A hole transport thin film, an optoelectronic device, a 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 comprises a first polymer and a second polymer. 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, triphenylamine-containing groups, and self-crosslinking groups, wherein all or part of the hydrogen atoms in the second polymer are replaced by fluorine atoms. The hole transport thin film of this application is predominantly composed of the second polymer near the top layer. The crosslinked structure in the second polymer provides better solvent resistance, preventing the material components of the light-emitting layer from penetrating into the hole transport thin film, thereby reducing interfacial dissolution and improving the current efficiency of the 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, a preparation method thereon, and a display device. Background Technology

[0002] Optoelectronic devices are devices made based on the photoelectric effect. They have wide applications in new energy, sensing, communication, display, lighting and other fields, such as solar cells, photodetectors, organic light-emitting devices (OLEDs) or quantum dot light-emitting 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, and the electron mobility of inorganic nanoparticles is much greater than that of holes, hole transport materials with high hole mobility are needed to match them. Theoretically, hole transport materials with high hole mobility can improve the above problems, but the actual current efficiency of the devices is not high. Summary of the Invention

[0005] In view of this, this application provides a hole transport thin film, an optoelectronic device, a preparation method, and a display device, aiming to improve the problem of low current efficiency of optoelectronic devices made from 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;

[0007] The first polymer is a block copolymer formed from fluorene-containing groups and triphenylamine-containing groups;

[0008] The second polymer is a block copolymer formed by fluorene-containing groups, triphenylamine-containing groups and self-crosslinking groups, and all or part of the hydrogen atoms in the second polymer are replaced by fluorine atoms.

[0009] Optionally, the content of the second polymer increases or decreases from one side of the hole transport film to the other.

[0010] Optionally, in some embodiments of this application, the structural formula of the first polymer is as follows:

[0011]

[0012] Among them, n', m', and p' are mole fractions, n' + m' + p' = 1, 0 < n' < 1, 0 ≤ m' < 1, 0 ≤ p' < 1, and R1' to R6' are the same or different groups, and R1' to R6' are C1-C20 alkyl groups, aromatic groups or heteroaromatic groups.

[0013] Optionally, in some embodiments of the present application, the structural general formula of the second polymer is as follows:

[0014]

[0015] Among them, n, m, p, and q are mole fractions, n + m + p + q = 1, 0 < n < 0.95, 0 ≤ m < 0.95, 0 ≤ p < 0.95, 0 < p < 0.05;

[0016] R1 to R6 are the same or different groups, and R1 to R6 are C1-C20 alkyl groups, aromatic groups or heteroaromatic groups, and R7 contains a crosslinking bond.

[0017] Optionally, in some embodiments of the present application, R7 is one of the following structural formulas:

[0018]

[0019] Among them, R8 is a C1-C20 alkyl group, or R8 is a C1-C20 alkyl group and at least one carbon atom is replaced by a heteroatom. When multiple carbon atoms are replaced by heteroatoms, the heteroatoms are located at non-adjacent positions.

[0020] Optionally, in some embodiments of the present application, the mole fraction of the self-crosslinking group in the second polymer is greater than 0 and less than or equal to 5%.

[0021] Optionally, in some embodiments of the present application, the mole fraction of the group containing triphenylamine in the second polymer is less than the mole fraction of the group containing triphenylamine in the first polymer in the first polymer.

[0022] Optionally, in some embodiments of the present application, the weight percentage of the second polymer in the material of the hole transport film is greater than or equal to 5% and less than or equal to 40%.

[0023] The embodiments of the present application also provide a method for preparing an optoelectronic device, including the following steps:

[0024] A material solution comprising a first polymer and a second polymer is provided, wherein the first polymer is a block copolymer formed by a fluorene-containing group and a triphenylamine-containing group; the second polymer is a block copolymer formed by a fluorene-containing group, a triphenylamine-containing group and a self-crosslinking group, and all or part of the hydrogen atoms in the second polymer are replaced by fluorine atoms;

[0025] A substrate is provided, on which an anode is formed. A material solution is disposed on the anode and subjected to crosslinking treatment to obtain a hole transport film.

[0026] A cathode is fabricated on the hole transport film.

[0027] Optionally, in some embodiments of this application, the crosslinking treatment is a heat treatment or an ultraviolet irradiation treatment.

[0028] Accordingly, this application also provides an optoelectronic device, including a cathode, a light-emitting layer, a hole transport film and an anode stacked sequentially, wherein the hole transport film includes a first side and a second side, the first side facing the anode and the second side facing the light-emitting layer, and the hole transport film includes a first polymer and a second polymer.

[0029] 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, triphenylamine-containing groups and self-crosslinking groups, and all or part of the hydrogen atoms in the second polymer are replaced by fluorine atoms.

[0030] Optionally, from the first surface to the second surface, the content of the first polymer decreases and the content of the second polymer increases.

[0031] Accordingly, this application also provides a display device, which includes the above-mentioned optoelectronic device.

[0032] The hole transport film of this application comprises a first polymer and a second polymer. 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, triphenylamine-containing groups, and self-crosslinking groups, wherein all or part of the hydrogen atoms in the second polymer are replaced by fluorine atoms. The HOMO energy level of the hole transport film in this embodiment is determined by the fluorene-containing groups and the triphenylamine-containing groups. The HOMO energy level of the hole transport film can be in the range of -5.8 eV to -4.8 eV, located between the HOMO energy level of a typical hole injection layer and the HOMO energy level of a light-emitting layer, thus satisfying the energy level requirements for the hole injection layer to inject holes into the light-emitting layer.

[0033] Furthermore, in the process of fabricating the hole transport film in this embodiment, the second polymer, due to the presence of fluorine atoms, tends to be located in the upper layer of the hole transport film (i.e.,...). Figure 1 (The structure is for reference only). This is because fluorine atoms have high electronegativity, small atomic radii, short CF bonds with bond energies as high as 500 kJ / mol, and mutual repulsion between adjacent fluorine atoms, causing them to not lie in the same plane but 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 film formation, 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, with the content of the second polymer increasing closer to the top layer. At the same time, since the second polymer also includes self-crosslinking groups, crosslinking reactions occur between the block copolymer molecules of the second polymer during hole transport film formation, making the upper layer of the hole transport film (on the side closer to the light-emitting layer) mainly a crosslinked polymer, which has better solvent resistance and can prevent the material components of the light-emitting layer from penetrating into the hole transport film. This reduces the interfacial miscibility between the hole transport film and the light-emitting layer, thereby improving the current efficiency of the device. Attached Figure Description

[0034] 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.

[0035] Figure 1 This is a schematic diagram of the structure of an optoelectronic device provided in an embodiment of this application;

[0036] Figure 2 This is a schematic diagram of HOMO energy level matching for each functional layer provided in an embodiment of this application;

[0037] Figure 3 This is a schematic flowchart of a method for fabricating an optoelectronic device according to an embodiment of this application;

[0038] Figure 4 This is a current efficiency test curve of the optoelectronic device of Embodiment 1 of this application;

[0039] Figure 5 This is a current efficiency test curve of the optoelectronic device in Embodiment 2 of this application;

[0040] Figure 6 This is a current efficiency test curve of the optoelectronic device of Embodiment 1 of this application;

[0041] Figure 7 This is a current efficiency test curve of the optoelectronic device in Comparative Example 1.

[0042] Figure 8 This is a current efficiency test curve of the optoelectronic device in Comparative Example 2. Detailed Implementation

[0043] 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.

[0044] In optoelectronic devices such as QLEDs, hole transport is carried out by organic materials while electron transport is carried out by inorganic materials. Since the electron migration efficiency of inorganic nanoparticles is much higher than that of holes, hole transport materials with high hole migration efficiency are needed to match them. Theoretically, hole transport materials with high hole migration efficiency can improve the above-mentioned problems, but the actual current efficiency of the devices is not high.

[0045] Further research by the applicant revealed that the reason why devices using hole transport materials with high hole migration efficiency have low current efficiency is mainly because ligand-modified quantum dot materials have good solubility and stability in solvents. Since the quantum dot emitting layer is typically fabricated on a hole transport film, the good solubility of quantum dot materials makes it easy for the material to seep into the hole transport film along with the solvent during fabrication, leading to interfacial dissolution between the final emitting layer and the hole transport film, thus affecting the current efficiency of the optoelectronic device. Based on this, this application provides a hole transport film as described below to improve the problem of low current efficiency in devices using hole transport materials in related technologies.

[0046] 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 thin film 10 includes a first polymer and a second polymer; 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, triphenylamine-containing groups and self-crosslinking groups, and all or part of the hydrogen atoms in the second polymer are replaced by fluorine atoms.

[0047] It should be noted that the highest occupied molecular orbital (HOMO) level of the hole transport film 10 in this embodiment is determined by the fluorene-containing group and the triphenylamine-containing group. When the molar fraction of the triphenylamine-containing group approaches 100%, the HOMO level of the hole transport film 10 is close to the HOMO level of polytriphenylamine (-4.8 eV). When the molar fraction of the triphenylamine-containing unit is 0%, the HOMO level of the hole transport film 10 is close to the HOMO level of polyfluorene (-5.8 eV). Therefore, the HOMO level of the hole transport film 10 in this embodiment can be in the range of -5.8 eV to -4.8 eV, located between the HOMO level of a typical hole injection layer and the HOMO level of a light-emitting layer, which can meet the requirement of the hole injection layer injecting holes into the light-emitting layer.

[0048] Furthermore, in the process of fabricating the hole transport film 10 in this embodiment, the second polymer, due to the presence of fluorine atoms, tends to be located in 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 film formation, 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. The closer to the top layer, the higher the content of the second polymer. Meanwhile, since the second polymer also includes self-crosslinking groups, crosslinking reactions will occur between the block copolymer molecules of the second polymer during the molding of the hole transport film 10. This makes the upper layer (the side closest to the light-emitting layer) of the hole transport film 10 mainly a crosslinked polymer, which has better solvent resistance and can prevent the material components of the light-emitting layer from penetrating into the hole transport film 10. This can reduce the interfacial miscibility between the hole transport film 10 and the light-emitting layer, thereby improving the current efficiency of the device.

[0049] As an example, the content of the second polymer increases or decreases from one side of the hole transport film 10 to the other. For example, with Figure 1 Taking the optoelectronic device shown as an example, the hole transport film 10 can be formed by a wet process. During the wet film formation process, the second polymer, due to its fluorine-containing groups, tends to accumulate on the surface of the hole transport film 10 (i.e., the side near the light-emitting layer). Therefore, the hole transport film 10 can form a gradually cross-linked 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 bottom layer, the higher the content of the first polymer, meaning that the side near the hole injection layer is mainly a non-cross-linked structure; the closer to the top layer, the higher the content of the second polymer. The cross-linked structure formed by the self-cross-linking groups in the second polymer can prevent the material components of the light-emitting layer from penetrating into the hole transport film 10, thereby reducing the interfacial miscibility between the hole transport film 10 and the light-emitting layer, and thus improving the current efficiency of the optoelectronic device.

[0050] In one embodiment, the hole transport film 10 is a combination of a first polymer and a second polymer. 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, triphenylamine-containing groups, and crosslinking groups, 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.

[0051] When the materials of the hole transporting thin film 10 are only the first polymer and the second polymer, preferably, the weight percentage of the second polymer in the materials of the hole transporting thin film is greater than or equal to 5% and less than or equal to 40%. That is, the weight percentages of the second polymer and the first polymer can be 5% and 95%, 10% and 90%, 15% and 85%, 22% and 78%, 29% and 71%, 35% and 65%, 40% and 60%, etc. Since the second polymer contains self-crosslinking groups, if the proportion is too large, on the one hand, the components that do not play a hole transporting role account for a large proportion, which affects the hole transporting efficiency. On the other hand, too high crosslinking degree will also lead to a decrease in the hole transporting efficiency. Therefore, the weight percentage of the second polymer is preferably 5% - 40%.

[0052] In one embodiment, the general structural formula of the first polymer in the hole transporting thin film 10 is as follows:

[0053]

[0054] Wherein, n', m', p' are mole fractions, n' + m' + p' = 1, 0 < n' < 1, 0 ≤ m' < 1, 0 ≤ p' < 1, and R1' to R6' are the same or different groups, and R1' to R6' are alkyl groups, aromatic groups or heteroaromatic groups with 1 to 20 carbon atoms.

[0055] It can be understood that R1' to R6' can be the same substituents. For example, they can be alkyl groups, aromatic groups or heteroaromatic groups simultaneously. R1' to R6' can also be different substituents. For the convenience of description, the copolymer repeating unit formed by the above fluorene-containing group and triphenylamine-containing group is named A' unit, the homopolymer repeating unit formed by the above fluorene-containing group is named B' unit, and the homopolymer repeating unit formed by the above triphenylamine-containing group is named C' unit. It can be understood that the first polymer in this embodiment can only include A' unit, or can be a block copolymer including A' unit and B' unit, or can be a block copolymer including A' unit and C' unit, or can be a block copolymer including A' unit, B' unit and C' unit simultaneously. The embodiments of the present application are not particularly limited, and the mole fraction of the triphenylamine-containing group can be determined according to the need of HOMO energy level, and then the corresponding polymer structure can be selected.

[0056] In one embodiment, the general structural formula of the second polymer in the hole transporting thin film 10 is as follows:

[0057]

[0058] Where n, m, p, and q are mole fractions, n + m + p + q = 1, 0 < n < 0.95, 0 ≤ m < 0.95, 0 ≤ p < 0.95, 0 < p < 0.05, R1 to R6 are the same or different groups, and R1 to R6 are C1 - C20 alkyl groups, aromatic groups, or heteroaromatic groups, and R7 contains a crosslinking bond.

[0059] It should be noted that R1 to R6 can be the same groups as R1' to R6' correspondingly, and the same selection can be made as for the above R1' to R6'. R1 to R6 can also be different groups independent of R1' to R6'. For the convenience of description, the copolymer repeating unit formed by the above-mentioned fluorene-containing group and triphenylamine-containing group is named A unit, the homopolymer repeating unit formed by the above-mentioned fluorene-containing group is named B unit, the homopolymer repeating unit formed by the above-mentioned triphenylamine-containing group is named C unit, and the homopolymer repeating unit formed by the above-mentioned self-crosslinking group is named D unit. It can be understood that the second polymer in this embodiment can be only composed of A unit and D unit, or can be a block copolymer including A unit, D unit, and B unit, or can also be a block copolymer including A' unit, D unit, and C unit, or can also be a block copolymer including A unit, D unit, B unit, and C unit at the same time. The embodiments of the present application are not particularly limited, and the mole fractions of A unit and D unit can be determined according to the need of HOMO energy level and the need of crosslinking degree, and then the corresponding polymer structure can be selected.

[0060] It should be noted that in this embodiment, if the mole fraction of D unit is too high, it may lead to too high crosslinking degree in the polymer, affecting the conductivity of the material and thus reducing the hole mobility. Therefore, preferably, the mole fraction of the self-crosslinking group D unit is greater than 0 and less than or equal to 5%, that is, 0 < q / (n + m + p + q) ≤ 0.05, which can form a crosslinked polymer to prevent the light-emitting layer material from infiltrating into the hole transport film 10 without reducing the hole mobility of the hole transport film 10.

[0061] It can be understood that the substituent R7 in the self-crosslinking group D unit can be a group containing a thermal crosslinking bond, and the crosslinking reaction is carried out by heating, or can be a group containing a crosslinking bond responsive to ultraviolet light, and the crosslinking reaction is carried out by ultraviolet light irradiation.

[0062] In some embodiments, the self-crosslinking group can be a double bond or a group that can form a double bond during the reaction, and a crosslinked structure is formed between the molecules of the second polymer through the addition reaction of the double bond. For example, R7 of the second polymer can be one of the following structural formulas:

[0063]

[0064] In this formula, R8 is a C1-C20 alkyl group, and at least one carbon atom is substituted with a heteroatom. When multiple carbon atoms are substituted with heteroatoms, the heteroatoms are located in non-adjacent positions to improve the flexibility of the substituent. In the R7 group, the double bond in Formula 1 can undergo an addition reaction, thereby forming a cross-linked structure between the second polymers. The molecular structure of Formula 2 undergoes isomerization upon heating, as shown in the following reaction equation:

[0065]

[0066] After isomerization, two double bonds are formed, which can facilitate cross-linking reactions between the second polymers to obtain a cross-linked polymer. The cross-linked structure has better solvent resistance and can prevent small molecules in the light-emitting layer from penetrating into the hole transport film 10 (i.e., interfacial miscibility), thereby improving the hole migration efficiency and the stability of the optoelectronic device.

[0067] It should be noted that, due to the complexity of polymer chemical reactions, the cross-linking reaction in the above embodiments may not be able to proceed exactly according to the ideal cross-linking reaction model, but at least a certain proportion of cross-linked structures can be formed.

[0068] In one embodiment, 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. It is understood that the higher the content of triphenylamine-containing groups in a polymer, the higher its HOMO energy level. Since the hole transport film 10 of this embodiment forms 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 content of the second polymer is higher closer to the top layer, and the content of the first polymer is higher closer to the bottom layer. Therefore, when 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, the hole transport film 10 can form a gradient energy level structure from a high HOMO energy level at the bottom layer to a low HOMO energy level at the top layer. (See reference...) Figure 2 , Figure 2This is a schematic diagram of HOMO level matching for each functional layer provided in an embodiment of this application. The hole transport film 10 forms a gradient HOMO level from -5.2 eV (bottom layer) to -5.8 eV (top layer). The bottom HOMO level of the hole transport film 10 is close to the HOMO level of the hole transport layer (HJL), which can improve the injection efficiency of holes from the hole injection layer to the hole transport film 10. The top HOMO level of the hole transport film 10 is close to the HOMO level of the light-emitting layer, which reduces the energy level difference between the hole transport film 10 and the light-emitting layer, making it easier for holes to overcome the potential barrier from the hole transport film 10 to the light-emitting layer, thereby improving the migration efficiency of holes. Furthermore, the side of the hole transport film 10 near the light-emitting layer is mainly composed of a cross-linked polymer, which has better solvent resistance and can prevent the material components of the light-emitting layer from penetrating into the hole transport film 10, thereby reducing the possibility of interfacial missolution between the hole transport film 10 and the light-emitting layer, and improving current efficiency.

[0069] The hole transport film 10 in this embodiment can not only improve hole mobility, but also reduce the interfacial dissolution between the hole transport film 10 and the light-emitting layer, thereby improving current efficiency.

[0070] This application also provides a method for fabricating an optoelectronic device. Please refer to [link to relevant documentation]. Figure 3 , Figure 3 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:

[0071] Step S31: Provide a material solution comprising a first polymer and a second polymer, wherein the first polymer is a block copolymer formed by a fluorene-containing group and a triphenylamine-containing group; the second polymer is a block copolymer formed by a fluorene-containing group, a triphenylamine-containing group and a self-crosslinking group, and all or part of the hydrogen atoms in the second polymer are replaced by fluorine atoms.

[0072] In this step, the first polymer and the second polymer can be first prepared into a polymer material 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.

[0073] 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.

[0074] Step S32: Provide a substrate, on which an anode is formed, place the above material solution on the anode, and perform cross-linking treatment to obtain a hole transport film.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] In one embodiment, when the self-crosslinking groups in the second polymer contain thermally crosslinking bonds, crosslinking can be performed using a heating method. For example, a first heat treatment can be performed on the wet film on the substrate to evaporate the organic solvent in the wet film and form a molten hole transport film. Then, a second heat treatment can be performed on the hole transport film to crosslink and solidify the second polymer. The temperature of the second heat treatment is higher than that of the first heat treatment. For example, the temperature of the first heat treatment can be less than 100°C, such as 95°C, 80°C, 70°C, 60°C, 50°C, 40°C, etc. The higher the temperature, the faster the solvent evaporates. Vacuum drying at room temperature can also be used. The temperature of the second heat treatment can be between 100°C and 200°C, for example, the temperature of the second heat treatment can be 100°C, 120°C, 140°C, 160°C, 180°C, 190°C, 200°C, etc.

[0079] In one embodiment, when the self-crosslinking groups in the second polymer contain ultraviolet light-responsive crosslinking groups, the crosslinking reaction can be carried out by ultraviolet light irradiation. For example, the above-mentioned first heat treatment process can be used to evaporate the organic solvent to form a molten hole transport film, and then the film can be irradiated with ultraviolet light at a wavelength of 365 nm to crosslink and solidify the hole transport film.

[0080] 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.

[0081] Step S33: Fabricate a cathode on a hole transport film.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] In this embodiment, a material solution containing a first polymer and a second polymer is deposited on a substrate, and then a crosslinking reaction is performed to obtain a hole transport film 10. Since the HOMO energy level of the hole transport film 10 can be in the range of -5.8 eV to -4.8 eV, located between the HOMO energy level of a typical hole injection layer and the HOMO energy level of a light-emitting layer, it can meet the energy level requirements for the hole injection layer to inject holes into the light-emitting layer. Furthermore, during the film formation process, due to the presence of fluorine atoms in the second polymer, it tends to accumulate at the interface between the hole transport film 10 and air (on the side closer to the light-emitting layer) and extends into the air, thus forming a gradient molecular structure from the bottom layer to the top layer of the hole transport film 10. 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. Meanwhile, since the second polymer also includes self-crosslinking groups, crosslinking reactions will occur between the block copolymer molecules of the second polymer during the molding of the hole transport film 10. This results in the hole transport film 10 being mainly composed of crosslinked polymers on the side closest to the light-emitting layer, which has better solvent resistance. This can prevent the material components of the light-emitting layer from penetrating into the hole transport film 10, thereby reducing the interfacial miscibility between the hole transport film 10 and the light-emitting layer and improving the current efficiency of the device.

[0086] Please see Figure 1This 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 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 10 includes a first polymer and a second polymer. 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, triphenylamine-containing groups, and self-crosslinking groups, and all or part of the hydrogen atoms in the second polymer are replaced by fluorine atoms.

[0087] The cathode 20 is made of materials known in the art for cathodes, and the anode 40 is made of materials known in the art for anodes; please refer to the relevant descriptions above, which will not be repeated here. The light-emitting layer 30 can be a quantum dot light-emitting layer, in which case 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 thicknesses of light-emitting layers 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.

[0088] 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.

[0089] The hole transport thin film 10 can be referred to in the relevant description above, and will not be repeated here.

[0090] In this embodiment, the hole transport film 10 in the optoelectronic device 100 includes a first polymer and a second polymer. Since the HOMO energy level of the hole transport film 10 can be in the range of -5.8 eV to -4.8 eV, located between the HOMO energy level of a typical hole injection layer and the HOMO energy level of the light-emitting layer, it can improve the efficiency of hole injection from the hole injection layer to the light-emitting layer. In addition, during the film formation process, due to the presence of fluorine atoms, the second polymer tends 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. The closer to the top layer, the higher the content of the second polymer. At the same time, since the second polymer also includes self-crosslinking groups, crosslinking reactions occur between the block copolymer molecules of the second polymer during the molding of the hole transport film 10. This results in the side of the hole transport film 10 near the light-emitting layer being mainly crosslinked polymer, which has better solvent resistance and can prevent the material components of the light-emitting layer from penetrating into the hole transport film 10. This reduces the possibility of interfacial miscibility between the hole transport film 10 and the light-emitting layer, thereby improving the current efficiency of the optoelectronic device 100.

[0091] As an example, from the first side (facing the anode 40) to the second side (facing the light-emitting layer 30) of the hole transport film 10, the content of the first polymer decreases while the content of the second polymer increases. Due to its fluorine-containing groups, the second polymer tends to accumulate on the surface of the hole transport film 10 (i.e., the side near the light-emitting layer). Therefore, the hole transport film 10 can form a gradually cross-linked 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 bottom layer, the higher the content of the first polymer; that is, the side near the hole injection layer is predominantly non-cross-linked. The closer to the top layer, the higher the content of the second polymer. The cross-linked structure formed by the self-cross-linking groups in the second polymer can prevent the material components of the light-emitting layer from penetrating into the hole transport film 10, thereby reducing interfacial miscibility between the hole transport film 10 and the light-emitting layer, and thus improving the current efficiency of the optoelectronic device.

[0092] 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.

[0093] Further reading Figure 1 In 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.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] Example 1

[0099] 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.

[0100] The materials of each layer in a quantum dot light-emitting diode are:

[0101] The cathode 20 is made of Al.

[0102] The material of electron transport layer 60 is Zn 0.8 Mg 0.2 O.

[0103] The material of the light-emitting layer 30 is nano-ZnSe.

[0104] The hole transport film 10 is made of a first polymer (70% wt) and a second polymer (30% wt) as described in this application. The first polymer has a weight-average molecular weight of 83,000 and a molecular weight dispersion index of 1.8. R1, R2, R4, and R5 are ethyl groups, and R3 and R6 are alkyl groups containing 15 carbon atoms. The second polymer has a weight-average molecular weight of 100,000 and a molecular weight dispersion index of 2.0. Some H atoms are replaced by fluorine atoms. R1, R2, R4, and R5 are ethyl groups, R3 and R6 are alkyl groups containing 10 carbon atoms, and R7 is an olefin containing 15 carbon atoms. The second polymer has a molar fraction of 3% in the second polymer.

[0105] The material of the hole injection layer 50 is PEDOT:PSS.

[0106] The anode 40 is made of ITO, and a glass substrate is provided on one side of the anode 40.

[0107] The method for fabricating the quantum dot light-emitting diode in this embodiment includes the following steps:

[0108] Materials for preparing hole transport film 10: Dissolve the first polymer and the second polymer in ethyl benzoate (14 mg / mL) to obtain a hole transport material solution.

[0109] Anode 40 is prepared on a glass substrate.

[0110] PEDOT:PSS is spin-coated on the side of the anode 40 away from the glass substrate and then annealed to obtain the hole injection layer 50.

[0111] A material solution for the hole transport film 10 is spin-coated on the side of the hole injection layer 50 away from the anode 40, and then dried and annealed. The film is first heat-treated at 100°C and then at 170°C to obtain the hole transport film 10.

[0112] ZnSe 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.

[0113] Zn is spin-coated on the side of the light-emitting layer 30 away from the hole transport film 10. 0.9 Mg 0.1O, then undergoes annealing to obtain electron transport layer 60.

[0114] Al cathode 20 is prepared by vapor deposition on the side of electron transport layer 60 away from light-emitting layer 30.

[0115] Example 2

[0116] This embodiment provides a quantum dot light-emitting diode and its preparation method. Compared with the quantum dot light-emitting diode of Embodiment 1, the only difference of the quantum dot light-emitting diode of this embodiment is that the material of the hole transport film 10 is: comprising the first polymer (60% wt) and the second polymer (40% wt) of this application, wherein the weight average molecular weight of the first polymer is 78,000, the molecular weight dispersion index is 1.9, R1, R2, R4, and R5 are methyl, and R3 and R6 are alkyl groups containing 6 carbon atoms; the weight average molecular weight of the second polymer is 120,000, the molecular weight dispersion index is 2.5, R1, R2, R4, and R5 are methyl, R3 and R6 are alkyl groups containing 18 carbon atoms, R7 is phenylpropane-butane containing 10 carbon atoms, and the molar fraction of the second polymer is 4%.

[0117] Example 3

[0118] This embodiment provides a quantum dot light-emitting diode and its preparation method. Compared with the quantum dot light-emitting diode of Embodiment 1, the only difference of the quantum dot light-emitting diode of this embodiment is that the material of the hole transport film 10 is: comprising the first polymer (95% wt) and the second polymer (5% wt) of this application, wherein the weight average molecular weight of the first polymer is 50,000, the molecular weight dispersion index is 1.5, R1, R2, R4, and R5 are octyl, and R3 and R6 are methyl; the weight average molecular weight of the second polymer is 90,000, the molecular weight dispersion index is 2.2, R1, R2, R4, and R5 are octyl, R3 and R6 are methyl, R7 is an olefin containing 10 carbon atoms, and the molar fraction of the second polymer is 2%.

[0119] Comparative Example 1

[0120] 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 of Comparative Example 1 is made of cross-linked TFB.

[0121] Comparative Example 2

[0122] Comparative Example 1 provides a quantum dot light-emitting diode and its fabrication method. Compared with the quantum dot light-emitting diode of Example 1, the only difference of the quantum dot light-emitting diode of this comparative example is that the hole transport film 10 is made of non-crosslinked TFB.

[0123] Current efficiency tests were performed on Examples 1-3 and Comparative Examples 1 and 2, and the test curves are shown below. Figures 4-8 As shown, the maximum current efficiency (cd / A) of Examples 1-3 and Comparative Examples 1 and 2 can be obtained as follows: 85, 77, 93, 61, and 32, respectively.

[0124] The test results show that the maximum current efficiency of Comparative Example 1 is higher than that of Comparative Example 2, indicating that the cross-linked TFB hole transport film can improve the current efficiency of optoelectronic devices compared to the non-cross-linked TFB hole transport film. Furthermore, the maximum current efficiency of Examples 1-3 is higher than that of Comparative Example 1, indicating that the optoelectronic devices corresponding to the graded cross-linked hole transport films of Examples 1-3 of this application have higher current efficiency and better performance.

[0125] 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 method 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 thin film comprises a first polymer and a second polymer; The first polymer is a block copolymer formed by a fluorene-containing group and a triphenylamine-containing group; The second polymer is a block copolymer formed by a fluorene-containing group, a triphenylamine-containing group and a self-crosslinking group, and all or part of the hydrogen atoms in the second polymer are replaced by fluorine atoms; The mole fraction of the triphenylamine-containing group in the second polymer is less than the mole fraction of the triphenylamine-containing group in the first polymer in the first polymer; From one side to the other side of the hole transport thin film, the content of the second polymer increases or decreases.

2. The hole transport thin film according to claim 1, characterized in that, The structural general formula of the first polymer is as follows: ， Wherein, n', m', p' are mole fractions, n'+m'+p' = 1, 0 < n' < 1, 0 ≤ m' < 1, 0 ≤ p' < 1, R1'~R6' are the same or different groups, and R1'~R6' are C1~C20 alkyl groups, aromatic groups or heteroaromatic groups.

3. The hole transport thin film according to claim 1, characterized in that, The structural general formula of the second polymer is as follows: ， Where n, m, p, q are mole fractions, n+m+p+q = 1, 0 < n < 0.95, 0 ≤ m < 0.95, 0 ≤ p < 0.95, 0 < q < 0.05; R1~R6 are the same or different groups, and R1~R6 are C1~C20 alkyl groups, aromatic groups or heteroaromatic groups, and R7 contains a crosslinking bond.

4. The hole transport thin film according to claim 3, characterized in that, The R7 is one of the following structural formulas: 、 ， Wherein, R8 is a C1~C20 alkyl group, or R8 is a C1~C20 alkyl group and at least one carbon atom is replaced by a heteroatom. When there are multiple carbon atoms replaced by heteroatoms, the heteroatoms are located at non-adjacent positions.

5. The hole transport thin film according to claim 1, characterized in that, The mole fraction of the self-crosslinking group in the second polymer is greater than 0 and less than or equal to 5%.

6. The hole transport thin film according to claim 1, characterized in that, The weight percentage of the second polymer in the material of the hole transport thin film is greater than or equal to 5% and less than or equal to 40%.

7. A method for fabricating an optoelectronic device, characterized in that, Comprises the following steps: Providing a material solution comprising a first polymer and a second polymer, wherein the first polymer is a block copolymer formed by a fluorene-containing group and a triphenylamine-containing group; the second polymer is a block copolymer formed by a fluorene-containing group, a triphenylamine-containing group and a self-crosslinking group, and all or part of the hydrogen atoms in the second polymer are replaced by fluorine atoms; Providing a substrate, an anode is formed on the substrate, the material solution is disposed on the anode, and a crosslinking treatment is performed to obtain a hole transport thin film; Fabricating a cathode on the hole transport thin film; The mole fraction of the triphenylamine-containing group in the second polymer is less than the mole fraction of the triphenylamine-containing group in the first polymer in the first polymer; From one side to the other side of the hole transport thin film, the content of the second polymer increases or decreases.

8. The preparation method according to claim 7, characterized in that, The crosslinking treatment is a heat treatment or an ultraviolet irradiation treatment.

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 thin film comprises a first polymer and a second polymer; 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, triphenylamine-containing groups and self-crosslinking groups, and all or part of the hydrogen atoms in the second polymer are replaced by fluorine atoms; 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. From the first surface to the second surface, the content of the first polymer decreases, and the content of the second polymer increases.

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

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