Conjugated polymer based on triphenylamine, thiophene and carbazole copolymerization unit, preparation method and application of conjugated polymer in perovskite solar cell

Abstract

The invention discloses a conjugated polymer based on a triphenylamine, thiophene and carbazole copolymerization unit, a preparation method of the conjugated polymer and application of the conjugated polymer in a perovskite solar cell, and relates to a conjugated polymer, a preparation method of the conjugated polymer and application of the conjugated polymer in the perovskite solar cell. The invention aims to solve the problem that the hole transport layer material in the perovskite solar cell can provide high efficiency under the condition of no additional doping. The problem is solved by using a novel conjugated polymer based on (4-triphenylamine (at) 9-(2-ethylhexyl)-3, 6-di (thiophene-2-yl)-9H-carbazole) and using the novel conjugated polymer as a hole transport material in a perovskite solar cell. According to the invention, power can be generated by efficiently converting energy of sunlight, and stable and efficient energy can also be provided for modern low-power-consumption sensors, transducers and lighting panels, which shows that the material has practical application potential in PSCs. The invention belongs to the technical field of perovskite solar cells.

Description

Technical Field

[0001] This invention relates to a conjugated polymer and its preparation method, as well as its application in perovskite solar cells, belonging to the field of perovskite solar cell technology. Background Technology

[0002] In recent years, researchers worldwide have been conducting in-depth studies on perovskite solar cells (PSCs), viewing them as a promising technology for converting solar energy into electricity. In less than 10 years, the solar conversion efficiency (PCE) of PSCs has increased to 27.3%, comparable to the best crystalline silicon solar cells.

[0003] Special attention must be paid to the layers between the photoactive layer and the electrodes during the fabrication of PSCs, as they largely determine the efficiency and stability of the device [T.-W. Lee et al., Energy Environ. Sci., 2016, 9, 12-30; C.-Z. Li et al., Chem. Lett., 2017, 28, 503-511]. These buffer layers, composed of electron transport materials and hole transport materials, can selectively extract negative and positive charge carriers from the perovskite layer, respectively, and efficiently transport them to the corresponding electrodes in the device.

[0004] In most cases, the compound spiro-OMeTAD, namely 2,2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirodifluorene ( Figure 1The molecular formula of spiro-OMeTAD (Y. Qi et al., Adv. Mater. Interfaces, 2018, 5, 1700623) has been used as a hole transport material. However, spiro-OMeTAD exhibits poor charge transport properties, thus requiring doping with additional reagents such as oxygen and LiTFSI (lithium bis(trifluorosulfonyl)imide) and tBuPy (4-tert-butylpyridine) [A. Sellinger et al., Chem. Sci., 2019, 10, 1904]. The doping process itself, as well as the use of LiTFSI and tBuPy, negatively impacts the stability of crystalline solar cells; in particular, the spiro-OMeTAD cation radicals can oxidize the I- anions in the active layer, leading to their decomposition [T. Miyasaka et al., J. Chem. Sci., 2019, 10, 1904]. Miyasaka et al, J. Mater. Chem. A, 2018, 6, 2219; C. Adachi et al, Sol. rl, 2020, 4, 2000305; G. Chen et al, J. Renew. Sust. Energy, 2018, 10, 043702. Furthermore, spiro-OMeTAD is a low molecular weight compound that can crystallize at high temperatures, causing its thin film to lose integrity and rendering the solar cell inoperable.

[0005] Therefore, the development of novel hole transport materials based on amorphous polymeric compounds is a significant challenge. Using polymeric aromatic amines (such as PTAA-poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine]) Figure 2 The use of PTAA (the molecular formula of PTAA) can partially address this issue. However, this polymer has a non-conjugated structure, resulting in low charge carrier mobility and poor performance in undoped perovskite solar cells: light conversion efficiency is typically below 13% [C. Jia et al., Energy Environ. Sci., 2018, 11, 2035]. Higher efficiencies can be achieved by doping the polymer, such as by doping with oxygen from the air [J. Fang et al., Adv. Sci., 2018, 5, 1800159], but this also negatively impacts device stability. Therefore, using polymeric aromatic amines (such as PTAA) does not solve the problem of fabricating highly efficient and stable perovskite solar cells. To address this issue, it is necessary to prepare and use conjugated polymer structures with good hole transport properties without additional doping.

[0006] The typical construction of PSCs (nip structures) using polymer P1 as the hole transport layer material is as follows: Figure 5The diagram shows the overall structure of PSCs. It consists of a transparent conductive substrate of indium tin oxide (ITO), which also serves as the electron collecting electrode 0, the electron selective layer 1, the photoactive layer 2, the hole transport layer 3 (which contains at least 10% by weight of polymer P1), the electron blocking layer 4, and the top hole collecting electrode 5.

[0007] The electron-selective layer is used to block holes and transport electrons from the active layer of a solar cell to the electrode layer 0. The composition of the electron-selective layer can include metal oxides such as TiO2, SnO2, ZnO, In2O3, WO3, CeO2, Zn2SnO4, Nb2O5, Zn2Ti3O8, BaSnO3, BaTiO3, and SrSnO3; metal halides such as CdS, CdSe, PbS, PbSe, PbTe, ZnS, ZnSe, Sb2S3, Bi2S3, In2S3, MnS, SnS, and SnS2; organic compounds of carboxylic acids and phosphonic acids; fullerene derivatives; derivatives of perylene diimide, naphthimide, acridine, and oxadiazole; and any n-type organic semiconductor. The thickness of the electron-selective layer can range from 1 to 200 nm.

[0008] Photoactive layer 2 is any perovskite semiconductor material with the general formula ABX3, where A is a monovalent cation and B is Sn. 2+ Pb 2+ X is a halogen atom (Br) - I - The preferred organic cation A is methylammonium (MA). - CH3NH3 + and formamidin (FA) - [H2NCHNH2] + The preferred inorganic cation is Cs. + The photoactive layer can also be composed of a combination of organic cations and halogen atoms. For example, MA x FA 1-x PbIyBr 3-y Where x = 0–1 and y = 0–3. Variations in the exponents x and y affect the efficiency and stability of the device. The optimal composition of the photoactive layer is Cs. 0.12 FA 0.88 PbI3. The thickness of the photoactive layer can be from 100 to 1000 nm.

[0009] Hole transport layer 3 is a thin film with a thickness of 5 to 100 nm, and its composition contains at least 10% of the conjugated polymer P1.

[0010] Electron blocking layer 4 is composed of p-type metal oxides, such as MoO3 or MoO. x (x~3), V2O5 or VO x(x~2.5), CuO x (x = 0.5-1.0), with a thickness of 1 to 100 nm.

[0011] The hole collecting electrode 5 has a thickness of 30 to 300 nm and can be translucent or opaque within the visible light spectrum. The translucent hole collecting electrode can be fabricated using transparent conductive oxides: indium tin oxide (ITO), fluorine-doped tin oxide (TITO), zinc oxide (ZNO), and other conductive oxides. Conductive polymer films, such as PEDOT:PSS (poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)), polyaniline, and polypyrrole, can also be used as translucent electrode materials. Furthermore, the translucent electrode can be based on metal formation, i.e., using metal micromesh, nanowires, and ultrathin films of gold, silver, copper, nickel, aluminum, or other metals. The translucent electrode can also be fabricated based on carbon materials: graphene, carbon nanotubes, nanofibers, etc. Individual materials or any combination thereof can be used as the translucent electrode layer. To form an opaque hole collecting electrode, thin films of metals (such as Ag, Cu, Ni, Cr, Al, Au, Pt, etc.) or their alloys (nickel-chromium alloys, chromium-nickel alloys, etc.) can be used, as well as other materials with metallic or semi-metallic properties (such as titanium nitride, graphite, and various carbon blacks). Summary of the Invention

[0012] This invention addresses the problem of providing high efficiency in hole transport layer materials in perovskite solar cells without additional doping, and proposes a conjugated polymer based on triphenylamine, thiophene, and carbazole copolymer units, along with its preparation method and applications.

[0013] The technical solution adopted by the present invention to solve the above problems is as follows: the repeating unit of the conjugated polymer P1 is triphenylamine@9-(2-ethylhexyl)-3,6-bis(thiophene-2-yl)-9H-carbazole, wherein the 4 and 4' positions of the triphenylamine unit are connected with the 5 and 5' positions of the thiophene substituent in the carbazole system to form a polymer chain.

[0014] The molecular structure of the conjugated polymer P1 is as follows:

[0015]

[0016] Where n = 5 to 200.

[0017] The preparation method of the conjugated polymer based on triphenylamine, thiophene and carbazole copolymer units is achieved through the following steps:

[0018] Step 1: Add monomer M1, monomer M2, catalyst Pd2(dba)3(tris(dibenzylacetone)dipalladium(0)), auxiliary ligand triphenylphosphine and toluene to a 100 mL three-necked flask;

[0019] The reaction mixture was degassed three times, and then argon gas was introduced.

[0020] The mixture was heated under reflux until the target molecular weight was reached, and then trimethyl(2-thienyl)tin and 2-bromothiophene were added sequentially to terminate chain growth.

[0021] Step 2: Pour the reaction mixture into methanol, filter to collect the polymer and dry it, dissolve the polymer in 1,2-dichlorobenzene, heat and stir, then pour it into isopropanol to collect the precipitate. Wash the polymer with reagents, evaporate it, and precipitate it again with isopropanol.

[0022] Step 3: Separate using a Buchner funnel, dry, and analyze the purified polymer.

[0023] Furthermore, in step 1, the mixture was heated to 110°C in an oil bath, and the reaction was monitored every 30 minutes using gel permeation chromatography.

[0024] When the molecular weight reaches 50,000 to 60,000 g / mol, polymer precipitation begins to be observed. Trimethyl(2-thienyl) and 2-bromothiophene are continuously introduced into the reaction mixture at intervals of 30 to 60 minutes.

[0025] Furthermore, in step 2, 50 mL of methanol is poured in, followed by the addition of 1,2-dichlorobenzene to dissolve it.

[0026] Furthermore, 40 mL of 1,2-dichlorobenzene was stirred at 90°C for 3 hours, followed by washing and collection.

[0027] Further, the polymer solution was poured into 300 mL of isopropanol, the precipitated polymer was filtered through an extraction sleeve, and the sleeve containing the polymer was placed in a Soxhlet extractor. The polymer was washed sequentially with acetone, dichloromethane, and chlorobenzene. The chlorobenzene fraction was evaporated to 20 mL, and then precipitated with 150 mL of isopropanol.

[0028] Furthermore, in step 3, the precipitate is separated in a Buchner funnel and dried in a vacuum dryer. The yield of polymer P1 is 60%–70%, the weight average molecular weight is Mw = 60,000–75,000 g / mol, and the polydispersity index (PDI) is 1.2–2.4.

[0029] The conjugated polymer based on triphenylamine, thiophene and carbazole copolymer units described in this invention is applied to perovskite solar cells.

[0030] The reason this invention chose to prepare the conjugated polymer P1 material is that using polymer P1 as the hole transport layer in perovskite solar cells has the following advantages:

[0031] (1) It has excellent solubility in organic solvents (>10 mg / mL in chloroform), and can form a uniform, pinhole-free HTL film on the top surface of the perovskite light-absorbing layer, thus blocking the diffusion reaction of the metal electrode.

[0032] (2) Due to enhanced solubility, a higher molecular weight can be achieved compared to commonly used PTAA polymers with lower solubility. The higher molecular weight facilitates the transport of hole charge carriers to the top hole collection electrode;

[0033] (3) The triphenylamine, carbazole, and thiophene building units in the P1 molecule can interact with the surface of the perovskite absorber layer and with uncoordinated Pb. 2+ Surface ions form chelates, which repair defects, suppress nonradiative recombination of charge carriers, and improve device performance and stability.

[0034] (4) Polymer P1 can be used as a hole transport layer material in perovskite solar cells and has higher efficiency compared with the reference cell assembled using PTAA.

[0035] The beneficial effects of this invention are:

[0036] 1. The prototype of this invention is the polymer material and its application in perovskite solar cells disclosed in Russian Federation Patent Nos. 2789131, 2789132 and 2789133. Compared with the prototype, an important advantage of this invention is that the molecular structure of polymer P1 is simpler, which greatly reduces its synthesis cost.

[0037] 2. Importantly, the P1 molecule contains triphenylamine, thiophene, and carbazole building units, which can effectively chelate uncoordinated Pb. 2+ Surface ions repair defects, suppress nonradiative recombination of charge carriers, and improve device performance and stability; in addition, using P1 can achieve a solar cell power conversion efficiency of up to 20.2%;

[0038] 3. Polymer P1 is prepared according to the standard Stille polycondensation reaction, such as... Figure 4 The diagram shows the synthesis scheme for polymer P1. Stille polycondensation is widely used in the synthesis of organic electronic materials, especially conjugated polymers for organic solar cells.

[0039] 4. A key characteristic of the novel polymer P1 is its superior photoelectric properties. The highest occupied molecular orbital (HOMO) energy of polymer P1 closely matches the valence band position (-5.4 eV) of perovskite materials, which should ensure efficient extraction of positive charge carriers. Materials with these properties are the optimal choice for the hole transport layer in perovskite solar cells. Simultaneously, due to the presence of amine bridge centers in the polymer backbone, P1 has a relatively wide band gap, which prevents electron extraction and charge recombination. Materials with these properties are well-suited for use as top electrode materials in perovskite solar cells. Attached Figure Description

[0040] Figure 1 This is the molecular formula diagram of spiro-OMeTAD;

[0041] Figure 2 This is the molecular formula diagram of PTAA;

[0042] Figure 3 This is the molecular structure diagram of the conjugated polymer P1;

[0043] Figure 4 This is a diagram of the synthesis scheme for polymer P1;

[0044] Figure 5 This is a schematic diagram of the overall structure of the PSCs constructed in this invention;

[0045] Figure 6 This is a schematic diagram of the current-voltage characteristics recorded using the P1 polymer during forward and reverse potential scans, compared to a reference sample prepared using PTAA.

[0046] Figure 7 This is a schematic diagram illustrating the specific implementation method of external quantum efficiency (EQE) spectra of P1-based devices and PTAA reference devices. Detailed Implementation

[0047] Example 1. Synthesis of polymer P1

[0048] Step 1: Add monomer M1 (201.56 mg; 0.50 mmol), monomer (384.64 mg; 0.50 mmol), catalyst Pd2(dba)3(tris(dibenzylacetone)dipalladium(0)) (5 ​​mg; 0.005 mmol), auxiliary ligand triphenylphosphine (5 mg; 0.019 mmol) and toluene (50 mL) to a 100 mL three-necked flask. After degassing the reaction mixture three times, purge with argon gas.

[0049] Step 2: Immerse the flask in an oil bath and heat to 110°C. Monitor the reaction every 20 minutes using gel permeation chromatography (GPC). When the molecular weight reaches 50,000–60,000 g / mol, polymer precipitation begins to be observed. Add trimethyl(2-thienyl)tin (10 mg) continuously to the reaction mixture and continue reflux for 30 minutes. Then add 2-bromothiophene (100 μL) and reflux for another hour.

[0050] Step 3: Pour the reaction mixture into methanol (100 mL), filter the precipitated polymer using a Buchner funnel, and dry it in a vacuum desiccator;

[0051] Step 4: Dissolve the polymer in 1,2-dichlorobenzene (30 mL) and stir at 90 °C for 2 hours;

[0052] Step 5: Pour the polymer solution into isopropanol (200 mL) and filter the precipitated polymer using an extraction sleeve;

[0053] Step 6: Place the sleeve containing the polymer into a Soxhlet extractor, wash it sequentially with methanol, acetone, heptane and chlorobenzene, concentrate it under vacuum to 30 mL, and then precipitate it with isopropanol (200 mL).

[0054] Step 7: The precipitate was separated in a Buchner funnel and dried in a vacuum dryer at 30°C. The yield of polymer P1 was 68%. The purified polymer was analyzed on a GPC column against a series of standards F8BT (poly[(9,9-di-n-octylfluorene-2,7-diyl)@(benzo[2,1,3]thiadiazol-4,8-diyl)]) and Poly[(9,9-dioctylfluorenyl-2,7-diyl)@(benzo[2,1,3]thiadiazol-4,7-diyl)]). The weight average molecular weight was Mw = 60,000–75,000 g / mol, and the polydispersity index (PDI) was 1.2–2.4.

[0055] Example 2. Perovskite solar cells were fabricated using polymer P1 as the sole hole transport layer material.

[0056] Step 1: Conductive glass (25x25mm) was used in the fabrication of the solar cell. The conductive glass has a conductive film doped with indium oxide and tin oxide (ITO), with a resistance of 10-12 ohms / s and a conductive layer thickness of 125nm. The substrate was cleaned in sequence with distilled water, toluene (analytical grade) and acetone (analytical grade), and then ultrasonically cleaned with water, acetone (analytical grade) and isopropanol (analytical grade).

[0057] Step 2: Before using the charge transport layer, the substrate is incubated in air plasma for 5 minutes. The SnO2 precursor solution (50 μl) is prepared by diluting the 15% SnO2 (Alfa-Aesar) colloidal dispersion aqueous solution by 1.5 times with distilled water. The solution is then applied to the cleaned substrate at a substrate rotation speed of 4000 rpm for 40 seconds.

[0058] Step 3: Heat the film in air at 175°C for 15 minutes, and then heat it in a glove box at 120°C in an inert nitrogen atmosphere for 10 minutes.

[0059] Step 4: Add phenyl-C61-butyric acid (0.1 mg / mL) solution to chlorobenzene (3500 rpm / min, 30 seconds), and then anneal at 100°C for 10 minutes to passivate the SnO2 film;

[0060] Step 5: The MAPbI3 perovskite film was deposited by centrifugation at 4000 rpm in a mixture of N,N-dimethylacetamide and N-methylpyrrolidone in a volume ratio of 85:15, using a 1.4 M precursor solution (methylammonium iodide and PbI2 in an equimolar ratio, 60 μl) as the raw material.

[0061] Step 6: After adding the above solution to the film in step 5 for 43 seconds, pour 120 μl of toluene onto the rotating substrate to accelerate the crystallization of perovskite.

[0062] Step 7: Place the film on a 50°C heating plate, heat it to 100°C, and incubate it at this temperature in an inert nitrogen atmosphere for 5 minutes.

[0063] Step 8: Spin-coat the polymer P1 solution (10 mg / mL, chloroform) onto the MAPbI3 film prepared in step 7 at a speed of 6000 rpm / min;

[0064] Step 9, Electron blocking layer (30nm V2O) 5-δ The metal electrode (120 nm Ag) and the metal electrode (10 nm Ag) were obtained by vacuum (10 nm Ag). -6 The film is formed on the thin film prepared in step 8 by evaporating the starting material in mmHg.

[0065] Comparative Example 3: Perovskite solar cells were fabricated using PTAA as the sole hole transport layer material.

[0066] The method for manufacturing the perovskite solar cell is the same as that described in Example 2, up to the stage of applying the hole transport layer. In this example, only pure PTAA is used as the hole transport material, using a chloroform solution with a concentration of 6 mg / mL. The remaining process steps are the same as those in Example 2.

[0067] Product structure characterization

[0068] like Figure 3 As shown, the molecular structure of conjugated polymer P1 is a conjugated polymer based on (4-triphenylamine@9-(2-ethylhexyl)-3,6-bis(thiophen-2-yl)-9H-carbazole), where n = 5-200.

[0069] like Figure 4 As shown, the synthesis scheme of polymer P1 includes M1, M2, and catalyst Pd2(dba)3(tris(dibenzylacetone)dipalladium(0)).

[0070] Perovskite solar cell performance characterization

[0071] Example 2: Perovskite solar cells fabricated using polymer P1 as the sole hole transport layer exhibit the following characteristics:

[0072] Open circuit voltage (V) OC ): 1154mV; Short-circuit current density (J) sc ): 22.3 mA / cm 2 Fill factor (FF): 78.5%; Power conversion efficiency (PCE): 20.2%.

[0073] Under the same conditions, Comparative Example 3, a reference device fabricated using only PTAA as the hole transport layer material, exhibits even worse performance: open-circuit voltage: 1125mV; short-circuit current density: 20.2mA / cm². 2 Fill factor: 78.3%; Light conversion efficiency: 17.8%.

[0074] Table 1. Characteristics of perovskite solar cells using different hole transport layer materials

[0075]

[0076] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent substitutions, and improvements made to the above embodiments without departing from the scope of the present invention, based on the technical essence of the present invention and within the spirit and principles of the present invention, shall still fall within the protection scope of the present invention.

Claims

1. A conjugated polymer based on triphenylamine, thiophene, and carbazole copolymer units, characterized in that, The molecular structure of polymer P1 is as follows: The repeating unit is triphenylamine@9-(2-ethylhexyl)-3,6-bis(thiophene-2-yl)-9H-carbazole, wherein the 4 and 4' positions of the triphenylamine unit are connected to the 5 and 5' positions of the thiophene substituent in the carbazole system to form a polymer chain.

2. A method for preparing the conjugated polymer according to claim 1, characterized in that, The method for preparing the conjugated polymer based on triphenylamine, thiophene, and carbazole copolymer units is achieved through the following steps: Step 1: Add monomer M1, monomer M2, catalyst Pd2(dba)3(tris(dibenzylacetone)dipalladium(0)), auxiliary ligand triphenylphosphine and toluene to a 100 mL three-necked flask; The reaction mixture was degassed three times, and then argon gas was introduced. The mixture was heated under reflux until the target molecular weight was reached, and then trimethyl(2-thienyl)tin and 2-bromothiophene were added sequentially to terminate chain growth. Step 2: Pour the reaction mixture into methanol, filter to collect the polymer and dry it, dissolve the polymer in 1,2-dichlorobenzene, heat and stir, then pour it into isopropanol to collect the precipitate. Wash the polymer with reagents, evaporate it, and precipitate it again with isopropanol. Step 3: Separate using a Buchner funnel, dry, and analyze the purified polymer.

3. The method for preparing the conjugated polymer based on triphenylamine, thiophene, and carbazole copolymer units according to claim 2, characterized in that, In step 1, the mixture is heated to 110°C in an oil bath, and the reaction is monitored every 30 minutes using gel permeation chromatography. When the molecular weight reaches 50,000 to 60,000 g / mol, polymer precipitation begins to be observed. Trimethyl(2-thienyl) and 2-bromothiophene are continuously introduced into the reaction mixture at intervals of 30 to 60 minutes.

4. The method for preparing the conjugated polymer based on triphenylamine, thiophene, and carbazole copolymer units according to claim 2, characterized in that, In step 2, pour in 50 mL of methanol, and then add 1,2-dichlorobenzene to dissolve it.

5. The method for preparing the conjugated polymer based on triphenylamine, thiophene, and carbazole copolymer units according to claim 2, characterized in that, 40 mL of 1,2-dichlorobenzene was stirred at 90 °C for 3 hours, then washed and collected.

6. The method for preparing the conjugated polymer based on triphenylamine, thiophene, and carbazole copolymer units according to claim 5, characterized in that, The polymer solution was poured into 300 mL of isopropanol, the precipitated polymer was filtered through an extraction sleeve, and the sleeve containing the polymer was placed in a Soxhlet extractor. The polymer was washed successively with acetone, dichloromethane and chlorobenzene. The chlorobenzene fraction was evaporated to 20 mL and then precipitated with 150 mL of isopropanol.

7. The method for preparing the conjugated polymer based on triphenylamine, thiophene, and carbazole copolymer units according to claim 2, characterized in that, In step 3, the precipitate was separated in a Buchner funnel and dried in a vacuum dryer. The yield of polymer P1 was 60%–70%, the weight average molecular weight was Mw = 60,000–75,000 g / mol, and the polydispersity index (PDI) was 1.2–2.

4.

8. An application of the conjugated polymer according to claim 1, characterized in that, The conjugated polymer based on triphenylamine, thiophene and carbazole copolymer units is used in perovskite solar cells.

Images