PEDOT (poly (3, 4-ethylenedioxythiophene)) ink capable of realizing 3D (three-dimensional) printing, ink preparation method and transistor printed by ink

Abstract

The invention discloses PEDOT (poly (3, 4-ethylenedioxythiophene)) ink capable of realizing 3D (three-dimensional) printing, an ink preparation method and an ink-printed transistor, and belongs to the field of additive manufacturing, the ink comprises PEDOT: PSS (poly (3, 4-ethylenedioxythiophene)) aqueous dispersion serving as a conductive substrate, the printing ink is characterized by further comprising a polysaccharide derivative gel additive hydroxypropyl methyl cellulose, namely HPMC, which is used for inducing formation of a printable hydrogel network structure and accounts for 0.1 wt% of the total mass of PEDOT: PSS, DMSO, which is used for improving the conductivity of the printing ink and accounts for 5wt% of the total mass of PEDOT: PSS, and PEDOT: used for enhancing the adhesion with a flexible substrate. 3-glycidyl ether oxypropyl trimethoxy silane, namely GOPS, accounting for 1 wt% of the total mass of PSS, and a preparation method and a transistor manufactured by the GOPS. According to the novel printing ink disclosed by the invention, the reduction of the conductivity is reduced, the water-based PEDOT can be patterned, and only a simple physical crosslinking process is needed. The production process is simple and can be stored for a long time. And meanwhile, when the material is applied to a flexible organic electrochemical transistor (OECT), the response time is very short.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of additive manufacturing, in particular to a 3D printable PEDOT ink, an ink preparation method and an ink printed transistor. BACKGROUND

[0002] In the context of rapid iteration of 3D printing technology in additive manufacturing, direct ink writing (DIW) 3D printing has become an important development direction in the field of electronic device manufacturing due to its ability to achieve rapid customization of complex structures. The performance of functional conductive ink directly determines the forming quality and application value of such electronic devices. Among them, PEDOT:PSS ink is widely regarded as an ideal material for adapting to direct ink writing 3D printing technology and creating complex structure electronic devices due to its good conductivity and chemical stability, and its application potential has attracted much attention in the industry.

[0003] However, the inherent properties of standard PEDOT:PSS aqueous dispersion are in serious conflict with the process requirements of direct ink writing 3D printing, which has become a key bottleneck restricting its application. Typical PEDOT:PSS dispersion exhibits low viscosity behavior similar to Newtonian fluid, lacking the necessary shear thinning property in the printing process, i.e., the viscosity decreases under shear force to facilitate extrusion, and the viscosity rises to maintain the shape after the shear force is removed. It also does not have enough elastic modulus to support three-dimensional structures. This defect directly leads to the inability of the ink to maintain a stable filament shape during printing, and it is prone to flow, diffusion and collapse, making it difficult to form high-resolution, structurally complete three-dimensional electronic device structures.

[0004] To improve printability, the industry generally uses methods such as adding thickeners, viscosity modifiers or hydrogel networks such as agarose, sodium alginate and polyvinyl alcohol to PEDOT:PSS dispersion to adjust its rheological properties. However, such improvement methods often fall into the dilemma of "trade-off": the introduction of a large number of insulating additives will severely damage the continuity of the PEDOT:PSS conductive network, resulting in a sharp decrease in the conductivity of the printed structure. Even if stable formation is achieved, the lack of conductivity makes it impossible to meet the actual application needs of electronic devices.

[0005] This technical dilemma of balancing printability and conductivity greatly limits the application of PEDOT:PSS ink in the field of direct ink writing 3D printing, and also restricts the low-cost and efficient manufacturing of complex structure conductive electronic devices. Therefore, breaking through the existing material modification ideas and solving the compatibility problem of rheological properties and conductivity of PEDOT:PSS ink is a key requirement for the development of 3D printed electronic device technology. SUMMARY

[0006] The technical problem this invention aims to solve is to provide a 3D-printable PEDOT ink, an ink preparation method, and an ink-printed transistor. It seeks to address the difficulty of simultaneously achieving printability and conductivity in existing materials. By adding a small amount of the polysaccharide derivative gelling additive hydroxypropyl methylcellulose (HPMC), a novel ink is obtained, which minimizes the loss of conductivity, allows for the patterning of water-based PEDOT, and involves only a simple physical cross-linking process. The production process is not only simple but also allows for long-term storage. Furthermore, its application in flexible organic electrochemical transistors (OECTs) demonstrates a very rapid response time.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a 3D printable PEDOT ink, comprising a PEDOT:PSS aqueous dispersion as a conductive matrix, characterized in that: it further comprises 0.1 wt% of a polysaccharide derivative gel additive hydroxypropyl methylcellulose (HPMC) for inducing the formation of a printable hydrogel network structure, 5 wt% of DMSO for improving the conductivity of the ink, and 1 wt% of 3-glycidyl etheroxypropyltrimethoxysilane (GOPS) for enhancing adhesion to flexible substrates.

[0008] A method for preparing 3D printable PEDOT ink, the specific steps of which are as follows:

[0009] Step 1: Mix PEDOT:PSS aqueous dispersion with 5wt% DMSO and stir until homogeneous;

[0010] Step 2: Add 1 wt% GOPS and stir to homogenize;

[0011] Step 3: Slowly add 0.1wt% HPMC powder and magnetically stir at room temperature (25°C) for 2 hours to form a homogeneous hydrogel ink;

[0012] Step 4: Sonicate the homogeneous hydrogel ink for 30 minutes to eliminate air bubbles, and then squeeze it out through a filter syringe to eliminate small particles;

[0013] Step 5: Preparation complete.

[0014] A transistor 3D printed using 3D-printable PEDOT ink, as shown in the figure, consists of a source, a drain, and a gate. The electrodes are all printed on a flexible substrate using a 3D printing method. The structure from bottom to top is a PET substrate, a silver paste conductive layer, a carbon paste protective layer, and an insulating layer. The organic semiconductor layer is a PEDOT:PSS gel as the OECT active layer. An inert material is provided as a silver paste protective layer, covering the junction between the source and drain silver electrodes and the semiconductor layer.

[0015] The steps for fabricating transistors using ink 3D printing are as follows:

[0016] S1. Silver paste is deposited onto a PET substrate using a 3D printer via contactless technology to prepare electrodes and circuits. The electrode layer of the electrochemical transistor is obtained by drying and curing at 100°C for 30 minutes. The electrode layer includes a source, a drain, and a gate, with a gap left in the channel between the source and drain.

[0017] S2. Protect the source and drain of the device obtained in step S1 by covering them with carbon paste, with an aspect ratio of 7:30 at the channel.

[0018] S3. Print a semiconductor active layer at the device channel obtained in step S2. The semiconductor active layer is PEDOT:PSS ink.

[0019] S4. Protect the exposed electrode portion of the device obtained in step S3 with an insulating layer;

[0020] S5. Print a layer of gel electrolyte onto the channel of the device obtained in step S4.

[0021] S6. An electrochemical transistor capable of long-term response has been fabricated.

[0022] A further improvement of the technical solution of the present invention is that the circuit width in preparation method S1 is 0.2 mm.

[0023] A further improvement to the technical solution of the present invention is that: in the preparation method S2, the carbon paste protective layer is deposited onto the silver circuit by 3D printing carbon paste, the channel between the source and drain is 70um in length and 300um in width, and then dried and cured at 100°C.

[0024] The technological advancements achieved by this invention due to the adoption of the above technical solutions are as follows:

[0025] 1. Compared to traditional spin coating processes, 3D printing saves more material and significantly reduces costs. Furthermore, 3D printing can integrate PEDOT electrodes, silver paste, carbon paste, and semiconductor layers in a single process. The gel ink of this invention uses a fully water-based system, allowing it to be applied to human skin for use in biosensors.

[0026] 2. Traditional PEDOT:PSS gel inks require a large amount of gelling agent to form a printable structure; excessive amounts significantly reduce conductivity. In contrast, this invention requires only 0.1 wt% HPMC to achieve shear-refined hydrogels with a printed linewidth <60 micrometers. Furthermore, Raman and Fourier transform infrared spectroscopy demonstrates that only simple physical cross-linking occurs.

[0027] 3. This invention innovatively applies poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate (PEDOT:PSS) gel material to the fabrication of organic electrochemical transistors (OECTs). Based on the excellent aqueous stability of the PEDOT:PSS dispersion, the fabricated devices exhibit outstanding stability in cyclic pulse testing, capable of continuous operation for several days without significant performance degradation. Furthermore, both the ink system based on this material and the OECTs fabricated from it demonstrate excellent long-term storage stability. This characteristic significantly improves the reliability of the devices in practical applications. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a schematic diagram of the transistor structure printed with ink according to the present invention;

[0030] Figure 2 This is a graph showing the output characteristics of the 3D-printed organic electrochemical transistor (OECT) based on the gel-state PEDOT:PSS semiconductor layer of this invention.

[0031] Figure 3 This invention uses gel PEDOT as the organic semiconductor layer to 3D print organic electrochemical transistors with transfer curves and transconductance (6.7 mS) at Vg = 0.8 V;

[0032] Figure 4 This is a transient curve of an organic electrochemical transistor with a source-drain voltage of 0.6V, using gel PEDOT as the organic semiconductor layer in this invention.

[0033] Figure 5 This is the Fourier transform infrared spectrum curve of the physical cross-linking verified by this invention;

[0034] Figure 6 This is the Raman spectrum curve used to verify the physical cross-linking of this invention. Detailed Implementation

[0035] The present invention will be further described in detail below with reference to embodiments:

[0036] A 3D-printable PEDOT ink comprises a PEDOT:PSS aqueous dispersion as a conductive matrix, and further comprises 0.1 wt% of a polysaccharide derivative gelling additive, hydroxypropyl methylcellulose (HPMC), for inducing the formation of a printable hydrogel network structure; 5 wt% of DMSO, for improving the ink's conductivity; and 1 wt% of 3-glycidyl etheroxypropyltrimethoxysilane (GOPS), for enhancing adhesion to flexible substrates. The preparation method is as follows:

[0037] Step 1: Mix PEDOT:PSS aqueous dispersion with 5wt% DMSO and stir until homogeneous;

[0038] Step 2: Add 1 wt% GOPS and stir to homogenize;

[0039] Step 3: Slowly add 0.1wt% HPMC powder and magnetically stir at room temperature (25°C) for 2 hours to form a homogeneous hydrogel ink;

[0040] Step 4: Sonicate the homogeneous hydrogel ink for 30 minutes to eliminate air bubbles, and then squeeze it out through a filter syringe to eliminate small particles;

[0041] Step 5: Preparation complete.

[0042] The above ink can be loaded into a 3D printing syringe to print OECT (Optical Electron Conversion) needles with a diameter of 60 micrometers. This ink can also be used to 3D print transistors, producing transistors such as... Figure 1 As shown, the electrode consists of a source, drain, and gate electrode, all of which are 3D printed onto a flexible substrate. From bottom to top, the structure comprises a PET substrate, a silver paste conductive layer, a carbon paste protective layer, and an insulating layer. The organic semiconductor layer is a PEDOT:PSS gel as the OECT active layer. Because the organic semiconductor layer (PEDOT:PSS) readily undergoes a redox reaction with the silver paste via counter-ion exchange, the transient response of the organic electrochemical transistor is significantly slowed. This invention employs an inert material as the silver paste protective layer to suppress this reaction, covering the interface between the source / drain silver electrodes and the semiconductor layer. Figure 1 As shown. Because each layer of material needs to be printed only once, and each layer is a gel or viscous paste, the prints are extremely thin to facilitate subsequent application in biosensors. For example... Figure 1 As shown, the blue areas are due to ink buildup at the channel edges caused by printing onto the carbon paste structure first during the deposition process. The yellow areas represent electrolyte deposition that preferentially fills the blank areas near the upper layer of PEDOT.

[0043] The transistor adopts a top-gate structure, which can be seen from the cross-section from bottom to top:

[0044] The bottom layer (silver): Low cost, and silver's excellent conductivity makes it suitable for fabricating source / drain and gate electrodes. The circuit leads are also connected using silver paste printing, leaving a 1cm trench at the source / drain contact point. Figure 1 The bottom layer;

[0045] The second layer (carbon): An inert electrode is used. During the process of applying the gate voltage to PEDOT:PSS at the channel, the ions in PEDOT, PSS and the silver electrode undergo a redox reaction, which makes the transient time particularly slow. Therefore, a carbon circuit is printed at the source and drain to cover the silver circuit at the channel, leaving a 70-micron channel.

[0046] The third layer (PEDOT material): fills the channel of the OECT as an active material, deposited in the region between the source and drain.

[0047] The fourth layer (insulating layer material): As an isolation layer, it physically isolates the silver circuit and the electrolyte, preventing direct point contact between the silver and the electrolyte.

[0048] Fifth layer (electrolyte material): The electrolyte is printed on the top layer and connected to the gate electrode. By applying voltage to the gate electrode, positive ions in the electrolyte are driven to be incorporated into PEDOT, thereby causing a dedoping process.

[0049] Electrochemical transistors adopt the traditional three-electrode shape, corresponding to the electrodes in the three-electrode system of an electrochemical workstation. OECT is a solid-state electrochemical cell that miniaturizes and integrates the working electrode (corresponding to the channel in OECT), counter electrode (source / drain), and reference electrode (gate) in an electrochemical workstation onto the same substrate.

[0050] Electrochemical transistors drive the top layer by controlling the gate voltage and applying a positive gate voltage. Figure 1 The yellow portion of the electrolyte contains positive ions that enter the organic semiconductor material. Figure 1 The light blue portion undergoes a dedoping process, which reduces the conductivity at the channel and causes a change in the electron current in the source-drain circuit.

[0051] The three-electrode system in an electrochemical workstation drives the ions in the electrolyte to undergo a double-layer redox process at the working electrode interface by controlling the voltage between the reference electrode and the working electrode, thereby changing the state of the working electrode.

[0052] Both are based on the electrolyte interface, where ion-electron coupling processes occur.

[0053] The steps are as follows:

[0054] S1. Silver paste is deposited onto a PET substrate using a 3D printer via contactless technology to fabricate electrodes and circuits. The substrate is then dried and cured at 100°C for 30 minutes to obtain the electrode layers (source, drain, and gate) of the electrochemical transistor, leaving a gap in the channel between the source and drain. The circuit width in fabrication method S1 is 0.2 mm.

[0055] S2. Protect the source and drain electrodes of the device obtained in step S1 with carbon paste, with an aspect ratio of 7:30 at the channel. The carbon paste protective layer in step S2 is prepared by 3D printing carbon paste onto the silver circuit. The printed channel between the source and drain is 70µm long and 300µm wide, and then dried and cured at 100°C.

[0056] S3. Print a semiconductor active layer (PEDOT: PSS ink) on the channel of the device obtained in step S2;

[0057] S4. Protect the exposed electrode portion of the device obtained in step S3 with an insulating layer.

[0058] S5. A layer of gel electrolyte is printed on the channel of the device obtained in step S4 to fabricate an electrochemical transistor that can respond for a long time.

[0059] The printed electrochemical transistors were subjected to performance checks, such as... Figure 2 The diagram shows the output characteristic curves of a 3D-printed organic electrochemical transistor (OECT) based on a gel-state PEDOT:PSS semiconductor layer, using PEDOT gel as the organic semiconductor layer. Test results demonstrate that the device exhibits good current output characteristics under gate voltage regulation, and its output curve displays typical OECT operating characteristics. Figure 3 This invention uses gel PEDOT as the organic semiconductor layer to 3D print organic electrochemical transistors with transfer curves and transconductance (6.7mS) at Vg = 0.8V. Figure 4 This invention uses PEDOT gel as the organic semiconductor layer and 3D prints an organic electrochemical transistor with a source-drain voltage of 0.6V. The response time is ON: 170ms OFF: 170ms. Figure 5 This invention verifies the Fourier transform infrared (FTIR) spectral curves of the physical crosslinking. To investigate the crosslinking mechanism of PEDOT:PSS and HPMC, we performed FTIR tests, using spin-coated thin films for preparation and ATR (Automatic Transformer) infrared spectroscopy. The results show that HPMC molecules contain abundant hydroxyl groups. When a small amount of HPMC is introduced into the PEDOT system, a peak is observed at 1532 cm⁻¹. -1 A slight redshift occurs in the C=C double bond vibration peak at 3500 cm⁻¹, indicating that the conjugated electronic structure of PEDOT is perturbed. Meanwhile, at 3500 cm⁻¹... -1No significant shift of the hydroxyl characteristic peak was observed nearby. This phenomenon indicates that no significant chemical interaction occurred between the two, but only a physical cross-linking structure was formed. Figure 6 The present invention provides a Raman spectral curve to verify the physical cross-linking. To further verify the cross-linking form, we also conducted Raman spectroscopy tests. The film was also spin-coated onto a glass substrate, and using a 633nm laser, we observed a slight red shift in the characteristic peaks at 1570cm⁻¹ and 1630cm⁻¹ after the addition of HPMC. This is because the hydroxyl-rich structure in the HPMC molecule and the π-electron system between the PEDOT chain may have undergone weak physical adsorption or stacking. This interaction is sufficient to slightly change the vibrational environment of the C=C bond in PEDOT without generating new chemical bonds, further proving the physical cross-linking structure. Figure 5 Figure 6 Both analyses focused on inks, specifically infrared and Raman analyses performed on glass substrates via spin-coating. The spectra revealed that the physical crosslinking, rather than chemical crosslinking, between PEDOT:PSS and HPMC offers a series of significant advantages, demonstrating outstanding performance in the fabrication of flexible and stretchable electronic devices, thermoelectric devices, and biosensors. The high electrical conductivity of PEDOT:PSS stems from the integrity of its conjugated π-bond structure, while chemical crosslinking can disrupt this structure, leading to a decrease in conductivity. In contrast, physical crosslinking offers significant advantages in processing: it eliminates the need for harsh reaction conditions, making ink processing simpler, safer, and more environmentally friendly. Furthermore, physical crosslinking can impart rheological properties suitable for 3D printing while maintaining the intrinsic electrical properties of PEDOT:PSS molecular chain structure, making it highly suitable for printed electronics.

[0060] 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 3D-printable PEDOT ink, comprising a PEDOT:PSS aqueous dispersion as a conductive matrix, characterized in that: It also includes 0.1 wt% of PEDOT:PSS total mass of polysaccharide derivative gel additive hydroxypropyl methylcellulose (HPMC) for inducing the formation of printable hydrogel network structures, 5 wt% of PEDOT:PSS total mass of DMSO for improving ink conductivity, and 1 wt% of PEDOT:PSS total mass of 3-glycidyl etheroxypropyltrimethoxysilane (GOPS) for enhancing adhesion to flexible substrates.

2. A method for preparing 3D printable PEDOT ink as described in claim 1, characterized in that: The specific steps are as follows: Step 1: Mix PEDOT:PSS aqueous dispersion with 5wt% DMSO and stir until homogeneous; Step 2: Add 1 wt% GOPS and stir to homogenize; Step 3: Slowly add 0.1wt% HPMC powder and magnetically stir at room temperature (25°C) for 2 hours to form a homogeneous hydrogel ink; Step 4: Sonicate the homogeneous hydrogel ink for 30 minutes to eliminate air bubbles, and then squeeze it out through a filter syringe to eliminate small particles; Step 5: Preparation complete.

3. A transistor 3D printed using the 3D-printable PEDOT ink as described in claim 1, characterized in that: It consists of a source, a drain, and a gate. The electrodes are printed on a flexible substrate using 3D printing. The structure from bottom to top is a PET substrate, a silver paste conductive layer, a carbon paste protective layer, and an insulating layer. The organic semiconductor layer is PEDOT:PSS gel as the OECT active layer. An inert material is provided as a silver paste protective layer, covering the junction between the source and drain silver electrodes and the semiconductor layer.

4. A 3D-printable PEDOT ink-printable transistor according to claim 3, characterized in that: The steps for fabricating transistors using ink 3D printing are as follows: S1. Silver paste is deposited onto a PET substrate using a 3D printer via contactless technology to prepare electrodes and circuits. The electrode layer of the electrochemical transistor is obtained by drying and curing at 100°C for 30 minutes. The electrode layer includes a source, a drain, and a gate, with a gap left in the channel between the source and drain. S2. Protect the source and drain of the device obtained in step S1 by covering them with carbon paste, with an aspect ratio of 7:30 at the channel. S3. Print a semiconductor active layer at the device channel obtained in step S2. The semiconductor active layer is PEDOT:PSS ink. S4. Protect the exposed electrode portion of the device obtained in step S3 with an insulating layer; S5. Print a layer of gel electrolyte onto the channel of the device obtained in step S4. S6. An electrochemical transistor capable of long-term response has been fabricated.

5. The ink-printed transistor according to claim 4, characterized in that: In fabrication method S1, the circuit width is 0.2 mm.

6. The ink-printed transistor according to claim 4, characterized in that: In preparation method S2, the carbon paste protective layer is deposited onto the silver circuit by 3D printing. The channel between the source and drain is 70 μm long and 300 μm wide, and then dried and cured at 100 °C.

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