TWI901459B - Display panel and method for manufacturing the same - Google Patents

Abstract

A display panel is provided. The display panel includes a first substrate, a second substrate, a display medium layer and a first alignment layer. The second substrate is arranged opposite to the first substrate. The display medium layer is disposed between the first substrate and the second substrate, and includes plural display medium molecules. The first alignment layer is disposed on the first substrate, wherein the first alignment layer is form through condensation polymerization of a dianhydride compound, a diamine compound having an alkyl side chain and a diamine compound having no alkyl side chain, a molar ratio of the diamine compound having the alkyl side chain to the diamine compound having no alkyl side chain ranges from 0.1 to 0.5, and the alkyl side chain of the diamine compound having the alkyl side chain is a C1 to C12 alkyl group.

Description

Display panel and manufacturing method thereof

The present invention relates to an optoelectronic device and a manufacturing method thereof, and in particular to a display panel and a manufacturing method thereof.

Image sticking (IS) in bistable cholesterol-based liquid crystal displays (LCDs) has been a persistent problem for over a decade. Due to the bistable nature of liquid crystal molecules, the image can remain fixed for a day or even over a week without a driving signal. This often-visible and difficult-to-eliminate image sticking is a problem.

The present invention provides a display panel that can improve image retention.

The display panel of the present invention includes a first substrate, a second substrate, a display dielectric layer, and a first alignment layer. The second substrate is disposed opposite to the first substrate. The display dielectric layer is disposed between the first and second substrates and includes a plurality of display dielectric molecules. The first alignment layer is disposed on the first substrate, wherein the first alignment layer is formed by condensation polymerization of a dianhydride compound, a diamine compound having alkyl side chains, and a diamine compound without alkyl side chains, wherein the molar ratio of the diamine compound having alkyl side chains to the diamine compound without alkyl side chains is 0.1 to 0.5, and the carbon number of the alkyl side chains of the diamine compound having alkyl side chains is 1 to 12.

The present invention also provides a method for manufacturing a display panel, which can improve the image retention of the display panel.

The method for manufacturing a display panel of the present invention includes reacting a dianhydride compound with a diamine compound having alkyl side chains to produce a first precursor, and reacting the dianhydride compound with a diamine compound without alkyl side chains to produce a second precursor. The method further includes applying a mixture of the first precursor and the second precursor to a first substrate. The method further includes curing the mixture to form a first alignment layer on the first substrate. The method further includes assembling the first and second substrates together with the first alignment layer facing the second substrate, and filling a display medium molecule between the first alignment layer and the second substrate, wherein the display medium molecule has a pre-tilt angle of less than or equal to 4°.

In the accompanying drawings, the thickness of layers, films, panels, regions, etc. is exaggerated for clarity. Throughout the specification, the same figure numbers represent the same elements. It should be understood that when an element such as a layer, film, region or substrate is referred to as being "on" or "connected to" another element, it can be directly on or connected to another element, or an intermediate element can also exist. Conversely, when an element is referred to as being "directly on" or "directly connected to" another element, there is no intermediate element. As used herein, "connected" can refer to physical and/or electrical connections. Furthermore, "electrically connected" or "coupled" can mean the presence of other elements between two elements.

It should be understood that although the terms "first," "second," "third," etc. may be used herein to describe various elements, components, regions, layers, and/or portions, these elements, components, regions, layers, and/or portions should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer, or portion from another element, component, region, layer, or portion. Thus, a first "element," "component," "region," "layer," or "portion" discussed below could be termed a second element, component, region, layer, or portion without departing from the teachings of this document.

The terms used herein are for the purpose of describing particular embodiments only and are not intended to be limiting. As used herein, unless the context clearly indicates otherwise, the singular forms "a," "an," and "the" are intended to include the plural forms, including "at least one," or to mean "and/or." As used herein, the term "and/or" includes any and all combinations of one or more of the relevant listed items. It should also be understood that when used in this specification, the terms "include" and/or "comprising" specify the presence of the described features, regions, entireties, steps, operations, elements, and/or parts, but do not preclude the presence or addition of one or more other features, regions, entireties, steps, operations, elements, parts, and/or combinations thereof.

Furthermore, relative terms such as "lower" or "bottom" and "upper" or "top" may be used herein to describe one element's relationship to another element, as illustrated in the figures. It will be understood that relative terms are intended to encompass different orientations of a device in addition to the orientations depicted in the figures. For example, if a device in one of the figures were flipped over, an element described as being on the "lower" side of the other elements would be oriented on the "upper" side of the other elements. Thus, the exemplary term "lower" can encompass both "lower" and "upper" orientations, depending on the particular orientation of the figure. Similarly, if a device in one of the figures were flipped over, an element described as being "lower" or "beneath" other elements would be oriented "above" the other elements. Thus, the exemplary term "lower" or "beneath" can encompass both "lower" and "upper" orientations.

As used herein, "about," "approximately," or "substantially" includes the stated value and the average value within an acceptable range of deviation for the particular value as determined by one of ordinary skill in the art, taking into account the measurement in question and the particular amount of error associated with the measurement (i.e., the limitations of the measurement system). For example, "about" can mean within one or more standard deviations of the stated value, or within ±30%, ±20%, ±10%, or ±5%. Furthermore, as used herein, "about," "approximately," or "substantially" can be used to select an acceptable range of deviation or standard deviation depending on the optical, etching, or other properties, rather than applying a single standard deviation to all properties.

Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that those terms as defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant art and this invention, and will not be interpreted as idealized or overly formal meanings unless expressly defined as such herein.

Exemplary embodiments are described herein with reference to cross-sectional illustrations that are schematic representations of idealized embodiments. Thus, variations from the shapes illustrated as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, the embodiments described herein should not be construed as limited to the specific shapes of regions as illustrated herein, but rather include deviations in shape that result, for example, from manufacturing. For example, regions illustrated or described as flat may typically have rough and/or nonlinear features. Furthermore, sharp corners that are illustrated may be rounded. Thus, the regions illustrated in the figures are schematic in nature, and their shapes are not intended to illustrate the precise shape of the regions and are not intended to limit the scope of the claims.

Figure 1 is a partial cross-sectional schematic diagram of a display panel 10 according to an embodiment of the present invention. Referring to Figure 1 , the display panel 10 may include a substrate 110, a substrate 120, a display dielectric layer 130, and an alignment layer 140. The substrate 120 is disposed opposite the substrate 110. The display dielectric layer 130 is disposed between the substrates 110 and 120 and includes a plurality of display dielectric molecules DM. The alignment layer 140 is disposed on the substrate 110.

Substrates 110 and 120 may be transparent substrates. For example, substrates 110 and 120 may be made of glass, quartz, an organic polymer, or other suitable materials. Substrates 110 and 120 may be made of the same or different materials. In some embodiments, substrates 110 or 120 may be opaque substrates. In some embodiments, substrates 110 and/or 120 may be flexible substrates.

The display dielectric layer 130 is located in the space enclosed by the substrates 120 and 110. The display dielectric molecules DM in the display dielectric layer 130 are, for example, but not limited to, cholesteric liquid crystal (CLC) molecules. In some embodiments, the display dielectric molecules DM can switch between a focal conic state, a homeotropic state, and a planar state. For example, when the display dielectric molecules DM are in the focal conic state or the homeotropic state, the display dielectric layer 130 can exhibit a transmissive state. When the display dielectric molecules DM are in the planar state, the display dielectric layer 130 can exhibit a reflective state, thereby reflecting light entering the display panel 10. In some embodiments, the wavelength of light reflected by the display medium layer 130 may be determined by the pitch of the display medium molecules DM.

For example, the display panel 10 includes a plurality of pixels PX located in a display area, where the display area is, for example, the area where the pixels PX are located. When the display dielectric molecules DM in the pixels PX are all in a focal conical state or a vertical state, the display dielectric layer 130 in the pixels PX is in a transmissive state. When the display dielectric molecules DM in the pixels PX are all in a planar state, the display dielectric layer 130 in the pixels PX is in a reflective state. When a portion of the display dielectric molecules DM in the pixels PX are in a focal conical state or a vertical state and another portion of the display dielectric molecules DM in the pixels PX are in a planar state, the display dielectric layer 130 in the pixels PX is in a partially transmissive and partially reflective state, enabling the display dielectric layer 130 in the pixels PX to provide varying degrees of transmittance, thereby enabling the pixels PX to provide varying degrees of grayscale. In this way, the display dielectric layer 130 in any pixel PX can be switched between a reflective state (minimum transmittance), a transmissive state (maximum transmittance), and a transmittance between the reflective state and the transmissive state.

In some embodiments, when all display dielectric molecules DM in the display dielectric layer 130 are in a planar state, the transmittance of the display dielectric layer 130 is approximately 0%. In some embodiments, when all display dielectric molecules DM in the display dielectric layer 130 are in a conical state or a homeotropic state, the transmittance of the display dielectric layer 130 can be as high as 90% or greater. In some embodiments, when a portion of the display dielectric molecules DM in the display dielectric layer 130 are in a conical state or a homeotropic state and another portion of the display dielectric molecules DM in the planar state, the transmittance of the display dielectric layer 130 can be between 0% and 90%, for example, approximately 25%, approximately 50%, or approximately 75%.

The alignment layer 140 can be located between the substrate 110 and the display dielectric layer 130 to ensure that the display dielectric molecules DM in the display dielectric layer 130 are aligned and exhibit a good rotation effect, thereby improving image display quality. The alignment layer 140 can be formed by an imidization reaction of a dianhydride compound, a diamine compound with alkyl side chains, and a diamine compound without alkyl side chains.

Common dianhydride compounds include maleic anhydride, etc. In some embodiments, the dianhydride compound may have a structure shown in the following formula (1): Formula (1) wherein Ar represents an aromatic group having a 4- to 14-membered ring structure.

In some embodiments, Ar represents an aromatic group having a four-membered ring structure, a benzene ring structure, or a biphenyl structure. In some embodiments, the dianhydride compound of formula (1) is pyromellitic dianhydride (PMDA), 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA), or dicyclohexyl-3,4,3',4'-tetracarboxylic dianhydride (HBPDA).

Common diamine compounds include aromatic diamines such as 4,4’-oxydianiline (4,4’-ODA), p-phenylenediamine (PPD), and dimethyl-benzenediamine (DMBDA); or alkyl diamines such as 1,4-diaminobutane.

In some embodiments, the diamine compound having alkyl side chains is a compound having a polycyclic aromatic group Ar' with at least two _NH2 functional groups and at least one alkyl group attached to the ring. For example, the diamine compound having alkyl side chains can be represented by the chemical formula shown in Formula (2): Formula (2) wherein Ar' is a 5- to 14-membered aromatic group, _L1 is a single bond, -O-, -C(O)- or -C(O)O-, and _R1 is a C1 to C12 straight-chain alkyl group.

Alternatively, the diamine compound having an alkyl side chain may have a structure represented by the following formula (2'): Formula (2'): wherein Ar' is a 5- to 14-membered aromatic group, _L1 is a single bond, -O-, -C(O)-, or -C(O)O-, and R1 _is a C1 to C12 straight-chain alkyl group.

In some embodiments, Ar' in Formula (2) and Formula (2') is a 6-membered aromatic group or a 10-membered aromatic group. In some embodiments, Ar' in Formula (2) and Formula (2') is a benzene aromatic group or a naphthalene aromatic group.

In some embodiments, _R1 is a C1 to C10 linear alkyl group. In some embodiments, _R1 is methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, or n-octyl. In some embodiments, the diamine compound having alkyl side chains is ethyl 3,5-diaminobenzoate, n-propyl 3,5-diaminobenzoate, n-butyl 3,5-diaminobenzoate, n-hexyl 3,5-diaminobenzoate, or 3,5-diaminophenethyl ether.

A diamine compound without alkyl side chains may consist solely of a backbone chain and two _NH2 functional groups bonded to the backbone chain. In some embodiments, the backbone chain of the diamine compound without alkyl side chains includes a diphenyl ether group or a dinaphthyl ether group. In some embodiments, the diamine compound without alkyl side chains is 4,4'-diaminodiphenyl ether.

In some embodiments, the molar ratio of the diamine compound having alkyl side chains to the diamine compound without alkyl side chains is 0.1 to 0.5, for example, 0.2, 0.3, or 0.4. In some embodiments, the molar ratio of the dianhydride compound to the diamine compound without alkyl side chains is 1 to 1.5, for example, 1.2, 1.3, or 1.4. In some embodiments, the molar ratio of the dianhydride compound, the diamine compound having alkyl side chains, and the diamine compound without alkyl side chains is 1-1.5:0.1-0.5:1, for example, 1.5:0.5:1.

In some embodiments, the display panel 10 further includes an alignment layer 150, and the alignment layer 150 may be located between the substrate 120 and the display medium layer 130. In some embodiments, the material of the alignment layer 150 is the same as that of the alignment layer 140, but is not limited thereto. In some embodiments, the material of the alignment layer 150 is different from that of the alignment layer 140.

In some embodiments, the display panel 10 further includes a pixel array layer 160, and the pixel array layer 160 may be located in the substrate 110 or on the surface 112 of the substrate 110 adjacent to the display dielectric layer 130. In some embodiments, the pixel array layer 160 includes a plurality of pixel electrodes PE, and the plurality of pixel electrodes PE may be arranged in an array in the pixel array layer 160. For example, the pixel array layer 160 includes a plurality of pixel electrodes PE, a plurality of active devices (not shown), a plurality of data lines (not shown), and a plurality of scan lines (not shown). The active devices are, for example, thin film transistors having a source, a gate, and a drain. The data lines can be electrically connected to the sources of the plurality of active devices, the scan lines can be electrically connected to the gates of the plurality of active devices, and the plurality of pixel electrodes PE can be electrically connected to the drains of the plurality of active devices, respectively, but the present invention is not limited thereto.

In some embodiments, the display panel 10 further includes a common electrode layer 170, which may be located in the substrate 120 or on a side of the substrate 120 adjacent to the display dielectric layer 130. The electric field formed by the plurality of pixel electrodes PE of the pixel array layer 160 and the common electrode layer 170 can drive the display dielectric molecules DM in the display dielectric layer 130 to switch between different stable states.

In some embodiments, the display panel 10 further includes a color filter layer (not shown). The color filter layer may be located between the common electrode layer 170 and the substrate 120 to enable the display panel 10 to have a full-color display effect.

2 is a flow chart of a method 20 for manufacturing a display panel according to an embodiment of the present invention. In some embodiments, the alignment layer 140 can be formed on the substrate 110 in the following manner.

Referring to Figure 2, first, in step 210, a dianhydride compound can be reacted with a diamine compound having alkyl side chains to produce a first precursor, and the dianhydride compound can be reacted with a diamine compound without alkyl side chains to produce a second precursor. For example, referring to the following Reaction Scheme 1, a dianhydride compound (A) and a diamine compound (B) having alkyl side chains undergo a condensation polymerization reaction in a polar solvent to produce the first precursor (P1). Alternatively, referring to the following Reaction Scheme 2, a dianhydride compound (A) and a diamine compound (C) without alkyl side chains undergo a condensation polymerization reaction in a polar solvent to produce the second precursor (P2). In some embodiments, a dianhydride compound (A), a diamine compound having alkyl side chains (B), and a diamine compound without alkyl side chains (C) can be subjected to a condensation polymerization reaction in a polar solvent. The molar ratio of dianhydride compound (A): diamine compound having alkyl side chains (B): diamine compound without alkyl side chains (C) can be 1-1.5:0.1-0.5:1. In some embodiments, the first precursor (P1) and the second precursor (P2) are polyamide compounds. Reaction Formula 1: Reaction 2:

In some embodiments, the dianhydride compound (A) is pyromellitic dianhydride (PMDA). In some embodiments, the diamine compound (B) having alkyl side chains is ethyl 3,5-diaminobenzoate, n-propyl 3,5-diaminobenzoate, n-butyl 3,5-diaminobenzoate, n-hexyl 3,5-diaminobenzoate, or 3,5-diaminophenethyl ether. In some embodiments, the diamine compound (C) not having alkyl side chains is 4,4'-diaminodiphenyl ether. In some embodiments, the polar solvent is dimethylformamide (DMF) or dimethyl sulfoxide (DMSO).

Next, in step 220, a mixture of the first precursor and the second precursor can be applied to the first substrate. For example, the first precursor (P1) and the second precursor (P2) can be mixed, and the molar ratio of the first precursor (P1) to the second precursor (P2) can be 0.1-0.5:1. In some embodiments, the molar ratio of the first precursor (P1) to the second precursor (P2) is 1:2. Then, referring to FIG. 1 , the mixture of the first precursor (P1) and the second precursor (P2) can be applied to the surface 112 of the substrate 110 facing the display medium layer 130 by, for example, scraping or spin coating. In some embodiments, a mixture of the first precursor (P1) and the second precursor (P2) may be coated on the surface of the substrate 110 where the pixel array layer 160 is formed.

In some embodiments, a mixture of the first precursor (P1) and the second precursor (P2) may be applied to the surface 122 of the substrate 120 facing the display dielectric layer 130. In some embodiments, the mixture of the first precursor (P1) and the second precursor (P2) may be applied to the surface of the substrate 120 on which the common electrode layer 170 is formed.

Next, in step 230, the mixture of the first precursor and the second precursor can be cured to form a first alignment layer on the first substrate. For example, referring to Reaction Equation 3 below, the substrate 110 coated with the mixture of the first precursor (P1) and the second precursor (P2) can be heated to above 200°C, for example, 200°C to 250°C, to allow the first precursor (P1) and the second precursor (P2) to undergo a cyclization reaction and dehydrate and cure, thereby generating a polyimide polymer (PI). This polyimide polymer (PI) can form a polyimide film on the surface 112 of the substrate 110, serving as the alignment layer 140. In some embodiments, the heating can be continued for 30 to 60 minutes. Because the polyimide polymer (PI) of the alignment layer 140 includes alkyl side chains R ₁ , and the carbon number of the alkyl side chains R ₁ is less than or equal to 12, the angle between the alkyl side chains R ₁ and the horizontal surface 142 of the alignment layer 140 can cause the display medium molecules DM to have a pre-tilt angle θ less than or equal to 4°. Generally, the pre-tilt angle θ can be measured using optical instruments such as Axsosan and RENTS. In addition, because the polyimide polymer (PI) of the alignment layer 140 also includes diphenyl ether functional groups without side chains, it helps prevent excessive interactions between the display medium molecules DM and the polyimide polymer (PI), thereby reducing factors that interfere with the alignment of the display medium molecules DM. Reaction 3:

The alignment layer 140 may have a polyimide (PI) structure as shown in Reaction Formula 3. In some embodiments, in the polyimide (PI) structure as shown in Reaction Formula 3, n:n' is 0.1-0.5:1, for example, 1:5 or 1:2.

In some embodiments, in step 230, the substrate 120 coated with a mixture of the first precursor (P1) and the second precursor (P2) can be heated and cured simultaneously, so that the first precursor (P1) and the second precursor (P2) undergo a cyclization reaction, thereby forming a polyimide film on the surface 122 of the substrate 120 as the alignment layer 150. In some embodiments, the alignment layer 150 also has a polyimide (PI) structure shown in Reaction Formula 3.

Next, in step 240, the first and second substrates can be assembled with the first alignment layer facing the second substrate. Display medium molecules are then introduced between the first alignment layer and the second substrate. For example, a sealant (not shown) can be applied around the perimeter of surface 112 of substrate 110 (or the surface of alignment layer 140 facing substrate 110) or around surface 122 of substrate 120 (or the surface of alignment layer 150 facing substrate 120). Display medium molecules DM are then dropped into the space enclosed between surface 112 (or alignment layer 140) or surface 122 (or alignment layer 150) and the sealant. Afterwards, the alignment layer 140 can be positioned facing the alignment layer 150 to secure the substrates 110 and 120. Then, in a near-vacuum environment, one of the substrates 110 and 120 can be moved toward the other, thereby bonding the substrates 110 and 120 to each other via a sealant. This seals the display dielectric molecules DM between the alignment layer 140 and the alignment layer 150 to form the display dielectric layer 130, completing the fabrication of the display panel 10. In some embodiments, the display dielectric molecules DM can be introduced using a one-drop fill (ODF) method to fabricate the display panel 10, but this is not limited thereto. In other embodiments, the display dielectric molecules DM can be introduced using a liquid crystal injection method (LC injection) or other suitable methods to fabricate the display panel 10.

Figure 3 shows a test image of a display panel 10 according to an embodiment of the present invention. The display panel 10 was driven to a 3x1 black and white grid pattern and left at 50°C for one day before undergoing an image retention test. The image shown in Figure 3 was obtained. As can be seen from Figure 3, the display panel 10 exhibits virtually no image retention, demonstrating that the display panel of the present invention effectively reduces image retention.

In summary, the display panel of the present invention utilizes a diamine compound with alkyl side chains and a diamine compound without alkyl side chains to form an alignment layer. This prevents excessive interaction between the display medium molecules and the surface of the alignment layer, while also ensuring that the display medium molecules have a pre-tilt angle of less than or equal to 4°, thereby improving the image retention phenomenon of the display panel.

Although the present invention has been disclosed above by way of embodiments, they are not intended to limit the present invention. Any person having ordinary skill in the art may make slight modifications and improvements without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be determined by the scope of the attached patent application.

10: Display Panel 20: Method 110,120: Substrate 112,122,142: Surface 130: Display Dielectric Layer 140,150: Alignment Layer 160: Pixel Array Layer 170: Common Electrode Layer 210-240: Steps DM: Display Dielectric Molecule PE: Pixel Electrode PX: Pixel

Figure 1 is a partial cross-sectional schematic diagram of a display panel according to an embodiment of the present invention. Figure 2 is a flow chart of a method for manufacturing a display panel according to an embodiment of the present invention. Figure 3 is a test image of a display panel according to an embodiment of the present invention.

10: Display Panel

110,120:Substrate

112, 122, 142: Surface

130: Display media layer

140,150:Alignment layer

160: Pixel array layer

170: Common electrode layer

DM: Display mediator molecule

PE: Pixel electrode

PX: Pixel

Claims (12)

A display panel comprises: a first substrate; a second substrate disposed opposite to the first substrate; a display dielectric layer disposed between the first and second substrates and comprising a plurality of display dielectric molecules; and a first alignment layer disposed on the first substrate; wherein the first alignment layer is formed by condensation polymerization of a dianhydride compound, a diamine compound having alkyl side chains, and a diamine compound without alkyl side chains, wherein the molar ratio of the diamine compound having alkyl side chains to the diamine compound without alkyl side chains is 0.1 to 0.5, and the diamine compound having alkyl side chains is ethyl 3,5-diaminobenzoate, n-propyl 3,5-diaminobenzoate, n-butyl 3,5-diaminobenzoate, n-hexyl 3,5-diaminobenzoate, or 3,5-diaminophenyl ether. The display panel of claim 1, wherein the alkyl side chains of the diamine compound having alkyl side chains make the pre-tilt angle of the display medium molecule less than or equal to 4°. The display panel according to claim 1, wherein the molar ratio of the dianhydride compound, the diamine compound having alkyl side chains, and the diamine compound without alkyl side chains is 1-1.5:0.1-0.5:1. The display panel as claimed in claim 1, wherein the dianhydride compound has a structure represented by the following formula (1): Formula (1) wherein Ar represents an aromatic group having a 4- to 14-membered ring structure. A display panel as described in claim 4, wherein the aromatic group has a four-membered ring structure, a benzene ring structure or a biphenyl structure. The display panel as described in claim 1, wherein the diamine compound without alkyl side chains is 4,4'-diaminodiphenyl ether. The display panel as described in claim 1 further includes a second alignment layer, wherein the first alignment layer is located between the first substrate and the display medium layer, and the second alignment layer is located between the second substrate and the display medium layer. The display panel as described in claim 7, wherein the second alignment layer is made of the same material as the first alignment layer. A method for manufacturing a display panel comprises the following steps: reacting a dianhydride compound with a diamine compound having alkyl side chains to generate a first precursor, and reacting the dianhydride compound with a diamine compound without alkyl side chains to generate a second precursor, wherein the diamine compound having alkyl side chains is ethyl 3,5-diaminobenzoate, n-propyl 3,5-diaminobenzoate, n-butyl 3,5-diaminobenzoate, n-hexyl 3,5-diaminobenzoate, or 3,5-diaminophenyl ether; applying a mixture of the first precursor and the second precursor on a first substrate; curing the mixture to form a first alignment layer on the first substrate; and The first substrate and the second substrate are assembled together with the first alignment layer facing the second substrate, and display medium molecules are filled between the first alignment layer and the second substrate, wherein the display medium molecules have a pre-tilt angle less than or equal to 4°. The method of claim 9, wherein the molar ratio of the diamine compound having an alkyl side chain to the diamine compound not having an alkyl side chain is 0.1 to 0.5. The method of claim 9, wherein the ratio of the first precursor to the second precursor in the mixture is 0.1-0.5:1. The method of claim 9, wherein the curing reaction is carried out at a temperature of 200°C to 250°C for 30 to 60 minutes.