CN113555407B - Organic electroluminescent display substrate, preparation method thereof and display device - Google Patents

Abstract

The disclosure provides an organic electroluminescent display substrate, a preparation method thereof and a display device, and belongs to the technical field of display. The organic electroluminescent display substrate comprises a pixel defining layer arranged on a substrate, wherein the pixel defining layer comprises a flat part and an opening part; the organic electroluminescent display substrate further comprises a micro-nano composite film, wherein the micro-nano composite film covers the flat part and the opening part of the pixel defining layer; wherein, the micro-nano composite film covering the flat part can be changed from hydrophobicity to hydrophilicity in the illumination environment; the micro-nano composite film covering the opening part can be changed from hydrophilicity to hydrophobicity in dark state environment.

Description

Organic electroluminescent display substrate and preparation method thereof, and display device

Technical Field

The present disclosure belongs to the field of display technology, and specifically relates to an organic electroluminescent display substrate and a preparation method thereof, and a display device.

Background technique

Organic Light Emitting Diodes (OLED) are a new type of current-type semiconductor light-emitting device. They are a self-luminous technology that controls the injection and recombination of carriers in the device to excite organic materials to emit light. Compared with passive liquid crystal displays (LCD), self-luminous OLED displays have the advantages of fast response speed, high contrast, wide viewing angle, and easy to achieve flexible display. They are generally favored by the industry. The industry unanimously believes that OLED displays are very likely to become the mainstream products of the next generation of display technology.

At present, all functional material layers and cathode metal layer films of OLED are prepared by vacuum thermal evaporation process, that is, heating organic small molecule materials in a vacuum chamber to make them sublime or melt and vaporize into material vapor, which is then deposited on a glass substrate through the openings of a metal mask. However, the high cost of vacuum thermal evaporation has limited the large-scale commercialization of OLED displays. Inkjet printing (IJP) has the advantages of high material utilization and is a key technology to solve the cost problem of large-size OLED displays. Compared with the traditional vacuum evaporation process, IJP technology has many advantages in the preparation of the light-emitting layer of OLED devices, such as saving materials, mild process conditions, and more uniform film formation, so it has greater application potential. This method uses multiple nozzles to drip functional material ink into a predetermined pixel area, and then obtains the desired pattern film by drying.

However, due to the different hydrophilicities of different inks, inks with good hydrophilicity will climb higher on the inclined inner surface of the retaining wall to form a concave film layer, while inks with poor hydrophilicity will form a convex film layer in the groove of the retaining wall, resulting in uneven film thickness of the functional layer of the light-emitting element in each pixel area after drying, which will not only affect the uniformity of the light emission of the OLED device, but also reduce the quality of the OLED device.

Summary of the invention

The present disclosure aims to solve at least one of the technical problems existing in the prior art, and provides an organic electroluminescent display substrate and a preparation method thereof, and a display device.

In a first aspect, an embodiment of the present disclosure provides an organic electroluminescent display substrate, comprising a pixel defining layer disposed on a base substrate, wherein the pixel defining layer comprises a flat portion and an opening portion; the organic electroluminescent display substrate further comprises a micro-nano composite film, wherein the micro-nano composite film covers the flat portion and the opening portion of the pixel defining layer;

The micro-nano composite film covering the flat portion can change from hydrophobic to hydrophilic in a light environment; and the micro-nano composite film covering the opening can change from hydrophilic to hydrophobic in a dark environment.

Optionally, the micro-nano composite film includes at least one of a nanorod array structure, a needle-shaped array structure, and a hexagonal array structure formed of oxides.

Optionally, the oxide includes at least one of zinc oxide, titanium oxide and tin oxide.

Optionally, conductive particles are arranged in the micro-nano composite film covering the flat portion.

In a second aspect, the present disclosure provides a method for preparing an organic electroluminescent display substrate, which comprises:

providing a substrate base plate;

Forming a pixel defining layer on the base substrate by a patterning process, wherein the pixel defining layer includes a flat portion and an opening portion;

A micro-nano composite thin film is formed on the flat portion and the opening.

Optionally, forming a micro-nano composite thin film on the flat portion and the opening portion specifically includes:

The micro-nano composite thin film is formed on the flat portion and the opening by a hydrothermal method.

Optionally, after the step of forming the micro-nano composite thin film on the flat portion and the opening portion, the method further includes: forming an organic electroluminescent device functional layer in the opening portion.

Optionally, forming an organic electroluminescent device functional layer in the opening specifically includes:

Before the ink is dripped into the opening, the flat portion is shielded, and the micro-nano composite film is irradiated with ultraviolet light to change the micro-nano composite film covering the opening from being hydrophobic to being hydrophilic;

dripping a certain amount of ink into the opening;

During the ink drying process, the display substrate is placed in a dark environment, so that the micro-nano composite film covering the opening changes from hydrophilic to hydrophobic.

Optionally, after forming the organic electroluminescent device functional layer in the opening, the method further comprises:

An electrode layer of an organic electroluminescent device is formed on the organic electroluminescent device functional layer and the micro-nano composite film.

In a third aspect, an embodiment of the present disclosure provides a display device, comprising the above-mentioned organic electroluminescent display substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic plan view of an exemplary organic electroluminescent display substrate;

FIG2 is a circuit diagram of a pixel driving circuit in the display substrate shown in FIG1 ;

3 is a cross-sectional view of a connection position between a second light emitting control transistor and a light emitting device in the pixel driving circuit shown in FIG. 2 ;

FIG4 is a schematic structural diagram of another exemplary organic electroluminescent display substrate;

FIG5 is a schematic diagram of ink forming a concave film layer in the opening of the pixel defining layer shown in FIG4 ;

FIG6 is a schematic diagram of ink forming a convex film layer in the opening of the pixel defining layer shown in FIG4 ;

FIG. 7 is a schematic structural diagram of an organic electroluminescent display substrate provided by an embodiment of the present disclosure;

FIG8 is a schematic structural diagram of another organic electroluminescent display substrate provided by an embodiment of the present disclosure;

FIG. 9 is a flow chart of a method for preparing an organic electroluminescent display substrate provided in accordance with an embodiment of the present disclosure.

Detailed ways

In order to enable those skilled in the art to better understand the technical solution of the present disclosure, the present disclosure is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

Unless otherwise defined, the technical terms or scientific terms used in the present disclosure should be understood by people with ordinary skills in the field to which the present disclosure belongs. The "first", "second" and similar words used in the present disclosure do not indicate any order, quantity or importance, but are only used to distinguish different components. Similarly, similar words such as "one", "one" or "the" do not indicate quantity restrictions, but indicate that there is at least one. Similar words such as "include" or "comprise" mean that the elements or objects appearing before the word cover the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Similar words such as "connect" or "connected" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

It should be noted that the "composition process" refers to the steps of forming a structure with a specific pattern, which may be a photolithography process, and the photolithography process includes one or more steps of forming a material layer, applying a photoresist, exposing, developing, etching, and photoresist stripping; of course, the "composition process" may also be other processes such as an imprinting process and an inkjet printing process.

FIG1 is a schematic plan view of an exemplary organic electroluminescent display substrate. As shown in FIG1 , the display substrate includes a base substrate and a plurality of pixel units 0 formed on the base substrate, and a pixel driving circuit and an OLED device are provided in each pixel unit 0. The pixel driving circuit may include a 7T1C (i.e., seven transistors and one capacitor) structure, for example, including a driving transistor, a data writing transistor, a storage capacitor, a threshold compensation transistor, a first reset transistor, a second reset transistor, a first light emission control transistor, and a second light emission control transistor. FIG2 is a circuit diagram of a pixel driving circuit in the display substrate shown in FIG1 . Referring to FIG2 , the source of the data writing transistor T4 is electrically connected to the source of the driving transistor T3, the drain of the data writing transistor T4 is configured to be electrically connected to the data line Vd to receive the data signal, and the gate of the data writing transistor T4 is configured to be electrically connected to the first scanning signal line Ga1 to receive the scanning signal; the first plate CC1 of the storage capacitor Cst is electrically connected to the first power supply voltage terminal VDD, and the second plate CC2 of the storage capacitor Cst is electrically connected to the gate of the driving transistor T3; the source of the threshold compensation transistor T2 is electrically connected to the drain of the driving transistor T3, the drain of the threshold compensation transistor T2 is electrically connected to the gate of the driving transistor T3, and the gate of the threshold compensation transistor T2 is configured to be electrically connected to the second scanning signal line Ga2 to receive the compensation control signal; the source of the first reset transistor T1 is configured to be electrically connected to the first reset power supply terminal Vinit1 to receive the first reset signal, the drain of the first reset transistor T1 is electrically connected to the gate of the driving transistor T3, and the gate of the first reset transistor T1 is configured to be electrically connected to the first reset control signal The line Rst1 is electrically connected to receive the first sub-reset control signal; the source of the second reset transistor T7 is configured to be electrically connected to the first reset power supply terminal Vinit1 to receive the first reset signal, the drain of the second reset transistor T7 is electrically connected to the first electrode D1 of the light-emitting device D, and the gate of the second reset transistor T7 is configured to be electrically connected to the second reset control signal line Rst2 to receive the second sub-reset control signal; the source of the first light-emitting control transistor T5 is electrically connected to the first power supply voltage terminal VDD, the drain of the first light-emitting control transistor T5 is electrically connected to the source of the driving transistor T3, and the gate of the first light-emitting control transistor T5 is configured to be electrically connected to the first light-emitting control signal line EM1 to receive the first light-emitting control signal; the source of the second light-emitting control transistor T6 is electrically connected to the drain of the driving transistor T3, the drain of the second light-emitting control transistor T6 is electrically connected to the first electrode D1 of the light-emitting device D, and the gate of the second light-emitting control transistor T6 is configured to be electrically connected to the second light-emitting control signal line EM2 to receive the second light-emitting control signal; the second electrode D3 of the light-emitting device D is electrically connected to the second power supply voltage terminal VSS.

FIG3 is a cross-sectional view of the connection position between the second light-emitting control transistor and the light-emitting device in the pixel driving circuit shown in FIG2. As shown in FIG3, the driving circuit layer can be formed on the substrate. For example, as shown in FIG3, the driving circuit layer can be formed on the buffer layer 102. The driving circuit layer can include an interlayer dielectric layer 103, and the interlayer dielectric layer 103 is made of inorganic materials, such as silicon oxide, silicon nitride and other inorganic materials, to achieve the effect of blocking water and oxygen and blocking alkaline ions.

In detail, the driving circuit layer also includes a thin film transistor and a capacitor structure.

As shown in FIG3 , the thin film transistor may be a top gate type, and the thin film transistor may include an active layer 104, a first gate insulating layer 105, a gate electrode 106, a second gate insulating layer 108, an interlayer dielectric layer 103, a source electrode 110, and a drain electrode 111. Specifically, the active layer 104 may be formed on the buffer layer 102, the first gate insulating layer 105 covers the buffer layer 102 and the active layer 104, the gate electrode 106 is formed on a side of the first gate insulating layer 105 away from the active layer 104, the second gate insulating layer 108 covers the gate electrode 106 and the first gate insulating layer 105, the interlayer dielectric layer 103 covers the second gate insulating layer 108, the source electrode 110 and the drain electrode 111 are formed on a side of the interlayer dielectric layer 103 away from the substrate and are respectively located on opposite sides of the gate electrode 106, and the source electrode 110 and the drain electrode 111 may be in contact with opposite sides of the active layer 104 through vias (e.g., metal vias), respectively. It should be understood that the thin film transistor may also be a bottom-gate type.

As shown in FIG. 3 , the capacitor structure may include a first plate 130 and a second plate 131 . The first plate 130 is disposed in the same layer as the gate 106 . The second plate 131 is located between the second gate insulating layer 108 and the interlayer dielectric layer 103 and is disposed opposite to the first plate 130 .

As shown in FIG. 3 , the display device is located in the display area. The display device may include a first electrode 112 and a pixel defining portion 113 sequentially formed on the interlayer dielectric layer 103 . It should be understood that the display device may also include a light-emitting portion 114 a and a second electrode 115 .

In detail, when the thin film transistor is a top-gate type, a planarization layer can be further manufactured before manufacturing the display device. The planarization layer can be a single-layer structure or a multi-layer structure. The planarization layer is usually manufactured using organic materials, such as photoresist, acrylic-based polymers, silicon-based polymers and other materials. As shown in FIG. 3 , the planarization layer can include a planarization portion 116 formed between the interlayer dielectric layer 103 and the first electrode 112 . The first electrode 112 may be electrically connected to the drain electrode 111 through a metal via, and the first electrode 112 may be an anode, which may be made of materials such as ITO (indium tin oxide), indium zinc oxide (IZO), and zinc oxide (ZnO); the pixel defining portion 113 may cover the planarizing portion 116, and the pixel defining portion 113 may be made of an organic material, such as an organic material such as a photoresist, and the pixel defining portion 113 may have a pixel opening exposing the first electrode 112; the light-emitting portion 114a is located in the pixel opening and is formed on the first electrode 112, and the light-emitting portion 114a may include a small molecule organic material Or polymer molecular organic material, it can be a fluorescent light-emitting material or a phosphorescent light-emitting material, it can emit red light, green light, blue light, or white light, etc.; and, according to different actual needs, in different examples, the light-emitting portion 114a can further include functional layers such as an electron injection layer, an electron transport layer, a hole injection layer, and a hole transport layer; the second electrode 115 covers the light-emitting portion 114a, and the polarity of the second electrode 115 is opposite to the polarity of the first electrode 112; this second electrode 115 can be a cathode, and this cathode can be made of metal materials such as lithium (Li), aluminum (Al), magnesium (Mg), and silver (Ag).

It should be noted that, as shown in FIG3 , the first electrode 112, the light-emitting portion 114a and the second electrode 115 may constitute a light-emitting sub-pixel 1d. Among them, the display device may include a plurality of light-emitting sub-pixels 1d arranged in an array. In addition, it should be noted that the first electrodes 112 of each light-emitting sub-pixel 1d are independent of each other, and the second electrodes 115 of each light-emitting sub-pixel 1d are connected on the entire surface; that is, the second electrode 115 is a whole-surface structure provided on the display substrate 10, and is a common electrode for multiple display devices.

FIG4 is a schematic diagram of the structure of another exemplary organic electroluminescent display substrate, FIG5 is a schematic diagram of ink forming a concave film layer in the pixel defining layer opening shown in FIG4, and FIG5 is a schematic diagram of ink forming a convex film layer in the pixel defining layer opening shown in FIG4. It should be noted that FIG4 to FIG6 only illustrate the base substrate 1, the driving circuit 2, the planarization layer 3, the anode 4 of the organic electroluminescent device, and the pixel defining layer 5.

As shown in Figures 4-6, the organic electroluminescent display substrate includes a base substrate 1, a pixel driving circuit 2 arranged on the base substrate 1, a planarization layer 3 arranged on the side of the pixel driving circuit 2 away from the base substrate 1, an anode 4 of the organic electroluminescent device arranged on the side of the planarization layer 3 away from the base substrate 1, and a pixel defining layer 5 arranged on the side of the anode 4 of the organic electroluminescent device away from the base substrate 1, wherein the pixel defining layer 5 has a flat portion 52 and an opening portion 51, and an organic functional layer 6 can be arranged in the opening portion 51 of the pixel defining layer 5.

In the process of forming the organic functional layer 6 by inkjet printing technology, due to the different hydrophilicities of different inks, the ink with good hydrophilicity will climb higher on the inclined inner surface of the opening 51 to form a concave film layer (as shown in Figure 5), and the ink with poor hydrophilicity will form a convex film layer in the opening 51 (as shown in Figure 6). As a result, the film thickness of the light-emitting element functional layer 6 in each pixel area is uneven after drying, which affects the uniformity of the light emission of the organic electroluminescent display device OLED and reduces the quality of the organic electroluminescent display device OLED.

In order to solve at least one of the above technical problems, the present disclosure provides an organic electroluminescent display substrate and a preparation method thereof, and a display device. The organic electroluminescent display substrate and a preparation method thereof, and the display device provided by the present disclosure are further described in detail below in conjunction with the accompanying drawings and specific embodiments.

In the first aspect, Figure 7 is a structural schematic diagram of an organic electroluminescent display substrate provided by an embodiment of the present disclosure. As shown in Figure 7, an embodiment of the present disclosure provides an organic electroluminescent display substrate, and the organic electroluminescent display substrate includes a base substrate 11, a pixel driving circuit 12, a planarization layer 13, an anode layer 14 of an organic electroluminescent device, a pixel defining layer 15 and a micro-nano composite film 16.

Specifically, the pixel driving circuit 12 is arranged on the base substrate 11, and a planarization layer 13 is arranged on the side of the pixel driving circuit 12 facing away from the base substrate 11, and an anode layer 14 of the organic electroluminescent device is arranged on the side of the planarization layer 13 facing away from the base substrate, and a pixel defining layer 15 is arranged on the side of the anode layer 14 of the organic electroluminescent device facing away from the base substrate 11, and the pixel defining layer 15 includes an opening 151 and a flat portion 152 arranged around the opening. The micro-nano composite film 16 covers the opening 151 and the flat portion 152 of the pixel defining layer, and the micro-nano composite film 16 is hydrophobic, but under light, the micro-nano composite film can change from hydrophobic to hydrophilic, and in a dark environment, the micro-nano composite film converted to hydrophilic can also change to hydrophobic. In this embodiment, the micro-nano composite film 16 covering the opening 151 can change from hydrophobic to hydrophilic in a light environment, and the micro-nano composite film 16 covering the opening 151 can change from hydrophilic to hydrophobic in a dark environment.

In this embodiment, since the micro-nano composite film 16 covering the opening 151 can change from hydrophobic to hydrophilic in a light environment, the micro-nano composite film 16 covering the opening 151 can change from hydrophilic to hydrophobic in a dark environment. In this way, before the ink drips into the opening, the micro-nano composite film 16 covering the flat portion 152 can be blocked, and the micro-nano composite film 16 covering the opening 151 can be irradiated with light. After the irradiation, the micro-nano composite film 16 covering the opening 151 changes from hydrophobic to hydrophilic; after the ink drips into the opening 151, since the micro-nano composite film 16 covering the flat portion 152 is hydrophobic and the micro-nano composite film 16 covering the opening 151 is hydrophilic, the micro-nano composite film 16 covering the opening 151 has a pulling force on the ink, and the micro-nano composite film 16 covering the flat portion 152 has a repulsive force on the ink. The uniformity of the ink under the action of these two forces is increased, thereby ensuring that the ink is uniformly formed into a film in the opening 151 of the pixel defining layer 15, effectively improving the luminescence uniformity of the organic electroluminescent device. At the same time, during the ink drying process, the organic electroluminescent display substrate is placed in a dark environment. Since the micro-nano composite film 16 can change from hydrophilic to hydrophobic in a dark environment, the micro-nano composite film 16 covering the opening 151 changes from hydrophilic to hydrophobic. In this way, the surface properties of the organic functional film 16 can be restored, and the surface of the organic functional film can be homogenized.

In some embodiments, the micro-nano composite film 16 includes at least one of a nanorod array structure, a needle-shaped array structure, and a hexagonal array structure formed by oxides. Specifically, the oxides may include at least one of zinc oxide, titanium oxide, and tin oxide.

The following is an example of titanium dioxide TiO2 as the oxide in the micro-nano composite film 16: Titanium dioxide TiO2 is a semiconductor material with broad application prospects. Its excellent physical and chemical properties enable it to have attractive application prospects in solar cells, photocatalytic degradation of pollutants, sensors, and glass anti-fogging, and has become a hot topic of research at home and abroad. The current methods for preparing titanium dioxide film layers include hydrothermal method, plasma spraying, electrodeposition, electrochemical anodization method, sol-gel method, etc. It is known that the film layer formed by titanium dioxide is hydrophobic. In this embodiment, a layer of TiO2 nanofilm layer is deposited and grown on the surface of the pixel defining layer 15, and a hydrothermal method is used to grow it at 160°C for two hours. A TiO2 micro-nano composite film with micro-nano scale is prepared on the surface of the pixel defining layer 15. The TiO2 micro-nano composite film has a composite structure cluster, the size of the composite structure cluster is 0.1-0.2um, and the composite structure cluster is composed of a TiO2 nanorod array of 10-30nm. Since the TiO2 micro-nano composite film has a large number of pores, which can prevent the infiltration of droplets, the TiO2 micro-nano composite film has good hydrophobicity. In addition, after the surface of the composite structure cluster is irradiated with ultraviolet light or high-energy light, the composite structure changes in the forward direction, and the TiO2 micro-nano composite film becomes highly hydrophilic. In a dark environment (i.e., no light irradiation or trace light irradiation), the TiO2 micro-nano composite film can also become hydrophobic after releasing energy.

In this embodiment, a TiO2 micro-nano composite film is formed by a hydrothermal method. After the TiO2 micro-nano composite film is irradiated with ultraviolet light or high-energy light, the composite structure changes in a forward direction, and the TiO2 micro-nano composite film becomes highly hydrophilic. When not irradiated or under dim light, the TiO2 micro-nano composite film releases energy and becomes hydrophobic.

In some embodiments, micro-nano composite films with various morphologies can be prepared by changing the concentration of the hydrothermal growth solution, ion additives, growth time and other conditions. The micro-nano composite films may include needle-shaped arrays, nanorod arrays and hexagonal micron disks formed by oxides.

It should be noted that the oxide in the micro-nano composite film can also be tin dioxide, zinc oxide, etc. The method of preparing the micro-nano composite film using them is the same as the principle of forming the micro-nano composite film using titanium dioxide, and no examples will be given here one by one.

In some embodiments, as shown in FIG7 , the organic electroluminescent display substrate further includes an organic functional layer 17 and a cathode layer 18 of the organic electroluminescent device. Among them, the organic functional layer 17 is arranged on the side of the micro-nano composite film 16 away from the base substrate 11 and is formed in the opening 151 of the pixel defining layer 15. The cathode layer 18 of the organic electroluminescent device is arranged on the side of the micro-nano composite film 16 away from the base substrate 11. The organic functional layer 17 is generally composed of one or more layers of a hole injection layer, a hole transport layer, a light-emitting layer, a hole blocking layer, an electron blocking layer, an electron transport layer, an electron injection layer, etc. As shown in FIG7 , the top of the organic functional layer 17 is at a certain distance from the micro-nano composite film 16. The certain distance is to prevent short circuits. Those skilled in the art can select a suitable distance according to the specific structure, which will not be described in detail here.

In some embodiments, as shown in FIG8 , conductive particles 19 are evenly arranged in the micro-nano composite film 16 covering the flat portion 152 of the pixel defining layer. The conductive particles 19 may be conductive metal particles or conductive alloy particles, or a new type of conductive material, such as graphene.

In this embodiment, since the conductive particles 19 are evenly arranged in the micro-nano composite film 16 covering the flat portion 152 of the pixel defining layer 15, the micro-nano composite film 16 covering the flat portion 152 of the pixel defining layer 15 is overlapped with the cathode 18 of the organic electroluminescent device to form a parallel structure, which can reduce the resistance of the cathode 17, thereby reducing the voltage drop of the cathode film layer, and further improving the brightness uniformity of the OLED light-emitting device.

In a second aspect, an embodiment of the present disclosure provides a method for preparing an organic electroluminescent display substrate. As shown in FIG9 , the method for preparing an organic electroluminescent display substrate includes:

S101, providing a substrate.

Substrate The substrate is the support of the electrode layer and the organic functional thin film layer in the organic electroluminescent device. It has good light transmittance in the visible light region and a certain ability to resist water vapor and oxygen penetration, and has good surface flatness. It can generally be made of glass, or a flexible substrate, or an array substrate, etc. If a flexible substrate is selected, it can be made of polyester, polyphthalimide or a thinner metal.

S102, sequentially forming a pixel driving circuit and a planarization layer on the substrate. Forming the pixel driving circuit on the substrate may include, for example, sequentially forming a gate electrode, a gate insulating layer, an active layer, a source electrode, and a drain electrode on the substrate, wherein the drain electrode is connected to the pixel electrode through a via hole provided on the protective layer. The gate electrode, the gate insulating layer, the active layer, the source electrode, and the drain electrode constitute the structure of the thin film transistor 300.

S103, forming an anode layer of an organic electroluminescent device on the side of the planarization layer away from the substrate. The anode is usually made of inorganic metal oxides (such as indium tin oxide ITO, zinc oxide ZnO, etc.), organic conductive polymers (such as poly (3,4-ethylenedioxythiophene)/polystyrene sulfonate PEDOT: PSS, polyaniline PANI, etc.) or high work function metal materials (such as gold, copper, silver, platinum, etc.).

S104, forming a pixel defining layer on the side of the anode layer away from the substrate through a patterning process, wherein the pixel defining layer includes an opening and a flat portion arranged around the opening. Specifically, the opening and the flat portion in the pixel defining layer can be formed by using a mask of the pixel defining layer through exposure, development and etching processes.

S105, forming a micro-nano composite thin film on the opening and the flat portion. Optionally, PECVD or hydrothermal method can be used to form the micro-nano composite thin film on the opening and the flat portion.

For example, a micro-nano composite film with micro-nano scale is prepared on the surface of the pixel defining layer by growing at 160°C for two hours using a hydrothermal method. The micro-nano composite film has a composite structure cluster, the size of the composite structure cluster is 0.1-0.2um, and the composite structure cluster is composed of a 10-30nm nanorod array. Since the micro-nano composite film has a large number of pores, which can prevent the infiltration of droplets, the micro-nano composite film has good hydrophobicity. In addition, after the surface of the composite structure cluster is irradiated with ultraviolet light or high-energy light, the composite structure changes in the forward direction, and the micro-nano composite film becomes highly hydrophilic; when not irradiated or under dim light, the micro-nano composite film can also become hydrophobic after releasing energy.

S106 , forming a functional layer of an organic electroluminescent device in the opening.

The functional layer of an organic electroluminescent device is usually composed of one or more layers of a hole injection layer, a hole transport layer, a light-emitting layer, a hole blocking layer, an electron blocking layer, an electron transport layer, an electron injection layer, etc. The material of the hole injection layer includes any one of 2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazatriphenylene (HAT-CN), 2,3,5,6-tetrafluoro-7,7',8,8'-tetracyanodimethyl-p-phenylene (F4-TCNQ), and tris(4-bromophenyl)ammonium hexachloroantimonate (TBAHA). The material of the hole transport layer can be made of aromatic diamine compounds, triphenylamine compounds, aromatic triamine compounds, biphenyl diamine derivatives, triarylamine polymers, metal complexes, or carbazole polymers, preferably any one of: N, N'-di (1-naphthyl) -N, N'-diphenyl-1, 1'-biphenyl-4-4'-diamine (NPB), triphenyl diamine derivatives (TPD), TPTE, 1, 3, 5-tri (N-3-methylphenyl-N-phenylamino) benzene (TDAB). The light-emitting layer 3 can be made of an undoped fluorescent organic material composed of a light-emitting material having a hole transport capacity not less than an electron transport capacity, or made of an organic material doped with a fluorescent material composed of a fluorescent dopant and a matrix material, or made of an organic material doped with a phosphorescent material composed of a phosphorescent dopant and a matrix material. The material of the electron transport layer 6 includes any one of 2-(4-biphenyl)-5-phenyloxadiazole (PBD), 2,5-di(1-naphthyl)-1,3,5-oxadiazole (BND), and 2,4,6-triphenoxy-1,3,5-triazine (TRZ). The material of the electron injection layer 7 is any one of lithium fluoride, sodium fluoride, potassium fluoride, rubidium fluoride, cesium fluoride, lithium oxide, and lithium metaborate.

Optionally, forming a functional layer of an organic electroluminescent device in the opening (S106) specifically includes:

S1061, before the ink is dripped into the opening, the micro-nano composite film covering the flat portion is shielded, and the micro-nano composite film is irradiated with ultraviolet light to change the micro-nano composite film covering the opening from being hydrophobic to being hydrophilic;

S1062, dripping a certain amount of ink into the opening of the pixel defining layer;

S1063. During the ink drying process, the display substrate is placed in a dark environment to change the micro-nano composite film covering the opening from hydrophilic to hydrophobic.

S107, forming a cathode layer of the organic electroluminescent device on the organic electroluminescent device functional layer and the micro-nano composite thin film.

The cathode is usually made of low work function metal materials, such as lithium, magnesium, calcium, strontium, aluminum, indium, etc., or alloys of the above metals with copper, gold, and silver; or a very thin buffer insulating layer (such as lithium fluoride LiF, cesium carbonate CsCO3, etc.) and the above metals or alloys.

In this embodiment, since the micro-nano composite film 16 covering the opening 151 can change from hydrophobic to hydrophilic in a light environment, the micro-nano composite film 16 covering the opening 151 can change from hydrophilic to hydrophobic in a dark environment. In this way, before the ink drips into the opening, the micro-nano composite film 16 covering the flat portion 152 can be blocked, and the micro-nano composite film 16 covering the opening 151 can be irradiated with light. After the irradiation, the micro-nano composite film 16 covering the opening 151 changes from hydrophobic to hydrophilic; after the ink drips into the opening 151, since the micro-nano composite film 16 covering the flat portion 152 is hydrophobic and the micro-nano composite film 16 covering the opening 151 is hydrophilic, the micro-nano composite film 16 covering the opening 151 has a pulling force on the ink, and the micro-nano composite film 16 covering the flat portion 152 has a repulsive force on the ink. The uniformity of the ink under the action of these two forces is increased, thereby ensuring that the ink is uniformly formed into a film in the opening 151 of the pixel defining layer 15, effectively improving the luminescence uniformity of the organic electroluminescent device. At the same time, during the ink drying process, the organic electroluminescent display substrate is placed in a dark environment. Since the micro-nano composite film 16 can change from hydrophilic to hydrophobic in a dark environment, the micro-nano composite film 16 covering the opening 151 changes from hydrophilic to hydrophobic. In this way, the surface properties of the organic functional film 16 can be restored, and the surface of the organic functional film can be homogenized.

In a third aspect, an embodiment of the present disclosure provides a display device, comprising the above-mentioned organic electroluminescent display substrate.

It is to be understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of the present disclosure, but the present disclosure is not limited thereto. For those of ordinary skill in the art, various modifications and improvements can be made without departing from the spirit and substance of the present disclosure, and these modifications and improvements are also considered to be within the scope of protection of the present disclosure.

Claims (8)

1. An organic electroluminescent display substrate, characterized in that it comprises a pixel defining layer disposed on a base substrate, the pixel defining layer comprising a flat portion and an opening; the organic electroluminescent display substrate further comprises a micro-nano composite film, the micro-nano composite film covers the flat portion and the opening of the pixel defining layer; Wherein, the micro-nano composite film covering the opening changes from hydrophobic to hydrophilic under light environment; the micro-nano composite film covering the opening changes from hydrophilic to hydrophobic under dark environment; the micro-nano composite film includes at least one of a nanorod array structure, a needle-shaped array structure, and a hexagonal array structure formed by oxide; The oxide includes titanium dioxide. 2 . The organic electroluminescent display substrate according to claim 1 , wherein conductive particles are provided in the micro-nano composite film covering the flat portion. 3. A method for preparing an organic electroluminescent display substrate, comprising: providing a substrate base plate; Forming a pixel defining layer on the base substrate by a patterning process, wherein the pixel defining layer includes a flat portion and an opening portion; A micro-nano composite film is formed on the flat portion and the opening; the micro-nano composite film comprises at least one of a nanorod array structure, a needle-shaped array structure, and a hexagonal array structure formed by oxides; the oxides comprise titanium dioxide; Wherein, the micro-nano composite film covering the opening changes from hydrophobic to hydrophilic in a light environment; and the micro-nano composite film covering the opening changes from hydrophilic to hydrophobic in a dark environment. 4. The method for preparing an organic electroluminescent display substrate according to claim 3, characterized in that the step of forming a micro-nano composite thin film on the flat portion and the opening portion specifically comprises: The micro-nano composite thin film is formed on the flat portion and the opening by a hydrothermal method. 5. The method for preparing an organic electroluminescent display substrate according to claim 4, characterized in that after the step of forming a micro-nano composite thin film on the flat portion and the opening portion, the method further comprises: An organic electroluminescent device functional layer is formed in the opening. 6. The method for preparing an organic electroluminescent display substrate according to claim 5, characterized in that forming an organic electroluminescent device functional layer in the opening comprises: Before the ink is dripped into the opening, the flat portion is shielded, and the micro-nano composite film is irradiated with ultraviolet light to change the micro-nano composite film covering the opening from being hydrophobic to being hydrophilic; dripping a certain amount of ink into the opening; During the ink drying process, the display substrate is placed in a dark environment, so that the micro-nano composite film covering the opening changes from hydrophilic to hydrophobic. 7. The method for preparing an organic electroluminescent display substrate according to claim 6, characterized in that after forming the organic electroluminescent device functional layer in the opening, the method further comprises: An electrode layer of an organic electroluminescent device is formed on the organic electroluminescent device functional layer and the micro-nano composite film. 8. A display device, comprising the display substrate according to any one of claims 1 to 2.