Small-molecule electron transport material containing naphthalimide terminal group and preparation and application of small-molecule electron transport material

Abstract

The invention relates to the technical field of organic synthesis, in particular to a small-molecule electron transport material containing a naphthalimide terminal group and preparation and application thereof.4-bromo-1, 8-naphthalic anhydride is used as a raw material, brominated naphthalimide terminal groups are obtained through imidization, then different conjugated fused ring core units are used as raw materials, and the small-molecule electron transport material containing the naphthalimide terminal group is prepared through a one-step method. And coupling the conjugated fused ring core unit with naphthalimide through a coupling reaction to obtain the small-molecule electron transport material containing the naphthalimide terminal group. By virtue of high electron affinity, strong electron withdrawing property, good thermal stability and morphological stability and relatively strong designability of structure and function of naphthalimide, the micromolecule electron transport material shows excellent electron mobility, tight intermolecular accumulation and good three-dimensional charge transport characteristic; surface / interface defects can be effectively passivated, trap-assisted recombination is inhibited, and the photoelectric conversion efficiency and the stability of the perovskite solar cell are synergistically improved.

Description

Small molecule electron transport materials with naphthalimide end groups, their preparation and applications Technical Field

[0001] This invention relates to the field of organic synthesis technology, and in particular to small molecule electron transport materials containing naphthalimide end groups, their preparation and application. Background Technology

[0002] Perovskite solar cells have received widespread attention in the photovoltaic field in recent years due to their outstanding advantages such as high light absorption coefficient, tunable bandgap, long carrier diffusion length, and low-cost fabrication. Their photoelectric conversion efficiency has approached or even exceeded that of traditional silicon-based solar cells, making them an important direction for the development of the photovoltaic industry.

[0003] In the structure of perovskite solar cells, the electron transport layer, as one of the core functional layers, plays a crucial role in the efficient extraction and rapid transport of electrons, as well as the effective suppression of interfacial recombination, directly determining the photoelectric conversion efficiency and long-term operational stability of the cell device. Currently, inorganic metal oxides or fullerenes and their derivatives are commonly used as electron transport materials in existing perovskite solar cell devices. However, with the photovoltaic industry's ever-increasing demands for device performance and stability, traditional electron transport materials are gradually revealing many limitations, making it difficult to meet the industry's development needs.

[0004] For example, inorganic electron transport materials such as titanium dioxide and tin oxide typically require high reaction temperatures or complex post-processing, increasing preparation costs and hindering the development of flexible devices and large-area, low-cost fabrication. Furthermore, these inorganic materials are prone to surface defects and poor energy level matching, leading to interfacial carrier recombination and severely impacting device photoelectric conversion efficiency and long-term stability. While fullerene electron transport materials possess good electron mobility and some energy level compatibility, their complex synthesis routes, high raw material costs, and significant deficiencies in thermal and chemical stability limit their large-scale application. In addition, some existing organic electron transport materials suffer from poor solubility and film-forming properties, and their performance degrades significantly under actual operating conditions such as illumination, electric fields, and humidity, failing to meet the comprehensive requirements of perovskite solar cells for high efficiency, high stability, and scalable fabrication.

[0005] Therefore, developing a novel organic small molecule electron transport material that combines suitable lowest unoccupied molecular orbital energy levels, high electron mobility, excellent solubility and film-forming properties, while also exhibiting good chemical and environmental stability at the perovskite interface, has become a pressing technical problem to be solved in this field. Summary of the Invention

[0006] The purpose of this invention is to provide small molecule electron transport materials containing naphthalimide end groups, their preparation, and applications. Leveraging the high electron affinity and strong electron-withdrawing properties, good thermal and morphological stability, and strong structural and functional designability of naphthalimide, these small molecule electron transport materials exhibit excellent electron mobility, tight intermolecular packing, and good three-dimensional charge transport characteristics. They can effectively passivate surface / interface defects and suppress trap-assisted recombination. Simultaneously, the preparation method is simple, efficient, and low-cost. When applied to perovskite solar cells, it achieves a synergistic improvement in the photoelectric conversion efficiency and stability of perovskite solar cells.

[0007] To achieve the above objectives, this invention provides a small molecule electron transport material containing naphthalimide end groups. The small molecule electron transport material is a small molecule conjugated non-fullerene organic small molecule containing naphthalimide end groups, and its molecular structure is shown in Formula I: In Formula I, R includes one of the following: substituted or unsubstituted C1-C50 straight-chain alkyl, substituted or unsubstituted C3-C50 branched alkyl, substituted or unsubstituted C3-C50 amino, or substituted or unsubstituted C3-C50 dimethylammonium; Ar is a conjugated fused ring core unit with a conjugated structure and an electron acceptor.

[0008] Preferably, R is selected from one of the following structures: , .

[0009] Preferably, Ar is selected from one of the following structures, with the dashed lines indicating the connection points: (DPP) (ITIC) (TTIIG) (TIIG) (Y6); R2 each independently includes one of hydrogen, C1-C100 straight-chain alkyl, or C3-C100 branched alkyl.

[0010] The present invention also provides a method for preparing the above-mentioned small molecule electron transport material containing naphthalimide end groups, comprising the following steps: (1) preparing bromonaphthalimide intermediate A by imidization reaction of 4-bromo-1,8-naphthalenedicarboxylic anhydride and amino-substituted R; (2) coupling intermediate A with Ar monomer in the presence of a catalyst to obtain small molecule electron transport material containing naphthalimide end groups.

[0011] Preferably, in step (1), the molar ratio of 4-bromo-1,8-naphthalenedicarboxylic anhydride to the amino-substituted side chain R is 1:(1.05~1.10).

[0012] Preferably, in step (2), the Ar monomer is an organotin reagent or borate ester compound of the conjugated fused ring core unit Ar; the molar ratio of intermediate A to Ar monomer is (3-4):1.

[0013] Preferably, in step (2), the catalyst is one or more of bis(triphenylphosphine) palladium dichloride, diphenylphosphine ferrocene palladium dichloride, and tetra(triphenylphosphine) palladium.

[0014] Preferably, in step (2), the molar ratio of intermediate A to catalyst is 1:0.03.

[0015] Preferably, step (2) is carried out under a nitrogen atmosphere. After the reaction is completed, the reaction liquid is dropped into n-hexane, filtered, washed, dried, and the solid is collected.

[0016] This invention also provides the application of the above-mentioned small molecule electron transport material containing naphthalimide end groups as an organic optoelectronic material in perovskite solar cell devices.

[0017] Therefore, the present invention employs the above-mentioned small molecule electron transport material containing naphthalimide end groups and its preparation and application, which has the following beneficial effects: (1) The present invention uses a conjugated fused ring core unit as the molecular core structure. By introducing naphthalimide groups into the molecular end groups, the overall electron affinity of the molecule is effectively improved, making the lowest unoccupied molecular orbital energy level of the electron transport material more matched with the conduction band energy level of the perovskite light-absorbing layer. This is beneficial to reduce the electron injection barrier, improve the electron extraction and transport efficiency, passivate perovskite defects, and enhance the crystallinity of the perovskite film, thereby reducing the interfacial carrier recombination loss; (2) The molecular core structure of the present invention has a high degree of conjugation and good planarity, which helps to enhance the intermolecular π-π stacking and electron delocalization effect; the naphthalimide end groups, while ensuring molecular rigidity, play a role in the molecular stacking mode. The regulation effect enables the formation of continuous and uniform electron transport channels in the electron transport layer film, thereby improving the electron mobility of the electron transport material and improving the conductivity of the electron transport layer; at the same time, the organic small molecule electron transport material has good solubility and film-forming properties in the solution preparation process, and the formed electron transport layer film is dense, flat and has a low defect density, which is conducive to improving the interface contact quality between the electron transport layer and the perovskite layer and reducing non-radiative recombination caused by interface defect states; (3) The organic small molecule electron transport material of the present invention can be prepared by solution method under low temperature conditions, and has good compatibility with flexible substrates and large-area preparation processes. Without significantly increasing the complexity and cost of device preparation, it can achieve a synergistic improvement in the photoelectric conversion efficiency and stability of perovskite solar cells, and has good prospects for industrial application.

[0018] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0019] Figure 1 shows the HfNDIN prepared in Example 1 of this invention. 1 H NMR spectrum.

[0020] Figure 2 shows the ITIC-NDIN prepared in Example 1 of this invention. 1 H NMR spectrum.

[0021] Figure 3 shows the ITIC-NDIN prepared in Example 1 of this invention. 13 C10 NMR spectrum.

[0022] Figure 4 shows the HfNDINN prepared in Example 2 of this invention. 1 H NMR spectrum.

[0023] Figure 5 shows the ITIC-NDINN prepared in Example 2 of this invention. 1 H NMR spectrum.

[0024] Figure 6 shows the ITIC-NDINN prepared in Example 2 of this invention. 13 C10 NMR spectrum.

[0025] Figure 7 shows the DPP-NDIN prepared in Example 3 of this invention. 1 H NMR spectrum.

[0026] Figure 8 shows the DPP-NDIN prepared in Example 3 of this invention. 13 C10 NMR spectrum.

[0027] Figure 9 shows the DPP-NDINN prepared in Example 4 of this invention. 1 H NMR spectrum.

[0028] Figure 10 shows the DPP-NDINN prepared in Example 4 of this invention. 13 C10 NMR spectrum.

[0029] Figure 11 shows the TIIG-NDIN prepared in Example 5 of this invention. 1 H NMR spectrum.

[0030] Figure 12 shows the TIIG-NDIN prepared in Example 5 of this invention. 13 C10 NMR spectrum.

[0031] Figure 13 shows the TIIG-NDINN prepared in Example 6 of this invention. 1 H NMR spectrum.

[0032] Figure 14 shows the TIIG-NDINN prepared in Example 6 of the present invention. 13 C10 NMR spectrum.

[0033] Figure 15 shows the UV spectra of ITIC-NDIN, ITIC-NDINN, DPP-NDIN, DPP-NDINN, TIIG-NDIN and TIIG-NDINN prepared in this invention in chloroform solution.

[0034] Figure 16 shows the UV spectra of the thin films ITIC-NDIN, ITIC-NDINN, DPP-NDIN, DPP-NDINN, TIIG-NDIN and TIIG-NDINN prepared in this invention.

[0035] Figure 17 shows the energy level diagrams obtained by cyclic voltammetry testing of ITIC-NDIN, ITIC-NDINN, DPP-NDIN, DPP-NDINN, TIIG-NDIN, and TIIG-NDINN prepared in this invention.

[0036] Figure 18 shows the current density and voltage characteristic curves obtained from testing the application of ITIC-NDIN, DPP-NDIN, DPP-NDINN, TIIG-NDIN and TIIG-NDINN prepared in this invention as electron transport materials in perovskite solar cells.

[0037] Figure 19 shows the external quantum efficiency versus current integral curves obtained from testing the application of ITIC-NDIN, DPP-NDIN, DPP-NDINN, TIIG-NDIN, and TIIG-NDINN prepared in this invention as electron transport materials in perovskite solar cells. Detailed Implementation

[0038] The present invention will be further described below with reference to the accompanying drawings and embodiments. Unless otherwise defined, the technical or scientific terms used in this invention should be understood in their ordinary sense by those skilled in the art. The features mentioned above or in the specific examples mentioned in this invention can be combined arbitrarily, and these specific embodiments are only used to illustrate the invention and are not intended to limit the scope of the invention.

[0039] This invention provides a small molecule electron transport material containing naphthalimide end groups. The small molecule electron transport material is a small molecule conjugated non-fullerene organic small molecule containing naphthalimide end groups, and its molecular structure is shown in Formula I: In Formula I, R includes one of the following: substituted or unsubstituted C1-C50 straight-chain alkyl, substituted or unsubstituted C3-C50 branched alkyl, substituted or unsubstituted C3-C50 amino, or substituted or unsubstituted C3-C50 dimethylammonium; Ar is a conjugated fused ring core unit with a conjugated structure and an electron acceptor.

[0040] Preferably, R is selected from one of the following structures: , Its structure is an N-containing alkyl conjugated structure, which can effectively control the solubility, film formation and energy level structure of the material.

[0041] Preferably, Ar is selected from one of the following structures, with the dashed lines indicating the connection points: (DPP) (ITIC) (TTIIG) (TIIG) (Y6); R2 each independently includes one of hydrogen, C1-C100 straight-chain alkyl, or C3-C100 branched alkyl.

[0042] More preferably, small molecule electron transport materials containing naphthalimide end groups include one of the following structural formulas: , , , , , , , .

[0043] The core structure of this invention has a high degree of conjugation and good planarity, which helps to enhance the intermolecular π–π stacking and electron delocalization effect. The naphthalimide end group plays a regulatory role in the molecular stacking mode while ensuring molecular rigidity, so that a continuous and uniform electron transport channel is formed in the electron transport layer film, thereby improving the electron mobility of the material and improving the extraction efficiency between perovskite and electron transport layer, and effectively suppressing interfacial recombination.

[0044] This invention also provides a method for preparing the above-mentioned small molecule electron transport material containing a naphthylimide end group, comprising the following steps: (1) preparing bromonaphthalimide intermediate A by imidization reaction of 4-bromo-1,8-naphthalenedicarboxylic anhydride and amino-substituted R; the structural formula of intermediate A is as follows: .

[0045] (2) Intermediate A and Ar monomer are coupled in the presence of a catalyst to obtain a conjugated small molecule electron transport material with naphthalimide end groups.

[0046] Preferably, in step (1), the molar ratio of 4-bromo-1,8-naphthalenedicarboxylic anhydride to the amino-substituted side chain R is 1:(1.05~1.10).

[0047] Preferably, in step (2), the Ar monomer is an organotin reagent or borate ester compound of the conjugated fused ring core unit Ar; the molar ratio of intermediate A to Ar monomer is (3-4):1.

[0048] Preferably, in step (2), the catalyst is one or more of bis(triphenylphosphine) palladium dichloride, diphenylphosphine ferrocene palladium dichloride, and tetra(triphenylphosphine) palladium.

[0049] Preferably, in step (2), the molar ratio of intermediate A to catalyst is 1:0.03.

[0050] Preferably, step (2) is carried out under a nitrogen atmosphere. After the reaction is completed, the reaction liquid is dropped into n-hexane, filtered, washed, dried, and the solid is collected.

[0051] In a more preferred embodiment, step (2) uses anhydrous toluene as a solvent. After the reaction is complete, deionized water is added to quench the reaction, ethyl acetate is used to extract the organic phase, anhydrous Na2SO4 is used to dry the phase, the solvent is removed under reduced pressure, a small amount of toluene is used to dissolve the solid, and the solid is precipitated by adding it dropwise into n-hexane. The solid is then filtered, washed, dried, and collected.

[0052] The organic small molecule electron transport material provided by this invention can be prepared by solution method under low temperature conditions. It has good compatibility with flexible substrates and large-area fabrication processes. Without significantly increasing the complexity and cost of device fabrication, it can achieve a synergistic improvement in the photoelectric conversion efficiency and stability of perovskite solar cells, and has good prospects for industrial application.

[0053] This invention also provides the application of the above-mentioned small molecule electron transport material containing naphthalimide end groups as an organic optoelectronic material in perovskite solar cell devices.

[0054] Unless otherwise specified, "water" used in the following examples refers to deionized water. Proton NMR spectroscopy was performed on a Bruker AVANCE NEO 500MHz superconducting NMR spectrometer, Germany, using deuterated chloroform (CDCl3) as the solvent and tetramethylsilane (TMS) as the calibrator.

[0055] Example 1 This invention provides a small molecule electron transport material containing a naphthioimide end group, using indene dithiophene (ITIC) as the conjugated fused ring core unit Ar monomer and N,N-dimethyl-1,3-diaminopropane as the amino-substituted R, designated ITIC-NDIN. The preparation method includes the following steps: (1) At 0°C, N,N-dimethyl-1,3-diaminopropane (0.387 g, 3.79 mmol) is added to an ethanol (EtOH, 50 mL) solution of 4-bromo-1,8-naphthalenedicarboxylic anhydride (1.00 g, 3.61 mmol), the temperature is raised to 60°C and stirred for 2 h. After the reaction is detected to be complete by thin-layer chromatography, the reaction solution is poured into ice water (200 mL), filtered under reduced pressure, washed and dried to collect the crude solid to obtain a yellow solid as bromonaphthalimide intermediate A, designated HfNDIN (1.25 g, yield of this step 95.88%). The chemical reaction formula is as follows: .

[0056] 1 H NMR (500 MHz, CDCl3) δ 8.65 (dd, J = 7.2, 1.1 Hz, 1H), 8.56 (dd, J= 8.5, 1.2 Hz, 1H), 8.41 (d, J = 7.8 Hz, 1H), 8.04 (d, J = 7.9 Hz, 1H), 7.84(dd, J = 8.5, 7.3 Hz, 1H), 4.25 – 4.19 (m, 2H), 2.43 (t, J = 7.2 Hz, 2H), 2.25 (s, 6H), 1.91 (tt, J = 9.5, 6.5 Hz, 2H). Its 1 The H NMR is shown in Figure 1.

[0057] (2) Under a nitrogen atmosphere, the trimethyltin reagents of indene-dithiophene-thiophene, ITIC-Sn (0.20 g, 0.15 mmol), HfNDIN (0.16 g, 0.45 mmol), and tetrakis(triphenylphosphine)palladium (Pd(PPh3)4, 0.01 g, 0.015 mmol) were mixed in toluene (10 mL), and then heated to 110 °C and stirred for 4 h. After the reaction was confirmed to be complete by thin-layer chromatography, it was cooled to room temperature. The mixture was quenched with deionized water, the organic phase was extracted with ethyl acetate, dried over anhydrous Na2SO4, and the solvent was removed under reduced pressure. The solution was dissolved in a small amount of toluene, added dropwise to n-hexane (200 mL), filtered, washed with n-hexane and dried. The solid was collected to obtain a red solid, namely ITIC-NDIN (0.16 g, yield of 68.10% in this step). The chemical reaction formula is as follows: .

[0058] 1 H NMR (500 MHz, CDCl3) δ 8.72 (dd, J = 8.5, 1.2 Hz, 2H), 8.65 (dd, J= 7.2, 1.2 Hz, 2H), 8.58 (d, J = 7.6 Hz, 2H), 7.84 (d, J = 7.6 Hz, 2Hz). 7.78(dd, J = 8.5, 7.2 Hz, 2H), 7.60 (s, 2H), 7.57 (s, 2H), 7.25 (d, J = 8.5 Hz,8H), 7.17 – 7.09 (m, 8H), 4.25 (dd, J = 8.4 Hz, 4.4 Hz), 2.57 (dd, J = 9.1,6.6 Hz, 8H), 2.44 (t, J = 7.2 Hz, 4H), 2.26 (s, 12H), 1.98 – 1.88 (m, 4H),1.63 – 1.55 (m, 8H), (t, J = 6.9 Hz, 12H). 13 C NMR(126 MHz, CDCl3) δ 164.16, 163.90, 153.75, 146.36, 144.07, 142.37, 142.05,140.59, 140.02, 139.15, 131.8,65. 132.30, 131.44, 130.61, 129.61,129.00, 128.62, 128.49, 128.04, 127.29, 123.05, 122.28, 121.79, 11.78, 3.63, 63.39 45.45, 38.92, 35.60, 31.70, 31.26, 29.17, 26.15, 22.66, 14.13. 1 H NMR、 13 C NMR in Figure 2 and Figure 3.

[0059] Example 2 This invention provides a small molecule electron transport material containing a naphthioimide end group, with indene dithiophene (ITIC) as the conjugated fused ring core unit Ar monomer and N,N-dimethyldipropyltriamine as the amino-substituted R, designated ITIC-NDINN. The preparation method includes the following steps: (1) At 0°C, N,N-dimethyldipropyltriamine (0.604 g, 3.79 mmol) is added to an ethanol (50 mL) solution of 4-bromo-1,8-naphthalenedicarboxylic anhydride (1.00 g, 3.61 mmol). The temperature is raised to 60°C and stirred for 4 h. After the reaction is detected to be complete by thin-layer chromatography, the solvent is removed under reduced pressure. The crude product is dissolved in ethyl acetate and heated to 75°C. Impurities are removed by filtration. After removing the solvent from the filtrate under reduced pressure, a yellow solid is obtained as intermediate A of the compound bromonaphthalimide, designated HfNDINN (1.30 g, yield of 86.10% in this step). The chemical reaction formula is as follows: 1 H NMR (500 MHz, CDCl3) δ 8.58 (dd, J = 7.3, 1.2 Hz, 1H), 8.50 (dd, J= 8.5, 1.2 Hz, 1H), 8.34 (d, J = 7.8 Hz, 1H), 7.97 (d, J = 7.8 Hz, 1H), 7.77(dd, J = 8.5, 7.3 Hz, 1H), 4.18 (t, J = 7.1 Hz, 2H), 2.64 (t, J = 6.9 Hz,2H), 2.59 (t, J = 7.0 Hz, 2H), 2.25 (t, J = 7.3 Hz, 2H), 2.14 (s, 6H), 1.97 (s, 1H), 1.89 (p, J = 7.0 Hz, 2H), 1.60 (p, J = 7.2 Hz, 2H). Its 1H NMR is shown in Figure 4.

[0060] (2) Under a nitrogen atmosphere, the trimethyltin reagent of indene-dithiophene-thiophene, ITIC-Sn (0.20 g, 0.15 mmol), HfNDINN (0.187 g, 0.45 mmol), and tetra(triphenylphosphine)palladium (0.01 g, 0.015 mmol) were mixed in toluene (10 mL), and then heated to 110 °C and stirred for 4 h. After the reaction was confirmed to be complete by thin-layer chromatography, it was cooled to room temperature. The mixture was quenched with deionized water, the organic phase was extracted with ethyl acetate, dried over anhydrous Na2SO4, and the solvent was removed under reduced pressure. The solution was dissolved in a small amount of toluene, added dropwise to n-hexane (200 mL), filtered, washed with n-hexane, dried, and the solid was collected to obtain a red solid, namely ITIC-NDINN (0.16 g, yield of 63.51% in this step). The chemical reaction formula is as follows: 1 H NMR (500 MHz, CDCl3) δ 8.75 (d, J = 8.6 Hz, 2H), 8.69 – 8.62 (m,2H), 8.58 (d, J = 7.6 Hz, 2H), 7.84 (d, J = 7.6 Hz, 2H), 7.80 – 7.76 (m, 2H),7.75 – 7.71 (m, 2H), 7.59 (d, J = 5.5 Hz, 2H), 7.25 – 7.20 (m, 8H), 7.15 –7.12 (m, 8H), 4.28 (t, J = 6.9 Hz, 4H), 2.77 (d, J = 5.2 Hz, 4H), 2.61 – 2.51(m, 16H), 2.43 – 2.38 (m, 2H), 2.27 (s, 12H), 2.04 – 2.00 (m, 4H), 1.62 –1.55 (m, 12H), 1.37 – 1.28 (m, 24H), 0.86 – 0.84 (m, 12H). 13C NMR (126 MHz, CDCl3) δ 163.80, 163.77, 133.48, 133.41, 132.19, 132.06, 131.36, 131.17, 130.98, 130.69, 130.50, 130.25, 129.03, 128.64, 128.58, 128.47, 128.43,128.14, 128.05, 127.90, 127.85, 127.74, 125.95, 122.93, 122.06, 58.39, 48.70,46.62, 45.45, 38.05, 35.61, 31.70, 31.60, 31.27, 29.17, 27.48, 22.59, 14.13, 14.09. 1 H NMR, 13 The C NMR spectra are shown in Figures 5 and 6.

[0061] Example 3 This invention provides a small molecule electron transport material containing a naphthalene imide end group, using pyrrolopyrrole dione (DPP) as the conjugated fused ring core unit Ar monomer and N,N-dimethyl-1,3-diaminopropane as the amino-substituted R, designated as DPP-NDIN. Its preparation method includes the following steps: Step (1) is the same as in Example 1.

[0062] (2) Under a nitrogen atmosphere, trimethyltin reagents of pyrrolopyrrole dione, DPP-Eh-Sn (0.20 g, 0.235 mmol), HfNDIN (0.255 g, 0.706 mmol), and tetrakis(triphenylphosphine)palladium (0.027 g, 0.024 mmol), were mixed in toluene (10 mL), and then heated to 110 °C and stirred for 4 h. After the reaction was confirmed to be complete by thin-layer chromatography, it was cooled to room temperature. The mixture was quenched with deionized water, the organic phase was extracted with ethyl acetate, dried over anhydrous Na2SO4, and the solvent was removed under reduced pressure. The mixture was dissolved in a small amount of toluene, added to n-hexane (200 mL), filtered, washed with n-hexane, dried, and the solid was collected to obtain a black solid, namely DPP-NDIN (0.19 g, yield of 74.43% in this step). The chemical reaction formula is as follows: .

[0063] 1H NMR (500 MHz, CDCl3) δ 9.08 (d, J = 4.0 Hz, 2H), 8.69 (dd, J = 7.3,1.1 Hz, 2H), 8.65 (dd, J = 8.1, 1.5 Hz, 4H), 7.90 (d, J = 7.5 Hz, 2H), 7.83(dd, J = 8.6, 7.2 Hz, 2H), 7.54 (d, J = 4.0 Hz, 2H), 4.27 (dd, J = 8.6, 6.4Hz, 4H), 4.14 – 4.07 (m, 4H), 2.49 (t, J = 7.3 Hz, 4H), 2.30 (s, 12H), 2.08 –1.93 (m, 10H), 1.34 – 1.23 (m, 12H), 0.95 – 0.92 (m, 6H), 0.87 (d, J = 3.1Hz, 6H). 13 C NMR (126 MHz, CDCl3) δ 164.00, 163.73, 161.72, 145.11, 139.97,137.36, 136.16, 131.78, 131.66, 131.47, 130.56, 130.20, 129.76, 128.91,128.78, 127.70, 123.17, 122.86, 108.82, 57.26, 46.13, 45.33, 39.41, 38.93,30.35, 28.52, 26.01, 23.68, 23.11, 14.09, 10.59. 1 H NMR, 13 See Figures 7 and 8 for C NMR.

[0064] Example 4 This invention provides a small molecule electron transport material containing a naphthalene imide end group, with pyrrolopyrrole dione (DPP) as the conjugated fused ring core unit Ar monomer and N,N-dimethyldipropyltriamine as the amino-substituted R, designated as DPP-NDINN. Its preparation method includes the following steps: Step (1) is the same as in Example 2.

[0065] (2) Under a nitrogen atmosphere, the trimethyltin reagent of pyrrolopyrrole dione, DPP-Eh-Sn (0.20 g, 0.235 mmol), HfNDINN (0.295 g, 0.706 mmol), and tetrakis(triphenylphosphine)palladium (0.027 g, 0.024 mmol) were mixed in toluene (10 mL), and then heated to 110 °C and stirred for 4 h. After the reaction was confirmed to be complete by thin-layer chromatography, it was cooled to room temperature. The mixture was quenched with deionized water, the organic phase was extracted with ethyl acetate, dried over anhydrous Na2SO4, and the solvent was removed under reduced pressure. The solution was dissolved in a small amount of toluene, added dropwise to n-hexane (200 mL), filtered, washed with n-hexane, dried, and the solid was collected to obtain a black solid, namely DPP-NDINN (0.24 g, yield of 85.07% in this step). The chemical reaction formula is as follows: .

[0066] 1 H NMR (500 MHz, CDCl3) δ 9.07 (d, J = 4.0 Hz, 2H), 8.66 (dt, J =14.9, 7.2 Hz, 6H), 7.90 (d, J = 7.7 Hz, 2H), 7.83 (t, J = 7.9 Hz, 2H), 7.54(d, J = 4.0 Hz, 2H), 4.30 (t, J = 6.7 Hz, 4H), 4.13 – 4.06 (m, 4H), 2.98 (t,J = 6.2 Hz, 4H), 2.89 (t, J = 6.8 Hz, 4H), 2.59 (t, J = 6.4 Hz, 4H), 2.38 (s, 12H), 2.25 (s, 2H), 2.18 (q, J = 7.1 Hz, 4H), 2.05 – 1.81 (m, 10H), 1.40 (d,J = 21.5 Hz, 12H), 0.94 (t, J = 7.5 Hz, 6H), 0.88 – 0.85 (m, 6H). 13C NMR (126MHz, CDCl3) δ 164.25, 163.96, 161.70, 144.90, 139.93, 137.73, 136.13, 131.90,131.60, 130.82, 130.30, 129.76, 128.92, 128.88, 128.83, 127.78, 122.80,122.43, 108.87, 58.78, 53.44, 49.13, 46.14, 46.06, 45.37, 39.41, 37.59,30.34, 28.51, 26.59, 23.68, 23.11, 14.09, 10.60. 1 H NMR, 13 See Figures 9 and 10 for C NMR.

[0067] Example 5 This invention provides a small molecule electron transport material containing naphthalimide end groups, with indigofera tinigmata (TIIG) as the conjugated fused ring core unit Ar monomer and N,N-dimethyl-1,3-diaminopropane as the amino-substituted R, designated as TIIG-NDIN. Its preparation method includes the following steps: Step (1) is the same as in Example 1.

[0068] (2) Under a nitrogen atmosphere, the borate esters of isoindigo, TIIG-B(pin)2 (0.20 g, 0.27 mmol), HfNDIN (0.293 g, 0.81 mmol), and tetrakis(triphenylphosphine)palladium (0.03 g, 0.027 mmol), were mixed in toluene (20 mL). A saturated aqueous solution of potassium carbonate (20 mL) and anhydrous ethanol (8 mL) were added to the mixture, and the mixture was heated to 110 °C and stirred for 4 h. After the reaction was confirmed to be complete by thin-layer chromatography, it was cooled to room temperature. The mixture was quenched with deionized water, the organic phase was extracted with ethyl acetate, dried over anhydrous Na2SO4, and the solvent was removed under reduced pressure. The solution was dissolved in a small amount of toluene, added to n-hexane (200 mL), filtered, washed with n-hexane, dried, and the solid was collected to obtain a brown solid, TIIG-NDIN (0.22 g, yield of 77.58% in this step). The chemical reaction formula is as follows: .

[0069] 1H NMR (500 MHz, CDCl3) δ 9.38 (d, J = 8.2 Hz, 2H), 8.72 – 8.61 (m,4H), 8.37 (dd, J = 8.6, 1.2 Hz, 2H), 7.80 – 7.72 (m, 4H), 7.23 (dd, J = 8.2,1.6 Hz, 2H), 6.94 (d, J = 1.7 Hz, 2H), 4.28 (dd, J = 8.7, 6.4 Hz, 4H), 3.75(qdd, J = 14.1, 7.4, 4.4 Hz, 4H), 2.46 (t, J = 7.3 Hz, 4H), 2.27 (s, 12H),1.99 – 1.90 (m, 6H), 1.76 (s, 2H), 1.50 – 1.28 (m, 16H), 0.93 (t, J = 7.4 Hz, 6H), 0.84 (t, J = 6.9 Hz, 6H). 13 C NMR (126 MHz, CDCl3) δ 168.44, 164.20,163.98, 146.06, 145.73, 143.10, 133.32, 132.30, 131.40, 130.79, 130.03,129.86, 128.80, 127.52, 127.10, 124.06, 123.10, 122.36, 121.75, 109.69,57.34, 45.46, 44.50, 38.93, 37.75, 31.60, 30.73, 28.71, 26.19, 24.10, 14.05, 10.74. 1 H NMR, 13 The C NMR spectra are shown in Figures 11 and 12.

[0070] Example 6 This invention provides a small molecule electron transport material containing a naphthalene imide end group, with indigofera tinigmazone (TIIG) as the conjugated fused ring core unit Ar monomer and N,N-dimethyldipropyltriamine as the amino-substituted R, designated as TIIG-NDINN. Its preparation method includes the following steps: Step (1) is the same as in Example 2.

[0071] (2) Under a nitrogen atmosphere, the borate ester compound TIIG-B(pin)2 (0.20 g, 0.27 mmol), compound HfNDINN (0.34 g, 0.81 mmol), and tetrakis(triphenylphosphine)palladium (0.03 g, 0.027 mmol) of indigo were mixed in toluene (20 mL). A saturated aqueous solution of potassium carbonate (20 mL) and anhydrous ethanol (8 mL) were added to the mixture, and the mixture was heated to 110 °C and stirred for 4 h. After the reaction was confirmed to be complete by thin-layer chromatography, it was cooled to room temperature. The mixture was quenched with deionized water, the organic phase was extracted with ethyl acetate, dried over anhydrous Na2SO4, and the solvent was removed under reduced pressure. The solution was dissolved in a small amount of toluene, added dropwise to n-hexane (200 mL), filtered, washed with n-hexane, and dried. The solid was collected to obtain a brown solid, namely TIIG-NDINN (0.11 g, yield of 31.84% in this step). The chemical reaction formula is as follows: .

[0072] 1 H NMR (500 MHz, CDCl3) δ 9.38 (d, J = 8.1 Hz, 2H), 8.68 (t, J = 7.6Hz, 4H), 8.38 (d, J = 8.4 Hz, 2H), 7.80 – 7.72 (m, 2H), 7.25 – 7.21 (m, 2H), 6.94 (s, 2H), 4.30 (q, J = 6.5 Hz, 4H), 3.81 – 3.69 (m, 4H), 2.74 (t, J = 6.9Hz, 4H), 2.68 (t, J = 7.1 Hz, 4H), 2.36 – 2.30 (m, 4H), 2.23 (s, 12H), 2.04 –1.90 (m, 10H), 1.69 (p, J = 7.1 Hz, 4H), 1.48 – 1.33 (m, 16H), 0.93 (t, J =7.4 Hz, 6H), 0.84 (t, J = 7.1 Hz, 6H). 13C NMR (126 MHz, CDCl3) δ 168.44,164.28, 164.07, 146.14, 145.73, 143.07, 133.32, 132.37, 131.47, 130.86,130.04, 129.85, 128.81, 127.54, 127.11, 124.06, 123.01, 122.25, 121.75,109.68, 58.05, 48.33, 47.15, 45.52, 44.51, 38.40, 37.75, 30.73, 28.70, 28.35, 27.94, 24.09, 23.04, 14.05, 10.74. 1 H NMR, 13 See Figures 13 and 14 for C NMR.

[0073] Application Example: The small molecule electron transport materials prepared in Examples 1-6 are applied to perovskite solar cell devices, including the following steps: S1, Substrate Treatment: FTO glass (fluorinated tin oxide conductive glass) is sequentially subjected to ultrasonic cleaning and ozone treatment using a plasma cleaner; 2.8 mg of 4PADCB is dissolved in 4 mL of anhydrous ethanol, and the solution is spin-coated onto the FTO glass at a speed of 3000 rpm, followed by annealing in a nitrogen atmosphere at 100°C for 10 minutes to prepare a 4PADCB-modified substrate with a surface film thickness of approximately 5 nm. The structural formula of 4PADCB is: .

[0074] S2. Preparation of the perovskite absorber layer: 3.583 mg MABr, 11.744 mg PbBr2, 20.78 mg CsI, 256 mg FAI, 774 mg PbI2, and 16 mg MACl were dissolved in a mixed solvent of 800 μL DMF and 200 μL DMSO, and stirred to form a clear perovskite solution. The perovskite solution was spread evenly on a 4PADCB modified substrate and spin-coated at 1000 rpm for 5 s and 5000 rpm for 35 s. At the 35-second mark of spin-coating, 150 μL of a 0.25 mg / mL chlorobenzene solution of the small molecule electron transport material prepared in Examples 1-6 of this invention was dropped onto the center of the sample.

[0075] S3, Annealing and Functional Layer Deposition: The substrate obtained in S2 was thermally annealed (110℃, 20 min), and then C layers with a thickness of 20 nm were vacuum deposited. 60 The thin film and the 5nm BCP dense thin film were then deposited. Finally, a 100nm thick silver layer was deposited on top of the electron transport layer by vapor deposition as the back electrode to obtain the perovskite solar cell device.

[0076] Performance testing: Perovskite devices without a dedicated electron transport layer (PVSK) were used as the reference device. Perovskite solar cell devices prepared in Examples 1 and 3-6 with ITIC-NDIN, ITIC-NDINN, DPP-NDIN, DPP-NDINN, TIIG-NDIN, and TIIG-NDINN as electron transport layers were also tested for photoelectric performance. The equipment used was the 7SCSpec solar cell testing system, and the silicon standard photodetector was used for calibration. The results are shown in Figure 18 and Table 1.

[0077] Table 1. Photoelectric performance of different perovskite solar cell devices

[0078] As shown in Table 1 and Figure 18, when the small molecule electron transport material prepared in this invention is used as the electron transport layer, the photoelectric conversion efficiency (PCE) of the perovskite solar cell device is significantly higher than that of the reference device (17.39%). Among them, when ITIC-NDIN is used as the electron transport layer, the open-circuit voltage (V) of the cell is significantly higher. OC The voltage reached 1.093V, and the short-circuit current density (J) was [missing information]. SC ) reached 21.98 mA·cm -2 The fill factor (FF) reaches 80.85%, and the photoelectric conversion efficiency is as high as 19.44%, achieving optimal performance. This is because the small molecule electron transport material of this invention achieves a high degree of energy level matching with the perovskite light-absorbing layer through the synergistic structural design of the naphthalimide end group and the ITIC electron-withdrawing core. It also possesses excellent molecular stacking characteristics, electron transport efficiency, interface passivation ability, and film formation performance. It can efficiently extract transport electrons, effectively suppress carrier recombination, and ensure good interfacial contact quality of the device, thereby optimizing the photovoltaic parameters of the perovskite solar cell device.

[0079] The EQE spectrum of the perovskite solar cell device was tested and analyzed using a certified 7SCSpec solar cell testing system. As shown in Figure 19, the EQE spectrum is consistent with the values ​​obtained from the integral JSC and JV curves of the solar spectrum (AM1.5G), with an error of less than 5%. This indicates that the small molecule electron transport material prepared in this embodiment of the invention has more efficient internal charge transfer and generates more charge carriers from absorbed photons.

[0080] The optical absorption spectra of small molecule electron transport materials were obtained using a Hitachi U-4100 UV-Vis spectrophotometer: The small molecule electron transport materials prepared in Examples 1-6 were dissolved in chloroform to prepare chloroform solutions with concentrations of 0.01 mg / mL and 15.0 mg / mL, respectively. The UV-Vis absorption spectra of the 0.01 mg / mL chloroform solution (SOL) were measured at room temperature. The 15.0 mg / mL chloroform solution was spin-coated onto a quartz plate at 3000 rpm to form a thin film (FILM), and the UV-Vis absorption spectra of the film were tested. The results are shown in Figures 15 and 16. As can be seen from Figure 15, in the absorption spectra of the solution state, the materials described in each example all exhibit obvious absorption peaks in the visible light region, with the main absorption range distributed between approximately 350-650 nm. The positions of the maximum absorption peaks corresponding to different substituent structures differ to some extent, indicating that the molecular structure affects its light absorption behavior. At the same time, characteristic absorption bands can be observed in the short-wavelength region (approximately 350-420 nm), reflecting the conjugated structure characteristics within the molecule. As shown in Figure 16, the absorption spectra in the film state changed significantly compared to the solution state. The absorption bands of all samples in the film generally extended towards longer wavelengths, and the maximum absorption peaks of some samples showed varying degrees of redshift compared to the solution state, with a significant broadening of the absorption bands. Simultaneously, the absorption tails in the longer wavelength direction (approximately 650-900 nm) were enhanced, indicating spectral changes resulting from enhanced intermolecular interactions under solid-state conditions.

[0081] The small molecule electron transport materials prepared in Examples 1-6 were tested on a CHI660D electrochemical workstation using a three-electrode system (glassy carbon electrode as the working electrode, Ag / Ag...). + Electrochemical tests were performed using a platinum wire counter electrode (with the electrode serving as both a reference and a platinum wire counter electrode). A nitrogen-saturated solution of 0.1 mol / L tetrabutylammonium hexafluorophosphate in acetonitrile was used as the electrolyte. Cyclic voltammetry (CV) was performed at a scan rate of 100 mV / s. Ferrocene-ferrocene salt (Fc / Fc) was employed. + As an internal standard, its absolute energy compared to vacuum is -4.7 eV. The HOMO and LUMO energy levels of the material are determined according to the equations.

[0082] Figure 17 shows the frontier molecular orbital energy level distribution of different embodiments. The vertical axis represents the energy level, and the unit is electron volt (eV). Figure 17 shows the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of compounds such as DPP-NDIN, ITIC-NDIN, and TIG-NDIN. Specifically, the HOMO energy level of DPP-NDIN is approximately -5.34 eV, and the LUMO energy level is approximately -3.94 eV; the HOMO energy level of ITIC-NDIN is approximately -5.43 eV, and the LUMO energy level is approximately -3.87 eV; and the HOMO energy level of TIG-NDIN is approximately -5.62 eV, and the LUMO energy level is approximately -3.77 eV. Furthermore, another group of DPP-NDIN, ITIC-NDIN, and TIIG-NDIN systems exhibited HOMO levels of approximately -4.95 eV, -5.01 eV, and -5.12 eV, respectively, with corresponding LUMO levels of approximately -3.94 eV, -3.90 eV, and -3.97 eV. These results demonstrate that naphthalimide compounds with different substitution structures exhibit significant differences in the HOMO and LUMO energy levels, indicating that their electronic structure can be controlled through molecular structure design. The LUMO energy levels of the prepared compounds can match the conduction band of the active layer in perovskite solar cells, suggesting that the structure is suitable as an electron transport material for perovskite solar cells.

[0083] Therefore, this invention constructs a small molecule electron transport material containing naphthalimide end groups. This novel material not only has fewer synthesis steps and lower cost, but also maintains high electron transport efficiency and high device efficiency. It has a unique and well-defined molecular structure, and the batch-to-batch differences between materials and devices are very small, giving it a unique advantage in the commercialization of perovskite solar cells.

[0084] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A small molecule electron transport material containing naphthalimide end groups, characterized in that: The small molecule electron transport material is a small molecule conjugated non-fullerene organic molecule containing a naphthalimide end group, and its molecular structure is shown in Formula I: In Formula I, R includes one of the following: substituted or unsubstituted C1-C50 straight-chain alkyl, substituted or unsubstituted C3-C50 branched alkyl, substituted or unsubstituted C3-C50 amino, or substituted or unsubstituted C3-C50 dimethylammonium; Ar is a photoactive conjugated fused ring core unit with a conjugated structure and an electron acceptor.

2. The small molecule electron transport material containing naphthalimide end groups according to claim 1, characterized in that: R is selected from one of the following structures: 、 。 3. The small molecule electron transport material containing naphthalimide end groups according to claim 1, characterized in that: Ar is selected from one of the following structures, with the dashed lines indicating the connection points: 、 、 、 、 R2 independently includes one of hydrogen, C1-C100 straight-chain alkyl, or C3-C100 branched alkyl.

4. The method for preparing small molecule electron transport materials containing naphthalimide end groups as described in any one of claims 1-3, characterized in that: Includes the following steps: (1) 4-bromo-1,8-naphthalenedicarboxylic anhydride and amino-substituted R were reacted with an imidization reaction to prepare bromonaphthalimide intermediate A; (2) Intermediate A was coupled with Ar monomer in the presence of a catalyst to obtain a conjugated small molecule electron transport material containing naphthalimide end groups.

5. The method for preparing small molecule electron transport materials containing naphthalimide end groups according to claim 4, characterized in that: In step (1), the molar ratio of 4-bromo-1,8-naphthalenedicarboxylic anhydride to amino-substituted side chain R is 1:(1.05~1.10).

6. The method for preparing small molecule electron transport materials containing naphthalimide end groups according to claim 4, characterized in that: In step (2), the Ar monomer is an organotin reagent or borate ester compound of the conjugated fused ring core unit Ar; the molar ratio of intermediate A to Ar monomer is (3-4):

1.

7. The method for preparing small molecule electron transport materials containing naphthalimide end groups according to claim 4, characterized in that: In step (2), the catalyst is one or more of bis(triphenylphosphine) palladium dichloride, diphenylphosphine ferrocene palladium dichloride, and tetra(triphenylphosphine) palladium.

8. The method for preparing small molecule electron transport materials containing naphthalimide end groups according to claim 4, characterized in that: In step (2), the molar ratio of intermediate A to catalyst is 1:0.

03.

9. The method for preparing small molecule electron transport materials containing naphthalimide end groups according to claim 4, characterized in that: Step (2) is carried out under a nitrogen atmosphere. After the reaction is completed, the reaction solution is dropped into n-hexane, filtered, washed, dried, and the solid is collected.

10. The application of the small molecule electron transport material containing naphthalimide end groups as described in any one of claims 1-3, characterized in that: It is used as an organic optoelectronic material in perovskite solar cell devices.

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