitting layer.

In some embodiments, after completing the preparation of the top electrode, the method further includes encapsulating the obtained light-emitting diode. Of course, the heat treatment can be performed after the device is packaged.

The following description will be given in conjunction with specific embodiments.

Example 1

A preparation method of a quantum dot light-emitting diode, comprising:

PEDOT:PSS was spin-coated on the anode ITO 1 to prepare hole injection layer 2; TFB was spin-coated on hole injection layer 2 to prepare hole transport layer 3; Cd _0.6 Zn _0.4 Se was spin-coated on hole transport layer 3 /ZnSeS/ZnS red quantum dots, Cd _0.6 Zn _0.4 Se/ZnSeS/ZnS red quantum dots The surface ligand is octanethiol, and the mass percentage of the ligand is 8% to prepare quantum dot light-emitting layer 4; emit light in the quantum dots ZnO is spin-coated on layer 4 to prepare electron transport layer 5; Al is evaporated to prepare cathode 6, which is packaged to form a quantum dot electroluminescent device. Among them, the electroluminescence wavelength of the red quantum dots is 630 nm, the half-peak width is 22 nm, the particle size is 14 nm, and the film thickness of the quantum dot light-emitting layer is 28 nm.

The packaged devices were placed on a hot plate at 100°C for 30 minutes.

In Example 1, before the heating treatment, the stacking of quantum dots in the light-emitting layer in the device structure is shown in Figure 2, and after the heating treatment, the schematic diagram of the interface fusion between the light-emitting layer and the adjacent transport layer in the device structure is shown in Figure 3.

Example 2

A preparation method of a quantum dot light-emitting diode is different from Embodiment 1 in that the quantum dot material in the quantum dot light-emitting layer is Cd _0.35 Zn _0.65 Se/ZnSeS/ZnS green quantum dots, and the surface ligands of the quantum dots are positive Octylamine, the mass percentage of the ligand is 15%, the electroluminescence wavelength of the green quantum dot is 533nm, the half-peak width is 25nm, the particle size is 10nm, and the film thickness of the quantum dot light-emitting layer is 20nm; Cd _0.35 Zn _0.65 Se/ZnSeS/ZnS green quantum dots were spin-coated on the transport layer, and after preparing the quantum dot light-emitting layer, the samples were placed on a hot plate at 120 °C for 20 min.

Example 3

A preparation method of a quantum dot light-emitting diode is different from Embodiment 1 in that the quantum dot material in the quantum dot light-emitting layer is Cd _0.2 Zn _0.8 Se/ZnSeS/ZnS blue quantum dots, and the surface ligands of the quantum dots are Dodecanethiol, the mass percentage of the ligand is 10%, the electroluminescence wavelength of the blue quantum dot is 473nm, the half-peak width is 22nm, the particle size is 8nm, and the film thickness of the quantum dot light-emitting layer is 20nm; and Cd _0.2 Zn _0.8 Se/ZnSeS/ZnS blue quantum dots were spin-coated on the hole transport layer, and after preparing the quantum dot light-emitting layer, the samples were placed on a hot plate at 130 °C for 30 min.

Comparative Example 1

The preparation method of the quantum dot light-emitting diode device of the comparative example 1 is substantially the same as that of the embodiment 1, and the difference is only that: the preparation of the device is completed, and no heating treatment is performed.

Comparative Example 2

The preparation method of the quantum dot light-emitting diode device of Comparative Example 2 is substantially the same as that of Example 1, except that the mass percentage of the ligand is 25%.

Comparative Example 3

The preparation method of the quantum dot light-emitting diode device of Comparative Example 3 is substantially the same as that of Example 1, except that the temperature of the heating treatment is 50° C. and the heating time is 100 min.

The photoelectric properties and lifespan of the quantum dot light-emitting diode devices prepared in Examples 1-3 and Comparative Examples 1-3 were tested, and the lifespan test of the devices was performed using a 128-channel lifespan test system customized by Guangzhou New Vision Company. The system architecture is to drive the QLED with a constant voltage and constant current source, and test the change of voltage or current; the photodiode detector and test system test the change of the brightness (photocurrent) of the QLED; the luminance meter tests and calibrates the brightness (photocurrent) of the QLED. The test results are shown in Table 1 below, where EL represents the electroluminescence peak position of the quantum dot light emitting diode device, FWHM represents the half-peak width, EQE represents the external quantum efficiency of the quantum dot light emitting diode device, CE represents the current efficiency of the quantum dot light emitting diode device, T ₉₅ @1000nit represents the working life of the quantum dot light-emitting diode device in constant current mode, that is, the time it takes for the brightness to decay to 95% at 1000nit.

Table 1

	EL (nm) EL (nm)	FWHM (nm) FWHM (nm)	EQE (%) EQE (%)	CE (cd/A) CE (cd/A)	T95@1000nit (h) T95@1000nit (h)
实施例 1 Example 1	630 630	22 twenty two	19 19	21 twenty one	2200 2200
实施例 2 Example 2	533 533	25 25	18 18	73 73	4500 4500
实施例 3 Example 3	473 473	22 twenty two	15 15	12 12	85 85
对比例 1 Comparative Example 1	630 630	22 twenty two	10 10	11 11	450 450
对比例 2 Comparative Example 2	630 630	22 twenty two	5 5	5.5 5.5	60 60
对比例 3 Comparative Example 3	630 630	22 twenty two	11 11	12 12	530 530

It can be seen from Table 1 that, compared with the comparative example, the quantum dot light-emitting diodes prepared in the examples of the present application have better external quantum efficiency and service life, which is attributed to: after heating the device after the quantum dot light-emitting layer is prepared , to promote the fusion of the organic ligands on the surface of the stacked quantum dots and the adjacent functional layers at the interface, effectively increase the transport efficiency of carriers in the light-emitting layer and the interface, reduce the internal equivalent resistance of the device, and improve the device's working state. stability and reliability; at the same time, a buffer layer is formed at the interface between the quantum dot light-emitting layer and the adjacent functional layers on both sides, which can flatten the interface barrier between the light-emitting layer and the adjacent functional layers on both sides, which is conducive to loading The carrier injection efficiency is improved, and the optoelectronic performance of the device is improved.

The above descriptions are only preferred embodiments of the present application, and are not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present application shall be included in the protection of the present application. within the range.

Claims

A method for preparing a quantum dot light-emitting diode, comprising the following steps:

providing a bottom electrode substrate, and preparing a first functional layer on the bottom electrode substrate;

forming a quantum dot material with organic ligands bound on the surface on the first functional layer to prepare a quantum dot light-emitting layer, and the number of carbon atoms of the organic ligand is 4-12;

preparing a second functional layer on the quantum dot light-emitting layer, and preparing a top electrode on the second functional layer to prepare a quantum dot light-emitting diode;

heat treatment of the device;

Wherein, the bottom electrode substrate is an anode substrate, the first functional layer is a hole functional layer, the second functional layer is an electron functional layer, and the top electrode is a cathode; or

The bottom electrode substrate is a cathode substrate, the first functional layer is an electron functional layer, the second functional layer is a hole functional layer, and the top electrode is an anode.
The method for preparing a quantum dot light-emitting diode according to claim 1, wherein the temperature of the heat treatment is 60°C to 150°C, and the heating time is 1 to 120 minutes.
The method for preparing a quantum dot light-emitting diode according to claim 1, wherein, in the quantum dot material, the mass percentage of the organic ligand is 5% to 20%.
The method for preparing a quantum dot light-emitting diode according to any one of claims 1 to 3, wherein the quantum dot light-emitting layer has a thickness of 8 to 30 nm, and the heat treatment temperature is 80° C. to 140° C. Heating time 1~30min.
The method for preparing a quantum dot light-emitting diode according to claim 4, wherein the quantum dot light-emitting layer is a red light quantum dot light-emitting layer, and the particle size of the red light quantum dots in the red light quantum dot light-emitting layer is 10 -16nm; and/or

The quantum dot light-emitting layer is a green light quantum dot light-emitting layer, and the particle size of the green light quantum dots in the green light quantum dot light-emitting layer is 8-12 nm; and/or

The quantum dot light emitting layer is a blue quantum dot light emitting layer, and the particle size of the blue quantum dots in the blue light quantum dot light emitting layer is 5-10 nm.
The method for preparing a quantum dot light-emitting diode according to any one of claims 1 to 3, wherein the heating treatment occurs after preparing the quantum dot light-emitting layer or before preparing the second functional layer.
The method for preparing a quantum dot light-emitting diode according to any one of claims 1 to 3, wherein the heating treatment occurs after preparing the second functional layer or before preparing the top electrode.
The method for manufacturing a quantum dot light-emitting diode according to any one of claims 1 to 3, wherein the heating treatment occurs after the top electrode is prepared.
The method for preparing a quantum dot light-emitting diode according to any one of claims 1 to 3, wherein the organic ligand is selected from ligands containing a carboxyl group, an amine group, a sulfhydryl group and a phosphine group.
The method for preparing a quantum dot light-emitting diode according to any one of claims 1 to 3, wherein the quantum dot material is selected from Cd x Zn 1-x Se/ZnSe 1-y S y /ZnS, wherein x The values of , y satisfy: 0≤x≤1, 0≤y≤1.
The method for preparing a quantum dot light-emitting diode according to any one of claims 1 to 3, wherein the preparation method further comprises encapsulating the prepared quantum dot light-emitting diode, and the heating treatment is performed on the quantum dot light-emitting diode. After the quantum dot light-emitting diode is encapsulated.
The method for preparing a quantum dot light-emitting diode according to any one of claims 1 to 3, wherein the heating treatment method is hot plate heating, oven heating or infrared heating.
The method for preparing a quantum dot light-emitting diode according to any one of claims 1 to 3, wherein the electronic functional layer comprises at least one of an electron injection layer, an electron transport layer and a hole blocking layer.
The method for preparing a quantum dot light-emitting diode according to any one of claims 1 to 3, wherein the hole functional layer comprises at least one of a hole injection layer, a hole transport layer and an electron blocking layer.
The method for preparing a quantum dot light-emitting diode according to any one of claims 1 to 3, wherein the quantum dot material comprises an inorganic nanoparticle body and an organic ligand bound on the surface of the inorganic nanoparticle body.
The method for preparing a quantum dot light-emitting diode according to any one of claims 1 to 3, wherein the anode is selected from indium tin oxide, fluorine-doped tin oxide, indium zinc oxide, graphene, carbon nanotubes one or more of.
The method for preparing a quantum dot light-emitting diode according to claim 14, wherein the material of the hole injection layer is PEDOT: PSS, nickel oxide, molybdenum oxide, tungsten oxide, vanadium oxide, molybdenum sulfide, tungsten sulfide, One or more of copper oxides.
The method for preparing a quantum dot light-emitting diode according to claim 14, wherein the material of the hole transport layer is selected from the group consisting of PVK, Poly-TPD, CBP, TCTA and TFB. one or more.
The method for preparing a quantum dot light-emitting diode according to claim 13, wherein the material of the electron transport layer is n-type ZnO, TiO 2 , SnO, Ta 2 O 3 , AlZnO, ZnSnO, InSnO, Alq 3 , One or more of Ca, Ba, CsF, LiF, CsCO3 .
The method for preparing a quantum dot light-emitting diode according to any one of claims 1 to 3, wherein the cathode is selected from one or more of Al, Ca, Ba, and Ag.