A method for preparing a stable free radical N-type small molecule cathode interface layer

Abstract

The present invention discloses a method for preparing a stable free radical N-type small molecule cathode interface layer. The synthesis process of the present invention is simple and the product can be obtained in only two steps. Since the side chain of the cathode interface layer PDI-TEMPO-NN contains polar groups, the material is endowed with environmentally friendly water / alcohol solubility. At the same time, the introduction of air-stable nitroxide radicals promotes the extraction and transmission of charges, which is beneficial to improving the electrical conductivity of the material; thanks to the amino groups in the side chains of PDI-TEMPO-NN, an interface dipole can be formed, the interface potential barrier can be reduced, an ohmic contact can be formed, the selective transmission of electrons and the built-in electric field can be improved, the cathode can collect electrons, and ultimately the performance of the device can be improved. Therefore, the device based on the cathode interface layer PDI-TEMPO-NN of the present invention achieved an energy conversion efficiency of 16.01%, which is higher than the energy conversion efficiency of 15.23% based on the classic cathode interface layer PDINN.

Description

Technical Field

[0001] The present invention relates to the technical field of organic solar cell cathode interface layers, and in particular to a method for preparing a stable free radical N-type small molecule cathode interface layer. Background Art

[0002] To meet the growing global energy demand, using organic solar cells to directly convert solar energy into electricity is one of the best solutions. Therefore, a lot of research is focused on developing a new generation of photovoltaic technologies, such as dye-sensitized solar cells, organic solar cells (OSCs), quantum dot solar cells, and perovskite solar cells.

[0003] Organic solar cells (OSCs) have attracted considerable attention from researchers both domestically and internationally due to their solution-processability, low cost, lightweight, flexibility, and ease of fabrication for large-area flexible devices. Since the advent of non-fullerene acceptors, the power conversion efficiency (PCE) of organic solar cells has rapidly improved. To date, the highest PCE for single-junction binary OSCs (OSCs) has exceeded 19%, demonstrating the enormous potential of this next-generation photovoltaic technology. Organic solar cells are composed of an anode, an anode interface layer, an active layer, a cathode interface layer, and a cathode. In addition to optimizing the active layer, interface engineering plays a crucial role in improving the performance and stability of organic solar cell devices. The cathode interface layer can modulate the energy level alignment between the organic material and the electrode and the work function of the Ag electrode, thereby forming an ohmic contact between the organic interface and the electrode. Furthermore, the cathode interface layer can facilitate carrier extraction by doping the active layer. Perylene diimide derivatives are among the most popular candidates for the cathode interface layer due to their readily available raw materials, diverse synthesis methods, and strong electron affinity. Summary of the Invention

[0004] The present invention provides a method for preparing a stable free radical N-type small molecule cathode interface layer. Perylene diimide derivatives have good electron affinity. The present invention improves the electron mobility of the material by introducing 4-amine-2,2,6,6-tetramethyl diphenylpiperidin nitroxide free radicals; at the same time, the introduction of an amino side chain at the bay position gives the material environmentally friendly water / alcohol-soluble processing characteristics, which meets the national green and low-carbon development needs.

[0005] The technical solution of the present invention is: an N-type small molecule cathode interface layer with stable free radicals, comprising a structure of Formula 1, wherein the structural expression of Formula 1 is:

[0006]

[0007] Furthermore, a method for preparing a stable free radical N-type small molecule cathode interface layer comprises the following steps:

[0008] Step 1: Synthesis of 1,7-dibromoperylene diimide side chain PDI-TEMPO-Br:

[0009] (1) 1,7-Dibromo-3,4,9,10-perylenetetracarboxylic dianhydride (0.4 mmol, 0.22 g) and 4-amino-2,2,6,6-tetramethyldiphenylpiperidinol (1.19 mmol, 0.20 g) were added to a round-bottom flask. N-methylpyrrolidone (10 mL) and acetic acid (2 mL) were then added to the round-bottom flask. The mixture was evacuated and filled with nitrogen for three cycles. The mixture was heated and stirred at 90°C for 24 h.

[0010] (2) After the reaction is completed, the mixture is poured into methanol (200 mL), allowed to stand, and filtered to obtain an orange-red solid crude product;

[0011] (3) The crude product was dissolved in a small amount of dichloromethane and eluted with dichloromethane: ether = 12:1. It was then recrystallized from chloroform and ethanol to obtain an orange-red solid PDI-TEMPO-Br with a yield of 65%;

[0012] Step 2: Synthesis of a stable radical N-type small molecule cathode interface layer PDI-TEMPO-NN;

[0013] (1) PDI-TEMPO-Br (0.5 mmol, 0.43 g) and N,N-dimethyl-1,3-propanediamine (4 mmol, 0.8 mL) were added to a round-bottom flask. N,N-dimethylformamide (20 mL) was then added. The mixture was evacuated and filled with nitrogen for three cycles. The mixture was heated and stirred at 140°C for 24 h.

[0014] (2) After the reaction is completed, the reaction solvent is removed by vacuum distillation, dichloromethane and saturated brine are added thereto for extraction, and vacuum rotary evaporation is performed to obtain a dark green solid;

[0015] (3) The crude product was dissolved in a small amount of dichloromethane, added dropwise to n-hexane while stirring, allowed to stand, and centrifuged to obtain a dark green solid product PDI-TEMPO-NN with a yield of 85%.

[0016] Furthermore, the preparation method of the organic solar cell based on the stable free radical N-type small molecule cathode interface layer is specifically as follows:

[0017] The cleaned ITO was first blown dry with nitrogen and then cleaned in a plasma cleaner PLAMA for 6 min. PEDOT:PSS was filtered through a 0.45 μm polytetrafluoroethylene filter, drop-coated on the ITO, and spin-coated at 3500 rpm for 40 s. The ITO was then transferred to a heating stage and annealed at 135°C for 10 min.

[0018] The PM6:Y6 active layer solution was transferred using a pipette and spin-coated at a speed of 3000 rpm for 40 s, followed by annealing on a heating plate at 100 °C for 10 min.

[0019] Take the prepared 1 mg / mL PDI-TEMPO-NN methanol solution and spin-coat it on the surface of the active layer at a spin-coating speed of 3000 rpm for 40 seconds;

[0020] Finally, the sample after spin coating the cathode interface layer was transferred to the evaporation chamber of the thermal evaporation vacuum coating machine, and the vacuum was pumped to a pressure of 4×10 -4 Below Pa;

[0021] Switch the evaporation source to Ag and control the evaporation rate so that the thickness of Ag deposited on the cathode interface is 80 nm. This completes the preparation of the organic solar cell device.

[0022] Furthermore, the synthesis method of the N-type small molecule cathode interface layer PDI-TEMPO-NN based on the stable free radical is as follows: The specific synthesis route reaction equation is as follows:

[0023]

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The preparation process of the stable free radical N-type small molecule cathode interface layer PDI-TEMPO-NN disclosed by the present invention is simple, and the product can be obtained in only two steps; (2) The stable free radical N-type small molecule cathode interface layer developed by the present invention has environmentally friendly water / alcohol soluble processing characteristics due to the presence of side chain polar groups, which is convenient for large-scale roll-to-roll printing production in the future; (3) The introduction of air-stable nitroxide radicals promotes the extraction and transmission of charges, which is beneficial to improving the electrical conductivity of the material; (4) Thanks to the small molecule amino functional groups, an interface dipole can be formed, the interface potential barrier can be reduced, and an ohmic contact can be formed, thereby improving the selective transport of electrons and the built-in electric field, which is beneficial to improving device performance. Compared with the PCE and FF obtained based on the existing classic cathode interface layer PDINN device, which are 15.23% and 72.48% respectively. The PCE and FF of the PDI-TEMPO-NN cathode interface layer device based on the present invention are increased to 16.01% and 74.47% respectively (see Appendix). Figure 4 ). (5) The secondary amine in the amino side chain can form hydrogen bonds with F and H in the active layer, thereby improving the interface compatibility and interface stability and improving the interface contact; the tertiary amine group at the end can form a large number of interface dipoles to reduce the work function of the Ag electrode, thereby forming a good ohmic contact between the active layer and the electrode, enhancing the built-in electric field and ultimately improving the device efficiency. The cathode interface layer PDI-TEMPO-NN developed by the present invention is applied to an organic solar cell with PM6:Y6 as the active layer, which effectively improves the open circuit voltage (VOC ), fill factor (FF) and short-circuit current density (J SC ). Compared with the PCE of organic solar cells based on the classic cathode interface layer PDINN, which is 15.23% (V OC =0.834V, J SC =25.19mAcm -2 , FF=72.48%), the PCE of the organic solar cell as the cathode interface layer of the present invention is increased to 16.01% (V OC =0.846V, J SC =25.35mA cm -2 , FF = 74.47%), J obtained from the EQE spectrum integration SC The value is also based on the fact that PDI-TEMPO-NN is higher than PDINN ( Figure 5 ), which is consistent with the JV curve ( Figure 4 ) obtained J SC The values ​​match. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a structural diagram of the N-type small molecule cathode interface layer PDI-TEMPO-NN that stabilizes free radicals of the present invention.

[0026] Figure 2 This is a specific synthesis route for the free radical-stabilizing N-type small molecule cathode interface layer PDI-TEMPO-NN of the present invention.

[0027] Figure 3 This is a device structure diagram of an N-type small molecule cathode interface layer PDI-TEMPO-NN with stable free radicals based on the present invention.

[0028] Figure 4 This is the JV curve of the organic solar cell with PDI-TEMPO-NN as the cathode interface layer of the present invention.

[0029] Figure 5 This is the EQE curve of the organic solar cell with PDI-TEMPO-NN as the cathode interface layer of the present invention. DETAILED DESCRIPTION

[0030] The reaction of the present invention is as shown in the attached Figure 2 The specific reaction steps are as follows: Synthesis steps of a method for preparing a stable free radical N-type small molecule cathode interface layer PDI-TEMPO-NN:

[0031] Step 1: Synthesis of 1,7-dibromoperylene diimide side chain PDI-TEMPO-Br:

[0032] (1) 1,7-Dibromo-3,4,9,10-perylenetetracarboxylic dianhydride (0.4 mmol, 0.22 g) and 4-amino-2,2,6,6-tetramethyldiphenylpiperidinol (1.19 mmol, 0.20 g) were added to a round-bottom flask. N-methylpyrrolidone (10 mL) and acetic acid (2 mL) were then added. The mixture was evacuated and filled with nitrogen for three cycles. The mixture was heated and stirred at 90°C for 24 h.

[0033] (2) After the reaction is completed, the mixture is poured into methanol (200 mL), allowed to stand, and filtered to obtain an orange-red solid crude product.

[0034] (3) The crude product was dissolved in a small amount of dichloromethane and eluted with dichloromethane: ether = 12:1. It was then recrystallized from chloroform and ethanol to obtain an orange-red solid PDI-TEMPO-Br with a yield of 65%.

[0035] Step 2: Synthesis of a stable radical N-type small molecule cathode interface layer PDI-TEMPO-NN.

[0036] (1) PDI-TEMPO-Br (0.5 mmol, 0.43 g) and N,N-dimethyl-1,3-propanediamine (4 mmol, 0.8 mL) were added to a round-bottom flask. N,N-dimethylformamide (20 mL) was then added. The flask was evacuated and filled with nitrogen for three cycles. The mixture was heated and stirred at 140°C for 24 h.

[0037] (2) After the reaction is completed, the reaction solvent is removed by vacuum distillation, dichloromethane and saturated brine are added thereto for extraction, and vacuum rotary evaporation is performed to obtain a dark green solid.

[0038] (3) The crude product was dissolved in a small amount of dichloromethane, added dropwise to n-hexane while stirring, allowed to stand, and centrifuged to obtain a dark green solid product PDI-TEMPO-NN with a yield of 85%.

[0039] An organic solar cell device with a stable free radical N-type small molecule cathode interface layer, characterized by:

[0040] (1) The ITO conductive glass sheet was sequentially ultrasonicated with deionized water, acetone, and ethanol for 20 minutes each, blown dry with a nitrogen gun, and then treated with a plasma cleaning machine for 6 minutes.

[0041] (2) The hole transport layer PEDOT:PSS was spin-coated on a cleaned ITO glass slide using a 0.45 μm polytetrafluoroethylene filter at a speed of 3500 rpm for 30 s. The film was then annealed at 135°C for 10 min and subsequently transferred to a glove box.

[0042] (3) Prepare an active layer chloroform solution with a donor:acceptor mass ratio of 1:1.2 at a concentration of 15.2 mg / mL. Add 0.5% by mass of chloronaphthalene additive and heat-shock at 50°C for at least 2 h. Pipette the PM6:Y6 active layer solution and spin-coat it at 3000 rpm for 40 s. Then anneal it at 100°C on a heating plate for 10 min.

[0043] (4) Take the 1 mg / mL PDI-TEMPO-NN methanol solution prepared in advance and apply it on the surface of the active layer at a spin coating speed of 3000 rpm for 40 seconds.

[0044] (5) Finally, the sample after spin coating the cathode interface layer was transferred to the evaporation chamber of the thermal evaporation vacuum coating machine, and the vacuum was pumped to a pressure of 4×10 -4 The evaporation source was switched to Ag, and the evaporation rate was controlled to ensure that the thickness of Ag deposited on the cathode interface was 80 nm. This completed the fabrication of the organic solar cell device.

[0045] Under the optimal conditions of the device (test area of ​​0.043cm 2 ) for performance testing, where the JV test conditions are: AM1.5 G, 100mW cm -2 The JV characteristic curve was measured using a Keithley 2400 current / voltage data source meter under conditions of high-intensity simulated sunlight (SAN-EI model: XES-40S3-TT). The EQE was measured using a QE-R3011 (Enli Technology Co., Ltd.).

[0046] Figure 4 The JV curve of the organic solar cell with PDI-TEMPO-NN as cathode interface layer is shown in the figure. The test results include open circuit voltage (V OC ), short-circuit current (J SC ), fill factor (FF) and power conversion efficiency (PCE), where: PCE = V OC *J SC *FF / P in (P in The test results of the device are shown in Table 1.

[0047] Table 1 Photovoltaic performance of organic solar cells based on PM6:Y6 as active layer with different cathode interface layers

[0048]

[0049] As can be seen from the results in Table 1, the organic solar cell device using PDI-TEMPO-NN, a stable free radical N-type small molecule cathode interface layer developed by the present invention, achieved a PCE of 16.01%, which is higher than the device efficiency of 15.23% of the reference device, an organic solar cell based on the classic cathode interface layer PDINN. In addition, the simultaneous improvements in short-circuit current density, fill factor, and open-circuit voltage demonstrate that the PDI-TEMPO-NN cathode interface layer developed by the present invention has good potential application value in the field of organic solar cells.

[0050] The present invention has the following beneficial effects: the synthesis process is simple, with the product obtained in just two steps; the cathode interface layer PDI-TEMPO-NN developed by the present invention has the characteristics of environmentally friendly water / alcohol solubility; the introduction of air-stable nitroxide radicals promotes charge extraction and transfer, which is beneficial for improving the conductivity of the material PDI-TEMPO-NN; and the amino functional groups in the PDI-TEMPO-NN side chains can form an interface dipole, reduce the interfacial potential barrier, form an ohmic contact, and improve the device's PCE. Compared to the PCE of 15.23% obtained with the existing classic cathode interface layer PDINN device, the PCE of the PDI-TEMPO-NN cathode interface layer device based on the present invention is improved to 16.01%.

Claims

1. An N-type small molecule cathode interface layer that stabilizes free radicals, comprising a structure of Formula 1, wherein the structural expression of Formula 1 is:

2. The method for preparing a stable free radical N-type small molecule cathode interface layer according to claim 1, comprising the following steps: Step 1: Synthesis of 1,7-dibromoperylene diimide side chain PDI-TEMPO-Br: (1) 1,7-Dibromo-3,4,9,10-perylenetetracarboxylic dianhydride (0.4 mmol, 0.22 g) and 4-amino-2,2,6,6-tetramethyldiphenylpiperidinol (1.19 mmol, 0.20 g) were added to a round-bottom flask, and then N-methylpyrrolidone (10 mL) and acetic acid (2 mL) were added to the round-bottom flask. The mixture was evacuated and filled with nitrogen for three cycles. Finally, the mixture was heated and stirred at 90 °C for 24 h. (2) After the reaction is completed, the mixture is poured into methanol (200 mL), allowed to stand, and filtered to obtain an orange-red solid crude product; (3) The crude product was dissolved in a small amount of dichloromethane and eluted with dichloromethane: ether = 12:

1. It was then recrystallized from chloroform and ethanol to obtain an orange-red solid PDI-TEMPO-Br with a yield of 65%; Step 2: Synthesis of a stable radical N-type small molecule cathode interface layer PDI-TEMPO-NN; (1) PDI-TEMPO-Br (0.5 mmol, 0.43 g) and N,N-dimethyl-1,3-propanediamine (4 mmol, 0.8 mL) were added to a round-bottom flask, followed by N,N-dimethylformamide (20 mL). The mixture was evacuated and filled with nitrogen for three cycles. The mixture was heated and stirred at 140 °C for 24 h. (2) After the reaction is completed, the reaction solvent is removed by vacuum distillation, dichloromethane and saturated brine are added thereto for extraction, and vacuum rotary evaporation is performed to obtain a dark green solid; (3) The crude product was dissolved in a small amount of dichloromethane, added dropwise to n-hexane while stirring, allowed to stand, and centrifuged to obtain a dark green solid product PDI-TEMPO-NN with a yield of 85%.

3. The method for preparing an organic solar cell with a stable free radical N-type small molecule cathode interface layer according to claim 1, specifically comprising: The cleaned ITO was first blown dry with nitrogen and then cleaned in a plasma cleaner PLAMA for 6 min. PEDOT:PSS was filtered through a 0.45 μm polytetrafluoroethylene filter, drop-coated on the ITO, and spin-coated at 3500 rpm for 40 s. The ITO was then transferred to a heating stage and annealed at 135°C for 10 min. The PM6:Y6 active layer solution was transferred using a pipette and spin-coated at a speed of 3000 rpm for 40 s, followed by annealing on a heating plate at 100 °C for 10 min. Take the prepared 1 mg / mL PDI-TEMPO-NN methanol solution and spin-coat it on the surface of the active layer at a spin-coating speed of 3000 rpm for 40 seconds; Finally, the sample after spin coating the cathode interface layer was transferred to the evaporation chamber of the thermal evaporation vacuum coating machine, and the vacuum was pumped to a pressure of 4×10 -4 Below Pa; The evaporation source was switched to Ag, and the evaporation rate was controlled so that the thickness of Ag deposited on the cathode interface was 80 nm. Thus, the preparation of the organic solar cell device was completed.

4. The method for synthesizing a stable free radical N-type small molecule cathode interface layer PDI-TEMPO-NN according to claim 1, specifically: the specific synthesis route reaction equation is as follows:

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