Flexible material surface wettability patterning treatment method and application thereof

Abstract

The invention discloses a flexible material surface wettability patterning treatment method and application thereof. The flexible material surface wettability patterning treatment method comprises the following steps that S1, the surface of a hydrophilic flexible substrate is coated with a patterned polyvinyl alcohol aqueous solution, a patterned area covered with the polyvinyl alcohol aqueous solution and an exposed area not covered with the polyvinyl alcohol aqueous solution are formed, and a flexible substrate I in an intermediate state is obtained; s2, a hydrophobic material layer is deposited in the exposed area, a hydrophobic area is formed, and a flexible substrate II in an intermediate state is obtained; and S3, removing the polyvinyl alcohol aqueous solution on the surface of the flexible substrate through washing, and forming a hydrophilic region on the surface of the substrate to obtain the flexible substrate with the wettability patterned surface. The treatment method has the characteristics of soft treatment means and difficulty in damaging the flexible substrate, and the flexible material subjected to surface wetting patterning treatment can be used for preparing a patterned organic semiconductor material and has a good application prospect.

Description

Technical Field

[0001] The present invention belongs to the technical field of flexible electronic materials, and in particular relates to a method for patterning wettability of a flexible material surface and an application thereof. Background Art

[0002] With the rapid development of the Internet of Things, organic semiconductors have become ideal materials for future flexible electronic devices due to their advantages such as high flexibility, low cost, low processing temperature and suitability for large-scale solution processing.

[0003] In order to prepare high-performance organic electronic and optoelectronic devices, it is necessary to pattern organic semiconductors. The patterning of organic semiconductors helps to build addressing circuits, is the basis for preparing electronic and optoelectronic device arrays, and is of great significance to the integration of organic electronic and optoelectronic devices. In addition, the patterning of organic semiconductors can avoid crosstalk between adjacent devices and reduce leakage current at the edge of the substrate. At present, the method for patterning organic semiconductors includes printing, micropatterning of substrates, etching of large-area organic semiconductors (such as oxygen plasma etching, ultraviolet ozone treatment, laser ablation), etc. However, the process of etching organic semiconductors using plasma and laser ablation will damage the structure of organic semiconductors and affect device performance. However, the current substrate pre-patterning methods are usually based on rigid substrates, and the commonly used photolithography process will introduce organic solvents and high-temperature processing. The etching process is also easy to damage the flexible substrate under the rigid substrate, which is not conducive to the preparation of electronic devices and affects the application of electronic devices to a certain extent. Summary of the invention

[0004] The present invention aims to solve at least one of the technical problems existing in the above-mentioned prior art. To this end, the present invention proposes a method for patterning the wettability of a flexible material surface, which has the characteristics of gentle treatment means and is not easy to cause damage to the flexible substrate. The flexible material subjected to the patterning treatment of the surface wettability can be used to prepare patterned organic semiconductor materials, and has good application prospects.

[0005] The invention also provides a method for preparing the patterned organic semiconductor material.

[0006] The invention also provides a patterned organic semiconductor material.

[0007] The present invention also proposes the application of the above-mentioned method for patterning wettability of the surface of a flexible material or the method for preparing a patterned organic semiconductor material.

[0008] The invention also provides an electronic device.

[0009] The invention also provides a method for preparing the electronic device.

[0010] In a first aspect of the present invention, a method for patterning wettability of a flexible material surface is provided, comprising the following steps:

[0011] S1, coating a patterned polyvinyl alcohol aqueous solution on the surface of a hydrophilic flexible substrate to form a patterned area covered with the polyvinyl alcohol aqueous solution and a bare area not covered with the polyvinyl alcohol aqueous solution, to obtain an intermediate flexible substrate I;

[0012] S2, depositing a hydrophobic material layer on the exposed area to form a hydrophobic area, thereby obtaining an intermediate flexible substrate II;

[0013] S3, removing the polyvinyl alcohol aqueous solution on the surface of the flexible substrate by water washing, forming a hydrophilic area on the surface of the substrate, and obtaining a flexible substrate with a surface wettability pattern.

[0014] The method for patterning wettability of a flexible material surface according to an embodiment of the present invention has at least the following beneficial effects:

[0015] The present invention provides a mild surface wettability patterning method compatible with a flexible substrate, which can be used to prepare a patterned organic semiconductor material. A patterned polyvinyl alcohol aqueous solution is deposited on the surface of a flexible substrate by a coating method, and then a hydrophobic material layer is deposited on the exposed surface of the flexible substrate. After the polyvinyl alcohol aqueous solution pattern is removed by simple water washing, the area protected by the polyvinyl alcohol still maintains hydrophilic properties, while the exposed area exhibits hydrophobic properties after self-deposition modification, thereby achieving patterning of surface wettability on the flexible substrate. In addition, polyvinyl alcohol is soluble in water and can be easily removed, and the processing method is gentle and is not easy to cause damage to the flexible substrate.

[0016] In some embodiments of the present invention, in step S1, the coating method includes screen printing. The pattern is formed by screen printing of polyvinyl alcohol aqueous solution, which can avoid the pattern distortion problem caused by the distance between the mask and the substrate used in oxygen plasma etching, ultraviolet ozone treatment, etc. in related technologies.

[0017] In some embodiments of the present invention, the screen template used in the screen printing is a screen template containing a metal material.

[0018] Through the above implementation, a metal screen template is used to produce a pattern with higher precision, smoother edges and higher fidelity.

[0019] In some embodiments of the present invention, the wire mesh template includes a stainless steel wire mesh template, and specifically a 301 stainless steel wire mesh template.

[0020] In some embodiments of the present invention, the mass fraction of polyvinyl alcohol in the polyvinyl alcohol aqueous solution is 15-35%, preferably 24-27%.

[0021] Compared with the mass fraction of polyvinyl alcohol greater than 27%, when the mass fraction of polyvinyl alcohol is 24-27%, the viscosity of the polyvinyl alcohol solution is relatively low, which is more conducive to the complete presentation of the pattern shape; compared with the mass fraction of polyvinyl alcohol less than 24%, when the mass fraction of polyvinyl alcohol is 24-27%, the polyvinyl alcohol solution is more able to maintain the shape and is not easy to deform the pattern due to surface tension and capillary force.

[0022] In some embodiments of the present invention, the viscosity of the polyvinyl alcohol aqueous solution is in the range of about 0.15 to 0.6 Pa·s. The pattern is less likely to be distorted.

[0023] In some embodiments of the present invention, the molecular weight of the polyvinyl alcohol is 20,000 to 100,000.

[0024] In some embodiments of the present invention, the polyvinyl alcohol may be PVA-203.

[0025] In some embodiments of the present invention, step S1 comprises the following operations: mixing polyvinyl alcohol and water, stirring at 15-40° C. for 5-50 hours to obtain the polyvinyl alcohol aqueous solution; screen printing the patterned polyvinyl alcohol aqueous solution on the surface of the flexible substrate to obtain an intermediate flexible substrate I.

[0026] In some embodiments of the present invention, the flexible substrate comprises a polyamic acid layer, and a patterned polyvinyl alcohol aqueous solution is screen-printed on the surface of the polyamic acid layer.

[0027] Through the above implementation, the polyamic acid in the polyamic acid layer has good hydrophilicity, and the hydrophilic region formed after patterning is more conducive to the selective deposition of organic semiconductors, and has good application prospects. In the present invention, the obtained flexible substrate with patterned surface wettability is used to prepare patterned organic semiconductor materials, because polyamic acid has unique surface properties, which can induce the organic semiconductor molecules to arrange in an orderly manner.

[0028] In some embodiments of the present invention, in step S2, the deposition method includes vapor deposition.

[0029] Through the above-mentioned implementation mode, the polyvinyl alcohol pattern is formed by screen printing in the present invention, and then the hydrophobic material layer is gas-phase modified. Compared with the traditional photolithography technology, the cost of screen printing technology is greatly reduced. In addition, the polyvinyl alcohol solution in the present invention has a certain viscosity due to hydrogen bonding, and it is not easy to deform the pattern during the screen printing process, and the polyvinyl alcohol is soluble in water and can be easily removed without causing damage to the substrate. The hydrophilic region and the hydrophobic region of the obtained surface wettability patterned flexible substrate have a significant difference in surface free energy. For example, in some embodiments of the present invention, after surface energy measurement, the difference between the hydrophilic and hydrophobic regions can reach 23.11mN / m.

[0030] The flexible substrate subjected to surface wettability patterning treatment in the present invention can be applied to the selective deposition of organic semiconductors, thereby realizing the patterning of organic semiconductors and further preparing the application of organic electronic devices, which is helpful for the integration of organic electronic devices.

[0031] In some embodiments of the present invention, the hydrophobic material layer includes halogenated siloxane, such as a hydrophobic halogenated siloxane layer, and the thickness may be less than 5 nm.

[0032] In some embodiments of the present invention, the hydrophobic material layer is a halogenated siloxane layer.

[0033] In some embodiments of the present invention, the halogenated siloxane includes at least one of heptadecafluorodecyltrimethoxysilane, octadecyltrichlorosilane, or tridecafluorooctyltriethoxysilane.

[0034] In some embodiments of the present invention, in step S2, the vapor deposition is physical vapor deposition. The polyvinyl alcohol solution is deposited on the surface of the flexible substrate using screen printing, and the hydrophobic material layer is deposited using physical vapor deposition. The hydrophobic material layer is modified by vapor deposition to avoid the introduction of toxic and corrosive organic solvents, and high temperature is not required. For example, in some embodiments of the present invention, the heating temperature can be selected to be 70°C.

[0035] In some embodiments of the present invention, the physical vapor deposition step includes: the halogenated siloxane and the intermediate flexible substrate I are vapor deposited at 20-30°C for 10-15 hours at a pressure of 0.05-0.3 MPa, and then vapor deposited at 65-75°C for 0.5-3 hours. Specifically, it can be: the halogenated siloxane and the intermediate flexible substrate I are vapor deposited at 25°C for 12 hours at a pressure of 0.1 MPa, and then vapor deposited at 70°C for 2 hours.

[0036] In some embodiments of the present invention, step S2 includes the following operations: placing the intermediate flexible substrate I and the open container containing the halogenated siloxane in a vacuum oven, evacuating to a pressure of 0.05-0.3 MPa, placing at 20-30° C. for 10-15 hours, and then heating to 65-75° C. for 0.5-3 hours. A halogenated siloxane layer is formed on the surface of the substrate by physical vapor deposition.

[0037] In the second aspect of the present invention, a method for preparing a patterned organic semiconductor material is proposed, comprising the following steps: preparing a flexible substrate with surface wettability patterning by the above-mentioned flexible material surface wettability patterning treatment method, depositing organic semiconductor molecules in the hydrophilic area of ​​the substrate surface, and obtaining a patterned organic semiconductor material.

[0038] In some embodiments of the present invention, in the preparation method, the step of depositing organic semiconductor molecules on the hydrophilic region of the substrate surface specifically comprises the following operations:

[0039] S4, coating a solution containing an organic semiconductor on the surface of the flexible substrate with a patterned surface wettability, and selectively depositing the organic semiconductor on the hydrophilic region of the substrate to form a patterned organic semiconductor material on the surface of the substrate.

[0040] In some embodiments of the present invention, in step S4, the coating method includes scraping.

[0041] The present invention adopts a scraping method to grow an organic semiconductor on a pre-patterned substrate, which has low processing cost and high processing efficiency. For example, in some embodiments of the present invention, the scraping speed can be about 200 μm / s. The scraping method is compatible with industrial roll-to-roll technology and is expected to be used for the preparation of large-scale patterned organic semiconductors. The preparation method of the present invention also has high processing accuracy. For example, the width of the pattern line obtained in some embodiments of the present invention can be about 160 μm.

[0042] In some embodiments of the present invention, the pattern includes a preset starting point for scraping the solution containing an organic semiconductor, and along the preset scraping direction, the size of the pattern in a direction perpendicular to the preset scraping direction tends to increase. Optionally, the increasing trend includes but is not limited to a variety of ways such as gradual increase or stepwise increase. Optionally, the pattern may include at least one of a pattern with a bottleneck shape or a pattern with a small tip angle. Optionally, the preset scraping direction may be defined as a first direction, and the direction perpendicular to the preset scraping direction may be defined as a second direction.

[0043] For organic semiconductor small molecules, according to the classical nucleation and growth theory, as the solvent in the solution containing organic semiconductor evaporates, the organic semiconductor concentration increases, and the solution is locally supersaturated with organic semiconductors. At the supersaturated position, the organic semiconductor nucleates and the organic semiconductor molecules self-assemble. In order to make the orientation of the organic semiconductor crystal as consistent as possible, multi-point nucleation needs to be suppressed. The present invention designs a pre-pattern substrate shape, designs a point with a small radius of curvature (preset starting point of scraping the solution containing organic semiconductor) in the pattern, and the evaporation flux of the solution is large, so that other positions have a large radius of curvature (the size of the pattern in the direction perpendicular to the preset scraping direction tends to increase), and the evaporation flux is relatively small relative to the starting point, so that the nucleation point is located at the minimum radius of curvature, thereby controlling the number and position of nucleation. By designing the bottleneck shape and the tip small angle pattern, the nucleation position is concentrated during the scraping process, and the crystal growth direction is controlled by the scraping direction, and a patterned organic semiconductor crystal with basically consistent orientation is obtained.

[0044] In some embodiments of the present invention, the solution containing an organic semiconductor includes an organic semiconductor, an additive and a solvent.

[0045] In some embodiments of the present invention, the organic semiconductor includes 2,8-dioctylbenzothiophene (C8-BTBT).

[0046] In some embodiments of the present invention, the additive includes polystyrene. Polystyrene is a polymer that can enhance its film-forming property when miscible with small molecule semiconductors, and miscible polystyrene can increase the viscosity of the solution, thereby inhibiting Marangoni flow and increasing the coverage of the semiconductor inside the wetting pattern.

[0047] In some embodiments of the invention, the solvent comprises toluene.

[0048] In some embodiments of the present invention, in the solution containing organic semiconductors, the ratio of the amount of organic semiconductor, additive and solvent is (6-10) mg: (2-6) mg: 1 mL, such as 8 mg: 4 mg: 1 mL. In some embodiments of the present invention, the solution containing organic semiconductors is prepared by a method comprising the following steps: taking an organic semiconductor, an additive and a solvent, stirring at room temperature for 5-30 hours, and obtaining the solution containing organic semiconductors.

[0049] In some embodiments of the present invention, in step S4, a solution containing an organic semiconductor is dropped between a scraper of a scraper and a flexible substrate with a surface wettability pattern, and the organic semiconductor is selectively deposited on the hydrophilic region of the flexible substrate by a scraper coating method. By designing the shape of the wettability pattern and coordinating with the directional movement of the scraper, the nucleation and growth process of the organic semiconductor can be regulated.

[0050] In some embodiments of the present invention, the thickness of the patterned organic semiconductor material is 10 to 60 nm.

[0051] The third aspect of the present invention provides a patterned organic semiconductor material, which is prepared by adopting the above-mentioned method for preparing the patterned organic semiconductor material.

[0052] In a fourth aspect of the present invention, a method for patterning wettability of a flexible material surface or a method for preparing a patterned organic semiconductor material or an application of the patterned organic semiconductor material in preparing a flexible electronic device is proposed.

[0053] In a fifth aspect of the present invention, an electronic device is provided, comprising a patterned organic semiconductor material, wherein the organic semiconductor material is prepared by the method for preparing the patterned organic semiconductor material.

[0054] In some embodiments of the present invention, the electronic device is an organic field effect transistor, which includes a flexible substrate and a patterned organic semiconductor material layer stacked together; the patterned organic semiconductor material layer includes a patterned organic semiconductor material.

[0055] In some embodiments of the present invention, the flexible substrate comprises a substrate layer, a gate electrode layer, a dielectric layer and a polyamic acid layer stacked in sequence, and the patterned organic semiconductor material layer is disposed on a side of the polyamic acid layer facing away from the dielectric layer.

[0056] In some embodiments of the present invention, the thickness of the substrate layer is 1.5-5 μm.

[0057] In some embodiments of the present invention, the substrate layer comprises parylene.

[0058] In some embodiments of the present invention, the thickness of the gate electrode layer is 5-100 nm.

[0059] In some embodiments of the present invention, the gate electrode layer includes at least one of chromium or gold.

[0060] In some embodiments of the present invention, the thickness of the dielectric layer is 600-1500 nm.

[0061] In some embodiments of the present invention, the dielectric layer comprises SU8 photoresist.

[0062] In some embodiments of the present invention, the thickness of the polyamic acid layer is 1 to 100 nm, such as 5 to 10 nm.

[0063] In some embodiments of the present invention, the thickness of the patterned organic semiconductor material layer is 10 to 60 nm.

[0064] In some embodiments of the present invention, a source electrode and a drain electrode are disposed on a side of the patterned organic semiconductor material layer facing away from the polyamic acid layer.

[0065] A sixth aspect of the present invention provides a method for preparing an electronic device, comprising the following steps:

[0066] preparing a flexible substrate having a substrate layer, a gate electrode layer, a dielectric layer and a polyamic acid layer stacked in sequence;

[0067] The method for preparing the patterned organic semiconductor material is used to prepare a patterned organic semiconductor material layer on the surface of the flexible substrate.

[0068] The screen printing method used in the present invention can directly obtain regional wettability patterning on the polymer-based dielectric layer, and regulate the nucleation of organic semiconductors during coating (such as scraping) to achieve patterning. There is no need for a subsequent transfer process, and the organic semiconductor grows directly on the polymer-based dielectric layer. The screen printing cost is low, and the scraping-induced organic semiconductor growth is compatible with the roll-to-roll process, and the preparation efficiency is high (such as the scraping rate of about 200μm / s in some embodiments of the present invention). The preparation method of the present invention also has high processing accuracy. For example, the pattern line width obtained in some embodiments of the present invention can be about 160μm, with high accuracy.

[0069] In some embodiments of the present invention, the preparation method further comprises disposing a source electrode and a drain electrode on the surface of the patterned organic semiconductor material layer.

[0070] In some embodiments of the present invention, the step of preparing the flexible substrate specifically comprises the following operations:

[0071] S0-1, coating a sacrificial layer on the surface of a hard sheet, and preparing a substrate layer on the surface of the sacrificial layer by vacuum coating;

[0072] S0-2, evaporating a gate electrode layer on the surface of the substrate layer;

[0073] S0-3, coating the gate electrode layer with epoxy resin and curing the epoxy resin to form a dielectric layer;

[0074] S0-4, spin-coating a polyamic acid solution on the dielectric layer to form a polyamic acid layer to obtain the flexible substrate.

[0075] In some embodiments of the present invention, in step S0-1, a glass sheet is used as a rigid support material, and fluoride is spin-coated on the surface of the glass sheet to obtain the sacrificial layer.

[0076] In some embodiments of the present invention, in step S0-1, the glass sheet is cleaned and then spin-coated with fluoride, wherein the cleaning step comprises: soaking the glass sheet in a piranha solution for 0.5-5 hours, ultrasonicating in water, isopropanol, and ethanol in sequence, and blowing dry with nitrogen to obtain a cleaned glass sheet.

[0077] In some embodiments of the present invention, in step S0-3, the epoxy resin may be applied by spin coating. Optionally, SU8 epoxy resin may be spin coated and cross-linked to serve as a dielectric layer.

[0078] In some embodiments of the present invention, in step S0-3, the dielectric layer is subjected to oxygen plasma etching and then spin-coated with polyamic acid solution. Optionally, the oxygen plasma etching power is 20 to 50 W, and / or the etching time is 0.5 to 5 min. BRIEF DESCRIPTION OF THE DRAWINGS

[0079] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein:

[0080] Figure 1 This is a schematic diagram of the preparation process of the organic field effect transistor in Example 1 of the present invention;

[0081] Figure 2 This is a microscopic test result diagram of the material obtained by performing organic semiconductor on the silicon dioxide surface modified / unmodified with polyamic acid according to the present invention;

[0082] Figure 3 This is a microscopic test result diagram of the flexible substrate with a patterned organic semiconductor layer grown thereon obtained in Examples 1 and 3 of the present invention;

[0083] Figure 4 The atomic force microscope topography images of the hydrophilic region and the hydrophobic region of the flexible substrate with surface wettability patterning prepared in Example 1 of the present invention;

[0084] Figure 5 The surface contact angle test result diagram of the hydrophilic region and the hydrophobic region of the flexible substrate with surface wettability pattern prepared by deionized water and diiodomethane in Example 1;

[0085] Figure 6 This is a diagram showing the optical microscope observation result of the flexible substrate with a polyvinyl alcohol pattern obtained in step (II) of Example 1-2 of the present invention;

[0086] Figure 7 This is a test diagram of the microscopic results of the patterned organic semiconductor in Example 4 of the present invention;

[0087] Figure 8 This is a test result diagram of the transfer characteristic curve and output characteristic curve of the organic field effect transistor prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0088] The following will be combined with the embodiments to clearly and completely describe the concept of the present invention and the technical effects produced, so as to fully understand the purpose, characteristics and effects of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0089] The experimental methods without specific conditions in the following examples and comparative examples are generally based on conventional conditions in the art or conditions recommended by the manufacturers; the raw materials, reagents, etc. used, unless otherwise specified, are all raw materials and reagents available from commercial channels such as conventional markets.

[0090] Polyvinyl alcohol: PVA-203, M w ~31000, purchased from Aladdin; can also be purchased from other manufacturers;

[0091] Metal mask: purchased from Shenzhen Grace Electronics Co., Ltd., made of 301 stainless steel.

[0092] Example 1

[0093] This embodiment discloses a method for patterning wettability of a flexible material surface, which comprises the following steps:

[0094] (I) Polyvinyl alcohol (PVA-203) was dissolved in deionized water at a concentration of 24% by mass, and stirred at room temperature for 12 hours to fully dissolve the polyvinyl alcohol solution.

[0095] A flexible substrate is obtained, wherein the flexible substrate comprises a polyparaxylene layer, a gate electrode layer, a dielectric layer (SU8 photoresist) and a polyamic acid layer which are stacked in sequence.

[0096] (II) The obtained polyvinyl alcohol aqueous solution is screen-printed (a metal mask is used as the screen template, 301 stainless steel, thickness 0.1 mm) to form a pattern on the surface of the polyamic acid layer of the flexible substrate (as an example, the patterns are as follows Figure 6 The flexible substrate with polyvinyl alcohol pattern is obtained by combining pattern 1 and pattern 2 in the above method. Pattern 1 is in the shape of a water droplet, which is a closed figure composed of a 40-60° acute angle and an arc, where the arc radius is 250-500 μm. Pattern 2 is a closed figure composed of a narrow rectangle and a square, and the side length of the square part is 500-1000 μm.

[0097] (III) The flexible substrate obtained in step (II) is placed in a vacuum oven together with 15 μL of 17-fluorodecyltrimethoxysilane (FAS) placed in an open position, evacuated to a pressure of 0.1 MPa, placed at room temperature for 12 hours, and then heated to 70°C and maintained for 2 hours. The 17-fluorodecyltrimethoxysilane forms a halogenated siloxane layer with low surface energy on the polymer surface by physical vapor deposition to form a hydrophobic area. The polyvinyl alcohol on the surface of the flexible substrate is removed by washing with deionized water (forming hydrophilicity), and a flexible substrate with surface wettability patterning is obtained.

[0098] This embodiment discloses a patterned organic semiconductor material, the preparation process of which includes the following steps:

[0099] The organic semiconductor 2,8-dioctylbenzothiophene (C8-BTBT) and polystyrene are mixed in toluene (the dosage ratio of C8-BTBT to polystyrene and toluene is 8mg:4mg:1mL), and stirred at room temperature for 12h to fully dissolve it. The resulting solution is dropped between the scraper of the scraper and the flexible substrate with surface wettability pattern obtained in this embodiment. The gap between the scraper and the flexible substrate is 100μm, and the horizontal movement speed of the scraper is 200-250μm / s; using the scraping method, as the scraper moves in a directional manner, the organic semiconductor is selectively deposited in the hydrophilic area of ​​the flexible substrate. By designing the shape of the wettability pattern, the nucleation and growth process of the organic semiconductor can be regulated. Thus, a patterned organic semiconductor material is obtained. During the scraping process of the organic semiconductor solution, the scraper drags the solution to move, and the three-phase line (gas-liquid-solid three-phase boundary line) first passes through the tip of pattern 1 and one end of the narrow rectangle of pattern 2. Since the solution has a large evaporation flux here, the organic semiconductor crystals are first nucleated at these two places, and then grow along the scraping direction.

[0100] This embodiment discloses an organic field effect transistor, and its preparation process includes the following steps. The preparation process diagram is shown in FIG. Figure 1 As shown:

[0101] The flexible substrate is prepared, including: using a glass sheet as a rigid support material, soaking the glass sheet in a piranha solution for 2 hours, ultrasonicating in deionized water, isopropanol, and ethanol in turn, and blowing dry with nitrogen. Spin-coating fluoride on the cleaned glass sheet as a sacrificial layer to facilitate the subsequent peeling of the flexible substrate from the glass sheet. Using a parylene coater to deposit 1.5 μm thick polyparaxylene (thickness of 1.5 to 5 μm). Using an evaporation coater to deposit chromium and gold on polyparaxylene as gate electrodes (G, wherein Cr thickness is 5 nm and Au thickness is 45 nm). Spin-coating SU8 epoxy resin, after exposure and baking and curing, the interior thereof is fully cross-linked to obtain a dielectric layer (thickness of 600 to 1000 nm). Performing oxygen plasma etching on the dielectric layer (power: 50 W, time: 2 min), and then spin-coating polyamic acid with good wettability on the surface of the dielectric layer (epoxy resin) to form a polyamic acid layer (thickness of 5 to 10 nm) to obtain a flexible substrate.

[0102] The method for processing the surface wettability patterning of a flexible material described in this embodiment is used to process the surface wettability patterning of a flexible substrate, thereby obtaining a flexible substrate with a surface wettability patterning.

[0103] Preparation of patterned organic semiconductor material layer (thickness of about 30nm): organic semiconductor 2,8-dioctylbenzothiophene (C8-BTBT) and polystyrene are mixed in toluene (the ratio of C8-BTBT to polystyrene and toluene is 8mg:4mg:1mL), and stirred at room temperature for 12h to fully dissolve. The resulting solution is dropped between the scraper of the scraper and the prepared flexible substrate with surface wettability pattern. The gap between the scraper and the flexible substrate is 100μm, and the horizontal movement speed of the scraper is 200-250μm / s; using the scraper coating method, as the scraper moves in a directional manner, the organic semiconductor is selectively deposited in the hydrophilic area of ​​the flexible substrate. By designing the shape of the wettability pattern, the nucleation and growth process of the organic semiconductor can be regulated to form a patterned organic semiconductor material layer. During the scraping process of the organic semiconductor solution, the scraper drags the solution to move, and the three-phase line (the boundary line of the gas-liquid-solid three-phases) first passes through the tip of pattern 1 and one end of the narrow rectangle of pattern 2. Since the evaporation flux of the solution is large here, the organic semiconductor crystals first nucleate at these two places and then grow along the scraping direction.

[0104] Using an evaporation coating machine and a mask, patterned chromium and gold were deposited as source electrodes (S) and drain electrodes (D) to obtain an organic field effect transistor array. The hole mobility of the organic field effect transistor reached 1.3 cm 2 V -1 s -1 , the switching ratio reaches 10 5 .

[0105] Example 2

[0106] This embodiment discloses a method for patterning wettability of a flexible material surface, which differs from Embodiment 1 only in that in this embodiment, a traditional silk screen (material: polymer grid + photosensitive film) is used instead of the metal mask used in Embodiment 1.

[0107] Example 3

[0108] This embodiment discloses an organic field effect transistor, which is different from Embodiment 1 only in that in this embodiment: in the step of preparing a flexible substrate, polyamic acid is directly spin-coated on the SU8 photoresist (the SU8 photoresist is not etched by oxygen plasma).

[0109] Example 4

[0110] This embodiment discloses an organic field effect transistor, which is different from the embodiment 1 only in that the patterned pattern formed on the surface of the polyamic acid layer of the flexible substrate in this embodiment is as follows Figure 7 The pattern in the lower left area of ​​(c) (referred to as pattern 3).

[0111] Test example

[0112] This test example tests the performance of the intermediates, flexible substrates and organic field effect transistors obtained in each step of the embodiment and the comparative example, specifically including:

[0113] (1) In the present invention, SU8 photoresist is a cross-linked epoxy resin, which has excellent dielectric and insulating properties and is highly solvent resistant. Polyamic acid is a highly polar polymer and a precursor polymer of polyimide. Polyamic acid has unique surface properties. Its surface contains periodically distributed polar group carboxyl groups, which can induce the orderly deposition of organic semiconductor molecules. Figure 2 As shown (scale: 200 μm), (a) is a microscope image of silicon dioxide spin-coated with polyamic acid after drop coating of an organic semiconductor solution; (b) is a microscope image of a semiconductor deposited on a silicon dioxide surface by drop coating. Specifically:

[0114] A silicon wafer with a 100nm thick silicon dioxide layer on the surface, with a size of 1.5*2cm, was soaked in piranha solution for 2 hours, then ultrasonicated in deionized water, isopropanol, and ethanol, and dried with nitrogen. The silicon wafer was treated with surface oxygen plasma to increase its surface wettability, with a power of 20W and a duration of 2min. A clean silicon dioxide surface was obtained (sample 1).

[0115] The surface of the silicon wafer treated with oxygen plasma was spin-coated with a polyamic acid N,N-dimethylacetamide (DMAc) solution at a concentration of 10 mg / mL, a spin-coating speed of 2000 rpm, and a duration of 120 seconds. After spin-coating the polyamic acid solution, the sample was placed in a drying cabinet at room temperature for 24 hours to allow the solvent to fully evaporate. A sample (sample 2) with a surface covered with a polyamic acid layer was obtained.

[0116] Prepare a toluene solution of C8-BTBT with a concentration of 0.5 mg / mL. Drop 40 μL of the toluene solution of C8-BTBT on the surface of two samples (samples 1 and 2) respectively, place them in a closed plastic petri dish to provide a stable vapor pressure, and allow the solvent to evaporate slowly at room temperature. Observe under an optical microscope to obtain Figures (a) and (b).

[0117] It can be seen that the organic semiconductor solution is drop-coated on the silicon dioxide surface with spin-coated polyamic acid to obtain crystal strips with uniform thickness, and the direction of the strips is parallel to the retreat direction of the three-phase line (the boundary line of the gas-liquid-solid three-phase). On the silicon dioxide surface not modified with polyamic acid, the organic semiconductor grows unevenly and has poor continuity, showing obvious "stick-slip" characteristics, that is, there are lateral strips perpendicular to the retreat direction of the three-phase line.

[0118] (2) To illustrate the effect of oxygen plasma etching on the dielectric layer, microscopic tests were performed on the flexible substrates with patterned organic semiconductor layers grown in Examples 1 and 3. The test results are as follows: Figure 3 As shown: wherein, (a) is an atomic force microscope image of Example 3 after polyamic acid is directly spin-coated on SU8 photoresist; (b) is an atomic force microscope image of Example 1 after polyamic acid is spin-coated on SU8 photoresist after oxygen plasma etching;

[0119] The SU8 photoresist is spin-coated to obtain a flat surface, and then fully cured by exposure and baking. A polyamic acid layer is deposited on the surface of the SU8 photoresist to enhance the surface wettability. Specifically, after the SU8 photoresist is exposed and cured by baking, its interior is fully cross-linked. Since the surface of the SU8 photoresist lacks polar groups after curing, its surface exhibits relatively hydrophobic properties. (The water contact angle is about 62.89°) When polyamic acid is directly spin-coated on its surface, it will agglomerate to form an island structure, as shown in Figure (a), and cannot form a uniform film. In organic field-effect transistors, the formation of a conductive channel is often participated by one or several layers of organic semiconductor molecules close to the dielectric layer, so the dielectric layer / organic semiconductor interface is crucial to its electrical properties. The thickness of the conductive channel is usually at the nanometer level, while the thickness of the island structure formed by the agglomeration of polyamic acid is at the micrometer level, which will have a negative impact on carrier transport. After the surface of the SU8 photoresist is etched by oxygen plasma, the surface hydrophilicity can be increased, and spin-coating polyamic acid can obtain a smooth surface, as shown in Figure (b).

[0120] (3) The surface wettability patterned flexible substrate prepared in Example 1 was observed using an atomic force microscope. The atomic force microscope morphology of the hydrophilic region and the hydrophobic region in the flexible substrate is as follows: Figure 4 As shown: Atomic force microscopy images of the hydrophilic region and the hydrophobic region show that it has low surface roughness, wherein the surface roughness of the hydrophilic region is 1.3 nm and the surface roughness of the hydrophobic region is 0.924 nm.

[0121] (4) For the flexible substrate with surface wettability pattern prepared in Example 1, the surface contact angles in the hydrophilic and hydrophobic regions were measured using deionized water and diiodomethane, respectively, and the surface free energies of the hydrophilic and hydrophobic regions were calculated using the two-liquid method (water and diiodomethane). The test results are shown in Figure 2. Figure 5 As shown in Table 1, according to the calculation results, the surface free energy of the hydrophilic region is 48.89 mN / m, and the surface free energy of the hydrophobic region is 25.78 mN / m, which is significantly different.

[0122] Table 1

[0123]

[0124] In the present invention, polyvinyl alcohol is removed after washing with deionized water. Water is a mild solvent and is not easy to damage the flexible substrate. The area below the polyvinyl alcohol pattern is not modified by the hydrophobic material layer, so it maintains a relatively hydrophilic property. The area not covered with polyvinyl alcohol is modified by the hydrophobic material layer and exhibits hydrophobic properties. In this way, the patterning of surface wettability is achieved on the surface of the polymer substrate. On the substrate after patterning, the organic semiconductor tends to nucleate and grow in the wetting area with higher surface energy, thus achieving the patterning of the organic semiconductor.

[0125] (5) To illustrate the difference in effect caused by different screen materials, the flexible substrate with a polyvinyl alcohol pattern obtained in step (II) of Example 1-2 was observed using an optical microscope. The results are as follows: Figure 6 Shown (scale bar is 500 μm): Figure 6 Figure (a) is a test result diagram of pattern 1 and pattern 2 on the flexible substrate in Example 2; Figure 6 Figure (b) is a test result diagram of pattern 1 and pattern 2 on the flexible substrate in Example 1;

[0126] In the present invention, a screen printing device is used, and a polyvinyl alcohol aqueous solution is deposited onto the surface of a flexible substrate through holes at specific positions on a screen plate under the action of a scraper, thereby obtaining a polyvinyl alcohol droplet pattern deposited on a specific position of the flexible substrate. The screen-printed pattern can be defined by a pre-designed and manufactured screen printing screen. Since the polyvinyl alcohol aqueous solution has a certain viscosity, the shape of the pattern can be maintained on the surface of the polymer substrate. Traditional screen printing uses a composite structure of a grid and a film to form a hollow pattern on the film by exposure, but the grid structure is retained. When screen printing a high-precision pattern, the grid structure will make the pattern edge corrugated, such as Figure 6 (a) It is not conducive to high-precision and high-fidelity printing of patterns. In Example 1, a metal mask is used as a screen template, which can produce a pattern with higher precision, smooth edges and high fidelity. Figure 6 (b). It should be noted that: Figure 6 The circular area in the middle of the polyvinyl alcohol solution layer is a bubble. Since the polyvinyl alcohol solution has a certain viscosity, bubbles may remain in the middle of the polyvinyl alcohol solution layer. The polyvinyl alcohol solution at the bottom of the bubble is in contact with the substrate, and the polyvinyl alcohol pattern plays a role in assisting the modification of the hydrophobic material layer. Water washing will be used to remove the polyvinyl alcohol later, so the presence of bubbles will not affect the hydrophilic area or the subsequent deposition of organic semiconductors.

[0127] (6) Crystal nucleation can be divided into homogeneous nucleation and heterogeneous nucleation. In the process of solution deposition of organic semiconductor material layer, the organic semiconductor solution often has the highest evaporation rate at the contact line between the solution and the substrate, so it first reaches supersaturation at the contact line and heterogeneous nucleation occurs. The contact line between the organic semiconductor solution and the substrate is called the three-phase line because it is at the junction of the solution phase, gas phase and substrate. After the organic semiconductor crystal is nucleated at the three-phase line, it grows as the three-phase line moves. In order to obtain more uniform and high-quality organic semiconductor crystals, the nucleation density and position must be controlled first, and then a stable moving three-phase line must be obtained. Usually, random and multiple nucleations of organic semiconductor solutions on the three-phase line often induce disordered crystal orientation and lead to the formation of grain boundaries. Grain boundaries have a significant negative impact on the transport of carriers. Disordered crystal orientation can cause large fluctuations in device performance. High-quality organic semiconductor crystals should avoid the formation of grain boundaries (especially large-angle grain boundaries) as much as possible. In addition, the assembly growth of organic semiconductor molecules is highly correlated with the movement of the triple line. To obtain more uniform semiconductors, it is necessary to find a way to induce the stable movement of the triple line.

[0128] The microscopic test results of the patterned organic semiconductor in Example 4 of the present invention are shown in FIG. Figure 7 As shown: (a)-(b) are optical microscope images, (c)-(d) are polarizing microscope images, scale: 500μm; the sample obtained in Example 1 is observed under an optical microscope, and the sample is rotated 45°. The crystals under the orthogonal polarizing field of view show a uniform change from light to dark, indicating that their orientation is consistent. (a)-(b) are images under an optical microscope, and (c)-(d) are images under the orthogonal polarizing field of view. Specifically:

[0129] Polarizing microscope can be used to check crystallization. When the polarizing microscope is in the orthogonal polarization position, no matter how the stage is rotated, the non-crystalline in the field of view is dark. Crystals have birefringence. When in the orthogonal polarization field of the polarizing microscope, the polarization angle changes with the rotation of the stage, and the brightness of the crystal will show periodic changes with the change of the polarization angle, that is, from light to dark or from dark to light every 45° rotation. Figure 7 (a)-(b) Optical microscope images with stage angles of 0° and 45°, respectively. Since the organic semiconductor crystals used are colorless under visible light, clear outlines cannot be observed in ordinary optical microscope images. The brighter rectangle in the image is the gate electrode located under the dielectric layer. Figure 7 (c)-(d) are orthogonal polarizing microscope images at the same position, where Figure 7(c) The inset at the lower left shows the designed pattern 3, and the direction indicated by the white arrow is the direction of the scraper movement. The orthogonal polarizing microscope image shows that when the stage angle is 0°, the crystals inside the pattern are continuous and the brightness is uniform, indicating that the crystals evenly cover the inside of the pattern. When the stage angle is rotated from 0° to 45°, the brightness of the crystals changes evenly from bright to dark, indicating that the crystal orientation inside the pattern is consistent.

[0130] For pattern 3, along the preset scraping direction (first direction), the size (width) in the direction perpendicular to the scraping direction (second direction) increases progressively. The first section of pattern 3 is a rectangle with a smaller width, the second section is a trapezoid with a gradually increasing width, and the third section is a square with a larger width. The first section has a smaller width in the second direction, inducing crystal nucleation. The width of the second section gradually increases, and the third section remains unchanged, allowing the crystal to grow along the first direction (i.e., the scraping direction) during the scraper coating process.

[0131] It can be seen that the present invention adopts a method of combining blade coating with wetting / non-wetting shape design. Through the design and optimization of the wetting / non-wetting pattern shape, the edge of the wetting area has a most convex point, that is, it has a curvature radius significantly lower than other places. In order to obtain a stably moving three-phase line, a blade coating method is adopted, and a servo motor is used to drive the blade to move at a stable speed in the horizontal direction to drive the organic semiconductor solution. When the stable state is reached, the organic semiconductor solution and the substrate contact line move stably behind the direction of the blade movement. When the contact line is in the non-wetting area, nucleation is not easy to occur due to the low surface energy of the substrate. The high point of the curvature radius of the wetting area pattern is located at the front end of the scraping direction, that is, the three-phase line first meets this point. When the three-phase line meets this point, since the surface energy of the wetting area is significantly higher than that of the non-wetting area, and the shape of the organic semiconductor solution is affected by the shape of the wetting area, the three-phase line bends here, and the solution at this point has the highest surface area / volume ratio and the highest evaporation flux, so nucleation occurs. In this way, the nucleation events are no longer random and multiple, but are anchored at the designed sites. After nucleation, as the three-phase line moves at an optimized speed, the organic semiconductor molecules are orderly assembled and grown inside the wetting area pattern, and the crystals are oriented along the direction of the scraper movement. When the three-phase line passes through the wetting area and meets the non-wetting area again, the organic semiconductor stops assembling due to the low binding force between the substrate and the organic semiconductor in the non-wetting area, similar to the sliding in the "stick-slip phenomenon", and the three-phase line moves stably on the surface of the non-wetting area again without nucleation.

[0132] The present invention designs the shape of the pre-patterned substrate, designs a point with a smaller curvature radius in the pattern, makes other positions have a larger curvature radius, and makes the nucleation point located at the minimum curvature radius, thereby controlling the number and position of nucleation. By designing the bottleneck shape and the tip small angle pattern, the nucleation position is concentrated during the scraping process, and the crystal growth direction is controlled by the scraping direction, thereby obtaining patterned organic semiconductor crystals with basically consistent orientation. Figure 7 As shown in the orthogonal polarized light microscope image, the sample is rotated 45°, and the crystal shows a consistent change from light to dark, indicating that the crystal orientation inside the crystal region is consistent. In the pattern above, the top of the "bottleneck" structure has the smallest radius of curvature, where the nucleation of the organic semiconductor is induced.

[0133] (7) The transfer characteristic curve and output characteristic curve of the organic field effect transistor (having an organic semiconductor material layer patterned using pattern 2) prepared in Example 1 were tested. The test results are as follows: Figure 8 The performance of the organic field effect transistor made by the organic semiconductor material layer patterned by pattern 1 in Example 1 is comparable to that of the organic field effect transistor made by the organic semiconductor material layer patterned by pattern 2.

[0134] Figure 8 (a) is the transfer characteristic curve of the organic field effect transistor. The average carrier mobility calculated based on the saturation region is 1.2 cm 2 V -1 s -1 , the highest value is 1.7cm 2 V -1 s -1 . It surpasses amorphous silicon (the carrier mobility of amorphous silicon is about 1cm 2 V -1 s -1 ) Device switching ratio up to 10 4 ~10 5 .

[0135] Figure 8 (b) is the output characteristic curve of the organic field effect transistor. In the output characteristic curve, the source-drain current increases linearly with the voltage at a lower source-drain voltage, and becomes stable after reaching saturation, showing a relatively ideal output characteristic.

[0136] In summary, the present invention provides a mild surface wettability patterning method that is compatible with flexible substrates. Screen printing of polyvinyl alcohol aqueous solution is used to assist patterning, thereby avoiding the introduction of toxic and corrosive organic solvents. Physical vapor deposition is used to deposit a hydrophobic material layer at a relatively low temperature (such as 70°C) to avoid the effects of high temperature on the performance of the flexible substrate. The above-mentioned surface wettability patterning method has the advantages of mild conditions, low cost and high processing efficiency, and provides a new solution for the patterning of organic semiconductors on flexible substrates, on this basis of which flexible electronic device arrays based on organic semiconductors can be prepared.

[0137] If there is no special explanation, the actual meaning of "about" in the present invention is that the error is allowed within the range of ±2%, for example, about 100 is actually 100±2%×100. The "normal temperature" and "room temperature" in the present invention, if there is no special explanation, are about 20-30°C. The "between" in the present invention includes the number itself, for example, "between 2-3" includes the endpoint values ​​2 and 3.

[0138] The embodiments of the present invention are described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above embodiments. Various changes can be made within the knowledge of ordinary technicians in the relevant technical field without departing from the purpose of the present invention. In addition, the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

Claims

1. A method for patterning wettability of a flexible material surface, characterized in that: The steps include: S1, coating a patterned polyvinyl alcohol aqueous solution on the surface of a hydrophilic flexible substrate to form a patterned area covered with the polyvinyl alcohol aqueous solution and a bare area not covered with the polyvinyl alcohol aqueous solution, to obtain an intermediate flexible substrate I; S2, depositing a hydrophobic material layer on the exposed area to form a hydrophobic area, thereby obtaining an intermediate flexible substrate II; S3, removing the polyvinyl alcohol aqueous solution on the surface of the flexible substrate by water washing, forming a hydrophilic area on the surface of the substrate, and obtaining a flexible substrate with a surface wettability pattern.

2. The method for patterning wettability of a flexible material surface according to claim 1, characterized in that: In step S1, the coating method includes screen printing; Preferably, the screen template used in the screen printing is a screen template containing a metal material; Preferably, the mass fraction of polyvinyl alcohol in the polyvinyl alcohol aqueous solution is 24-27%; Preferably, the flexible substrate comprises a polyamic acid layer, and a patterned polyvinyl alcohol aqueous solution is screen-printed on the surface of the polyamic acid layer.

3. The method for patterning wettability of a flexible material surface according to claim 1, characterized in that: In step S2, the deposition method includes vapor deposition; Preferably, the hydrophobic material layer comprises halogenated siloxane; Preferably, the halogenated siloxane comprises at least one of heptadecafluorodecyltrimethoxysilane, octadecyltrichlorosilane or tridecafluorooctyltriethoxysilane; Preferably, in step S2, the vapor deposition is physical vapor deposition; Preferably, the physical vapor deposition step comprises: vapor deposition of halogenated siloxane and intermediate flexible substrate I at a pressure of 0.05 to 0.3 MPa at 20 to 30° C. for 10 to 15 hours, and then vapor deposition at 65 to 75° C. for 0.5 to 3 hours; Preferably, step S2 comprises the following operations: placing the intermediate flexible substrate I and the open container containing halogenated siloxane in a vacuum oven, evacuating to a pressure of 0.05-0.3 MPa, placing at 20-30°C for 10-15 hours, and then heating to 65-75°C and maintaining for 0.5-3 hours.

4. A method for preparing a patterned organic semiconductor material, characterized in that: The method comprises the following steps: preparing a flexible substrate with a surface wettability pattern by the method for treating the surface wettability pattern of a flexible material according to any one of claims 1 to 3, and depositing organic semiconductor molecules in the hydrophilic area on the surface of the substrate to obtain a patterned organic semiconductor material; Preferably, in the preparation method, the step of depositing organic semiconductor molecules on the hydrophilic region of the substrate surface specifically comprises the following operations: S4, coating a solution containing an organic semiconductor on the surface of the flexible substrate with a patterned surface wettability, and selectively depositing the organic semiconductor on the hydrophilic region of the substrate to form a patterned organic semiconductor material on the surface of the substrate; Preferably, in step S4, the coating method includes scraping.

5. The method for preparing a patterned organic semiconductor material according to claim 4, characterized in that: The pattern includes a preset starting point for scraping the solution containing the organic semiconductor, and along the preset scraping direction, the size of the pattern in a direction perpendicular to the preset scraping direction tends to increase; Preferably, the solution containing an organic semiconductor comprises an organic semiconductor, an additive and a solvent; Preferably, the organic semiconductor includes 2,8-dioctylbenzothiophene; and / or the additive includes polystyrene; and / or the solvent includes toluene.

6. A patterned organic semiconductor material, characterized in that: It is prepared by the preparation method according to any one of claims 4 to 5.

7. Use of the method for patterning wettability of a flexible material surface according to any one of claims 1 to 3, the method for preparing a patterned organic semiconductor material according to any one of claims 4 to 5, or the patterned organic semiconductor material according to claim 6 in preparing a flexible electronic device.

8. An electronic device, characterized in that: It comprises a patterned organic semiconductor material, wherein the organic semiconductor material is prepared by the preparation method according to any one of claims 4 to 5 or the patterned organic semiconductor material according to claim 6.

9. The electronic device according to claim 8, characterized in that: The electronic device is an organic field effect transistor, which comprises a flexible substrate and a patterned organic semiconductor material layer which are stacked; the patterned organic semiconductor material layer comprises a patterned organic semiconductor material; Preferably, the flexible substrate comprises a substrate layer, a gate electrode layer, a dielectric layer and a polyamic acid layer which are stacked in sequence, and the patterned organic semiconductor material layer is disposed on a side of the polyamic acid layer away from the dielectric layer.

10. A method for preparing an electronic device, characterized in that: The steps include: preparing a flexible substrate having a substrate layer, a gate electrode layer, a dielectric layer and a polyamic acid layer stacked in sequence; A patterned organic semiconductor material layer is prepared on the surface of the flexible substrate by using the method for preparing a patterned organic semiconductor material according to any one of claims 4 to 5.

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