One-dimensional ultrathin organic monocrystal array film, preparation method and application thereof

Abstract

This invention belongs to the field of organic semiconductor material preparation technology, and discloses a one-dimensional ultrathin organic single-crystal array thin film, its preparation method, and its application. The preparation method of the one-dimensional ultrathin organic single-crystal array thin film includes the following steps: patterning a substrate with octadecyltrichlorosilane or perfluorosilane, then adding a first organic semiconductor solution and performing a first coating with a doctor blade, followed by adding a second organic semiconductor solution and performing a second coating with a doctor blade to obtain the one-dimensional ultrathin organic single-crystal array thin film; the thickness of the prepared one-dimensional ultrathin organic single-crystal array thin film is 1nm-15nm. This invention achieves stable formation of one-dimensional organic single-crystal arrays and precise control of ultrathin film and high orientation, and the process is suitable for large-scale industrial production, providing reliable technical support for the research and development and application of high-performance organic electronic devices.

Description

Technical Field

[0001] This invention belongs to the field of organic semiconductor material preparation technology, and specifically relates to a one-dimensional ultrathin organic single crystal array thin film, its preparation method and application. Background Technology

[0002] Organic field-effect transistors (OFETs), as the most basic and core active components in organic electronic devices, have shown broad application prospects in many fields such as flexible displays, signal amplification, RFID tags, and sensors. In common top-contact OFET configurations, device performance is often significantly limited by contact resistance. In recent years, one-dimensional ultrathin organic semiconductor crystal arrays have attracted widespread attention due to their unique structural advantages: this structure not only integrates the intrinsic properties of one-dimensional organic single crystals, such as long-range molecular order, absence of grain boundary defects, and π–π stacking direction aligned with the long axis of the crystal, but also possesses excellent integrability, flexibility, and high transparency. More importantly, its ultrathin shape effectively shortens the charge transport path in the semiconductor layer, thereby significantly reducing contact resistance, providing a highly promising technical path for developing high-performance, integrable organic electronic devices. Currently, the fabrication technology of one-dimensional organic single crystal array thin films is still immature: physical vapor deposition (PVD) is costly and difficult to scale up; solution methods have poor crystal quality control. Developing new fabrication processes is an inevitable way to overcome these bottlenecks. Summary of the Invention

[0003] The present invention aims to improve at least one technical problem in the prior art.

[0004] The first aspect of this invention provides a method for preparing a one-dimensional ultrathin organic single-crystal array thin film, comprising the following steps:

[0005] The substrate is patterned using octadecyltrichlorosilane or perfluorosilane, then a first organic semiconductor solution is dropped in and coated for the first time using a doctor blade. Subsequently, a second organic semiconductor solution is dropped in and coated for the second time using a doctor blade to obtain the one-dimensional ultrathin organic single crystal array film.

[0006] The thickness of the one-dimensional ultrathin organic single crystal array film is 1nm-15nm;

[0007] The solute of the first organic semiconductor solution is an organic semiconductor, and the solvent is a volatile organic solvent; the solute and solvent of the second organic semiconductor solution are the same as those of the first organic semiconductor solution.

[0008] Wherein, the concentration of the first organic semiconductor solution is 0.5 mg / mL-5 mg / mL, and the concentration of the second organic semiconductor solution is 0.1 mg / mL-1 mg / mL;

[0009] The blade moving speed for the first coating is 30μm / s-50μm / s, and the blade moving speed for the second coating is 10μm / s-20μm / s.

[0010] In the method for preparing a one-dimensional ultrathin organic single-crystal array thin film provided in this application, the substrate is first patterned using octadecyltrichlorosilane or perfluorosilane. Patterning optimizes the interfacial properties of the substrate surface, creating conditions for the selective crystallization and ordered arrangement of organic semiconductor molecules, thus improving the orientation consistency of the crystals. During the first coating, a first organic semiconductor solution is uniformly spread on the patterned substrate surface. The shear force generated by the movement of the scraper induces the initial crystallization of the organic semiconductor molecules, forming a regular basic crystal structure. In the second coating, a second organic semiconductor solution with the same solute and solvent as the first solution is used. After dissolving some crystals, an ultrathin crystal layer is further grown on the undissolved small crystals using the principle of epitaxial growth, ultimately obtaining a one-dimensional ultrathin organic single-crystal array thin film with precisely controlled thickness. The concentration gradient design of the first and second organic semiconductor solutions in this application ensures the forming quality of the basic crystals while precisely controlling the ultrathin characteristics of the final thin film through a low-concentration second organic semiconductor solution, solving the problems of excessive thickness and disordered orientation in existing solution-based preparation methods. Furthermore, the scraping process in this application employs a relatively slow scraper movement speed, and the scraper movement speed in the second scraping is even slower than that in the first scraping. Combined with a second organic semiconductor solution that has the same solute and solvent as the first solution but at a lower concentration, the slower speed allows the solution sufficient time to dissolve a sufficient amount of crystal, laying a good foundation for subsequent epitaxial growth. At the same time, the slow scraping process also reduces disturbance to crystal growth, helps organic semiconductor molecules to stack in an orderly manner, promotes slow and stable crystal growth, and ultimately forms an ultrathin crystal layer on the base crystal through epitaxial action.

[0011] Preferably, the organic semiconductor is TIPS-pentacene, C8-BTBT, C10-BTBT, DTT-8, or C6-DPA.

[0012] Preferably, the organic volatile solvent is toluene, chlorobenzene, or o-dichlorobenzene.

[0013] Preferably, a fluorocarbon surfactant is added to the second organic semiconductor solution, and the concentration of the fluorocarbon surfactant is 0.001 mg / mL to 0.002 mg / mL.

[0014] This application further adds a specific concentration of fluorocarbon surfactant to the second organic semiconductor solution, which can synergistically interact with the shear-induced effect of the second coating process and the rapid evaporation of the solvent, playing a key regulatory role in crystal growth. During the second coating process, the fluorocarbon surfactant spreads along with the liquid film and redistributes at the gas-liquid interface under the action of solvent evaporation, thereby forming a surface tension gradient that varies along the liquid surface. This gradient gives the central region of the liquid film a relatively higher surface tension, thereby stimulating strong inward Marangoni convection. This flow driven by the high-tension region in the center can effectively counteract the outward capillary flow caused by evaporation, significantly suppress the coffee ring effect, and prevent solute from accumulating at the edge of the liquid film. The final effect is that the solute is more uniformly transported to the central region of the liquid film during the second coating process, which helps to form a dense, continuous, and controllable thickness organic molecular layer. At the same time, this regulatory mechanism can further optimize the crystallization kinetics, promote the uniform nucleation and anisotropic ordered growth of ultrathin single crystals, and provide important kinetic advantages for the large-area controllable preparation of high-quality one-dimensional ultrathin organic single crystal array films using the coating technology.

[0015] Preferably, the fluorocarbon surfactant is sodium perfluorooctanoate.

[0016] As a highly efficient fluorocarbon surfactant, sodium perfluorooctanoate's perfluorocarbon chain can significantly reduce the surface tension at the gas-liquid interface, forming a surface tension gradient at the gas-liquid interface, thereby stimulating inward Marangoni convection to suppress the coffee ring effect.

[0017] Preferably, the dropping volume of the first organic semiconductor solution is 80 μL-100 μL, and the dropping volume of the second organic semiconductor solution is 120 μL-200 μL.

[0018] The difference in drop volume between the first and second organic semiconductor solutions in this application is based on the different functional designs of the two coating processes. The volume required for the first coating is sufficient to form a base crystal structure of sufficient thickness, providing a stable crystal substrate for subsequent epitaxial growth. The larger volume of the second coating ensures that the solution fully covers the base crystal on the substrate surface. By moderately dissolving some of the base crystal, it provides a good growth environment for the growth of new crystals, while avoiding insufficient growth or uneven thickness due to insufficient volume, and also preventing excessive dissolution of the base crystal due to excessive volume, thus ensuring the final formation of a continuous and uniform ultrathin array film.

[0019] Preferably, the temperature of the substrate is 30°C-60°C during the first coating process and the temperature of the substrate is 30°C-60°C during the second coating process.

[0020] The specific substrate temperature range in this application allows the solvent evaporation rate to match the coating speed and crystal growth rate. This avoids excessively high temperatures leading to premature solvent evaporation and crystallization defects, while also preventing excessively low temperatures that would hinder the orderly arrangement of crystals and film formation efficiency. The stable temperature environment provides favorable conditions for the directional migration and orderly stacking of organic semiconductor molecules, helping to improve crystal orientation and overall film quality, and ensuring consistent performance across different batches of one-dimensional ultrathin organic single-crystal array films.

[0021] Preferably, the distance between the scraper and the substrate is 0.05mm-0.15mm.

[0022] A second aspect of the present invention provides a one-dimensional ultrathin organic single crystal array film, which is prepared according to the above-described preparation method.

[0023] The third aspect of the present invention provides the application of one-dimensional ultrathin organic single crystal array thin films, which are used to fabricate field-effect transistor devices.

[0024] The field-effect transistor device, from bottom to top, includes a substrate, the one-dimensional ultrathin organic single crystal array film, and electrodes.

[0025] The electrode is either an Au electrode or an Ag electrode.

[0026] The beneficial effects of this invention are: This invention achieves stable formation of one-dimensional organic single crystal arrays and precise control of ultra-thin thin films and high orientation, and the process is adapted to large-scale industrial production, providing reliable technical support for the research and development and application of high-performance organic electronic devices. Attached Figure Description

[0027] Figure 1 An optical photograph of the one-dimensional ultrathin organic single-crystal array thin film prepared in Example 1;

[0028] Figure 2 This is a transmission electron microscope image of the one-dimensional ultrathin organic single crystal array film prepared in Example 1;

[0029] Figure 3 for Figure 2 Selected area electron diffraction patterns at points a and b in the middle;

[0030] Figure 4 An atomic force microscope image of the one-dimensional ultrathin organic single crystal array film prepared in Example 1;

[0031] Figure 5 This is a structural diagram of a field-effect transistor device;

[0032] Figure 6The graph shows the transfer characteristics of device 1 at a drain voltage of -60V.

[0033] Figure 7 The output characteristic curves of device 1 under different gate voltages are shown.

[0034] Figure 8 The graph shows the transfer characteristics of device 2 at a drain voltage of -60V.

[0035] Figure 9 The output characteristic curves of device 2 under different gate voltages are shown. Detailed Implementation

[0036] The present invention will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the description of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0037] Example 1

[0038] A method for preparing a one-dimensional ultrathin organic single-crystal array thin film includes the following steps:

[0039] Patterning of SiO2 / Si substrates is achieved by using octadecyltrichlorosilane. Specifically, octadecyltrichlorosilane is dropped onto the surface of an elastic stamp (made of polydimethylsiloxane) to form a very thin liquid film. After drying, the octadecyltrichlorosilane is adsorbed onto the surface of the elastic stamp. At this point, the elastic stamp is gently brought into contact with a clean SiO2 / Si substrate. After the elastic stamp is removed, the octadecyltrichlorosilane molecules are transferred from the raised areas of the elastic stamp to the surface of the SiO2 / Si substrate, forming patterned hydrophilic and hydrophobic regions.

[0040] Then, 80 μL of the first organic semiconductor solution (solute DTT-8, solvent chlorobenzene, DTT-8 concentration 2 mg / mL) was dropped onto the patterned SiO2 / Si substrate surface. The first coating was performed using a doctor blade with a distance of 0.1 mm between the doctor blade and the SiO2 / Si substrate, a doctor blade moving speed of 40 μm / s, and a SiO2 / Si substrate temperature of 40 °C. At this time, due to the stronger adhesion between the organic molecules and octadecyltrichlorosilane, during the first coating process, DTT-8 molecules preferentially crystallize selectively in the octadecyltrichlorosilane patterned area, forming a relatively thick (thickness often >100 nm) patterned crystal structure.

[0041] Subsequently, 150 μL of a second organic semiconductor solution (solute: DTT-8, solvent: chlorobenzene, DTT-8 concentration: 0.3 mg / mL) was dropped onto the surface of the SiO2 / Si substrate after the first coating. Sodium perfluorooctanoate (PFOA) was also added, with a concentration of 0.001 mg / mL. A second coating was then performed using a doctor blade, with the distance between the doctor blade and the SiO2 / Si substrate being 0.1 mm, the doctor blade moving at a speed of 15 μm / s, and the temperature of the SiO2 / Si substrate being 40 °C. The organic semiconductor solution was introduced again into the crystals already prepared in the first coating, which could dissolve part of the crystals. At the same time, due to epitaxy, the growth of ultrathin organic single crystals was achieved, resulting in a one-dimensional ultrathin organic single crystal array film.

[0042] Optical photographs of the one-dimensional ultrathin organic single-crystal array thin films prepared in Example 1 are shown below. Figure 1 As shown, the one-dimensional ultrathin organic single crystal array film has a regular shape and large-area uniformity.

[0043] The transmission electron microscope image of the one-dimensional ultrathin organic single crystal array film prepared in Example 1 is shown below. Figure 2 As shown, Figure 2 The selected area electron diffraction pattern at point a is shown below. Figure 3 As shown in Figure a. Figure 2 The selected area electron diffraction pattern at point b is as follows: Figure 3 As shown in Figure b, by Figure 2 It can be seen that the regular morphology, flat surface, and morphological uniformity of this one-dimensional ultrathin organic single crystal array film are due to... Figure 3 Consistent electron diffraction patterns in different regions demonstrate that this one-dimensional ultrathin organic single-crystal array film possesses single-crystal properties.

[0044] An atomic force microscope image of the one-dimensional ultrathin organic single-crystal array film prepared in Example 1 is shown below. Figure 4 As shown, the single crystal thickness of this one-dimensional ultrathin organic single crystal array film is 10.3 nm, corresponding to the thickness of 3 molecular layers, proving its ultrathin property.

[0045] Comparative Example 1

[0046] A method for preparing a one-dimensional organic single-crystal array thin film, which differs from Example 1 in that the SiO2 / Si substrate is not patterned. Otherwise, it is the same as Example 1.

[0047] Comparative Example 2

[0048] A method for preparing a one-dimensional organic single-crystal array thin film, which differs from Example 1 in that: no fluorocarbon surfactant is added to the second organic semiconductor solution. Otherwise, it is the same as Example 1.

[0049] Comparative Example 3

[0050] A method for preparing a one-dimensional organic single-crystal array thin film differs from Example 1 in that 80 μL of a second organic semiconductor solution is added dropwise. Everything else is the same as in Example 1.

[0051] Comparative Example 4

[0052] A method for preparing a one-dimensional organic single-crystal array thin film, which differs from Example 1 in that the concentration of DTT-8 in the second organic semiconductor solution is 2 mg / mL. Everything else is the same as in Example 1.

[0053] Comparative Example 5

[0054] A method for preparing a one-dimensional organic single-crystal array thin film, which differs from Example 1 in that the blade moving speed is 40 μm / s during the second coating. Everything else is the same as in Example 1.

[0055] Array thickness test

[0056] The array thickness of the films prepared in Example 1 and Comparative Examples 1-5 was measured using atomic force microscopy, and the test results are shown in Table 1.

[0057] Table 1 Array thickness results

[0058]

[0059] Based on the data in Table 1, it can be seen that Comparative Example 1 lacks octadecyltrichlorosilane patterning treatment, and the substrate surface cannot form a selective crystallization interface guide, making it difficult for organic semiconductor molecules to stack in an orderly and oriented manner, thus failing to form a one-dimensional array structure; Comparative Example 2 does not add fluorocarbon surfactants, which cannot effectively suppress the coffee ring effect during the coating process, solutes tend to accumulate at the edge of the liquid film, and the molecular distribution cannot be optimized by Marangoni convection, resulting in a thick and uneven film thickness; In Comparative Example 3, the volume of the second organic semiconductor solution is insufficient, making it difficult to fully cover the base crystal and dissolve some of the crystals, resulting in a lack of a uniform growth environment for subsequent epitaxial growth, ultimately leading to a thick film thickness; In Comparative Example 4, the concentration of the second organic semiconductor solution is too high, and the excessive solute content causes excessive molecular stacking during crystallization, exceeding the concentration range for ultrathin growth, resulting in a thick film thickness; In Comparative Example 5, the second coating speed is too fast, which neither provides sufficient time for the second solution to dissolve the base crystal nor facilitates the slow and orderly stacking of organic semiconductor molecules, resulting in a thick film thickness.

[0060] Field-effect transistor device applications

[0061] The one-dimensional ultrathin organic single-crystal array thin film prepared in Example 1 was used to fabricate a field-effect transistor device (denoted as Device 1). This field-effect transistor device includes a SiO2 / Si substrate, a one-dimensional ultrathin organic single-crystal array thin film formed on the SiO2 / Si substrate, and two Au electrodes. Its structure is as follows: Figure 5 As shown ( Figure 5 1-SiO2 / Si substrate; 11-Si in SiO2 / Si substrate; 12-SiO2 in SiO2 / Si substrate; 2-One-dimensional ultrathin organic single crystal array film; 3-Au electrode).

[0062] The transfer characteristic curve of this field-effect transistor device at a drain voltage of -60V is shown in the figure below. Figure 6 As shown in the figure, its mobility can be calculated to be 6.5 cm. 2 ·V -1 ·s -1 .

[0063] The output characteristic curves of this field-effect transistor device at different gate voltages (-60V to 0V) are shown below. Figure 7 As shown in the figure, it can be seen that in the lower source-drain voltage range, the current changes linearly with the voltage, proving that it has a small contact resistance.

[0064] The one-dimensional organic array thin film prepared in Comparative Example 4 was used to fabricate a field-effect transistor device (denoted as Device 2), with the same structure as Device 1. The transfer characteristic curve of this field-effect transistor device at a drain voltage of -60V is shown in the figure below. Figure 8 As shown, calculations show that its mobility is only 2.8 cm. 2 ·V -1 ·s -1 The performance of the device is significantly lower than that of the device 1.

[0065] The output characteristic curves of this field-effect transistor device at different gate voltages (-60V to 0V) are shown below. Figure 9 As shown in the figure, in the lower source-drain voltage range, there is a poor linear relationship between current and voltage, indicating that device 2 has a large contact resistance. This phenomenon can be attributed to the increased thickness of the organic thin film: the thicker film structure prolongs the vertical path of charge carriers from the electrode to the channel region, thereby increasing the overall contact resistance and affecting the current output capability of device 2.

[0066] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and additions without departing from the method of the present invention, and these improvements and additions should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a one-dimensional ultrathin organic single crystal array film, characterized in that, The method comprises the following steps: The substrate is subjected to a patterning treatment by octadecyltrichlorosilane, then a first organic semiconductor solution is added dropwise, a first blade coating is performed, then a second organic semiconductor solution is added dropwise, a second blade coating is performed, and the one-dimensional ultrathin organic monocrystal array film is obtained. The thickness of the one-dimensional ultrathin organic monocrystal array film is 1-15 nm. The solute of the first organic semiconductor solution is an organic semiconductor, the organic semiconductor is DTT-8, and the solvent is an organic volatile solvent; the solute and the solvent of the second organic semiconductor solution are the same as those of the first organic semiconductor solution; a fluorocarbon surfactant is added to the second organic semiconductor solution, and the concentration of the fluorocarbon surfactant is 0.001-0.002 mg / mL. The concentration of the first organic semiconductor solution is 0.5-5 mg / mL, and the concentration of the second organic semiconductor solution is 0.1-1 mg / mL. The moving speed of the blade in the first blade coating is 30-50 μm / s, and the moving speed of the blade in the second blade coating is 10-20 μm / s. The patterning treatment comprises the following steps: dropping the octadecyltrichlorosilane on the surface of an elastic stamp, and adsorbing the octadecyltrichlorosilane on the surface of the elastic stamp by drying; The elastic stamp is contacted with the substrate, the octadecyltrichlorosilane is transferred from the elastic stamp to the surface of the substrate, and the patterned hydrophilic and hydrophobic regions are formed.

2. The method for preparing a one-dimensional ultrathin organic single-crystal array thin film according to claim 1, characterized in that, The organic volatile solvent is toluene, chlorobenzene or o-dichlorobenzene.

3. The method for preparing a one-dimensional ultrathin organic single-crystal array thin film according to claim 1, characterized in that, The dropwise volume of the first organic semiconductor solution is 80-100 μL, and the dropwise volume of the second organic semiconductor solution is 120-200 μL.

4. The method for preparing a one-dimensional ultrathin organic single-crystal array thin film according to claim 1, characterized in that, When the first blade coating is performed, the temperature of the substrate is 30-60 ℃; when the second blade coating is performed, the temperature of the substrate is 30-60 ℃.

5. The method for preparing a one-dimensional ultrathin organic single-crystal array thin film according to claim 1, characterized in that, The distance between the blade and the substrate is 0.05-0.15 mm.

6. A one-dimensional ultrathin organic single crystal array film, characterized in that, The one-dimensional ultrathin organic monocrystal array film The method is prepared according to any one of claims 1-5.

7. Use of a one-dimensional ultrathin organic single crystal array film according to claim 6, wherein the one-dimensional ultrathin organic single crystal array film is used as a material for a flexible display device. The one-dimensional ultrathin organic monocrystal array film is used for preparing a field effect transistor device.

8. Use of a one-dimensional array of ultrathin organic single crystals according to claim 7, characterized in that, The field effect transistor device comprises, from bottom to top, a substrate, the one-dimensional ultrathin organic monocrystal array film and an electrode; the electrode is an Au electrode or an Ag electrode.

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