An intrinsically stretchable crosslinked polymer, its preparation method and applications, and reverse organic solar cells.

Abstract

This invention relates to the field of organic functional materials technology, and more particularly to an intrinsically stretchable crosslinked polymer, its preparation method and application, and reverse organic solar cells. The invention provides an intrinsically stretchable crosslinked polymer, the raw materials of which include quinone small molecules and amine-containing polymers. The crosslinked polymer can be used as an electron transport layer in reverse organic solar cells.

Description

Technical Field

[0001] This invention relates to the field of organic functional materials technology, and in particular to an intrinsically stretchable crosslinked polymer, its preparation method and application, and reverse organic solar cells. Background Technology

[0002] In recent years, wearable electronic devices have seen tremendous development in fields such as wearable electronic displays, energy devices, biomedicine, and robotics. To meet these demands, the research and development of intrinsically flexible and stretchable organic electronic devices is crucial. Among these, portable wearable power supplies, as power supply devices, represent a significant challenge limiting the development of this field.

[0003] Organic solar cells (OSCs) possess advantages such as lightweight, flexibility, and the ability to be produced through large-area roll-to-roll printing. In particular, the superior mechanical properties of organic materials make OSCs a strong candidate power source for wearable electronic devices. The energy conversion efficiency of OSCs based on rigid substrates has exceeded 19%, essentially meeting the requirements for commercial use. However, fully stretchable OSC devices are still in their early stages. Current research on fully stretchable OSCs is based on traditional configuration devices, which suffer from poor air stability due to the top electrode being the cathode. Numerous studies have confirmed that inverted configuration devices with the top electrode as the anode can significantly improve the air stability of the device, making OSCs more practical. However, intrinsically stretchable electron transport materials are limited by their solubility in conventional solvents and low conductivity; therefore, intrinsically stretchable devices based on inverted configurations have never been reported. Therefore, developing intrinsically stretchable electron transport materials is a pressing problem that needs to be solved in this field. Summary of the Invention

[0004] The purpose of this invention is to provide an intrinsically stretchable crosslinked polymer, its preparation method and application, and a reverse organic solar cell. The crosslinked polymer can be used as an electron transport layer in a reverse organic solar cell.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides an intrinsically stretchable crosslinked polymer, the raw materials of which include quinone small molecules and amine-containing polymers;

[0007] The quinone-type small molecule has the structure shown in Formula 1 or 2:

[0008] Preferably, the mass ratio of the quinone small molecule to the amine-containing polymer is (7-3):(3-7).

[0009] Preferably, the amine-containing polymer includes one or more of polyethyleneimine, polyethoxyethyleneimine, and ε-polylysine.

[0010] Preferably, the method for preparing the quinone small molecule includes the following steps:

[0011] A compound having the structure shown in Formula 3 or Formula 4, 1,3-indanedione, palladium catalyst, sodium hydride, and solvent are mixed and subjected to C-C bond coupling reaction and air oxidation in sequence to obtain the quinone small molecule.

[0012]

[0013] When the reactant is a compound having the structure shown in Formula 3, the quinone molecule has the structure shown in Formula 1; when the reactant is a compound having the structure shown in Formula 4, the quinone molecule has the structure shown in Formula 2.

[0014] The palladium catalyst is methanesulfonic acid (2-di-tert-butylphosphino-2',4',6'-triisopropyl-1,1'biphenyl)(2'-amino-1,1'-biphenyl-2-yl)palladium(II).

[0015] Preferably, the molar ratio of the compound having the structure shown in Formula 3 or Formula 4, 1,3-indanedione, palladium catalyst and sodium hydride is 1:(2.2-3):(0.01-0.10):(4.2-5).

[0016] Preferably, the temperature of the C-C bond coupling reaction is 70–100°C, and the time is 1–12 h.

[0017] The air oxidation temperature is room temperature to 60°C, and the time is 10 to 60 minutes.

[0018] The present invention also provides a method for preparing the crosslinked polymer described in the above technical solution, comprising the following steps:

[0019] The crosslinked polymer is obtained by mixing quinone small molecules, amine-containing polymers and organic solvents, followed by spin coating and thermal annealing.

[0020] Preferably, the heat annealing temperature is room temperature to 200°C, and the time is 10 to 30 minutes.

[0021] The present invention also provides the application of the crosslinked polymer described in the above technical solution or the crosslinked polymer prepared by the preparation method described in the above technical solution as an electron transport material in a reverse organic solar cell device.

[0022] The present invention also provides a reverse organic solar cell, comprising a substrate, a cathode, an electron transport layer, an active layer, a hole transport layer, and an anode stacked sequentially from bottom to top, characterized in that the electron transport layer is made of the cross-linked polymer described in the above technical solution or a cross-linked polymer prepared by the preparation method described in the above technical solution.

[0023] This invention provides an intrinsically stretchable crosslinked polymer, the raw materials of which include quinone small molecules and amine-containing polymers;

[0024] The quinone-type small molecule has the structure shown in Formula 1 or 2:

[0025] The introduction of the quinone-type small molecule described in this invention can improve the electron transport properties of the cross-linked polymer, enabling its conductivity to reach 0.049 S·m. -1 Meanwhile, since the amine groups on the amine-containing polymer can react with the acceptor materials (e.g., L8-BO, BTP-eC9, etc.) in subsequent solar cells, causing their chemical structure to decompose, the quinone-type small molecule with the structure shown in Formula 1 of this application reacts with the amine groups in the polyethyleneimine to form quaternary ammonium salts (ionizing the amine groups), which can passivate the chemical reactivity of PEI with non-fullerene acceptors. The cross-linked polymer network can effectively dissipate stress, giving the cross-linked polymer good mechanical properties, with a crack initiation strain (COS) reaching 46%.

[0026] This invention also provides the application of the cross-linked polymer described in the above-described technical solution or the cross-linked polymer prepared by the above-described preparation method as an electron transport material in a reverse organic solar cell device. Because the cross-linked polymer contains abundant strongly polar amine groups, it can modify the metallized electrode, forming an ohmic contact between the active layer and the metal electrode, promoting electron extraction and transport, and thus improving the energy conversion efficiency of the organic solar cell. The energy conversion efficiency of the reverse organic solar cell device prepared based on it reaches 18.27%. The energy conversion efficiency of the fully stretchable reverse organic solar cell prepared based on it reaches 14.01%, and under 20% strain conditions, it can still maintain about 70% of its initial efficiency after 500 cyclic stretching cycles. Attached Figure Description

[0027] Figure 1 The 1H NMR spectrum of the quinone small molecule with the structure shown in Formula 1 described in Example 1 of this invention;

[0028] Figure 2 The carbon NMR spectrum of the quinone-type small molecule with the structure shown in Formula 1 described in Example 1 of this invention;

[0029] Figure 3 This is a high-resolution mass spectrum of the quinone-type small molecule with the structure shown in Formula 1 as described in Example 1 of the present invention;

[0030] Figure 4 The diagram below shows the structure of the reverse organic solar cell device described in Application Example 2, where 1 is the TPU layer, 2 is the PH1000 layer, 3 is the QBr-PEI-50 layer, 4 is the active material layer, 5 is the PEDOT:F layer, and 6 is the EGArn layer.

[0031] Figure 5 The JV curve of the reverse organic solar cell device described in Example 1;

[0032] Figure 6 The JV curve is for the reverse organic solar cell device described in Example 2. Detailed Implementation

[0033] This invention provides an intrinsically stretchable crosslinked polymer, the raw materials of which include quinone small molecules and amine-containing polymers;

[0034] The quinone-type small molecule has the structure shown in Formula 1 or 2:

[0035]

[0036] In this invention, the preferred mass ratio of the quinone small molecule to the amine-containing polymer is (7-3):(3-7), more preferably (6-4):(4-6), and most preferably (5.5-4.5):(4.5-5.5). In embodiments of this invention, the mass ratio of the quinone small molecule to the amine-containing polymer can be 1:1.

[0037] In this invention, the amine-containing polymer preferably includes one or more of polyethyleneimine (PEI), polyethoxyethyleneimine (PEIE), and ε-polylysine (ε-PL).

[0038] In this invention, the method for preparing the quinone small molecule includes the following steps:

[0039] A compound having the structure shown in Formula 3 or Formula 4, 1,3-indanedione, palladium catalyst, sodium hydride, and solvent are mixed and subjected to C-C bond coupling reaction and air oxidation in sequence to obtain the quinone small molecule.

[0040]

[0041] When the reactant is a compound having the structure shown in Formula 3, the quinone molecule has the structure shown in Formula 1; when the reactant is a compound having the structure shown in Formula 4, the quinone molecule has the structure shown in Formula 2.

[0042] The palladium catalyst is methanesulfonic acid (2-di-tert-butylphosphino-2',4',6'-triisopropyl-1,1'biphenyl)(2'-amino-1,1'-biphenyl-2-yl)palladium(II).

[0043] In this invention, the solvent is preferably one or more of 1,6-dioxane, tetrahydrofuran, and toluene. In embodiments of this invention, the solvent may be 1,6-dioxane.

[0044] In this invention, the preferred molar ratio of the compound having the structure shown in Formula 3 or Formula 4, 1,3-indanedione, palladium catalyst, and sodium hydride is 1:(2.2-3):(0.01-0.10):(4.2-5). In embodiments of this invention, the molar ratio of the compound having the structure shown in Formula 3, 1,3-indanedione, palladium catalyst, and sodium hydride can be 1:2.2:0.02:4.6. This invention does not impose any special limitations on the amount of solvent used; any amount well-known to those skilled in the art that ensures the smooth progress of the reaction can be used.

[0045] The present invention does not impose any special limitations on the mixing process; any process known to those skilled in the art can be used.

[0046] In this invention, the temperature of the C / C bond coupling reaction is preferably 70–100°C, more preferably 70°C, and the time is preferably 1–12 h, more preferably 2 h; the temperature of the air oxidation is preferably room temperature to 60°C, more preferably room temperature, and the time is preferably 10–60 min, more preferably 30 min. In embodiments of this invention, the temperature of the C / C bond coupling reaction can be 70°C, the time can be 2 h, and the temperature of the air oxidation can be room temperature, the time can be 30 min.

[0047] The present invention also provides a method for preparing the crosslinked polymer described in the above technical solution, comprising the following steps:

[0048] The crosslinked polymer is obtained by mixing quinone small molecules, amine-containing polymers and organic solvents, followed by spin coating and thermal annealing.

[0049] In this invention, the organic solvent preferably includes one or more of chloroform, chlorobenzene, toluene, N,N-dimethylformamide (DMF), and dimethyl sulfoxide (DMSO). When the organic solvent is two or more of the above-mentioned specific selections, this invention does not impose any special limitation on the ratio of the above-mentioned substances; they can be mixed in any ratio. This invention does not impose any special limitation on the amount of the organic solvent used; amounts well known to those skilled in the art are sufficient to ensure the smooth progress of the reaction. In the embodiments of this invention, the ratio of PEI to organic solvent can be 2.5 mg: 1 mL.

[0050] The present invention does not impose any special limitations on the mixing process; any process known to those skilled in the art can be used.

[0051] In this invention, the spin coating speed is preferably 1000–3000 rpm, and the spin coating time is preferably 30–90 s. In an embodiment of this invention, the spin coating speed can be 2000 rpm, and the spin coating time can be 60 s.

[0052] In this invention, the temperature of the heat annealing is preferably room temperature to 200°C, more preferably 100 to 150°C; the time is preferably 10 to 30 minutes, more preferably 20 minutes. In an embodiment of this invention, the temperature of the heat annealing can be 120°C, and the time can be 20 minutes.

[0053] The present invention also provides the application of the crosslinked polymer described in the above technical solution or the crosslinked polymer prepared by the preparation method described in the above technical solution as an electron transport material in a reverse organic solar cell device.

[0054] In this invention, the reverse organic solar cell device is preferably a rigid substrate cell or a fully stretchable cell.

[0055] In this invention, the reverse organic solar cell device comprises a substrate, a cathode, an electron transport layer, an active layer, a hole transport layer, and an anode, stacked sequentially from bottom to top. The electron transport layer is made of the cross-linked polymer described in the above-described technical solution or a cross-linked polymer prepared by the preparation method described in the above-described technical solution.

[0056] When the reverse organic solar cell device is a rigid substrate cell, the substrate material of the reverse organic solar cell device is preferably a glass substrate, and the cathode material is preferably ITO; the electron transport layer material is preferably the cross-linked polymer described in the above technical solution or the cross-linked polymer prepared by the preparation method described in the above technical solution; the active layer material is preferably a donor and acceptor with a mass ratio of 1:1.3, wherein the donor is preferably PM6 (structure shown in Formula 5), ​​and the acceptor is preferably L8-B0 (structure shown in Formula 6) and BTP-eC9 (structure shown in Formula 7) with a mass ratio of 0.9:0.4; the hole transport layer material is preferably molybdenum oxide; and the anode material is preferably silver.

[0057] When the reverse organic solar cell device is a fully stretchable cell, the substrate material of the reverse organic solar cell device is preferably thermoplastic polyurethane elastomer (TPU), the cathode material is preferably poly(3,4-ethylenedioxythiophene):polystyrene sulfonic acid (PH1000), the electron transport layer material is preferably the cross-linked polymer described in the above technical solution or the cross-linked polymer prepared by the preparation method described in the above technical solution, the active layer material is preferably PM6 and FDA-m-TAT (structural formula as shown in Formula 8) with a mass ratio of 1:1.2, the hole transport layer material is preferably PEDOT:F, and the anode material is preferably gallium indium alloy (EGaIn).

[0058]

[0059] The following detailed description, in conjunction with embodiments, illustrates the intrinsically stretchable crosslinked polymer, its preparation method, and its applications provided by the present invention. However, these descriptions should not be construed as limiting the scope of protection of the present invention.

[0060] Example 1

[0061] The compound having the structure shown in Formula 2, 1,3-indanedione, methanesulfonic acid (2-di-tert-butylphosphino-2',4',6'-triisopropyl-1,1'biphenyl)(2'-amino-1,1'-biphenyl-2-yl)palladium(II) and sodium hydride were mixed in a molar ratio of 1:2.2:0.02:4.6 and then mixed with an organic solvent (1,6-dioxane) to obtain a reaction solution with a concentration of 0.1 mol / L of the compound having the structure shown in Formula 2.

[0062] The obtained reaction solution was heated and stirred at 70°C for 2 hours, and then oxidized in air for 30 minutes (at room temperature) to obtain a quinone-type small molecule with the structure shown in Formula 1.

[0063] In an argon-filled glove box, 2.5 mg of the quinone small molecule with the structure shown in Formula 1, 2.5 mg of PEI and 1 mL of DMF were added to a sample vial. The resulting spin-coating solution was spin-coated at 2000 rpm for 60 s. The prepared film was then heat-annealed on a hot plate at 120 °C for 20 min to obtain a crosslinked polymer film (denoted as QBr-PEI-50).

[0064] Figure 1 The 1H NMR spectrum of the quinone-type small molecule having the structure shown in Formula 1 is obtained from... Figure 1 It can be seen that the number of hydrogen atoms is consistent with the molecule described in Formula 1, and the number of hydrogen atoms at chemical shifts of 8.02, 7.92 and 7.72 ppm is consistent with the molecular structure, thus confirming that the structure described in Formula 1 is correct;

[0065] Figure 2 The NMR carbon spectrum of the quinone-type small molecule having the structure shown in Formula 1 is obtained from... Figure 2 It can be seen that the number of carbon atoms is consistent with the molecule described in Formula 1, thus confirming that the structure described in Formula 1 is correct;

[0066] Figure 3 The high-resolution mass spectrum of the quinone-type small molecule having the structure shown in Formula 1 is obtained from... Figure 3 It can be seen that the mass-to-nucleus ratio obtained from the test is consistent with the theoretical value, which confirms that the structure described in Equation 1 is correct.

[0067] Example 2

[0068] Referring to Example 1, the difference is that the total concentration of quinone small molecules with the structure shown in Formula 1 and PEI in the spin-coating solution is 10 mg / mL.

[0069] Test case

[0070] The conductivity of QBr-PEI-50 described in Example 2 was tested using the four-probe method: The spin-coating solution described in Example 2 was spin-coated onto Corning glass with gold electrodes at 3000 rpm. After annealing on a hot stage at 120°C for 20 min, the conductivity was tested using a Keysight B2902A probe. The test result was: conductivity of 0.049 S·m. -1 ;

[0071] Poly(4-styrene sulfonic acid) (PSS) and water were mixed at a volume ratio of 1:4 and then spin-coated onto glass at a speed of 3000 rpm for 40 seconds. The mixture was then placed in an oven at 160°C and baked for 20 minutes to obtain the PSS layer.

[0072] The spin-coating solution described in Example 2 was spin-coated onto the surface of the PSS layer at 3000 rpm. After annealing on a hot plate at 120°C for 20 min, the resulting cross-linked polymer film was adhered to a polydimethylsiloxane (PDMS) substrate. After immersing the PSS in water to dissolve it, the film was transferred to the PDMS substrate for crack initiation strain (COS) testing. The test method was as follows: the initial length l0 of the film after transfer was measured, and an in-situ tensile test was performed under a polarizing microscope. When a crack appeared, the film length l was measured, and then COS = (l-l0) / l0. The test result showed that the COS was 46%.

[0073] Application Example 1

[0074] Fabrication of reverse organic solar cells on ITO substrates:

[0075] The ITO glass was ultrasonically cleaned with soapy water, deionized water, acetone and isopropanol for 20 minutes in sequence, and then treated with ultraviolet ozone (UVO) cleaner for 25 minutes to obtain the pretreated ITO substrate (thickness of 100 nm).

[0076] In an argon-filled glove box, the spin coating solution with a concentration of 5 mg / mL described in Example 1 was spin coated at 2000 rpm for 60 s, and then annealed on a hot plate at 120°C for 20 min to obtain an electron transport layer (thickness of 30 nm).

[0077] PM6, L8-BO and BTP-eC9 were mixed in a mass ratio of 1:0.9:0.4 and then prepared into a 17 mg / mL solution with chloroform. The resulting solution was then spin-coated onto the surface of the electron transport layer (3000 rpm for 30 s) and annealed at 100 °C for 10 min to obtain an active layer (100 nm thick).

[0078] A hole transport layer (2nm thick) was obtained by evaporating molybdenum oxide using a vacuum evaporation device.

[0079] A 150 nm thick silver layer is deposited on the surface of the hole transport layer to obtain an anode layer (150 nm thick), and finally a rigid substrate cell (reverse organic solar cell device) is obtained. The performance parameters are shown in Table 1.

[0080] Performance parameters of the reverse organic solar cell devices described in Table 1

[0081] <![CDATA[V OC (V)]]> <![CDATA[J SC (mA / cm 2 )]]> FF (%) PCE (%) 0.859 77.56 27.43 18.27

[0082] Note: V in the table OC J is the open-circuit voltage. SC is the short-circuit current, FF is the fill factor, and PCE is the power conversion efficiency.

[0083] Figure 5 The JV curve of the reverse organic solar cell device is given by... Figure 5 As shown in Table 1, the V of the reverse organic solar cell oc =0.859V,J sc =77.56mA / cm 2 The efficiency of the electron transport layer is 27.43%; with QBr-PEI-50 as the electron transport layer, an energy conversion efficiency of 18.27% can be obtained, which is one of the highest values ​​based on the inverting device structure.

[0084] Application Example 2

[0085] Fabrication of reverse organic solar cells (fully stretchable reverse organic solar cells):

[0086] TPU (2 μm thick) was treated with oxygen plasma (O-Plasma) for 10 min, then PH1000 was spin-coated at 1000 rpm for 30 s, and annealed on a hot stage at 110 °C for 20 min to obtain a cathode layer (100 nm thick).

[0087] In an argon-filled glove box, the spin coating solution with a concentration of 5 mg / mL described in Example 1 was spin coated at 2000 rpm for 60 s, and then annealed on a hot plate at 120°C for 20 min to obtain an electron transport layer (thickness of 30 nm).

[0088] PM6 and FDA-m-TAT were mixed at a mass ratio of 1:1.2 and then prepared into a 17 mg / mL solution with chloroform. The resulting solution was spin-coated onto the surface of the electron transport layer (3000 rpm, 30 s) and then annealed at 100 °C for 10 min to obtain an active layer (100 nm thick).

[0089] PEDOT:F was spin-coated onto the surface of the active layer (4000 rpm, 30 s), and then annealed at 100 °C for 5 min to obtain a hole transport layer (thickness 30 nm).

[0090] Finally, liquid metal EGaIn is sprayed onto the surface of the hole transport layer to obtain the anode layer (1000 nm thick), ultimately resulting in a fully stretchable cell (reverse organic solar cell device, structural schematic shown in Figure 1). Figure 4 As shown in the figure), the performance parameters are shown in Table 2;

[0091] Performance parameters of the reverse organic solar cell devices listed in Table 2

[0092] <![CDATA[V OC (V)]]> <![CDATA[J SC (mA / cm 2 )]]> FF (%) PCE (%) <![CDATA[PCE 80％ (%)]]> 0.901 66.24 23.50 14.01 21

[0093] Note: V in the table OC J is the open-circuit voltage.SC FF is the short-circuit current, FF is the fill factor, PCE is the power conversion efficiency, and PCE is the short-circuit current. 80％ The strain is the strain when the device efficiency decays to 80% of its initial efficiency.

[0094] Figure 6 The JV curve of the reverse organic solar cell device is given by... Figure 6 It can be seen that the Voc of the fully stretchable reverse organic solar cell is 0.901V, and Jsc is 66.24mA / cm. 2 FF is 23.50%. (From Table 2 and...) Figure 6 It is evident that the cross-linked polymer described in this invention can successfully prepare fully stretchable batteries, achieving a maximum energy conversion efficiency of 14.01%. Tensile testing of the device yielded PCE... 80％ The efficiency reaches 21%, and under 20% strain conditions, it can still maintain about 70% of the initial efficiency after 500 cycles of cyclic stretching, indicating that the device has good mechanical properties.

[0095] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An intrinsically stretchable crosslinked polymer, characterized in that, The raw materials for preparation include quinone small molecules and amine-containing polymers; The quinone-type small molecule has the structure shown in Formula 1 or 2: Formula 1 or Formula 2; The mass ratio of the quinone small molecule to the amine-containing polymer is (7~3):(3~7); The amine-containing polymer is polyethyleneimine; The method for preparing the crosslinked polymer includes the following steps: The crosslinked polymer is obtained by mixing quinone small molecules, amine-containing polymers and organic solvents, followed by spin coating and thermal annealing.

2. The crosslinked polymer according to claim 1, characterized in that, The preparation method of the quinone small molecule includes the following steps: A compound having the structure shown in Formula 3 or Formula 4, 1,3-indanedione, palladium catalyst, sodium hydride, and solvent are mixed and subjected to C-C bond coupling reaction and air oxidation in sequence to obtain the quinone small molecule. Formula 3, Equation 4; When the reactant is a compound having the structure shown in Formula 3, the quinone molecule has the structure shown in Formula 1; when the reactant is a compound having the structure shown in Formula 4, the quinone molecule has the structure shown in Formula 2. The palladium catalyst is methanesulfonic acid (2-di-tert-butylphosphino-2',4',6'-triisopropyl-1,1'biphenyl) (2'-amino-1,1'-biphenyl-2-yl)palladium(II).

3. The crosslinked polymer as described in claim 2, characterized in that, The molar ratio of the compound having the structure shown in Formula 3 or Formula 4, 1,3-indanedione, palladium catalyst and sodium hydride is 1:(2.2~3):(0.01~0.10):(4.2~5).

4. The crosslinked polymer according to claim 3, characterized in that, The temperature of the C-C bond coupling reaction is 70~100℃, and the time is 1~12h; The air oxidation temperature is room temperature to 60°C, and the time is 10 to 60 minutes.

5. A method for preparing the crosslinked polymer according to any one of claims 1 to 4, characterized in that, Includes the following steps: The crosslinked polymer is obtained by mixing quinone small molecules, amine-containing polymers and organic solvents, followed by spin coating and thermal annealing.

6. The preparation method according to claim 5, characterized in that, The heat annealing temperature is room temperature to 200°C, and the time is 10 to 30 minutes.

7. The application of the crosslinked polymer according to any one of claims 1 to 4 or the crosslinked polymer prepared by the preparation method according to claim 5 or 6 as an electron transport material in a reverse organic solar cell device.

8. A reverse organic solar cell, comprising a substrate, a cathode, an electron transport layer, an active layer, a hole transport layer, and an anode, stacked sequentially from bottom to top, characterized in that, The material of the electron transport layer is the cross-linked polymer according to any one of claims 1 to 4 or the cross-linked polymer prepared by the preparation method according to claim 5 or 6.

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