Cathode interface material and preparation method and application thereof

Abstract

The invention relates to the technical field of organic solar cells, in particular to a cathode interface material and a preparation method and application thereof. The NDI-X cathode interface material is obtained by taking naphthalene-1, 4, 5, 8-tetracarboxylic dianhydride as a starting material through amidation reaction, and the material not only can form good interface contact with a non-fullerene active layer and greatly reduce charge recombination, but also has conductivity higher than that of a traditional naphthalene-1, 4, 5, 8-tetracarboxylic dianhydride material and can realize rapid electron conduction; meanwhile, the work function adjusting capacity is high, the work function of the metal cathode can be effectively reduced, energy level matching of the cathode and the active layer is optimized, efficient electron injection and extraction are assisted, and then the photoelectric conversion efficiency of the device is improved. The novel cathode interface material designed through the structure is a key way for realizing cooperative control of a nanoscale phase separation form and a photophysical process, so that a high-efficiency organic solar cell can be prepared.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of organic solar cells, and particularly relates to a cathode interlayer material and a preparation method and application thereof. BACKGROUND

[0002] As a new type of photovoltaic technology, organic solar cells (OSCs) have attracted extensive attention in recent years due to their potential advantages such as light weight, flexibility, solution processability and low cost. The improvement of the photoelectric conversion efficiency of OSCs depends on the synergistic development of the design of the photoactive layer material, the optimization of the device structure and the interface engineering. In the device structure, the cathode interlayer (CIL) is located between the photoactive layer and the metal cathode, and it plays a key role in energy level matching, selective charge extraction and transport, and suppression of charge recombination. It has a decisive influence on the core performance parameters of the device such as open-circuit voltage (VOC), short-circuit current density (JSC) and fill factor (FF).

[0003] At present, the photoactive layer of high-performance OSCs is mostly based on a bulk heterojunction blending system of polymer donor and non-fullerene acceptor (NFA). The efficiency of this system not only depends on the photoelectric properties of the donor and acceptor materials themselves, but also is closely related to the nanoscale phase separation morphology formed by the blending film. The ideal phase separation morphology can provide sufficient donor-acceptor interface for exciton dissociation, and at the same time form a continuous and interpenetrating double-continuous transport channel to facilitate the rapid separation and transport of charges. However, how to accurately regulate the morphology of the active layer and make it highly efficient in the subsequent charge collection process is still an important challenge. On the other hand, non-fullerene acceptors usually have a deep LUMO energy level, which requires the cathode interlayer material in contact with it to have a lower work function and good electron affinity to achieve precise alignment of the energy levels and reduce the potential barrier for electron injection or extraction.

[0004] Although traditional cathode interface materials such as PFN-Br, PDINO and the like have achieved certain success, when matched with non-fullerene acceptor systems, they often face problems such as unsatisfactory energy level matching, high interface contact resistance, or limited ability to regulate the morphology of the active layer. This may lead to low electron extraction efficiency, serious interface charge recombination, and limit the further improvement of JSC and FF. In addition, the synthesis path of many high-performance interface materials is complex, difficult to purify, and high in cost, which is not conducive to large-scale practical application. Therefore, the development of a new type of cathode interface material requires that it not only can realize efficient energy level alignment with the cathode and the active layer (especially non-fullerene acceptor) through its own energy level structure, reduce the electron transport barrier, and inhibit the reverse diffusion of holes and charge recombination; but also can positively affect the phase separation morphology of the active layer, realize the synergistic optimization of morphology regulation and photophysical processes (such as charge generation, transport, and collection); at the same time, the material also needs to have the characteristics of simple synthesis and easy purification to meet the needs of industrial application.

[0005] Therefore, it is urgent to develop a new type of cathode interface layer material with excellent comprehensive performance to meet the above requirements, in order to promote the further improvement and practical application of organic solar cells, especially based on non-fullerene acceptor system. SUMMARY

[0006] The purpose of the present application is to provide a cathode interface material with excellent performance, good intermolecular packing effect, and help to improve the charge mobility, which has good photovoltaic performance in the test of organic solar cells.

[0007] The first object of the present application is to provide a cathode interface material, the structure of which is shown as formula I: wherein n is 2, 3 or 6.

[0008] The second object of the present application is to provide a preparation method of the cathode interface material as described above, which uses naphthalene-1,4,5,8-tetracarboxylic dianhydride as raw material and obtains the cathode interface material through amidation reaction.

[0009] Further, the specific operation is as follows: under nitrogen protection, naphthalene-1,4,5,8-tetracarboxylic dianhydride is added to a reaction container, dimethylformamide is injected, and stirred at a certain temperature T for half an hour. After the temperature is stabilized, the amine compound is injected, and the mixture is reacted at temperature T for one hour. Then, the dimethylformamide is dried by rotary evaporator to obtain a brown solid compound NDI-X.

[0010] Further, when n is 2, the amine compound is 2-(piperidin-1-yl)ethan-1-amine.

[0011] Furthermore, when n is 3, the amine compound is 2-(piperidin-1-yl)propane-1-amine.

[0012] Furthermore, when n is 6, the amine compound is one of 2-(piperidin-1-yl)hexane-1-amine and N1-(3-aminopropyl)-N3,N3-dimethylpropane-1,3-diamine.

[0013] Furthermore, the molar ratio of naphthalene-1,4,5,8-tetracarboxylic dianhydride to the amine compound is 1:(1~3). Preferably, it is 1:1.

[0014] Furthermore, T is 100-120℃.

[0015] A third object of the present invention is to provide an electron transport layer for an organic solar cell, the electron transport layer comprising the cathode interface material as described above.

[0016] A fourth objective of this invention is to provide an organic solar cell device, comprising, in sequence, an ITO substrate, a PEDOT:PSS layer, an active layer, an electron transport layer, and an electrode; the electron transport layer is as described above.

[0017] Compared with the prior art, the present invention has the following beneficial effects: (1) The cathode interface layer material provided by the present invention can achieve synergistic control of the phase separation morphology and photophysical processes of the blend film. By adjusting its own energy level structure, CIL can achieve energy level alignment between the cathode and the active layer, reduce the potential barrier for electron transport from the active layer (acceptor material) to the cathode, and suppress hole back diffusion (reduce charge recombination), ensuring efficient and selective extraction and collection of electrons, and directly improving the short-circuit current (JSC) and fill factor (FF) of the device.

[0018] NDI-X exhibits high electron affinity and electron mobility. On one hand, it can significantly reduce the work function of metal cathodes (such as Al and Ag) through interfacial dipole interactions, enabling precise matching of the lowest unoccupied molecular orbitals (LUMOs) with the photoactive layer (especially non-fullerene acceptors), thus greatly reducing the electron transport barrier. On the other hand, its excellent electron conductivity can accelerate interfacial electron extraction while suppressing hole back diffusion, effectively reducing nonradiative recombination losses and directly increasing the device's open-circuit voltage (V). o c) and short-circuit current (Jsc).

[0019] (2) The novel cathode interface material designed by the present invention through structure is a key way to achieve synergistic control of nanoscale phase separation morphology and photophysical process, thereby enabling the fabrication of high-efficiency organic solar cells.

[0020] (3) The synthesis process provided by the present invention is simple and easy to purify, and has good prospects for practical application. Attached Figure Description

[0021] Figure 1 The compound NDI-X (C2) prepared in Example 1 of this invention 1 H NMR spectrum; Figure 2 The compound NDI-X (C3) prepared in Example 2 of this invention 1 H NMR spectrum; Figure 3 The compound NDI-X (C6) prepared in Example 2 of this invention 1 H NMR spectrum; Figure 4 Current density-voltage (V) of the organic solar energy device prepared for Example 1 of the present invention J-V )test; Figure 5 The external quantum efficiency (EQE) test diagram of the organic solar energy device prepared in Example 1 of the present invention is shown. Detailed Implementation

[0022] To more clearly explain the technical solution and beneficial effects of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and embodiments. It should be noted that the described accompanying drawings are only some embodiments of the present invention and are used only to explain the present invention, and should not be construed as limiting the present invention. Unless otherwise specified, the equipment and reagents used in the present invention are commercially available products conventional in this technical field.

[0023] The present invention provides a novel cathode interface material with the structural formula shown in Formula I. , where n is 2, 3, or 6.

[0024] It can be synthesized from the starting material naphthalene-1,4,5,8-tetracarboxylic dianhydride (CAS No.: 81-30-1), and the specific process route is as follows: Step 1: Under nitrogen protection, naphthalene-1,4,5,8-tetracarboxylic dianhydride was added to a flask, followed by dimethylformamide (DMF). The mixture was stirred at 110 °C for half an hour. After the temperature stabilized, n=2: 2-(piperidin-1-yl)ethane-1-amine; n=3: 2-(piperidin-1-yl)propane-1-amine; n=6: 2-(piperidin-1-yl)hexane-1-amine, N1-(3-aminopropyl)-N3,N3-dimethylpropane-1,3-diamine were added. The mixture was reacted at 110 °C for one hour. The dimethylformamide was then evaporated to dryness using a rotary evaporator to obtain a brown solid compound, NDI-X.

[0025] The molar ratio of the compound naphthalene-1,4,5,8-tetracarboxylic dianhydride to n=2:2-(piperidin-1-yl)ethane-1-amine; n=3:2-(piperidin-1-yl)propane-1-amine; n=6:2-(piperidin-1-yl)hexane-1-amine is 1:(1~3), preferably 1:1; the molar ratio of the compound naphthalene-1,4,5,8-tetracarboxylic dianhydride to N1-(3-aminopropyl)-N3,N3-dimethylpropane-1,3-diamine is 1:(1~3), preferably 1:1.

[0026] The prepared cathode interface material NDI-X enables synergistic control of the phase separation morphology and photophysical processes in blended films. It inhibits excessive polymer aggregation, promotes the formation of a bicontinuous interpenetrating network between donor and acceptor, and balances exciton dissociation and charge transport efficiency, making it fully suitable for the fabrication of organic solar cell devices.

[0027] Unless otherwise specified, the "water" used in the following examples is deionized water.

[0028] In the following tests of this invention, proton nuclear magnetic resonance (NMR) spectra were performed on an AVANCE NEO 400MHz NMR spectrometer from Bruker GmbH, Germany. The solvent used was deuterated chloroform (CDCl3), and the instrument was calibrated with tetramethylsilane (TMS).

[0029] Liquid chromatography was performed using a Shimadzu LCMS-2010EV liquid chromatography-mass spectrometry system.

[0030] The synthetic route for compound NDI-X is as follows:

[0031] Example 1 Synthesis of compound NDI-X: When n=2 for NDI-X, under a nitrogen (N2) atmosphere, naphthalene-1,4,5,8-tetracarboxylic dianhydride (2 g, 7.80 mmol) was dissolved in 50 mL of DMF. The mixture was heated to 110 °C and stirred for half an hour. Then, 2-(piperidin-1-yl)ethane-1-amine (0.89 g, 7.80 mmol) and N1-(3-aminopropyl)-N3,N3-dimethylpropane-1,3-diamine (1.24 g, 7.80 mmol) were simultaneously added to a flask. The mixture was reacted at 110 °C for one hour. The dimethylformamide was then evaporated to dryness using a rotary evaporator to obtain a brown solid compound NDI-X (3.6 g, yield: 88%). The compound NDI-X... 1 HNMR spectrum as follows Figure 1shown. 1H NMR (400 MHz, Chloroform-d) δ 8.74 (s, 4H), 4.35 (s, 2H), 4.27 (s, 2H), 2.69 (d, J = 21.9 Hz, 6H), 2.53 (s, 4H), 2.30 (s, 2H), 2.20 (d,J = 2.6 Hz, 6H), 1.95 (s, 4H), 1.64 (s, 2H), 1.54 (s, 2H), 1.41 (s, 2H).

[0032] Example 2 Synthesis of compound NDI-X: When n=3 for NDI-X, under a nitrogen (N2) atmosphere, naphthalene-1,4,5,8-tetracarboxylic dianhydride (2 g, 7.80 mmol) was dissolved in 50 mL of DMF. The mixture was heated to 110 °C and stirred for half an hour. Then, 2-(piperidin-1-yl)propane-1-amine (1.1 g, 7.80 mmol) and N1-(3-aminopropyl)-N3,N3-dimethylpropane-1,3-diamine (1.24 g, 7.80 mmol) were added to a flask, and the mixture was reacted at 110 °C for one hour. The dimethylformamide was then evaporated to dryness using a rotary evaporator to obtain a brown solid compound NDI-X (3.42 g, yield: 82%). The compound NDI-X... 1 H NMR spectrum as shown Figure 2 shown. 1H NMR (400 MHz, Chloroform-d) δ 8.75 (s, 4H), 4.28 (s, 2H), 4.26(s, 2H), 2.82 -2.63 (m, 6H), 2.45 (d, J = 7.7 Hz, 4H), 2.34 (d, J = 7.6 Hz, 6H), 2.22 (s, 6H), 1.97 (q, J = 7.4 Hz, 4H), 1.67 (t, J = 7.5 Hz, 2H), 1.35 (s, 2H).

[0033] Example 3 When n=6 for NDI-X, under a nitrogen (N2) atmosphere, naphthalene-1,4,5,8-tetracarboxylic dianhydride (2 g, 7.80 mmol) was dissolved in 50 mL of DMF. The mixture was heated to 110 °C and stirred for half an hour. Then, 2-(piperidin-1-yl)hexane-1-amine (1.44 g, 7.80 mmol) and N1-(3-aminopropyl)-N3,N3-dimethylpropane-1,3-diamine (1.24 g, 7.80 mmol) were added to a flask. The mixture was reacted at 110 °C for one hour. Dimethylformamide was then evaporated to dryness using a rotary evaporator to obtain a brown solid compound NDI-X (3.9 g, yield: 87%). The compound NDI-X... 1 H NMR spectrum as shown Figure 3 shown. 1H NMR (400 MHz, Chloroform-d) δ 8.79 (s, 4H), 4.29 (t, J = 7.3 Hz, 2H), 4.19 (t, J = 7.8 Hz, 2H), 2.71 (dt, J = 24.7, 7.0 Hz, 6H), 2.43 -2.28(m, 10H), 2.22 (s, 8H), 1.98 (t, J = 7.2 Hz, 2H), 1.72 (dd, J = 32.8, 7.3 Hz, 4H), 1.50 -1.34 (m, 6H).

[0034] Comparative Example 1 When NDI-X n=4, under a nitrogen (N2) atmosphere, naphthalene-1,4,5,8-tetracarboxylic dianhydride (2 g, 7.80 mmol) was dissolved in 50 mL of DMF. The mixture was heated to 110 °C and stirred for half an hour. Then, 2-(piperidin-1-yl)butane-1-amine (1.22 g, 7.80 mmol) and N1-(3-aminopropyl)-N3,N3-dimethylpropane-1,3-diamine (1.24 g, 7.80 mmol) were added to a flask. The mixture was reacted at 110 °C for one hour. The dimethylformamide was then evaporated to dryness using a rotary evaporator to obtain a brown solid compound. NMR could not characterize it, possibly because it had formed a salt. This is because the four-carbon reactant readily forms a five-membered ring with the nitrogen atom.

[0035] Comparative Example 2 When NDI-X n=5, under a nitrogen (N2) atmosphere, naphthalene-1,4,5,8-tetracarboxylic dianhydride (2 g, 7.80 mmol) was dissolved in 50 mL of DMF. The mixture was heated to 110 °C and stirred for half an hour. Then, 2-(piperidin-1-yl)pentane-1-amine (1.33 g, 7.80 mmol) and N1-(3-aminopropyl)-N3,N3-dimethylpropane-1,3-diamine (1.24 g, 7.80 mmol) were added to a flask. The mixture was reacted at 110 °C for one hour. The dimethylformamide was then evaporated to dryness using a rotary evaporator to obtain a brown solid compound. NMR could not characterize it, possibly because it had formed a salt. This is because the five-carbon reactant readily forms a six-membered ring with the nitrogen atom.

[0036] Characterization of small molecule organic solar cell devices.

[0037] Fabrication of organic photovoltaic devices: The organic solar cell device comprises, in sequence, an ITO substrate, a PEDOT:PSS layer, an active layer, an electron transport layer, and electrodes. (1) After ultrasonic cleaning, ITO glass (indium tin oxide conductive glass) is treated with oxygen-Plasma. PEDOT:PSS poly(3,4-ethylenedioxythiophene):poly(styrene sulfonic acid) (Xi’an Yuri Solar Energy Technology Co., Ltd., PEDOT:PSS AI4083, product number: 306020, a mixed solution prepared at the time of purchase) is first spin-coated on ITO at 5000 rpm. The substrate is annealed at 150℃ for 15 minutes to obtain a substrate with a surface film thickness of about 40 nm.

[0038] (2) Then, the donor material PM6 and the acceptor L8-BO (structure shown below) are mixed to form a binary organic solar energy device (the mass ratio of donor and acceptor materials and additives is preferably 1:1:1). A mixed solvent of diiodomethane and chloroform (the volume ratio of diiodomethane to chloroform is 0.3 μL:100 μL) is added to prepare a blend solution (the total concentration of donor and acceptor is 20 mg / mL). The blend solution is coated onto the substrate in step (1) at a spin coating speed of 2000 rpm. An active layer with a thickness of about 130 nm is coated on the surface of the substrate.

[0039] (3) The substrate obtained in step (2) was placed in a 60 nm petri dish. Then, 60 μL of chlorobenzene was evenly coated on its surface and annealed with solvent vapor (85 °C, 5 min). Next, an electron transport layer NDI-X film (1 mg / ml methanol 1 mg NDI-X) was coated on the active layer at a spin coating speed of 3000 rpm, with a film thickness of about 10 nm. Finally, a 100 nm thick silver layer was deposited on top of the electron transport layer by vapor deposition.

[0040] The specific solar cell efficiencies are shown in Table 1 (the equipment used in the laboratory of this invention was a solar simulator, calibrated with silicon solar cells, and all tests were conducted under simulated sunlight, 100 mW / cm²). 2 ).

[0041]

[0042]

[0043] As can be seen from the data in Table 1, the compound NDI-X prepared in this invention, when used as a cathode interface material in organic photovoltaics, improves the photoelectric conversion efficiency of binary photovoltaic devices. This type of cathode interface material has unique advantages in the commercialization of organic solar cells.

[0044] Table 1. Photovoltaic parameters for optimal performance of NDI-X cathode interface devices.

[0045]

[0046] The donor PM6 and acceptor L8-BO were mixed to form a binary organic solar cell device (the preferred mass ratio of donor and acceptor materials and additives was 1:1:1). The NDI-X cathode interface material prepared in Example 1 was then used in the binary device to fabricate the organic solar cell device. The JV curve was then measured under simulated sunlight (at 100 mW / cm² on a solar simulator (SAN-EI, XES-40S2-CE)). 2 The current-voltage (JV) characteristics were measured using a Keithley 2450 source meter under an irradiation intensity of (AM 1.5G).

[0047] The results are as follows Figure 4 As shown in the figure, the compound NDI-X prepared in Example 1 exhibits characteristics in four aspects: efficient hole extraction and transport, energy level matching and interface modulation, high transmittance and film-forming properties, and stability and compatibility. It needs to possess high hole mobility and conductivity to rapidly collect and transport photogenerated holes while effectively blocking electrons and reducing carrier recombination. Its HOMO energy level needs to be precisely matched with the active layer donor material and the anode work function to reduce the interface barrier and improve charge separation and injection efficiency. Furthermore, the HTL needs to have high transmittance in the visible light region to ensure light absorption in the active layer, and can be uniformly formed using solution methods with controllable thickness. Simultaneously, it needs to possess chemical stability and interface compatibility to avoid electrode corrosion or side reactions with the active layer, balancing device efficiency and long-term lifespan.

[0048] like Figure 5The figure shows the external quantum efficiency (EQE) test results: the EQE spectrum was analyzed using a certified Newport IPCE measurement system. High-sensitivity EQE was measured using an integrated system (PECT-600, Enlitech), where the photocurrent is amplified and modulated via a locked instrument. This test confirms that the EQE spectrum of the NDI-X device is consistent with the values ​​obtained from the integral Jsc vs. JV curves of the solar spectrum (AM 1.5 G), with an error of less than 5%.

[0049] In summary, the interface material prepared by this invention, as a cathode interface material, not only forms good interfacial contact with the non-fullerene active layer, significantly reducing charge recombination, but also possesses a higher conductivity than traditional naphthalene-1,4,5,8-tetracarboxylic dianhydride materials, enabling rapid electron conduction. Simultaneously, its work function regulation capability is strong, effectively reducing the work function of the metal cathode, optimizing the energy level matching between the cathode and the active layer, facilitating efficient electron injection and extraction, and thus improving the photoelectric conversion efficiency of the device.

[0050] For any points not covered above, existing technologies shall apply.

[0051] Although specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them, without departing from the direction of the invention or exceeding the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc., made to the above embodiments based on the technical essence of the present invention should be included within the protection scope of the present invention.

Claims

1. A cathode interface material, characterized in that, The structural formula of the interface material is shown in Formula I: , where n is a natural number of 2, 3, or 6.

2. A method for preparing the cathode interface material as described in claim 1, characterized in that, The cathode interface material was obtained by amidation reaction using naphthalene-1,4,5,8-tetracarboxylic dianhydride as a raw material.

3. The preparation method according to claim 2, characterized in that, The specific operation is as follows: under nitrogen protection, naphthalene-1,4,5,8-tetracarboxylic dianhydride is added to the reaction vessel, dimethylformamide is injected, and the mixture is stirred at a certain temperature T for half an hour. After the temperature stabilizes, an amine compound is added, and the mixture is reacted at temperature T for one hour. Then, the dimethylformamide is evaporated to dryness using a rotary evaporator to obtain a brown solid compound NDI-X.

4. The preparation method according to claim 3, characterized in that, When n is 2, the amine compound is 2-(piperidin-1-yl)ethane-1-amine.

5. The preparation method according to claim 3, characterized in that, When n is 3, the amine compound is 2-(piperidin-1-yl)propane-1-amine.

6. The preparation method according to claim 3, characterized in that, When n is 6, the amine compound is one of 2-(piperidin-1-yl)hexane-1-amine or N1-(3-aminopropyl)-N3,N3-dimethylpropane-1,3-diamine.

7. The preparation method according to claim 3, characterized in that, The molar ratio of naphthalene-1,4,5,8-tetracarboxylic dianhydride to amine compounds is 1:(1~3).

8. The preparation method according to claim 3, characterized in that, T is 100-120℃.

9. An electron transport layer for an organic solar cell, characterized in that, The electron transport layer comprises the cathode interface material as described in claim 1.

10. An organic solar cell device, characterized in that, It comprises, in sequence, an ITO substrate, a PEDOT:PSS layer, an active layer, an electron transport layer, and an electrode; the electron transport layer is as described in claim 9.

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