Conjugated molecular material based on naphthalimide, preparation and application

Abstract

The invention discloses an organic small molecule of a naphthalimide unit (NI) and a preparation method and application thereof, a series of brand-new planar conjugated molecules with good solubility and good thermal stability are synthesized by taking the naphthalimide unit as an electron withdrawing group and taking benzodithiophene (BDT-T) as a conjugated connection core, and the organic small molecule is used as an electron withdrawing group. Naphthalimide has relatively high electron affinity, relatively good thermal stability, relatively high conductivity, easily modified structural units, rich sources and strong electron withdrawing capability of a terminal electron withdrawing unit, so that the molecules have strong visible light absorption capability, high charge transfer performance and proper electron energy level; the material is suitable for preparing organic solar cells as an electron transport material.

Description

Technical Field

[0001] The present invention relates to the technical field of organic chemistry, and particularly relates to a planar conjugated molecular material based on naphthalimide, its preparation, and its application as an electron transport material in organic solar cells (OPVs).

[0002] Background and Applications

[0003] With the implementation of the "carbon peak and carbon neutrality" policy, the development of large-area organic solar cells has attracted more and more attention from researchers and the industrial community. Due to their advantages such as ultrathin, lightweight, flexible, and can be fabricated into semi-transparent devices, large-area organic solar cells have shown great application prospects in wearable electronic devices, building-integrated photovoltaics, etc. (F. Yang, et al., NPJ Flex. Electron. 2021, 5, 30; Y. Liu, et al., Sci. China Chem. 2022, 65, 224-268; B. Jia, et al., Fused-ring electron acceptors in China, Sci. China Chem. 2020, 63, 1179; G. Li, et al., Nat. Rev. Mater. 2017, 2, 17043.). After more than 20 years of research, China's research work in the field of organic solar cells has changed from "following" to "leading", especially in the preparation of photoactive layer materials (Y. Lin, et al., Adv. Mater. 2015, 27, 1170; Q. Liu, et al., Sci. Bull. 2020, 65, 272; J. Yuan, et al., Joule 2019, 3, 1140; W. Feng, et al., Adv. Energy Mater. 2022, 12, 2104060; S. Liu, et al., Chinese J. Polym. Sci. 2022, 40, 944; Z. Chen, et al., Joule 2021, 5, 2395; M. Zhou, et al., Adv. Mater. 2022, 35, 2208279; Z. Luo, et al., Natl. Sci. Rev. 2022, 9, nwac076; J. Song, et al., Adv. Mater. 2019, 31, 1905645; W. Liu, et al., CCS Chem. 2022, 5, 654; Z. Hu, et al., Sci. Bull. 2020, 65, 131; S. Qu, et al., Sci. China Mater. 2021, 64, 808; W. Lin, et al., Acta Chim. Sinica 2022, 80, 724.) have exceeded 19% and 14% respectively (L. Zhu, et al., Nat. Mater. 2022, 21, 656; H. Chen, et al., Nat. Energy 2021, 6, 1045.). Research shows that compared with small-area organic solar cells, large-area organic solar cells usually have the problem of decreasing energy conversion efficiency.There are many reasons for the efficiency decline, such as geometric loss, optical loss, electrical loss, etc. These three kinds of losses mainly reduce the photocurrent density and fill factor of the device, and have little impact on the open-circuit voltage (G. Wang, et al., Adv. Mater. 2019, 31, 1805089.).

[0004] Among the various components of large-area organic solar cells, as the device area increases from small to large, the most affected part is the electron transport layer: First, the commonly used electron transport layer in the laboratory is the imide-based organic electron transport layer, and its electron mobility is generally low (about 10 -4 cm 2 V -1 s -1 ), resulting in a relatively high dependence of the transport performance of such materials on the film thickness (generally required to be about 10 nm). During the large-area coating process, uneven coating of the electron transport layer film thickness may lead to an increase in the internal resistance of the material, and then cause a decrease in the photocurrent density and fill factor of the device. Second, the organic electron transport layer has high requirements for processing conditions and storage environment, and moisture, heat, etc. will reduce the transport performance and stability of the thin film. As is well known, in the forward organic solar cell, the PEDOT:PSS hole transport layer and the photoactive layer can be processed and prepared in air, but there are few reports on the electron transport layer (such as PFN-Br (T. Yang, et al., Energy Environ. Sci. 2012, 5, 8208.)) being processed in air. This is because the water vapor in the air easily makes PFN-Br absorb moisture, which is not conducive to the transport performance and stability of the material. In 2022, the group of Welch Gregory C. used the slot-die coating technology to prepare a large-area organic solar cell with the device structure of ITO / PEDOT:PSS / PM6:Y6C12 / PFN-Br / Ag in air, and under the condition of no encapsulation, the energy conversion efficiency measured in air was only 10.1% (F. Tintori, et al., Adv. Mater. Interfaces 2021, 9, 2101418.), which is much lower than the efficiency value measured for similar devices prepared in a nitrogen atmosphere. Therefore, developing organic electron transport materials with high electron mobility and air stability is a necessary way to ensure high-performance large-area organic solar cells.

[0005] Recently, researchers have made some progress in the study of 1,8-naphthalimide derivatives as electron transport materials (H. Liu, et al., Dyes Pigments 2023, 209, 110911; Y. Zhao, et al., ChemSusChem 2021, 14, 4783; Y. Zhao, et al., Chem. Eng. J. 2022, 441, 135894; Y. Zhao, et al., J. Colloid Interface Sci. 2022, 627, 880 - 890.). Experimental results show that the electron transport performance of these materials has been comparable to that of the traditional organic electron transport material PDINO, and their thermal stability is better than that of PDINO. 1,8-Naphthalimide-based electron transport materials have a high electron affinity, are more likely to form an ohmic contact with the active layer; have good thermal stability; low raw material cost and wide sources; simple molecular synthesis and purification processes; and the conductivity of the thin film is as high as 1.9×10 -4 S / cm. The above shows that 1,8-naphthalimide derivatives can be fully used as electron transport materials. Summary of the Invention

[0006] The purpose of the present invention is to provide an organic small molecule containing naphthalimide, its preparation method and application.

[0007] One technical solution of the present invention is:

[0008] An organic small molecule containing naphthalimide, wherein the organic small molecule is a planar conjugated organic small molecule with a naphthalimide unit as an electron-withdrawing core, and has a structural general formula shown in Formula I:

[0009]

[0010] Among them, X is selected from any one of O, S or Se;

[0011] R1 is independently selected from any one of hydrogen, fluorine, chlorine, bromine, iodine, C1 - C 30 alkyl, C1 - C 30 alkoxy or 4-alkylphenyl.

[0012] Furthermore, X is S; R1 is independently any one of hydrogen, fluorine, chlorine, bromine or iodine.

[0013] Furthermore, the structural formula of the organic small molecule is shown in Formula II, Formula III or Formula IV:

[0014]

[0015] The present invention also provides a preparation method of the organic small molecule containing naphthalimide, and its synthetic route is shown in Reaction Scheme I:

[0016]

[0017] Further, the preparation method includes the following steps: under the conditions of 100°C to 120°C and in an inert gas atmosphere, 107.0 mg of the compound 1, 260.0 mg of the compound 2, i.e., 2-bromo-2-(3-(dimethylamino)propyl)-1H-benzo[de]isoquinoline-1,3(2H)-dione, absolute ethanol, saturated potassium carbonate solution and the catalyst (triphenylphosphine)palladium are stirred in toluene for 72 to 96 hours, and after separation and purification, the organic small molecule material compound 3 containing naphthalimide is obtained.

[0018] The present invention also provides an application of the organic small molecule containing naphthalimide in the preparation of an electron transport material.

[0019] Further, the electron transport material is an electron transport material for an organic solar cell.

[0020] The present invention also provides an application of the organic small molecule containing naphthalimide in the preparation of a non-fullerene organic photovoltaic device.

[0021] The beneficial effects of the present invention are:

[0022] 1. The synthesized planar conjugated organic small molecule based on naphthalimide can be processed by solution method and can be dissolved in organic solvents such as chloroform, tetrahydrofuran and chlorobenzene;

[0023] 2. The synthesized planar conjugated organic small molecule based on naphthalimide has good thermal stability, and the initial thermal decomposition temperature exceeds 225°C;

[0024] 3. The synthesized planar conjugated organic small molecule based on naphthalimide has good light absorption property and is suitable for being used as an organic solar cell material;

[0025] 4. The synthesized planar conjugated organic small molecule based on naphthalimide has appropriate electron energy levels and is suitable for being used as an electron transport material in an organic solar cell;

[0026] 5. The synthesized planar conjugated organic small molecule based on naphthalimide shows high photoelectric conversion efficiency as an electron transport material in an organic solar cell. Description of the Drawings

[0027] The drawings described herein are used to provide a further understanding of the present invention, form a part of this application, and the schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0028] Figure 1 Schematic diagram of the general structural formula of an organic small molecule containing naphthalimide;

[0029] Figure 2 Thermogravimetric analysis curve of an organic small molecule (4NIN) containing naphthalimide;

[0030] Figure 3 UV-Vis absorption spectrum of a chloroform solution of an organic small molecule (4NIN) containing naphthalimide;

[0031] Figure 4 UV-Vis absorption spectrum of a thin film of an organic small molecule (4NIN) containing naphthalimide;

[0032] Figure 5 Cyclic voltammogram of an organic small molecule (4NIN) containing naphthalimide;

[0033] Figure 6 J-V curve of an organic small molecule (4NIN) containing naphthalimide when applied to an organic solar cell.

[0034] Figure 7 Thermogravimetric analysis curve of an organic small molecule (4NIN-F) containing naphthalimide;

[0035] Figure 8 UV-Vis absorption spectrum of a chloroform solution of an organic small molecule (4NIN-F) containing naphthalimide;

[0036] Figure 9 UV-Vis absorption spectrum of a thin film of an organic small molecule (4NIN-F) containing naphthalimide;

[0037] Figure 10 Cyclic voltammogram of an organic small molecule (4NIN-F) containing naphthalimide;

[0038] Figure 11 J-V curve of an organic small molecule (4NIN-F) containing naphthalimide when applied to an organic solar cell.

[0039] Figure 12 Thermogravimetric analysis curve of an organic small molecule (4NIN-Se) containing naphthalimide;

[0040] Figure 13 UV-Vis absorption spectrum of a chloroform solution of an organic small molecule (4NIN-Se) containing naphthalimide;

[0041] Figure 14 UV-Vis absorption spectrum of a thin film of an organic small molecule (4NIN-Se) containing naphthalimide;

[0042] Figure 15 Cyclic voltammogram of the organic small molecule (4NIN-Se) containing naphthalimide;

[0043] Figure 16 J-V curve of the organic small molecule (4NIN-Se) containing naphthalimide when applied to organic solar cells. Detailed implementation mode

[0044] When describing the embodiments of the present invention, specific terms are used for clarity. However, the present invention is not intended to be limited to the specific terms selected. It should be understood that each specific element includes all technical equivalents that operate in a similar manner to achieve a similar purpose.

[0045] The embodiments of the present invention can adopt conventional techniques in the field of chemistry. In the following examples, efforts are made to ensure the accuracy of the numbers used (including amounts, temperatures, reaction times, etc.), but some experimental errors and deviations should be considered. In the following examples, °C represents temperature, h represents hour, min represents minute, and the pressure is atmospheric pressure or close to atmospheric pressure. All solvents are purchased at HPLC grade, and all reactions are carried out under a nitrogen inert atmosphere. Unless otherwise indicated, all reagents are commercially available.

[0046] The following will refer to the drawings and in combination with the examples to detail the organic small molecule containing naphthalimide prepared by the present invention. The schematic diagram of the structural general formula is as Figure 1 shown.

[0047] Example 1

[0048] An organic small molecule containing naphthalimide, which is a planar conjugated organic small molecule with a naphthalimide unit as an electron-withdrawing core and has the structure shown in Formula II (named 4NIN):

[0049]

[0050] The organic small molecule adopts the synthesis route of Reaction Scheme I, including the following steps:

[0051] (1) First, 2,2'-((2,6-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzo[1,2-b:4,5-b']dithiophene-4,8-diyl)bis(thiophene-5,2-diyl))bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolane), 2-bromo-2-(3-(dimethylamino)propyl)-1H-benzo[de]isoquinoline-1,3(2H)-dione, and tetrakis(triphenylphosphine)palladium catalyst are added to a two-necked flask.

[0052] (2) The two-necked flask was flushed with nitrogen to create an anaerobic condition. An aqueous solution of saturated K2CO3, anhydrous toluene, and anhydrous ethanol were added to the anaerobic and anhydrous flask. Under a N2 atmosphere, the resulting mixture was heated under reflux at 110 °C for 72 - 96 hours.

[0053] (3) After the reaction ended and cooled to room temperature, the crude product was rotary evaporated under reduced pressure. Then the residue was separated and purified by silica gel column using methanol / chloroform (volume ratio 1:3) as the eluent to obtain the organic small molecule material 4NIN containing naphthalimide.

[0054] The structure confirmation data are as follows: 1 H NMR (600 MHz, CDCl3) δ 8.77 (d, J = 7.8 Hz, 2H), 8.73 (d, J = 7.9 Hz, 2H), 8.67 (s, 4H), 8.63 (s, 2H), 8.05 (s, 2H), 8.01 (d, J = 6.8 Hz, 2H), 7.94 (d, J = 6.3 Hz, 2H), 7.84 (s, 2H), 7.76 (d, J = 33.7 Hz, 4H), 7.55 (s, 2H), 7.43 (s, 2H), 4.26 (d, J = 5.3 Hz, 8H), 2.45 (s, 8H), 2.27 (s, 24H), 1.79 (s, 8H). 13 C NMR (151 MHz, CDCl3) δ 164.12, 164.05, 163.88, 163.83, 131.63, 130.72, 130.52, 130.09, 129.79, 129.60, 129.42, 129.31, 128.97, 128.81, 128.76, 127.77, 127.54, 123.16, 122.98, 122.40, 57.26, 45.44, 38.96, 26.10.

[0055] The relevant physical properties of 4NIN were studied as follows:

[0056] As Figure 2 shown, the thermal decomposition temperature (T d ) at which the small molecule loses 5% of its weight is 225 °C, indicating that the small molecule 4NIN has good thermal stability;

[0057] As Figure 3 and Figure 4 shown, the small molecule has strong absorption in the range of 300 - 450 nm, and there is an obvious absorption shoulder peak at 400 nm in the thin film absorption, indicating strong intermolecular interactions and aggregation.

[0058] As Figure 5 shown, the onset oxidation potential of the small molecule is 0.37V vs Ag / Ag+, the starting reduction potential is -1.13V vs Ag / Ag+. Through the formulas HOMO = -(E ox + 4.73)(eV) and LUMO = -(E re + 4.73)(eV), the HOMO energy level and LUMO energy level of IFIC-4F can be calculated to be -5.10 eV and -3.60 eV respectively.

[0059] Preparation and performance testing of organic photovoltaic devices:

[0060] Device preparation: ITO glass was ultrasonically cleaned with dish soap, ultrapure water, acetone (then wiped with lint-free paper), and isopropyl alcohol for 20 min each, twice. After the wafer was dried, 15 nm of PEDOT:PSS was spin-coated on it at a speed of 4000 rpm. In a glove box filled with a nitrogen atmosphere, a chloroform solution of D18:L8BO (1:1.2, w / w, 20 mg / mL) with 0.6% v of DIO additive was spin-coated on top of PEDOT:PSS to form an active layer film with a thickness of about 100 nm. Then, a 4NIN methanol (1 mg / mL) solution was spin-coated on the active layer at a speed of 1000 - 4000 rpm for 35 s to prepare devices with different thickness interface layers. Finally, 80 nm of Al was evaporated as the cathode to obtain the organic small molecule solar cell device. The effective area of the device is 0.05 cm 2 . In a glove box filled with N2, the open circuit voltage, short circuit current, and fill factor of the prepared device were tested under the intensity of AM1.5G (100 mW cm -2 ) of a xenon lamp solar simulator; the light intensity was calibrated with a standard single crystal silicon solar cell; the J-V curve was measured using a Keithley 2450.

[0061] The corresponding device structure of the non-fullerene system is: ITO / PEDOT:PSS / D18:L8BO / 4NIN / Al

[0062] Among them: ITO is indium tin oxide, and PEDOT:PSS is poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate).

[0063] The chemical structural formulas of the acceptor material L8-BO and the donor material D18 in the photovoltaic device are as follows:

[0064]

[0065] Figure 6 is the J-V curve of an organic small molecule (4NIN) based on naphthalimide applied to an organic solar cell. As Figure 6As shown, the measured open-circuit voltage Voc of the device is 0.91 V, and the short-circuit current Jsc is 26.67 mA cm -1 , the fill factor FF is 75.96%, and the power conversion efficiency PCE is 18.55%.

[0066] Example 2

[0067] An organic small molecule containing naphthalimide, the organic small molecule is a planar conjugated organic small molecule with a naphthalimide unit as an electron-withdrawing core, and has the structure shown in Formula III (named 4NIN-F):

[0068]

[0069] The organic small molecule adopts the synthesis route of Reaction Formula I, including the following steps:

[0070] (1) First, add 2,2'-((2,6-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzo[1,2-b:4,5-b']dithiophene-4,8-diyl)bis(3-fluorothiophene-5,2-diyl))bis(4,4,5,5-tetramethyl-1,3,2-dioxaborane), 2-bromo-2-(3-(dimethylamino)propyl)-1H-benzo[de]isoquinoline-1,3(2H)-dione and tetrakis(triphenylphosphine)palladium catalyst into a two-necked flask.

[0071] (2) Use nitrogen to flush the two-necked flask to create an anaerobic condition, and add saturated K2CO3 aqueous solution, anhydrous toluene and anhydrous ethanol to the anhydrous and anaerobic flask. Under N2 atmosphere, heat the resulting mixture at 110 °C for 72 - 96 hours under reflux.

[0072] (3) After the reaction is completed and cooled to room temperature, the crude product is rotary evaporated under reduced pressure, and then the residue is separated and purified by silica gel column using methanol / chloroform (volume ratio 1:3) as the eluent to obtain the organic small molecule material 4NIN-F containing naphthalimide.

[0073] The structure confirmation data is as follows: 1 H NMR(600MHz,CDCl3)δ8.79(d,J=7.8Hz,2H),8.75(d,J=7.9Hz,2H),8.69(s,4H),8.65(s,2H),8.07(s,2H),8.03(d,J=6.8Hz,2H),7.96(d,J=6.3Hz,2H),7.86(s,2H),7.78(d,J=33.7Hz,4H),7.57(s,2H),4.28(d,J=5.3Hz,8H),2.47(s,8H),2.29(s,24H),1.81(s,8H).13 13C NMR (151 MHz, CDCl3) δ 164.13, 164.06, 163.89, 163.85, 131.65, 130.74, 130.54, 130.09, 129.79, 129.62, 129.43, 129.33, 128.99, 128.83, 128.78, 127.79, 127.56, 123.18, 122.98, 122.41, 57.28, 45.46, 38.98, 26.12.

[0074] The relevant physical properties of 4NIN-F were studied as follows:

[0075] As Figure 7 shown, the thermal decomposition temperature (T d ) at 5% weight loss of the small molecule is 219 °C, indicating that the small molecule 4NIN-F has good thermal stability;

[0076] As Figure 8 and Figure 9 shown, the small molecule has strong absorption in the range of 300 - 450 nm, and the thin film absorption has an obvious absorption shoulder peak at 400 nm, indicating strong intermolecular interactions and aggregation.

[0077] As Figure 10 shown, the initial oxidation potential of the small molecule is 1.08 V vs Ag / Ag+, and the initial reduction potential is -1.02 V vs Ag / Ag+. Through the formulas HOMO = -(E ox + 4.73) (eV) and LUMO = -(E re + 4.73) (eV), the HOMO energy level and LUMO energy level of IFIC-4F can be calculated to be -5.81 eV and -3.71 eV respectively.

[0078] Preparation and performance testing of organic photovoltaic devices:

[0079] Device Fabrication: ITO glass was ultrasonically cleaned twice for 20 min each with dishwashing liquid, ultrapure water, acetone (then wiped with lint-free paper), and isopropyl alcohol. After drying the wafers, 15 nm of PEDOT:PSS was spin-coated on them at a speed of 4000 rpm. In a glove box filled with a nitrogen atmosphere, a chloroform solution of D18:L8BO (1:1.2, w / w, 20 mg / mL) with 0.6% v of DIO additive was spin-coated on top of the PEDOT:PSS to form an active layer film with a thickness of approximately 100 nm. Then, a solution of 4NIN-F in methanol (1 mg / mL) was spin-coated on the active layer at a speed of 1000 - 4000 rpm for 35 s to fabricate devices with different thickness interfacial layers. Finally, 80 nm of Al was evaporated as the cathode to obtain the organic small molecule solar cell device. The effective area of the device is 0.05 cm 2 . In a glove box filled with N2, the open-circuit voltage, short-circuit current, and fill factor of the fabricated devices were tested under the AM1.5G intensity (100 mW cm -2 ) of a xenon lamp solar simulator; the light intensity was calibrated using a standard single-crystalline silicon solar cell; the J-V curve was measured using a Keithley 2450.

[0080] The corresponding device structure of the non-fullerene system is: ITO / PEDOT:PSS / D18:L8BO / 4NIN-F / Al

[0081] Where: ITO is indium tin oxide, and PEDOT:PSS is poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate).

[0082] The chemical structural formulas of the acceptor material L8-BO and the donor material D18 in the photovoltaic device are as follows:

[0083]

[0084] Figure 11 The J-V curve for the application of an organic small molecule (4NIN-F) based on naphthalimide in an organic solar cell. As Figure 11 shown, the open-circuit voltage Voc of the measured device is 0.92 V, the short-circuit current Jsc is 26.58 mA cm -1 , and the fill factor FF is 78.55%, and the power conversion efficiency PCE is 19.28%.

[0085] Example 3

[0086] An organic small molecule containing naphthalimide, the organic small molecule is a planar conjugated organic small molecule with a naphthalimide unit as an electron-withdrawing core, and has the structure shown in Formula IV (named 4NIN-Se):

[0087]

[0088] The organic small molecule adopts the synthesis route of Reaction Scheme I, including the following steps:

[0089] (1) First, 2,2'-((2,6-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzo[1,2-b:4,5-b']dithiophene-4,8-diyl)bis(selenophene-5,2-diyl))bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolane), 2-bromo-2-(3-(dimethylamino)propyl)-1H-benzo[de]isoquinoline-1,3(2H)-dione and tetrakis(triphenylphosphine)palladium catalyst are added into a two-necked flask.

[0090] (2) The two-necked flask is flushed with nitrogen to create an anaerobic condition, and saturated K2CO3 aqueous solution, anhydrous toluene and anhydrous ethanol are added into the anhydrous and anaerobic flask. Under N2 atmosphere, the obtained mixture is heated under reflux at 110 °C for 72 - 96 hours.

[0091] (3) After the reaction is completed and cooled to room temperature, the crude product is rotary evaporated under reduced pressure, and then the residue is separated and purified by silica gel column using methanol / chloroform (volume ratio 1:3) as the eluent to obtain the organic small molecule material containing naphthalimide, namely 4NIN-Se.

[0092] The structure confirmation data are as follows: 1 H NMR(600MHz,CDCl3)δ8.87(d,J=7.8Hz,2H),8.83(d,J=7.9Hz,2H),8.77(s,4H),8.73(s,2H),8.15(s,2H),8.11(d,J=6.8Hz,2H),8.04(d,J=6.3Hz,2H),7.94(s,2H),7.86(d,J=33.7Hz,4H),7.65(s,2H),7.53(s,2H),4.36(d,J=5.3Hz,8H),2.55(s,8H),2.37(s,24H),1.89(s,8H). 13 C NMR(151MHz,CDCl3)δ164.22,164.15,163.98,163.93,131.73,130.82,130.62,130.19,129.89,129.70,129.52,129.41,129.07,128.91,128.86,127.87,127.64,123.26,123.08,122.50,57.36,45.54,39.06,26.20。

[0093] The relevant physical properties of 4NIN-Se are studied as follows:

[0094] As Figure 12 shown, the thermal decomposition temperature (T d ) at which the small molecule loses 5% of its weight is 217 °C, indicating that the small molecule 4NIN-Se has good thermal stability;

[0095] As Figure 13 and Figure 14 shown, the small molecule has strong absorption in the range of 300 - 450 nm, and the film absorption has an obvious absorption shoulder peak at 350 nm, indicating strong intermolecular interactions and aggregation.

[0096] As Figure 15 shown, the onset oxidation potential of the small molecule is 0.90 V vs Ag / Ag⁺, and the onset reduction potential is -0.85 V vs Ag / Ag⁺. Through the formulas HOMO = -(E ox + 4.73) (eV) and LUMO = -(E re + 4.73) (eV), the HOMO energy level and LUMO energy level of IFIC-4F can be calculated to be -5.63 eV and -3.88 eV respectively.

[0097] Preparation and performance testing of organic photovoltaic devices:

[0098] Device preparation: ITO glass was ultrasonically cleaned twice for 20 min each with dishwashing liquid, ultrapure water, acetone (then wiped with lint-free paper), and isopropanol. After the wafers were dried, 15 nm of PEDOT:PSS was spin-coated on them at a speed of 4000 rpm. In a glove box filled with a nitrogen atmosphere, a chloroform solution of D18:L8BO (1:1.2, w / w, 20 mg / mL) with 0.6% v of DIO additive was spin-coated on top of the PEDOT:PSS to form an active layer film with a thickness of approximately 100 nm. Then, a methanol (1 mg / mL) solution of 4NIN-Se was spin-coated on the active layer at a speed of 1000 - 4000 rpm for 35 s to prepare devices with different thickness interface layers. Finally, 80 nm of Al was evaporated as the cathode to obtain the organic small molecule solar cell device. The effective area of the device is 0.05 cm 2 . In a glove box filled with N₂, the open-circuit voltage, short-circuit current, and fill factor of the prepared devices were tested under the intensity of AM1.5G (100 mW cm -2 ) of a xenon lamp solar simulator; the light intensity was calibrated with a standard single-crystalline silicon solar cell; the J-V curve was measured using a Keithley 2450.

[0099] The device structure of the corresponding non-fullerene system is: ITO / PEDOT:PSS / D18:L8BO / 4NIN / Al

[0100] Among them: ITO is transparent indium tin oxide, and PEDOT:PSS is poly(3,4-ethylenedioxythiophene) doped with the polymer poly(styrenesulfonate).

[0101] The chemical structural formulas of the acceptor material L8-BO and the donor material D18 in the photovoltaic device are as follows respectively:

[0102]

[0103] Figure 16 The J-V curve of the application of the naphthalimide-based organic small molecule (4NIN-Se) in the organic solar cell is as follows. As Figure 16 shown, the open-circuit voltage Voc of the measured device is 0.91 V, the short-circuit current Jsc is 27.20 mA cm -1 , the fill factor FF is 77.83%, and the power conversion efficiency PCE is 19.34%.

[0104] According to the above results, it can be known that for the naphthalimide-based organic small molecules of the present invention, a series of brand-new, well-soluble and thermally stable planar conjugated molecules are synthesized by using the naphthalimide unit as an electron-withdrawing group and benzodithiophene (BDT-T) as the conjugated connection core. Due to the relatively high electron affinity, good thermal stability, high conductivity, easy modification of the structural unit, rich source and strong electron-withdrawing ability of the terminal electron-withdrawing unit of naphthalimide, such molecules have strong visible light absorption ability, high charge transport performance and appropriate electron energy levels, and are suitable for being used as electron transport materials in the preparation of organic solar cells.

[0105] 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 the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. An organic small molecule containing naphthimide, characterized in that: The organic small molecule is a planar conjugated organic small molecule with a naphthoimide unit as an electron-withdrawing core, and has a general structural formula shown in Formula I: Wherein, X is selected from any one of O, S or Se, and R1 is independently selected from hydrogen, fluorine, chlorine, bromine, iodine, C1-C 30 Alkyl or C1~C 30 Any one of the alkoxy groups.

2. The organic small molecule containing naphthoimide according to claim 1, characterized in that: The X is S, and the R1 is independently any one of hydrogen, fluorine, chlorine, bromine and iodine.

3. The organic small molecule containing naphthoimide according to claim 1, characterized in that: The structural formula of the organic small molecule is shown in Formula II, Formula III or Formula IV:

4. A method for preparing an organic small molecule containing naphthoimide according to any one of claims 1 to 3, characterized in that: The synthetic route is shown in Reaction Scheme I:

5. The preparation method according to claim 4, characterized in that: The reaction atmosphere is a nitrogen atmosphere or an argon atmosphere, the reaction temperature is 100° C. to 120° C., and the reaction time is 72 to 96 hours.

6. Use of the naphthoimide-containing organic small molecule according to any one of claims 1 to 3 for preparing electron transport materials.

7. The use according to claim 6, characterized in that The electron transport material is an electron transport material for an organic solar cell.

8. The naphthoimide-containing organic small molecule according to any one of claims 1 to 3 is used for preparing a non-fullerene organic photovoltaic device.

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