Preparation method of organic small molecule single crystal and organic field effect transistor

Abstract

The application provides a preparation method of an organic small-molecule single crystal and an organic field effect transistor. The preparation method comprises the following steps: preparing a patterned template by using a photolithography method, the patterned template is provided with a plurality of grooves arranged in an array; printing an ink solution of the organic small molecule into the plurality of grooves of the patterned template to obtain the organic small-molecule single crystal, the ink solution is a solution of the organic small molecule dissolved in a good solvent and a poor solvent, the boiling point of the poor solvent is higher than that of the good solvent, and the good solvent and the poor solvent are mutually soluble; the shape of each groove is configured to have a tip portion, and the volatilization speed of the ink solution at the tip portion is greater than that at other portions of the groove, so that the ink solution preferentially crystallizes at the tip portion, and with the volatilization of the good solvent, the crystal grows epitaxially on the surface of the poor solvent, thereby obtaining the organic small-molecule single crystal. The method can prepare an organic crystal with high integration and high crystallization quality by one-step printing.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of organic field effect transistors, and particularly relates to a preparation method of an organic small-molecule single crystal and an organic field effect transistor. BACKGROUND

[0002] At present, inkjet printing of organic crystals is a way to prepare organic crystals. There are various specific schemes in the prior art, such as the following two schemes.

[0003] The first scheme is to use 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS_PEN) with a mass fraction of 1% as a solute to be dissolved in tetrahydrofuran solvent to prepare ink for printing, and then use an experimental Microfab Jet Drive III inkjet printer to print the ink on a substrate. When the ink begins to volatilize, the evaporation rate of the ink edge is faster, which leads to edge preferential crystallization, and then the solute in the droplet continuously transports to the edge, resulting in a "coffee ring effect" with more edge crystals and less internal crystals. This effect also makes it difficult to prepare organic single crystals by this printing method, and the obtained crystals are polycrystals. However, for the application of organic field effect transistors, high-crystalline-quality organic single crystals have an extremely important influence on the electrical properties thereof.

[0004] The second scheme is to use a two-step printing method to prepare a single crystal thin film. First, a template pattern is printed on a substrate using a poor solvent Dimethyl Formamide (DMF) as ink A. Then, 2,7-dioctyl[1]-benzothieno[3,2-b][1]benzothiophene (C8-BTBT) with a mass fraction of 1% is used as a solute to be dissolved in o-dichlorobenzene as ink B, and ink B is printed on the ink A of the poor solvent, so that the good solvent diffuses and volatilizes on the surface of the poor solvent and crystallizes to obtain a C8-BTBT organic single crystal thin film. However, this method is relatively complex and requires two steps for printing, which has a high requirement for equipment. In addition, since the A ink still exists when the B ink is printed, it is necessary to increase the size of the printed pattern, otherwise the A ink will be completely volatilized before the B ink is printed, which makes it difficult to obtain a high-integration organic single crystal array with a PPI (Pixels Per Inch) of only 48. High-integration organic field effect transistors have an extremely important significance in actual application. SUMMARY

[0005] An object of the present application is to provide an organic single crystal with high crystallinity and high integration.

[0006] A further object of the present application is to provide an organic single crystal with high crystalline quality.

[0007] In particular, the present application provides a method for preparing an organic small molecule single crystal, comprising the following steps:

[0008] A patterned template is prepared by using a photolithography method, wherein the patterned template has a plurality of grooves arranged in an array;

[0009] An ink solution of the organic small molecule is printed into the plurality of grooves of the patterned template to obtain the organic small molecule single crystal, wherein the ink solution is a solution of the organic small molecule dissolved in a good solvent and a poor solvent, the boiling point of the poor solvent is higher than that of the good solvent, and the good solvent and the poor solvent are miscible;

[0010] The shape of each groove is configured to have a tip portion, and the evaporation rate of the ink solution at the tip portion is greater than that at other portions of the groove, so that the ink solution preferentially crystallizes at the tip portion, and as the good solvent evaporates, the crystal grows epitaxially on the surface of the poor solvent, thereby obtaining the organic small molecule single crystal.

[0011] Optionally, the profile surface of the groove is composed of a first inner wall surface, a second inner wall surface and a third inner wall surface connected in sequence;

[0012] The cross sections of the first inner wall surface and the second inner wall surface are both straight lines, and they intersect to define the tip portion;

[0013] The third inner wall surface extends towards a direction away from the tip portion, and its two ends are connected with the first inner wall surface and the second inner wall surface respectively, and the third inner wall surface defines the other portions.

[0014] Optionally, the third inner wall surface is configured to be arc-shaped or a shape composed of an arc segment and a planar segment.

[0015] Optionally, the third inner wall surface is configured to be a shape composed of an arc segment and a planar segment, and the planar segment has two segments and the arc segment has one segment, and the arc segment is located between the two planar segments.

[0016] Optionally, one end of each of the two planar segments of the third inner wall surface is connected with one end of the first inner wall surface and one end of the second inner wall surface respectively;

[0017] One of the planar segments and the first inner wall surface form a first preset included angle, and the other of the planar segments and the second inner wall surface form a second preset included angle;

[0018] The first preset included angle and the second preset included angle are both greater than the angle of the tip portion.

[0019] Optionally, the plane section and the first inner wall surface, and the plane section and the second inner wall surface are rounded.

[0020] Optionally, the boiling point of the good solvent is in the range of any value from 100℃ to 200℃.

[0021] The boiling point of the poor solvent is in the range of any value from 100℃ to 300℃.

[0022] Optionally, the good solvent is chlorobenzene, o-dichlorobenzene, toluene, m-xylene or mesitylene.

[0023] The poor solvent is n-dodecane, N,N-dimethylformamide, dimethyl phthalate or dimethyl sulfoxide.

[0024] Optionally, in the ink solution, the mass ratio of the organic small molecule, the good solvent and the poor solvent is in the range of any value from 20:1 to 2:1.

[0025] In particular, the application also provides an organic field effect transistor comprising the organic small molecule single crystal prepared by the preparation method.

[0026] According to the scheme of the embodiment of the application, the organic single crystal with high crystallization quality can be obtained. In the printing process, due to the presence of the poor solvent, the delamination effect is generated in the volatilization process, which causes the good solvent and the poor solvent to be delaminated. Since the boiling point of chlorobenzene is low, the volatilization is generated preferentially, which causes the concentration of C8-BTBT to rise until the crystal is precipitated. When the crystal begins to crystallize, the solute is diffused and transported due to the crystallization on the surface of the poor solvent, so that the crystal with high crystallization quality can be obtained and the generation of the "coffee ring effect" is avoided, thereby the crystallization of the crystal is improved and the organic single crystal with high crystallization quality can be obtained. Moreover, the method of the application is a one-step printing method, the printing process is simple, the requirement for the equipment is low, and the patterned template used has a tip portion, so that the crystallization nucleation of the ink is induced by using the pattern, and the organic crystal with high integration and high crystallization quality can be prepared.

[0027] Moreover, by designing the shape of the groove, the evaporation flux of the tip portion is higher than that of other sites, so that the crystallization nucleation is preferentially performed when the ink is volatilized, and the crystal obtained finally is crystallized into the single crystal with high crystallization quality.

[0028] The above and other objects, advantages and features of the application will become more apparent from the following detailed description of specific embodiments thereof, taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0029] Some specific embodiments of the present application will be described in detail in the following with reference to the accompanying drawings, which are provided by way of illustration only and therefore are not intended to limit the present application in any manner. The same reference numbers in the drawings indicate the same or similar components or parts. Those skilled in the art should understand that the drawings are not necessarily drawn to scale. In the drawings:

[0030] Figure 1 A schematic flow chart of a method for preparing an organic small molecule single crystal according to an embodiment of the present application is shown;

[0031] Figure 2 A schematic structural flow chart of a method for preparing an organic small molecule single crystal according to an embodiment of the present application is shown;

[0032] Figure 3 A polarized light photo of printing an organic small molecule single crystal on a patterned template with a PPI of 90 according to an embodiment of the present application is shown;

[0033] Figure 4 A polarized light photo of printing an organic small molecule single crystal on a patterned template with a PPI of 150 according to an embodiment of the present application is shown;

[0034] Figure 5 A schematic polarized light photo of a crystal prepared in a control experiment according to the present application is shown;

[0035] Figure 6 A schematic polarized light photo of a crystal prepared by a method according to an embodiment of the present application is shown;

[0036] Figure 7 A schematic polarized light photo of a crystallization process of a crystal according to an embodiment of the present application is shown;

[0037] Figure 8 Simulation calculations of evaporation fluxes of different groove structures and corresponding printing results according to embodiments of the present application are shown;

[0038] Figure 9 A transmission electron microscope photo of an organic small molecule single crystal prepared by a method according to an embodiment of the present application and electron diffraction photos of selected five sites are shown;

[0039] Figure 10 An AFM photo of a C8-BTBT single crystal according to an embodiment of the present application is shown;

[0040] Figure 11 A high resolution AFM photo of a C8-BTBT single crystal according to an embodiment of the present application is shown;

[0041] Figure 12 Synchrotron radiation data of a C8-BTBT single crystal according to an embodiment of the present application is shown.

[0042] Figure 13 A cross-sectional TEM image of a C8-BTBT single crystal is shown according to an embodiment of the present application;

[0043] Figure 14 A schematic side view of an organic field effect transistor is shown according to an embodiment of the present application;

[0044] Figure 15 A schematic top view of an organic field effect transistor is shown according to an embodiment of the present application;

[0045] Figure 16 A schematic enlarged view of a part of the region is shown; Figure 15

[0046] Figure 17 A transfer characteristic curve of an organic field effect transistor is shown according to an embodiment of the present application;

[0047] Figure 18 An output characteristic curve of an organic field effect transistor is shown according to an embodiment of the present application;

[0048] Figure 19 A voltage-current curve of an organic field effect transistor is shown according to an embodiment of the present application;

[0049] Figure 20 A transfer characteristic curve of an organic field effect transistor is shown according to an embodiment of the present application. DETAILED DESCRIPTION

[0050] Figure 1 A schematic flow chart of a method for preparing an organic small molecule single crystal according to an embodiment of the present application is shown. As shown in the figure, the method comprises: Figure 1

[0051] In step S100, a patterned template is prepared by using a photolithography method, and the patterned template has a plurality of grooves arranged in an array on the template;

[0052] In step S200, an ink solution of the organic small molecule is printed into the plurality of grooves of the patterned template to obtain the organic small molecule single crystal, the ink solution being a solution of the organic small molecule dissolved in a good solvent and a poor solvent, the boiling point of the poor solvent being higher than that of the good solvent, and the good solvent and the poor solvent being mutually soluble;

[0053] The shape of each groove is configured to have a tip portion, and the evaporation speed of the ink solution at the tip portion is greater than that at other portions of the groove, so that the ink solution preferentially crystallizes at the tip portion, and as the good solvent evaporates, the crystal grows epitaxially on the surface of the poor solvent, thereby obtaining the organic small molecule single crystal. ​​

[0054] According to the scheme of the embodiment of the present application, the organic single crystal with high crystallization quality can be obtained. In the printing process, due to the presence of the poor solvent, the delamination effect will occur in the volatilization process, which will cause the delamination of the good solvent and the poor solvent. Since the boiling point of chlorobenzene is relatively low, the volatilization will occur preferentially, which will cause the concentration of C8-BTBT to rise until the crystal precipitates. When the crystal begins to crystallize, since the crystallization is on the surface of the poor solvent, it is beneficial to the diffusion transport of the solute, so that the crystal with high crystallization quality can be obtained and the "coffee ring effect" can be avoided, so that the crystallization of the crystal can be improved, and then the organic single crystal with high crystallization quality can be obtained. Moreover, the method of the present application is a one-step printing method, the printing process is simple, the requirement for the equipment is relatively low, and the patterned template used has a tip portion, so that the crystallization nucleation of the pattern-induced ink is used, so that the organic crystal with high integration and high crystallization quality can be prepared.

[0055] The profile surface of the groove is composed of the first inner wall surface, the second inner wall surface and the third inner wall surface connected in sequence. The cross sections of the first inner wall surface and the second inner wall surface are straight lines, and the two straight lines intersect to define the tip portion. The third inner wall surface extends towards the direction away from the tip portion, and the two ends of the third inner wall surface are connected with the first inner wall surface and the second inner wall surface respectively, and the third inner wall surface defines the other portion. The third inner wall surface is configured to be arc-shaped or a shape combined by an arc segment and a plane segment.

[0056] In one embodiment, the third inner wall surface is configured to be a continuous arc shape, and the two ends of the third inner wall surface are connected with the first inner wall surface and the second inner wall surface respectively.

[0057] In another embodiment, the third inner wall surface is configured to be a shape combined by an arc segment and a plane segment, and the plane segment has two segments and the arc segment has one segment, and the arc segment is located between the two plane segments. In one embodiment, the two plane segments can be parallel to each other, and the lengths of the plane segments can be designed as required. In one embodiment, one end of each of the two plane segments of the third inner wall surface is connected with one end of the first inner wall surface and one end of the second inner wall surface respectively, and the one plane segment and the first inner wall surface form a first preset included angle, and the other plane segment and the second inner wall surface form a second preset included angle, and the first preset included angle and the second preset included angle are both greater than the angle of the tip portion. The angle of the tip portion is preferably an acute angle, and the first preset angle and the second preset angle are preferably obtuse angles. In another embodiment, the plane segment and the first inner wall surface, and the plane segment and the second inner wall surface are rounded. The shape of the third inner wall surface does not matter as long as the evaporation flux of the tip portion is higher than the evaporation flux of any other portion of the groove.

[0058] In the preparation method, the good solvent has a boiling point in a range of any value between 100°C and 200°C, for example, 100°C, 120°C, 140°C, 160°C or 180°C. The poor solvent has a boiling point in a range of any value between 100°C and 300°C, for example, 100°C, 150°C, 180°C, 200°C or 280°C. The good solvent is chlorobenzene, o-dichlorobenzene, toluene, m-xylene or mesitylene. The poor solvent is n-dodecane, N,N-dimethylformamide, dimethyl phthalate or dimethyl sulfoxide. In one embodiment, the good solvent is chlorobenzene and the poor solvent is n-dodecane. In a second embodiment, the good solvent is o-dichlorobenzene and the poor solvent is N,N-dimethylformamide. In a third embodiment, the good solvent is toluene and the poor solvent is dimethyl sulfoxide. In a fourth embodiment, the good solvent is mesitylene and the poor solvent is dimethyl phthalate. The organic small molecule can be, for example, C8-BTBT, C10-BTBT, dif-TES-ADT, tips-pen, etc., and the mass ratio of the organic small molecule, the good solvent and the poor solvent in the ink solution can be in a range of any value between 20:1 and 2:1, for example, 20:1, 15:1, 10:1, 5:1 or 2:1.

[0059] Figure 2 A schematic structural flow chart of a method for preparing an organic small molecule single crystal according to an embodiment of the present application is shown. Figure 2 A schematic diagram of printing an ink solution into a groove of a patterned template and crystallizing the ink solution in the groove is shown. Figure 3 A polarized light photo of printing an organic small molecule single crystal on a patterned template according to an embodiment of the present application is shown, with a PPI of 90. Figure 4 A polarized light photo of printing an organic small molecule single crystal on a patterned template according to an embodiment of the present application is shown, with a PPI of 150. Figure 3 and Figure 4 It can be seen that the PPI of the array of organic small molecule single crystals prepared by the method of the present application is much greater than the PPI in the prior art.

[0060] The mechanism of the present application is that, during printing, the presence of the poor solvent produces a delamination effect during volatilization, which causes the good solvent and the poor solvent to delaminate. Since the good solvent has a lower boiling point, it volatilizes preferentially, which causes the concentration of the organic small molecule to rise until crystals precipitate. At the beginning of crystallization, the crystals precipitate on the surface of the poor solvent, which facilitates the diffusion and transport of the solute, thereby obtaining crystals with high crystallization quality and avoiding the generation of a "coffee ring effect".

[0061] The inventors made a control experiment in which the ink solution in step S200 above contains a good solvent and an organic small molecule, but does not contain a poor solvent, and other conditions and methods are completely consistent with the scheme of the present application. Figure 5 A schematic polarized light image of a crystal prepared according to a control experiment of the present application is shown. Figure 6 A schematic polarized light image of a crystal prepared according to a preparation method of an embodiment of the present application is shown. As can be seen from Figure 5 and Figure 6 It can be seen that a serious coffee ring effect is produced in the control experiment, while the double-solvent system in the scheme of the present application produces a uniform single crystal.

[0062] Figure 7 A schematic polarized light image of a crystal prepared according to a preparation method of an embodiment of the present application is shown. As can be seen from Figure 7 It can be seen that, during the evaporation of the ink, due to the faster evaporation speed of the tip, the crystal preferentially nucleates at the tip, and after nucleation, the organic small molecule crystal grows epitaxially on the surface of the poor solvent and covers the entire pattern. Then, as the poor solvent evaporates and floats, the crystal gradually falls and contacts the substrate, and finally a high-crystallinity patterned organic small molecule single crystal can be obtained.

[0063] Figure 8 Simulation calculations of evaporation fluxes of different groove structures and corresponding printing results according to multiple embodiments of the present application are shown. As can be seen from Figure 8 It can be seen that when the evaporation flux of the tip is lower than that of other sites, the obtained crystal has multiple orientations. When the angle of the tip of the pattern is small, the corresponding evaporation flux value is large, and the crystal can preferentially nucleate during the evaporation of the ink, and the obtained crystal will be a single crystal with uniform crystallization.

[0064] In order to verify that the crystal obtained by the scheme of the present application has single crystal properties, the inventors performed transmission electron microscopy (TEM) characterization on the obtained crystal. Figure 9 A transmission electron microscope image of an organic small molecule single crystal prepared according to a preparation method of an embodiment of the present application and electron diffraction images of five selected sites are shown. As can be seen from Figure 9 As shown, clear diffraction spots can be obtained at the five sites, proving that the five sites have high crystalline quality. At the same time, by analyzing, it can be concluded that the orientations of the diffraction spots of the five sites are consistent, indicating that the crystal orientations of the five sites are consistent, which proves from the side that the organic small molecule crystal in the pattern has single crystal properties.

[0065] In order to explore the crystalline quality of organic small molecules such as C8-BTBT, the inventors performed atomic force microscopy (AFM), high-resolution AFM, synchrotron radiation, and cross-sectional TEM characterization on the obtained C8-BTBT single crystal. Figure 10An AFM pattern of a C8-BTBT single crystal according to an embodiment of the present invention is shown. Figure 10 It can be seen that the C8-BTBT crystal has a uniform layered film structure, with each layer having a height of about 3 nm. Figure 11 A high-resolution AFM image of a C8-BTBT single crystal according to an embodiment of the present invention is shown. Figure 11 It can be seen that the crystal has a high degree of crystallinity, and the unit cells exhibit a "human" shaped stacking. Figure 12 A synchrotron radiation data diagram of a C8-BTBT single crystal according to an embodiment of the present invention is shown. Figure 12 As can be seen, the test results show a clear spot distribution, and the crystals in the surface test area have good single crystal properties. Figure 13 A cross-sectional TEM image of a C8-BTBT single crystal according to an embodiment of the present invention is shown. Figure 13 It can be seen that the thickness of the entire crystal is approximately 20 nm.

[0066] In particular, embodiments of the present invention also provide an organic field-effect transistor. Figure 14 A schematic side view of an organic field-effect transistor according to an embodiment of the present invention is shown. Figure 15 A schematic top view of an organic field-effect transistor according to an embodiment of the present invention is shown. Figure 16 It shows Figure 15 A schematic enlarged view of the central area. (See attached image.) Figure 14 to Figure 16 As shown, the organic field-effect transistor includes a Si / SiO2 substrate, a BCB material layer, a C8-BTBT single crystal prepared by the aforementioned preparation method, F4-TCNQs formed on both sides of the C8-BTBT single crystal, and a source and drain formed on the F4-TCNQs.

[0067] Figure 17 The transfer characteristic curve of an organic field-effect transistor according to an embodiment of the present invention is shown. Figure 18 The output characteristic curve of the transistor is shown. Figure 19 Voltage-current plots of organic field-effect transistors according to 50 embodiments of the present invention are shown. Figure 20 The transfer characteristic curves of organic field-effect transistors from 50 embodiments are shown. Figure 17 to Figure 20 It can be seen that the device is a bottom-gate top-contact transistor with a diameter of 11.62 cm. 2 V -1 s -1 and 8.54cm 2 V -1 s -1The average mobility of the printed organic single crystal is higher than that of the organic field effect transistor array. At present, there is no method for printing organic field effect transistor devices with high carrier mobility by one-step pattern-induced method.

[0068] The scheme provided by the inventor provides a new idea for printing high-integration organic patterned single crystals, and lays a foundation for the preparation of sensor, photodetector, flexible wearable device and other devices. It provides strong research potential and practical value for realizing low-cost, high-performance and industrial-scale two-dimensional electronic products.

[0069] At this point, those skilled in the art should recognize that although the present application has been fully shown and described with reference to a number of exemplary embodiments, many other variations or modifications can be directly determined or deduced from the disclosure of the present application in accordance with the principles of the present application without departing from the spirit and scope of the present application. Therefore, the scope of the present application should be understood and recognized as covering all these other variations or modifications.

Claims

1. A method for preparing an organic small-molecule single crystal, characterized by, The method comprises the following steps: a patterned template is prepared by photolithography, and the patterned template has a plurality of grooves arranged in an array; an ink solution of organic small molecules is printed into the plurality of grooves of the patterned template to obtain an organic small molecule single crystal, the ink solution being a solution of organic small molecules dissolved in a good solvent and a poor solvent, the poor solvent having a boiling point higher than that of the good solvent, and the good solvent and the poor solvent being mutually soluble; a shape of each groove is configured to have a tip portion, and a volatilization rate of the ink solution at the tip portion is greater than that at other portions of the groove, so that the ink solution preferentially crystallizes at the tip portion, and as the good solvent volatilizes, a crystal grows epitaxially on a surface of the poor solvent, thereby obtaining the organic small molecule single crystal; a profile surface of the groove is composed of a first inner wall surface, a second inner wall surface, and a third inner wall surface connected in a head-tail manner; cross sections of the first inner wall surface and the second inner wall surface are both straight lines, and the two straight lines intersect to define the tip portion; the third inner wall surface extends towards a direction away from the tip portion, and two ends of the third inner wall surface are connected with the first inner wall surface and the second inner wall surface respectively, and the third inner wall surface defines the other portions; the third inner wall surface is configured to be arc-shaped or a shape combined by an arc segment and a plane segment; a mass ratio of the organic small molecules, the good solvent, and the poor solvent in the ink solution is any value in a range of 20:1-2:

1.

2. The production method according to claim 1, characterized by, the third inner wall surface is configured to be a shape combined by an arc segment and a plane segment, and the plane segment has two segments, and the arc segment has one segment, and the arc segment is located between the two plane segments.

3. The method of claim 2, wherein, one end of each of the two plane segments of the third inner wall surface is connected with one end of the first inner wall surface and one end of the second inner wall surface respectively; one of the plane segments and the first inner wall surface forms a first preset included angle, and the other of the plane segments and the second inner wall surface forms a second preset included angle; the first preset included angle and the second preset included angle are both greater than an angle of the tip portion.

4. The preparation method according to claim 2, characterized in that, corners are formed between the plane segment and the first inner wall surface, and between the plane segment and the second inner wall surface.

5. The production method according to any one of claims 1 to 4, characterized by, the good solvent has a boiling point of any value in a range of 100-200℃; the poor solvent has a boiling point of any value in a range of 100-300℃.

6. The preparation method according to claim 5, characterized in that, the good solvent is chlorobenzene, o-dichlorobenzene, toluene, m-xylene, or mesitylene; the poor solvent is n-dodecane, N,N-dimethylformamide, dimethyl phthalate, or dimethyl sulfoxide.

7. An organic field effect transistor, characterized by The method comprises an organic small molecule single crystal prepared by the preparation method of any one of claims 1-6. The method comprises an organic small molecule single crystal prepared by the preparation method of any one of claims 1-6.

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