A triphenylamine-based hole transport material, its preparation method and application

Abstract

The present invention relates to the technical field of energy materials, and specifically discloses a triphenylamine-based hole transport material, a preparation method thereof, and an application thereof. The triphenylamine-based hole transport material has a structure as shown in formula (I), wherein R1, R2, and R3 are each independently selected from a methyl group, a methoxy group, or 2-formylthiophene, and at least one 2-formylthiophene is included. The triphenylamine-based hole transport material provided by the present invention uses a triphenylamine molecule as a core unit and is chemically modified by introducing a 2-formylthiophene group, so that the hole transport material has good solubility, as well as high quantum efficiency and high hole mobility. When applied as a hole transport layer in a perovskite solar cell, the photoelectric conversion efficiency and stability of the solar cell can be effectively improved. #imgabs0#

Description

Technical Field

[0001] The present invention relates to the technical field of energy materials, and particularly relates to a triphenylamine-based hole transport material, a preparation method thereof, and an application thereof. Background Art

[0002] In recent years, organic-inorganic hybrid perovskite solar cells (PSCs) have become a research hotspot for a new generation of solar cells due to advantages such as wide material sources, simple preparation processes, and high efficiency. Among them, the hole transport material in perovskite solar cells has functions such as extracting and transporting holes, suppressing charge recombination, optimizing the energy band structure, increasing the open-circuit voltage and fill factor of solar cells, and preventing the perovskite light-harvesting layer from being eroded by moisture, and is an indispensable part of perovskite solar cells.

[0003] Triphenylamine (TPA) is a classic spiro compound. Its molecular structure consists of three benzene rings and one nitrogen atom, presenting a planar spiral shape. In the TPA structural unit, the N atom can attract electrons from the aromatic ring through the inductive effect, and at the same time, the non-shared electrons of the N atom provide electrons to the aromatic ring. Due to the p-p conjugation effect in the molecule, TPA shows electron-rich properties. Since the conjugation effect in the TPA molecule is greater than the inductive effect, the electron cloud of the molecule is widely distributed along the TPA unit, so electrons are very easy to lose to form positively charged vacancies, and this phenomenon is very conducive to hole transport. Therefore, the application of the TPA group in HTM can significantly improve the hole mobility. The organic small molecules based on the TPA unit have a low ionization potential, a rigid structure, show excellent photothermal stability in organic solvents, often have a high Tg, and at the same time, the specific spatial structure reduces the π-π* stacking between molecules, thereby increasing the solubility of the material and obtaining a hole layer with higher film quality, which greatly improves the efficiency of the device.

[0004] In the prior art, the hole transport materials used in perovskite solar cells are complex to synthesize, difficult to purify, have poor solubility, low hole mobility, and unstable performance, while the materials with high hole transport rate are expensive and have poor stability, affecting the use effect of battery devices. Therefore, it is of great significance for the development of perovskite solar cells to develop a hole transport material with a simple synthesis method, high stability, high hole mobility, and a suitable energy level structure. Summary of the Invention

[0005] In view of the above problems, the present invention provides a triphenylamine-based hole transport material, a preparation method thereof and an application thereof. The triphenylamine-based hole transport material uses a triphenylamine molecule as a core unit and is chemically modified by introducing 2-aldehydethiophene groups, so that the hole transport material has good solubility, as well as high quantum efficiency and high hole mobility. When applied as a hole transport layer in a perovskite solar cell, it can effectively improve the photoelectric conversion efficiency and stability of the solar cell.

[0006] To achieve the above invention object, the present invention adopts the following technical solutions:

[0007] In the first aspect of the present invention, a triphenylamine-based hole transport material is provided, and its structure is shown in formula (Ⅰ):

[0008]

[0009] Wherein, R1, R2 and R3 are the same or different, and are respectively methyl, methoxy or 2-aldehydethiophene, and at least one 2-aldehydethiophene is included.

[0010] The specific structures are shown in formulas (Ⅰ1) to (Ⅰ6):

[0011]

[0012] Compared with the prior art, the "star-shaped" spatial structure with triphenylamine as the core backbone group in the present invention has good anti-crystallization ability, which is beneficial to improving the thermal stability of the material. At the same time, the introduction of substitution units helps to enhance the hole extraction and transport ability of the material. By introducing substitution units, triphenylamine presents a spatial structure with a relatively large degree of distortion. This distorted spatial structure can weaken the π-π between molecules *The stacking ability increases the steric hindrance between molecules, thereby improving the solubility of the material in solvents such as chlorobenzene and the film quality. The molecules exhibit a relatively distorted spatial structure, so the stacking between molecules is reduced, and the molecules occupy a larger space, which is beneficial to improving the Tg of the material, thereby obtaining better device efficiency and stability. The introduction of the thiophene group significantly deepens the HOMO energy level of the material, and at the same time the LUMO energy level is also relatively increased. This situation indicates that the introduction of the thiophene group makes the energy level valence band of the HTM closer to that of the perovskite material, and can receive holes from the perovskite layer more efficiently, while obtaining better Voc. And the higher LUMO energy level can bring a higher energy level barrier, which can effectively block electrons from the perovskite material and reduce the loss of carriers and charge recombination. Therefore, the introduction of thiophene and methoxy is beneficial to improving the energy level matching between the material and the perovskite, thereby obtaining better device efficiency. In addition, the conjugated chain length in the aldehyde thiophene unit structure is relatively large, and it has a relatively higher hole mobility. Combining the triphenylamine structure with the aldehyde thiophene unit can obtain a three-dimensional structure with a higher degree of complexity and a larger steric hindrance, which is beneficial to obtaining a hole layer with higher film quality, and thus obtaining better device efficiency.

[0013] Preferably, at least one of R1, R2 and R3 contains a 2-aldehyde thiophene and a methoxy group. The methoxy group has a deeper relative energy level than the methyl group, which is beneficial to forming good coordination with the perovskite layer. The introduction of the thiophene group significantly deepens the HOMO energy level of the material, and at the same time the LUMO energy level is also relatively increased. This situation indicates that the introduction of the thiophene group makes the energy level valence band of the HTM closer to that of the perovskite material, and can receive holes from the perovskite layer more efficiently, while obtaining better Voc. And the higher LUMO energy level can bring a higher energy level barrier, which can effectively block electrons from the perovskite material and reduce the loss of carriers and charge recombination. At the same time, the introduction of thiophene and methoxy is beneficial to improving the energy level matching between the material and the perovskite, thereby obtaining better device efficiency.

[0014] Preferably, at least two of R1, R2 and R3 of the triphenylamine-based hole transport material contain 2-aldehyde thiophenes.

[0015] The second aspect of the present invention provides a preparation method of the above triphenylamine-based hole transport material, comprising the following steps:

[0016] Under an inert atmosphere, the triphenylamine derivative shown in formula (Ⅱ) and the thiophene heterocyclic compound react in an organic solvent under the action of a palladium catalyst and a basic substance to carry out a Suzuki coupling reaction to obtain the triphenylamine-based hole transport material shown in formula (Ⅰ);

[0017]

[0018] Among them, R4, R5, and R6 are the same or different, and are respectively halogen, methyl, or methoxy, and at least one of them is halogen.

[0019] In the present invention, a triphenylamine derivative represented by formula (II) and a thiophene heterocyclic compound are used as raw materials. Under the action of a basic substance and using a palladium catalyst, a Suzuki coupling reaction is carried out in an organic solvent to obtain a triphenylamine hole transport material represented by the general structural formula (I). The aldehyde group thiophene group is introduced into the triphenylamine structure through a direct arylation reaction, which simplifies the synthesis route, improves the yield, and avoids the generation of many by-products.

[0020] Preferably, the thiophene heterocyclic compound is at least one of 5-formyl-2-thiopheneboronic acid or 2-thiophenecarboxaldehyde.

[0021] Preferably, the basic substance is at least one of potassium carbonate, cesium carbonate, sodium carbonate, potassium tert-butoxide, sodium tert-butoxide, or tripotassium phosphate.

[0022] Preferably, the palladium catalyst is at least one of tetrakis(triphenylphosphine)palladium, diphenylphosphine dichloride palladium, or palladium acetate.

[0023] Preferably, the organic solvent is at least one of 1,4-dioxane or dimethyl sulfoxide.

[0024] Preferably, the molar ratio of the thiophene heterocyclic compound to the triphenylamine derivative is (1.2 - 3.6):1.

[0025] Preferably, the molar ratio of the palladium catalyst to the triphenylamine derivative is (0.05 - 0.12):1.

[0026] Preferably, the molar ratio of the basic substance to the triphenylamine derivative is (2.0 - 6.9):1.

[0027] Preferably, the volume molar ratio of the organic solvent to the triphenylamine derivative is (17.5 - 28) L:1 mol.

[0028] Preferably, the temperature of the Suzuki coupling reaction is 75°C - 125°C, and the time is 6 h - 48 h.

[0029] The third aspect of the present invention provides the application of the above triphenylamine hole transport material or the triphenylamine hole transport material prepared by the preparation method of the above triphenylamine hole transport material in a perovskite solar cell.

[0030] Compared with the prior art, the introduction of the aldehyde thienyl group deepens the HOMO energy level of the material, and at the same time the LUMO energy level is also relatively increased, indicating that the introduction of the thienyl group makes the energy level valence band of the HTM closer to that of the perovskite material, enabling it to receive holes from the perovskite layer more efficiently, while obtaining a better Voc, and the higher LUMO energy level can bring a higher energy level barrier, thereby effectively blocking electrons from the perovskite material and reducing carrier loss and charge recombination. The HOMO energy level of the triphenylamine-based hole transport material provided by the present invention is relatively matched with that of the perovskite material. Therefore, the corresponding PSCs device achieves a higher open-circuit voltage and fill factor, and obtains a higher device efficiency.

[0031] The fourth aspect of the present invention provides a hole transport layer, comprising the above triphenylamine-based hole transport material or a triphenylamine-based hole transport material prepared by the preparation method of the above triphenylamine-based hole transport material.

[0032] The fifth aspect of the present invention provides a perovskite solar cell, comprising the above hole transport layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0034] Figure 1 It is the ultraviolet-visible absorption spectrum of the triphenylamine-based hole transport materials prepared in Example 1, Example 5 and Example 6 of the present invention;

[0035] Figure 2 It is the cyclic voltammetry curve of the triphenylamine-based hole transport materials prepared in Example 1, Example 5 and Example 6 of the present invention;

[0036] Figure 3 It is the hole mobility curve diagram of the triphenylamine-based hole transport materials prepared in Example 1, Example 5 and Example 6 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0037] In order to make the objectives, technical solutions and advantages of the present invention clearer, the following further details the present invention with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, and are not used to limit the present invention.

[0038] In order to better illustrate the present invention, the following further gives examples for illustration.

[0039] Example 1

[0040] This embodiment provides a triphenylamine-based hole transport material, the structure of which is shown in formula (Ⅰ1):

[0041]

[0042] This embodiment also provides a preparation method of the above triphenylamine-based hole transport material, including the following steps:

[0043] Under a nitrogen atmosphere, accurately weigh 2.46 mmol of tris(4-bromophenyl)amine shown in formula (Ⅱ1), 8.85 mmol of 5-formyl-2-thiopheneboronic acid, and 17.04 mmol of potassium carbonate and add them to a three-necked flask. Then add 50 mL of 1,4-dioxane as the solvent for the reaction system, and bubble nitrogen for 15 min. Then weigh 0.15 mmol of tetrakis(triphenylphosphine)palladium as the palladium catalyst and add it to the reaction system. Slowly start stirring, and after stirring evenly, gradually heat up to 105 °C for reflux reaction for 24 h. After the reaction is completed, turn off the heating. After the system cools to room temperature, remove the excess solvent by rotary evaporation, and then separate and purify the product by column chromatography. The eluent ratio is petroleum ether:ethyl acetate = 20:1. After obtaining the yellow solid product, continue to purify it by recrystallization. Finally, 1.129 g of the yellow powdery triphenylamine-based hole transport material is obtained, and the yield is 79.8%.

[0044]

[0045] 1 H NMR(500MHz,Chloroform-d)δ9.92(s,2H),7.77(d,J=3.9Hz,2H),7.68-7.61(m,4H),7.39(d,J=4.0Hz,2H),7.25-7.19(m,4H).

[0046] 13 C NMR(126MHz,Chloroform-d)δ182.72,137.64,127.71,124.70,123.63.

[0047] Example 2

[0048] This embodiment provides a triphenylamine-based hole transport material, the structure of which is shown in formula (Ⅰ2):

[0049]

[0050] This embodiment also provides a preparation method of the above triphenylamine-based hole transport material, including the following steps:

[0051] Under a nitrogen atmosphere, accurately weigh 2.5 mmol of 4,4'-dibromo-4”-methoxytriphenylamine shown in formula (Ⅱ2), 5.4 mmol of 5-formyl-2-thiopheneboronic acid, and 12 mmol of potassium carbonate into a three-necked flask. Then add 60 mL of 1,4-dioxane as the solvent for the reaction system, and bubble nitrogen for 15 min. Then weigh 0.2 mmol of tetrakis(triphenylphosphine)palladium as the palladium catalyst and add it to the reaction system. Slowly start stirring, and after stirring evenly, gradually heat up to 125 °C for reflux reaction for 6 h. After reacting for 4 h, continuously detect the reaction by TLC. After the reaction is completed, turn off the heating. After the system cools to room temperature, remove the excess solvent by rotary evaporation under reduced pressure, and then separate and purify the product by column chromatography. The eluent ratio is petroleum ether:ethyl acetate = 25:1. After obtaining the solid product, continue to purify it by recrystallization, and finally obtain 0.947 g of the triphenylamine-based hole transport material with a yield of 76.5%.

[0052]

[0053] Example 3

[0054] This example provides a triphenylamine-based hole transport material, whose structure is shown in formula (Ⅰ3):

[0055]

[0056] This example also provides a preparation method of the above triphenylamine-based hole transport material, including the following steps:

[0057] Under a nitrogen atmosphere, accurately weigh 2.5 mmol of 4,4'-dibromo-4”-methyltriphenylamine shown in formula (Ⅱ3), 5.4 mmol of 2-thiophenecarboxaldehyde, and 12 mmol of sodium carbonate into a three-necked flask. Then add 70 mL of dimethyl sulfoxide as the solvent for the reaction system, and bubble nitrogen for 15 min. Then weigh 0.3 mmol of palladium acetate as the palladium catalyst and add it to the reaction system. Slowly start stirring, and after stirring evenly, gradually heat up to 75 °C for reflux reaction for 48 h. After reacting for 4 h, continuously detect the reaction by TLC. After the reaction is completed, turn off the heating. After the system cools to room temperature, remove the excess solvent by rotary evaporation under reduced pressure, and then separate and purify the product by column chromatography. The eluent ratio is petroleum ether:ethyl acetate = 25:1. After obtaining the solid product, continue to purify it by recrystallization, and finally obtain 0.893 g of the triphenylamine-based hole transport material with a yield of 74.6%.

[0058]

[0059] Example 4

[0060] This example provides a triphenylamine-based hole transport material, whose structure is shown in formula (Ⅰ4):

[0061]

[0062] This embodiment also provides a preparation method of the above triphenylamine-based hole transport material, which includes the following steps: Under a nitrogen atmosphere, accurately weigh 2.5 mmol of 4-bromo-4'-methyl-4”-methoxytriphenylamine shown in formula (Ⅱ4), 3.0 mmol of 5-formyl-2-thiopheneboronic acid, and 5.5 mmol of potassium carbonate and add them to a three-necked flask. Then add 50 mL of 1,4-dioxane as the solvent for the reaction system, and bubble nitrogen for 15 min. Then weigh 0.2 mmol of tetrakis(triphenylphosphine)palladium as the palladium catalyst and add it to the reaction system. Slowly start stirring, and after stirring evenly, gradually heat up to 105 °C and reflux for 24 h. After the reaction is completed, turn off the heating. After the system cools to room temperature, remove the excess solvent by rotary evaporation under reduced pressure, and then separate and purify the product by column chromatography. The ratio of the eluent is petroleum ether:ethyl acetate = 20:1. After obtaining the solid product, continue to purify it by recrystallization. Finally, 0.751 g of the triphenylamine-based hole transport material is obtained, and the yield is 75.3%.

[0063]

[0064] Example 5

[0065] This embodiment provides a triphenylamine-based hole transport material, and its structure is shown in formula (Ⅰ5):

[0066]

[0067] This embodiment also provides a preparation method of the above triphenylamine-based hole transport material, which includes the following steps:

[0068] Under a nitrogen atmosphere, accurately weigh 0.993 g of 4-bromo-N,N-bis(4-methoxyphenyl)aniline (2.85 mmol) shown in formula (Ⅱ5), 0.53 g of 5-formyl-2-thiopheneboronic acid (3.4 mmol), and 2.0 g of potassium carbonate (5.68 mmol) and add them to a three-necked flask. Then add 50 mL of 1,4-dioxane as the solvent for the reaction system, and bubble nitrogen for 15 min. Then weigh 0.164 g of tetrakis(triphenylphosphine)palladium (0.15 mmol) as the palladium catalyst and add it to the reaction system. Slowly start stirring, and after stirring evenly, gradually heat up to 105 °C and reflux for 6 h. After reacting for 4 h, continuously detect the reaction by TLC. After the reaction is completed, turn off the heating. After the system cools to room temperature, remove the excess solvent by rotary evaporation under reduced pressure, and then separate and purify the product by column chromatography. The ratio of the eluent is petroleum ether:ethyl acetate = 30:1. After obtaining the yellow solid product, continue to purify it by recrystallization. Finally, 0.844 g of the yellow powdery triphenylamine-based hole transport material is obtained, and the yield is 71.3%.

[0069]

[0070] 1 1H NMR (500 MHz, Chloroform-d) δ 9.88 (s, 1H), 7.73 (d, J = 4.0 Hz, 1H), 7.55 - 7.49 (m, 2H), 7.33 - 7.28 (m, 1H), 7.15 (d, J = 8.4 Hz, 4H), 7.10 - 7.05 (m, 4H), 7.05 - 7.00 (m, 2H), 2.37 (s, 6H).

[0071] 13 13C NMR (126 MHz, Chloroform-d) δ 182.63, 154.96, 149.60, 144.46, 141.08, 137.86, 133.76, 130.18, 127.20, 125.46, 125.22, 122.62, 121.13, 20.95.

[0072] Example 6

[0073] This example provides a triphenylamine-based hole transport material, whose structure is shown in formula (Ⅰ6):

[0074]

[0075] This example also provides a preparation method for the above triphenylamine-based hole transport material, including the following steps:

[0076] Under a nitrogen atmosphere, accurately weigh 1.0 g of 4-bromo-4',4''-dimethyltriphenylamine (2.85 mmol) shown in formula (Ⅱ6), 0.53 g of 5-formyl-2-thiopheneboronic acid (3.4 mmol), and 2.0 g of potassium carbonate (5.68 mmol), and add them to a three-necked flask. Then add 50 mL of 1,4-dioxane as the solvent for the reaction system, and bubble nitrogen for 15 min. Then weigh 0.164 g of tetrakis(triphenylphosphine)palladium (0.15 mmol) as a palladium catalyst and add it to the reaction system. Slowly start stirring, and after stirring evenly, gradually heat up to 105 °C and reflux for 6 h. After reacting for 4 h, continuously detect the reaction by TLC. After the reaction is completed, turn off the heating. After the system cools to room temperature, remove the excess solvent by rotary evaporation, and then purify the product by column chromatography. The eluent ratio is petroleum ether:ethyl acetate = 30:1. After obtaining a yellow solid product, continue to purify it by recrystallization to finally obtain 0.849 g of a yellow powdery triphenylamine-based hole transport material, with a yield of 77.8%.

[0077]

[0078] 1 1H NMR (500 MHz, Chloroform-d) δ 9.87 (s, 1H), 7.72 (d, J = 4.0 Hz, 1H), 7.53 - 7.46 (m, 2H), 7.29 (d, J = 3.9 Hz, 1H), 7.17 - 7.10 (m, 4H), 6.95 - 6.88 (m, 6H), 3.85 (s, 6H).

[0079] 13 13C NMR (126 MHz, Chloroform-d) δ 182.60, 156.59, 155.17, 150.07, 140.86, 139.94, 137.92, 127.29, 127.20, 124.29, 122.36, 119.32, 114.93, 55.56.

[0080] Comparative Example 1

[0081] This comparative example provides a triphenylamine-based hole transport material, and its structure is shown in formula (Ⅰ11):

[0082]

[0083] This comparative example also provides a preparation method of the above triphenylamine-based hole transport material, including the following steps:

[0084] Under a nitrogen atmosphere, accurately weigh 2.46 mmol of tris(4-bromophenyl)amine shown in formula (Ⅱ1), 8.85 mmol of 2-tri-n-butylstannylthiophene, and 17.04 mmol of potassium carbonate and add them to a three-necked flask. Then add 50 mL of 1,4-dioxane as the solvent for the reaction system, and use nitrogen to bubble for 15 min. Then weigh 0.15 mmol of tetrakis(triphenylphosphine)palladium as a palladium catalyst and add it to the reaction system. Slowly start stirring, and after stirring evenly, gradually heat up to 105 °C and reflux for 24 h. After the reaction is completed, turn off the heating. After the system cools to room temperature, remove the excess solvent by rotary evaporation, and then separate and purify the product by column chromatography. The eluent ratio is petroleum ether:ethyl acetate = 20:1. After obtaining the solid product, continue to purify by recrystallization to finally obtain the triphenylamine-based hole transport material.

[0085] Test Example 1

[0086] At room temperature, dissolve the triphenylamine-based hole transport materials prepared in Example 1, Example 5, and Example 6 in dichloromethane to prepare a test solution with a concentration of 1×10 -5 M, and then perform ultraviolet-visible spectroscopy detection. The detection results are shown in Figure 1 . From Figure 1It was found that the three triphenylamine-based hole transport materials had very close maximum absorption peaks. This result was due to the same core skeleton structure of the three materials. The three types of materials showed two strong absorption peaks at 300 nm - 420 nm, which should be attributed to the π-π* transition of the core triphenylamine group and the peripheral thiophene and other groups of the compound, indicating that the three triphenylamine-based hole transport materials had very similar π-conjugated systems. According to the UV-vis data, the optical band gap Eg of the triphenylamine-based hole transport material prepared in Example 6 was calculated to be 2.64 eV, the optical band gap Eg of the triphenylamine-based hole transport material prepared in Example 5 was 2.58 eV, and the optical band gap Eg of the triphenylamine-based hole transport material prepared in Example 1 was 2.68 eV.

[0087] To further calculate the HOMO energy level and LUMO energy level of the material molecules, the inventors conducted electrochemical tests on the three triphenylamine-based hole transport materials. The cyclic voltammetry (CV) method was used to test the electrical properties of the HTM. The test was mainly carried out with an electrochemical workstation, and a three-electrode system was built. A platinum plate electrode and a platinum wire electrode were respectively selected as the working electrode and the counter electrode of the test system, and an Ag / AgCl electrode was selected as the reference electrode for testing. A dichloromethane solution of 0.1 M tetrabutylammonium hexafluorophosphate (nBu4NPF6) was configured as the electrolyte solution. The thickness of the platinum plate electrode was 0.2 mm. A solution of the triphenylamine-based hole transport material with a concentration of 1×10 -4 M was configured in the dichloromethane solution as the solution to be tested. Before the test, nitrogen was used to expel the air, and the scanning speed was set at 100 mV s -1 , and the scanning range was set at -0.2 V - 1.4 V. Before testing the material, ferrocene was used as an internal standard for determination. Then, according to the obtained redox potential, the orbital energy level distribution of the two types of materials could be obtained. According to the values of ferrocene relative to the standard hydrogen electrode and the standard hydrogen electrode relative to the vacuum energy level, substituting into E HOMO = -(E ox + 4.8) eV, LUMO = HOMO + Eg. The detection results are as Figure 2 shown. According to Figure 2It can be seen that the oxidation potential of the triphenylamine-based hole transport material prepared in Example 6 is 0.729 V, the reduction potential is 0.689 V, the calculated HOMO energy level is -5.389 eV, and the LUMO energy level is -2.749 eV. According to the CV curve, the oxidation potential of the triphenylamine-based hole transport material prepared in Example 5 is 0.731 V, the reduction potential is 0.692 V, the calculated HOMO energy level is -5.391 eV, and the LUMO energy level is -2.811 eV. The oxidation potential of the triphenylamine-based hole transport material prepared in Example 1 is 0.742 V, the reduction potential is 0.693 V, the calculated HOMO energy level is -5.40 eV, and the LUMO energy level is -2.72 eV. The △Ep values of the triphenylamine-based hole transport materials prepared in Example 6, Example 5, and Example 1 are 0.048 V, 0.062 V, and 0.059 V respectively. Therefore, the triphenylamine-based hole transport material prepared in Example 6 has better oxidation and reduction properties. Under the condition that the end group changes from methyl to methoxy, the methoxy group has a deeper relative energy level, which is beneficial to form a good coordination with the perovskite layer. The introduction of the aldehyde group thiophene group significantly deepens the HOMO energy level of the material, and at the same time the LUMO energy level is also relatively increased. This situation shows that the introduction of the aldehyde group thiophene group makes the energy level valence band of the hole transport material closer to that of the perovskite material, can receive holes from the perovskite layer more efficiently, and at the same time obtain better Voc. And the higher LUMO energy level can bring a higher energy level barrier, which can effectively block electrons from the perovskite material, reduce the loss of carriers and charge recombination. Therefore, the introduction of the aldehyde group thiophene and methoxy group is beneficial to improve the energy level matching between the material and the perovskite, thereby obtaining better device efficiency.

[0088] Test Example 2

[0089] The Td and Tg of the triphenylamine-based hole transport materials prepared in Example 1, Example 5, and Example 6 were measured by TGA and DSC. Before the test, the products need to be dried in advance. Under a nitrogen atmosphere, the heating rate was set to 10 °C / min, and the weight change of the samples in the range from room temperature to 500 °C was measured. The Td and Tg of the three materials were obtained according to the corresponding temperatures at which the weight loss was 5% and the endothermic peak appeared in the curve. It was detected that the Td values of the triphenylamine-based hole transport materials prepared in Example 6, Example 5, and Example 1 were 300 °C, 251.2 °C, and 369.9 °C respectively, and the Tg values were 130.0 °C, 126.2 °C, and 224.1 °C respectively. The test data of TGA and DSC show that all three materials have good thermal stability, which can ensure the structural stability during the preparation of PSCs devices and extend the service life of the devices.

[0090] Test Example 3

[0091] The space charge limited current method (SCLC) was used to test the hole mobility of the triphenylamine-based hole transport materials prepared in Example 1, Example 5, and Example 6. A pure hole single-carrier device was tested, and the device structure was ITO / PEDOT:PSS / HTM / MoO3 / Al. The parameters related to hole mobility were tested under dark conditions, and the test results are shown in Figure 3 . The hole mobility relative to the hole material was estimated by the Mott-Gurney law. According to Figure 3 the corresponding data, the hole mobility of the triphenylamine-based hole transport material prepared in Example 6 was calculated to be 1.78×10 -5 cm 2 V -1 S -1 . The hole mobility of the triphenylamine-based hole transport material prepared in Example 5 was 4.51×10 -5 cm 2 V -1 S -1 . The hole mobility of the triphenylamine-based hole transport material prepared in Example 1 was 7.73×10 -5 cm 2 V -1 S -1 . It can be seen that after changing the peripheral substituents from methyl and methoxy to aldehyde thiophene structure, the hole mobility increases, indicating that molecules with better planarity tend to have lower recombination energy, so higher hole mobility can be obtained. Molecules based on the tri-aldehyde thiophene group as the end group obtained better hole mobility.

[0092] Test Example 4

[0093] While the hole transport material undertakes the transmission of holes and blocks electrons, more importantly, it protects the perovskite material from moisture erosion in the external environment. The hydrophobicity of the triphenylamine-based hole transport materials prepared in Example 1, Example 5, and Example 6 was measured. The three materials were configured into corresponding chlorobenzene solutions at a concentration of 20 mg / mL, and the corresponding HTM films were prepared by spin-coating on a clean ITO glass at a spin-coating speed of 1000 rpm for 60 s. After testing, the water contact angle of the triphenylamine-based hole transport material prepared in Example 6 was 83.6°, the water contact angle of the triphenylamine-based hole transport material prepared in Example 5 was 81.4°, and the water contact angle of the triphenylamine-based hole transport material prepared in Example 1 was 79.4°. According to the water contact angle test results, it was confirmed that all three types of materials had good hydrophobicity, which could effectively prevent moisture in the air from entering the device interior and could play a good protective role for the perovskite layer.

[0094] Application Example

[0095] The triphenylamine-based hole transport materials prepared in Examples 1 to 6 and Comparative Examples 1 to 2 were used to fabricate a battery. The battery structure was a formal structure prepared by a two-step method, and the structures were FTO glass substrate / SnO2 / perovskite light-absorbing layer / HTL / Au electrode, respectively.

[0096] (1) Treatment of transparent conductive glass FTO: The fluorine-doped tin dioxide (SnO2:F, FTO) transparent conductive glass was ultrasonically treated with detergent, deionized water, acetone, and ethanol solution for 15 minutes in sequence, and then the glass plate was treated with a vacuum plasma machine for 10 minutes to finally obtain a clean FTO glass meeting the experimental requirements.

[0097] (2) Preparation of a dense SnO2 layer: Urea, SnCl2·2H2O, and distilled water were mixed evenly, and HCL and TGA (98%) were added to obtain a chemical deposition solution. Take out the glass substrate prepared in step (1), first place it in an acetone solution and ultrasonically clean it for 10 minutes, then dry it with nitrogen and place it in an oven at 90°C for heat deposition for 6 hours. Then transfer the cooled substrate to a glove box in an inert gas environment for 10 minutes. After taking it out, ultrasonically clean it with distilled water and isopropanol for 10 minutes each, blow off the loose materials on the edge with nitrogen, and then place it on a hot plate at 170°C for annealing for 60 minutes. After cooling to room temperature, spin-coat 10 mM KCl for 30 seconds at a speed of 3000 rpm, and then place it in an oven at 100°C for annealing for 10 minutes after purging with nitrogen.

[0098] (3) Preparation of the perovskite light-absorbing layer: Treat the FTO / SnO2 substrate with ultraviolet ozone again for 15 minutes. After mixing 0.692 g of lead iodide, 0.519 g of methylammonium chloride, and 0.086 g of methylammonium iodide evenly, dissolve them in a mixed solution of anhydrous N,N-dimethylformamide and anhydrous dimethyl sulfoxide with a volume ratio of 7.2:1 to obtain a precursor solution. Then spin-coat 100 μL of the above precursor solution on the dense SnO2 layer. In the first stage, spin-coat at a speed of 1000 rpm for 10 seconds, and in the second stage, spin-coat at a speed of 5000 rpm for 30 seconds to deposit the perovskite solution. Anneal the obtained perovskite layer film at 110°C for 60 minutes. After completely cooling to room temperature, drop a 5 mg / mL isopropanol solution onto the spin-coated substrate and spin-coat at 5000 rpm for 30 seconds without annealing.

[0099] (4) Preparation of the hole transport layer: Dissolve 0.4 g of the organic hole transport material in 10 mL of chlorobenzene, add 0.45 g of 4-tert-butylpyridine and 0.4 g of lithium bis(trifluoromethanesulfonyl)imide, stir for 2 hours to mix evenly, and then spin-coat at a speed of 4000 rpm for 40 seconds and coat it on the perovskite layer to obtain the hole transport layer.

[0100] (5) Fabricate the metal electrode: Deposit MoO3 and a 120-nm Au electrode on the coated substrate by thermal evaporation. After the electrode is fabricated, a solar cell panel with an effective area of 0.09 cm 2 is obtained.

[0101] The photoelectric conversion efficiencies of the solar cells fabricated with the triphenylamine-based hole-transporting materials prepared in Examples 1 to 6 and Comparative Example 1 are shown in Table 1 in detail. In addition, due to the defects on the surface of the perovskite material and its easy deliquescence under the action of moisture, how to ensure that the perovskite material reduces contact with moisture to extend the device life is a very important research direction. The presence of the hole-transporting layer can not only transport holes but also act as a protective layer to well protect the perovskite material from erosion by moisture and oxygen. Therefore, in order to judge the performance of the hole-transporting layer, the long-term stability of the device also needs to be tested. To test the long-term stability of the device, the inventor placed the unencapsulated perovskite solar cells fabricated with the above triphenylamine-based hole-transporting materials under environmental conditions of 25 °C and a relative humidity of 45% for 500 h, and measured the efficiency of the device at fixed intervals. The test results are shown in Table 1 in detail. As can be seen from Table 1, the solar cells fabricated with the triphenylamine-based hole-transporting materials provided by the present invention have better photovoltaic performance parameters; the perovskite layer modified with the triphenylamine-based hole-transporting materials provided by the present invention can, to a certain extent, ensure that the perovskite material is not interfered by the external environment, showing better device stability.

[0102] Table 1

[0103]

[0104] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, or improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. Application of a triphenylamine-based hole transport material in a perovskite solar cell, characterized in that, The structure of the aniline-based hole transport material is shown in Formula (Ⅰ2)-Formula (I6):

2. The preparation method of the triphenylamine-based hole transport material according to claim 1, characterized in that, It includes the following steps: Under an inert atmosphere, the triphenylamine derivative shown in Formula (Ⅱ) and the thiophene heterocyclic compound react in an organic solvent under the action of a palladium catalyst and a basic substance to carry out a Suzuki coupling reaction to obtain the triphenylamine-based hole transport material shown in Formula (Ⅰ); Among them, R4, R5 and R6 are the same or different, and are respectively halogen, methyl or methoxy, and at least one halogen is included.

3. The preparation method of the triphenylamine-based hole transport material according to claim 2, characterized in that The thiophene heterocyclic compound is at least one of 5-formyl-2-thiopheneboronic acid or 2-thiophenecarboxaldehyde; and / or The basic substance is at least one of potassium carbonate, cesium carbonate, sodium carbonate, potassium tert-butoxide, sodium tert-butoxide or tripotassium phosphate; and / or The palladium catalyst is at least one of tetrakis(triphenylphosphine)palladium, diphenylphosphine dichloride or palladium acetate; and / or The organic solvent is at least one of 1,4-dioxane or dimethyl sulfoxide.

4. The preparation method of the triphenylamine-based hole transporting material according to claim 2 or 3, characterized in that, The molar ratio of the thiophene heterocyclic compound to the triphenylamine derivative is (1.2-3.6):1; and / or The molar ratio of the palladium catalyst to the triphenylamine derivative is (0.05-0.12):1; and / or The molar ratio of the basic substance to the triphenylamine derivative is (2.0-6.9):1; and / or The volume molar ratio of the organic solvent to the triphenylamine derivative is (17.5-28.0) L:1 mol.

5. The preparation method of the triphenylamine-based hole transport material according to claim 2, characterized in that, The temperature of the Suzuki coupling reaction is 75°C to 125°C, and the time is 6h to 48h.

6. A hole transport layer, characterized in that, It includes the triphenylamine-based hole transport material described in Claim 1 or the triphenylamine-based hole transport material prepared by the preparation method of the triphenylamine-based hole transport material described in any one of Claims 2-5.

7. A perovskite solar cell, characterized in that: It includes the hole transport layer described in Claim 6.

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