Naphthalene diimide electron transport layer and preparation method thereof

Abstract

The invention relates to the technical field of organic solar cell electron transport layers, and provides a naphthalimide electron transport layer and a preparation method thereof. The naphthalimide electron transport layer has a structural formula as shown in a formula (I). The synthesis process is simple, an intermediate product does not need to be separated, histidine, 1, 4, 5, 8-naphthalene tetracarboxylic anhydride and N, N-dimethyl dipropyl triamine are used as raw materials, and the naphthalene diimide electron transport layer is prepared through two-step continuous reaction in an N, N-dimethyl formamide (DMF) solvent. And amido in an acyl polar side chain endows the material with environment-friendly water / alcohol-soluble green processing. Meanwhile, due to the fact that the NDI-His-NN based on the histidine imidazole ring contains more nitrogen atoms, the work function of an Ag electrode is reduced, the interface potential barrier is remarkably reduced, ohmic contact is formed, extraction and transmission of charges are promoted, and finally the performance of the organic solar device is improved.

Description

Technical Field

[0001] This invention belongs to the field of electron transport layer technology for organic solar cells, and particularly relates to a naphthalimide-based electron transport layer and its preparation method. Background Technology

[0002] Solar energy, as the most abundant clean energy source on Earth, has always been a key research area for efficient utilization technologies. Organic solar cells, with their advantages of solution processing, low cost, light weight, and flexibility, have shown broad application prospects. To promote the practical application of organic solar cells, the performance of their core components is crucial. The electron transport layer, as a key component, plays a vital role in the device's power conversion efficiency (PCE). Naphthalimide derivatives, due to their excellent electron transport capabilities, good chemical stability, and photochemical stability, have become an important research direction for electron transport layer materials. However, the preparation of traditional naphthalimide electron transport materials often involves complex synthesis processes and requires multiple separations of intermediate products. Furthermore, the processing performance of many existing materials needs improvement; some materials rely on toxic and harmful organic solvents for processing, which is inconsistent with the development trend of environmentally friendly materials and limits their promotion in large-scale production and practical applications.

[0003] Furthermore, the energy conversion efficiency of organic solar cells has always been a core research objective, and the interfacial barrier between the electron transport layer and the electrode is a key factor affecting charge extraction and transport efficiency. While traditional naphthalimide-based materials exhibit certain performance in electron transport, there is still room for improvement in reducing the electrode work function and the interfacial barrier, hindering further breakthroughs in energy conversion efficiency when applied in devices. Therefore, developing a naphthalimide-based electron transport layer with a simple synthesis process, environmental friendliness, and the ability to effectively reduce the electrode work function and improve device energy conversion efficiency, along with its preparation method, has become a significant research challenge in this field. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a naphthalimide-based electron transport layer and its preparation method, aiming to solve the problems mentioned in the background art.

[0005] In a first aspect, the present invention provides a naphthalimide-based electron transport layer having a structural formula as shown in formula (I): Formula (I).

[0006] Secondly, the present invention provides a method for preparing a naphthalimide-based electron transport layer, comprising the following steps: Step 1: Mix 1,4,5,8-naphthalenetetracarboxylic anhydride and histidine separately, then add N,N-dimethylformamide. Heat and stir the mixture at 140 ºC under nitrogen protection. Step 2: After the reaction is complete, cool to room temperature, then add N,N-dimethyldipropyltriamine, and continue heating and stirring at 140 ºC; Step 3: After the reaction is complete, cool to room temperature, distill the reaction solution under reduced pressure until it becomes viscous, then dialyze through water and methanol, filter, distill under reduced pressure to dryness, and dry to obtain NDI-His-NN.

[0007] Further, step one specifically involves adding 1 mmol of 1,4,5,8-naphthalenetetracarboxylic anhydride and 2.2 mmol of histidine to a round-bottom flask, then adding 10 mL of N,N-dimethylformamide to the round-bottom flask, evacuating to replace the nitrogen gas, circulating the mixture three times, and finally heating and stirring the mixture at 140 ºC for 12 h.

[0008] Further, step two specifically involves: after the reaction is completed, cooling to room temperature, adding 2.2 mmol of N,N-dimethyldipropyltriamine, and continuing to heat and stir at 140 ºC for 12 h.

[0009] Further, step three is as follows: After the reaction is completed, cool to room temperature, transfer the reaction solution to a single-necked flask and distill under reduced pressure until it becomes viscous, transfer the liquid to a dialysis bag, clamp the dialysis bag and dialyze in deionized water for 12 h, dialyze twice with deionized water, then dialyze with methanol for 12 h, dialyze twice with methanol, then filter the liquid in the dialysis bag, distill under reduced pressure to dryness, and finally dry at 60 ºC for 12 h to obtain NDI-His-NN.

[0010] Furthermore, the molecular weight cutoff of the dialysis bag is 500.

[0011] Furthermore, a method for preparing a naphthalimide-based electron transport layer yields a naphthalimide-based electron transport layer.

[0012] Thirdly, the present invention provides a method for preparing an organic solar cell based on a naphthalimide electron transport layer, comprising the following steps: (1) ITO was ultrasonically cleaned for 20 min in a bath filled with deionized water, acetone and isopropanol containing detergent. Then the electrode was dried with nitrogen and cleaned in a plasma cleaner for 10 min before use. PEDOT:PSS was spin-coated onto ITO at a spin speed of 3500 rpm for 40 s and then transferred to a heating stage for annealing at 135 ºC for 10 min. (2) Using a pipette, transfer 17.3 mg / mL chloroform solution (ratio of 1.0:1.2 w / w, containing 0.5% 1-chloronaphthalene) of PM6:Y6 active layer onto PEDOT:PSS layer at 3000 rpm for 30 s, and then anneal on a heating stage at 100 ºC for 10 min. (3) Dissolve 8.0 mg / mL NDI-His-NN and 1.0 mg / mL PDINN in methanol solution and spin coat them onto the active layer at a spin coating speed of 5000 rpm for 30 s. Then scrape off the ITO surface with a doctor blade to expose the ITO anode. In a vacuum evaporation machine, deposit an 80 nm Ag electrode.

[0013] The present invention has the following beneficial effects: (1) The one-pot synthesis effectively avoids the complex intermediate product separation and purification process in traditional multi-step reactions. This method is simple and significantly reduces the reagent consumption, energy input and equipment usage required for separation and purification, greatly shortens the preparation cycle, and is more suitable for large-scale industrial production. While improving experimental efficiency, the product yield reaches 68.5%, showing good prospects for practical application.

[0014] (2) The introduction of natural and low-cost histidine into the synthesis system of naphthalimide materials breaks through the raw material limitations of traditional synthesis routes. Histidine, as a natural amino acid widely found in organisms, is widely available and inexpensive, providing a greener and more sustainable synthesis route for the preparation of this type of electron transport layer material and significantly improving its industrialization feasibility.

[0015] (3) Based on the histidine imidazole ring, NDI-His-NN contains more nitrogen atoms, which can effectively reduce the work function of the Ag electrode by 0.62 eV, which is 0.17 eV higher than PDINN (0.45 eV), thus significantly promoting electron transport and collection efficiency. At the same time, the amino group in its polar side chain at the acyl site endows the material with environmentally friendly water / alcohol soluble processing, which is beneficial to subsequent large-area roll-to-roll printing processing.

[0016] (4) Organic solar energy devices based on PM6:Y6 active layers were fabricated using NDI-His-NN and PDINN as electron transport layers. Compared with PDINN-based devices, the photovoltaic parameters of the devices using NDI-His-NN as the electron transport layer were significantly improved, including open-circuit voltage, short-circuit current density, fill factor, and final PCE. Furthermore, EQE integrated current density results showed that the NDI-His-NN-based device reached 24.40 mA / cm², higher than the 23.10 mA / cm² of the PDINN-based device, indicating that the NDI-His-NN-based device possesses superior photogenerated charge collection capability. Therefore, NDI-His-NN is a high-performance electron transport layer material with application potential. Attached Figure Description

[0017] Exemplary embodiments of the present invention can be more fully understood by referring to the following figures: Figure 1 This is a specific synthetic route for a naphthalimide-based electron transport layer according to Example 1 of the present invention.

[0018] Figure 2 This is a schematic diagram of the synthesis of a naphthalimide-based electron transport layer NDI-His-NN according to Example 1 of the present invention.

[0019] Figure 3 This is the 1H NMR spectrum of a naphthalimide electron transport layer NDI-His-NN according to Example 1 of the present invention.

[0020] Figure 4 This is a schematic diagram of the organic solar cell structure in Embodiment 2 of the present invention, in which the NDI-His-NN electron transport layer is used as the electron transport layer.

[0021] Figure 5 The images show the Kelvin probe diagrams of the naphthalimide-based electron transport layer NDI-His-NN and the comparative material PDINN as electron transport layers in Example 2 of this invention.

[0022] Figure 6 Organic solar cells using naphthalimide-based electron transport layer NDI-His-NN and comparative material PDINN as electron transport layers in Example 2 of this invention. JV Line graph.

[0023] Figure 7 The graphs show the EQE curves of organic solar cell devices using NDI-His-NN (a naphthalimide-based electron transport layer) and PDINN (a comparative material) as electron transport layers in Example 2 of this invention. Detailed Implementation

[0024] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention.

[0026] This invention provides a naphthalimide-based electron transport layer having the structural formula shown in formula (I): Formula (I).

[0027] In some embodiments, the present invention provides a method for preparing a naphthalimide-based electron transport layer, comprising the following steps: Step 1: Mix 1,4,5,8-naphthalenetetracarboxylic anhydride and histidine separately, then add N,N-dimethylformamide. Heat and stir the mixture at 140 ºC under nitrogen protection. Step 2: After the reaction is complete, cool to room temperature, then add N,N-dimethyldipropyltriamine, and continue heating and stirring at 140 ºC; Step 3: After the reaction is complete, cool to room temperature, distill the reaction solution under reduced pressure until it becomes viscous, then dialyze through water and methanol, filter, distill under reduced pressure to dryness, and dry to obtain NDI-His-NN.

[0028] In some embodiments, step one specifically involves: adding 1 mmol of 1,4,5,8-naphthyltetracarboxylic anhydride and 2.2 mmol of histidine to a round-bottom flask, then adding 10 mL of N,N-dimethylformamide to the round-bottom flask, evacuating to replace the nitrogen gas, circulating the mixture three times, and finally heating and stirring the mixture at 140 ºC for 12 h.

[0029] In some embodiments, step two specifically involves: after the reaction is completed, cooling to room temperature, adding 2.2 mmol of N,N-dimethyldipropyltriamine, and continuing to heat and stir at 140 ºC for 12 h.

[0030] In some embodiments, step three specifically involves: cooling to room temperature after the reaction is complete, transferring the reaction solution to a single-necked flask and distilling under reduced pressure until it becomes viscous, transferring the liquid to a dialysis bag, clamping the dialysis bag and dialyzing it in deionized water for 12 h, dialyzing twice with deionized water, then dialyzing with methanol for 12 h, dialyzing twice with methanol, then filtering the liquid in the dialysis bag, distilling under reduced pressure to dryness, and finally drying at 60 ºC for 12 h to obtain NDI-His-NN.

[0031] In some embodiments, the molecular weight cutoff of the dialysis bag is 500.

[0032] In some embodiments, a naphthalimide-based electron transport layer is prepared by a method for preparing a naphthalimide-based electron transport layer.

[0033] In some embodiments, the present invention provides a method for preparing an organic solar cell based on a naphthalimide electron transport layer, comprising the following steps: (1) ITO was ultrasonically cleaned for 20 min in a bath filled with deionized water, acetone and isopropanol containing detergent. Then the electrode was dried with nitrogen and cleaned in a plasma cleaner for 10 min before use. PEDOT:PSS was spin-coated onto ITO at a spin speed of 3500 rpm for 40 s and then transferred to a heating stage for annealing at 135 ºC for 10 min. (2) Use a pipette to transfer 17.3 mg / mL chloroform solution of PM6:Y6 active layer with 0.5% 1,8-diiodooctane as additive, spin-coat it onto PEDOT:PSS layer at 3000 rpm for 30 s, and then anneal it on a heating stage at 100 ºC for 10 min. (3) Dissolve 8.0 mg / mL NDI-His-NN and 1.0 mg / mL PDINN in methanol solution and spin coat them onto the active layer at a spin coating speed of 5000 rpm for 30 s. Then scrape off the ITO surface with a doctor blade to expose the ITO anode. In a vacuum evaporation machine, deposit an 80 nm Ag electrode.

[0034] Example 1: Preparation of naphthalimide-based electron transport layer NDI-His-NN (1) Add 1,4,5,8-naphthalenetetracarboxylic anhydride (1 mmol, 268 mg) and histidine (2.2 mmol, 341 mg) to a round-bottom flask, then add 10 mL of N,N-dimethylformamide (DMF) to the round-bottom flask, evacuate and replace with nitrogen gas, circulate three times, and finally heat and stir the mixture at 140 ºC for 12 h, then stop heating and cool to room temperature; (2) Add N,N-dimethyldipropyltriamine (2.2 mmol, 350 mg) to the above reaction system, and continue heating and stirring at 140 ºC for 12 h. The synthesis schematic diagram is shown below. Figure 2 As shown; (3) After the reaction was completed, the mixture was cooled to room temperature and transferred to a single-necked flask for vacuum distillation until it became viscous. The liquid was then transferred to a dialysis bag with a molecular weight cutoff of 500. The dialysis bag was clamped and placed in a 1000 mL beaker containing deionized water for dialysis for 12 h. The mixture was then dialyzed twice with deionized water, and then dialyzed twice with methanol for 12 h. The liquid in the dialysis bag was filtered, evaporated to dryness under vacuum, and finally dried in a vacuum drying oven at 60 ºC for 12 h to obtain the dark red solid target product NDI-His-NN with a yield of 68.5%.

[0035] The specific synthetic route of the naphthalimide electron transport layer NDI-His-NN is as follows: Figure 1 As shown.

[0036] The 1H NMR spectrum of the naphthalimide electron transport layer NDI-His-NN is as follows: Figure 3 As shown, the results are as follows: 1 H-NMR(400 MHz, DMSO)δ: 8.52 (d, J=8.4 Hz, 4H), 8.01 (s, 2H), 7.23 (d, J=1.8 Hz,2H), 7.15 (d, J=1.8 Hz, 2H), 2.35 (t, 16H), 1.98 (m, 8H), 1.76 (m, 12H).

[0037] This embodiment employs a one-pot synthesis process, which is simple to operate, significantly reduces separation and purification steps, shortens the reaction cycle, and improves synthesis efficiency, achieving a yield of 68.5% for the product NDI-His-NN. Using natural, low-cost histidine as a raw material not only reduces production costs but also enhances environmental friendliness and sustainability, facilitating large-scale industrial applications. Furthermore, the amino group in the polar side chain at the acyl position of NDI-His-NN imparts water / alcohol solubility to the material, making it even more suitable for environmentally friendly processing methods.

[0038] Example 2: Fabrication of an organic solar cell based on a naphthalimide electron transport layer (1) The ITO was ultrasonically cleaned for 20 min in a bath filled with deionized water, acetone and isopropanol containing detergent; then the electrode was dried with nitrogen and cleaned in a plasma cleaner for 10 min before use; PEDOT:PSS was spin-coated onto the ITO at a spin coating speed of 3500 rpm for 40 s and then transferred to a heating stage for annealing at 135 ºC for 10 min. (2) Pipette a chloroform solution of PM6:Y6 active layer (mass ratio PM6:Y6=1.0:1.2, containing 0.5% 1-chloronaphthalene) with a concentration of 17.3 mg / mL and 1,8-diiodooctane (0.5%) as additive, spin-coat it onto the PEDOT:PSS layer at 3000 rpm for 30 s, and then anneal it on a heating stage at 100 ºC for 10 min; (3) NDI-His-NN (8.0 mg / mL) and PDINN (1.0 mg / mL) were dissolved in methanol and spin-coated onto the active layer at a spin-coating speed of 5000 rpm for 30 s. The ITO surface was scraped off with a doctor blade to expose the ITO anode. An 80 nm Ag electrode was then deposited in a vacuum evaporation machine to complete the fabrication of the organic solar cell device, with a device area of ​​0.055 cm². 2 .

[0039] A schematic diagram of an organic solar cell structure with a naphthalimide-based electron transport layer, NDI-His-NN, as the electron transport layer is shown below. Figure 4 As shown.

[0040] Photovoltaic performance tests were conducted on organic solar cells with PM6:Y6 as the active layer and different electron transport layers (naphthalimide-based electron transport layer NDI-His-NN and the comparative material PDINN). The test results are shown in Table 1. Organic solar cells using NDI-His-NN as the electron transport layer and PDINN as the comparative material are also included. J- V Curve graph as Figure 6 As shown.

[0041] Table 1. Photovoltaic performance of organic solar cells with PM6:Y6 as the active layer and different electron transport layers.

[0042] Note: J SC a Integrated current density refers to the value obtained by integrating the current density generated by a solar cell over a certain wavelength range. This value reflects the energy conversion efficiency of the solar cell across the entire spectrum.

[0043] The results show that when applied to organic solar cell devices with PM6:Y6 as the active layer, the device based on the NDI-His-NN electron transport layer achieved a PCE of 17.08%, which is an improvement of 11.78% compared to the device based on the PDINN electron transport layer (15.28%). All specific device performance parameters are superior to those of PDINN. V OCIncrease by 0.01 V. J SC Increased by 1.34 mA / cm² (an increase of 5.13%), and FF increased by 3.57% (an increase of 5.03%).

[0044] The EQE curves of organic solar cell devices using naphthalimide-based electron transport layers NDI-His-NN and the comparative material PDINN as electron transport layers are shown in the figure. Figure 7 As shown, the EQE spectral integrated current is 1.30 mA / cm² higher than that of the PDINN-based device (an increase of 5.63%), indicating that the naphthalimide-based electron transport layer NDI-His-NN has better energy level matching and stronger charge transport capability.

[0045] Kelvin probe diagrams of the naphthalimide electron transport layer NDI-His-NN and the contrast material PDINN are shown below. Figure 5 As shown, the work function of the Ag electrode is -4.17 eV, the work function of Ag / PDINN is -3.72 eV, and the work function of Ag / NDI-His-NN is -3.55 eV. The results show that NDI-His-NN, based on the histidine imidazole ring, can effectively reduce the work function of the Ag electrode by 0.62 eV due to the presence of more nitrogen atoms, which is 0.17 eV higher than that of PDINN (0.45 eV), thus effectively improving the electron transport and collection efficiency.

[0046] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A naphthalimide electron transport layer, characterized by: The naphthalene diimide electron transport layer has a structural formula as shown in formula (I): Formula (I).

2. A method for preparing a naphthalimide-based electron transport layer, characterized by: The method comprises the following steps: Step one, 1,4,5,8-naphthalene tetracarboxylic anhydride and histidine are mixed respectively, and then N,N-dimethylformamide is added, and the mixture is heated and stirred under nitrogen protection at 140 °C; Step two, after the reaction is completed, the temperature is cooled to room temperature, and then N,N-dimethyl amines is added, and the heating and stirring is continued at 140 °C; Step three, after the reaction is completed, the temperature is cooled to room temperature, the reaction liquid is distilled under reduced pressure to a thick paste, and then dialysis is performed with water and methanol, suction filtration is performed, rotary evaporation is performed under reduced pressure, and finally drying is performed to obtain NDI-His-NN.

3. The production method according to claim 2, characterized by: Step one is specifically as follows: 1 mmol of 1,4,5,8-naphthalene tetracarboxylic anhydride and 2.2 mmol of histidine are added into a round-bottom flask, 10 mL of N,N-dimethylformamide is added into the round-bottom flask, vacuum replacement with nitrogen is performed for three cycles, and finally the mixture is heated and stirred at 140 °C for 12 h.

4. The production method according to claim 3, characterized by: Step two is specifically as follows: after the reaction is completed, the temperature is cooled to room temperature, 2.2 mmol of N,N-dimethyl amines is added, and the heating and stirring is continued at 140 °C for 12 h.

5. The production method according to claim 4, characterized by: Step three is specifically as follows: after the reaction is completed, the temperature is cooled to room temperature, the reaction liquid is transferred to a single-neck flask and distilled under reduced pressure to a thick paste, the liquid is transferred to a dialysis bag, the dialysis bag is clamped and placed in deionized water for dialysis for 12 h, dialysis is performed twice with deionized water, dialysis is performed for 12 h with methanol, dialysis is performed twice with methanol, then the liquid in the dialysis bag is suction filtered, rotary evaporation is performed under reduced pressure, and finally drying is performed at 60 °C for 12 h to obtain NDI-His-NN.

6. The production method according to claim 5, characterized by: The molecular weight cut-off of the dialysis bag is 500.

7. The naphthalene diimide electron transport layer obtained by the preparation method of any one of claims 2-6.

8. A method for preparing an organic solar cell based on a naphthalimide electron transport layer, characterized in that: The method comprises the following steps: (1) ITO is ultrasonically cleaned in a bath filled with deionized water containing detergent, deionized water, acetone and isopropanol for 20 min, then the electrode is dried with nitrogen, and then the electrode is placed in a plasma cleaning machine for cleaning for 10 min and is ready for use, PEDOT:PSS is spin-coated on ITO at a spin-coating speed of 3500 rpm for 40 s, and is transferred to a heating table for annealing at 135 °C for 10 min; (2) 17.3 mg / mL PM6:Y6 active layer solution containing chloroform is taken out with a pipette, and 0.5% of 1,8-diiodooctane is added as an additive, and then the solution is spin-coated on the PEDOT:PSS layer at a speed of 3000 rpm for 30 s, and then the solution is annealed on a 100 °C heating table for 10 min; (3) 8.0 mg / mL NDI-His-NN and 1.0 mg / mL PDINN are dissolved in a methanol solution, and then the solution is spin-coated on the active layer at a spin-coating speed of 5000 rpm for 30 s, and then the ITO surface is scraped with a doctor blade to expose the ITO anode, and then 80 nm of Ag electrode is evaporated in a vacuum evaporation machine.

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