A method for preparing a conjugated polymer ultrathin film with high toughness and high electrical conductivity

Abstract

The application discloses a method for preparing a conjugated polymer ultrathin film with high toughness and high conductivity, and comprises the following steps: dissolving a nucleating agent and a conjugated polymer in a solvent, ultrasonic treatment, and film forming on the prepared mixed solution to obtain the conjugated polymer ultrathin film. The nucleating agent is added to provide a nucleation surface for the conjugated polymer, accelerate the crystallization of the conjugated polymer, and generate a large number of connecting molecules. Ultrasonic treatment is adopted to cause the concentration fluctuation of the conjugated polymer solution, form a relatively concentrated area and a relatively dilute area in the solution, and meanwhile, the ultrasonic treatment has the effect of disentangling the entangled chains of the polymer.

Description

Technical Field

[0001] This invention belongs to the field of conjugated polymer film modification technology, specifically, it relates to a method for preparing conjugated polymer ultrathin films with high toughness and high electrical conductivity. Background Technology

[0002] Ultrathin films, consisting of only one or a few molecular layers, are typically referred to as two-dimensional materials and possess structures and properties not found in bulk three-dimensional materials. Organic conjugated ultrathin films exhibit outstanding flexibility and transparency, showing broad application prospects in wearable electronics, stretchable field-effect transistors, and artificial intelligence. Compared to small organic conjugated molecules, conjugated polymers offer better mechanical flexibility, can be solution-processed into films, and exhibit stable and reproducible device performance. Furthermore, interlayer diffusion does not occur during device fabrication; therefore, conjugated polymer ultrathin films with thicknesses below 10 nm have attracted widespread attention. However, due to thickness limitations and substrate influences, conjugated polymer ultrathin films exhibit lower modulus and glass transition temperature, but improved tensile properties compared to bulk three-dimensional materials. However, similar to three-dimensional bulk materials, the carrier transport performance and mechanical properties of conjugated polymer ultrathin films are closely related to the arrangement and aggregation structure of polymer molecules. The improvement of crystallinity and molecular order in ultrathin films is beneficial to the improvement of electrical performance, but at the same time, it is accompanied by the reduction of tensile properties. How to prepare conjugated polymer ultrathin films with excellent electrical and tensile properties to meet the needs of practical applications is a key issue of concern.

[0003] In recent years, people have developed different methods for preparing conjugated polymer ultrathin films according to their needs. The main methods are as follows: (1) Langmuir-Blodgett (LB) method, where conjugated polymers form ultrathin films at the water / organic solvent interface. (2) Spin coating method, where conjugated polymer ultrathin films can be generated by directly spin coating a dilute polymer solution, or conjugated polymer nanowires can be prepared in a dilute solution and then spin coated to prepare ultrathin films with nanowire aggregation structures. (3) Dip coating method, where conjugated polymers generate nanowire aggregation structures in a dilute solution, and then the substrate is immersed in the solution and slowly pulled up to generate conjugated polymer ultrathin films with oriented nanowire structures on the substrate. The substrate pulling rate affects the thickness and orientation of the ultrathin film. (4) Solution shearing method, where a dilute polymer solution is dropped onto the substrate and then quickly scraped into a film with a doctor blade. The polymer is subjected to shear force along the scraping direction to form an oriented ultrathin film. The scraping rate of the doctor blade affects the thickness and orientation of the ultrathin film.

[0004] However, all of the above methods have limitations. The LB method requires the conjugated polymer to be amphiphilic, limiting the preparation of hydrophobic conjugated polymer ultrafilms. Ultrafilms prepared by dip coating and solution shearing methods are anisotropic and unsuitable for preparing isotropic conjugated polymer ultrafilms. Spin coating is the most commonly used method for preparing isotropic conjugated polymer ultrafilms. Because ultrafilms are to be prepared, the polymer solution in spin coating is usually an extremely dilute solution (concentration far below the critical sub-concentration concentration c*). When the solvent is a good solvent for the polymer, the crystallinity of the ultrafilm obtained by spin coating is low, requiring post-treatment methods such as annealing to optimize the aggregated structure and improve crystallinity. However, the ultrafilm thickness is extremely low, restricting polymer molecular movement and limiting the improvement in crystallinity. Furthermore, the orientation of the lamellar crystals in the ultrafilm is greatly affected by the substrate, making it difficult to prepare ultrafilms with ideal aggregated structures, resulting in poor electrical properties. When the solvent is a marginal solvent or a non-good solvent is added to a good solvent solution, the conjugated polymer ages and aggregates in the solution to form nanowires. After spin coating, an ultrathin film with a nanowire structure is obtained. This ultrathin film has high carrier transport performance but poor tensile properties. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for preparing conjugated polymer ultrathin films, the method comprising:

[0006] The nucleating agent and conjugated polymer are dissolved in a solvent, and the mixture is sonicated to form a film, thus preparing a conjugated polymer ultrathin film.

[0007] According to an embodiment of the present invention, the nucleating agent is at least one selected from the following: disodium bicyclo[2.2.1]heptane-2,3-dicarboxylate (HPN-68L), dibenzyl sorbitol (DBS, Millad 3905), (1,3:2,4)-di(p-methyldibenzyl)sorbitol (MDBS, Millad 3940), di(3,4-dimethyldibenzyl)sorbitol (DMDBS, Millad 3988), 1,3,5-tri-tert-butyltriphenylamine (BTA, Ciba's transparent nucleating agent IRGACLEAR XT386), preferably disodium bicyclo[2.2.1]heptane-2,3-dicarboxylate (HPN-68L).

[0008] According to an embodiment of the present invention, the conjugated polymer is at least one selected from poly(3-alkylthiophene) (P3AT), polyfluorene, polyselenophene, and poly(p-phenylenevinylene), preferably poly(3-alkylthiophene). ； The poly(3-alkylthiophene) is, for example, poly(3-hexylthiophene) (P3HT). The conjugated polymer of the present invention is crystallizable, and chain folding can occur during crystallization.

[0009] According to embodiments of the present invention, the solvent is a pure solvent such as chloroform or tetrahydrofuran, or a mixed solvent of an edge solvent and a good solvent. The edge solvent is dichloromethane (DCM) or toluene (Tol), and the good solvent is chlorobenzene (CB) or o-dichlorobenzene (ODCB), such as a mixed solvent of dichloromethane and chlorobenzene, or a mixed solvent of toluene and o-dichlorobenzene. The volume ratio of the edge solvent to the good solvent is 99-60:1-40, preferably 95-80:5-20, and exemplary ratios are 99:1, 95:5, 90:10, 85:15, 80:20, 75:25, 70:30, 65:35, or 60:40. Also exemplary, the volume ratio of toluene to o-dichlorobenzene is 99-60:1-40, preferably 95-80:5-20, and exemplary ratios are 95:5, 90:10, 85:15, or 80:20.

[0010] According to an embodiment of the present invention, the nucleating agent is 1-10 wt% of the conjugated polymer, preferably 3-6 wt%, and exemplaryly 3.0 wt%, 3.5 wt%, 4.0 wt%, 4.5 wt%, 5.0 wt%, 5.5 wt%, or 6.0 wt%.

[0011] According to an embodiment of the present invention, the concentration of the mixed solution (i.e., the concentration of the nucleating agent and the conjugated polymer in the solvent) is 0.1-5 mg / mL, preferably 0.5-3 mg / mL.

[0012] According to an embodiment of the present invention, the ultrasound duration is 1-200s, preferably 10s-150s, and exemplary durations are 10s, 40s, 50s, 70s, 80s, 100s, 120s, 140s or 150s.

[0013] According to an embodiment of the present invention, the temperature of the ultrasound is 15-35°C, for example, room temperature.

[0014] According to an embodiment of the present invention, the thickness of the conjugated polymer ultrafilm is less than 10 nm.

[0015] According to an embodiment of the present invention, a thin film can be formed by spin coating; the spin coating speed is 500-5000 rpm, preferably 1000-4000 rpm; exemplary speeds are 1000 rpm, 1500 rpm, 2000 rpm, 2500 rpm, 3000 rpm, 3500 rpm or 4000 rpm.

[0016] According to an embodiment of the present invention, the spin coating time is 0.5-5 min, preferably 1-3 min.

[0017] The solution is prepared using a pure solvent or a mixture of an edge solvent and a good solvent, both with suitable solubility for the conjugated polymer. The following explanation uses a mixture of an edge solvent and a good solvent as an example. When the solvent is an edge solvent, the solubility of the conjugated polymer is low at lower temperatures (e.g., room temperature). After ultrasonication, the crystallinity of the conjugated polymer is high under the action of the nucleating agent, resulting in a significant reduction in the tensile properties of the prepared film. Therefore, this invention uses a mixture of an edge solvent and a good solvent to increase the solubility of the conjugated polymer. As the volume content of the good solvent increases, the crystallization ability of the conjugated polymer decreases during spin-coating, the crystallization induction period increases, the crystallization rate decreases, and the effect of concentration fluctuations caused by ultrasonication on the crystallization of the conjugated polymer gradually weakens with the increase of the crystallization induction period, leading to a decrease in the crystallinity of the conjugated polymer. When the content of the good solvent is too high, the crystallization of the conjugated polymer is too slow, the induction period is too long, and the effect of ultrasonication on crystallization almost disappears completely. At this point, the crystallinity of the conjugated polymer ultrafilm is low, and the conductivity is also low. This invention employs a volume ratio of edge solvent to good solvent of 90:10-80:20. After ultrasonication of a dilute solution of a mixture of conjugated polymer and nucleating agent, the solution concentration fluctuates. Upon stopping the ultrasonication, the spin-coated ultrafilm exhibits a uniform distribution of high-concentration and low-concentration regions. In the more concentrated regions, the nucleating agent provides a nucleation surface for the conjugated polymer, effectively promoting its nucleation and crystallization. The longer the ultrasonication time, the higher the concentration of both conjugated polymer and nucleating agent in the more concentrated regions, resulting in faster crystallization, a greater number of crystal nuclei, a higher number of connecting molecules, and higher crystallinity. In the low-concentration regions, as the solvent evaporates, the concentration of the conjugated polymer gradually increases. The nucleating agent provides a nucleation surface, and the number of connecting molecules between ordered regions after crystallization is also greater than that between ordered regions of a pure conjugated polymer (without a nucleating agent) under the same conditions. High crystallinity and a large number of connecting molecules facilitate carrier transport and improve electrical performance; however, high crystallinity makes the material brittle, while a large number of connecting molecules enhances the tensile properties of the ultrafilm. These factors collectively influence the tensile properties of the ultrafilm. The number of linking molecules needs to be sufficiently high to offset the adverse effects of high crystallinity on tensile properties. The longer the ultrasonic time, the higher the concentration of conjugated polymer and nucleating agent in the concentrated regions, resulting in a greater number of linking molecules. However, excessively long ultrasonic times lead to too few conjugated polymer chains in low-concentration regions, making crystallization difficult and prone to forming defects that hinder charge carrier transport, thus reducing conductivity and tensile properties. This invention induces concentration fluctuations in a dilute conjugated polymer solution through ultrasonication. After spin-coating, the nucleating agent accelerates conjugated polymer crystallization in the concentrated regions, increasing crystallinity and the number of linking molecules. In the dilute regions, as the solvent evaporates, the nucleating agent also provides a nucleation surface to accelerate crystallization. The number of linking molecules generated is greater than that of pure conjugated polymer under the same crystallization conditions. The numerous linking molecules in the conjugated polymer ultrafilm play a role in transporting charge carriers and resisting stress, resulting in high toughness and high conductivity in the prepared conjugated polymer ultrafilm.

[0018] The beneficial effects of this invention are:

[0019] Compared with existing technologies, the method of this invention does not require post-treatment such as annealing of the conjugated polymer ultrafilm, thus avoiding problems such as difficulty in molecular chain diffusion, difficulty in improving crystallinity, and significant influence of the substrate on the crystal structure of the conjugated polymer ultrafilm due to thickness limitations. Furthermore, this invention eliminates the need to prepare nanowire structures in solution before spin coating, avoiding poor tensile properties of the ultrafilm. This invention uses a mixed solvent of edge solvent and good solvent to prepare a dilute solution of the nucleating agent and conjugated polymer, which, after ultrasonic treatment, can be spin-coated to prepare high-toughness, high-conductivity conjugated polymer ultrafilms. The operation is simple and the experiments are highly reproducible.

[0020] The conjugated polymer ultrafilms prepared by this invention exhibit superior electrical and tensile properties compared to ultrafilms treated by traditional annealing methods.

[0021] This invention adds a nucleating agent to provide a nucleation surface for the conjugated polymer, accelerates the crystallization of the conjugated polymer, and generates a large number of connecting molecules; it uses ultrasonic treatment to cause fluctuations in the concentration of the conjugated polymer solution, forming concentrated and dilute regions in the solution; at the same time, ultrasound also has the effect of detangling polymer entanglement chains.

[0022] This invention allows for the control of the solubility of the conjugated polymer by selecting a pure solvent or changing the ratio of mixed solvents, thereby enabling the polymer to have a suitable crystallization rate during spin coating and resulting in a conjugated polymer ultrafilm with appropriate crystallinity, thus exhibiting excellent electrical and tensile properties. Attached Figure Description

[0023] Figure 1 a is the DSC cooling curve of the polymer powder in Example 1 (ultrasound 0s), Examples 5-6, and Comparative Example 1.

[0024] Figure 1 b is the fraction of connected molecules in P3HT from the ultrasound 0s in Example 1, Examples 5-6, and Comparative Example 1 (f) TC )Calculation results graph.

[0025] Figure 2 This is a graph showing the change in specific viscosity and solution concentration of the P3HT toluene solution in Examples 7-11.

[0026] Figure 3 The graph shows the change in thickness of the conjugated polymer ultrafilm with ultrasonic time for different volume ratios of toluene and o-dichlorobenzene in Examples 1-4.

[0027] Figure 4 a is a graph showing the change in conductivity of the P3HT film as a function of ultrasonic time in Comparative Example 1 and Comparative Example 2.

[0028] Figure 4 b is a graph showing the change in conductivity of P3HT thin films and conjugated polymer ultrathin films with nucleating agent content in Comparative Examples 1 and 3.

[0029] Figure 4 c is a graph showing the change in conductivity of the P3HT thin film subjected to 0 s of ultrasonication as a function of toluene content in Comparative Examples 1 and 4.

[0030] Figure 5 The graph shows the changes in conductivity and elongation at break of the P3HT film and conjugated polymer ultrafilm in Comparative Example 1 and Examples 1-4 as a function of ultrasonic time.

[0031] Figure 6 The graph shows the changes in conductivity and elongation at break of the P3HT films subjected to ultrasound for 40s, 80s, and 150s in Comparative Example 4 as a function of toluene content.

[0032] Figure 7 The graph shows the changes in electrical conductivity and elongation at break of the modified annealed film in Comparative Example 5.

[0033] Figure 8 The σ values ​​of the conjugated polymer ultrafilm (P3HT5-80-80s) after 80s of ultrasonication in Example 3 and the P3HT film (P3HT0-100-0s) in Comparative Example 1 are... N The ratio of the initial conductivity σ0 (i.e., the conductivity of the ultrathin film at 0 cycles) to the number of cycles is plotted.

[0034] Figure 9 a represents comparative examples 1, 6-8 (i.e.) Figure 9 In Example 2, the ultrasonic waves were 80s and 12-14s respectively for the ultrathin film (i.e., P3HT) and the ultrathin film (i.e., P3HT). Figure 9 The thickness of P3HT-HPN varies with spin coating rate;

[0035] Figure 9 b represents comparative examples 1, 6-8 (i.e.) Figure 9 In Example 2, the ultrasonic waves were 80s and 12-14s respectively for the ultrathin film (i.e., P3HT) and the ultrasonic waves were 12-14s respectively. Figure 9 The electrical conductivity of P3HT-HPN varies with spin coating rate;

[0036] Figure 9 c represents comparative examples 1, 6-8 (i.e.) Figure 9 In Example 2, the ultrasonic waves were 80s and 12-14s respectively for the ultrathin film (i.e., P3HT) and the ultrasonic waves were 12-14s respectively. Figure 9 The graph shows the change in elongation at break of P3HT-HPN with spin coating rate. Detailed Implementation

[0037] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention, and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0038] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0039] Material:

[0040] Conjugated polymer: poly(3-hexylthiophene) (P3HT), nucleating agent: disodium bicyclo[2.2.1]heptane-2,3-dicarboxylic acid (HPN-68L), solvent: a mixture of toluene and o-dichlorobenzene.

[0041] Example 1

[0042] P3HT and HPN-68L were dissolved together in a mixed solvent of toluene and o-dichlorobenzene (volume ratio of toluene to o-dichlorobenzene was 100:0) and stirred until homogeneous. The concentration of the mixed solution (i.e., the concentration of P3HT and HPN-68L in the mixed solvent) was 1.0 mg / mL, and the mass of HPN-68L was 5.0 wt% of P3HT. The mixed solution was sonicated at room temperature for 0 s, 40 s, 80 s and 150 s, respectively. Immediately after sonication was stopped, the mixture was spin-coated into a film at a spin speed of 1000 rpm for 1 min to prepare a conjugated polymer ultrathin film.

[0043] In this process, the mixed solution with an ultrasonic time of 0 seconds (i.e., no ultrasonic treatment) is dried to form a polymer powder, which is then used for DSC testing.

[0044] Based on the nucleating agent content, the volume content of toluene in the mixed solvent, and the ultrasonic time, the conjugated polymer ultrafilm is named P3HTa-bc, where a represents the nucleating agent content, b represents the volume content of toluene in the mixed solvent, and c represents the ultrasonic time. For example, P3HT0-100-0s indicates that the nucleating agent content is 0, the solvent is pure toluene, and there is no ultrasonic treatment; another example is P3HT5-90-80s, which indicates that the nucleating agent HPN-68L content is 5.0 wt% of P3HT, the volume ratio of toluene to o-dichlorobenzene in the mixed solvent is 90:10, and the ultrasonic time is 80s.

[0045] Examples 2-4

[0046] The difference between Examples 2-4 and Example 1 is that the volume ratio of toluene to o-dichlorobenzene in the mixed solvent is 90:10, 80:20, and 70:30, respectively; and the mixed solution is ultrasonicated at room temperature for 0s, 40s, 80s, and 150s, respectively.

[0047] Examples 5-6

[0048] The difference between Examples 5-6 and Example 1 is that HPN-68L contains 1.0 wt% and 2.0 wt% of P3HT, respectively, and the polymer solution is not ultrasonicated.

[0049] The mixed solution is dried to form a polymer powder, which is then used for DSC testing.

[0050] Comparative Example 1

[0051] P3HT was dissolved in toluene and stirred until homogeneous, with a solution concentration of 1.0 mg / mL. The P3HT solution was then spin-coated into a film at a spin-coating rate of 1000 rpm for 1 min, resulting in a P3HT film P3HT0-100-0s.

[0052] The P3HT film has an electrical conductivity of 2.7 ± 0.1 S / cm and an elongation at break (COS) of 82% ± 12%.

[0053] The difference between Comparative Example 1 and Example 1 is that HPN-68L was not added in Comparative Example 1, that is, the mass of HPN-68L was 0 of P3HT, and the polymer solution was not sonicated.

[0054] In this process, the P3HT solution is dried to form a polymer powder, which is then used for DSC testing.

[0055] The polymer powders from Example 1 (ultrasonic 0s), Examples 5-6, and Comparative Example 1 were subjected to DSC testing. The test results are as follows: Figure 1 As shown in Figure a, the results indicate that the crystallization temperature Tc of the conjugated polymer P3HT increased after the addition of different amounts of HPN-68L, suggesting that HPN-68L has a nucleation effect on P3HT.

[0056] Figure 1 b is the fraction of linking molecules in the conjugated polymer P3HT with different HPN-68L contents in Examples 5-6 and Comparative Example 1, where the ultrasound was performed for 0 seconds in Example 1. TCThe calculation results are shown in the figure. We used the Huang-Brown model to calculate the change in the number of linking molecules in P3HT with HPN-68L added [see Huang, Y.; Brown, N. The effect of molecular weight on slow crack growth in linear polyethylene homopolymers. J. Mater. Sci. 1988, 23, 3648-3655; and Huang, Y.; Brown N. Dependence of slow crack growth in polyethylene on butyl branch density: morphology and theory. J. Polym. Sci. Part B: Polym. Phys. 1991, 29, 129-137.]. The relevant parameters were obtained from DSC tests and parameters in the literature [see Gu, K.; Snyder CR; Onorato, J.; Luscombe, CK; Bosse, AW; Loo, YL. Assessing the Huang-Brown description of the tie chains for charge transport in conjugated polymers. ACS Macro Lett. 2018, 7, 1333-1338]. Based on the molecular structure characteristics of P3HT, the critical distance required for calculation in the model was set to l. c +l a , where l c l represents the thickness of the crystal region. a The thickness of the amorphous region is given. The fraction of connected molecules (f) in pure P3HT (i.e., Comparative Example 1) is calculated. TC ) is 1.5x10 -4 After adding HPN-68L, as follows Figure 1 As shown in b, f TC The number of P3HT linkage molecules increases with the increase of nucleating agent content, indicating that the addition of HPN-68L can effectively increase the number of linkage molecules. The higher the HPN-68L content, the more linkage molecules there are.

[0057] Examples 7-11

[0058] P3HT was dissolved in toluene to obtain P3HT toluene solutions with concentrations of 0.50 mg / mL, 0.67 mg / mL, 1.0 mg / mL, 1.34 mg / mL, and 2.0 mg / mL, respectively, and the sonication time was 0 s (i.e., no sonication).

[0059] The changes in specific viscosity and solution concentration of P3HT in toluene in Test Examples 7-11 are shown in the following test results. Figure 2 As shown, the specific viscosity increase of P3HT toluene solutions at different concentrations was tested using an Ubbelohde viscometer. The specific viscosity increase exhibited a linear change, and the reciprocal of the intercept of the slope on the ordinate was the critical sub-concentration concentration c* of the P3HT toluene solution (5.3 mg / mL). This means that when the concentration of the P3HT toluene solution exceeds c*, the P3HT molecular chains begin to contact in the solution, and with further increases in concentration, entanglement occurs between the P3HT molecular chains. However, the polymer solution used in this invention can be reduced to a concentration of 1.0 mg / mL, far below c*. Even with the use of a Tol-ODCB mixed solvent, the change in volume ratio has only a slight effect on c*. The mixed solvent solution used in this invention remains a dilute solution, and the polymer molecular chains do not entangle in the solution.

[0060] Figure 3 The graphs show the variation of the thickness of the conjugated polymer ultrafilm with ultrasonic time under different volume ratios of toluene and o-dichlorobenzene in Examples 1-4. The thickness of the conjugated polymer ultrafilm was measured using AFM, and the test results are as follows. Figure 3 As shown, the average thickness of the conjugated polymer ultrafilm of the present invention is less than 10 nm. When the ODCB ratio is above 20%, the thickness of the conjugated polymer ultrafilm is slightly reduced. The ultrasonic time has virtually no effect on the thickness of the ultrafilm.

[0061] Comparative Example 2

[0062] P3HT was dissolved in toluene and stirred until homogeneous. The concentration of the P3HT solution was 1.0 mg / mL. The P3HT solution was sonicated at room temperature for 40 s, 80 s and 150 s respectively. Immediately after the sonication stopped, the film was spin-coated at a spin-coating rate of 1000 rpm for 1 min to obtain a P3HT film.

[0063] Comparative Example 3

[0064] P3HT and HPN-68L were dissolved together in toluene and stirred until homogeneous. The concentration of the mixed solution was 1.0 mg / mL. The mass of HPN-68L was 2.0 wt% and 5.0 wt% of P3HT, respectively. The mixed solution was spin-coated into a film at a spin-coating rate of 1000 rpm for 1 min to prepare a conjugated polymer ultrathin film.

[0065] Comparative Example 4

[0066] P3HT was dissolved in a mixed solvent of toluene and o-dichlorobenzene (volume ratios of toluene and o-dichlorobenzene were 90:10, 80:20, and 70:30, respectively) and stirred until homogeneous. The concentration of the P3HT solution was 1.0 mg / mL. The P3HT solution was sonicated at room temperature for 0 s, 40 s, 80 s, and 150 s, respectively. Immediately after sonication was stopped, the solution was spin-coated to form a film at a spin-coating rate of 1000 rpm for 1 min, thus obtaining a P3HT film.

[0067] Figure 4 a is a graph showing the change in conductivity of the P3HT film as a function of ultrasonic time in Comparative Example 1 and Comparative Example 2. Figure 4 b is a graph showing the change in conductivity of P3HT thin films and conjugated polymer ultrathin films as a function of nucleating agent content in Comparative Examples 1 and 3. Figure 4 c shows the change in conductivity of the P3HT thin film subjected to ultrasonication for 0 s as a function of toluene content in Comparative Examples 1 and 4. Figure 4 a and Figure 4 As shown in b, neither applying ultrasound alone nor adding a nucleating agent alone resulted in a significant change in the conductivity of the thin film. Figure 4 As shown in Figure c, the conductivity of the P3HT film decreases slightly with the increase of the proportion of o-dichlorobenzene. Figure 4 The results show that the present invention requires the simultaneous action of ultrasound, mixed solvent and nucleating agent to improve the electrical properties of conjugated polymer ultrafilms. Using any one of these alone does not improve the electrical properties of conjugated polymer ultrafilms.

[0068] Figure 5 The graphs show the changes in conductivity and elongation at break of the P3HT thin film and conjugated polymer ultrathin film in Comparative Example 1 and Examples 1-4. Figure 5 In the figure, the dashed line corresponds to the electrical conductivity (2.7 S / cm) and elongation at break (COS) (82%) of the P3HT film (i.e., corresponding to scale 1). Figure 5 As shown in Figure a, under the combined effects of adding 5.0 wt% nucleating agent and ultrasound, when the ODCB content in the mixed solvent is 20% or less, the conductivity of the conjugated polymer ultrafilm is higher than that of P3HT0-100-0s (i.e., Comparative Example 1). Figure 5In b, when the ODCB content in the mixed solvent is 10% or higher, the elongation at break of the conjugated polymer ultrafilm is higher than that of P3HT0-100-0s (i.e., Comparative Example 1). The combined results of conductivity and COS indicate that the addition of 5.0 wt% nucleating agent HPN-68L to a mixed solvent with a Tol:ODCB volume ratio of 90:10 and 80:20, along with ultrasonication, can simultaneously improve the conductivity and COS of the conjugated polymer ultrafilm. The ultrafilm with an ultrasonication time of 80 s exhibits the best overall performance. The conductivity and COS of P3HT5-90-80s are 5.9 ± 0.1 S / cm and 122 ± 7%, respectively 2.2 times and 1.5 times that of P3HT0-100-0s. The conductivity and COS of P3HT5-80-80s are 4.9 ± 0.1 S / cm and 155 ± 1%, respectively 1.8 times and 1.9 times that of P3HT0-100-0s. Therefore, P3HT5-90-80s exhibits superior electrical and tensile properties. Experiments show that, in a mixed solvent system of toluene and o-dichlorobenzene, the present invention, with the synergistic effect of adding nucleating agents and applying ultrasound, can obtain conjugated polymer ultrafilms with excellent electrical and tensile properties through spin coating alone, without the need for complex post-processing.

[0069] Figure 5 In Example 1, with a Tol:ODCB ratio of 100:0, the conductivity and COS of the conjugated polymer ultrafilm prepared under ultrasound-nucleating agent-only effects after 40s, 80s, and 150s of sonication were all higher than those of P3HT0-100-0s. P3HT5-100-80s exhibited the highest conductivity at 4.7 ± 0.3 S / cm, but this was lower than that of P3HT5-90-80s and P3HT5-80-80s. Simultaneously, the COS of the films prepared under Tol:ODCB-100:0 in Example 1 were all lower than that of P3HT0-100-0s, indicating that the tensile properties of the conjugated polymer ultrafilm prepared under ultrasound-nucleating agent-only effects are relatively poor. Figure 5 In Examples 2-4, the conductivity and COS of the conjugated polymer ultrafilm prepared by ultrasound at 0s represent the results of the nucleating agent-mixed solvent treatment alone. The conductivity and COS of P3HT5-90-0s and P3HT5-80-0s are improved compared to P3HT0-100-0s, but are lower than those of P3HT5-90-80s and P3HT5-80-80s. This indicates that the performance of the conjugated polymer ultrafilm prepared by the nucleating agent-mixed solvent treatment alone is not as good as the electrical and tensile properties of the conjugated polymer ultrafilm prepared by the method of this invention.

[0070] Figure 6For Comparative Example 4, the conductivity and COS of P3HT films subjected to ultrasound-mixed solvent alone for 40s, 80s, and 150s of ultrasound treatment as a function of toluene content were compared. Only when the ODCB content in the mixed solvent was 10% did the conductivity of the P3HT film exceed that of P3HT0-100-0s, with the highest being the conductivity of P3HT0-90-80s at only 3.5 ± 0.1 S / cm, which is lower than the conductivity of the conjugated polymer ultrafilm prepared in this invention. Although the COS of the P3HT film subjected to ultrasound-mixed solvent alone was higher than that of P3HT0-100-0s, it was lower than the COS of P3HT5-90-80s and P3HT5-80-80s prepared in this invention. This indicates that the performance of the P3HT film prepared by ultrasound-mixed solvent alone is inferior to the electrical and tensile properties of the conjugated polymer ultrafilm prepared by the method of this invention.

[0071] Comparative Example 5

[0072] P3HT was dissolved in toluene and stirred until homogeneous, with a solution concentration of 1.0 mg / mL. The solution was sonicated at room temperature for 0 s. The prepared solution was then spin-coated into a film at a spin speed of 1000 rpm for 1 min. The prepared P3HT film was then annealed at room temperature under o-dichlorobenzene saturated vapor pressure for 0 h, 1 h, 2 h, and 3 h, respectively, to obtain the P3HT modified annealed film.

[0073] Figure 7 a is a graph showing the change in electrical conductivity of the modified annealed film in Comparative Example 5; Figure 7 Figure b shows the change in elongation at break of the modified annealed film in Comparative Example 5. The annealing apparatus is as follows: Figure 7 As shown in the bottom left illustration in b. Figure 7 The conductivity of the modified annealed film in Comparative Example 5 hardly increases with the extension of annealing time, reaching a maximum of only 3.1 ± 0.1 S / cm, which is lower than the conductivity of the conjugated polymer ultrafilm prepared by the method of this invention. From... Figure 7 The results showed that the unannealed film had the highest COS, at 82±12%, which was much lower than the COS of the conjugated polymer ultrafilm prepared by the method of this invention. Figure 7 The results show that the electrical and tensile properties of the conjugated polymer ultrafilm prepared by the method of the present invention are superior to those of annealed films prepared by the traditional annealing method.

[0074] With a fixed elongation at break of 80%, and a tensile-recovery cycle of 1, the electrical conductivity (σ) was measured in the recovered state. N ), where N is the number of cycles of stretching. Figure 8 The σ values ​​of the conjugated polymer ultrafilm (P3HT5-80-80s) after 80s of ultrasonication in Example 3 and the P3HT film (P3HT0-100-0s) in Comparative Example 1 are... NThe ratio of the initial conductivity σ0 (i.e., the conductivity of the ultrathin film at 0 cycles) to the number of cycles is shown in the graph. Figure 8 As shown. From Figure 8 As can be seen, the conductivity of P3HT0-100-0s decreased rapidly after 30 cycles, and then remained basically stable. After 90 cycles of stretching, the conductivity was 0.12±0.06 S / cm, only 4% of its σ0 (2.7±0.1 S / cm). In contrast, the conductivity of the P3HT5-80-80s ultrafilm did not show a significant decrease during stretching cycles. After 90 cycles, the conductivity was 4.5±0.1 S / cm, 92% of its σ0 (4.9±0.1 S / cm). Furthermore, this conductivity is 37.5 times that of the P3HT0-100-0s film after 90 cycles of stretching, and even 1.7 times the σ0 of the unstretched P3HT0-100-0s film, indicating that the P3HT5-80-80s ultrafilm of this invention maintains excellent electrical properties during stretching cycles.

[0075] Comparative Examples 6-8

[0076] The difference between Comparative Examples 6-8 and Comparative Example 1 is that the spin coating rates were 1500 rpm, 2500 rpm, and 3500 rpm, respectively, to prepare P3HT films.

[0077] Examples 12-14

[0078] The difference between Examples 12-14 and Example 2 is that the ultrasonic time in Examples 12-14 is 80s, and the spin coating rates are 1500rpm, 2500rpm, and 3500rpm, respectively, to prepare conjugated polymer ultrathin films.

[0079] Figure 9 a represents comparative examples 1, 6-8 (i.e.) Figure 9 In Example 2, the ultrasonic waves were 80s and 12-14s respectively for the ultrathin film (i.e., P3HT) and the ultrasonic waves were 12-14s respectively. Figure 9 The thickness of P3HT-HPN varies with spin coating rate;

[0080] Figure 9 b represents comparative examples 1, 6-8 (i.e.) Figure 9 In Example 2, the ultrasonic waves were 80s and 12-14s respectively for the ultrathin film (i.e., P3HT) and the ultrasonic waves were 12-14s respectively. Figure 9 The electrical conductivity of P3HT-HPN varies with spin coating rate;

[0081] Figure 9 c represents comparative examples 1, 6-8 (i.e.) Figure 9 In Example 2, the ultrasonic waves were 80s and 12-14s respectively for the ultrathin film (i.e., P3HT) and the ultrasonic waves were 12-14s respectively. Figure 9The graph shows the change in elongation at break of P3HT-HPN with spin coating rate.

[0082] like Figure 9 As shown in Figure a, the thickness of both the P3HT thin film and the P3HT-HPN ultrathin film decreases with increasing spin coating rate. Figure 9 b shows that the conductivity of both P3HT thin film and P3HT-HPN ultrathin film decreases with increasing spin coating rate (i.e., decreasing film thickness), but at the same spin coating rate, the conductivity of P3HT-HPN ultrathin film is better than that of P3HT thin film. Figure 9 c shows that the COS of both P3HT thin films and P3HT-HPN ultrathin films increases with increasing spin coating rate (i.e., decreasing film thickness), but at the same spin coating rate, the COS of P3HT-HPN ultrathin films is better than that of pure P3HT films. Figure 9 The results show that the electrical and tensile properties of the conjugated polymer ultrafilm with a thickness of less than 10 nm prepared in this invention are superior to those of directly spin-coated P3HT films of similar thickness (i.e., Comparative Examples 1, 6-8).

[0083] The embodiments of the present invention have been described above by way of example. However, the scope of protection of the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made by those skilled in the art within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a conjugated polymer ultrathin film, characterized in that, The method includes: The nucleating agent and conjugated polymer are dissolved in a solvent, ultrasonicated, and the prepared mixed solution is formed into a film to obtain a conjugated polymer ultrathin film. The nucleating agent is disodium bicyclo[2.2.1]heptane-2,3-dicarboxylic acid; The conjugated polymer is poly(3-hexylthiophene). The solvent is a mixture of toluene and o-dichlorobenzene; The volume ratio of toluene to o-dichlorobenzene is 99-60:1-40; The nucleating agent is present in an amount of 1-10 wt% of the conjugated polymer. The concentration of the mixed solution is 0.1-5 mg / mL.

2. The method according to claim 1, characterized in that, The ultrasound duration is 1-200 seconds.

3. The method according to claim 1, characterized in that, The thickness of the conjugated polymer ultrafilm is less than 10 nm.

4. The method according to claim 1, characterized in that, Thin films are prepared by spin coating; the spin coating speed is 500-5000 rpm.

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