A triphenylamine-based polymer hole transport material applied to perovskite solar cells

Abstract

The present invention belongs to the field of organic optoelectronic polymer materials, and discloses a triphenylamine-based polymer hole transport material applied to a perovskite solar cell. The corresponding triphenylamine-based polymer has a triphenylamine as the main chain backbone structure, and pyridine groups are inserted into the main chain. By using a polymer with a specific chemical structure, with a triphenylamine structure as the main chain backbone structure and inserting pyridine units into the main chain structure, these pyridine units can serve as anchoring functional groups. The obtained material is an overall random copolymer, which can be especially used as a non-doped hole transport material in a perovskite solar cell, capable of improving the perovskite growth quality, obtaining a high energy conversion efficiency, and effectively solving the technical problem of the low efficiency of existing perovskite solar cells.

Description

Technical Field

[0001] The present invention belongs to the field of organic optoelectronic polymer materials, and more specifically, relates to a triphenylamine-based polymer hole transport material applied to a perovskite solar cell. Background Art

[0002] Since the development of perovskite solar cells (PVSCs) in 2009, their energy conversion efficiency has reached 25.7%, showing great potential for commercialization. Among them, the inverted perovskite solar cell (using a p-i-n structure; the formal device uses an n-i-p structure) has received extensive attention due to its simple preparation process, high device stability, insignificant hysteresis effect, and suitability for the preparation of flexible and tandem devices. In the inverted perovskite solar cell, the hole transport material not only plays a role in extracting and transporting holes, but also affects the crystallization growth of perovskite, and plays an important role in improving the performance and stability of perovskite solar cells. However, most of the current hole transport materials are not suitable for the crystallization growth of perovskite.

[0003] Currently, the hole transport material for highly efficient inverted perovskite solar cells is poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA), which often needs to be chemically doped by adding dopants and additives. However, the device efficiency based on PTAA still has an obvious gap with that of the formal device (the efficiency of the formal device can reach 25.7%), and its strong hydrophobicity is not suitable for the preparation of large-area solar cells with an area exceeding 1 cm 2 This limits its large-scale application. Therefore, the development of new high-performance non-doped hole transport materials is crucial for the development of efficient and large-area inverted perovskite solar cells. Summary of the Invention

[0004] Aiming at the above defects or improvement requirements of the prior art, the purpose of the present invention is to provide a triphenylamine-based polymer hole transport material applied to an inverted perovskite solar cell. By using a polymer with a specific chemical structure, with a triphenylamine structure as the main chain backbone structure, pyridine units are inserted into the main chain structure. These pyridine units can serve as anchoring functional groups, and the resulting material is an overall random copolymer, which can be used as a non-doped hole transport material in an inverted perovskite solar cell (such as an inverted planar perovskite solar cell), can promote the growth of perovskite, improve the growth quality of perovskite, obtain a high energy conversion efficiency, effectively solve the technical problem of low efficiency of existing inverted perovskite solar cells, and effectively expand the types of non-doped hole transport materials in perovskite solar cells. Taking the following examples as an example, the highest energy conversion efficiency of the prepared small-area inverted perovskite solar cell reaches 24.89%, and the highest energy conversion efficiency of the large-area device is 23.12%, showing great application potential.

[0005] To achieve the above object, according to one aspect of the present invention, a triphenylamine-based polymer is provided, characterized in that the polymer has a triphenylamine as the main chain backbone structure, and pyridine groups are also inserted into the main chain.

[0006] As a further preference of the present invention, the connection sites of pyridine in the main chain are the 3- and 5-positions.

[0007] As a further preference of the present invention, the triphenylamine-based polymer specifically has the chemical structure shown in the general formula (A):

[0008]

[0009] In the formula, R is an alkyl substituent, 0 < x < 1, and n is an integer from 10 to 30.

[0010] As a further preference of the present invention, the R is selected from methyl, ethyl, butyl, tert-butyl, pentyl and hexyl.

[0011] According to another aspect of the present invention, a preparation method of the above triphenylamine-based polymer is provided, characterized in that the preparation method is to perform a Suzuki coupling reaction on a triphenylamine boronic acid pinacol ester intermediate, a dibromo-substituted triphenylamine intermediate and 3,5-dibromopyridine to obtain a triphenylamine-based polymer, wherein the triphenylamine boronic acid pinacol ester intermediate has the chemical structure shown in the formula (I), and the dibromo-substituted triphenylamine intermediate has the chemical structure shown in the formula (I):

[0012]

[0013] As a further preference of the present invention, the preparation method specifically is to mix and dissolve the triphenylamine boronic acid pinacol ester intermediate, the dibromo-substituted triphenylamine intermediate and 3,5-dibromopyridine in an organic solvent, add a phase transfer catalyst, a catalyst, a base, a ligand and water under the protection of an inert atmosphere, and raise the temperature to 80 - 100 °C for the Suzuki coupling reaction; after sufficient reaction, perform extraction and separation, dry the obtained organic phase, remove the solvent, and then perform Soxhlet extraction, and obtain the triphenylamine-based polymer after drying.

[0014] As a further preference of the present invention, the molar ratio of the triphenylamine boronic acid pinacol ester intermediate, the dibromo-substituted triphenylamine intermediate and 3,5-dibromopyridine is 1:x:(1 - x), 0 < x < 1;

[0015] The reaction time of the Suzuki coupling reaction is 60 - 72 hours.

[0016] According to another aspect of the present invention, the present invention provides the application of the above triphenylamine-based polymer as a hole transport material in a perovskite solar cell;

[0017] Preferably, the perovskite solar cell is a perovskite solar cell with a reverse planar structure.

[0018] Through the above technical solutions conceived by the present invention, compared with the prior art, the following

[0019] beneficial effects can be achieved:

[0020] (1) The triphenylamine-based polymer containing a pyridine group in the present invention uses triphenylamine as the polymer backbone structure, and inserts a pyridine group into the main chain. It can not only effectively regulate the energy level and charge transport ability of the material, but also passivate the surface defects of the perovskite and provide an anchoring effect to promote the growth of the perovskite. This triphenylamine-based polymer, especially as a non-doped hole transport material, can be applied to a perovskite solar cell, which can promote the growth of the perovskite, achieve high performance of the device, and obtain a high energy conversion efficiency. The content of pyridine in the triphenylamine-based polymer can be any value between 0 and 1 (corresponding to 0 < x < 1 in the general formula A). The introduction of the pyridine group can regulate the energy level of the material, while providing an effective passivation effect to precisely regulate the properties of the material, but does not change the hole transport property of the material.

[0021] (2) The triphenylamine-based polymer containing a pyridine group in the present invention has appropriate HOMO and LUMO energy levels, as well as a high hole mobility and good film-forming property. When applied as a non-doped hole transport material in a perovskite solar cell, it can promote the growth of the perovskite. In the preferred embodiment, the energy conversion efficiency of the device of the polymer PTAA-P1 proposed by the present invention reaches 24.89%.

[0022] The triphenylamine-based polymer containing a pyridine group in the present invention can be directly used as a hole transport material in a perovskite solar cell without adding a dopant and an additive for chemical doping, avoiding the oxidation reaction caused by doping and the accompanying ion migration, which will deteriorate the long-term stability of the device. The triphenylamine-based polymer provided by the present invention is a high-efficiency and high-stability non-doped hole transport material.

[0023] When the triphenylamine-based polymer PTAA-P1 exemplified in the following examples of the present invention is used as a non-doped hole transport material in a perovskite solar cell, under the irradiation condition of simulated sunlight AM 1.5G with an illumination intensity of 100 mW cm -2 the highest photoelectric conversion efficiency can reach 24.89%.

[0024] Similarly, taking the following examples as an illustration, based on the present invention, triphenylamine polymers containing pyridine groups are directly used as hole transport materials in small-area planar-structured perovskite solar cells (0.08 cm 2 ), achieving an energy conversion efficiency of 24.89%. For large-area inverted cells (1.0 cm 2 ), an energy conversion efficiency of 23.21% is obtained, solving the problem that current PTAA is not suitable for fabricating large-area perovskite solar cells.

[0025] (3) Moreover, in the present invention, triphenylamine polymers containing pyridine groups have triphenylamine and pyridine groups as the main chain, and the synthesis process is simple. In particular, they can be obtained by Suzuki coupling reaction of dibromo-substituted triphenylamine intermediates, triphenylamine boronic acid pinacol esters intermediates with 3,5-dibromopyridine, and the preparation method is simple and feasible. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Synthesis route of PTAA-P1 in Example 1.

[0027] Figure 2 1H NMR spectrum of PTAA-P1 in Example 1.

[0028] Figure 3 UV-Vis absorption spectrum of PTAA-P1 in Example 2.

[0029] Figure 4 Cyclic voltammetry curve of PTAA-P1 in Example 2.

[0030] Figure 5 Hole mobility test chart of PTAA and PTAA-P1 in Example 3.

[0031] Figure 6 Contact angle of PTAA and PTAA-P1 thin films with water droplets in Example 3.

[0032] Figure 7 XPS chart of perovskite grown on PTAA-P1 in Example 3.

[0033] Figure 8 XRD chart of perovskite grown on PTAA and PTAA-P1 in Example 3.

[0034] Figure 9 SEM chart of perovskite grown on PTAA and PTAA-P1 in Example 3.

[0035] Figure 10 Small-area inverted planar-structured perovskite solar cell (0.08 cm) with PTAA-P1 as the non-doped hole transport material in Example 3 2) Optimal device J-V curve.

[0036] Figure 11 For the large-area inverted planar perovskite solar cell with PTAA-P1 as the undoped hole transport material in Example 3 (1 cm 2 ) Optimal device J-V curve. Detailed implementation manners

[0037] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and 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. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0038] Based on the present invention, triphenylamine can be used as the polymer main chain backbone structure, and 3,5-substituted pyridine can be inserted into the main chain to regulate the polymer molecular configuration and charge transport performance, as well as improve the passivation and anchoring functions.

[0039] The corresponding triphenylamine polymer, its chemical structure can be, for example, as shown in the general formula (A):

[0040]

[0041] In the formula, R is an alkyl substituent, 0 < x < 1, and n is an integer from 10 to 30.

[0042] In a preferred embodiment, x = 0.1, the substituent is methyl, and the triphenylamine polymer has a structural general formula as shown in formula PTAA-P1:

[0043]

[0044] Among them, n takes an integer from 10 to 30.

[0045] Taking PTAA-P1 as an example, the synthesis method of PTAA-P1 can be obtained by the Suzuki coupling reaction of dibromo-substituted triphenylamine, triphenylamine diboronic acid pinacol ester intermediate and 3,5-dibromopyridine. Among them, the triphenylamine diboronic acid pinacol ester intermediate and the dibromo-substituted triphenylamine intermediate have the structures shown in formula (III) and formula (IV) respectively, and they can be synthesized by referring to the existing methods in the prior art:

[0046]

[0047] In some embodiments, the synthesis method is specifically as follows: Dissolve the triphenylamine diborate pinacol ester intermediate, the dibromo-substituted triphenylamine intermediate, and 3,5-dibromopyridine in an organic solvent, add a phase transfer catalyst, a catalyst, a base, a ligand, and water under the protection of an inert atmosphere, heat up to 80-100 °C, after sufficient reaction, perform extraction and separation, dry the obtained organic phase, remove the solvent, then perform Soxhlet extraction, and after drying, obtain the polymer.

[0048] The molar ratio of the triphenylamine borate pinacol ester intermediate, the dibromo-substituted triphenylamine intermediate, and 3,5-dibromopyridine is 1:x:(1-x), and the value of x corresponds to x in the general formula (A), where 0 < x < 1.

[0049] In some embodiments, the reaction time of the synthesis reaction is 60-72 hours.

[0050] In some embodiments, after the reaction ends and cools down, add water and dichloromethane for extraction, dry the organic phase through anhydrous sodium sulfate, remove the solvent, and then perform Soxhlet extraction on the solid with methanol, acetone, and n-hexane as solvents in sequence, and dry to obtain the above-mentioned triphenylamine polymer.

[0051] The following are examples:

[0052] Example 1

[0053] Synthesis of compound PTAA-P1:

[0054] The synthesis route is as Figure 1 shown, wherein, intermediate 1 (i.e., compound 1) can be obtained by Ullmann coupling reaction of simple trimethylaniline and p-bromoiodobenzene based on the existing methods in the prior art, and intermediate 2 (i.e., compound 2) can be obtained from intermediate 1 by Suzuki coupling reaction based on the existing methods in the prior art. The synthesis process details of these two intermediates can be referred to the relevant prior art.

[0055] The synthesis process of polymer PTAA-P1 is as follows: Add compound 1 (327 mg, 0.60 mmol), compound 2 (244 mg, 0.54 mmol), 3 (14 mg, 0.06 mmol), anhydrous K2CO3 (828 mg, 6.0 mmol), Pd2(dba)3 (33 mg, 0.04 mmol), P(o-tol)3 (33 mg, 0.11 mmol), 2 drops of Aliquat 336, 10 mL of dry toluene and 5 mL of deionized water into a 50 mL dry Schlenk flask. Conduct three freeze-pump-thaw cycles for deoxygenation under N2 conditions, and then heat to 80 - 100 °C for reaction for 72 - 80 h. After cooling, add water and dichloromethane for extraction, drying. After rotary evaporation, a light yellow solid is obtained. Dissolve it in a small amount of chloroform and perform reprecipitation in methanol, then filter. Load the obtained precipitate into a Soxhlet extractor for extraction, and extract with 50 - 60 mL of methanol, acetone, and n-hexane for 24 - 30 h each to remove small molecules and catalysts, obtaining 0.31 g of dark yellow solid with a yield of 94%. M n = 19.2 kDa and 1 1H NMR (400 MHz, Chloroform-d) δ 8.88 (s, ArH), 8.72 (s, ArH), 8.35 (s, ArH), 7.97 (s, ArH), 7.40 (d, J = 8.4 Hz, 4H, ArH), 7.02 (d, J = 8.3 Hz, 4H, ArH), 6.95 (s, 2H, ArH), 2.33 (s, 3H, -CH3), 2.03 (s, 6H, -CH3). 13 13C NMR (101 MHz, Chloroform-d) δ 144.68, 139.97, 137.65, 136.81, 133.02, 129.95, 126.93, 119.82, 21.0, 18.60.

[0056] The PTAA-P1 polymerization reaction itself is an uncontrollable polymerization reaction, but under the above conditions, the molecular weight can be stabilized at 1000 - 20000 g / mol, that is, n in the corresponding structural general formula is 10 - 30, and the repeatability is good (this invention has been verified by multiple syntheses during the experiment). The 1H nuclear magnetic resonance spectrum of PTAA-P1 is as attached Figure 2 shown.

[0057] Example 2

[0058] Detect the PTAA-P1 material obtained in Example 1 to obtain the basic photophysical properties of PTAA-P1:

[0059] The UV-visible absorption spectrum of the polymer PTAA-P1 film was measured using a SHIMADZU UV-3600 UV-visible spectrophotometer, as shown in Figure 3 . The highest occupied molecular orbital (HOMO) energy level of the polymer PTAA-P1 was measured by cyclic voltammetry, and the test results are shown in Figure 4 . It was calculated that its HOMO energy level was -5.26 eV. The lowest unoccupied molecular orbital (LUMO) energy level of PTAA-P1 was calculated to be -2.25 eV through the optical band gap obtained from the UV absorption spectrum.

[0060] Example 3

[0061] For the PTAA-P1 material obtained in Example 1, the device performance of PTAA-P1 as the hole transport layer of a perovskite solar cell is as follows:

[0062] The hole mobilities of PTAA and PTAA-P1 were measured by the space charge limited current (SCLC) method to be 1.95×10 -4 cm 2 V -1 s -1 and 1.74×10 -4 cm 2 V -1 s -1 (see Appendix Figure 5 ), indicating that the polymer PTAA-P1 designed in the present invention can fully meet the requirements of the hole transport material.

[0063] The above experimental results show that the polymer PTAA-P1 designed in the present invention can meet the requirements of the hole transport layer of perovskite solar cells.

[0064] Subsequently, we measured the contact angles of PTAA and PTAA-P1 films with water. As shown in Appendix Figure 6 , the contact angle of the PTAA-P1 film was only 76.8°, significantly smaller than that of the PTAA film, which was 93.1°. This result indicates that the introduction of pyridine groups reduces the hydrophobicity of the polymer, which is beneficial to solving the problem of low perovskite quality caused by strong hydrophobicity in large-area devices.

[0065] The polymer PTAA-P1 was used as the non-doped hole transport material in the preparation of a planar perovskite solar cell. The specific device structure was ITO / HTM / perovskite / C 60 / Bathocuproine (BCP) / Ag. Cs 0.05 (FA 0.98 MA 0.02 ) 0.95 Pb(I0.98 Br 0.02 )3(FA: NH=CHNH3 + ;MA: CH3NH3 + ) as the perovskite layer material. Meanwhile, an undoped PTAA material (i.e., poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine]) is used as the hole transport material to construct a reverse planar perovskite solar cell as a control.

[0066] Figure 7 The X-ray photoelectron spectroscopy (XPS) of the perovskite grown on PTAA-P1 is shown. The characteristic peaks of Pb 4f and I 3d of the perovskite grown on PTAA-P1 shift to the low energy region, indicating a strong interaction between PTAA-P1 and the perovskite, which is beneficial to reducing perovskite defects and improving the perovskite crystal quality.

[0067] Figure 8 The X-ray diffraction (XRD) patterns of the perovskite grown on PTAA and PTAA-P1 are shown. The diffraction peak intensity of the perovskite grown on PTAA-P1 is higher and the full width at half maximum is smaller, indicating a higher quality of the perovskite grown on PTAA-P1. Figure 9 The scanning electron microscope images (SEM) of the perovskite grown on PTAA and PTAA-P1 are shown. The morphology of the perovskite grown on PTAA-P1 is flatter and the grain size is more uniform. These results show that the introduction of pyridine groups can enhance the interaction between the hole transport material and the perovskite and promote the growth of the perovskite.

[0068] Under the illumination condition of simulated sunlight AM1.5G with an illumination intensity of 100 mW cm -2 the J-V curve of the small-area device (0.08 cm 2 ) with the polymer PTAA-P1 as the undoped hole transport material is as Figure 10 shown, and the highest PCE can reach 24.89%; while the PTAA device prepared under the same conditions performs worse than the corresponding PTAA-P1 device in terms of Voc, FF, or PCE. In addition, as Figure 11 shown, the device efficiency of the large-area perovskite solar cell (1 cm 2 ) based on PTAA-P1 reaches 23.12%, and there is little difference between the forward scan and the reverse scan.

[0069] It can be seen that when the compound PTAA-P1 is used as a hole transport material in a trans-planar perovskite solar cell, its PCE is among the highest efficiencies of current devices of this structure. On the one hand, this benefits from the high hole mobility of the material itself. On the other hand, the introduction of pyridine groups in the main chain can enhance the interaction between the hole transport material and the perovskite material, promote the formation of high-quality crystal films of perovskite, and thus obtain high-performance devices.

[0070] In addition, the above embodiments are only examples. For example, the content of pyridine in the triphenylamine polymer can be selected as any value between 0 and 1 (corresponding to 0 < x < 1 in the general formula A). The introduction of pyridine groups can regulate the energy level and charge transport ability of the material, and at the same time provide an effective passivation effect to precisely regulate the properties of the material, but will not change the hole transport property of the material. Therefore, it can be inferred that polymers with different pyridine contents can also be used as hole transport materials in perovskite solar cells like PTAA-P1 of the present invention.

[0071] Those skilled in the art can easily understand that the above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A triphenylamine-based polymer, characterized in that, The polymer has a triphenylamine-based main chain skeleton structure, and pyridine groups are inserted into the main chain; the polymer has a chemical structure as shown in the general formula (A): In the formula, R is an alkyl substituent, 0 < x < 1, and n is an integer from 10 to 30.

2. The triphenylamine-based polymer according to claim 1, characterized in that, The R is selected from methyl, ethyl, butyl, pentyl and hexyl.

3. The triphenylamine-based polymer according to claim 1, wherein The R is tert-butyl.

4. The preparation method of the triphenylamine-based polymer according to any one of claims 1 to 3, characterized in that, The preparation method is to subject a triphenylamine boronic acid pinacol ester intermediate, a dibromo-substituted triphenylamine intermediate and 3,5-dibromopyridine to a Suzuki coupling reaction to obtain a triphenylamine-based polymer. Among them, the triphenylamine boronic acid pinacol ester intermediate has a chemical structure as shown in formula (I), and the dibromo-substituted triphenylamine intermediate has a chemical structure as shown in formula (II):

5. The preparation method according to claim 4, wherein Specifically, the preparation method is to dissolve the triphenylamine boronic acid pinacol ester intermediate, the dibromo-substituted triphenylamine intermediate and 3,5-dibromopyridine in an organic solvent, add a phase transfer catalyst, a catalyst, a base, a ligand and water under the protection of an inert atmosphere, and raise the temperature to 80-100 °C for the Suzuki coupling reaction; after sufficient reaction, extract and separate, dry the obtained organic phase, remove the solvent, and then perform Soxhlet extraction, and obtain the triphenylamine-based polymer after drying.

6. The preparation method according to claim 4, wherein, The molar ratio of the triphenylamine boronic acid pinacol ester intermediate, the dibromo-substituted triphenylamine intermediate and 3,5-dibromopyridine is 1:x:(1-x), 0 < x < 1; The reaction time of the Suzuki coupling reaction is 60-72 hours.

7. Use of the triphenylamine-based polymer according to any one of claims 1-3 as a hole transport material in a perovskite solar cell.

8. The application according to claim 7, wherein The perovskite solar cell is a perovskite solar cell with a reverse planar structure.

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