Cross-linked polyion liquid ultraviolet photoelectric conversion material based on azobenzene as well as preparation method and application of cross-linked polyion liquid ultraviolet photoelectric conversion material

Abstract

The invention belongs to the technical field of semiconductor materials, and provides an azobenzene-based cross-linked polyion liquid ultraviolet photoelectric conversion material as well as a preparation method and application thereof. The material is formed by polymerizing an azobenzene photosensitive unit and an ionic liquid dipole unit, the ionic liquid dipole unit takes a trimer structure as a crosslinking core, and the tail end of the structure is grafted with an ionic liquid dipole monomer. According to the ultraviolet photoelectric device made of the material, on the premise that the electrical property is kept, the resistance of the device to mechanical stress (such as bending and pressure) is greatly improved, and the dimensional stability is improved.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor materials technology, and relates to photoelectric conversion materials, specifically to a cross-linked polyionic liquid ultraviolet photoelectric conversion material based on azobenzene, its preparation method and application. Background Technology

[0002] Photoelectric conversion polymer materials based on photosensitive units are a class of materials capable of converting optical signals into electrical signals. Currently reported photoelectric conversion polymer materials based on photosensitive units are all linear structures, prepared by introducing azobenzene photosensitive units and ionic liquid dipole units into the same polymer backbone. Under ultraviolet light irradiation, the azobenzene units undergo cis-trans isomerization, inducing endogenous forces. These forces are transferred to the ionic liquid units through the polymer chain, causing the separation of their positive and negative charge centers, thereby generating an electrical signal. The polymer was dissolved in a good solvent to prepare a 0.05 g / mol polymer solution. Then, it was spin-sprayed onto a PET transparent electrode with a Ni-Cu alloy deposited on its surface and vacuum-dried in an oven to constant weight. Next, a layer of the same PET transparent electrode was laminated to the other side of the polymer and pressed at 10 kN for 5 min at room temperature to ensure sufficient contact between the polyionic liquid and the electrode. Finally, after copper wires were led out, the device was encapsulated using dimethylsiloxane (PDMS) to obtain an ultraviolet optoelectronic device. The core of this device consists of three layers, from top to bottom: Ni-Cu alloy, polymer (polyionic liquid), and Ni-Cu alloy.

[0003] Although the above methods can obtain photoelectric conversion polymer materials based on photosensitive units, there are still many problems: (1) Most linear polymers have poor mechanical strength, resistance to mechanical stress, dimensional stability and high temperature resistance. (2) The azobenzene unit structure is simple, all of which are 4,4'-dihydroxyethylazobenzene. Moreover, due to the short carbon chain of the substituent, this structure has the characteristics of being hard and brittle, and is prone to cracking under external force. (3) The performance of optoelectronic devices containing only a single layer of polymer is unstable. Once subjected to a large external force, it is easy to short circuit (the two Ni-Cu alloy layers are separated by polymer. Once the polymer is damaged and cracked, the two alloy layers will conduct). Summary of the Invention

[0004] To address the aforementioned problems in the existing technology, one objective of this invention is to provide a cross-linked polyionic liquid ultraviolet photoelectric conversion material and its preparation method, thereby improving the mechanical stability of the photoelectric conversion material by introducing a cross-linked structure.

[0005] The second objective of this invention is to provide the application of the above-mentioned cross-linked polyionic liquid ultraviolet photoelectric conversion material based on azobenzene in the fabrication of optoelectronic devices.

[0006] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0007] This invention provides a cross-linked polyionic liquid ultraviolet photoelectric conversion material based on azobenzene. The ultraviolet photoelectric conversion material is polymerized from azobenzene photosensitive units and ionic liquid dipole units. The ionic liquid dipole units are cross-linked with a trimer structure as the core and ionic liquid dipole monomers grafted to the ends of the structure.

[0008] The structural formula of the ionic liquid dipole unit is as follows: ; -R represents an ionic liquid dipole monomer.

[0009] In the above-mentioned cross-linked polyionic liquid ultraviolet photoelectric conversion material technical solution, the azobenzene photosensitive unit is obtained by polymerization of azobenzene monomer and isocyanate.

[0010] Furthermore, the isocyanate is one of hexamethylene diisocyanate, dicyclohexylmethane diisocyanate (HMDI), diphenylmethane diisocyanate (MDI), toluene diisocyanate (TDI), and isophorone diisocyanate (IPDI).

[0011] Furthermore, the azobenzene monomer is generated by reacting 4,4'-dihydroxyazobenzene with a heteroalkane containing an ether bond, and the type and length of the substituents can be selected as needed.

[0012] Furthermore, the heteroalkane containing ether bonds has a straight-chain or non-straight-chain structure, and the number of ether bonds in the heteroalkane can be selected according to the actual situation.

[0013] Furthermore, the azobenzene photosensitive monomer is preferably 4,4'-bis[2-(2-(2-(2-(2-hydroxyethoxy)ethoxy)ethoxy)ethoxy]azobenzene.

[0014] In the above-mentioned cross-linked polyionic liquid ultraviolet photoelectric conversion material technical solution, the ionic liquid dipole monomer only needs to meet the piezoelectric unit function when used. In actual use, the type of ionic liquid dipole monomer can be selected according to the type of azobenzene unit used. Preferably, at least one of imidazole ionic liquid and quaternary ammonium salt ionic liquid can be used.

[0015] Furthermore, the structural formula of the ionic liquid dipole unit is as follows: .

[0016] This invention also provides a method for preparing the above-mentioned cross-linked polyionic liquid ultraviolet photoelectric conversion material, the steps of which are as follows: Preparation of azobenzene photosensitive unit; Preparation of ionic liquid dipole units; Azobenzene photosensitive units and ionic liquid dipole units were reacted at 55-65℃ to obtain a cross-linked polyionic liquid ultraviolet photoelectric conversion material based on azobenzene.

[0017] In one feasible implementation, the preparation steps of the azobenzene photosensitive unit are as follows: 4,4'-dihydroxyazobenzene, 2-(2-(2-(2-(bromoethoxy)ethoxy)ethoxy)ethanol, carbonate and iodide salt were dissolved in a first organic solvent and reacted at 75-85℃ for 12-14 h. The crude product obtained from the reaction was then extracted, washed and dried to obtain the dark red paste-like target product 4,4'-bis[2-(2-(2-(2-hydroxyethoxy)ethoxy)ethoxy)ethoxy]azobenzene monomer. The monomers 4,4'-bis[2-(2-(2-(2-(2-hydroxyethoxy)ethoxy)ethoxy)ethoxy]azobenzene and isocyanate were mixed and reacted at 25-30℃ for 1-1.5 h, and then reacted at 75-85℃ for 2-4 h to obtain the azobenzene photosensitive unit.

[0018] In one feasible implementation, the molar ratio of 4,4'-dihydroxyazobenzene, 2-(2-(2-(2-(bromoethoxy)ethoxy)ethoxy)ethanol, carbonate, and iodide is 10:(20-21):20:1; the molar ratio of 4,4'-bis[2-(2-(2-(2-hydroxyethoxy)ethoxy)ethoxy)ethoxy]azobenzene monomer to hexamethylene diisocyanate is 1:2. The first organic solvent is dimethyl sulfoxide (DMSO) or N,N-dimethylformamide (DMAC), etc.; the carbonate has no special requirements other than being able to absorb the hydrogen bromide produced after the reaction, and the type of carbonate can be selected as needed in actual use, with potassium carbonate or sodium carbonate being preferred; the iodide has no special requirements other than being able to catalyze the reaction, and the type of iodide can be selected as needed in actual use, with potassium iodide or sodium iodide being preferred.

[0019] In one feasible implementation, the preparation method of the ionic liquid dipole unit includes:

[0020] Diethanolamine was added to a second organic solvent and stirred until homogeneous at 55-65°C. Then, bromobutane was added, and the mixture was heated and stirred under reflux at 85-95°C for 45-55 hours. The second organic solvent and unreacted bromobutane were removed by rotary evaporation to obtain a quaternary ammonium salt-Br ionic liquid.

[0021] The quaternary ammonium salt-Br ionic liquid was mixed with 1-ethyl-3-methylimidazoline bis(trifluoromethanesulfonyl)imine in a third organic solvent and stirred at 25-30°C for 20-30 h, followed by refrigeration at 0-5°C for 18-25 h; then the third organic solvent was removed by rotary evaporation to obtain the quaternary ammonium salt-tetrafluoroborate ionic liquid monomer.

[0022] The quaternary ammonium salt-tetrafluoroborate ionic liquid monomer and the diisocyanate trimer are reacted at 25-30℃ for 1-1.5h, and then at 75-85℃ for 2-4h to obtain the ionic liquid dipole unit.

[0023] In one feasible preparation method, the molar ratio of diethanolamine, bromobutane, and 1-ethyl-3-methylimidazoline bis(trifluoromethanesulfonyl)imine is 1:(2-2.2):1; the molar ratio of the quaternary ammonium salt-tetrafluoroborate ionic liquid monomer to the diisocyanate trimer is 3:1; the diisocyanate trimer is one of hexamethylene diisocyanate trimer, toluene diisocyanate trimer, and isophorone diisocyanate trimer; the second organic solvent and the third organic solvent are good solvents for the solvent substance, and can be the same solvent or different solvents, preferably both the second organic solvent and the third organic solvent are acetonitrile.

[0024] In one feasible implementation, an azobenzene photosensitive unit and an ionic liquid dipole unit are reacted at 55-65°C for 0.5-1 hour to obtain a mixture containing photoelectric conversion material. This facilitates subsequent dissolution and coating for device fabrication. If the reaction time exceeds 1 hour, the reaction may proceed completely, resulting in directly cured photoelectric conversion material. Once cured, the material cannot be dissolved again for device fabrication via coating.

[0025] In practical applications, the types and amounts of the first, second, and third organic solvents are determined based on the type and amount of solute used, as long as the actual needs are met. The amount of the first organic solvent is such that the final concentration of 4,4'-dihydroxyazobenzene is 0.25 mol / L to 0.45 mol / L, the amount of the second organic solvent is such that the final concentration of diethanolamine is 0.3 mol / L to 0.5 mol / L, and the amount of the third organic solvent is such that the final concentration of 1-ethyl-3-methylimidazoline bis(trifluoromethanesulfonyl)imine is 0.3 mol / L to 0.5 mol / L.

[0026] Based on the above-mentioned cross-linked polyionic liquid ultraviolet photoelectric conversion material, the present invention also provides the application of the azobenzene-based cross-linked polyionic liquid ultraviolet photoelectric conversion material in the fabrication of optoelectronic devices.

[0027] A photoelectric device is obtained by curing a cross-linked polyionic liquid ultraviolet photoelectric conversion material between two electrode sheets. The specific steps are as follows:

[0028] Azobenzene photosensitive units and ionic liquid dipole units were reacted at a molar ratio of 3:2 at 55-65℃ for 0.5-1 h. The resulting azobenzene-based cross-linked polyionic liquid UV photoelectric conversion material was then uniformly coated onto two electrode sheets and cured at 75-85℃ to constant weight. The two electrode sheets coated with the azobenzene-based cross-linked polyionic liquid UV photoelectric conversion material were then bonded together, pressed, and encapsulated to obtain an azobenzene-based cross-linked polyionic liquid UV optoelectronic device. The electrode sheet thickness was 7-8 μm, and the coating photoelectric conversion material thickness was 15-20 μm.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows: 1) The polyionic liquid ultraviolet photoelectric conversion material provided by this invention is a cross-linked material, with the trimer structure contained in the ionic liquid dipole unit as the cross-linking core, which is then polymerized to form a cross-linked structure. This cross-linked polyionic liquid ultraviolet photoelectric conversion material has excellent mechanical robustness and resistance to mechanical stress, thereby improving the dimensional stability and long-term durability of the material; moreover, its high-temperature resistance is also superior to that of linear photoelectric conversion materials.

[0030] 2) This invention uses azobenzene photosensitive units with a large number of ether bonds. By adjusting the type, length and number of substituents and ether bonds, the structure of the azobenzene unit is enriched, thereby improving the toughness and flexibility of the azobenzene unit structure and reducing cracking under external force.

[0031] 3) The cross-linked polyionic liquid ultraviolet optoelectronic device based on azobenzene provided by the present invention adopts a double-layer cross-linked polyionic liquid ultraviolet photoelectric conversion material in the middle, which greatly increases the device's resistance to mechanical stress (such as bending and pressure) and improves dimensional stability while maintaining electrical performance; at the same time, the four-layer structure also improves the device's durability. Attached Figure Description

[0032] Figure 1 The optoelectronic device prepared in Example 2 is shown in (a), which corresponds to an electrode sheet coated with cross-linked polyionic liquid ultraviolet photoelectric conversion material (C-AZ-IL) on one side, (b) which corresponds to an electrode sheet with double-layer C-AZ-IL, and (c) which corresponds to a C-AZ-IL ultraviolet optoelectronic device with a four-layer structure.

[0033] Figure 2 The results are the open-circuit voltage test results of the optoelectronic devices prepared in Example 2, Comparative Example 2, and Comparative Example 3.

[0034] Figure 3Images of the optoelectronic device prepared in Example 2 after mechanical testing and high-temperature resistance testing; where (a) corresponds to the initial state of the optoelectronic device, (b) corresponds to the state after 30 bending and twisting, and (c) corresponds to the state after 30 bending and twisting and then placing it in a 100°C oven for 2 hours.

[0035] Figure 4 for Figure 3 Test results of open-circuit voltage of optoelectronic devices under three different conditions. Detailed Implementation

[0036] The following embodiments are provided to further illustrate the present invention. It should be noted that the following embodiments should not be construed as limiting the scope of protection of the present invention. If those skilled in the art make some non-essential improvements and adjustments to the present invention based on the above description, they shall still fall within the scope of protection of the present invention.

[0037] Example 1

[0038] This embodiment provides a cross-linked polyionic liquid ultraviolet photoelectric conversion material (C-AZ-IL) based on azobenzene, and the specific steps of its preparation method are as follows:

[0039] (1) Preparation of azobenzene photosensitive unit (prepolymer 1)

[0040]

[0041] In a 100 mL single-necked flask, 2.14 g (10 mmol) of 4,4'-dihydroxyazobenzene, 5.27 g (20.5 mmol) of 2-(2-(2-(2-(bromoethoxy)ethoxy)ethoxy)ethanol, 2.76 g (20 mmol) of anhydrous potassium carbonate, 0.166 g (1 mmol) of potassium iodide, and 30 mL of dehydrated N,N-dimethylformamide (DMF) were added sequentially, and the mixture was reacted at 80 °C for 13 h. The reaction result... After the reaction, the crude product obtained was dissolved in 500 mL of deionized water, and dichloromethane was added to extract the product. The extract was washed three times with deionized water, and the aqueous phase was collected and subjected to rotary evaporation at 80 °C to remove the solvent. The product was then vacuum dried at 85 °C to obtain the dark red paste-like target product 4,4'-bis[2-(2-(2-(2-hydroxyethoxy)ethoxy)ethoxy)ethoxy]azobenzene monomer (AZ) (5.11 g, 68.9% yield).

[0042] 20 g (0.0359 mol) of 4,4'-bis[2-(2-(2-(2-hydroxyethoxy)ethoxy)ethoxy)ethoxy]azobenzene monomer (AZ) and 12.08 g (0.0718 mol) of hexamethylene diisocyanate (HDI) were weighed into a 250 mL three-necked flask and reacted at 30 °C for 1.5 h and 80 °C for 3 h, respectively. The resulting prepolymer 1 is the azobenzene photosensitive unit, which was sealed in a brown glass bottle.

[0043]

[0044] (2) Preparation of ionic liquid dipole units (prepolymer 2)

[0045]

[0046] Weigh 10.514 g (0.10 mol) of diethanolamine (a colorless, transparent, viscous liquid) into a 500 mL single-necked flask, then add 250 mL of acetonitrile and stir at 60 °C until homogeneous and without layering. Measure 28.56 g (0.21 mol) of n-butane bromodiphenyl ether using a syringe and inject it into the single-necked flask. Reflux and stir at 90 °C for 50 h to obtain a transparent solution. Then, remove the acetonitrile by rotary evaporation at 80 °C, followed by the removal of residual n-butane bromodiphenyl ether by rotary evaporation at 110 °C, yielding a slightly yellowish, transparent, viscous fluid, which is the quaternary ammonium salt-Br ionic liquid.

[0047] 39.1 g (0.1 mol) of 1-ethyl-3-methylimidazoline bis(trifluoromethanesulfonyl)imine was added to the quaternary ammonium salt-Br ionic liquid obtained in the previous step, followed by 250 mL of acetonitrile. The mixture was stirred at 30 °C for 25 h to allow anion exchange reaction, yielding a pale yellow solution. The solution was then placed in a refrigerator at 2 °C for 25 h to ensure complete anion exchange reaction. The solution was removed from the refrigerator and acetonitrile was removed by rotary evaporation at 80 °C to obtain the quaternary ammonium salt-tetrafluoroborate ionic liquid monomer (IL). However, 1-ethyl-3-methylimidazoline bromide was not removed and remained in the system.

[0048] Weigh 20 g IL into a 250 mL three-necked flask and dehydrate under vacuum at 103 °C for 2 h. Then add 4.88 g hexamethylene diisocyanate trimer (brand name WANNATE). ® The prepolymer 2 (HT-100) was reacted at 30℃ for 1.5h and then at 80℃ for 4h to obtain the ionic liquid dipole unit, which was then packaged in a brown glass bottle.

[0049]

[0050] (3) Preparation of cross-linked polyionic liquid ultraviolet photoelectric conversion material based on azobenzene (C-AZ-IL)

[0051] Weigh 10g of prepolymer 1 and 18.82g of prepolymer 2 into a 100mL single-necked flask and react at 60℃ for 0.5h (the reaction is not complete; after complete reaction and solidification, it cannot be dissolved again, and the device cannot be prepared by coating). The cross-linked polyionic liquid ultraviolet photoelectric conversion material (C-AZ-IL) based on azobenzene is obtained for later use.

[0052] Comparative Example 1

[0053] This comparative example provides a linear polyionic liquid ultraviolet photoelectric conversion material (L-AL-IL) based on azobenzene, and the specific steps of its preparation method are as follows:

[0054] (1) Preparation of azobenzene photosensitive unit (prepolymer 1): The preparation steps are the same as in Example 1.

[0055] (2) Preparation of dihydroxy ionic liquid prepolymer (prepolymer 3)

[0056] Weigh 20g IL (preparation steps are described in Example 1) into a 250mL three-necked flask, remove water under vacuum at 103℃ for 2h, then add 2.44g hexamethylene diisocyanate (HDI), react at 30℃ for 1.5h first, then at 80℃ for 4h, and the resulting prepolymer 3 is the dihydroxy ionic liquid prepolymer, which is packaged in a brown glass bottle.

[0057]

[0058] (3) Preparation of linear polyionic liquid based on azobenzene (L-AZ-IL)

[0059] Weigh 10g of prepolymer 1 and 17.13g of prepolymer 3 into a 100mL single-necked flask and react at 60℃ for 0.5h (incomplete reaction) to obtain a linear polyionic liquid (L-AZ-IL) based on azobenzene, for later use.

[0060] Table 1. Prepolymer Formulation Table (Equivalent)

[0061]

[0062] Table 2 Polymer Formulation Table (Equivalent)

[0063]

[0064] Example 2

[0065] This embodiment provides a four-layer optoelectronic device, denoted as Device 1, prepared using the cross-linked polyionic liquid ultraviolet photoelectric conversion material (C-AZ-IL) based on azobenzene provided in Example 1. The specific preparation method is as follows:

[0066] a. Cut the PET transparent electrode film with Ni-Cu alloy deposited on its surface into electrode sheets of 1.5cm × 3cm for later use.

[0067] b. Using a 20 μm wire rod, the C-AZ-IL mixture prepared in Example 1 was coated onto the electrode sheet, with a coating area of ​​1.5 cm × 1.5 cm, resulting in an electrode sheet partially covered by the C-AZ-IL mixture. The electrode sheet was then placed in an 80°C oven to continue the cross-linking and curing reaction, and dried to constant weight, yielding an electrode sheet partially covered by C-AZ-IL, as shown below. Figure 1 As shown in (a) of the diagram.

[0068] c. Attach another identical electrode partially covered by C-AZ-IL to its surface (C-AZ-IL side down, no C-AZ-IL side up, and the C-AZ-IL layers of the two electrode sheets completely overlap, with the non-C-AZ-IL portions facing opposite directions). Press at 10 kN for 5 minutes at room temperature to ensure sufficient contact between C-AZ-IL layers and between C-AZ-IL and the Ni-Cu alloy electrode, obtaining a double-layer C-AZ-IL electrode sheet, as shown. Figure 1 As shown in (b) above. Finally, copper wires are led out and encapsulated using dimethylsiloxane (PDMS) to obtain a C-AZ-IL ultraviolet optoelectronic device with a four-layer structure, as shown in Figure 1. Figure 1 As shown in (c) in the figure. Its core consists of four layers, from top to bottom: Ni-Cu alloy, C-AZ-IL, C-AZ-IL, and Ni-Cu alloy, with thicknesses of 8μm, 20μm, 20μm, and 8μm, respectively.

[0069] Comparative Example 2

[0070] This comparative example provides a four-layer optoelectronic device, referred to as device 2, prepared from the linear polyionic liquid ultraviolet photoelectric conversion material based on azobenzene provided in Comparative Example 1. Its preparation method is the same as that of Example 2, except that the C-AZ-IL mixture in step b is replaced with the L-AL-IL mixture in Comparative Example 1.

[0071] The obtained L-AZ-IL ultraviolet optoelectronic device (device 2) with a four-layer structure consists of four layers, from top to bottom: Ni-Cu alloy, L-AZ-IL, L-AZ-IL, and Ni-Cu alloy, with thicknesses of 8μm, 20μm, 20μm, and 8μm, respectively.

[0072] Comparative Example 3

[0073] This comparative example provides a three-layer optoelectronic device, denoted as device 3, prepared from the linear polyionic liquid ultraviolet photoelectric conversion material based on azobenzene provided in Comparative Example 1. The specific preparation method is as follows:

[0074] a. Cut the PET transparent electrode film with Ni-Cu alloy deposited on its surface into electrode sheets of 1.5cm × 3cm for later use.

[0075] b. Using a 20 μm wire rod, the L-AZ-IL mixture prepared in Comparative Example 1 was coated onto the electrode sheet, with a coating area of ​​1.5 cm × 1.5 cm, resulting in an electrode sheet partially covered by the L-AZ-IL mixture. The electrode sheet was then placed in an 80 °C oven to continue the cross-linking and curing reaction, and dried to constant weight, yielding an electrode sheet partially covered by L-AZ-IL.

[0076] c. Attach another electrode sheet without L-AZ-IL coverage to its surface (conductive side down, in complete contact with L-AZ-IL). Press at 10 kN for 5 min at room temperature to ensure sufficient contact between L-AZ-IL and the Ni-Cu alloy electrode, obtaining a single-layer L-AZ-IL electrode sheet. Finally, lead out copper wires and encapsulate with dimethylsiloxane (PDMS) to obtain a conventional three-layer L-AZ-IL ultraviolet optoelectronic device (device 3). Its core consists of three layers, from top to bottom: Ni-Cu alloy, L-AZ-IL, and Ni-Cu alloy, with thicknesses of 8 μm, 20 μm, and 8 μm, respectively.

[0077] (a) Open-circuit voltage test of different devices

[0078] Device 1 prepared in Example 2, device 2 prepared in Comparative Example 2, and device 3 prepared in Comparative Example 3 were tested at 6412.8 µm / cm. 2 Under ultraviolet light irradiation, the output open-circuit voltage was tested, and the test results are as follows: Figure 2 As shown.

[0079] The results show that the maximum open-circuit voltage of device 1 is 24.95V, that of device 2 is 27.36V, and that of device 3 is 26.97V. This indicates that the electrical performance of device 1 is only slightly lower than that of devices 2 and 3, and it still exhibits good electrical performance.

[0080] Table 3 Maximum Open-Circuit Voltage Values ​​of Different Devices

[0081]

[0082] (ii) Mechanical performance testing

[0083] Device 1 in Example 2 was subjected to 30 bending and twisting cycles before being placed in a 100°C oven for 2 hours to test its dimensional stability.

[0084] Figure 3 (a), (b), and (c) are images of the same device 1 at its initial state, after 30 bending and twisting cycles, and after being placed in a 100°C oven for 2 hours, respectively. It can be seen that after 30 bending, twisting, and high-temperature baking, device 1 can still maintain the integrity of its structure and the uniformity of its appearance. Figure 4 The results show the open-circuit voltage of the same device 1 after 30 bending and torsion cycles, followed by 2 hours of baking in a 100°C oven. It can be seen that device 1 maintains its original output performance after 30 bending, torsion, and high-temperature baking. Therefore, the introduction of the cross-linked structure increases the device's resistance to mechanical stress (such as bending and pressure) and improves dimensional stability. The four-layer structure also improves the device's durability. Having two active polymer layers means that if one layer suffers minor defects or localized stress, the other layer may still function or help distribute the load.

Claims

1. A cross-linked polyionic liquid ultraviolet photoelectric conversion material based on azobenzene, characterized in that, The ultraviolet photoelectric conversion material is polymerized from azobenzene photosensitive units and ionic liquid dipole units; the ionic liquid dipole unit is a trimer structure with crosslinking core and ionic liquid dipole monomers grafted to the end of the structure. The structural formula of the ionic liquid dipole unit is as follows: ； -R represents an ionic liquid dipole monomer.

2. The azobenzene-based cross-linked polyionic liquid ultraviolet photoelectric conversion material according to claim 1, characterized in that, The azobenzene photosensitive unit is obtained by polymerization of azobenzene monomer and isocyanate.

3. The azobenzene-based cross-linked polyionic liquid ultraviolet photoelectric conversion material according to claim 2, characterized in that, The azobenzene monomer is 4,4'-bis[2-(2-(2-(2-(2-hydroxyethoxy)ethoxy)ethoxy)ethoxy]azobenzene; the isocyanate is one of hexamethylene diisocyanate, dicyclohexylmethane diisocyanate, diphenylmethane diisocyanate, toluene diisocyanate, and isophorone diisocyanate.

4. The cross-linked polyionic liquid ultraviolet photoelectric conversion material based on azobenzene according to claim 1, characterized in that, The ionic liquid dipole monomer is at least one of imidazole ionic liquid and quaternary ammonium salt ionic liquid.

5. The cross-linked polyionic liquid ultraviolet photoelectric conversion material based on azobenzene according to claim 4, characterized in that, The structural formula of the ionic liquid dipole unit is: 。 6. The method for preparing the azobenzene-based crosslinked polyionic liquid ultraviolet photoelectric conversion material according to any one of claims 1-5, characterized in that, Includes the following steps: Preparation of azobenzene photosensitive unit; Preparation of ionic liquid dipole units; Azobenzene photosensitive units and ionic liquid dipole units were reacted at 55-65℃ to obtain a cross-linked polyionic liquid ultraviolet photoelectric conversion material based on azobenzene.

7. The preparation method of the cross-linked polyionic liquid ultraviolet photoelectric conversion material based on azobenzene according to claim 6, characterized in that, The preparation steps of the azobenzene photosensitive unit are as follows: 4,4'-dihydroxyazobenzene, 2-(2-(2-(2-(bromoethoxy)ethoxy)ethoxy)ethanol, carbonate and iodide salt were dissolved in a first organic solvent and reacted at 75-85℃ for 12-14 h. The crude product obtained from the reaction was then extracted, washed and dried to obtain the dark red paste-like target product 4,4'-bis[2-(2-(2-(2-hydroxyethoxy)ethoxy)ethoxy)ethoxy]azobenzene monomer. The monomers 4,4'-bis[2-(2-(2-(2-(2-hydroxyethoxy)ethoxy)ethoxy)ethoxy]azobenzene and isocyanate were mixed and reacted at 25-30℃ for 1-1.5 h, and then reacted at 75-85℃ for 2-4 h to obtain the azobenzene photosensitive unit.

8. The preparation method of the cross-linked polyionic liquid ultraviolet photoelectric conversion material based on azobenzene according to claim 7, characterized in that, The molar ratio of 4,4'-dihydroxyazobenzene, 2-(2-(2-(2-(bromoethoxy)ethoxy)ethoxy)ethanol, carbonate, and iodide is 10:(20-21):20:1; the molar ratio of 4,4'-bis[2-(2-(2-(2-hydroxyethoxy)ethoxy)ethoxy)ethoxy]azobenzene monomer to isocyanate is 1:2; the first organic solvent is N,N-dimethylformamide or dimethyl sulfoxide; the carbonate is potassium carbonate or sodium carbonate; the iodide is potassium iodide or sodium iodide; the isocyanate is one of hexamethylene diisocyanate, dicyclohexylmethane diisocyanate, diphenylmethane diisocyanate, toluene diisocyanate, and isophorone diisocyanate.

9. The method for preparing the azobenzene-based cross-linked polyionic liquid ultraviolet photoelectric conversion material according to claim 6, characterized in that, The preparation method of the ionic liquid dipole unit includes: Diethanolamine was added to a second organic solvent and stirred evenly at 55-65°C. Then, bromobutane was added, and the mixture was heated and stirred under reflux at 85-95°C for 45-55 hours. The second organic solvent and unreacted bromobutane were removed by rotary evaporation to obtain a quaternary ammonium salt-Br ionic liquid. The quaternary ammonium salt-Br ionic liquid was mixed with 1-ethyl-3-methylimidazoline bis(trifluoromethanesulfonyl)imine in a third organic solvent and stirred at 25-30°C for 20-30 h, followed by refrigeration at 0-5°C for 18-25 h; then the third organic solvent was removed by rotary evaporation to obtain the quaternary ammonium salt-tetrafluoroborate ionic liquid monomer. The quaternary ammonium salt-tetrafluoroborate ionic liquid monomer and the diisocyanate trimer are reacted at 25-30℃ for 1-1.5h, and then at 75-85℃ for 2-4h to obtain the ionic liquid dipole unit.

10. The method for preparing the azobenzene-based cross-linked polyionic liquid ultraviolet photoelectric conversion material according to claim 9, characterized in that, The molar ratio of diethanolamine, bromobutane, and 1-ethyl-3-methylimidazoline bis(trifluoromethanesulfonyl)imine is 1:(2-2.2):1; the molar ratio of the quaternary ammonium salt-tetrafluoroborate ionic liquid monomer to the diisocyanate trimer is 3:1; the diisocyanate trimer is one of hexamethylene diisocyanate trimer, toluene diisocyanate trimer, and isophorone diisocyanate trimer; both the second and third organic solvents are acetonitrile.

11. The application of the azobenzene-based crosslinked polyionic liquid ultraviolet photoelectric conversion material according to any one of claims 1-5 in the fabrication of optoelectronic devices.

12. The application according to claim 11, characterized in that, A photoelectric device is obtained by curing a cross-linked polyionic liquid ultraviolet photoelectric conversion material between two electrode sheets. The specific steps are as follows: Azobenzene photosensitive units and ionic liquid dipole units were reacted at a molar ratio of 3:2 at 55-65℃ for 0.5-1h. The resulting azobenzene-based cross-linked polyionic liquid ultraviolet photoelectric conversion material was then uniformly coated onto two electrode sheets and cured at 75-85℃ to constant weight. The two electrode sheets coated with the azobenzene-based cross-linked polyionic liquid ultraviolet photoelectric conversion material were then bonded together, pressed, and encapsulated to obtain an azobenzene-based cross-linked polyionic liquid ultraviolet optoelectronic device. The thickness of the coated photoelectric conversion material was 15-20μm.

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