Method for preparing high-quality organic semiconductor film by solution static micro-tilting film forming method

Abstract

The invention discloses a method for preparing a high-quality organic semiconductor film by a solution static micro-tilt film forming method, which introduces a static micro-tilt film forming method, combines an ingenious cover plate design to form a micro gap of a semi-closed space between an inclined cover plate and a horizontal substrate, reduces the exposed area of a three-phase interface, and improves the film forming efficiency. The method has the advantages that the influence of interface dynamic change on deposition quality in the solvent evaporation process is reduced, the uniformity, compactness and adhesion of a deposition layer are remarkably improved, Meniscus circulation is induced, solute is efficiently transmitted to a three-phase junction, accurate deposition of the solute on a leading edge interface is realized, uniform and compact deposition of the film is promoted, uniform and ordered growth of the high-quality film is realized, and the deposition quality of the film is improved. The method is especially suitable for uniform and ordered deposition of a solution with high surface tension and strong intermolecular force on a substrate, has extremely obvious advantages, and can greatly reduce the condition selection difficulty of an organic material deposition process and obviously improve the performance of a device.

Description

Technical field:

[0001] The invention relates to the technical field of organic semiconductor film preparation, and in particular to a method for preparing high-quality organic semiconductor film by a solution static micro-tilt film forming method. Background technology:

[0002] Organic electronics has become a booming research field, especially in flexible electronic devices. Organic thin-film transistors (OTFTs) have shown great potential in sensors, displays, and biomedicine due to their thinness, flexibility, and ease of mass production. However, one of the key technical challenges to achieve high-performance OTFTs is how to prepare high-quality organic semiconductor films while improving the stability and consistency of the devices.

[0003] In the frontier field of organic materials science, solution-based film-forming techniques such as blade coating, spin coating, roller coating and drop coating have become common means of preparing high-performance organic thin films due to their simplicity and wide applicability. These techniques are not only widely used in the field of organic semiconductors, but also significantly promote the improvement of the optoelectronic properties of organic thin films, opening up new possibilities for scientific research and industrial applications. However, when it comes to complex systems with strong intermolecular interactions, these traditional techniques reveal their limitations. When dealing with these systems, it is often difficult to balance the optimization of solubility and the control of solution wettability, forcing researchers to face a dilemma when choosing appropriate processing conditions. This trade-off not only increases the difficulty and time of process optimization, but also directly restricts the further improvement of the optoelectronic properties of materials, becoming a technical bottleneck that needs to be solved urgently.

[0004] Solution film-forming techniques based on external shear force, such as spin coating, scraper coating, and roller coating, have been widely used in the preparation of organic semiconductor films. These methods are simple and easy to implement and suitable for large-area preparation, but they have some inherent limitations. For example, although spin coating can prepare uniform thin films, it is difficult to control the crystallinity and orientation of the thin films in some cases, which directly affects the electrical properties of the device. In addition, although scraper coating and roller coating techniques are suitable for continuous production, for some organic semiconductor materials (for example, for solutions with slightly poor wettability), it is difficult to obtain good crystal quality while ensuring the uniformity of the thin film.

[0005] Organic semiconductor thin films are prepared by physical deposition methods such as vacuum evaporation. Although this method can obtain highly ordered thin films, it is costly, requires stringent conditions, and is not suitable for large-scale production of large-area substrates. To overcome these limitations, researchers have explored various improvement schemes. For example, by introducing nanoparticles (NPs) or using special solution processing techniques to improve the crystallinity and orientation of the film. However, it still faces the problems of increased process complexity and rising costs.

[0006] In the prior art, there are also studies focusing on how to achieve the preparation of high-quality films by controlling the flow of solutions. For example, using gravure printing technology, uniform deposition of thin films can be achieved by controlling pattern parameters such as hue, screen angle, line density, and stylus angle. However, this method still has many challenges in actual operation, such as maintaining consistency in film thickness under high-speed conditions.

[0007] In summary, although there are many technologies available for the preparation of organic semiconductor films, there are still many deficiencies in achieving high-performance, low-cost, and large-scale production of OTFTs. Especially for complex organic systems, how to achieve precise control of high-quality films while ensuring material solubility and good wettability of solutions remains an urgent problem to be solved. Therefore, a new preparation technology is needed that can significantly improve film quality and device performance while simplifying the process. Summary of the invention:

[0008] The purpose of the present invention is to provide a method for preparing high-quality organic semiconductor thin films by a solution static micro-tilt film forming method.

[0009] The present invention is achieved through the following technical solutions:

[0010] A method for preparing a high-quality organic semiconductor thin film by a solution static micro-tilt film forming method, the method comprising the following steps:

[0011] 1) Select a material with a clean and flat surface as a horizontal substrate for thin film growth;

[0012] 2) Evenly drip the solution onto the horizontal substrate;

[0013] 3) placing one end of the cover plate precisely tilted at a predetermined angle of no more than 0.6° on top of the substrate, so that a stable semi-enclosed space gap is formed between the tilted cover plate and the horizontal substrate;

[0014] 4) Maintain a constant temperature environment below the boiling point of the solution to ensure uniform evaporation and reduce film bubbles and perforations.

[0015] The order of step 2) and step 3) in the above method can be exchanged and both fall within the scope of protection of this patent.

[0016] In particular, the horizontal substrate may also undergo necessary pretreatment to increase wettability and adhesion.

[0017] In particular, the cover plate has smooth edges without sharp corners to avoid adverse effects on the deposition process. The cover plate material must be compatible with the deposition environment and resistant to solvent corrosion.

[0018] The predetermined angle can be determined by calculating the height distance between the other end of the cover plate and the horizontal substrate and the horizontal length of the base to be covered with a film through a formula.

[0019] In particular, the solution contains organic molecules with strong intermolecular interactions (e.g., containing electron donating groups and electron donating groups), and the recommended concentration of organic molecules is higher than 5 mg / mL to obtain a thicker film (if the solubility of the material is too low, then try to get close to the saturation concentration of the material), and solvents with low surface tension and high stability such as chlorobenzene and toluene are selected to reduce the formation of bubbles and defects.

[0020] Preferably, the organic molecules containing strong intermolecular interaction forces are PDCBT-DP2F and P5TCN-2F, and their structures are as follows:

[0021]

[0022] The substrate is selected from a glass sheet, a silicon sheet rigid substrate or a polyethylene terephthalate, polyimide flexible substrate.

[0023] The present invention utilizes a tiny gap in a semi-enclosed space formed between a cover plate inclined at no more than 0.6° and a horizontal substrate to effectively optimize the contact state of the solid-liquid-gas three-phase interface to promote the orderly deposition of the solute on the substrate. By reducing the exposed area of ​​the three-phase interface, the influence of the dynamic change of the interface during solvent evaporation on the deposition quality is reduced. At the same time, Meniscus circulation is induced to efficiently transport the solute to the junction of the three phases, thereby achieving precise deposition of the solute at the front interface, promoting uniform and dense deposition of the film, and achieving uniform and orderly growth of high-quality films. The present invention is particularly suitable for the deposition process of solutions with high surface tension and strong intermolecular forces.

[0024] In particular, the surface of the cover plate close to the substrate can be etched with a solution mass transfer guide groove by laser or chemical methods to further guide the flow direction of the solution and reduce unnecessary lateral diffusion; and by changing the surface tension distribution, the evaporation rate of the solution and the solute deposition position can be precisely controlled.

[0025] Furthermore, after the solution is completely evaporated, the substrate with the deposited material is annealed at 90 degrees Celsius for 12 hours to reduce the impact of residual solvent on device performance and enhance the stability and performance of the deposited layer. For high-boiling point solvents, both the annealing temperature and annealing time need to be increased to completely remove the solvent residue.

[0026] The beneficial effects of the present invention are as follows:

[0027] 1) The present invention introduces a static micro-tilt film-forming method, and combines a clever cover plate design to form a small gap in a semi-enclosed space between the inclined cover plate and the horizontal substrate, thereby reducing the exposed area of ​​the three-phase interface, reducing the impact of dynamic changes in the interface during solvent evaporation on the deposition quality, and significantly improving the uniformity, density and adhesion of the deposited layer. At the same time, it induces Meniscus circulation, efficiently transports solutes to the three-phase junction, achieves precise deposition of solutes at the front interface, promotes uniform and dense deposition of thin films, and achieves uniform and orderly growth of high-quality thin films. It is particularly suitable for uniform and orderly deposition of solutions with high surface tension and strong intermolecular forces on substrates, and has extremely obvious advantages, which can greatly reduce the difficulty of selecting conditions for organic material deposition processes and significantly improve device performance. It effectively solves the problems of uniformity, surface tension control and production efficiency in the film preparation process of the prior art, and provides a new way to prepare high-quality thin films.

[0028] 2) The present invention does not require a complex external force driving mechanism, simplifies the operation process, reduces equipment cost and maintenance difficulty, and improves the stability and reliability of the deposition process.

[0029] 3) The present invention requires fewer parameters to be controlled and adjusted, and the internal driving force of the material itself is the main driving force, which can greatly reduce the work of optimizing the film-forming conditions of the material, realize rapid evaluation of material properties, and greatly improve the speed of initial screening of organic semiconductor material properties, which is of great significance for material screening. Description of the drawings:

[0030] Figure 1 This is a schematic diagram of the static micro-tilt film formation of the solution when the cover plate of the present invention is placed obliquely;

[0031] Figure 2 The performance curves of the field effect transistor device prepared by the chlorobenzene solution of PDCBT-DP2F in Example 1 under the blade coating and static micro-tilt film forming technology are compared, where a and b are the field effect transistor output and transfer curves of the blade coating film, respectively. c and d are the field effect transistor output and transfer curves under static micro-tilt film forming. The structure, size and test parameters of the device are exactly the same. In the output curve, V g Set from 0V to 30V, step size 5V. In the transfer curve, V d Set to 30V.

[0032] Figure 3The performance curves of the field effect transistor prepared by the trichloro solution of P5TCN-2F in the scraping and roller coating modes and the field effect transistor prepared by the chlorobenzene solution of P5TCN-2F in the static micro-tilt film forming technology in Example 2 are compared. a and b are the output and transfer curves of the field effect transistor of the scraping film, respectively. c and d are the output and transfer curves of the field effect transistor of the roller coating film, respectively. e and f are the output and transfer curves of the field effect transistor under the static micro-tilt film forming. The structure, size and test parameters of the device are exactly the same. In the output curve, V g Set from 0V to -35V, step size 5V. In the transfer curve, V d Set to -50V. Specific implementation method:

[0033] The following is a further description of the present invention, rather than a limitation of the present invention.

[0034] Embodiment 1:

[0035] The cut silicon wafers were cleaned with chloroform and ethanol. The silicon wafers were then immersed in a solution of concentrated sulfuric acid and hydrogen peroxide in a volume ratio of 7:3 for 10 minutes to remove surface metal impurities and perform surface hydroxylation. The surface was then washed 50 times with deionized water and dried. The hydroxylated silicon wafers were then immersed in a hexane solution of octahydroxysilane (OTS) (V OTS :V 正己烷 =1:1000), control the temperature to 70℃, reflux for 24 hours, take out the silicon wafer, wash it with chromatographically pure cyclohexane, and keep it at 90℃ for 24 hours in a nitrogen environment. Using chlorobenzene solution of PCDBT-DP2F (similar benzene solvents are also acceptable), try many times with traditional film forming methods such as scraper coating and roller coating, but there will be very serious film adhesion problems, so that no film can be formed. However, at 70℃, if Figure 1 As shown, the height of the partition is set to 50 microns (corresponding to an inclination angle of arctan0.005, i.e. 0.29°), the cover plate is configured with a completely flat and smooth surface, and is precisely tilted at a predetermined angle of 0.29° above the horizontal substrate. The tilted cover plate and the horizontal substrate form a stable semi-enclosed space gap. The concentration of the PCDBT-DP2F solution is controlled at 5 mg / mL, and 7uL of PCDBT-DP2F solution is evenly dripped on the horizontal substrate below the semi-enclosed space for film formation experiments. The film formation time is about 3 minutes, and it is found that the film is formed very well with excellent film uniformity. The obtained film was used to prepare a field effect transistor. When the device structure and test conditions are completely consistent, the mobility of the device is increased by more than 5 times (0.11cm 2 V -1 s -1 , the reference object is the optimal device data formed by repeated scraping multiple times).

[0036] Embodiment 2:

[0037] Referring to Example 1, the difference is that another material P5TCN-2F is selected instead of PCDBT-DP2F, and its trichloroethylene solution is used for scraping and roller coating. After half a year of optimization and thousands of devices are repeated, the field effect transistor mobility obtained is the highest: 0.44 (scrape coating) and 0.29 (roller coating) cm 2 V -1 s -1 In contrast, the chlorobenzene solution of P5TCN-2F was used, and the static micro-tilt film-forming technology of the present invention was used. The concentration of the P5TCN-2F solution was controlled to 7 mg / mL, the tilt angle was 0.57° (calculated in the same way as above), 7uL of the P5TCN-2F solution was evenly dripped onto the horizontal substrate below the semi-enclosed space, the film-forming temperature was still set to 70°C, and the film-forming time was about 3 minutes. The highest mobility of 0.54 cm was achieved in the first experiment. 2 V -1 s -1 Other device parameters such as device switching ratio and threshold voltage are close to those of traditional scraper coating and roller coating techniques. This is very beneficial for the rapid screening of organic semiconductor materials.

Claims

1. A method for preparing high-quality organic semiconductor thin films by a solution static micro-tilt film forming method, characterized in that: The method comprises the following steps: 1) Select a material with a clean and flat surface as a horizontal substrate for thin film growth; 2) Evenly drip the solution onto the horizontal substrate; 3) placing one end of the cover plate precisely tilted at a predetermined angle of no more than 0.6° on top of the substrate, so that a stable semi-enclosed space gap is formed between the tilted cover plate and the horizontal substrate; 4) Maintain a constant temperature environment below the boiling point of the solution for uniform evaporation.

2. The method according to claim 1, characterized in that The order of step 2) and step 3) is swapped.

3. The method according to claim 1, characterized in that The horizontal substrate also undergoes necessary pre-treatment.

4. The method according to claim 1, characterized in that: The edge of the cover plate is smooth and has no sharp angles.

5. The method according to claim 1, characterized in that The solution contains organic molecules with strong intermolecular interaction, and the concentration of the organic molecules is higher than 5 mg / mL or as close to the saturated solution concentration as possible.

6. The method according to claim 5, characterized in that The organic molecules are PDCBT-DP2F and P5TCN-2F, and their structures are as follows:

7. The method according to claim 1, characterized in that The substrate is selected from a glass sheet, a silicon sheet rigid substrate or a polyethylene terephthalate, polyimide flexible substrate.

8. The method according to claim 1, characterized in that The surface of the cover plate close to the substrate adopts a completely smooth plane or a solution mass transfer guiding groove is etched by laser or chemical method.

9. The method according to claim 1, characterized in that: After the solution is completely evaporated, the substrate with the deposited material is annealed at above 90°C for more than 12 hours.

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