Synthesis and application of organic semiconductor electron transport layer material

Abstract

The invention discloses synthesis and application of an organic semiconductor electron transport layer material. The structural formula of the organic semiconductor electron transport layer material is shown as a formula (I): # imgabs0 # formula (I), wherein the number-average molecular weight is 5000 mol / L to 50000 mol / L, and the PDI is 1.5 to 2.5; the organic semiconductor electron transport layer material disclosed by the invention is applied to preparation of perovskite solar cells and has relatively high Voc value, Jsc value and FF value, so that a high PCE value can be obtained. In addition, a perovskite solar cell prepared from the organic semiconductor electron transport layer material provided by the invention can maintain relatively high cell energy conversion efficiency in long-time use, and can maintain relatively high stability in an atmospheric environment for a long time.

Description

Technical Field

[0001] The present invention belongs to the technical field of organic polymer copolymers, and particularly relates to the synthesis and application of organic semiconductor electron transport layer materials. Background Art

[0002] As a renewable energy source, solar energy is one of the important energy sources to meet the growing energy demand globally. A solar cell is a device that directly converts light energy into electrical energy through the photovoltaic effect or a photochemical reaction, and is the technical basis for the wide application of solar photovoltaic power generation. Among them, perovskite solar cells have attracted worldwide attention and become a very promising new type of photovoltaic device.

[0003] In recent years, perovskite solar cells have developed rapidly, but there are still common problems such as difficult improvement of the battery conversion efficiency and poor stability. Research shows that introducing polymer-type organic semiconductor materials into perovskite solar cells can effectively increase the output voltage, fill factor, and short-circuit current density of perovskite solar cells, thereby effectively improving the battery energy conversion efficiency.

[0004] Polymer-type organic semiconductor electron transport layer materials have three major advantages: 1. Solution processability; 2. Excellent film-forming property; 3. Good adhesion to the perovskite layer. Among them, the copolymer of benzothiadiazole and dioctylfluorene is a relatively common electron transport material with high efficiency and has a wide application in the preparation of organic solar cells. However, as an electron transport material, the copolymer of benzothiadiazole and dioctylfluorene has a large energy level difference with perovskite and poor interfacial contact with the perovskite layer, resulting in low photoelectric conversion effect and poor long-term stability of the prepared perovskite solar cells. Summary of the Invention

[0005] Aiming at the above deficiencies in the prior art, the present invention provides an organic semiconductor electron transport layer material by introducing two fluorine substituents into the benzothiadiazole side chain of the organic semiconductor electron transport layer material. Fluorine is the element with the strongest electronegativity. Molecules containing fluorine atoms can form many non-covalent interactions. The strong electron-withdrawing effect of the fluorine substituents optimizes the energy level structure of the organic semiconductor electron transport layer material and improves the electron transport ability. As an electron transport layer material, due to the strong interaction between fluorine atoms and perovskite, the interfacial contact with the perovskite layer is improved, which not only has some passivation effects but also reduces the charge transport resistance, is conducive to the transport of electrons, and improves the photoelectric conversion efficiency of perovskite solar cells.

[0006] The object of the present invention is to provide an organic semiconductor electron transport layer material, and the structural formula of the organic semiconductor electron transport layer material is shown in formula (Ⅰ):

[0007]

[0008] Formula (I);

[0009] Wherein, the number-average molecular weight is 5,000 - 50,000 mol / L, and the PDI is 1.5 - 2.5.

[0010] Preferably, the number-average molecular weight of the organic semiconductor electron transport layer material is 5,000 - 20,000 mol / L, and the PDI is 1.5 - 2.

[0011] Preferably, the number-average molecular weight of the organic semiconductor electron transport layer material is 30,000 - 50,000 mol / L, and the PDI is 2 - 2.5.

[0012] Another object of the present invention is to provide a preparation method of the organic semiconductor electron transport layer material, which is characterized by including the following steps:

[0013] Under the action of a N-heterocyclic carbene palladium complex and an auxiliary agent, 4,7-dibromo-5,6-difluoro-benzo[c][1,2,5]thiadiazole and 9,9-dioctylfluorene-2,7-bis(pinacol borate) undergo a polymerization reaction to obtain a N-heterocyclic carbene palladium complex.

[0014] Preferably, the structural formula of the N-heterocyclic carbene palladium complex is as shown in Formula (II):

[0015]

[0016] Formula (II).

[0017] Preferably, the structural formula of the N-heterocyclic carbene palladium complex is as shown in Formula (III):

[0018]

[0019] Formula (III).

[0020] Preferably, the molar ratio of 4,7-dibromo-5,6-difluoro-benzo[c][1,2,5]thiadiazole to 9,9-dioctylfluorene-2,7-bis(pinacol borate) is 1:1.

[0021] Preferably, the molar ratio of 4,7-dibromo-5,6-difluoro-benzo[c][1,2,5]thiadiazole to the N-heterocyclic carbene palladium complex is 1:0.005 - 0.05.

[0022] Preferably, the auxiliary agent includes an organic base and a solvent.

[0023] Preferably, the organic base is selected from potassium tert-butoxide.

[0024] Preferably, the solvent is a mixture of tetrahydrofuran and water, and the volume ratio of tetrahydrofuran to water is 2 to 4:1.

[0025] Preferably, the temperature of the polymerization reaction is 60 to 100 °C, and the time is 12 to 36 hours.

[0026] Preferably, the molar ratio of 4,7-dibromo-5,6-difluoro-benzothiadiazole to the organic base is 1:3 to 5.

[0027] Another object of the present invention is to provide the application of the organic semiconductor electron transport layer material or the organic semiconductor electron transport layer material prepared by the preparation method of the organic semiconductor electron transport layer material in the preparation of perovskite solar cells.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] (1) The organic semiconductor electron transport layer material provided by the present invention has a high Voc value, Jsc value and FF value when used in the preparation of perovskite solar cells, so that a high PCE value can be obtained.

[0030] (2) The perovskite solar cell prepared from the organic semiconductor electron transport layer material provided by the present invention can maintain a high battery energy conversion efficiency during long-term use and can maintain high stability in the atmospheric environment for a long time. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 1H NMR spectrum of the organic semiconductor electron transport layer material prepared in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0032] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0033] All raw materials of the present invention can be obtained through commercial channels.

[0034] The structure of 4,7-dibromo-5,6-difluoro-benzothiadiazole used in all embodiments of the present invention for preparing the organic semiconductor electron transport layer material is as follows:

[0035] ;

[0036] The structure of 9,9-dioctylfluorene-2,7-bis(pinacol borate) used in all examples of preparing the organic semiconductor electron transport layer material of the present invention is as follows:

[0037] ;

[0038] The structure of the N-heterocyclic carbene palladium complex C1 used in all examples of preparing the organic semiconductor electron transport layer material of the present invention is as follows:

[0039] ;

[0040] The structure of the N-heterocyclic carbene palladium complex C2 used in all examples of preparing the organic semiconductor electron transport layer material of the present invention is as follows:

[0041] 。

[0042] Example 1

[0043] This example provides an organic semiconductor electron transport layer material, and its preparation method includes the following steps:

[0044] Under nitrogen protection, add 4,7-dibromo-5,6-difluoro-benzothiadiazole (1.0 mmol), 9,9-dioctylfluorene-2,7-bis(pinacol borate) (1.0 mmol), potassium tert-butoxide (4.0 mmol), N-heterocyclic carbene palladium complex C2 (0.03 mmol) and 12 mL of tetrahydrofuran / water (4:1) as a solvent into a clamped round-bottom microwave reaction tube. Stir the mixture at 70 °C for 30 hours. After the reaction is completed, cool to room temperature, precipitate the polymer with methanol, wash it several times, dry it, weigh it to obtain the organic semiconductor electron transport layer material. The yield is 66%. The number-average molecular weight of the organic semiconductor electron transport layer material is 5103 - 49935 g / mol, and the PDI is 1.5 - 2.4. Nuclear magnetic resonance characterization of the organic semiconductor electron transport layer material is shown in Figure 1 , and the structure of the organic semiconductor electron transport layer material is as follows:

[0045] 。

[0046] Example 2

[0047] This example provides an organic semiconductor electron transport layer material, and its preparation method includes the following steps:

[0048] Under nitrogen protection, 4,7-dibromo-5,6-difluoro-benzothiadiazole (1.0 mmol), 9,9-dioctylfluorene-2,7-bis(pinacol borate) (1.0 mmol), potassium tert-butoxide (4.0 mmol), N-heterocyclic carbene palladium complex C1 (0.005 mmol) and 12 mL of tetrahydrofuran / water (3:1) as a solvent were added to a clamped round-bottom microwave reaction tube. The mixture was stirred at 60 °C for 28 hours. After the reaction was completed, it was cooled to room temperature. The polymer was precipitated with methanol, washed repeatedly, dried, and weighed to obtain an organic semiconductor electron transport layer material with a yield of 65%. The number-average molecular weight of the organic semiconductor electron transport layer material was 5250 - 12536 g / mol, and the PDI was 1.5 - 1.9. The structure of the organic semiconductor electron transport layer material is as follows:

[0049] 。

[0050] Example 3

[0051] This example provides an organic semiconductor electron transport layer material, and its preparation method includes the following steps:

[0052] Under nitrogen protection, 4,7-dibromo-5,6-difluoro-benzothiadiazole (1.0 mmol), 9,9-dioctylfluorene-2,7-bis(pinacol borate) (1.0 mmol), potassium tert-butoxide (3.0 mmol), N-heterocyclic carbene palladium complex C1 (0.02 mmol) and 12 mL of tetrahydrofuran / water (2:1) as a solvent were added to a clamped round-bottom microwave reaction tube. The mixture was stirred at 80 °C for 36 hours. After the reaction was completed, it was cooled to room temperature. The polymer was precipitated with methanol, washed repeatedly, dried, and weighed to obtain an organic semiconductor electron transport layer material with a yield of 71%. The number-average molecular weight of the organic semiconductor electron transport layer material was 10046 - 19463 g / mol, and the PDI was 1.6 - 2.0. The structure of the organic semiconductor electron transport layer material is as follows:

[0053] 。

[0054] Example 4

[0055] This example provides an organic semiconductor electron transport layer material, and its preparation method includes the following steps:

[0056] Under nitrogen protection, 4,7-dibromo-5,6-difluoro-benzo[1,2,5]thiadiazole (1.0 mmol), 9,9-dioctylfluorene-2,7-bis(pinacol borate) (1.0 mmol), potassium tert-butoxide (5.0 mmol), N-heterocyclic carbene palladium complex C1 (0.025 mmol) and 12 mL of tetrahydrofuran / water (4:1) as the solvent were added to a clamped round-bottom microwave reaction tube. The mixture was stirred at 85 °C for 24 hours. After the reaction was completed, it was cooled to room temperature. The polymer was precipitated with methanol, washed repeatedly, dried, and weighed to obtain an organic semiconductor electron transport layer material with a yield of 69%. The number-average molecular weight of the organic semiconductor electron transport layer material was 16232 - 25134 g / mol, and the PDI was 1.7 - 2.3. The structure of the organic semiconductor electron transport layer material is as follows:

[0057] .

[0058] Example 5

[0059] This example provides an organic semiconductor electron transport layer material, and its preparation method includes the following steps:

[0060] Under nitrogen protection, 4,7-dibromo-5,6-difluoro-benzo[1,2,5]thiadiazole (1.0 mmol), 9,9-dioctylfluorene-2,7-bis(pinacol borate) (1.0 mmol), potassium tert-butoxide (4.0 mmol), N-heterocyclic carbene palladium complex C2 (0.04 mmol) and 12 mL of tetrahydrofuran / water (4:1) as the solvent were added to a clamped round-bottom microwave reaction tube. The mixture was stirred at 90 °C for 18 hours. After the reaction was completed, it was cooled to room temperature. The polymer was precipitated with methanol, washed repeatedly, dried, and weighed to obtain an organic semiconductor electron transport layer material with a yield of 73%. The number-average molecular weight of the organic semiconductor electron transport layer material was 31387 - 44845 g / mol, and the PDI was 2.0 - 2.4. The structure of the organic semiconductor electron transport layer material is as follows:

[0061] .

[0062] Example 6

[0063] This example provides an organic semiconductor electron transport layer material, and its preparation method includes the following steps:

[0064] Under nitrogen protection, 4,7-dibromo-5,6-difluoro-benzothiadiazole (1.0 mmol), 9,9-dioctylfluorene-2,7-bis(pinacol borate) (1.0 mmol), potassium tert-butoxide (5.0 mmol), N-heterocyclic carbene palladium complex C2 (0.05 mmol) and 12 mL of tetrahydrofuran / water (4:1) as a solvent were added to a round-bottomed microwave reaction tube with jaws. The mixture was stirred at 100 °C for 12 hours. After the reaction was completed, it was cooled to room temperature. The polymer was precipitated with methanol, washed several times, dried, and weighed to obtain an organic semiconductor electron transport layer material with a yield of 70%. The number-average molecular weight of the organic semiconductor electron transport layer material was 36,897 - 50,439 g / mol, and the PDI was 2.1 - 2.5. The structure of the organic semiconductor electron transport layer material is shown below:

[0065] 。

[0066] Comparative Example 1

[0067] This comparative example provides an organic semiconductor electron transport layer material, and its preparation method includes the following steps:

[0068] Under nitrogen protection, 4,7-dibromo-2,1,3-benzothiadiazole (1.0 mmol), 9,9-dioctylfluorene-2,7-bis(pinacol borate) (1.0 mmol), potassium tert-butoxide (5.0 mmol), N-heterocyclic carbene palladium complex C1 (0.035 mmol) and 12 mL of tetrahydrofuran / water (3:1) as a solvent were added to a round-bottomed microwave reaction tube with jaws. The mixture was stirred at 95 °C for 20 hours. After the reaction was completed, it was cooled to room temperature. The polymer was precipitated with methanol, washed several times, dried, and weighed to obtain an organic semiconductor electron transport layer material with a yield of 77%. The number-average molecular weight of the organic semiconductor electron transport layer material was 15,482 - 23,476 g / mol, and the PDI was 1.7 - 2.2. The structure of the organic semiconductor electron transport layer material is shown below:

[0069] 。

[0070] Comparative Example 2

[0071] This comparative example provides an organic semiconductor electron transport layer material, and its preparation method includes the following steps:

[0072] Under nitrogen protection, 4,7-dibromo-5-fluorobenzo[c][1,2,5]thiadiazole (1.0 mmol), 9,9-dioctylfluorene-2,7-bis(pinacol borate) (1.0 mmol), potassium tert-butoxide (3.0 mmol), N-heterocyclic carbene palladium complex C1 (0.032 mmol) and 12 mL of tetrahydrofuran / water (5:1) were added as a solvent to a round-bottomed microwave reaction tube with jaws. The mixture was stirred at 90 °C for 24 hours. After the reaction was completed, it was cooled to room temperature. The polymer was precipitated with methanol, washed several times, dried, and weighed to obtain an organic semiconductor electron transport layer material with a yield of 73%. The number-average molecular weight of the organic semiconductor electron transport layer material was 13,451 - 21,098 g / mol, and the PDI was 1.6 - 2.0. The structure of the organic semiconductor electron transport layer material is shown below:

[0073] 。

[0074] Example 7

[0075] This example provides a p-i-n type perovskite solar cell. The specific cell structure is ITO / PTAA / perovskite active layer / electron transport layer material / BCP / Ag. The specific implementation steps are as follows:

[0076] (1) Cleaning of the transparent base layer: First, take out the ITO transparent conductive glass, tear off the surface plastic protective film, gently wipe and clean the surface oil stain with dish soap, rinse it once with deionized water, and then ultrasonically clean it in a dish soap aqueous solution with a concentration of 0.2 wt%, deionized water, and isopropanol for 15 minutes each. Finally, blow dry the isopropanol on the ITO surface with nitrogen, and put it in a box for later use.

[0077] (2) Deposition of the hole transport layer: Add 2.5 mg of PTAA to 1 mL of chlorobenzene, shake it on a shaker for 1 h to fully dissolve it, and prepare a 2.5 mg / mL solution for later use. First, place the cleaned ITO transparent conductive glass in an ultraviolet ozone cleaning instrument for 15 minutes of surface hydrophilic treatment. Then place it on a spin coater, use a pipette to suck 15 μL of the prepared hole layer solution and inject it into the gap between the doctor blade and the ITO transparent conductive glass, set the spin speed to 5 mm / s, and coat it on the ITO glass by spin coating. After spin coating, put it in a hot stage at 100 °C for annealing for 10 minutes.

[0078] (3) Preparation of the perovskite active layer: 0.95 mmol of FAI, 0.05 mmol of CsI, 1.1 mmol of PbI 2, 0.15 mmol MACl was dissolved in 1 ml of the NMP and 2-Me mixed solvent, and shaken in a shaker for 2 h to fully dissolve it, to prepare a 1 mmol / ml FA+Cs system perovskite precursor solution for later use. First, the ITO glass coated with the hole transport layer was placed on the doctor blade coater, and then 15 μl of the perovskite precursor solution was aspirated with a pipette and injected into the gap between the doctor blade and the ITO transparent conductive glass. The doctor blade speed was set at 4 mm / s. After doctor blade coating, it was quickly placed in a flash evaporation film former and evacuated for 10 s. The perovskite active layer was deposited on the surface of the hole transport layer by the doctor blade coating + flash evaporation method, and then annealed on a hot plate at 100 °C for 30 - 60 min.

[0079] (4) Deposition of the electron transport layer: 2 mg of the organic semiconductor electron transport layer material of Example 1 and 18 mg of PCBM were dissolved in 1 ml of chlorobenzene, and shaken in a shaker for 2 h to fully dissolve it for later use. First, the ITO glass coated with the perovskite active layer was placed on the doctor blade coater, and then 15 μl of the electron transport layer solution was aspirated with a pipette and injected into the gap between the doctor blade and the ITO transparent conductive glass. The doctor blade speed was set at 20 mm / s. The electron transport layer was deposited on the surface of the perovskite active layer, and then annealed on a hot plate at 100 °C for 10 min.

[0080] (5) Deposition of the hole blocking layer: 8 mg of BCP was added to 16 mL of isopropanol and ultrasonicated for 1 h to fully dissolve it, to prepare a 0.5 mg / ml solution for later use. First, the ITO glass coated with the electron transport layer was placed on the doctor blade coater, and then 15 μl of the BCP solution was aspirated with a pipette and injected into the gap between the doctor blade and the ITO transparent conductive glass. The doctor blade speed was set at 5 mm / s. The hole blocking layer was deposited on the surface of the electron transport layer.

[0081] (6) Deposition of the metal electrode layer: A 100 nm thick Ag film was thermally evaporated under high vacuum. The evaporation rate was: 20 nm was deposited at a rate of 0.3 Å / s, and then 80 nm was deposited at a rate of 1 Å / s.

[0082] Example 8

[0083] This example provides a p-i-n type perovskite solar cell, which is different from Example 7 in that the "organic semiconductor electron transport layer material of Example 1" in step (4) of Example 7 is replaced with the "organic semiconductor electron transport layer material of Example 2" to obtain the p-i-n type perovskite solar cell of Example 8.

[0084] Example 9

[0085] This embodiment provides a p-i-n type perovskite solar cell, which is different from that of Embodiment 7 in that the "organic semiconductor electron transport layer material of Embodiment 1" in step (4) of Embodiment 7 is replaced with the "organic semiconductor electron transport layer material of Embodiment 3" to obtain the p-i-n type perovskite solar cell of Embodiment 9.

[0086] Embodiment 10

[0087] This embodiment provides a p-i-n type perovskite solar cell, which is different from that of Embodiment 7 in that the "organic semiconductor electron transport layer material of Embodiment 1" in step (4) of Embodiment 7 is replaced with the "organic semiconductor electron transport layer material of Embodiment 4" to obtain the p-i-n type perovskite solar cell of Embodiment 10.

[0088] Embodiment 11

[0089] This embodiment provides a p-i-n type perovskite solar cell, which is different from that of Embodiment 7 in that the "organic semiconductor electron transport layer material of Embodiment 1" in step (4) of Embodiment 7 is replaced with the "organic semiconductor electron transport layer material of Embodiment 5" to obtain the p-i-n type perovskite solar cell of Embodiment 11.

[0090] Embodiment 12

[0091] This embodiment provides a p-i-n type perovskite solar cell, which is different from that of Embodiment 7 in that the "organic semiconductor electron transport layer material of Embodiment 1" in step (4) of Embodiment 7 is replaced with the "organic semiconductor electron transport layer material of Embodiment 6" to obtain the p-i-n type perovskite solar cell of Embodiment 12.

[0092] Comparative Example 3

[0093] This comparative example provides a p-i-n type perovskite solar cell, which is different from that of Embodiment 7 in that the "organic semiconductor electron transport layer material of Embodiment 1" in step (4) of Embodiment 7 is replaced with the "organic semiconductor electron transport layer material of Comparative Example 1" to obtain the p-i-n type perovskite solar cell of Comparative Example 3.

[0094] Comparative Example 4

[0095] This comparative example provides a p-i-n type perovskite solar cell, which is different from that of Embodiment 7 in that the "organic semiconductor electron transport layer material of Embodiment 1" in step (4) of Embodiment 7 is replaced with the "organic semiconductor electron transport layer material of Comparative Example 2" to obtain the p-i-n type perovskite solar cell of Comparative Example 4.

[0096] The p-i-n type perovskite solar cells of Examples 7 to 12 and Comparative Examples 3 to 4 were subjected to performance tests. The test methods are as follows, and the results are shown in Table 1.

[0097] (1) Volt-ampere characteristic curve (J-V): Under the simulated AM1.5G spectrum, the J-V characteristic curve of the device was measured using a Keithley 2440 light source.

[0098] Using a solar simulator (Newport, 91160), the light intensity was calibrated by NREL using a standard silicon solar cell device. The effective measurement area was 0.07 cm 2 , under reverse and forward bias scans, the scan rate was 100 mV / s, and the bias range was from -0.2 V to 1.2 V.

[0099] Table 1. Performance of the perovskite solar cells of Examples 7 to 12 and Comparative Examples 3 to 4.

[0100] Sample Voc (V) <![CDATA[Jsc (mA / cm 2 )]]> FF (%) PCE (%) Example 7 0.92 23.86 61.54 13.51 Example 8 0.97 24.88 66.84 16.13 Example 9 0.96 24.93 66.98 16.03 Example 10 0.95 23.94 62.32 14.17 Example 11 0.98 23.89 70.56 16.52 Example 12 0.98 23.91 71.23 16.69 Comparative Example 3 0.81 19.95 52.47 8.48 Comparative Example 4 0.86 20.07 56.08 9.68

[0101] As can be seen from Table 1, the organic semiconductor electron transport layer materials prepared in Examples 7 to 12 of the present invention have high Voc, Jsc, and FF values when used to prepare perovskite solar cells, and thus can obtain a high PCE value.

[0102] The unencapsulated p-i-n type perovskite solar cells of Examples 7 to 12 and Comparative Examples 3 to 4 were stored in the atmospheric environment for 30 days and then subjected to performance tests. The results are shown in Table 2.

[0103] Table 2. Performance of the perovskite solar cells of Examples 7 to 12 and Comparative Examples 3 to 4.

[0104] Sample PCE (%) Example 7 13.02 Example 8 15.67 Example 9 15.59 Example 10 13.73 Example 11 15.11 Example 12 15.28 Comparative Example 3 7.34 Comparative Example 4 8.25

[0105] The organic semiconductor electron transport layer materials prepared in Examples 7 to 12 of the present invention can be used to prepare perovskite solar cells, enabling the perovskite solar cells to maintain a high energy conversion efficiency during long-term use, so that the unencapsulated perovskite solar cells can maintain high stability in the atmospheric environment for a long time.

[0106] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that after reading the specification of this application, they can still modify the specific implementation manners of the present invention or make equivalent replacements, but these modifications or changes do not depart from the scope of protection of the pending claims of this invention application.

Claims

1. An organic semiconductor electron transport layer material, characterized in that: The structural formula of the organic semiconductor electron transport layer material is shown in formula (I): Formula (I); Among them, the number average molecular weight is 5000-50000 mol / L, and the PDI is 1.5-2.

5.

2. The organic semiconductor electron transport layer material according to claim 1, characterized in that: The number average molecular weight of the organic semiconductor electron transport layer material is 5000-20000 mol / L, and the PDI is 1.5-2.

3. The organic semiconductor electron transport layer material according to claim 1, characterized in that: The number average molecular weight of the organic semiconductor electron transport layer material is 30000-50000 mol / L, and the PDI is 2-2.

5.

4. The method for preparing an organic semiconductor electron transport layer material according to any one of claims 1 to 3, characterized in that: The steps include: Under the action of the nitrogen heterocyclic carbene palladium complex and an auxiliary agent, 4,7-dibromo-5,6-difluoro-benzothiadiazole and 9,9-dioctylfluorene-2,7-bis(boric acid pinacol ester) undergo polymerization reaction to obtain the nitrogen heterocyclic carbene palladium complex.

5. The method for preparing an organic semiconductor electron transport layer material according to claim 4, characterized in that: The structural formula of the nitrogen heterocyclic carbene palladium complex is shown in formula (II): Formula (II).

6. The method for preparing an organic semiconductor electron transport layer material according to claim 4, characterized in that: The structural formula of the nitrogen heterocyclic carbene palladium complex is shown in formula (III): Formula (III).

7. The method for preparing an organic semiconductor electron transport layer material according to claim 4, characterized in that: The molar ratio of 4,7-dibromo-5,6-difluoro-benzothiadiazole to 9,9-dioctylfluorene-2,7-bis(boric acid pinacol ester) is 1:1; And / or, the molar ratio of the 4,7-dibromo-5,6-difluoro-benzothiadiazole to the nitrogen heterocyclic carbene palladium complex is 1:0.005-0.

05.

8. The method for preparing an organic semiconductor electron transport layer material according to claim 4, characterized in that: The auxiliary agent includes an organic base and a solvent.

9. The method for preparing an organic semiconductor electron transport layer material according to claim 8, characterized in that: The organic base is selected from potassium tert-butoxide; And / or, the solvent is a mixture of tetrahydrofuran and water, and the volume ratio of tetrahydrofuran to water is 2-4:1; And / or, the polymerization reaction temperature is 60-100° C. and the time is 12-36 hours; And / or, the molar ratio of the 4,7-dibromo-5,6-difluoro-benzothiadiazole to the organic base is 1:3-5.

10. Use of the organic semiconductor electron transport layer material according to any one of claims 1 to 3 or the organic semiconductor electron transport layer material prepared by the preparation method of the organic semiconductor electron transport layer material according to any one of claims 4 to 9 in the preparation of perovskite solar cells.

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