Preparation method of organic single crystal c8-btbt, organic field effect transistor and integrated circuit

Abstract

The application provides a preparation method of an organic single crystal C8-BTBT. The preparation method comprises the following steps: obtaining a patterned water droplet structure by using a photolithography method, wherein the patterned water droplet structure comprises a silicon substrate and a non-crystalline high-transparency fluorinated polymer formed on the silicon substrate from bottom to top, a surface of the patterned water droplet structure is provided with a plurality of arrayed water droplet-shaped concave parts, and the water droplet-shaped concave parts expose the silicon substrate; dissolving C8-BTBT in a mixed solvent system formed by mixing a good solvent and a poor solvent to obtain a mixed solution of C8-BTBT; and printing the mixed solution into the patterned water droplet structure by using an inkjet printing method, so that nucleation is preferentially performed at a tip of the water droplet-shaped concave part, then growth is started from the tip, and self-assembly growth is performed along a single orientation to grow the entire water droplet-shaped concave part, so as to obtain the organic single crystal C8-BTBT. According to the application, the single-oriented high-quality organic single crystal C8-BTBT can be obtained.

Description

Technical Field

[0001] This invention relates to the field of organic semiconductor single crystal fabrication technology, and more particularly to a method for fabricating organic single crystal C8-BTBT, organic field-effect transistors, and integrated circuits. Background Technology

[0002] Organic semiconductor single crystals (OSSCs), due to their long-range order, absence of grain boundaries, and low defect density, have been applied to many electronic and optoelectronic devices, such as organic field-effect transistors (OFETs), organic light-emitting transistors (OLEDs), organic light-emitting diodes (OLEDs), and photovoltaic cells. The realization of patterned OSSCs is of great significance for the integrated fabrication of devices with high uniformity and complex integrated circuits.

[0003] Currently, commonly used methods for patterning organic semiconductor crystals include template-assisted methods and inkjet printing. However, because the conjugated molecules in organic crystals are bound together only by weak van der Waals forces (<10 kcal / mol), the bonding strength is limited. -1 Even slight external disturbances or perturbations can affect the crystallization quality of organic crystals. To date, the nucleation and crystallization process of organic semiconductors remains difficult to control effectively, resulting in significant differences in morphology and structure between the obtained crystals and random distribution of deposition positions. This makes it difficult to guarantee the repeatability and stability of organic single-crystal device performance. For example, patterned organic small molecules C8-BTBT can be obtained through inkjet printing, template-assisted methods, and methods utilizing substrate wettability differences. However, due to the instability of the random nucleation positions of the seed crystals during the self-assembly process, it is often difficult to obtain patterned, high-quality organic semiconductor single crystals. This leads to uneven quality of the formed crystal films, numerous defects, and ultimately, the inability to achieve ideal, stable, and high-performance devices. Summary of the Invention

[0004] One object of the present invention is to provide a method for accurately anchoring the nucleation sites of organic crystals.

[0005] A further objective of this invention is to improve the performance and uniformity of organic single-crystal C8-BTBT.

[0006] Specifically, this invention provides a method for preparing organic single-crystal C8-BTBT, comprising the following steps:

[0007] A patterned water droplet structure was prepared by photolithography. The patterned water droplet structure includes a silicon substrate and an amorphous, highly transparent fluorinated polymer formed on the silicon substrate from bottom to top. The surface of the patterned water droplet structure has a plurality of arrayed water droplet-shaped recesses, and the water droplet-shaped recesses expose the silicon substrate.

[0008] C8-BTBT is dissolved in a mixed solvent system consisting of a good solvent and a poor solvent to obtain a mixed solution of C8-BTBT;

[0009] The mixed solution is printed into the patterned droplet structure using an inkjet printing method, so that nucleation is preferentially formed at the tip of the droplet-shaped recess, and then growth starts from the tip and self-assembles along a single orientation to fill the entire droplet-shaped recess to obtain organic single crystal C8-BTBT.

[0010] Optionally, the fluorinated polymer is Cytop fluorinated polymer or polytetrafluoroethylene.

[0011] Optionally, the good solvent is chlorobenzene; the poor solvent is dodecane or N,N-dimethylformamide.

[0012] Optionally, the fabrication of the patterned water droplet structure using photolithography includes the following steps:

[0013] The fluorinated polymer is spin-coated onto a silicon substrate and heated at a preset temperature for a preset time.

[0014] Thermally evaporated metal layer;

[0015] Photoresist is formed on the metal layer, and the patterned water droplet structure is obtained by photolithography using a mask.

[0016] Optionally, the preset temperature is any value within the range of 100-200℃;

[0017] The preset time is any value within the range of 10-60 minutes.

[0018] Optionally, the evaporation rate of the metal layer is in the range of 0.2-0.6 Å / s;

[0019] The thickness of the metal layer is any value in the range of 20-80 nm.

[0020] Optionally, the step of forming photoresist on the metal layer and obtaining the patterned waterdrop structure by photolithography using a mask includes the following steps:

[0021] Spin-coat the photoresist at a speed of 2000-5000 r / min for 20-60s, and bake it at 80-120℃ for 1-5min.

[0022] The substrate on which photoresist, a metal layer and a fluorinated polymer are formed is exposed to ultraviolet light using the mask, thereby performing photolithography on the photoresist;

[0023] The photoresist is developed in a developing solution to obtain a patterned photoresist.

[0024] The patterned droplet structure is obtained by removing the metal layer and the fluorinated polymer from the patterned photoresist surface.

[0025] Optionally, in the step of removing the metal layer and the fluorinated polymer from the patterned photoresist surface to obtain the patterned droplet structure, the metal layer on the photoresist surface is removed by immersion in a saturated ammonium persulfate solution, and the fluorinated polymer is etched away using oxygen.

[0026] In particular, the present invention also provides an organic field-effect transistor comprising an organic single-crystal C8-BTBT prepared by any of the above-described methods.

[0027] In particular, the present invention also provides an integrated circuit comprising organic single-crystal C8-BTBT prepared by any of the above-described preparation methods.

[0028] According to the present invention, a patterned droplet structure is prepared, and a mixed solution of C8-BTBT is printed onto the patterned droplet structure. Due to the droplet structure design of the surface microstructure of the pattern, the evaporation rate of the solution at various locations within the pattern is effectively controlled; that is, the evaporation flux at the tip is much greater than that at the surrounding area. This causes the solution to preferentially nucleate at the tip, achieving the effect of anchoring the nucleation site of the organic crystal. Subsequently, C8-BTBT grows from the tip, self-assembling along a single orientation to fill the entire droplet pattern. As the solvent gradually evaporates, the organic single-crystal C8-BTBT is finally deposited in the droplet pattern. The present invention can obtain high-quality, single-oriented organic single-crystal C8-BTBT. The devices fabricated using this organic single crystal exhibit excellent repeatability and stability.

[0029] The above and other objects, advantages and features of the present invention will become more apparent to those skilled in the art from the following detailed description of specific embodiments of the invention in conjunction with the accompanying drawings. Attached Figure Description

[0030] The following sections will describe some specific embodiments of the invention in a detailed manner by way of example and not limitation, with reference to the accompanying drawings. The same reference numerals in the drawings denote the same or similar parts or portions. Those skilled in the art should understand that these drawings are not necessarily drawn to scale. In the drawings:

[0031] Figure 1A schematic flowchart of a method for preparing organic single-crystal C8-BTBT according to an embodiment of the present invention is shown;

[0032] Figure 2 It shows Figure 1 A schematic flowchart of the method for preparing patterned water droplet structures using photolithography in step S100;

[0033] Figure 3 It shows Figure 2 A schematic flowchart of the method for step S130;

[0034] Figure 4 A schematic structural diagram is shown showing the process of printing the mixed solution into the patterned droplet structure using an inkjet printing method.

[0035] Figure 5 A solvent evaporation flux curve along the contact line of the teardrop-shaped recess is shown according to an embodiment of the present invention;

[0036] Figure 6 The solute concentration and velocity field distribution of a water droplet during evaporation according to an embodiment of the present invention are shown.

[0037] Figure 7 A microscope image of the formation process of organic single-crystal C8-BTBT according to an embodiment of the present invention is shown;

[0038] Figure 8 The image shows polarized light microscope images of organic single-crystal C8-BTBT at different incident angles of polarized light;

[0039] Figure 9 The variation of polarized light reflection intensity of organic single-crystal C8-BTBT under different incident angles of polarized light is shown;

[0040] Figure 10 Transmission electron microscopy (TEM) image and selected area electron diffraction (SED) characterization pattern of organic single-crystal C8-BTBT according to an embodiment of the present invention are shown.

[0041] Figure 11 A microscope image of an organic field-effect transistor according to an embodiment of the present invention is shown;

[0042] Figure 12 The transfer characteristic curves of 64 organic field-effect transistors according to an embodiment of the present invention are shown;

[0043] Figure 13 A three-dimensional histogram of the mobility of an organic field-effect transistor according to an embodiment of the present invention is shown.

[0044] Figure 14The statistical quantities of various mobilities and threshold voltages of an organic field-effect transistor according to an embodiment of the present invention are shown.

[0045] Figure 15 An image is shown of multiple binary multipliers fabricated on a 1.5cm × 1.5cm silicon oxide wafer according to an embodiment of the present invention;

[0046] Figure 16 A microscope photograph of a single binary multiplier according to an embodiment of the present invention is shown;

[0047] Figure 17 V, a binary multiplier according to an embodiment of the present invention, is shown. in -V out Line graph. Detailed Implementation

[0048] Figure 1 A schematic flowchart illustrating a method for preparing organic single-crystal C8-BTBT according to an embodiment of the present invention is shown. Figure 1 As shown, the preparation method includes:

[0049] Step S100: A patterned water droplet structure is prepared by photolithography. The patterned water droplet structure includes a silicon substrate and an amorphous, highly transparent fluorinated polymer formed on the silicon substrate from bottom to top. The surface of the patterned water droplet structure has multiple arrayed water droplet-shaped recesses, and the water droplet-shaped recesses expose the silicon substrate.

[0050] Step S200: Dissolve C8-BTBT in a mixed solvent system consisting of a good solvent and a poor solvent to obtain a mixed solution of C8-BTBT;

[0051] In step S300, the mixed solution is printed onto a patterned droplet structure using an inkjet printing method to preferentially nucleate at the tip of the droplet-shaped recess, and then grows from the tip and self-assembles along a single orientation to fill the entire droplet-shaped recess to obtain organic single crystal C8-BTBT.

[0052] According to the present invention, a patterned water droplet structure is prepared, and a mixed solution of C8-BTBT is printed into the patterned water droplet structure. Due to the water droplet structure design of the surface microstructure of the pattern, the evaporation rate of the solution at various positions of the pattern is effectively controlled. That is, the evaporation flux at the tip is much greater than the evaporation flux around the edge, causing the solution to preferentially nucleate at the tip, achieving the effect of anchoring the nucleation position of the organic crystal. Subsequently, C8-BTBT grows from the tip and self-assembles along a single orientation to fill the entire water droplet pattern. As the solvent gradually evaporates, the organic single crystal C8-BTBT is finally deposited in the water droplet pattern.

[0053] Figure 2 It shows Figure 1 A schematic flowchart illustrating the method for fabricating patterned water droplet structures using photolithography in step S100. Figure 2 As shown, in step S100, the fabrication of the patterned water droplet structure using photolithography includes:

[0054] Step S110: Spin-coat the fluorinated polymer onto the cleaned silicon substrate and heat it at a preset temperature for a preset time.

[0055] Step S120: Thermally evaporate the metal layer;

[0056] In step S130, photoresist is formed on the metal layer, and photolithography is performed using a mask to obtain the patterned water droplet structure.

[0057] Before step S110, the silicon substrate needs to be cleaned, which can be done using conventional cleaning methods in the prior art. For example, the substrate is immersed in concentrated sulfuric acid at 90°C for 2 hours, and then ultrasonically cleaned sequentially in acetone, isopropanol, and deionized water for 15 minutes each. After drying with a nitrogen stream, the substrate is further treated with an oxygen plasma cleaner (PVA, Ion 40) at 100W for 300 seconds.

[0058] In step S110, the fluorinated polymer is a non-crystalline, highly transparent, hydrophobic material, such as Cytop fluorinated polymer or polytetrafluoroethylene. When spin-coating the fluorinated polymer, it can be done at a speed of 1000-2000 r / min for 10-30 seconds. Preferably, it is spin-coated at 1500 r / min for 20 seconds. The preset temperature is any value between 100-200°C, for example, 100°C, 150°C, or 200°C. The preset time is any value within the range of 10-60 minutes, for example, 10 minutes, 30 minutes, 40 minutes, or 60 minutes. This heating process can be performed, for example, on a heating plate.

[0059] In step S120, the thermal evaporation process can be performed, for example, on a thermal evaporation apparatus. The evaporation rate of the metal layer is in the range of 0.2-0.6 Å / s, for example, 0.2 Å / s, 0.4 Å / s, 0.5 Å / s, or 0.6 Å / s. The thickness of the metal layer is any value in the range of 20-80 nm, such as 20 nm, 40 nm, 60 nm, or 80 nm. The material of the metal layer can be, for example, copper.

[0060] Figure 3 It shows Figure 2 A schematic flowchart illustrating step S130. (See attached flowchart.) Figure 3 As shown, step S130 includes:

[0061] Step S131: Spin-coat the photoresist at a speed of 2000-5000 r / min for 20-60s, and bake at 80-120℃ for 1-5min;

[0062] Step S132: Using a mask, the substrate on which photoresist, metal layer and fluorinated polymer are formed is exposed to ultraviolet light, thereby performing photolithography on the photoresist;

[0063] Step S133: Develop in developer to obtain patterned photoresist;

[0064] Step S134: Remove the metal layer and fluorinated polymer from the patterned photoresist surface to obtain a patterned water droplet structure.

[0065] In step S131, the photoresist is AR-P5350. The spin-coating speed can be, for example, 2000 r / min, 3000 r / min, 4000 r / min, or 5000 r / min, or any other value between 2000 and 5000 r / min. The spin-coating time can be, for example, 20 s, 40 s, 50 s, or 60 s, or any other value between 20 and 60 s. The baking temperature can be, for example, 80℃, 100℃, or 120℃, or any other value between 80 and 120℃. The baking time can be, for example, 1 min, 2 min, 3 min, 4 min, or 5 min, or any other value between 1 and 5 min.

[0066] In step S132, the irradiation time under ultraviolet light is any value between 1 and 2 seconds, such as 1 second, 1.5 seconds, 1.8 seconds, or 2 seconds. In step S133, the development time in the developing solution is, for example, any value between 5 and 10 seconds, such as 5 seconds, 8 seconds, or 10 seconds.

[0067] In step S134, the metal layer on the photoresist surface is removed by soaking in a saturated ammonium persulfate solution, and the fluorinated polymer is etched away using oxygen in a reactive ion etching machine.

[0068] In step S200, the good solvent is chlorobenzene; the poor solvent is dodecane or N,N-dimethylformamide. The boiling point of the good solvent is lower than that of the poor solvent, so that the good solvent, which dissolves the material, will preferentially evaporate and nucleate at the tip. In addition, the surface tension of the poor solvent is lower than that of the good solvent, so that as the good solvent evaporates, a higher concentration of the poor solvent can be continuously replenished below the liquid surface, providing a flat liquid surface for stable growth of the material.

[0069] Figure 4 A schematic structural diagram is shown illustrating the printing of the mixed solution into the patterned droplet structure using an inkjet printing method. (See diagram for reference.) Figure 4As shown, the C8-BTBT mixture is applied to the teardrop-shaped recess. A suitable distance exists between the printer nozzle and the teardrop-shaped recess.

[0070] Figure 5 A solvent evaporation flux curve along the contact line of a teardrop-shaped recess is shown according to an embodiment of the present invention. Figure 5 As shown, the volatile flux is greatest at the tip of the teardrop-shaped concave portion. Figure 6 The solute concentration and velocity field distribution of a water droplet during the evaporation process according to an embodiment of the present invention are shown.

[0071] Figure 7 A microscope image of the formation process of organic single-crystal C8-BTBT according to an embodiment of the present invention is shown. Figure 7 As shown, i to iv represent the nucleation and crystallization processes, and v to vi represent the evaporation of undesirable solvents.

[0072] Figure 8 Polarized microscope images of organic single-crystal C8-BTBT at different incident angles of polarized light are shown. Figure 9 The variation of polarized light reflection intensity of organic single-crystal C8-BTBT under different incident angles of polarized light is shown. Figure 8 and Figure 9 It is known that the organic single crystal C8-BTBT prepared by this invention has a single growth orientation.

[0073] To further characterize the crystal quality of organic single-crystal C8-BTBT, it was characterized by selected area electron diffraction (TEM). Figure 10 Transmission electron microscopy (TEM) image and selected area electron diffraction (SED) characterization of organic single-crystal C8-BTBT according to an embodiment of the present invention are shown. Figure 10 (a) shows a uniform distribution of material in a teardrop shape (the black area inside the teardrop shape is the copper mesh used to prepare the TEM sample). Figure 10 (b) shows the selected area electron diffraction (SAED) pattern of the selected area. It can be seen that in a water droplet, any five different selected areas can exhibit a consistent diffraction lattice. These diffraction lattices are different from the diffraction rings of the polycrystalline sample, which shows that the C8-BTBT prepared in this invention has excellent single-crystal properties.

[0074] In particular, embodiments of the present invention also provide an organic field-effect transistor. This organic field-effect transistor includes the aforementioned organic single-crystal C8-BTBT. Figure 11A microscopic image of an organic field-effect transistor according to an embodiment of the present invention is shown. The organic field-effect transistor is an 8×8 organic field-effect transistor array obtained by thermal evaporation. Specifically, a metal mask for aligning the source and drain electrodes is placed on top of the crystal array, and 50 nm of Ag is thermally evaporated at a rate of 0.4 Å / s, followed by 1.5 nm of F4-TCNQ being thermally evaporated at a rate of 0.1 Å / s. The channel length and effective width of the mask are 100 μm and 80 μm, respectively.

[0075] Figure 12 The transfer characteristic curves of 64 organic field-effect transistors according to an embodiment of the present invention are shown. Figure 12 It can be seen that the highest mobility of the device is as high as 17.3 cm⁻¹. 2 V -1 s -1 The average migration rate can reach 12.5 cm. 2 V -1 s -1 . Figure 13 A three-dimensional histogram of the mobility of an organic field-effect transistor according to an embodiment of the present invention is shown. Figure 13 It can be seen that the performance of the device is uniformly distributed, and the coefficient of variation of the device mobility is calculated to be 16.7%, which shows the uniformity of the device performance. Figure 14 The statistical values ​​of various mobilities and threshold voltages of organic field-effect transistors according to an embodiment of the present invention are shown. It can be seen that the mobility of the vast majority of devices exceeds 10 cm⁻¹. 2 V -1 s -1 Furthermore, the threshold voltage does not exceed -2V, further demonstrating the excellent performance of the devices. All electrical performance characterizations were performed in air using a Keithley 4200-SCS semiconductor analyzer.

[0076] In particular, the present invention also provides an integrated circuit comprising the aforementioned organic single-crystal C8-BTBT. In one embodiment, the integrated circuit may be, for example, a binary multiplier. Figure 15 An image is shown of multiple binary multipliers fabricated on a 1.5cm × 1.5cm silicon oxide wafer according to an embodiment of the present invention. Figure 16 A microscope photograph of a single binary multiplier according to an embodiment of the present invention is shown. Figure 17 V, a binary multiplier according to an embodiment of the present invention, is shown. in -V out A line graph. For example... Figure 17 It can be seen that V in -V outThe curve shows normal multiplication logic, indicating that all devices are working properly.

[0077] In one embodiment, the binary multiplier is fabricated as follows: An Ag bottom electrode is patterned on a clean SiO2 / Si substrate using photolithography and a lift-off process. The Ag bottom electrode consists of a square region and a rectangular region connected to the square region. Then, SU-8 photoresist is spin-coated onto the substrate where the Ag bottom electrode has been deposited, and soft baking is performed to form a dielectric layer. Subsequently, the SU-8 photoresist above the square region of the Ag electrode is selectively removed using photolithography to form vias for further electrical connections. Next, according to the aforementioned method for fabricating patterned droplet structures, patterned droplet structures are arranged on the Ag bottom electrode in the rectangular region. Then, patterned C8-BTBT single crystals are inkjet-printed onto these patterned droplet structures. Finally, an Ag top electrode is deposited on the C8-BTBT single crystal through thermal evaporation using an aligned metal mask, completing the fabrication of the binary multiplier. The evaporation rate of both the Ag bottom electrode and the Ag top electrode is 0.4 Å / s.

Claims

1. A method for preparing an organic single crystal of C8-BTBT, characterized by, The method comprises the following steps: The patterned water droplet structure is prepared by photolithography, and comprises a silicon substrate and an amorphous high-transparency fluorinated polymer formed on the silicon substrate from bottom to top; the fluorinated polymer is a Cytop fluorinated polymer or polytetrafluoroethylene; a surface of the patterned water droplet structure has a plurality of arrayed water droplet-shaped recesses, the water droplet-shaped recesses expose the silicon substrate, so that a bottom surface of the water droplet-shaped recesses forms a hydrophilic region and an inner circumferential wall of the water droplet-shaped recesses forms a hydrophobic region; C8-BTBT is dissolved in a mixed solvent system composed of a good solvent and a poor solvent to obtain a mixed solution of C8-BTBT; The mixed solution is printed into the patterned water droplet structure by an inkjet printing method, so that nucleation is preferentially performed at a tip of the water droplet-shaped recess, then growth is performed from the tip, and the water droplet-shaped recess is grown full along a single orientation to obtain an organic single crystal C8-BTBT.

2. The production method according to claim 1, characterized by, The good solvent is chlorobenzene, and the poor solvent is dodecane or N,N-dimethylformamide.

3. The production method according to any one of claims 1 to 2, characterized by, The patterned water droplet structure is prepared by photolithography, and comprises the following steps: The fluorinated polymer is spin-coated on the silicon substrate, and heated at a preset temperature for a preset time; A metal layer is thermally evaporated; A photoresist is formed on the metal layer, and photolithography is performed by using a mask to obtain the patterned water droplet structure.

4. The production method according to claim 3, characterized by, The preset temperature is any value in a range of 100-200°C. The preset time is any value in a range of 10-60 min.

5. The preparation method according to claim 3, characterized in that, The evaporation rate of the metal layer is in the range of The thickness of the metal layer is any value in a range of 20-80 nm.

6. The preparation method according to claim 3, characterized in that, The photoresist is spin-coated at a speed of 2000-5000 r / min for 20-60 s, and baked at 80-120°C for 1-5 min; The substrate on which the photoresist, the metal layer and the fluorinated polymer are formed is exposed to ultraviolet light by using the mask, so that photolithography is performed on the photoresist; Developing in a developing solution to obtain a patterned photoresist; The metal layer on the surface of the patterned photoresist and the fluorinated polymer are removed, so that the patterned water droplet structure is obtained. In the step of removing the metal layer on the surface of the patterned photoresist and the fluorinated polymer to obtain the patterned water droplet structure, the metal layer on the surface of the photoresist is removed by soaking in a saturated ammonium persulfate solution, and the fluorinated polymer is etched by using oxygen.

7. The production method according to claim 6, wherein The organic single crystal C8-BTBT is prepared by using the preparation method in any one of claims 1-7.

8. An organic field effect transistor, characterized by The organic single crystal C8-BTBT is prepared by using the preparation method in any one of claims 1-7.

9. An integrated circuit, characterized by ​

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