CN111223901A

CN111223901A - Display panel and preparation method thereof

Info

Publication number: CN111223901A
Application number: CN201911205338.XA
Authority: CN
Inventors: 刘娜; 刘操; 过配配; 陈营营; 李梦萍; 朱平
Original assignee: Yungu Guan Technology Co Ltd
Current assignee: Yungu Guan Technology Co Ltd
Priority date: 2019-11-29
Filing date: 2019-11-29
Publication date: 2020-06-02
Anticipated expiration: 2039-11-29
Also published as: CN111223901B

Abstract

The invention provides a display panel and a preparation method thereof, and solves the problem of poor ink-jet printing quality in the prior art. The display panel comprises a plurality of pixel units arranged at intervals and a dam for spacing the pixel units, and is characterized in that the dam comprises a top layer and a bottom layer which are arranged on top of each other, the top layer comprises a matrix and a hydrophobic component doped in the matrix, the bottom layer comprises the matrix and a hydrophilic component doped in the matrix, and the matrix is diamond-like.

Description

Display panel and preparation method thereof

Technical Field

The invention relates to the technical field of display, in particular to a display panel and a preparation method thereof.

Background

In the process of manufacturing an organic light emitting display panel, an organic light emitting material is typically printed into a pixel pit using an inkjet printing technique to form an organic light emitting layer in a pixel unit. However, the process of preparing the organic light emitting layer by using the inkjet printing technology is still not mature, and there is a phenomenon that printed liquid drops are easy to drop on the pixel defining layer or the printed liquid drops are not well filled in the pixel pits, so that the printing quality is poor.

Disclosure of Invention

In view of the above, embodiments of the present invention are directed to a display panel and a method for manufacturing the same, so as to solve the problem of poor quality of inkjet printing in the prior art.

The invention provides a display panel, which comprises a plurality of pixel units arranged at intervals and a dam for spacing the pixel units, wherein the dam comprises a top layer and a bottom layer which are stacked up and down, the top layer comprises a matrix and a hydrophobic component doped in the matrix, the bottom layer comprises the matrix and a hydrophilic component doped in the matrix, and the matrix is diamond-like carbon. Thus, a bank structure in which the bottom layer is hydrophilic and the top layer is hydrophobic can be formed, so that it can be ensured that the organic light emitting material dropped into the pixel pits can be uniformly spread in the process of preparing the pixel unit, and the organic light emitting material is prevented from overflowing, thereby improving the ink jet printing quality of the organic light emitting material.

In one embodiment, the bottom layer is progressively less hydrophilic in the direction from the bottom layer to the top layer; and/or the hydrophobicity of the top layer gradually increases. Thus, the difference of wettability of the top layer and the bottom layer at the interface can be reduced, so that the boundary between the top layer and the bottom layer becomes fuzzy, and the phenomenon that the film layer is separated at the interface between the top layer and the bottom layer to influence the structural stability is avoided.

In one embodiment, the pixel unit includes an organic light emitting layer having a top surface lower than or equal to a top surface of the bottom layer in a direction along the bottom layer to the top layer. Therefore, the periphery of the organic light-emitting layer can be ensured to be hydrophilic components, and the spreading uniformity of an organic light-emitting material is facilitated when the organic light-emitting layer is prepared by ink-jet printing, so that the ink-jet printing quality of the pixel unit is improved.

In one embodiment, the dike further comprises an intermediate layer located between the top layer and the bottom layer, the material of the intermediate layer being a base material. Further reducing the difference of wettability of the top layer and the bottom layer at the interface and improving the structural stability.

In one embodiment, the liquid crystal display further comprises a thin film encapsulation structure on the plurality of pixel cells and the bank, the thin film encapsulation structure comprising an inorganic layer and an organic layer stacked, and a reinforcing layer between the inorganic layer and the organic layer; the material of the strengthening layer comprises a matrix and a hydrophobic component doped in the matrix, and the matrix is diamond-like carbon. The water and oxygen blocking effect of the film packaging structure is improved by arranging the reinforcing layer with hydrophobicity.

In one embodiment, the hydrophobicity of the stiffening layer gradually decreases in a direction from the inorganic layer to the organic layer. The inorganic layer has good hydrophobicity, and the organic layer has poor hydrophobicity, so that the hydrophobicity of the reinforcing layer is gradually reduced from the inorganic layer to the organic layer, so that the hydrophobicity of the reinforcing layer gradually decreases from the inorganic layer to the organic layer, and thus, the interface between adjacent membrane layers can be blurred from the aspect of hydrophobicity, and the structural stability is improved.

In one embodiment, the hydrophobic component includes a metal and a non-metal; and/or the hydrophilic component comprises a non-metal. By doping hydrophilic nonmetallic elements in the diamond-like carbon, the nonmetallic elements can form stable chemical bonds with carbon elements in the diamond-like carbon so as to regulate and control the contents of SP2 carbon bonds and SP3 carbon bonds, thereby reducing the internal stress of the diamond-like carbon and reducing the delamination and peeling phenomena of the diamond-like carbon.

In one embodiment, the hydrophobic component includes a metal and a non-metal; the atomic percent of the metal gradually increases and the atomic percent of the nonmetal gradually decreases in a direction from the bottom layer to the top layer. The co-doping of metal and nonmetal can play a synergistic effect, and the internal stress, the stability and the surface roughness of the diamond-like carbon can be improved while the hydrophobicity of the diamond-like carbon is enhanced.

In one embodiment, the hydrophobic component comprises at least one of molybdenum, tungsten, cobalt, nickel, iron, lead, fluorine; and/or the hydrophilic component comprises any one of silicon and nitrogen.

The second aspect of the present invention provides a method for manufacturing a display panel, including: preparing a first electrode layer on a substrate; preparing a pixel defining layer on the substrate and the first electrode layer, wherein the pixel defining layer comprises a top layer and a bottom layer which are stacked up and down, the top layer comprises a matrix and a hydrophobic component doped in the matrix, the bottom layer comprises a matrix and a hydrophilic component doped in the matrix, and the matrix is diamond-like carbon; etching the pixel defining layer to form a dam to expose the first electrode layer, wherein a pixel pit is defined by the side wall of the dam; preparing an organic light emitting layer in the pixel pits; a second electrode is prepared on the organic light emitting layer. Thus, a bank structure in which the bottom layer is hydrophilic and the top layer is hydrophobic can be formed, so that it can be ensured that the organic light emitting material dropped into the pixel pits can be uniformly spread in the process of preparing the pixel unit, and the organic light emitting material is prevented from overflowing, thereby improving the ink jet printing quality of the organic light emitting material.

According to the invention, the display panel comprises a top layer and a bottom layer which are superposed up and down, the top layer and the bottom layer jointly form a dam structure, the top layer comprises diamond-like carbon and hydrophobic components doped in the diamond-like carbon, the bottom layer comprises diamond-like carbon and hydrophilic components doped in the diamond-like carbon, and the hydrophobic components and the hydrophilic components doped in the diamond-like carbon can change the wettability of the top layer and the bottom layer according to requirements due to the characteristic that the wettability of the diamond-like carbon can be regulated and controlled in a large range, so that the wettability of the bottom layer is increased, the wettability of the top layer is decreased, the organic luminescent materials dropped into pixel pits can be uniformly spread in the process of preparing pixel units, the organic luminescent materials are prevented from overflowing, and the ink-jet printing quality of the organic luminescent materials is improved.

Drawings

Fig. 1 is a schematic cross-sectional structure diagram of a display panel according to a first embodiment of the present invention.

Fig. 2 is a schematic cross-sectional structure diagram of a display panel according to a second embodiment of the invention.

Fig. 3 is a schematic cross-sectional structure diagram of a display panel according to a third embodiment of the invention.

Fig. 4 is a flowchart of a method for manufacturing a display panel according to a first embodiment of the invention.

Fig. 5 is a flowchart illustrating a method for manufacturing a display panel according to a second embodiment of the invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

It should be noted first that spatial relationship terms, such as "upper" and "lower," are intended to refer to two opposite directions. The terms "upper" and "lower" are used herein to correspond to the orientation of the figures and to facilitate description. Spatial relational terms should also be interpreted accordingly when the orientation of the figure is changed, for example, if a device or element in the figure is turned over, then "lower" should be interpreted as "upper".

Fig. 1 is a schematic cross-sectional structure diagram of a display panel according to a first embodiment of the present invention. As shown in fig. 1, the display panel 100 includes a plurality of pixel units 20 arranged at intervals and a bank 10 for spacing the plurality of pixel units 20 apart. The dam 10 includes a top layer 11 and a bottom layer 12 stacked one on another, the top layer 11 including a matrix and a hydrophobic component doped in the matrix, the bottom layer 12 including a matrix and a hydrophilic component doped in the matrix, the matrix material being diamond-like.

The display panel 100 is an Organic Light-Emitting Diode (OLED) display panel, and the specific structure thereof can be as shown in fig. 1, and includes: a substrate 21, a Thin Film Transistor (TFT) array structure layer 22 stacked on the substrate 21, a plurality of pixel cells 20 on the TFT array structure layer 22, and a bank 10 spacing the plurality of pixel cells 20. The pixel unit 20 is a sandwich structure of two electrode layers 201 and an organic light emitting layer 202 sandwiched therebetween, the two electrode layers 201 are respectively used as a cathode and an anode of the pixel unit, and it can be known that the pixel unit 20 can be a red sub-pixel, a green sub-pixel or a blue sub-pixel.

Diamond-like carbon is a substance composed of carbon elements, similar to diamond in properties, and has a graphite atom composition structure, is an amorphous metastable state structure of carbon, and has good hydrophobicity and light transmittance. The wettability of the diamond-like carbon can be regulated and controlled in a large range through doping, and the doping of the diamond-like carbon is easy to realize through technologies such as magnetron sputtering, radio frequency bias auxiliary magnetron sputtering and the like. The hydrophobic element incorporated into the diamond-like carbon may be a metal or a non-metal, and the hydrophilic component incorporated into the diamond-like carbon may also be a metal or a non-metal.

In one embodiment, the hydrophobic component incorporated into the diamond-like carbon is a non-metal. The diamond-like chemical bonds are mainly SP2 carbon bonds and SP3 carbon bonds, which have strong internal stress. By doping the nonmetal elements in the diamond-like carbon, the nonmetal elements can form stable chemical bonds with carbon elements in the diamond-like carbon so as to regulate and control the contents of SP2 carbon bonds and SP3 carbon bonds, thereby reducing the internal stress of the diamond-like carbon and reducing the layering and peeling phenomena of the diamond-like carbon.

For example, the hydrophobic component incorporated into diamond-like carbon is fluorine. The addition of the fluorine element can passivate the adsorption of the fluorine-doped diamond-like carbon film to water vapor and oxygen, thereby improving the hydrophobicity of the diamond-like carbon film. In addition, compared with a pure diamond-like carbon film, the fluorine-doped diamond-like carbon film also has the following excellent characteristics: first, by partially or completely replacing hydrogen atoms in the diamond-like structure with fluorine atoms, internal stress of the diamond-like thin film is reduced, thereby improving structural stability and strength of bonding with a substrate. Second, fluorine doped diamond-like films have higher optical transmission than pure diamond-like films.

In one embodiment, the hydrophobic component incorporated into the diamond-like carbon includes metals and non-metals. The co-doping of metal and nonmetal can play a synergistic effect, and the internal stress, the stability and the surface roughness of the diamond-like carbon can be improved while the hydrophobicity of the diamond-like carbon is enhanced.

In this case, considering that the bank 10 needs to be in contact with the electrode layer 201 in the pixel unit 20 in the structure of the display panel 100, the hydrophobic component to be doped includes a metal of low conductivity, for example, at least one of molybdenum, tungsten, cobalt, nickel, iron, lead, in order to prevent a short circuit between the bank 10 and the electrode layer 201. The doped hydrophobic nonmetal can be fluorine, for example, and the specific effect is as described above, which is not described herein again.

In one embodiment, the hydrophilic component incorporated into the diamond-like carbon comprises a non-metal. The diamond-like chemical bonds are mainly SP2 carbon bonds and SP3 carbon bonds, which have strong internal stress. By doping the nonmetal elements in the diamond-like carbon, the nonmetal elements can form stable chemical bonds with carbon elements in the diamond-like carbon so as to regulate and control the contents of SP2 carbon bonds and SP3 carbon bonds, thereby reducing the internal stress of the diamond-like carbon and reducing the layering and peeling phenomena of the diamond-like carbon.

For example, the hydrophilic component incorporated into diamond includes at least one of nitrogen and silicon. The process of doping nitrogen and silicon in the diamond-like carbon has low requirements on process conditions and is easy to realize industrially.

According to the display panel provided by any of the above embodiments, the top layer 11 includes diamond-like carbon and hydrophobic component doped therein, the bottom layer 12 includes diamond-like carbon and hydrophilic component doped therein, and the top layer 11 and the bottom layer 12 together constitute a bank for spacing a plurality of pixel units, so that it is ensured that the organic light emitting material dropped into the pixel pits can be uniformly spread during the process of preparing the pixel units 20, and the organic light emitting material is prevented from overflowing, thereby improving the quality of the ink jet printing of the organic light emitting material.

In one embodiment, as shown in fig. 1, the pixel unit 20 includes an organic light emitting layer 202, and the height of the top surface of the organic light emitting layer 202 is lower than or equal to the top surface of the bottom layer 12 in the direction from the bottom layer 12 to the top layer 11, that is, the distance from the side of the organic light emitting layer 202 away from the substrate 21 to the substrate 21 is less than or equal to the distance from the side of the bottom layer 12 away from the substrate 21 to the substrate 21. Therefore, the hydrophilic components can be ensured to be arranged around the organic light-emitting layer 202, and the spreading uniformity of the organic light-emitting material is facilitated when the organic light-emitting layer is prepared by ink-jet printing, so that the ink-jet printing quality of the pixel unit is improved.

In one embodiment, as shown in FIG. 1, the top layer 11 has a gradually increasing hydrophobicity in a direction along the bottom layer 12 to the top layer 11. Thus, the bottom of the top layer 11 can be made to have low hydrophobicity, so that the boundary between the top layer 11 and the bottom layer 12 having hydrophilicity therebelow can be blurred, and the occurrence of film separation at the interface between the top layer 11 and the bottom layer 12 is avoided, which affects the structural stability.

Further, in the direction from the bottom layer 12 to the top layer 11, the hydrophilicity of the bottom layer 12 gradually decreases while the hydrophobicity of the top layer 11 gradually increases. Thus, the wettability of the entire dam 10 is gradually decreased in the direction from bottom to top, and the boundary between the top layer 11 and the bottom layer 12 is further blurred, thereby preventing film separation from occurring at the interface between the top layer 11 and the bottom layer 12 and affecting the structural stability.

For example, the top layer 11 is doped with hydrophobic metals and non-metals, and the atomic percent of the metals gradually increases and the atomic percent of the non-metals gradually decreases in a direction along the bottom layer 12 to the top layer 11. In this way it is ensured that the hydrophobicity of the top layer 11 gradually increases in the direction from the bottom layer 12 to the top layer 11. The bottom layer 12 is doped with a hydrophilic non-metal, the atomic percentage of the non-metal in the bottom layer 12 decreasing in a direction along the bottom layer 12 to the top layer 11. In this way, it is ensured that the hydrophilicity of the bottom layer 12 gradually decreases in the direction from the bottom layer 12 to the top layer 11.

In one solution, which is easy to implement industrially, the hydrophobic metal doped in the top layer 11 is molybdenum, and the hydrophobic non-metal is fluorine; the hydrophilic non-metal doped in the bottom layer 12 is nitrogen or silicon.

It should be understood that the hydrophobicity of the top layer 11 and the hydrophilicity of the bottom layer 12 may also be uniformly distributed, in which case the atomic percent of the hydrophobic component incorporated in the top layer 11 may be uniformly distributed and the atomic percent of the hydrophilic component incorporated in the bottom layer 12 may be uniformly distributed.

In an embodiment, as shown in fig. 2, which is a schematic cross-sectional structure diagram of a display panel provided by a second embodiment of the present invention, the dam 30 in the display panel 200 further includes an intermediate layer 33 located between the top layer 31 and the bottom layer 32, and the material of the intermediate layer 33 is a base material, i.e., diamond-like carbon.

In this way, the intermediate layer 33 may act as a transition layer between the top layer 31 having hydrophobic properties and the bottom layer 32 having hydrophilic properties, thereby further obscuring the boundary between the top layer 31 and the bottom layer 32. Meanwhile, since the diamond-like carbon itself has a good water and oxygen blocking capability, it can well prevent water and oxygen from laterally diffusing between adjacent pixel cells 20.

Fig. 3 is a schematic cross-sectional structure diagram of a display panel according to a third embodiment of the invention. As shown in fig. 3, the display panel 300 is different from the display panel 100 and the display panel 200 in that the display panel 300 further includes a film encapsulation structure 40 covering a plurality of pixel units and banks, the film encapsulation structure 40 includes an inorganic layer 41 and an organic layer 42 which are stacked, and a reinforcing layer 43 located between the inorganic layer 41 and the organic layer 42, the reinforcing layer 43 includes a matrix and a hydrophobic component doped in the matrix, the matrix is diamond-like, and the reinforcing layer 43 has a strong water-oxygen barrier effect to enhance the water-oxygen barrier effect of the film encapsulation structure 40.

The doped hydrophobic nonmetal can be fluorine, for example, and the specific effect is as described above, which is not described herein again. The hydrophobic metal to be incorporated may be a transparent metal.

In one embodiment, the hydrophobicity of the stiffening layer 43 gradually decreases in a direction from the inorganic layer 41 to the organic layer 42. Since the inorganic layer 41 has good hydrophobicity and the organic layer 42 has poor hydrophobicity, the hydrophobicity of the reinforcing layer 43 gradually decreases from the inorganic layer to the organic layer, so that the hydrophobicity of the inorganic layer 41 to the organic layer 42 gradually decreases, and thus, from the viewpoint of hydrophobicity, the interface between adjacent films can be blurred, and the structural stability can be improved.

For example, as shown in fig. 3, for convenience of description, the inorganic layer 41 in the thin film encapsulation structure 40 is referred to as a first inorganic layer, and the reinforcing layer 43 is referred to as a first reinforcing layer. On this basis, the thin film encapsulation structure 40 further includes a second stiffening layer 44 and a second inorganic layer 45 sequentially stacked on the organic layer 42. The hydrophobicity of the first reinforcing layer 43 gradually decreases and the hydrophobicity of the second reinforcing layer 44 gradually increases in a direction along the inorganic layer 41 to the organic layer 42.

It should be understood that the second stiffening layer 44 is optional. The numbers of the inorganic layer 41, the organic layer 42, and the reinforcing layer 43 given here are merely exemplary. The inorganic layer 41, the reinforcing layer 43, and the organic layer 42 serve as one repeating unit, and the thin film encapsulation structure 40 may include a plurality of repeating units, and the number of the repeating units is not limited in the present invention.

Fig. 4 is a flowchart of a method for manufacturing a display panel according to a first embodiment of the invention. As shown in fig. 4, the method 400 for manufacturing a display panel includes:

step S410, a first electrode layer is prepared on the substrate.

The substrate may be any one of a glass substrate, a quartz substrate, and an organic substrate for supporting; the TFT array structure layer may be an integral body including any one of the above-described support substrates and the TFT array structure layer on the support substrate.

According to the difference of the light-emitting direction of the display panel, when the display panel is a top-emitting display panel, the first electrode is a metal electrode, and correspondingly, the subsequently formed second electrode is a transparent cathode; when the display panel is a bottom emission display panel, the first electrode is a transparent cathode, and correspondingly, the subsequently formed second electrode is a metal electrode. It can be known that, when the display panel is a top-emitting display panel, the first electrode layer is an anode, and a step of etching the first electrode layer needs to be added to form a patterned anode structure.

In step S420, a pixel defining layer is prepared on the substrate and the first electrode layer. The pixel defining layer comprises a top layer and a bottom layer which are arranged on top of each other, wherein the top layer comprises a matrix and a hydrophobic component doped in the matrix, the bottom layer comprises a matrix and a hydrophilic component doped in the matrix, and the matrix is diamond-like.

The pixel defining layer is subsequently used to form a bank that separates a plurality of pixel cells. The pixel defining layer can be prepared here using magnetron sputtering techniques or radio frequency bias assisted magnetron sputtering techniques.

Step S430, the pixel defining layer is etched to form a dam, so as to expose the first electrode layer, and a pixel pit is surrounded by sidewalls of the dam.

Step S440 is to prepare an organic light emitting layer in the pixel pit.

Step S450, a second electrode is prepared on the organic light emitting layer.

In one embodiment, the manufacturing method 400 further includes the step of manufacturing a thin film encapsulation structure on the second electrode. Specifically, as shown in fig. 5, which is a flowchart of a manufacturing method of a display panel according to a second embodiment of the present invention, the manufacturing method 400 further includes:

step S510 is to prepare a first inorganic layer on the second electrode.

Step S520, a first reinforcing layer is prepared on the first inorganic layer, the material of the reinforcing layer includes a matrix and a hydrophobic component doped in the matrix, and the matrix is diamond-like carbon.

In step S530, an organic layer is prepared on the first stiffening layer.

Step S540, a second inorganic layer is prepared on the organic layer.

In one embodiment, before step S540, the method further includes: and a step of preparing a second reinforcing layer on the organic layer. According to the manufacturing method of the display panel provided by any embodiment of the invention, the same inventive concept is adopted as the display panel provided by any embodiment, the film layer structure related in the manufacturing method of the display panel is the same as the corresponding film layer structure in the display panel, and the corresponding beneficial effects are achieved, and the parts which are not described in the manufacturing method embodiment can be referred to the display panel embodiment.

It should be understood that the terms "first" and "second" used in the description of the embodiments of the present invention are only used for clearly illustrating the technical solutions, and are not used for limiting the protection scope of the present invention.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and the like that are within the spirit and principle of the present invention are included in the present invention.

Claims

1. A display panel comprises a plurality of pixel units arranged at intervals and a dam for spacing the pixel units, wherein the dam comprises a top layer and a bottom layer which are arranged on top of each other, the top layer comprises a matrix and a hydrophobic component doped in the matrix, the bottom layer comprises a matrix and a hydrophilic component doped in the matrix, and the matrix is diamond-like.

2. The display panel according to claim 1, wherein the bottom layer has a gradually decreasing hydrophilicity in a direction from the bottom layer to the top layer; and/or

The hydrophobicity of the top layer gradually increases.

3. The display panel according to claim 1 or 2, wherein the pixel unit includes an organic light emitting layer having a top surface height lower than or equal to a top surface of the bottom layer in a direction from the bottom layer to the top layer.

4. The display panel according to any one of claims 1 to 3, wherein the bank further comprises an intermediate layer between the top layer and the bottom layer, and a material of the intermediate layer is a base material.

5. The display panel according to claim 1, further comprising a thin film encapsulation structure on the plurality of pixel cells and the bank, the thin film encapsulation structure comprising an inorganic layer and an organic layer stacked, and a stiffening layer between the inorganic layer and the organic layer; the material of the strengthening layer comprises a matrix and a hydrophobic component doped in the matrix, and the matrix is diamond-like carbon.

6. The display panel according to claim 5, wherein the hydrophobicity of the stiffening layer gradually decreases in a direction from the inorganic layer to the organic layer.

7. The display panel according to any one of claims 1 to 6, wherein the hydrophobic component includes a metal and a nonmetal; and/or

The hydrophilic component includes a non-metal.

8. The display panel of claim 7, wherein the hydrophobic component comprises a metal and a non-metal; the atomic percent of the metal gradually increases and the atomic percent of the nonmetal gradually decreases in a direction from the bottom layer to the top layer.

9. The display panel according to any one of claims 1 to 8, wherein the hydrophobic component comprises at least one of molybdenum, tungsten, cobalt, nickel, iron, lead, fluorine; and/or

The hydrophilic component includes any one of silicon and nitrogen.

10. A method for manufacturing a display panel, comprising:

preparing a first electrode layer on a substrate;

preparing a pixel defining layer on the substrate and the first electrode layer, wherein the pixel defining layer comprises a top layer and a bottom layer which are arranged on top of each other, the top layer comprises a matrix and a hydrophobic component doped in the matrix, the bottom layer comprises a matrix and a hydrophilic component doped in the matrix, and the matrix is diamond-like carbon;

etching the pixel defining layer to form a dam to expose the first electrode layer, wherein the side wall of the dam encloses a pixel pit;

preparing an organic light emitting layer in the pixel pits;

and preparing a second electrode on the organic light-emitting layer.