A hole transport thin film, an optoelectronic device and its preparation method, and a display device.

Abstract

This application discloses a hole transport thin film, an optoelectronic device, a fabrication method, and a display device. The hole transport thin film includes a first polymer and a second polymer, with the content of the second polymer increasing or decreasing from one side of the thin film to the other. The first polymer is a block copolymer formed by fluorene-containing groups and triphenylamine-containing groups, and the second polymer is also a block copolymer formed by fluorene-containing groups and triphenylamine-containing groups. The molar fraction of triphenylamine-containing groups in the second polymer is less than the molar fraction of triphenylamine-containing groups in the first polymer, and all or part of the hydrogen atoms in the second polymer are replaced by fluorine atoms. The hole transport thin film of this application does not have a material interface, eliminating the problem of interfacial miscibility and improving the current efficiency of the optoelectronic device.

Description

Technical Field

[0001] This application relates to the field of display technology, and in particular to a hole transport thin film, an optoelectronic device and its preparation method, and a display device. Background Technology

[0002] Optoelectronic devices have wide applications in new energy, sensing, communication, display and lighting fields, such as solar cells, photodetectors, organic electroluminescent devices (OLEDs or quantum dot electroluminescent devices (QLEDs)).

[0003] Traditional optoelectronic devices mainly consist of an anode, a hole injection layer, a hole transport layer (i.e., a hole transport film), a light-emitting layer, an electron transport layer, an electron injection layer, and a cathode. Under the influence of an electric field, holes generated at the anode and electrons generated at the cathode move and are injected into the hole transport layer and electron transport layer, respectively, eventually migrating to the light-emitting layer. When the two meet in the light-emitting layer, they generate excitons, which excite the light-emitting molecules to ultimately produce visible light.

[0004] Since hole transport is carried out by organic materials and electron transport by inorganic materials, the electron mobility of inorganic nanoparticles is much greater than that of holes. Therefore, hole transport materials with high hole mobility are needed to match this. However, quantum dot luminescent materials generally have deep valence band energy levels. A single organic hole transport material is insufficient to meet the energy level difference between the HOMO energy level of the anode or hole injection layer and the valence band of the quantum dot. Theoretically, using double or multilayer hole transport layers can improve the above problem, but the actual current efficiency of the device is not high. Summary of the Invention

[0005] In view of this, this application provides a hole transport thin film, an optoelectronic device and its preparation method, and a display device, aiming to improve the problem of low current efficiency of optoelectronic devices made of double-layer or multi-layer hole transport materials in related technologies.

[0006] The embodiments of this application are implemented as follows: a hole transport film, the hole transport film comprising a first polymer and a second polymer, wherein the content of the second polymer increases or decreases from one side of the hole transport film to the other side.

[0007] The first polymer is a block copolymer formed by fluorene-containing groups and triphenylamine-containing groups, and the second polymer is a block copolymer formed by fluorene-containing groups and triphenylamine-containing groups; wherein, the molar fraction of triphenylamine-containing groups in the second polymer is less than the molar fraction of triphenylamine-containing groups in the first polymer, and all or part of the hydrogen atoms in the second polymer are replaced by fluorine atoms.

[0008] Optionally, in some embodiments of this application, the molar fraction of triphenylamine-containing groups in the first polymer is greater than or equal to 50% and less than 100%.

[0009] The molar fraction of triphenylamine-containing groups in the second polymer is less than 50% and greater than 0.

[0010] Optionally, in some embodiments of this application, the weight-average molecular weight of the block copolymer is greater than or equal to 50,000 and less than or equal to 250,000.

[0011] Optionally, in some embodiments of this application, the block copolymer has the following general structural formula:

[0012]

[0013] Where n>0, m≥0, p≥0, R1~R6 are the same or different groups, and R1~R6 are C1~C20 alkyl, aromatic or heteroaromatic groups.

[0014] Optionally, in some embodiments of this application, the HOMO energy level of the first polymer is greater than or equal to -5.3 eV and less than -4.8 eV;

[0015] The highest occupied molecular orbital energy level of the second polymer is greater than -5.8 eV and less than -5.3 eV.

[0016] Optionally, in some embodiments of this application, the weight percentage of the first polymer is 1-20%, and the weight percentage of the second polymer is 80-99%.

[0017] This application also provides a method for fabricating an optoelectronic device, comprising the following steps:

[0018] A material solution comprising a first polymer and a second polymer is provided, wherein the first polymer is a block copolymer formed of a fluorene-containing group and a triphenylamine-containing group, the second polymer is a block copolymer formed of a fluorene-containing group and a triphenylamine-containing group, wherein the molar fraction of the triphenylamine-containing group in the second polymer is less than the molar fraction of the triphenylamine-containing group in the first polymer, and all or part of the hydrogen atoms in the second polymer are replaced by fluorine atoms;

[0019] A substrate is provided, on which an anode is formed. A material solution is disposed on the anode and subjected to heat treatment to obtain a hole transport film.

[0020] A cathode is fabricated on the hole transport film.

[0021] Optionally, in some embodiments of this application, the heat treatment step includes: performing a first heat treatment first, and then performing a second heat treatment;

[0022] Wherein, the temperature of the first heat treatment is less than 100℃ and greater than or equal to 40℃, and the temperature of the second heat treatment is greater than or equal to 100℃ and less than or equal to 250℃.

[0023] Accordingly, this application also provides an optoelectronic device, including a cathode, a light-emitting layer, a hole transport film and an anode stacked sequentially. The hole transport film includes a first side and a second side, with the first side facing the anode and the second side facing the light-emitting layer. The hole transport film includes a first polymer and a second polymer, and from the first side to the second side, the content of the first polymer decreases and the content of the second polymer increases.

[0024] The first polymer is a block copolymer formed by fluorene-containing groups and triphenylamine-containing groups, and the second polymer is a block copolymer formed by fluorene-containing groups and triphenylamine-containing groups, wherein the molar fraction of triphenylamine-containing groups in the second polymer is less than the molar fraction of triphenylamine-containing groups in the first polymer, and all or part of the hydrogen atoms in the second polymer are replaced by fluorine atoms.

[0025] Optionally, in some embodiments of this application, the thickness of the hole transport film is 10-50 nm.

[0026] Accordingly, this application also provides a display device, which includes the above-mentioned optoelectronic device.

[0027] The hole transport film of this application includes a first polymer and a second polymer, and the content of the second polymer increases or decreases from one side of the hole transport film to the other side. The first polymer is a block copolymer formed by fluorene-containing groups and triphenylamine-containing groups, and the second polymer is a block copolymer formed by fluorene-containing groups and triphenylamine-containing groups. The molar fraction of triphenylamine-containing groups in the second polymer is less than the molar fraction of triphenylamine-containing groups in the first polymer, and all or part of the hydrogen atoms in the second polymer are replaced by fluorine atoms.

[0028] In the hole transport film of this embodiment, during film formation, the second polymer, due to the presence of fluorine atoms, tends to be located on the upper layer of the hole transport film. This is because fluorine atoms have high electronegativity, small atomic radii, short CF bonds with bond energies as high as 500 kJ / mol, and the mutual repulsion between adjacent fluorine atoms causes them to not lie in the same plane, but rather to be distributed helically along the carbon chain. Especially in perfluorocarbon chains, the sum of the van der Waals radii of two fluorine atoms is approximately 0.27 nm, essentially surrounding and filling the CCC bond. This almost gapless spatial barrier prevents any atom or group from entering and breaking the CCC bond. Therefore, during the hole transport film formation process, fluorine-containing groups tend to accumulate at the interface between the hole transport film and air (on the side closer to the light-emitting layer) and extend into the air, thus forming a gradient molecular structure from the bottom layer (the side closer to the hole injection layer) to the top layer (the side closer to the light-emitting layer). The closer to the top layer, the higher the content of the second polymer; the closer to the bottom layer, the higher the content of the first polymer. Because the hole transport film has a gradient molecular structure, unlike traditional bilayer transport films formed by two transport films, there are no material interface or material miscibility issues between different transport film layers. Furthermore, since the first polymer contains a relatively large number of triphenylamine groups while the second polymer contains relatively few, the first polymer has a higher HOMO energy level, and the second polymer has a lower HOMO energy level. Corresponding to the gradient molecular structure from the bottom to the top of the film, the hole transport film forms a gradient energy level from high to low. The high HOMO energy level of the bottom layer matches the hole injection layer, facilitating the injection of holes into the hole transport film. The low HOMO energy level of the top layer reduces the energy level difference between the hole transport film and the light-emitting layer, making it easier for holes to cross the potential barrier between the hole transport film and the light-emitting layer to jump to the light-emitting layer. Therefore, the hole transport film of this embodiment can improve hole mobility, thereby improving the current efficiency of the corresponding optoelectronic device. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a schematic diagram of the structure of an optoelectronic device provided in an embodiment of this application;

[0031] Figure 2 This is a schematic flowchart of a method for fabricating an optoelectronic device according to an embodiment of this application;

[0032] Figure 3This is a schematic diagram of the energy levels of each functional layer of an optoelectronic device provided in Embodiment 1 of this application;

[0033] Figure 4 This is a schematic diagram of the energy levels of each functional layer of an optoelectronic device provided in Embodiment 2 of this application;

[0034] Figure 5 This is a schematic diagram of the energy levels of each functional layer of an optoelectronic device provided in Embodiment 3 of this application;

[0035] Figure 6 This is a schematic diagram of the energy levels of each functional layer of an optoelectronic device provided in Comparative Example 1. Detailed Implementation

[0036] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. In addition, it should be understood that the specific embodiments described herein are only for illustration and explanation of this application and are not intended to limit this application. In this application, unless otherwise stated, directional terms such as "upper" and "lower" specifically refer to the drawing directions in the accompanying drawings. In addition, in the description of this application, the term "including" means "including but not limited to". Various embodiments of the present invention 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 conciseness and should not be construed as a hard limitation on the scope of the present invention; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single values ​​within that range. For example, it should be assumed that the description of a range from 1 to 6 specifically discloses subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the range referred to.

[0037] In optoelectronic devices such as QLEDs, hole transport is carried out by organic materials while electron transport is carried out by inorganic materials. The electron mobility of inorganic nanoparticles is much greater than that of holes, thus requiring hole transport materials with high hole mobility to match them. However, quantum dot light-emitting materials generally have deep valence band energy levels, and a single organic hole transport material is insufficient to meet the energy level difference between the HOMO energy level of the anode or hole injection layer and the valence band of the quantum dot. Theoretically, using double or multilayer hole transport layers can solve the above problem, but the actual current efficiency of the device is not high.

[0038] Further research by the applicant revealed that the low current efficiency of devices with two or more hole transport layers is mainly due to interfacial solubility issues during the wet fabrication process of the two-layer hole transport layers. Based on this, this application provides the hole transport thin film described below to improve the low current efficiency of optoelectronic devices fabricated from two or more hole transport materials in related technologies.

[0039] This application provides a hole transport thin film 10, mainly used in optoelectronic devices 100. Please refer to... Figure 1 , Figure 1 This is a schematic diagram of the structure of an optoelectronic device provided in an embodiment of this application. The hole transport film 10 includes a first polymer and a second polymer, and the content of the second polymer increases from the bottom surface to the top surface of the hole transport film. The first polymer is a block copolymer formed by fluorene-containing groups and triphenylamine-containing groups, and the second polymer is a block copolymer formed by fluorene-containing groups and triphenylamine-containing groups. The molar fraction of triphenylamine-containing groups in the second polymer is less than the molar fraction of triphenylamine-containing groups in the first polymer, and all or part of the hydrogen atoms in the second polymer are replaced by fluorine atoms.

[0040] It is understood that, during the film formation process of the hole transport film 10 in this embodiment, the second polymer, due to the presence of fluorine atoms, tends to be located on the upper layer of the hole transport film 10 (i.e.,...). Figure 1(The structure is for reference only). This is because fluorine atoms have high electronegativity, small atomic radii, short CF bonds, and bond energies as high as 500 kJ / mol. The mutual repulsion between adjacent fluorine atoms causes them to not lie in the same plane, but rather to be distributed helically along the carbon chain. Especially in perfluorocarbon chains, the sum of the van der Waals radii of two fluorine atoms is approximately 0.27 nm, essentially surrounding and filling the CCC bond. This almost gapless spatial barrier prevents any atom or group from entering and breaking the CCC bond. Therefore, during the hole transport film formation process, fluorine-containing groups tend to accumulate at the interface between the hole transport film 10 and air (on the side near the light-emitting layer) and extend into the air, thus forming a gradient molecular structure from the bottom layer (the side near the hole injection layer) to the top layer (the side near the light-emitting layer). The closer to the top layer, the higher the content of the second polymer; the closer to the bottom layer, the higher the content of the first polymer. Since the hole transport film has a gradient molecular structure, unlike the traditional bilayer transport film formed by two transport films, there is no material interface or material miscibility problem between different transport film layers. Meanwhile, since the first polymer contains a relatively large number of triphenylamine groups and the second polymer contains a relatively small number of triphenylamine groups, the first polymer has a higher highest occupied molecular orbital (HOMO) energy level, while the second polymer has a lower HOMO energy level. Corresponding to the gradient molecular structure from the bottom to the top of the film, the hole transport film 10 forms a gradient energy level from high to low from the bottom to the top. The high HOMO energy level of the bottom layer matches the hole injection layer, facilitating the injection of holes from the hole injection layer into the hole transport film 10. The low HOMO energy level of the top layer reduces the energy level difference between the hole transport film 10 and the light-emitting layer, making it easier for holes to cross the potential barrier between the hole transport film 10 and the light-emitting layer and jump to the light-emitting layer. Therefore, the hole transport film 10 of this embodiment can improve hole mobility, thereby improving the current efficiency of the corresponding optoelectronic device.

[0041] In one embodiment, the hole transport film 10 is a composition of a first polymer and a second polymer. The first polymer is a block copolymer formed by fluorene-containing groups and triphenylamine-containing groups, and the second polymer is a block copolymer formed by fluorene-containing groups and triphenylamine-containing groups. The molar fraction of triphenylamine-containing groups in the second polymer is less than the molar fraction of triphenylamine-containing groups in the first polymer, and all or part of the hydrogen atoms in the second polymer are replaced by fluorine atoms. That is, the hole transport film 10 is made only of the first polymer and the second polymer. It is understood that the hole transport film 10 may include other materials besides the first polymer and the second polymer, such as high thermal conductivity materials to enhance the heat dissipation of the hole transport film 10, or magnetic materials to enhance the magnetism of the hole transport film 10.

[0042] In one embodiment, the block copolymer in the hole transport film 10 has the following general structural formula:

[0043]

[0044] Where n>0, m≥0, p≥0, R1~R6 are the same or different groups, and R1~R6 are C1~C20 alkyl, aromatic or heteroaromatic groups.

[0045] It is understood that R1 to R6 can be the same substituent, for example, they can be alkyl, aromatic, or heteroaromatic groups simultaneously. R1 to R6 can also be different substituents. For ease of description, the copolymer repeating unit formed by the fluorene-containing group and the triphenylamine-containing group is named unit A, the homopolymer repeating unit formed by the fluorene-containing group is named unit B, and the homopolymer repeating unit formed by the triphenylamine-containing group is named unit C. It is understood that the block copolymer of this embodiment can include only unit A, or it can be a block copolymer including units A and B, or it can be a block copolymer including units A and C, or it can be a block copolymer including units A, B, and C simultaneously. This application does not impose any particular limitation; the molar fraction of the triphenylamine-containing group can be determined according to the HOMO energy level requirements, and then the corresponding polymer structure can be selected.

[0046] It should be noted that the block copolymer structures of the first and second polymers can both refer to the above structural formulas. However, the values ​​of n, m, and p in the structures of the first and second polymers are independent of each other, which allows the molar fractions of the triphenylamine-containing groups in the first and second polymers to be different. Furthermore, the selection of substituents (R1 to R6) in the structures of the first and second polymers is also independent; that is, the substituents in the structures of the first and second polymers can be the same or different, but the first polymer does not contain fluorine atoms.

[0047] In one embodiment, the block copolymer in the hole transport film 10 has a weight-average molecular weight greater than or equal to 50,000 and less than or equal to 250,000. The degree of polymerization of the block copolymer has a significant impact on interfacial miscibility. When the weight-average molecular weight of the block copolymer is low, the hole transport film 10 may become interfacially miscible with adjacent functional films. When the weight-average molecular weight of the block copolymer is too high, the solubility of the first and second polymers of the hole transport film 10 will decrease, thereby affecting the film-forming performance. For example, when the weight-average molecular weight of the block copolymer is low, the hole transport film 10 may become interfacially miscible with the hole injection layer, or the hole transport film 10 may become interfacially miscible with the light-emitting layer. Therefore, the weight-average molecular weight of the block copolymer is preferably greater than or equal to 50,000 to avoid interfacial miscibility between the hole transport film 10 and adjacent functional films.

[0048] In one embodiment, the HOMO level of the first polymer is greater than or equal to -5.3 eV and less than -4.8 eV, and the HOMO level of the second polymer is greater than -5.8 eV and less than -5.3 eV. The first polymer is mainly located on the side closer to the hole injection layer on the hole transport film 10. When the HOMO level of the first polymer is between -5.3 eV and -4.8 eV, the bottom layer of the hole transport film 10 can better match the HOMO level of the hole injection layer, thereby improving the hole injection efficiency from the hole injection layer to the hole transport film 10. The second polymer is mainly located on the side closer to the light-emitting layer on the hole transport film 10. When the HOMO level of the second polymer is between -5.8 eV and -5.3 eV, the energy level difference between the hole transport film 10 and the light-emitting layer can be reduced when the first polymer is used alone as the hole transport film 10, making it easier for holes to overcome the potential barrier from the hole transport film 10 to the light-emitting layer, thereby improving the hole migration efficiency.

[0049] In one embodiment, the molar fraction of triphenylamine-containing groups in the first polymer is greater than or equal to 50% and less than 100%, while the molar fraction of triphenylamine-containing groups in the second polymer is less than 50% and greater than 0. It should be noted that the higher the content of triphenylamine-containing units in the polymer, the higher the HOMO energy level of the polymer. For example, when the molar fraction of triphenylamine-containing units approaches 100%, i.e., p is much larger than n and m in the general formula of the block copolymer, the HOMO energy level of the block copolymer is close to the HOMO energy level of polytriphenylamine (-4.8 eV). When the molar fraction of triphenylamine-containing units is 0%, i.e., m is much larger than n and p in the general formula of the block copolymer, the HOMO energy level of the block copolymer is close to the HOMO energy level of polyfluorene (-5.8 eV). In the hole transport film 10 of this application, the molar fraction of triphenylamine-containing groups in the first polymer is greater than or equal to 50% and less than 100%. This allows the HOMO energy level of the hole transport film 10 near the hole injection layer to be between -5.3 eV and -4.8 eV, reducing the energy level difference between the hole transport film 10 and the hole injection layer to a suitable range, which is beneficial for improving hole injection efficiency. Similarly, the molar fraction of triphenylamine-containing groups in the second polymer is less than 50% and greater than 0. This allows the HOMO energy level of the hole transport film 10 near the light-emitting layer to be between -5.8 eV and -5.3 eV, reducing the energy level difference between the hole transport film 10 and the light-emitting layer to a suitable range, which is beneficial for improving hole migration efficiency.

[0050] In one embodiment, the weight percentage of the first polymer is 1-20%, and the weight percentage of the second polymer is 80-99%. Since the first polymer is mainly enriched on the lower side of the hole transport film 10, i.e., close to the hole injection layer, and the first polymer contains a high molar fraction of triphenylamine units, excessive addition of the first polymer would significantly affect the HOMO energy level of the upper layer, thereby affecting the efficiency of hole transitions to the light-emitting layer. Therefore, in this embodiment, the weight percentages of the first polymer and the second polymer are set to 1-20% and 80-99%, respectively.

[0051] This application also provides a method for fabricating an optoelectronic device. Please refer to [link to relevant documentation]. Figure 2 , Figure 2 This is a schematic flowchart of a method for fabricating an optoelectronic device according to an embodiment of this application. The fabrication method includes the following steps:

[0052] Step S21: Provide a material solution comprising a first polymer and a second polymer, wherein the first polymer is a block copolymer formed by fluorene-containing groups and triphenylamine-containing groups, the second polymer is a block copolymer formed by fluorene-containing groups and triphenylamine-containing groups, the molar fraction of triphenylamine-containing groups in the second polymer is less than the molar fraction of triphenylamine-containing groups in the first polymer, and all or part of the hydrogen atoms in the second polymer are replaced by fluorine atoms.

[0053] In this step, the first polymer and the second polymer can be first prepared into a polymer solution. For example, conventional organic solvents can be used to dissolve the first polymer and the second polymer, such as toluene, chlorobenzene, cyclohexylbenzene, methyl benzoate, ethyl benzoate, anisole, etc. The solvent can be a single type or a mixture of two or more different solvents.

[0054] In this embodiment, the order of adding the first polymer, the second polymer, and the solvent is not limited, as long as the three are fully mixed to obtain a polymer solution.

[0055] Step S22: Provide a substrate on which an anode is formed. Place the above-mentioned material solution on the anode and perform heat treatment to obtain a hole transport film.

[0056] In this step, there are no restrictions on the type of substrate. The substrate can be a conventionally used substrate, such as a rigid substrate made of glass, or a flexible substrate made of polyimide. The anode 40 can be made of one or more of metals, carbon materials, and metal oxides. For example, metals can be one or more of Al, Ag, Cu, Mo, Au, Ba, Ca, and Mg. Carbon materials can be one or more of graphite, carbon nanotubes, graphene, and carbon fibers. Metal oxides can be doped or undoped metal oxides, including one or more of ITO, FTO, ATO, AZO, GZO, IZO, MZO, and AMO. Composite electrodes can also include those with metal sandwiched between doped or undoped transparent metal oxides. Composite electrodes include, but are not limited to, one or more of AZO / Ag / AZO, AZO / Al / AZO, ITO / Ag / ITO, ITO / Al / ITO, ZnO / Ag / ZnO, ZnO / Al / ZnO, TiO2 / Ag / TiO2, TiO2 / Al / TiO2, ZnS / Ag / ZnS, ZnS / Al / ZnS, TiO2 / Ag / TiO2, and TiO2 / Al / TiO2. In one embodiment, an anode 40 is formed on a substrate, and a hole transport film 10 comprising a first polymer and a second polymer material is disposed on the anode 40. In another embodiment, an anode 40 and a hole injection layer 50 are formed on a substrate, and a hole transport film 10 comprising a first polymer and a second polymer material is disposed on the hole injection layer 50. If the optoelectronic device further includes other functional layers, then correspondingly, other functional layers may also be formed on the substrate.

[0057] The first polymer and the second polymer in this embodiment can be referred to the relevant descriptions in the above embodiments, and will not be repeated here.

[0058] Specifically, a solution method can be used to deposit a material solution comprising a first polymer and a second polymer onto a substrate. Solution methods include, but are not limited to, spin coating, drop coating, coating, inkjet printing, blade coating, dip coating, immersion coating, spray coating, roller coating, vapor deposition, or casting, etc., to obtain a wet film. Then, heat treatment is performed to obtain the hole transport film 10. Due to the presence of fluorine atoms, the second polymer tends to be located on the upper layer of the hole transport film 10 (i.e., with...). Figure 1 (Referring to the structure of the first polymer), thus the hole transport film 10 forms a gradient molecular structure from the bottom layer to the top layer. The closer to the top layer, the higher the content of the second polymer; the closer to the bottom layer, the higher the content of the first polymer. That is, the content of the second polymer increases from the side facing the anode to the side away from the anode.

[0059] In one embodiment, the heat treatment steps include: performing a first heat treatment and then performing a second heat treatment, wherein the temperature of the first heat treatment is less than 100°C and greater than or equal to 40°C, and the temperature of the second heat treatment is greater than or equal to 100°C and less than or equal to 250°C.

[0060] In the heat treatment process, the wet film on the substrate can first undergo a first heat treatment to evaporate the organic solvent in the wet film and form a hole transport film. Then, the hole transport film undergoes a second heat treatment at a temperature higher than the first heat treatment. This second heat treatment is used to eliminate residual stress within the hole transport film, thereby reducing the risk of layer deformation and cracking. For example, the temperature of the first heat treatment can be less than 100℃, such as 95℃, 80℃, 70℃, 60℃, 50℃, 40℃, etc. Higher temperatures result in faster drying of the wet film. Vacuum drying at room temperature can also be used. The temperature of the second heat treatment can be between 100℃ and 250℃, for example, 100℃, 130℃, 160℃, 180℃, 200℃, 220℃, 240℃, 250℃, etc. It is understandable that the second heat treatment can be an annealing process, which includes sequential heating, holding and cooling processes. For example, the dry hole transport film is heated to 220°C and held for 30 minutes, and then cooled to room temperature at a rate of 5°C / min.

[0061] In this embodiment, the thickness of the final hole transport film can be controlled and adjusted by controlling and adjusting conditions such as the solution concentration used in the solution method. The thickness of the hole transport film can range from 10 to 50 nm, such as 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 40 nm, and 50 nm. Taking spin coating as an example, the thickness of the hole transport film can be controlled by adjusting the solution concentration, spin coating speed, and spin coating time.

[0062] Step S23: Fabricate a cathode on a hole transport film.

[0063] The material of cathode 20 is a known cathode material in the art, and the material of anode 40 described above can be selected. This step will not be repeated. The thickness of cathode 20 is a known cathode thickness in the art, for example, it can be from 10nm to 200nm, such as 10nm, 35nm, 50nm, 80nm, 120nm, 150nm, 200nm, etc.

[0064] It should be noted that the anode 40, the light-emitting layer 30, the cathode 20, and other functional layers in this application can all be prepared using conventional techniques in the art, including but not limited to solution methods and deposition methods. Solution methods include, but are not limited to, spin coating, coating, inkjet printing, blade coating, dip-coating, immersion, spraying, roller coating, or casting. Deposition methods include chemical methods and physical methods. Chemical methods include, but are not limited to, chemical vapor deposition, continuous ion layer adsorption and reaction, anodic oxidation, electrolytic deposition, or co-precipitation. Physical methods include, but are not limited to, thermal evaporation coating, electron beam evaporation coating, magnetron sputtering, multi-arc ion plating, physical vapor deposition, atomic layer deposition, or pulsed laser deposition. When the anode 40, the light-emitting layer 30, the cathode 20, and other functional layers are prepared using solution methods, a drying process must be added.

[0065] It is understandable that the preparation method of optoelectronic devices may also include an encapsulation step. The encapsulation material may be acrylic resin or epoxy resin. The encapsulation may be machine encapsulation or manual encapsulation. Ultraviolet curing adhesive may be used. The concentration of oxygen and water in the environment where the encapsulation step is carried out is less than 0.1 ppm to ensure the stability of the optoelectronic device.

[0066] In this embodiment, a material solution containing a first polymer and a second polymer is deposited onto the anode 40 of a substrate to form a hole transport film. During film formation, the second polymer containing fluorine groups tends to accumulate at the interface between the hole transport film 10 and air (the side near the cathode) and extends into the air. Therefore, the hole transport film 10 forms a gradient molecular structure from the bottom layer (the side near the anode) to the top layer (the side near the cathode). The closer to the top layer, the higher the content of the second polymer; the closer to the bottom layer, the higher the content of the first polymer. Simultaneously, since the first polymer contains relatively more triphenylamine groups and the second polymer contains relatively fewer triphenylamine groups, the HOMO energy level of the first polymer is higher, and the HOMO energy level of the second polymer is lower. Corresponding to the gradient molecular structure of the film from the bottom layer to the top layer, the hole transport film 10 forms a gradient energy level from high to low from the bottom layer to the top layer. The high HOMO energy level of the bottom layer matches the anode, facilitating hole injection from the anode into the hole transport film 10. The low HOMO energy level of the top layer reduces the energy level difference between the hole transport film 10 and the light-emitting layer, making it easier for holes to cross the potential barrier between the hole transport film 10 and the light-emitting layer and migrate to the light-emitting layer. Therefore, the hole transport film 10 fabricated in this embodiment can improve hole mobility. Furthermore, since the first polymer and the second polymer contained in the hole transport film 10 of this embodiment are of the same type of polymer material, and the film has a gradient molecular structure, it is not a traditional bilayer transport film. Therefore, there is no material interface or material miscibility problem between different transport film layers. Thus, the hole transport film 10 fabricated in this embodiment can improve hole mobility and avoids interface miscibility issues.

[0067] Please see Figure 1 This application also provides an optoelectronic device 100, which includes a cathode 20, a light-emitting layer 30, a hole transport film 10, and an anode 40 stacked sequentially. The hole transport film 10 includes a first surface and a second surface, with the first surface facing the anode 40 and the second surface facing the light-emitting layer 30. The hole transport film 10 includes a first polymer and a second polymer, and the content of the first polymer decreases from the first surface to the second surface, while the content of the second polymer increases. The first polymer is a block copolymer formed by fluorene-containing groups and triphenylamine-containing groups, and the second polymer is a block copolymer formed by fluorene-containing groups and triphenylamine-containing groups. The molar fraction of triphenylamine-containing groups in the second polymer is less than the molar fraction of triphenylamine-containing groups in the first polymer, and all or part of the hydrogen atoms in the second polymer are replaced by fluorine atoms.

[0068] The cathode 20 is made of materials known in the art for use as cathodes, and the anode 40 is made of materials known in the art for use as anodes. Please refer to the relevant descriptions above, which will not be repeated here.

[0069] The light-emitting layer 30 can be a quantum dot light-emitting layer, and the optoelectronic device 100 can be a quantum dot optoelectronic device. The thickness of the light-emitting layer 30 can be within the range of the thickness of the light-emitting layer in quantum dot optoelectronic devices known in the art, for example, it can be 5nm to 100nm, such as 5nm, 10nm, 20nm, 50nm, 80nm, 100nm, etc.; or it can be 60-100nm.

[0070] The material of the quantum dot emitting layer is a quantum dot known in the art for use in quantum dot emitting layers, such as one of red quantum dots, green quantum dots, and blue quantum dots. The quantum dots can be selected from, but are not limited to, at least one of single-structure quantum dots and core-shell structure quantum dots. For example, quantum dots may be selected from, but are not limited to, at least one of group II-VI compounds, group III-V compounds, and group I-III-VI compounds; the group II-VI compounds are selected from at least one of CdSe, CdS, CdTe, ZnSe, ZnS, CdTe, ZnTe, CdZnS, CdZnSe, CdZnTe, ZnSeS, ZnSeTe, ZnTeS, CdSeS, CdSeTe, CdTeS, CdZnSeS, CdZnSeTe, and CdZnSTe; the group III-V compounds are selected from InP, InAs, GaP, GaAs, GaSb, AlN, AlP, InAsP, InNP, InNSb, GaAlNP, and InAlNP; and the group I-III-VI compounds are selected from at least one of CuInS2, CuInSe2, and AgInS2.

[0071] The hole transport thin film 10 can be referred to in the relevant description above, and will not be repeated here.

[0072] In this embodiment, the hole transport film 10 in the optoelectronic device 100 includes a first polymer and a second polymer. The second polymer, containing fluorine groups, tends to accumulate at the interface between the hole transport film 10 and air (on the side near the light-emitting layer 30) and extends into the air. Thus, the hole transport film 10 forms a gradient molecular structure from the bottom layer (the side near the anode 40) to the top layer (the side near the light-emitting layer 30). The closer to the top layer, the higher the content of the second polymer; the closer to the bottom layer, the higher the content of the first polymer. Simultaneously, since the first polymer contains relatively more triphenylamine groups and the second polymer contains relatively fewer triphenylamine groups, the HOMO energy level of the first polymer is higher, and the HOMO energy level of the second polymer is lower. Corresponding to the gradient molecular structure of the film from the bottom layer to the top layer, the hole transport film 10 forms a gradient energy level from high to low from the bottom layer to the top layer. The high HOMO energy level of the bottom layer is close to the energy level of the anode 40, which facilitates the supply of holes from the anode 40 to the hole transport film 10. The low HOMO energy level of the top layer reduces the energy level difference between the hole transport film 10 and the light-emitting layer 40, making it easier for holes to jump from the hole transport film 10 to the light-emitting layer 40, overcoming the potential barrier between them. Furthermore, since the hole transport film 10 in this embodiment has a gradient molecular structure and is not a traditional double-layer transport film, there are no material interface or material miscibility issues between different transport film layers. Therefore, the hole transport film 10 in the optoelectronic device 100 of this embodiment can improve hole mobility, thereby improving the current efficiency of the optoelectronic device.

[0073] Further reading Figure 1 In one embodiment, the optoelectronic device 100 may further include a hole injection layer (HIL) 50. The hole injection layer 50 is located between the hole transport film 10 and the anode 40. The material of the hole injection layer 50 may be selected from materials with hole injection capability, including but not limited to one or more of PEDOT:PSS, MCC, CuPc, F4-TCNQ, HATCN, transition metal oxides, and transition metal chalcogenides. PEDOT:PSS is a polymer, and its Chinese name is poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonic acid). The thickness of the hole injection layer 50 may be, for example, from 10 nm to 100 nm, such as 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 100 nm, etc.

[0074] Further reading Figure 1In one embodiment, the optoelectronic device 100 may further include an electron transport layer 60, which is located between the cathode 20 and the light-emitting layer 30. The electron transport layer 60 may be an oxide semiconductor nanomaterial with electron transport capability, and the oxide semiconductor nanomaterial may be selected from, but is not limited to, at least one of ZnO, TiO2, SnO2, Ta2O3, ZrO2, NiO, TiLiO, ZnAlO, ZnMgO, ZnSnO, ZnLiO, and InSnO.

[0075] It is understandable that, in addition to the functional layers mentioned above, the optoelectronic device 100 may also have some conventional functional layers used in optoelectronic devices to improve their performance, such as electron blocking layers, hole blocking layers, electron injection layers, and interface modification layers. It is also understandable that the materials and thicknesses of each layer of the optoelectronic device 100 can be adjusted according to the light-emitting requirements of the optoelectronic device 100.

[0076] In some embodiments of this application, the optoelectronic device 100 is a quantum dot light-emitting diode, and its structure can be glass substrate-anode-(hole injection layer)-hole transport layer-quantum dot light-emitting layer-electron transport layer-cathode. The hole injection layer is optional; the quantum dot light-emitting diode structure may or may not include a hole injection layer.

[0077] This application also provides a display device, including the optoelectronic device provided in this application. The display device can be any electronic product with display function, including but not limited to smartphones, tablets, laptops, digital cameras, digital camcorders, smart wearable devices, smart weighing scales, in-vehicle displays, televisions, or e-book readers. Among them, smart wearable devices can be, for example, smart bracelets, smartwatches, virtual reality (VR) headsets, etc.

[0078] The technical solutions and effects of this application will be described in detail below through specific embodiments, comparative examples and experimental examples. The following embodiments are only some embodiments of this application and are not intended to limit this application.

[0079] Example 1

[0080] This embodiment provides a quantum dot light-emitting diode and its fabrication method. The structural composition of the quantum dot light-emitting diode is described in [reference]. Figure 1 The quantum dot light-emitting diode of this embodiment includes a cathode 20, an electron transport layer 60, a light-emitting layer 30, a hole transport film 10, a hole injection layer 50 and an anode 40 stacked sequentially from top to bottom.

[0081] The materials of each layer in a quantum dot light-emitting diode are:

[0082] The cathode 20 is made of Al and has a thickness of 25 nm.

[0083] The material of electron transport layer 60 is Zn 0.9 Mg 0.1 O.

[0084] The material of the light-emitting layer 30 is nano-CdZnSe.

[0085] The hole transport film 10 is made of the following materials: the mass fraction of the first polymer is 15%, wherein the molar fraction of the triphenylamine-containing groups is 60%; and the mass fraction of the second polymer is 85%, wherein the molar fraction of the triphenylamine-containing groups is 1%.

[0086] The material of the hole injection layer 50 is PEDOT:PSS.

[0087] The anode 40 is made of ITO with a thickness of 100 nm, and a glass substrate is provided on one side of the anode 40.

[0088] The method for fabricating the quantum dot light-emitting diode in this embodiment includes the following steps:

[0089] Materials for preparing hole transport film 10: Dissolve the first polymer and the second polymer in chlorobenzene to obtain a hole transport material solution.

[0090] Anode 40 is prepared on a glass substrate.

[0091] PEDOT:PSS was spin-coated on the side of the anode 40 away from the glass substrate at a speed of 5000 for 30 seconds, followed by annealing at 200°C for 15 minutes to obtain the hole injection layer 50.

[0092] A hole transport material solution is spin-coated on the side of the hole injection layer 50 away from the anode 40 at a speed of 3000 rpm for 30 seconds. Then, it is dried at 90°C and annealed at 140°C to obtain the hole transport film 10.

[0093] CdZnSe quantum dots are spin-coated on the side of the hole transport film 10 away from the hole injection layer 50, and then annealed to obtain the light-emitting layer 30.

[0094] Zn is spin-coated on the side of the light-emitting layer 30 away from the hole transport film 10. 0.9 Mg 0.1 O, then undergoes annealing to obtain electron transport layer 60.

[0095] Al cathode 20 is prepared by vapor deposition on the side of electron transport layer 60 away from light-emitting layer 30.

[0096] Example 2

[0097] This embodiment provides a quantum dot light-emitting diode and its preparation method. The only difference from the quantum dot light-emitting diode of Embodiment 1 is that the material of the hole transport film 10 is: the molar fraction of triphenylamine groups in the first polymer is 75%, and the molar fraction of triphenylamine groups in the second polymer is 20%.

[0098] Example 3

[0099] This embodiment provides a quantum dot light-emitting diode and its preparation method. The only difference from the quantum dot light-emitting diode of Embodiment 1 is that the material of the hole transport film 10 is: the molar fraction of triphenylamine groups in the first polymer is 90%, and the molar fraction of triphenylamine groups in the second polymer is 40%.

[0100] Comparative Example 1

[0101] Comparative Example 1 provides a quantum dot light-emitting diode and its fabrication method. The only difference between this comparative example and the quantum dot light-emitting diode of Example 1 is the material of the hole transport film 10. The hole transport film 10 in Comparative Example 1 is made of TFB (tungsten bicarbonate).

[0102] The energy level diagrams of each functional layer in Examples 1-3 and the comparative examples are shown in the reference diagrams. Figures 3-6 The energy levels of the hole transport film 10 can be seen from the figure, and the energy level difference between the hole injection layer 50 and the hole transport film 10, as well as the energy level difference between the hole transport film 10 and the light-emitting layer 30, can be calculated in each example. The calculation results are shown in Table 1, and the current efficiency test results of the optoelectronic devices in Examples 1-3 and the comparative examples are also shown in Table 1.

[0103] Table 1:

[0104]

[0105] As shown in Table 1, the hole transport film 10 in Examples 1-3 of this application can achieve a gradient HOMO energy level, and the energy level difference between the hole injection layer 50 and the hole transport film 10 is lower than that in Comparative Example 1, which is beneficial for holes to be injected from the hole injection layer 50 into the hole transport film 10. The energy level difference between the hole transport film 10 and the light-emitting layer 30 is also lower than the corresponding energy level difference in Comparative Example 1, making it easier for holes to cross the potential barrier between the hole transport film 10 and the light-emitting layer 30 and jump to the light-emitting layer. Combined with the current efficiency test results of the optoelectronic devices, it can be seen that the devices in Examples 1-3 have higher current efficiency. The hole transport film 10 of this application can provide hole mobility, thereby improving the current efficiency of the corresponding optoelectronic devices. This is because the hole transport film 10 in Examples 1-3 of this application can be fabricated by a single wet process, and the film has a gradient molecular structure inside, which is not a traditional double-layer transport film fabricated by two wet processes. Therefore, there is no material interface or material miscibility problem between different transport film layers. In summary, the hole transport thin film 10 of the present application embodiments can improve the current efficiency of optoelectronic devices.

[0106] The hole transport thin film, optoelectronic device, preparation method, and display device provided in the embodiments of this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the methods and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A hole transport thin film, characterized in that, The hole transport film includes a first polymer and a second polymer, and the content of the second polymer increases or decreases from one side of the hole transport film to the other side. The first polymer is a block copolymer formed by fluorene-containing groups and triphenylamine-containing groups, and the second polymer is a block copolymer formed by fluorene-containing groups and triphenylamine-containing groups; wherein, the molar fraction of triphenylamine-containing groups in the second polymer is less than the molar fraction of triphenylamine-containing groups in the first polymer, and all or part of the hydrogen atoms in the second polymer are replaced by fluorine atoms.

2. The hole transport thin film according to claim 1, characterized in that, The molar fraction of triphenylamine-containing groups in the first polymer is greater than or equal to 50% and less than 100%. The molar fraction of triphenylamine-containing groups in the second polymer is less than 50% and greater than 0.

3. The hole transport thin film according to claim 1, characterized in that, The block copolymer has a weight-average molecular weight greater than or equal to 50,000 and less than or equal to 250,000.

4. The hole transport thin film according to claim 1, characterized in that, The general structural formula of the block copolymer is as follows: Where n>0, m≥0, p≥0, R1~R6 are the same or different groups, and R1~R6 are C1~C20 alkyl, aromatic or heteroaromatic groups.

5. The hole transport thin film according to claim 1, characterized in that, The HOMO level of the first polymer is greater than or equal to -5.3 eV and less than -4.8 eV; The highest occupied molecular orbital energy level of the second polymer is greater than -5.8 eV and less than -5.3 eV.

6. The hole transport thin film according to claim 1, characterized in that, The first polymer has a weight percentage of 1-20%, and the second polymer has a weight percentage of 80-99%.

7. A method for fabricating an optoelectronic device, characterized in that, Includes the following steps: A material solution comprising a first polymer and a second polymer is provided, wherein the first polymer is a block copolymer formed of a fluorene-containing group and a triphenylamine-containing group, the second polymer is a block copolymer formed of a fluorene-containing group and a triphenylamine-containing group, wherein the molar fraction of the triphenylamine-containing group in the second polymer is less than the molar fraction of the triphenylamine-containing group in the first polymer, and all or part of the hydrogen atoms in the second polymer are replaced by fluorine atoms; A substrate is provided, on which an anode is formed. A material solution is disposed on the anode and subjected to heat treatment to obtain a hole transport film. A cathode is fabricated on the hole transport film.

8. The preparation method according to claim 7, characterized in that, The heat treatment steps include: first performing a first heat treatment, and then performing a second heat treatment; Wherein, the temperature of the first heat treatment is less than 100℃ and greater than or equal to 40℃, and the temperature of the second heat treatment is greater than or equal to 100℃ and less than or equal to 250℃.

9. A photoelectric device comprising a cathode, a light-emitting layer, a hole transport film, and an anode sequentially stacked, wherein the hole transport film includes a first surface and a second surface, the first surface facing the anode and the second surface facing the light-emitting layer, characterized in that... The hole transport film comprises a first polymer and a second polymer, and the content of the first polymer decreases from the first surface to the second surface, while the content of the second polymer increases. The first polymer is a block copolymer formed by fluorene-containing groups and triphenylamine-containing groups, and the second polymer is a block copolymer formed by fluorene-containing groups and triphenylamine-containing groups, wherein the molar fraction of triphenylamine-containing groups in the second polymer is less than the molar fraction of triphenylamine-containing groups in the first polymer, and all or part of the hydrogen atoms in the second polymer are replaced by fluorine atoms.

10. A display device, characterized in that, The display device includes the optoelectronic device as described in claim 9.

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