Patent Publication Number: US-2021191225-A1

Title: Substrate and display panel

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Chinese Patent Application No. 201911309325.7, filed on Dec. 18, 2019, which is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     The present disclosure relates to the field of display technologies, and in particular, to a substrate and a display panel. 
     BACKGROUND 
     A liquid light-emitting device includes a light-emitting layer including a liquid light-emitting material. The liquid light-emitting devices may be widely used in flexible display devices and non-flexible display devices. 
     SUMMARY 
     In an aspect, a substrate is provided. The substrate includes a base, a pixel defining layer, a plurality of electrode pairs, and a plurality of light-emitting devices. The pixel defining layer is disposed on the base, and layer includes a plurality of through holes. At least one electrode pair includes a first electrode and a second electrode that are disposed at least on a hole wall of one of the through holes and at least partially opposite to each other, and the first electrode and the second electrode are insulated from each other. One of the plurality of light-emitting devices includes a liquid functional layer, and the liquid functional layer is disposed in the through hole. The liquid functional layer is in direct contact with the first electrode and the second electrode. The liquid functional layer includes a liquid light-emitting layer configured to emit light. 
     In some embodiments, the first electrode and the second electrode each extend along the hole wall from an edge of the hole wall away from the base to a lower surface of the liquid light-emitting layer proximate to the base. 
     In some embodiments, the liquid functional layer further includes a liquid encapsulation layer. The liquid encapsulation layer is disposed on a side of the liquid light-emitting layer away from the base and is in direct contact with the liquid light-emitting layer. The liquid light-emitting layer includes a first liquid, and the liquid encapsulation layer includes a second liquid immiscible with the first liquid. A density of the second liquid is less than a density of the first liquid. 
     In some embodiments, the first electrode and the second electrode each extend along the hole wall from an edge of the hole wall away from the base to a surface of the liquid encapsulation layer in contact with the liquid light-emitting layer. 
     In some embodiments, a relative molecular mass of the first is greater than a relative molecular mass of the second liquid. 
     In some embodiments, the first liquid includes an organic solvent and a dispersant dissolved in the organic solvent. 
     In some embodiments, the plurality of electrode pairs includes at least one electrode pair which includes a first electrode connected to and integrated with another first electrode of an adjacent electrode pair, and second electrodes of any two adjacent electrode pairs are insulated from each other. 
     In some embodiments, the first electrode and the second electrode are disposed in a same layer. 
     In some embodiments, the substrate further includes a plurality of first power lines and a plurality of second power lines that are disposed on the base and insulated from each other. The first electrode is electrically connected to a corresponding one of the first power lines, and the second electrode is electrically connected to a corresponding one of the second power lines. 
     In some embodiments, the light-emitting device further includes a third electrode and a fourth electrode, and the third electrode and the fourth electrode are both insulated from the first electrode and the second electrode. The third electrode is located at a side of the liquid functional layer proximate to the base, and the fourth electrode is located at a side of the liquid functional layer away from the base. 
     In some embodiments, fourth electrodes in the plurality of light-emitting devices are integrated to form an integrated structure, and the integrated structure covers the pixel defining layer. 
     In some embodiments, the substrate further includes an insulating layer disposed between the fourth electrodes and the plurality of electrode pairs. The insulating layer includes a plurality of hollowed-out portions, each hollowed-out portion corresponds to a through hole, and a projection of the hollowed-out portion on the base overlaps with an orthographic projection of the through hole on the base. 
     In some embodiments, the light-emitting device further includes a hole injection layer, a hole transport layer, an electron injection layer, and an electron transport layer. The hole injection layer is located between the third electrode and the liquid functional layer. The hole transport layer is located between the hole injection layer and the liquid functional layer. The electron injection layer is located between the fourth electrode and the liquid functional layer. The electron transport layer is located between the electron injection layer and the liquid functional layer. 
     In some embodiments, the substrate further includes a plurality of pixel driver circuits disposed between the base and the plurality of light-emitting devices. Each pixel driver circuit is electrically connected to a third electrode of a corresponding light-emitting device, and the pixel driver circuit is configured to drive the liquid light-emitting layer to emit light. 
     In some embodiments, the substrate further includes a solid encapsulation layer disposed on a side of the light-emitting device away from the base. The solid encapsulation layer covers the pixel defining layer. 
     In some embodiments, the first electrode and the second electrode are made of the same material. 
     In some embodiments, the liquid light-emitting layer includes a first liquid and particles suspended in the first liquid, and the particles are quantum dots. 
     In another aspect, a display panel is provided. The display panel includes the substrate in any one of the above embodiments. 
     In some embodiments, the display panel further includes a backlight, and the substrate is disposed at a light-exit side of the backlight. The liquid light-emitting layer includes a first liquid and particles suspended in the first liquid, and the particles are quantum dots. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to explain technical solutions in embodiments of the present disclosure more clearly, the accompanying drawings used in some embodiments of the present disclosure will be introduced briefly below. However, the accompanying drawings to be described below are merely some illustrative embodiments of the present disclosure, and a person of ordinary skill in the art can obtain other drawings according to these drawings without paying any creative effort. In addition, the accompanying drawings to be described below may be regarded as schematic diagrams, and are not limitations on actual sizes of products, an actual process of a method and actual timings of signals that the embodiments of the present disclosure relate to. 
         FIG. 1  is a top view of a substrate, in accordance with some embodiments; 
         FIG. 2A  is a sectional diagram of the substrate taken along direction B-B′ in  FIG. 1 , in accordance with some embodiments; 
         FIG. 2B  is a sectional diagram of the substrate taken along direction B-B′ in  FIG. 1 , in accordance with some embodiments; 
         FIG. 3  is a schematic diagram of a contact angle in a three-phase system, in accordance with some embodiments; 
         FIG. 4  is a schematic diagram of a contact angle in another three-phase system, in accordance with some embodiments; 
         FIG. 5  is a plan view of a display panel, in accordance with some embodiments; 
         FIG. 6  is a sectional diagram of a display panel, in accordance with some embodiments; 
         FIG. 7A  is a sectional diagram of the substrate taken along direction B-B′ in  FIG. 1 , in accordance with some embodiments; 
         FIG. 7B  is a sectional diagram of the substrate taken along direction B-B′ in  FIG. 1 , in accordance with some embodiments; 
         FIG. 8A  is a partial sectional diagram of a substrate, in accordance with some embodiments; 
         FIG. 8B  is a partial sectional diagram of another substrate, in accordance with some embodiments; 
         FIG. 8C  is a partial sectional diagram of yet another substrate, in accordance with some embodiments; 
         FIG. 9  is a structural diagram of a display panel, in accordance with some embodiments; 
         FIG. 10A  is a sectional diagram of the substrate taken along direction B-B′ in  FIG. 1 , in accordance with some embodiments; 
         FIG. 10B  is a sectional diagram of the substrate taken along direction B-B′ in  FIG. 1 , in accordance with some embodiments; 
         FIG. 10C  is a sectional diagram of the substrate taken along direction B-B′ in  FIG. 1 , in accordance with some embodiments; 
         FIG. 11A  is a partial sectional diagram of yet another substrate, in accordance with some embodiments; 
         FIG. 11B  is a partial sectional diagram of yet another substrate, in accordance with some embodiments; 
         FIG. 11C  is a partial sectional diagram of yet another substrate, in accordance with some embodiments; 
         FIG. 12  is a schematic diagram showing a relationship between a voltage between a first electrode and a second electrode and a contact angle between a liquid encapsulation layer and a liquid light-emitting layer, in accordance with some embodiments; 
         FIG. 13  is a schematic diagram showing a relationship between a contact angle between a liquid encapsulation layer and a liquid light-emitting layer and a curvature of a surface of the liquid encapsulation layer in contact with the liquid light-emitting layer, in accordance with some embodiments; 
         FIG. 14  is a structural diagram of another substrate, in accordance with some embodiments; 
         FIG. 15  is a sectional diagram of the substrate in  FIG. 14  taken along direction C-C′, in accordance with some embodiments; 
         FIG. 16  is a top view of another substrate, in accordance with some embodiments; 
         FIG. 17  is a sectional diagram of yet another substrate, in accordance with some embodiments; 
         FIG. 18  is a sectional diagram of yet another substrate, in accordance with some embodiments; 
         FIG. 19  is a schematic diagram of an electric field in a substrate, in accordance with some embodiments; 
         FIG. 20  is a sectional diagram of yet another substrate, in accordance with some embodiments; and 
         FIG. 21  is a sectional diagram of yet another substrate, in accordance with some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Technical solutions in some embodiments of the present disclosure will be described below clearly and completely with reference to the accompanying drawings. However, the described embodiments are merely some but not all embodiments of the present disclosure. All other embodiments obtained on a basis of the embodiments of the present disclosure by a person of ordinary skill in the art shall be included in the protection scope of the present disclosure. 
     Unless the context requires otherwise, the term “comprise” and other forms thereof such as the third-person singular form “comprises” and the present participle form “comprising” throughout the description and the claims are construed as open and inclusive, i.e., “inclusive, but not limited to”. In the description, the terms such as “one embodiment,” “some embodiments,” “exemplary embodiments,” “example,” “specific example,” or “some examples” are intended to indicate that specific features, structures, materials or characteristics related to the embodiment(s) or example(s) are included in at least one embodiment or example of the present disclosure. Schematic representations of the above terms do not necessarily refer to the same embodiment(s) or example(s). In addition, the specific features, structures, materials or characteristics may be included in any one or more embodiments or examples in any suitable manner. 
     Hereinafter, the terms such as “first” and “second” are used for descriptive purposes only, and are not to be construed as indicating or implying the relative importance or implicitly indicating the number of indicated technical features below. Thus, features defined as “first” and “second” may explicitly or implicitly include one or more of the features. In the description of the embodiments of the present disclosure, the terms “a plurality of” and “the plurality of” each mean two or more unless otherwise specified. The phrase “A and/or B” includes the following three combinations: only A, only B, and a combination of A and B. 
     That C and D are disposed in a same layer means that C and D are formed on a same bearing surface by a process as follows: forming a film for forming a specific pattern by using a same film-forming process; performing a patterning process on the film by using a same mask to form a layer structure with specific patterns including C and D. Depending on the different specific patterns, the patterning process may include exposure, development and etching processes, and the specific patterns in the formed layer structure may be continuous or discontinuous, and these specific patterns may also be at different heights or have different thicknesses. 
     In the description of some embodiments, the term “connected” and its extensions may be used. For example, the term “connected” may be used in the description of some embodiments to indicate that two or more components are in direct physical or electric contact with each other. However, the term “connected” may also mean that two or more components are not in direct contact with each other but still cooperate or interact with each other. The embodiments disclosed herein are not necessarily limited to the contents herein. 
     “Approximately” as used herein is inclusive of the stated value and means within an acceptable range of deviation for the particular value as determined by one of ordinary skill in the art, considering the measurement in question and the error associated with measurement of the particular quantity (i.e., the limitations of the measurement system). For example, “approximately” can mean within one or more standard deviations, or within ±30%, 20%, 10% or 5% of the stated value. 
     A liquid display device, such as a quantum dot light-emitting diode (QLED) display device, an electronic ink display device, a microcapsule display device, and a microlens array display device, may have a light-emitting layer that includes a clear liquid and a light-emitting material suspended in the organic solvent. The light-emitting layer is usually called a liquid light-emitting layer. 
     Some embodiments of the present disclosure provide a substrate, which may be applied to the liquid display device. As shown in  FIGS. 1, 2A and 2B , the substrate  100  includes a base  10 , a pixel defining layer  20 , a plurality of electrode pairs  30 , and a plurality of light-emitting devices  40 . 
     As shown in  FIGS. 2A and 2B , the pixel defining layer  20  is disposed on the base  10  and includes a pixel defining layer body  21  and a plurality of through holes  22 . Every two adjacent through holes  22  are separated by a portion of the pixel defining layer body  21  disposed therebetween. 
     In some examples, a material of the pixel defining layer body  21  includes an organic material and/or an inorganic material. For example, the organic material includes polystyrene or polyimide, and the inorganic material includes silicon nitride (SiNx), silicon oxide, or silicon oxynitride. 
     As shown in  FIGS. 2A and 2B , the plurality of electrode pairs  30  are disposed on the pixel defining layer  20 . 
     In some embodiments, as shown in  FIGS. 2A and 2B , at least one electrode pair  30 , such as each electrode pair  30 , includes a first electrode  31  and a second electrode  32  that are insulated from each other. The first electrode  31  and the second electrode  32  are disposed at least on a hole wall  221  of a through hole  22  corresponding to the electrode pair  30 . 
     In some examples, as shown in  FIG. 2A , part of the first electrode  31  and part of the second electrode  32  are disposed opposite to each other on the hole wall  221  of the through hole  22 , and the other part of the first electrode  31  and the other part of the second electrode  32  are disposed on a surface of the pixel defining layer body  21  facing away from the base  10 , and in regions that are at a periphery of the through hole  22 . 
     In some other examples, as shown in  FIG. 2B , the whole first electrode  31  and the whole second electrode  32  are disposed opposite to each other on the hole wall  221  of the through hole  22 . 
     It will be noted that the first electrode  31  and the second electrode  32  of each electrode pair  30  are disposed on a hole wall  221  of a same through hole  22 , i.e., the through hole  22  corresponding to the electrode pair  30 . In addition, there may be a preset distance between the first electrode  31  and the second electrode  32  to ensure that the first electrode  31  and the second electrode  32  of the electrode pair  30  are insulated from each other. 
     When two different voltages are applied to the first electrode  31  and the second electrode  32 , an electric field is formed between the first electrode  31  and the second electrode  32  (in the case shown by  FIG. 2B ), or between a portion of the first electrode  31  located in the through hole  22  and a portion of the second electrode  32  located in the through hole  22  (in a case shown by  FIG. 2A ). A direction of the electric field is perpendicular to a thickness direction D of the base  10 . The thickness direction D of the base  10  is a vertical direction in  FIGS. 2A and 2B . 
     For example, as shown in  FIG. 2A , in a case where a voltage at the first electrode  31  in a region C 1  is less than a voltage at the second electrode  32  in the region C 1 , the direction (shown by the dashed arrows in the region C 1 ) of the electric field points from the second electrode  32  to the first electrode  31 , and the direction of the electric field is perpendicular to the thickness direction D of the base  10 . 
     In another example, as shown in  FIG. 2A , in a case where the voltage at the second electrode  32  in a region C 2  is less than the voltage at the first electrode  31  in the region C 2 , the direction (shown by the dashed arrows in the region C 2 ) of the electric field points from the first electrode  31  to the second electrode  32 , and the direction of the electric field is perpendicular to the thickness direction D of the base  10 . 
     In some examples, the first electrode  31  and the second electrode  32  are both made of metallic conductive materials. For example, the first electrode  31  and the second electrode  32  are made of metal elements or metal alloys. The metal element may be, for example, copper, aluminum, steel, tungsten, tin or lead. The metal alloy is, for example, a copper aluminum alloy. 
     In some other examples, the first electrode  31  and the second electrode  32  are both made of transparent conductive materials. For example, the transparent conductive material includes indium zinc oxide (IZO), indium tin oxide (ITO), aluminum zinc oxide (AZO) or indium fluorine oxide (IFO). 
     In addition, the materials of the first electrode  31  and the second electrode  32  may be the same or different, as long as an electric field perpendicular to the thickness direction of the base  10  may be formed between the first electrode  31  and the second electrode  32 . 
     In some embodiments, as shown in  FIGS. 2A and 2B , at least one light-emitting device  40 , such as each light-emitting device  40 , includes a liquid functional layer  401 . The liquid functional layer  401  is disposed in the through hole  22  corresponding to the light-emitting device  40 . The liquid functional layer  401  is in direct contact with at least a portion of the first electrode  31  and at least a portion of the second electrode  32 . That is, as shown in  FIGS. 1 to 2B , assuming that there is a plane parallel to a side face  10 A of the base  10 , and an orthographic projection of the liquid functional layer  401  on the plane overlaps at least partially with both an orthographic projection of the first electrode  31  on the plane and an orthographic projection of the second electrode  32  on the plane. The liquid functional layer  401  includes a liquid light-emitting layer  4011  configured to emit light to achieve a light-emitting function of the light-emitting device  40 . 
     In some embodiments, as shown in  FIGS. 2A and 2B , the light-emitting device  40  further includes a first solid functional layer  402  disposed between the liquid functional layer  401  and the base  10 . The liquid functional layer  401  is in direct contact with the first solid functional layer  402 . In some examples, the first solid functional layer  402  includes a third electrode that acts as an electrode of the light-emitting device  40 . In some other examples, the first solid functional layer  402  includes a third electrode, a hole injection layer, and a hole transport layer that are sequentially stacked on the base  10  in the thickness direction D of the base  10 . 
     In the related art, a surface tension at a central region of the liquid light-emitting layer  4011  is weaker than a surface tension at an edge region of the liquid light-emitting layer  4011 , and thus gradients in surface tension may occur along the surface of the liquid light-emitting layer  4011 . Since the Marangoni effect takes place when there is a gradient of surface tension at an interface between two phases (such as a liquid and a gas), the Marangoni effect may take place at the surface of the liquid light-emitting layer  4011 . In addition, when the Marangoni effect takes place, the liquid flows in a direction from a low surface tension to a high surface tension. In this case, a portion at the central region of the liquid light-emitting layer  4011  may permeate into a portion at the edge region of the liquid light-emitting layer  4011 , thereby causing the light-emitting material suspended in the clear liquid included in the liquid light-emitting layer  4011  to climb to an edge of the clear liquid, and further causing the liquid display device to emit light non-uniformly. In addition, the light-emitting material is prone to aggregate to form coarse crystals, which may cause concentrations of the light-emitting material at different positions of the liquid light-emitting layer  4011  to be different, and thus affects luminance uniformity of the liquid display device. In addition, the liquid light-emitting layer  4011  may be deformed due to the influence of gravity, which may also affect the luminance uniformity of the liquid display device. 
     However, in the embodiments, the electrode pair  30  includes the first electrode  31  and the second electrode  32 . When different voltages are applied to the first electrode  31  and the second electrode  32 , the voltage difference between the first electrode  31  and the second electrode  32  may create an electric field (shown in  FIG. 2A ) between the first electrode  31  and the second electrode  32 . The electric field can electrowet the liquid functional layer  401  to change a contact angle of the liquid light-emitting layer  4011  of the liquid functional layer  401 , thereby changing a curvature of the surface of the liquid light-emitting layer  4011 , and causing the surface tension on the surface of the liquid light-emitting layer  4011  to be redistributed. A redistribution process of the surface tension makes the light-emitting material suspended in the clear liquid flow in a direction opposite to a flow direction caused by the Marangoni effect, thereby preventing the light-emitting material from climbing to the edge of the clear liquid of the liquid light-emitting layer  4011 , and effectively preventing the light-emitting material from aggregating to form coarse crystals. In addition, since the curvature of the surface of the liquid light-emitting layer  4011  is changed, and a shape of the liquid light-emitting layer  4011  is changed accordingly, which may prevent the liquid light-emitting layer  4011  from being deformed due to the influence of gravity, and further ensure the luminance uniformity of the liquid display device. 
     Referring to  FIGS. 3 and 4 , the contact angle and the curvature will be described below by taking an example in which a droplet is located on a surface of a solid  1  and the solid  1  is placed in the air. 
     As shown in  FIG. 3 , at the three-phase boundary where the liquid, the gas, and the solid intersect, an angle θ 1  between a solid-liquid interface and a gas-liquid interface is a contact angle between the droplet  2  and the solid  1 . 
     As shown in  FIG. 4 , in addition to the three-phase system (i.e., a solid-liquid-gas system) shown in  FIG. 3 , there is another three-phase system formed by a one-phase solid and a two-phase fluid (i.e., two liquids). In the three-phase system shown in  FIG. 4 , the droplet  2  is located on a surface of the solid  1 , and the droplet  3  and the droplet  2  are both in contact with and immiscible with the solid  1 . In this case, an angle θ 2  between a solid  1 -droplet  3  interface and a droplet  3 -droplet  2  interface is a contact angle between the droplet  2  and the droplet  3 . 
     As shown in  FIGS. 3 and 4 , a change in a magnitude of the contact angle can cause a curvature of a surface of the droplet  2  to be changed. The magnitude of the contact angle is related to a degree to which the droplet  2  wets a medium with which the droplet  2  is in contact. As shown in  FIG. 3 , the larger the degree to which the droplet  2  wets the solid  1  is, the smaller the contact angle θ 1  is. For example, the droplet  2  is a drop of water, and the solid  1  is a clean glass, a state in which the droplet  2  spreads out on the solid  1  is then a wet state, and the contact angle  1  is approximately 0°. In addition, the smaller the degree to which the droplet  2  wets the solid  1  is, the larger the contact angle θ 1  is. For example, the droplet  2  is a drop of water, and the solid  1  is a waxy plate, a state in which the droplet  2  is kept to be a water drop is a non-wetting state, and the contact angle θ 1  is approximately 180°. 
     As described above, the liquid light-emitting layer  4011  is in a liquid state, and may be taken as a droplet. It can be seen that, by changing the degree to which the liquid light-emitting layer  4011  wets the solid  1 , the contact angle of the liquid light-emitting layer  4011  may be changed, and thus the curvature of the surface of the liquid light-emitting layer  4011  may be changed. 
     In some embodiments, as shown in  FIGS. 7A and 7B , the liquid functional layer  401  only includes the liquid light-emitting layer  4011 . As shown in  FIG. 7A , the first electrode  31  and the second electrode  32  each extend along the hole wall  221  of the through hole  22  from the edge of the hole wall  221  away from the base  10  to a lower surface  4011 A of the liquid light-emitting layer  4011  proximate to the base  10 . Of course, the first electrode  31  and the second electrode  32  may also extend along the hole wall  221  from the edge of the hole wall  221  away from the base  10  to a portion of the liquid light-emitting layer  4011  above the lower surface  4011 A, such as a middle portion  4011 B (shown in  FIG. 7B ) of the liquid light-emitting layer  4011 . It will be noted that the middle portion  4011 B of the liquid light-emitting layer  4011  refers to a line of the liquid light-emitting layer  4011  from which a distance to the lower surface of the liquid light-emitting layer  4011  is about a half of the thickness of the liquid light-emitting layer  4011 . The thickness of liquid light-emitting layer  4011  is a dimension of the liquid light-emitting layer  4011  in the thickness direction D of the base  10 . 
     In this case, as shown in  FIG. 8A , two different voltages may be applied to the first electrode  31  and the second electrode  32  to change a contact angle θ 1  between the liquid light-emitting layer  4011  and the first electrode  31  and a contact angle θ 1 ′ between the liquid light-emitting layer  4011  and the second electrode  32 . In this way, a curvature of a light-exit surface of the liquid light-emitting layer  4011  is changed accordingly, which may make a thickness of the liquid light-emitting layer  4011  uniform. Therefore, the light (shown by the dashed arrows in  FIG. 8A ) emitted by the liquid light-emitting layer  4011  may be vertically emitted from the light-exit surface of the liquid light-emitting layer  4011 , so that the light-emitting device  40  may emit light uniformly. 
     In some examples, as shown in  FIGS. 7A to 8C , the liquid functional layer  401  only includes the liquid light-emitting layer  4011 , the light-emitting device further includes a second solid functional layer  403  (e.g., an electron injection layer described hereinafter) disposed on a side of the liquid light-emitting layer  4011  away from the base  10 , and there is a layer of air  404  between the liquid light-emitting layer  4011  and the second solid functional layer  403 . This layer of air  404  will be referred to as a contact layer of the liquid light-emitting layer  4011  hereinafter. 
     In this case, as shown in  FIG. 8A , the thickness of the liquid light-emitting layer  4011  is uniform, and a thickness of the contact layer is also uniform accordingly. The contact layer may be equivalent to a flat-plate lens, which will not converge or diverge the light emitted by the liquid light-emitting layer  4011 . The light emitted by the liquid light-emitting layer  4011  may directly pass through the contact layer, and thus a viewing angle of the liquid display device may not be changed. 
     In addition, since the contact layer is in contact with the light-exit surface of the liquid light-emitting layer  4011 , it is also possible to make the contact layer similar to a convex lens or a concave lens by appropriately adjusting the voltages applied to the first electrode  31  and the second electrode  32 . In this case, the light emitted by the liquid light-emitting layer  4011  is converged or diverged after being refracted by the contact layer, thereby increasing or decreasing the viewing angle of the liquid display device. 
     For example, as shown in  FIG. 8B , after the curvature of the light-exit surface of the liquid light-emitting layer  4011  is adjusted, the contact layer in contact with the light-exit surface of the liquid functional layer  401  may have a shape similar to a concave lens. In this case, the contact layer can diverge the light emitted by the liquid light-emitting layer  4011 , thereby increasing the viewing angle of the liquid display device. In another example, as shown in  FIG. 8C , the curvature of the light-exit surface of the liquid light-emitting layer  4011  is adjusted, so that the contact layer in contact with the light-exit surface of the liquid light-emitting layer  4011  has a shape similar to a convex lens. In this case, the contact layer can converge the light emitted by the liquid light-emitting layer  4011 , thereby decreasing the viewing angle of the liquid display device. 
     In some embodiments, the liquid light-emitting layer  4011  includes a first liquid and particles suspended in the first liquid. 
     The first liquid is used to disperse the particles such that the particles disperse uniformly in the first liquid. For example, the first liquid is a clear liquid, and includes an organic solvent and a dispersant dissolved in the organic solvent. The dispersant is used to prevent the particles from settling or clumping. In some examples, the organic solvent is made of a high molecular polymer material, such as an aliphatic hydrocarbon, an aromatic hydrocarbon, a silylating agent, an alkylating agent, or a fluorocarbon. 
     The particles may be made of an organic light-emitting material or a semiconductor light-emitting material. For example, the organic light-emitting material includes polyphenylene, polythiophene, polyfluorene, polytriphenylamine, or a polytriphenylamine derivative. The semiconductor light-emitting material includes, for example, cadmium selenide (CdSe), cadmium sulfide (CdS), zinc selenide (ZnSe), zinc sulfide (ZnS), gallium phosphide (GaP), gallium arsenide phosphide (GaAs1-xPx), gallium aluminum arsenide (GaAlAs), or gallium nitride (GaN). 
     In a case where the particles are made of a quantum dot material (such as CdSe, or CdS) of the semiconductor light-emitting material, the particles are quantum dots. In this case, since a diameter of a quantum dot determines a color of light emitted by the quantum dot, a diameter of a quantum dot emitting light of a first color in the liquid light-emitting layer  4011 , a diameter of a quantum dot emitting light of a second color in the liquid light-emitting layer  4011 , and a diameter of a quantum dot emitting light of a third color in the liquid light-emitting layer  4011  may be different from each other. For example, if the first color, the second color, and the third color are red, green, and blue, respectively, the diameter of the quantum dot emitting red light in the liquid light-emitting layer  4011  is approximately 2.4 nm (such as 2.3 nm, 2.4 nm, or 2.5 nm), the diameter of the quantum dot emitting green light in the liquid light-emitting layer  4011  is approximately 1.7 nm (such as 1.5 nm, 1.6 nm, 1.7 nm, or 1.8 nm), and the diameter of the quantum dot emitting blue light in the liquid light-emitting layer  4011  is approximately 1.0 nm (such as 0.9 nm, 1.0 nm, or 1.1 nm). 
     In some embodiments, in addition to the liquid light-emitting layer  4011 , the liquid functional layer  401  may further include other liquid layers. In this case, the liquid functional layer  401  has a multilayer structure, and adjacent liquid layers are in contact but immiscible. In some examples, the liquid light-emitting layer  4011  and/or the other liquid layers are formed in the through hole  22  by using an ink-jet printing process or a droplet-coating process. 
     In some embodiments, as shown in  FIGS. 10A-10C , the light-emitting function layer  401  further includes a liquid encapsulation layer  4012  disposed on a side of the liquid light-emitting layer  4011  away from the base  10 , and the surface of the liquid light-emitting layer  4011  facing away from the base  10  is in direct contact with the liquid encapsulation layer  4012 . The liquid encapsulation layer  4012  is immiscible with the liquid light-emitting layer  4011 . 
     In some embodiments, the liquid encapsulation layer  4012  includes a second liquid. A density of the second liquid is less than a density of the first liquid. 
     In some examples, the second liquid includes water and a solute dissolved in the water. The solute may be made of a material that is chemically stable and not easy to volatilize, decompose, crystallize or precipitate, such as an electrolyte. The electrolyte includes, for example, lithium bromide (LiBr), sodium sulfate (Na 2 SO 4 ), or potassium chloride (KCl). 
     In some embodiments, to ensure that the density of the second liquid is smaller than the density of the first, a relative molecular mass (in units of 1) of the second liquid may be smaller than the relative molecular mass of the first liquid. In some examples, the relative molecular mass (in units of 1) of the first liquid is greater than or equal to approximately 1000, such as 1000, 1200, or 1500. 
     Since the density of the second liquid of the liquid encapsulation layer  4012  is less than the density of the first liquid of the liquid light-emitting layer  4011 , when the substrate  100  is in a state of a vertical placement (the state of the substrate  100  during actual use) or a state of a horizontal placement (the state of the substrate  100  during manufacturing), the liquid light-emitting layer  4011  is always located on a side of the liquid encapsulation layer  4012  proximate to the base  10 .  FIGS. 10A to 10C  show examples in which the substrate  100  is placed horizontally. 
     Based on the above embodiments, the liquid encapsulation layer  4012  may isolate the liquid light-emitting layer  4011  from an external environment to protect the liquid light-emitting layer  4011 , which may effectively prevent the liquid light-emitting layer  4011  from condensing at a low temperature and evaporating at a high temperature. Furthermore, since the liquid encapsulation layer  4012  is in the liquid state, it may be ensured that a surface of the liquid encapsulation layer  4012  in contact with the liquid light-emitting layer  4011  is a smooth surface, which may effectively prevent the light emitted by the liquid light-emitting layer  4011  from interfering with each other, and which may prevent the total internal reflection from occurring at the interface between the liquid encapsulation layer  4012  and the liquid light-emitting layer  4011 . 
     In some examples, as shown in  FIG. 10A , the first electrode  31  and the second electrode  32  each extend along the hole wall  221  of the through hole  22  from the edge of the hole wall  221  away from the base  10  to the lower surface of the liquid light-emitting layer  4011  proximate to the base  10 . 
     In some other examples, as shown in  FIG. 10B , the first electrode  31  and the second electrode  32  each extend along the hole wall  221  of the through hole  22  from the edge of the hole wall  221  away from the base  10  to the surface of the liquid encapsulation layer  4012  in contact with the liquid light-emitting layer  4011 . 
     In this case, as shown in  FIGS. 11A to 11C , an electric field formed between the first electrode  31  and the second electrode  32  may act on the liquid encapsulation layer  4012 , and changes a contact angle θ 2  between the liquid light-emitting layer  4011  and the liquid encapsulation layer  4012 . 
     For example, as shown in  FIG. 11A , when the substrate is used, the contact angle  62  between the liquid encapsulation layer  4012  and the liquid light-emitting layer  4011  may be adjusted such that the thickness of the liquid light-emitting layer  4011  and a thickness of the liquid encapsulation layer  4012  may be made uniform, so that the light-emitting device may emit light uniformly. 
     In this case, the liquid encapsulation layer  4012  is equivalent to a flat-plate lens, and does not converge or diverge the light emitted by the liquid light-emitting layer  4011 . The light emitted by the liquid light-emitting layer  4011  may directly pass through the liquid encapsulation layer  4012  and then exit from the liquid encapsulation layer  4012 , and thus the viewing angle of the liquid display device may not be changed. 
     In another example, as shown in  FIG. 11B , when the substrate is used, the contact angle  62  between the liquid light-emitting layer  4011  and the liquid encapsulation layer  4012  may be adjusted such that the liquid encapsulation layer  4012  has a shape similar to a concave lens, and the liquid encapsulation layer  4012  can diverge the light emitted by the liquid light-emitting layer  4011 , thereby increasing the viewing angle of the liquid display device. 
     In another example, as shown in  FIG. 11C , the contact angle  62  between the liquid light-emitting layer  4011  and the liquid encapsulation layer  4012  may be adjusted such that the liquid encapsulation layer  4012  has a shape similar to a convex lens, and the liquid encapsulation layer  4012  can converge the light emitted by the liquid light-emitting layer  4011 , thereby decreasing the viewing angle of the liquid display device. 
     In some yet other examples, as shown in  FIG. 10C , the first electrode  31  and the second electrode  32  each extend along the hole wall  221  of the through hole  22  from the edge of the hole wall  221  away from the base  10  to a position that is between the lower surface of the liquid light-emitting layer  4011  proximate to the base  10  and an upper surface of the liquid light-emitting layer  4011  away from the base  10 . 
     In this case, an electric field formed between the first electrode  31  and the second electrode  32  may act on both the liquid light-emitting layer  4011  and the liquid encapsulation layer  4012 , and change the contact angle  62  between the liquid light-emitting layer  4011  and the liquid encapsulation layer  4012 . 
     It will be noted that, a length of a portion of each of the first electrode  31  and the second electrode  32  located between the lower surface of the liquid light-emitting layer  4011  and the upper surface of the liquid light-emitting layer  4011  is not limited in the embodiments of the present disclosure. The length herein refers to a dimension of the portion of the first electrode  31  or the second electrode  32  along the hole wall  221 . 
     In a case where the curvature of the surface of the liquid encapsulation layer  4012  in contact with the liquid light-emitting layer  4011  is changed, the shape of the liquid light-emitting layer  4011  and the shape of the liquid encapsulation layer  4012  are changed accordingly, and thus the uniformity of the light emitted by the light-emitting device  40  may be adjusted. In addition, by adjusting the curvature of the surface of the liquid encapsulation layer  4012  in contact with the liquid light-emitting layer  4011 , the light emitted by the light-emitting device  40  may be emitted from the light-emitting device  40  at a specific angle. 
     For example, as shown in  FIG. 11B , the curvature of the light-exit surface of the liquid light-emitting layer  4011  may be adjusted such that the liquid encapsulation layer  4012  has the shape similar to the concave lens, and the liquid encapsulation layer  4012  can diverge the light emitted by the liquid light-emitting layer  4011 . In another example, as shown in  FIG. 11C , the curvature of the light-exit surface of the liquid light-emitting layer  4011  may be changed such that the liquid encapsulation layer  4012  has the shape similar to the convex lens, and the liquid encapsulation layer  4012  can converge the light emitted by the liquid light-emitting layer  4011 . 
     As shown in  FIGS. 11A to 11C , the contact angle θ 2  satisfies the following formula: 
     
       
         
           
             
               
                 cos 
                  
                 
                   ( 
                   
                     π 
                     - 
                     
                       θ 
                        
                       
                           
                       
                        
                       2 
                     
                   
                   ) 
                 
               
               = 
               
                 
                   cos 
                    
                   
                       
                   
                    
                   
                     θ 
                     0 
                   
                 
                 + 
                 
                   
                     
                       U 
                       2 
                     
                      
                     ɛ 
                   
                   
                     2 
                      
                     
                         
                     
                      
                     d 
                      
                     
                         
                     
                      
                     η 
                   
                 
               
             
             , 
           
         
       
     
     where η is a surface tension of the surface of the liquid encapsulation layer  4012  in contact with the liquid light-emitting layer  4011 , U is a voltage difference between the first electrode  31  and the second electrode  32 , ε is a dielectric constant of the liquid encapsulation layer  4012 , d is the thickness of the liquid encapsulation layer  4012 , θ 0  is an initial contact angle between the liquid encapsulation layer  4012  and the liquid light-emitting layer  4011  (i.e., a contact angle between the liquid encapsulation layer  4012  and the liquid light-emitting layer  4011  in a case where no voltages are applied to the first electrode  31  and the second electrode  32 ). 
     It can be seen from the above formula that when the voltage difference between the first electrode  31  and the second electrode  32  is changed, the contact angle θ 2  between the liquid encapsulation layer  4012  and the liquid light-emitting layer  4011  is changed. If the contact angle θ 2  is changed, the curvature of the surface of the liquid encapsulation layer  4012  in contact with the liquid light-emitting layer  4011  is changed. 
     For example, as shown in  FIG. 12 , the abscissa axis of the coordinate system represents the voltage difference U between the first electrode  31  and the second electrode  32 , and the ordinate axis of the coordinate system represents the contact angle θ 2  between the liquid encapsulation layer  4012  and the liquid light-emitting layer  4011 . It can be seen that the contact angle θ 2  between the liquid encapsulation layer  4012  and the liquid light-emitting layer  4011  increases as the voltage difference U between the first electrode  31  and the second electrode  32  increases. 
     For example, as shown in  FIG. 13 , the abscissa axis of the coordinate system represents the contact angle θ 2  between the liquid encapsulation layer  4012  and the liquid light-emitting layer  4011 , and the ordinate axis of the coordinate system represents the curvature 1/γ of the surface of the liquid encapsulation layer  4012  in contact with the liquid light-emitting layer  4011 , wherein γ is a radius of the curvature of the surface of the liquid encapsulation layer  4012  in contact with the liquid light-emitting layer  4011 . In a process where the contact angle θ 2  increases from 0° to 90°, the curvature 1/γ of the surface of the liquid encapsulation layer  4012  in contact with the liquid light-emitting layer  4011  decreases. In a process where the contact angle θ 2  gradually increases from 90°, the curvature 1/γ of the surface of the liquid encapsulation layer  4012  in contact with the liquid light-emitting layer  4011  increases. 
     In some embodiments, as shown in  FIGS. 14 and 15 , a first electrode  31  of an electrode pair  30  is connected to and integrated with a first electrode  31  of an adjacent electrode pair  30 . Second electrodes  32  of any two adjacent electrode pairs  30  are insulated from each other. 
     For example, as shown in  FIGS. 14 and 15 , a second electrode pair  30 B is adjacent to a first electrode pair  30 A and a third electrode pair  30 C, the first electrode  31 B of the second electrode pair  30 B is connected to and integrated with the first electrode  31 A of the first electrode pair  30 A, and the second electrode  32 B of the second electrode pair  30 B is insulated from both the second electrode  32 A of the first electrode pair  30 A and the second electrode  32 C of the third electrode pair  30 C. 
     It will be understood that, voltages at two first electrodes  31  that are integrated together are the same. In this way, the voltage difference between the first electrode  31  and the second electrode  32  may be controlled by controlling the voltage applied to the second electrode  32 . 
     In some embodiments, the first electrode  31  and the second electrode  32  are disposed in a same layer. In this way, the first electrode  31  and the second electrode  32  may be formed synchronously through the same patterning process, thereby simplifying manufacturing processes and reducing the cost. 
     In some embodiments, as shown in  FIG. 16 , the substrate  100  further includes a plurality of first power lines  51  and a plurality of second power lines  52  that are disposed on the base  10  and insulated from each other. The first electrode  31  is electrically connected to a first power line  51 , and the second electrode  32  is electrically connected to a second power line  52 . A voltage may be applied to the first electrode  31  via the first power line  51 , and another voltage may be applied to the second electrode  32  via the second power line  52 . 
     In order to reduce the number of the first power lines  51  and the number of the second power lines  52 , in some examples, the first power line  51  may be electrically connected to first electrodes  31  of multiple electrode pairs  30  (e.g., the electrode pairs  30  located in sub-pixel regions in a same column), and the second power line  52  may be electrically connected to second electrodes  32  of multiple electrode pairs  30  (e.g., the electrode pairs  30  located in sub-pixel regions in a same row). The number of the first power lines  51  and the number of the second power lines  52  may be reasonably set in combination with the arrangement of other structures on the substrate  100 , as long as the voltage between the first electrode  31  and the second electrode  32  of each electrode pair  30  can be separately controlled. 
     For example, in a case where voltages applied to all the first electrodes  31  via the plurality of first power lines  51  are the same, and voltages applied to all the second electrodes  32  via the plurality of second power lines  52  are the same, curvatures of surfaces of liquid light-emitting layers  4011  of the plurality of light-emitting devices  40  have a same change. In another example, in a case where the voltages applied to all the first electrodes  31  via the plurality of first power lines  51  are the same, and the voltages applied to all the second electrodes  32  via the plurality of second power lines  52  are not completely the same, the curvatures of the surfaces of the liquid light-emitting layers  4011  of the plurality of light-emitting devices  40  may have different changes. 
     In some examples, the liquid display device may further include an integrated circuit (IC). The plurality of first power lines  51  and the plurality of second power lines  52  are electrically connected to the IC and receive electrical signals from the IC. 
     In some embodiments, as shown in  FIGS. 17 and 18 , the light-emitting device  40  further includes a third electrode  43  and a fourth electrode  44 . The third electrode  43  is located at a side of the liquid functional layer  401  proximate to the base  10 , and the fourth electrode  44  is located at a side of the liquid functional layer  401  away from the base  10 . The third electrode  43  and the fourth electrode  44  are both insulated from the first electrode  31  and the second electrode  32 . For example, the third electrode  43  is an anode, and the fourth electrode  44  is a cathode. 
     In some examples, as shown in  FIG. 17 , fourth electrodes  44  of the plurality of light-emitting devices  40  are connected and integrated to form an integrated structure, and the integrated structure covers the pixel defining layer  20 . 
     In this case, in order to avoid a short circuit between the fourth electrodes  44  and the electrode pairs  30 , as shown in  FIG. 17 , the substrate  100  further includes an insulating layer  60  disposed between the fourth electrodes  44  and the plurality of electrode pairs  30 . The insulating layer  60  includes a plurality of hollowed-out portions  601 . Each hollowed-out portion  601  corresponds to a through hole  22 , and an orthographic projection of the hollowed-out portion  601  on the base  10  overlaps with an orthographic projection of the through hole  22  on the base  10 . The fourth electrode  44  is insulated from the first electrode  31  and the second electrode  32  through the insulating layer  60 . 
     In some other examples, as shown in  FIG. 18 , the fourth electrodes  44  are located only in regions where the through holes  21  are located, respectively. 
     In some embodiments, as shown in  FIGS. 17 and 18 , the light-emitting device  40  further includes a hole injection layer  45 , a hole transport layer  46 , an electron injection layer  47  and an electron transport layer  48 . 
     The hole injection layer  45  is located between the third electrode  43  and the liquid functional layer  401 . The hole transport layer  46  is located between the hole injection layer  45  and the liquid functional layer  401 . The electron injection layer  47  is located between the fourth electrode  44  and the liquid functional layer  401 . The electron transport layer  48  is located between the electron injection layer  47  and the liquid functional layer  401 . 
     As shown in  FIG. 19 , a direction of a first electric field formed between the third electrode  43  and the fourth electrode  44  is shown by the solid arrows, a direction of a second electric field formed between the first electrode  31  and the second electrode  32  is shown by the dashed arrows, and the direction of the first electric field is perpendicular to the direction of the second electric field. In this case, the first electric field formed between the third electrode  43  and the fourth electrode  44  does not affect the curvature of the surface of the liquid light-emitting layer  4011 . 
     In some embodiments, as shown in  FIG. 20 , the substrate  100  further includes a plurality of pixel driver circuits  50  disposed between the base  10  and the plurality of light-emitting devices  40 . One of the plurality of pixel driving circuits  50  is electrically connected to a third electrode  43  of a corresponding light-emitting device  40 , and the pixel driver circuit  50  is configured to drive the liquid light-emitting layer  4011  to emit light. In some examples, each pixel driver circuit  50  is electrically connected to a third electrode  43  of a corresponding light-emitting device  40 . 
     For example, the pixel driver circuit  50  has a 2T1C structure. That is, the pixel driver circuit  50  includes two thin-film transistors (TFTs) and one capacitor, and the two TFTs include a switching TFT and a driving TFT. 
     The pixel driver circuit  50  may also have other structures, such as a 3T1C structure (i.e., the pixel driver circuit  50  includes three TFTs and one capacitor), a 5T1C structure (i.e., the pixel driver circuit  50  includes five TFTs and one capacitor), or a 7T1C structure (i.e., the pixel driver circuit  50  includes seven TFTs and one capacitor). That is, the pixel driver circuit  50  may include at least two TFTs and at least one capacitor. 
     In some embodiments, as shown in  FIG. 21 , the substrate  100  further includes a solid encapsulation layer  80  disposed on sides of the plurality of light-emitting devices  40  away from the base  10 . The solid encapsulation layer  80  covers the pixel defining layer  20 . For example, the solid encapsulation layer  80  is an encapsulation substrate of a display panel to which the substrate  10  is applied, and is a flexible film. In another example, the encapsulation substrate is a rigid substrate, and the solid encapsulation layer  80  is located between the encapsulation substrate and the base  10 . 
     In some examples, the solid encapsulation layer  80  has a multilayer structure. For example, the solid encapsulation layer  80  includes at least one organic encapsulation sub-layer and inorganic encapsulation sub-layers located on upper and lower sides of each organic encapsulation sub-layer in the thickness direction of the base  10  to block external water and oxygen. 
     In some embodiments, as shown in  FIG. 5 , a display panel  500  is provided. The display panel  500  includes the substrate  100 . For example, the display panel  500  may be applied to a liquid display device, such as a QLED display device, an electronic ink display device, a microcapsule display device, or a microlens array display device. 
     In some examples, the display panel  500  is a self-luminescent display panel. For example, the display panel  500  is an OLED display panel, or a QLED display panel. The substrate  100  is an array substrate of the self-luminescent display panel. 
     As shown in  FIG. 5 , the display panel  500  has an active area AA and a peripheral region S located at a periphery of the active area AA. Depending on the different designs of the active area AA, the position of the peripheral region S may be changed accordingly. For example, the active area AA is in a shape of a rectangle, and the peripheral area S may be located on one side, two opposite sides, three sides, or all sides (as shown in  FIG. 5 ) of the active area AA. Of course, the active area AA may also have other shapes, such as a circular shape. In this case, the peripheral area S may surround the active area AA. 
     As shown in  FIG. 5 , the active area AA includes a plurality of sub-pixel regions P. For example, the plurality of sub-pixels P are arranged in an array. 
     In some embodiments, each of the plurality of through holes  22  in the substrate  100  is located in a corresponding sub-pixel region P. Accordingly, the light-emitting device  40  located in the through hole  22  is also located in the sub-pixel region P corresponding to the through hole  22 . 
     In some examples, the plurality of light-emitting devices  40  include a plurality of first light-emitting devices, a plurality of second light-emitting devices, and a plurality of third light-emitting devices. Each first light-emitting device is configured to emit light of a first color, each second light-emitting device is configured to emit light of a second color, and each third light-emitting device is configured to emit light of a third color. The first color, the second color and the third color are three primary colors (e.g., red, green and blue, respectively). 
     In some other examples, the light emitted by the plurality of light-emitting devices  40  is white light. The display panel  500  further includes a color filter layer, and the color filter layer is disposed on a light-exit side of the plurality of light-emitting devices  40 . For example, the color filter layer includes a plurality of first color photoresist units, a plurality of second color photoresist units, and a plurality of third color photoresist units. Each first color photoresist unit is located in a corresponding sub-pixel region, each second color photoresist unit is located in a corresponding sub-pixel region, and each third color photoresist unit is located in a corresponding sub-pixel region. 
     In a case where the display panel  500  is the QLED display panel, as shown in  FIG. 6 , the display panel  500  further includes an encapsulation substrate  42 . The encapsulation substrate  42  is disposed on a side of the light-emitting devices  40  away from the base  10 . In this case, the liquid light-emitting layer  4011  of the light-emitting device  40  in the substrate  100  is made of a quantum dot material. 
     The encapsulation substrate  42  is a flexible film, or a rigid substrate such as a glass substrate. 
     In some examples, in a case where the liquid light-emitting layer  4011  includes the first liquid and the particles, and the particles are quantum dots, as shown in  FIG. 9 , the display panel  500  further includes a backlight  101 , and the substrate  100  is disposed at a light-exit side of the backlight  101 . The backlight  101  is configured to provide incident light to the substrate  100 . 
     For example, the dashed arrows shown in  FIG. 9  represent incident light emitted by the backlight  101 , so that the quantum dots in the liquid light-emitting layer  4011  of the light-emitting device  40  emits light in response to receiving incident light. 
     For example, the backlight  101  is configured to provide blue incident light, and the plurality of light-emitting devices  40  includes a plurality of first light-emitting devices and a plurality of second light-emitting devices. Each first light-emitting device is configured to emit red light in response to receiving blue incident light. Each second light-emitting device is configured to emit green light in response to receiving blue incident light. As for each sub-pixel region emitting blue light, a through hole  22  located in the sub-pixel region is filled with a transparent layer to transmit blue light. 
     In some embodiments, the substrate  100  of the display panel  500  is a color filter substrate. In this case, the display panel  500  may further include a glass cover plate disposed on a surface of the substrate  100  proximate to the pixel defining layer  20  to protect the substrate  100 . 
     The forgoing descriptions are merely specific implementations of the present disclosure, but the protection scope of the present disclosure is not limited thereto. Any changes or replacements that a person skilled in the art could readily conceive of within the technical scope of the present disclosure shall be included in the protection scope of the present disclosure. Therefore, the protection scope of the present disclosure shall be subject to the protection scope of the claims.