A two-step method for preparing large-area two-dimensional organic semiconductor crystalline thin films

Abstract

The present invention discloses a two-step method for preparing a large-area two-dimensional organic semiconductor crystalline film, comprising uniformly applying an organic semiconductor material on a lower substrate; constructing a rectangular growth cavity for crystallization of the organic semiconductor material on the lower substrate; at a first temperature, pre-crystallizing the organic semiconductor material in the rectangular growth cavity to generate a master; and at a second temperature, recrystallizing the master. The present invention pre-grows an organic crystalline film by a sublimation method, and can accurately control the number of layers of the crystalline film by temperature and time, and further heating and re-growth can obtain a large-area single-layer two-dimensional organic semiconductor crystalline film. Compared with other two-dimensional organic semiconductor crystalline film growth methods, it has a lower preparation cost and requires a lower operating level. More importantly, the prepared crystalline film has a large area, and this method may meet the growth of adjustable morphology organic semiconductors in different functional applications.

Description

Technical Field

[0001] The invention relates to the technical field of microelectronic device preparation, and in particular to a two-step method for preparing a large-area two-dimensional organic semiconductor crystalline film. Background Art

[0002] Compared with inorganic semiconductor materials, organic semiconductor materials can be prepared by solution method at low cost, and have obvious advantages in terms of good biocompatibility, flexibility and flexible structural tailorability. Based on this, organic semiconductor crystals can show good application potential in various multifunctional electronic devices, such as organic field effect transistors (OFETs), organic light emitting diodes (OLEDs), organic solar cells (OSCs), etc., which has led to a significant increase in the research on organic semiconductor materials. In recent years, two-dimensional organic semiconductor crystalline films have attracted the attention of a wide range of researchers as an emerging organic semiconductor material. Its inherent crystalline properties give it extremely high electrical properties. In addition, semiconductor films can show unique two-dimensional properties at low dimensional scales, such as high environmental sensitivity and peculiar interface properties. In addition, the two-dimensional scale can effectively shield the charge interaction between molecular layers, thus providing a good platform for studying intrinsic electrical and physical properties.

[0003] However, the existing methods for preparing two-dimensional organic semiconductor crystalline thin films are complicated and the quality of the prepared films is poor. Summary of the invention

[0004] Purpose of the invention: The present invention aims to provide a method for preparing large-area two-dimensional organic semiconductor crystalline thin films by a simple two-step method.

[0005] Technical solution: The two-step method of the present invention for preparing a large-area two-dimensional organic semiconductor crystalline thin film comprises the following steps:

[0006] (1) evenly applying an organic semiconductor material on a lower substrate;

[0007] (2) constructing a rectangular growth cavity on the lower substrate for crystallization of organic semiconductor materials;

[0008] (3) at a first temperature, pre-crystallizing the organic semiconductor material in the rectangular growth cavity to form a master;

[0009] (4) At the second temperature, the master is recrystallized to obtain the product.

[0010] Furthermore, in step (1), the organic semiconductor material is C8-BTBT, and the C8-BTBT raw material is evenly applied on the lower substrate to ensure that the raw material is not accumulated to prevent it from sticking to the upper substrate.

[0011] Furthermore, the lower substrate in step (1) and the lower substrate in step (2) are both subjected to substrate pretreatment, and the substrate pretreatment includes ultrasonic cleaning the substrates with acetone, isopropanol, and deionized water, respectively, and then drying them for standby use.

[0012] Furthermore, the rectangular growth cavity is constructed by placing two silver wires spaced a certain distance apart on the lower substrate, and covering an upper substrate on the silver wires.

[0013] Furthermore, the lower substrate and / or the upper substrate is a SiO2 / Si silicon wafer on which SiO2 is grown, and the thickness of SiO2 is any thickness, preferably 100 nanometers.

[0014] Furthermore, in step (3), the first temperature is 170-180°C, and the heating time is 5-6 minutes; preferably, the first temperature is 180°C, and the heating time is 5 minutes, wherein the constructed rectangular growth cavity is placed on a heating table for heating, and the temperature is controlled at 180°C. When heated and sublimated for 3 minutes, the grown second film layer accounts for about 1 / 3 of the first film layer; as the growth time increases, the area of ​​the second film layer gradually increases. When heated and sublimated for 5 minutes, the second film layer accounts for about 2 / 3 of the first film layer, but is discontinuous.

[0015] Furthermore, in step (4), the second temperature is 140-150°C, and the heating time is 5-6 minutes. Preferably, the second temperature is 150°C, and the heating time is 5 minutes. The motherboard is placed on a heating table and heated, and the temperature is controlled at 150°C for 5 minutes. The second layer of film is heated and grown. As the second layer of film disappears, the area of ​​the first layer of film gradually expands, the surface of the film becomes more uniform, and a better crystallization effect is presented.

[0016] Furthermore, in step (1), the organic semiconductor material is uniformly applied on the lower substrate in advance, and then a mask with a hollow pattern is placed on the lower substrate, and finally a patterned two-dimensional organic semiconductor crystalline film is generated. The present invention uses a mask to prepare a patterned master, and then heats and grows the master, so as to prepare a high-quality patterned two-dimensional organic semiconductor crystalline film. In the preparation of other two-dimensional organic semiconductor crystalline films, a solution method growth process is usually used, but the solution method process requires hydrophilic and hydrophobic treatment of the growth interface to achieve localized growth, and there are certain problems in the residual solvent and the purity of the growth system. The two-step preparation technology of the present invention has high purity in preparing patterned films.

[0017] The present invention pre-grows an organic crystalline film by a sublimation method, and can precisely control the number of layers of the crystalline film by temperature and time. Further heating and re-growth can obtain a large-area single-layer two-dimensional organic semiconductor crystalline film. Compared with other two-dimensional organic semiconductor crystalline film growth methods, it has a lower preparation cost and requires a lower level of operation. More importantly, the prepared crystalline film has a large area, and the film area depends on the raw material coating area of ​​the lower substrate. This method may meet the needs of adjustable morphology organic semiconductor growth in different functional applications in the future; on the other hand, it also shows obvious advantages in the growth of arrayed crystalline films. This controllable growth process provides conditions for the later development of optoelectronic device integration based on two-dimensional organic semiconductor crystalline films.

[0018] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The film has good quality and large area, and also shows obvious advantages in the growth of arrayed crystalline films. This controllable growth process provides conditions for the later development of optoelectronic device integration based on two-dimensional organic semiconductor crystalline films; (2) The preparation steps are simple, and the number of layers of the crystalline film can be precisely controlled by temperature and time. The operation process is not complicated and the conditions are highly controllable. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a rectangular cavity device diagram of the present invention;

[0020] Figure 2 This is the growth condition of the motherboard after sublimation growth at 180°C for 3 minutes in Example 1;

[0021] Figure 3 This is the growth condition of the motherboard after sublimation growth at 180°C for 5 minutes in Example 1;

[0022] Figure 4 The film grown at 150°C for 5 minutes in Example 1, left: before heating; right: after heating;

[0023] Figure 5 It is a large-area single-layer film prepared in Example 1;

[0024] Figure 6 AFM surface morphology and corresponding film thickness in Example 1 (inset);

[0025] Figure 7 This is the growth condition of the motherboard after sublimation growth at 170°C for 6 minutes in Example 2;

[0026] Figure 8 This is the case of the film grown at 140°C for 6 minutes in Example 2;

[0027] Fig. 9 is the mask in Example 3 (unit: mm);

[0028] Fig.10 The patterned master prepared in Example 3;

[0029] Fig.11 This is the patterned film grown in Example 3. DETAILED DESCRIPTION

[0030] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0031] Example 1

[0032] like Figure 1 As shown, the rectangular cavity device of the present invention includes a lower substrate a, silver wires c placed on the left and right sides of the lower substrate a, and an upper substrate d placed on the silver wires, wherein the lower substrate a and the upper substrate d are placed opposite to each other, the silver wires c separate the lower substrate a and the upper substrate d to form a rectangular cavity f, and the C8-BTBT raw material b is coated on the lower substrate a and crystallized in the rectangular cavity f.

[0033] The two-step method for preparing a large-area two-dimensional organic semiconductor crystalline thin film of the present invention comprises the following steps:

[0034] (1) Raw materials for coating the lower substrate: All substrates used must be ultrasonically cleaned with acetone, isopropanol, and deionized water for 15 minutes respectively, and then dried with a nitrogen gun before use. The upper and lower substrates are both SiO2 / Si silicon wafers grown with 100 nanometers of SiO2. Take about 0.05 mg of C8-BTBT raw material and evenly apply it on the lower substrate, leaving silver wires on the edges on both sides. No bulk raw materials should be present, otherwise they will easily be adsorbed to the upper substrate when the substrate is covered, resulting in growth failure.

[0035] (2) Constructing a rectangular growth cavity: placing 150 μm silver wires on both sides of the lower substrate coated with the raw material. After the silver wires are placed, the upper substrate is covered with the silver wires, and the silver wires are placed on the edges of both sides of the lower substrate;

[0036] (3) Preparing a pre-crystallization master: The master is prepared by a heating sublimation method. The constructed rectangular growth cavity is placed on a heating table and heated at 180°C for 5 minutes.

[0037] By observing the film growth, it is found that the number of film layers is closely related to the growth time: Figure 2 As shown in the figure, after 3 minutes of sublimation, the film has both the first layer and the second layer, and the second layer occupies about 1 / 3 of the area of ​​the first layer. Figure 3 As shown, when the sublimation time is 5 minutes, the second film layer occupies about 2 / 3 of the area of ​​the first film layer. As the growth time increases, the area of ​​the second film layer expands.

[0038] (4) Recrystallization growth of large-area two-dimensional organic semiconductor crystalline thin films: using a heating growth method, the obtained pre-crystallized master was placed on a heating table for heating growth, the temperature was controlled at 150°C, and the heating time was 5 minutes;

[0039] like Figure 4 As shown, after heating and growing for 5 minutes, the second film layer completely fades away, and the first film layer expands to the maximum area;

[0040] like Figure 5 As shown, the thin films on the whole silicon wafer (5 mm × 5 mm) are connected from left to right by splicing the pictures. It can be seen from the figure that the two-step method for preparing a large-area two-dimensional organic semiconductor crystalline thin film can prepare a 5 mm × 5 mm thin film covering the entire silicon wafer. The size of the prepared thin film depends on the coating area of ​​the lower substrate raw material;

[0041] like Figure 6 As shown, atomic force microscopy (AFM) was used to characterize the surface morphology of the film. The roughness Ra of the single-layer film was 0.84 nanometers, indicating that the prepared film had molecular-level flatness. The step height of the single-layer film was 2.9 nm, which was consistent with the height of the C8-BTBT molecules standing on the silica surface.

[0042] Example 2

[0043] The two-step method for preparing a large-area two-dimensional organic semiconductor crystalline thin film of the present invention comprises the following steps:

[0044] (1) Raw materials for coating the lower substrate: All substrates used must be ultrasonically cleaned with acetone, isopropanol, and deionized water for 20 minutes, and then dried with a nitrogen gun before use. The upper and lower substrates are both SiO2 / Si silicon wafers grown with 200 nanometers of SiO2. Take about 0.05 mg of C8-BTBT raw material and evenly apply it on the lower substrate, leaving silver wires on the edges on both sides. No blocky raw materials should exist, otherwise they will easily be adsorbed to the upper substrate when the substrate is covered, resulting in growth failure.

[0045] (2) Constructing a rectangular growth cavity: placing 150 μm silver wires on both sides of the lower substrate coated with the raw material. After the silver wires are placed, the upper substrate is covered with the silver wires, and the silver wires are placed on the edges of both sides of the lower substrate;

[0046] (3) Preparing a pre-crystallization master: The master was prepared by heating sublimation. The constructed rectangular growth cavity was placed on a heating table and heated at 170°C for 6 minutes.

[0047] like Figure 7 As shown, after 6 minutes of sublimation, the second film layer occupies about 2 / 3 of the area of ​​the first film layer.

[0048] (4) Recrystallization growth of large-area two-dimensional organic semiconductor crystalline thin films: The obtained pre-crystallized master was placed on a heating table for heating growth, the temperature was controlled at 140°C, and the heating time was 6 minutes;

[0049] like Figure 8 As shown, after 6 minutes of heating growth, the second film layer completely faded away and the first film layer expanded to its maximum area.

[0050] Example 3

[0051] The steps of growing a patterned two-dimensional organic semiconductor crystalline film using a mask are as follows:

[0052] (1) Construct a growth rectangular cavity, evenly apply a layer of C8-BTBT raw material on the lower substrate, and then place a 10 mm × 10 mm mask under the upper substrate so that the mask is located on the C8-BTBT raw material layer. The mask is as follows: Fig. 9 ;

[0053] (2) Place the rectangular growth cavity on a heating table and heat it at 250°C for 2 minutes. After the growth is completed, a patterned film grows out with a small amount of double layers, such as Fig.10 As shown, this will serve as a patterned master for the next step of recrystallization growth.

[0054] (3) Fig.11 As shown, the patterned pre-crystallized master was heated and grown at 120°C for 2 minutes, and the patterned master was heated and grown. As a small amount of double-layer film disappeared, the quality of the single-layer film improved.

Claims

1. A two-step method for preparing a large-area two-dimensional organic semiconductor crystalline thin film, characterized in that: The following steps are involved: (1) Uniformly applying the organic semiconductor material on the lower substrate; (2) constructing a rectangular growth cavity on the lower substrate for crystallization of organic semiconductor materials; (3) At a first temperature, the organic semiconductor material in the rectangular growth cavity is sublimated and pre-crystallized to form a master, the first temperature is 170-180°C, and the heating time is 5-6 minutes; wherein the rectangular growth cavity is constructed by placing two silver wires spaced a certain distance apart on a lower substrate, and covering an upper substrate on the silver wires; (4) At the second temperature, the master is recrystallized. The second temperature is 140-150 °C and the heating time is 5-6 minutes.

2. The method for preparing a large-area two-dimensional organic semiconductor crystalline thin film by two-step method according to claim 1, characterized in that: In step (1), the organic semiconductor material is C8-BTBT.

3. The two-step method for preparing a large-area two-dimensional organic semiconductor crystalline thin film according to claim 1, characterized in that: The lower substrate in step (1) and the lower substrate in step (2) are both subjected to substrate pretreatment, wherein the substrate pretreatment includes ultrasonic cleaning the substrates with acetone, isopropanol, and deionized water, respectively, and then drying them for standby use.

4. The two-step method for preparing a large-area two-dimensional organic semiconductor crystalline thin film according to claim 1, characterized in that: The lower substrate and / or the upper substrate is a SiO2 / Si silicon wafer on which SiO2 is grown.

5. The two-step method for preparing a large-area two-dimensional organic semiconductor crystalline thin film according to claim 1, characterized in that: In step (1), an organic semiconductor material is uniformly applied on the lower substrate in advance, and then a mask with a hollow pattern is placed on the lower substrate, thereby finally obtaining a patterned two-dimensional organic semiconductor crystalline thin film.

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