A method for growing organic semiconductor monolayers on amorphous substrates

Abstract

This invention relates to the field of organic materials technology, specifically to a method for growing organic semiconductor monolayer films on amorphous substrates. The specific technical solution involves using organic semiconductor molecules with alkyl side chains as raw materials, employing a physical vapor transport method under a hydrogen atmosphere and low pressure, ensuring close contact between the amorphous substrate and the raw materials, and epitaxially growing an organic semiconductor monolayer film. This invention achieves wafer-level, continuous, and thickness-controllable high-quality organic monolayer films through controlling the relative position between the raw materials and the amorphous substrate, introducing an auxiliary hydrogen atmosphere, and optimizing the crystal growth mechanism under low pressure.

Description

Technical Field

[0001] This invention relates to the field of organic materials technology, and more specifically to a method for growing organic semiconductor monolayer films on amorphous substrates. Background Technology

[0002] Organic single crystals, as highly ordered organic semiconductor materials without obvious grain boundaries, have shown broad application prospects in optoelectronic devices, flexible electronics, and biosensors due to their excellent electrical and optical properties. Their regular molecular arrangement and extremely low defect density significantly improve carrier mobility and reduce scattering and energy loss during charge transport, thus exhibiting significant advantages over polycrystalline or amorphous materials in terms of device operating efficiency, response speed, and stability. Furthermore, organic single crystals typically possess good physicochemical stability, maintaining performance even under complex environments, providing a material basis for the development of high-reliability devices. These characteristics make them not only an important platform for studying intrinsic charge transport mechanisms but also lay a solid foundation for developing next-generation high-performance optoelectronic devices.

[0003] However, traditional bulk organic single crystals are often thick, lack flexibility, and have poor processability, which limits their application in cutting-edge technology fields such as flexible electronics, ultrathin optoelectronic devices, and integrated circuits. Therefore, the preparation of organic monolayer or ultrathin single crystal films with controllable thickness, good uniformity, and sufficiently large size has become a key step in promoting the industrial application of organic semiconductor materials from laboratory research.

[0004] Currently, the controllable fabrication of large-area, high-quality organic monolayer films still faces many technical challenges, specifically: (1) Substrate limitations: Traditional epitaxial growth methods rely heavily on the lattice-matching interface provided by single-crystal substrates (such as graphene, hexagonal boron nitride, etc.) to induce the preferred orientation and stacking of organic molecules, thereby promoting the formation of high-quality single-crystal films. However, such substrates are costly to prepare, difficult to process, and have limited practicality, making it difficult to meet the industry's demand for low-cost, large-area substrates. (2) Scale and uniformity contradiction: Although vapor phase methods, represented by physical vapor transport (PVT), can achieve millimeter-scale high-quality single-crystal growth, they are usually limited to local areas and it is difficult to achieve a uniform film layer that continuously covers the entire wafer. While solution methods have advantages such as simple processes and the ability to be processed at low temperatures, they often lead to the formation of polycrystalline domain regions due to problems such as solvent evaporation kinetics and uneven nucleation, resulting in uneven film thickness distribution, high defect density, and are not conducive to the integrated fabrication of device arrays. (3) Inability to control monolayer growth: Current film fabrication processes still face technical bottlenecks in controlling the layer-by-layer stacking of organic molecules, often resulting in uneven or uncontrollable film thickness, making it difficult to achieve a true monolayer structure. Especially on amorphous substrates, the lack of ordered lattice information on the surface makes it impossible to provide clear guidance for the epitaxial arrangement of organic molecules, easily inducing the emergence of three-dimensional island-like growth patterns, hindering the formation of high-quality two-dimensional layered thin films. Therefore, constructing an epitaxial strategy for organic semiconductor monolayer films that can achieve wafer-level coverage and uniform morphology on amorphous substrates is a key technological path to promote the flexibility, low cost, and large-area manufacturing of organic electronic devices, and has significant scientific value and broad industrial prospects. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for growing organic semiconductor monolayer films on amorphous substrates. By controlling the relative positions between the raw materials and the amorphous substrate, introducing an auxiliary atmosphere of hydrogen, and optimizing the crystal growth mechanism in a low-pressure environment, a high-quality organic monolayer film with wafer-level, continuous, and controllable thickness can be epitaxially grown.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] This invention discloses a method for growing an organic semiconductor monolayer on an amorphous substrate. The method uses organic semiconductor molecules with alkyl side chains as raw materials, and employs a physical vapor transport method under a hydrogen atmosphere. Under low pressure, the amorphous substrate and the raw materials are in close contact, and an organic semiconductor monolayer is epitaxially grown.

[0008] Preferably, the organic semiconductor molecule is C 10 One of -DNTT, C6-DNTT, and C6-DPA.

[0009] Preferably, the epitaxial growth temperature is within the sublimation temperature range of the raw material, and the time is greater than or equal to 120 minutes.

[0010] Preferably, the flow rate of the hydrogen gas is 25 sccm.

[0011] Preferably, the amorphous substrate is one of a composite substrate composed of quartz glass, bare silicon wafer, silicon dioxide capping layer and heavily doped silicon substrate.

[0012] Preferably, the pressure of the low-pressure environment is <10 Torr.

[0013] The present invention has the following beneficial effects:

[0014] 1. This invention employs the PVT method, which, by controlling the distance between the substrate and the raw materials, introduces hydrogen as an auxiliary gas during the growth process to alter the surface energy of the amorphous substrate. This hydrogen synergizes with the alkyl side chains of organic molecules, enabling the growth of wafer-level continuous, uniform, and high-quality monolayer films on amorphous substrates. Compared to traditional epitaxial growth strategies for organic single-crystal films, which heavily rely on lattice-matched substrates (such as mica, sapphire, and graphene), this method can directly achieve the growth of ordered monolayers on ordinary Si / SiO2 and other amorphous substrates, significantly reducing material and equipment costs and providing a wider range of substrate options for flexible device manufacturing. The transfer steps used in traditional methods often introduce crystal breakage, contamination, and interface defects, affecting device performance and consistency. This invention enables in-situ deposition of films without crystal peeling or transfer processes, greatly improving process stability and repeatability. The prepared organic semiconductor monolayer film has a smooth surface and consistent crystal orientation, and can be directly used for standard photolithography processes, device patterning, and mass integration, providing an ideal material platform for next-generation applications such as flexible electronics, optoelectronic logic devices, and sensor arrays.

[0015] 2. This invention, by introducing hydrogen gas to regulate the surface energy of the amorphous substrate, not only modulates the interaction forces between the substrate surface and organic molecules at the molecular level, but also generates a van der Waals directional synergistic effect with the alkyl chains in the target organic molecules, inducing the molecules to tend towards ordered assembly in a two-dimensional orientation. Furthermore, by controlling the spatial arrangement between the raw materials and the substrate, their close-range sublimation effectively improves molecular transport efficiency while suppressing disordered spontaneous nucleation behavior in the gas phase. This arrangement allows organic molecules to preferentially achieve directional adsorption and lateral expansion on the substrate surface, which is beneficial for forming a continuous, crystal-oriented monolayer structure, significantly improving the uniformity and integrity of the film. Using the method of this invention, the epitaxial growth of organic monolayer films on Si / SiO2 substrates was successfully achieved. The resulting films still exhibit excellent macroscopic continuity and microstructural uniformity without any transfer or lattice template assistance. In actual preparation, the width of the monolayer film can reach 1 cm and the length can reach 8 cm; its growth size is mainly limited by the diameter of the PVT tube furnace used. This method, through comprehensive optimization of material selection, atmosphere control, and substrate arrangement, enables the fabrication of large-area, high-crystallinity organic monolayer films on amorphous substrates using the PVT method. This strategy provides high-quality material support and a stable fabrication path for the development of flexible electronics, ultrathin devices, and integrated organic optoelectronic systems, and has significant application prospects. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of a PVT growth apparatus;

[0017] Figure 2 C obtained from Example 1 10 -Image of a large-area monolayer membrane from DNTT;

[0018] Figure 3 C obtained from Example 1 10 - DNTT monolayer optical images; the left image shows the monolayer film itself, and the right image shows the natural growth boundary between the monolayer film and the substrate;

[0019] Figure 4 C obtained from Example 1 10 -Atomic force microscopy image of the boundary of a DNTT monolayer film;

[0020] Figure 5 C obtained from Example 1 10 -Electrical performance image of organic field-effect transistors fabricated from DNTT monolayer film;

[0021] Figure 6 An optical image of the boundary between the C6-DNTT monolayer film grown in Example 2 and the substrate;

[0022] Figure 7An atomic force microscope image of the boundary of the C6-DNTT monolayer film grown in Example 2;

[0023] Figure 8 Images showing the electrical performance of an organic field-effect transistor fabricated from the C6-DNTT monolayer film grown in Example 2;

[0024] Figure 9 An optical image of the boundary between the C6-DPA monolayer film grown in Example 3 and the substrate.

[0025] Figure 10 An atomic force microscope image of the boundary of the C6-DPA monolayer obtained in Example 3;

[0026] Figure 11 Images showing the electrical properties of an organic field-effect transistor fabricated from the C6-DPA monolayer film grown in Example 3. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Unless otherwise specified, the technical means used in the implementation examples are conventional means well known to those skilled in the art.

[0029] This invention discloses a method for growing an organic semiconductor monolayer film on an amorphous substrate, comprising the following steps:

[0030] (1) Selection of functional molecular materials: This invention selects organic semiconductor molecules with alkyl side chains, such as C 10 -DNTT, C6-DNTT, C6-DPA, etc., are used as evaporation source materials. These molecules possess excellent thermal stability and film-forming properties. Their alkyl chains can effectively control the stacking mode and orientation of molecules during growth, enhance intermolecular van der Waals interactions, promote the horizontal ordered assembly of molecules on amorphous surfaces, inhibit three-dimensional island nucleation, and help achieve two-dimensional layered growth.

[0031] Among them, C 10 The structural formula for -DNTT is: Under low-pressure hydrogen atmosphere, its sublimation temperature range is 190-230℃.

[0032] The structural formula for C6-DNTT is: Under low-pressure hydrogen atmosphere, its sublimation temperature range is 180-220℃.

[0033] The structural formula of C6-DPA is: Under low-pressure hydrogen atmosphere, its sublimation temperature range is 165-190℃.

[0034] (2) Close arrangement of amorphous substrate and raw materials: In the PVT tube furnace cavity, the raw materials and amorphous substrate are placed together, and their spacing is controlled to be close together. The optimization of this spatial layout plays a key role in the growth and preparation of monolayer films. The PVT tube furnace adopts a double-layer quartz tube structure design: the outer layer is a coarse quartz tube fixed in the furnace body, and the inner layer is a detachable fine quartz reaction tube. This structure helps to build a stable temperature gradient field and form a locally closed atmosphere in the inner tube, which significantly improves the uniformity and controllability of gas transport. In addition, the inner small quartz tube has good chemical inertness, which can effectively reduce secondary pollution caused by raw material deposition on the furnace wall, and is also convenient for cleaning and maintenance after the experiment, making it suitable for the growth of high-purity organic monolayer films. The substrate size depends on the PVT tube furnace and is usually limited by the diameter of the PVT tube furnace used. The amorphous substrate includes, but is not limited to, a composite substrate composed of quartz glass, bare silicon wafer, silicon dioxide capping layer and heavily doped silicon substrate.

[0035] (3) Hydrogen gas (flow rate of 25 sccm) is introduced as an auxiliary gas during crystal growth so that the entire growth process is carried out in a hydrogen atmosphere. In a low-pressure environment (<10 Torr), hydrogen gas can induce molecules to tend to two-dimensional spread-order stacking by adjusting the energy level state of the amorphous substrate surface and generating a synergistic effect between the alkyl chains, which significantly improves the uniformity of film formation.

[0036] The present invention will be further described below with reference to specific embodiments.

[0037] Figure 1 This invention utilizes a physical vapor transport (PVT) growth apparatus. The apparatus is simple in structure and suitable for the thermal sublimation growth of various organic semiconductor materials. In the following embodiments, a composite substrate consisting of a 300nm thermally oxidized SiO2 capping layer and a 500μm thick heavily doped Si substrate is selected as the amorphous substrate. The raw material and the substrate are kept in close contact to form a stable near-field sublimation environment. The entire system is operated under vacuum, maintaining a low pressure (below 10 Torr), while hydrogen is introduced as an auxiliary gas at a flow rate of 25 sccm. Hydrogen is continuously introduced during the growth process, and the epitaxial growth of organic semiconductor monolayer films is performed in a hydrogen atmosphere. The growth temperature is within the material sublimation temperature range, and the growth time is set to 120 minutes.

[0038] Example 1

[0039] A method for growing an organic semiconductor monolayer on an amorphous substrate, comprising the following steps: using a 300nm thermally grown silicon dioxide / 500μm heavily doped silicon wafer (Si / SiO2) as the amorphous substrate, with a substrate size of 1cm × 10cm. An organic semiconductor material with alkyl chains, C, is selected. 10 -DNTT was used as the sublimation feedstock and placed in the central high-temperature zone of a PVT tube furnace, with the amorphous substrate placed adjacent to the feedstock in the downstream temperature zone. After evacuating the apparatus to a low pressure (<10 Torr), hydrogen was introduced as an auxiliary atmosphere, with a flow rate controlled at 25 sccm. Under the hydrogen atmosphere, at a pressure of 0.22 Torr, sublimation and transport were carried out at 215°C, and growth was maintained at this constant temperature for at least 120 minutes. Experiments showed that continuous and uniform monolayer films could be obtained even with growth times greater than 120 minutes. In this embodiment, a growth time of 120 minutes was selected, which successfully prepared a large-area, high-quality C film. 10 -DNTT monolayer membrane, such as Figure 2 As shown.

[0040] Optical microscope images such as Figure 3 As shown, the left image represents the main body of the monolayer film, and the right image represents the natural growth boundary between the monolayer film and the substrate. The images clearly show that the film edges are neat and the interface is clear, indicating uniform film coverage, a smooth surface, and no obvious defects. The corresponding atomic force microscopy images are shown below. Figure 4 As shown, the results indicate that the membrane edge is clear and the step height is consistent, further confirming that the obtained structure is a single-layer membrane.

[0041] Figure 5 Images show the electrical performance of an organic field-effect transistor (OFET) device constructed based on this monolayer film. The left image shows the transfer curve, and the right image shows the output curve. The gate voltage was -60V, and the electrical performance in the saturation region was tested. As can be seen from the images, this organic semiconductor monolayer film exhibits high mobility, calculated to be 11.59 cm⁻¹. 2 V -1 s -1 It also features high on-state current, high switching ratio, and excellent electrical performance.

[0042] Example 2

[0043] A method for growing organic semiconductor monolayer films on an amorphous substrate is disclosed. The process involves using a 300nm thermally grown silicon dioxide / 500μm heavily doped silicon wafer (Si / SiO2) as the amorphous substrate. The substrate size is 1cm × 10cm. C6-DNTT, an organic semiconductor material with alkyl chains, is selected as the sublimation feedstock and placed in the central high-temperature zone of a PVT tube furnace. The amorphous substrate is placed adjacent to the feedstock in the downstream temperature zone. After the apparatus is evacuated to a low pressure (<10 Torr), hydrogen is introduced as an auxiliary atmosphere, with a flow rate controlled at 25 sccm. Under the hydrogen atmosphere (pressure 0.22 Torr), sublimation and transport are carried out at 200°C, and growth is maintained at this constant temperature for at least 120 minutes. Experiments have shown that continuous and uniform monolayer films can be obtained even with a growth time greater than 120 minutes. In this embodiment, a growth time of 120 minutes was selected, which successfully prepared a large-area, high-quality C6-DNTT monolayer film.

[0044] Figure 6 The optical microscope image shows the natural growth boundary between the grown C6-DNTT monolayer film and the substrate. It can be clearly observed that the film edge is neat and the interface is clear, indicating that the film layer is uniformly covered, the surface is flat, and there are no obvious defects. Figure 7 The atomic force microscopy (AFM) image of the corresponding area shows that the film edge is clear and the step height is consistent, further confirming that the obtained structure is a single-layer film. Figure 8 The electrical performance curves of the organic field-effect transistor (OFET) device based on this monolayer film are shown. The left graph is the transfer curve, and the right graph is the output curve. The gate voltage was -60V, and the electrical performance in the saturation region was tested. As can be seen from the figures, this organic semiconductor monolayer film exhibits high mobility, calculated to be 9.13 cm⁻¹. 2 V -1 s -1 It also features high on-state current, high switching ratio, and excellent electrical performance.

[0045] Example 3

[0046] A method for growing organic semiconductor monolayer films on an amorphous substrate is disclosed. The process involves using a 300nm thermally grown silicon dioxide / 500μm heavily doped silicon wafer (Si / SiO2) as the amorphous substrate. The substrate size is 1cm × 10cm. C6-DPA, an organic semiconductor material with alkyl chains, is selected as the sublimation feedstock and placed in the central high-temperature zone of a PVT tube furnace. The amorphous substrate is placed adjacent to the feedstock in the downstream temperature zone. After the apparatus is evacuated to a low pressure (<10 Torr), hydrogen is introduced as an auxiliary atmosphere, with a flow rate controlled at 25 sccm. Under the hydrogen atmosphere, at a pressure of 0.22 Torr, sublimation and transport are carried out at 180°C, and growth is maintained at this constant temperature for at least 120 minutes. Experiments have shown that continuous and uniform monolayer films can be obtained even with a growth time greater than 120 minutes. In this embodiment, a growth time of 120 minutes was selected, which successfully prepared a large-area, high-quality C6-DPA monolayer film.

[0047] Figure 9 The optical microscope image shows the natural growth boundary between the grown C6-DPA monolayer and the substrate. It can be clearly observed that the film edge is neat and the interface is clear, indicating that the film layer is uniformly covered, the surface is flat, and there are no obvious defects. Figure 10 The atomic force microscopy (AFM) image of the corresponding area shows that the film edge is clear and the step height is consistent, further confirming that the obtained structure is a single-layer film. Figure 11 The electrical performance curves of the organic field-effect transistor (OFET) device based on this monolayer film are shown. The left graph is the transfer curve, and the right graph is the output curve. The gate voltage was -60V, and the electrical performance in the saturation region was tested. As can be seen from the figures, this organic semiconductor monolayer film exhibits high mobility, calculated to be 2.93 cm⁻¹. 2 V -1 s -1 It also features high on-state current, high switching ratio, and excellent electrical performance.

[0048] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for growing a monolayer film of an organic semiconductor on an amorphous substrate, characterized by: The organic semiconductor molecules with alkyl side chains are used as raw materials, and a single layer of organic semiconductor film is epitaxially grown on an amorphous substrate in a low pressure environment under a hydrogen atmosphere, with the distance between the amorphous substrate and the raw materials being in close contact; The organic semiconductor molecule is C 10 one of C6-DNTT, C6-DPA.

2. The method of claim 1, wherein the method is characterized by: The temperature for epitaxial growth is in the sublimation temperature range of the raw materials, and the time is greater than or equal to 120 minutes.

3. The method of claim 1, wherein the method further comprises: depositing a first layer of organic semiconductor material on the amorphous substrate; and depositing a second layer of organic semiconductor material on the first layer of organic semiconductor material. The flow rate of the hydrogen gas is 25 sccm.

4. The method of claim 1, wherein the non-crystalline substrate is selected from the group consisting of glass, plastic, and polymer. The amorphous substrate is one of a quartz glass, a bare silicon wafer, a silicon dioxide cover layer, and a heavily doped silicon substrate.

5. The method of claim 1, wherein the method further comprises: depositing a first layer of organic semiconductor material on the amorphous substrate; and depositing a second layer of organic semiconductor material on the first layer of organic semiconductor material. The pressure of the low pressure environment is less than 10 Torr.

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