Preparation method of novel perovskite solar cell self-assembled hole transport layer

Abstract

The application relates to the technical field of perovskite solar cells, and discloses a preparation method of a novel perovskite solar cell self-assembled hole transport layer, which adopts a liquid-liquid interface transfer method to inject a hole transport solution into water for drag coating, then absorbs the solution, and finally prepares the hole transport layer. Different from a traditional method of first spin coating a self-assembled hole transport molecule and then cleaning with ethanol, the application selects the liquid-liquid interface transfer method to inject the hole transport solution into water for drag coating, then absorbs the solution, and finally prepares the hole transport layer. The method changes the arrangement mode of the hole transport molecule solution by using a water surface, improves the coverage rate of the hole transport molecule, is suitable for the preparation of various hole transport layers, and the hole transport layer prepared by the liquid-liquid interface transfer method has the characteristics of easy operation and is beneficial to the large-area production of perovskite solar cells.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of solar cells. Specifically, it relates to a preparation method of a novel perovskite solar cell self-assembled hole transport layer. BACKGROUND

[0002] In recent years, with the rapid development of social economy, the demand for energy is increasing, but the reserves of traditional non-renewable energy are rapidly decreasing, and its use will cause a series of environmental problems. Therefore, it is necessary to find a clean energy to replace traditional energy. Among them, solar energy is the most ideal renewable energy among many clean energies, so the development and utilization of solar energy is of great significance to the sustainable development of human society and the solution to the problem of energy shortage. Perovskite solar cells have been a research hotspot in the field of solar cells due to their high absorption coefficient, long carrier lifetime, adjustable band gap, and high carrier mobility. At the same time, its preparation process is simple, and the cost of raw materials is low. As a key functional layer of perovskite solar cells, the hole transport layer mainly functions to collect and transport holes, achieve effective separation of electrons and holes, and protect the perovskite layer from external water, oxygen, and light. The hole transport material has a significant impact on the efficiency and stability of the cell. Among the hole transport materials, self-assembled monomolecular materials (SAM) exhibit extremely high conductivity, thickness tolerance, and uniformity. These excellent properties significantly improve the light stability and scalability of organic solar cells. The common SAM solution processing method is spin coating, but during the spin coating process, the internal shear fluid of the solution flows, causing turbulent mass transfer, which ultimately leads to misalignment of molecular stacking and disorder of crystal orientation, which greatly hinders the effective transport of charges. In addition, the spin coating process also has the disadvantage of being unable to prepare large areas.

[0003] Therefore, it is of great significance to find a new preparation method of self-assembled hole transport layer, improve the coverage of self-assembled monolayer, adjust its crystal orientation, and facilitate large-area preparation for the performance improvement and industrial development of perovskite solar cells. SUMMARY

[0004] The present application aims to solve the problems of misalignment of molecular stacking, disorder of crystal orientation, and difficulty of spin coating process to meet the industrialization needs of perovskite solar cells in the preparation process of the commonly used self-assembled hole transport layer of current perovskite solar cells. The present application provides a novel self-assembled hole monolayer and a preparation method of a long-term high-efficiency stable perovskite solar cell containing a hole transport layer prepared by this method.

[0005] Self-assembled monolayer materials have the outstanding feature of hole extraction ability, so the organic self-assembled hole monolayer is often used in high-efficiency devices. However, in the process of spin coating, the internal shear fluid flow of the solution will cause turbulent mass transfer, which eventually leads to the dislocation of molecular accumulation and the disorder of crystal orientation. Therefore, it is urgent to develop a new deposition strategy to completely change the adverse fluid dynamics, so as to improve the coverage and crystallinity of the obtained thin film.

[0006] In order to achieve the above purpose, one aspect of the present application provides a novel preparation method of a self-assembled hole transport layer, which injects a hole transport solution into water by a liquid-liquid interface transfer method, then draws out the solution, and finally obtains a hole transport layer. The method comprises the following steps:

[0007] Put the ITO conductive glass substrate in an ultrasonic cleaner and wash it with pH=8 weak alkaline liquid detergent, deionized water, anhydrous ethanol and acetone for 5 minutes each time;

[0008] Weigh a certain mass of [4-(3,6-dimethyl-9H-carbazole-9-yl)butyl] phosphonic acid (Me-4PACz) powder, add an appropriate amount of ethanol (CH3CH2OH) solvent to prepare a solution with a concentration of about 0.5-1 mg / mL;

[0009] Put the ITO conductive glass in a polytetrafluoroethylene water tank, and add an appropriate amount of deionized water to completely immerse the ITO conductive glass in water;

[0010] Slowly inject the Me-4PACz solution along one side of the polytetrafluoroethylene water tank wall into the water surface, and the solution quickly spreads on the water surface. Take a thin glass rod to drag the solution until the solution completely spreads on the water surface;

[0011] After standing for 3-5 minutes, use a syringe to draw out the solution and deionized water;

[0012] Take out the ITO conductive glass and spin coat it with a certain amount of ethanol to obtain a self-assembled hole monolayer.

[0013] Another aspect of the present application provides a solar cell, the structure of the solar cell from bottom to top includes: a transparent conductive substrate, a self-assembled hole transport layer, a perovskite layer, an electron transport layer, a buffer layer and an electrode layer, and the hole transport layer is prepared by using the above-mentioned liquid-liquid interface transfer method.

[0014] Preferably, the perovskite light-absorbing material is ABX3, A=CH3NH3, NH2CHNH2, C or a mixture thereof; B=Pb or Sn or a mixture thereof; X=I, Br, Cl, CN, SCN or a mixture thereof.

[0015] Beneficial effects

[0016] The application adopts the self-assembled hole transport layer deposition strategy, changes the arrangement mode of the hole transport molecule solution by using the water surface, improves the coverage rate of the hole transport molecules, and can obtain a long-term high-efficiency stable perovskite solar cell. Meanwhile, the hole transport layer prepared by the liquid-liquid interface transfer method has the characteristics of easy operation, and is conducive to the large-area production of the perovskite solar cell. BRIEF DESCRIPTION OF DRAWINGS

[0017] The above and other objects, features and other advantages of the present application will become more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

[0018] Figure 1 A schematic diagram of a solar cell of an embodiment of the present application is shown;

[0019] Figure 2 A schematic diagram of a hole transport layer preparation process of a solar cell of embodiment 2 of the present application is shown;

[0020] Figure 3 A schematic diagram of a hole transport layer preparation process of a solar cell of embodiment 3 of the present application is shown;

[0021] Figure 4 A current-voltage characteristic curve diagram of a perovskite solar cell No. 1 (target device) and a perovskite solar cell No. 2 (control device) prepared in embodiments 2 and 3 of the present application is shown;

[0022] Figure 5 A maximum output power stability test diagram of the perovskite solar cell No. 1 (target device) and the perovskite solar cell No. 2 (control device) prepared in embodiments 2 and 3 of the present application under a standard solar light intensity is shown. DETAILED DESCRIPTION

[0023] The existing perovskite solar cell using the self-assembled hole transport layer has a relatively high photoelectric conversion efficiency, but the low coverage rate of the hole transport layer and the difficulty in large-area production are important factors restricting its commercialization. The present application provides a novel perovskite solar cell preparation process, which uses a liquid-liquid interface transfer method to inject a hole transport solution into water and draw the solution, and finally obtains a hole transport layer.

[0024] The self-assembled hole transport layer deposition strategy used in the present application is specifically as follows:

[0025] (1) Place the ITO conductive glass substrate in an ultrasonic cleaner and sequentially clean it with a pH = 8 weak alkaline liquid detergent, deionized water, anhydrous ethanol and acetone for 5 minutes each time;

[0026] (2) Weigh a certain amount of [4-(3,6-dimethyl-9H-carbazol-9-yl)butyl] phosphonic acid (Me-4PACz) powder, add an appropriate amount of ethanol (CH3CH2OH) solvent to prepare a solution with a concentration of about 0.5-1 mg / mL;

[0027] (3) Place the ITO conductive glass in a polytetrafluoroethylene water tank, and add an appropriate amount of deionized water to completely immerse the ITO conductive glass in water;

[0028] (4) Slowly inject the Me-4PACz solution along one side of the polytetrafluoroethylene water tank wall into the water surface, and the solution rapidly spreads on the water surface. Take a thin glass rod to drag the solution until the solution is completely spread on the water surface;

[0029] (5) After standing for 3-5 minutes, use a syringe to remove the solution and deionized water;

[0030] (6) Take out the ITO conductive glass, and spin-coat clean it with a certain amount of ethanol to obtain a self-assembled hole monolayer.

[0031] The novel self-assembled hole transport layer deposition strategy of the application can be used to prepare high-quality Me-4PACz thin films, which can be used as a hole transport layer in a perovskite solar cell. Preferably, the thickness of the Me-4PACz hole transport layer is 3-100 nm, preferably 10-15 nm. Controlling the thickness of the hole transport layer within the range can ensure the effective extraction of charges in the device. Since the hole transport layer prepared by the liquid-liquid interface transfer method has high crystallinity and uniform orientation, the perovskite solar cell prepared has better surface morphology and higher performance parameters. At the same time, the immersion plating method is used in the preparation process, so the preparation process is simpler, the repeatability is higher, and it can be applied to large-area devices. Therefore, using the self-assembled hole transport layer deposition strategy, a long-term high-efficiency stable perovskite solar cell can be obtained.

[0032] According to some embodiments of the application, a Me-4PACz self-assembled hole monolayer can be prepared by a liquid-liquid interface transfer method. This hole transport layer preparation method is simple, does not require expensive equipment and complex conditions, is convenient for device assembly, and can also be applied to the preparation of large-area devices, which is conducive to the commercial production of perovskite solar cells.

[0033] Using the self-assembled hole monolayer prepared by the liquid-liquid interface transfer method, the application provides an embodiment of a solar cell, the structure of which from bottom to top comprises a transparent conductive substrate, a self-assembled hole transport layer, a perovskite layer, an electron transport layer, and an electrode layer, wherein the hole transport layer is prepared by the above-mentioned liquid-liquid interface transfer method.

[0034] Preferably, the perovskite light-absorbing material is ABX3, A = CH3NH3, NH2CHNH2, C or a mixture thereof; B = Pb or Sn or a mixture thereof; X = I, Br, Cl, CN, SCN or a mixture thereof.

[0035] Preferably, the transparent conductive substrate is ITO conductive glass or ITO conductive glass.

[0036] Preferably, the hole transport layer is a Me-4PACz layer, more preferably, the hole transport layer has a thickness of 30-50 nm.

[0037] Preferably, the perovskite layer has a thickness of 300-500 nm.

[0038] Preferably, the electron transport layer is a dense C 60 layer, more preferably, the dense C 60 layer has a thickness of 40-100 nm.

[0039] Preferably, the electrode layer is Au or Ag, more preferably, the electrode layer has a thickness of 60-100 nm.

[0040] The above solar cell containing a hole transport layer prepared using a liquid-liquid interface transfer method can be prepared by the following method:

[0041] Preparation of a transparent conductive substrate;

[0042] Formation of a hole transport layer on the transparent conductive substrate;

[0043] Formation of a perovskite layer on the hole transport layer;

[0044] Formation of an electron transport layer on the perovskite layer;

[0045] Formation of a buffer layer on the electron transport layer;

[0046] Formation of an electrode layer on the buffer layer,

[0047] Preferably, the hole transport layer is a Me-4PACz monolayer prepared using a liquid-liquid interface transfer method, and has a thickness of 30-50 nm.

[0048] More specifically, the preparation of a transparent conductive substrate can be a step of cleaning the transparent conductive substrate. For example, the FTO or ITO conductive glass substrate can be cleaned in an ultrasonic cleaner, more preferably, it can be sequentially cleaned with a weakly alkaline liquid detergent with pH = 8-10, deionized water, anhydrous ethanol, acetone for 5-20 min. The transparent conductive substrate can be cleaned using other methods available in the art.

[0049] The step of forming a hole transport layer on the transparent conductive substrate employs a liquid-liquid interface transfer method. The hole transport solution is injected into water and dragged along the surface, then the solution is aspirated to obtain the hole transport layer. More specifically, for example, a cleaned ITO conductive glass substrate can be placed in a 200 mL polytetrafluoroethylene water tank, and 20 mL of deionized water can be added. A 1 mg / mL Me-4PACz solution is slowly injected along one side of the tank wall to the water surface. A thin glass rod is then used to drag the solution until it is completely spread on the water surface. The deionized water and solution are then aspirated with a syringe. Finally, the remaining Me-4PACz molecules are spin-coated and cleaned with ethanol to form a dense monolayer 30–50 nm thick.

[0050] The perovskite layer, preferably made of the perovskite material as described above, can be ABX3, wherein A = CH3NH3, NH2CHNH2, Cs or mixtures thereof; B = Pb or Sn or mixtures thereof; X = I, Br, Cl, CN, SCN or mixtures thereof. More specifically, a 1.0–1.5 mol / L perovskite solution is deposited on the substrate using a one-step or two-step spin-coating method, and heated at 100–150 °C for 0.5–1 h to form a perovskite active layer of 200–1000 nm.

[0051] The electron transport layer can be formed by vacuum deposition of C. 60 Evaporation is performed on a hole-transport mixed perovskite layer. More specifically, this is achieved by controlling C... 60 The evaporation rate and evaporation time control the thickness of the buffer layer, thereby forming an electron transport layer with a thickness of 10 to 100 nm.

[0052] The buffer layer can be formed by vacuum deposition of 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) onto a hole transport mixed perovskite layer. More specifically, the thickness of the buffer layer is controlled by adjusting the evaporation rate and evaporation time of BCP, thereby forming a buffer layer with a thickness of 1–10 nm.

[0053] The electrode layer can be deposited on the hole transport layer by vacuum deposition of Au or Ag. More specifically, the thickness of the electrode is controlled by adjusting the evaporation rate and evaporation time of Au or Ag, thereby forming an electrode layer with a thickness of 40–200 nm.

[0054] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below in combination with the drawings and specific examples. It should be understood that the specific examples described herein are only used to explain the present application and not to limit the present application. If the specific technology or condition is not specified in the examples, the technology or condition described in the literature in the art or according to the product instruction is used. If the reagent or instrument is not specified by the manufacturer, it is a conventional product that can be obtained by market purchase. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0055] Example 1: New deposition strategy of self-assembled hole transport layer

[0056] The self-assembled hole transport layer is prepared by liquid-liquid interface transfer method according to the following steps:

[0057] (1) Put the ITO conductive glass substrate in an ultrasonic cleaner and clean it with pH = 8 mild alkaline liquid detergent, deionized water, anhydrous ethanol and acetone for 5 minutes each time;

[0058] (2) Weigh a certain amount of [4-(3, 6-dimethyl-9H-carbazole-9-yl) butyl] phosphonic acid (Me-4PACz) powder, add an appropriate amount of ethanol (CH3CH2OH) solvent to prepare a solution with a concentration of 0.5 mg / mL;

[0059] (3) Put the ITO conductive glass in a polytetrafluoroethylene water tank, and add an appropriate amount of deionized water to completely immerse the ITO conductive glass in water;

[0060] (4) Slowly inject the Me-4PACz solution along one side of the polytetrafluoroethylene water tank wall, and the solution quickly spreads on the water surface. Take a thin glass rod to drag the solution until the solution is completely spread on the water surface;

[0061] (5) After standing for 3 minutes, use a syringe to remove the solution and deionized water;

[0062] (6) Take out the ITO conductive glass and spin-coat it with a certain amount of ethanol to obtain a self-assembled hole monolayer.

[0063] Example 2: Preparation of perovskite solar cell No. 1

[0064] According to the following steps, the perovskite solar cell No. 1 shown in the hole transport layer preparation process is prepared, which includes a transparent conductive substrate, a self-assembled hole transport layer, a perovskite layer, an electron transport layer and an electrode layer distributed from bottom to top in sequence: Figure 1

[0065] ​(1) Cleaning: The ITO conductive glass substrate was placed in an ultrasonic cleaner and sequentially cleaned with pH = 8 weak alkaline liquid detergent, deionized water, anhydrous ethanol, and acetone for 5 min each;

[0066] (2) Hole transport layer preparation: The cleaned ITO conductive glass substrate was placed in a 200 mL polytetrafluoroethylene water tank, and 20 mL of deionized water was added. A 1 mg / mL Me-4PACz solution was slowly injected along one side of the water tank wall, and a thin glass rod was used to drag the solution until it was completely spread on the water surface. Then, a syringe was used to suck the deionized water and the solution. Finally, ethanol was used to spin-coat clean the remaining Me-4PACz molecules to form a 10 nm thick dense monolayer;

[0067] (3) Perovskite layer preparation: 50 uL of prepared perovskite solution was dropped on the above hole blocking layer, and rotated at a speed of 5000 rpm / s for 30 s. At the 5th second, chlorobenzene was added as an anti-solvent, and the perovskite material was heated at 100°C for 40 min to evaporate the solvent and obtain a perovskite active layer;

[0068] (4) Electron transport layer preparation: The half-cell prepared in steps (1)-(3) was placed in an evaporation machine, and the evaporation rate was adjusted to obtain a 30 nm thick C 60 electron transport layer;

[0069] (5) Buffer layer preparation: The half-cell prepared in steps (1)-(4) was placed in an evaporation machine, and the evaporation rate was adjusted to obtain a 5 nm thick BCP electrode layer;

[0070] (6) Electrode layer preparation: The half-cell prepared in steps (1)-(5) was placed in an evaporation machine, and the evaporation rate was adjusted to obtain a 100 nm thick Au electrode layer, and finally a perovskite solar cell No. 1 was prepared.

[0071] Example 3: Preparation of perovskite solar cell No. 2

[0072] According to the following steps, a perovskite solar cell No. 2 with a hole transport layer preparation process as shown in FIG. 1 was prepared, and its structure from bottom to top includes: a transparent conductive substrate, a self-assembled hole transport layer, a perovskite layer, an electron transport layer, a buffer layer, and an electrode layer: Figure 2

[0073] (1) Cleaning: The ITO transparent conductive glass substrate was placed in an ultrasonic cleaner and sequentially cleaned with pH = 10 weak alkaline liquid detergent, deionized water, anhydrous ethanol, and acetone for 10 min each;

[0074] ​(2) Hole transport layer preparation: clean ITO conductive glass substrate was heated at 500°C, and 1 mg / mL Me-4PACz ethanol solution was prepared and spin-coated on the substrate, and heated on a heating table at 100°C for 10 min to obtain a 80 nm hole transport layer;

[0075] (3) Perovskite active layer preparation: 100 μL of perovskite solution was spin-coated on the dense CuCrO2-Cl hole transport layer, and heated on a heating table at 100°C for 60 min to obtain a 500 nm perovskite active layer;

[0076] (4) Electron transport layer preparation: the half-cell prepared in steps (1)-(3) above was placed in an evaporation machine, and the evaporation rate was adjusted to obtain a 30 nm thick C 60 electron transport layer;

[0077] (5) Buffer layer preparation: the half-cell prepared in steps (1)-(4) above was placed in an evaporation machine, and the evaporation rate was adjusted to obtain a 5 nm thick BCP electrode layer;

[0078] (6) Electrode layer preparation: the half-cell prepared in steps (1)-(5) above was placed in an evaporation machine, and the evaporation rate was adjusted to obtain a 100 nm thick Ag electrode layer, to obtain perovskite solar cell No. 2.

[0079] The perovskite solar cell No. 1 was placed under a standard solar simulator for testing, as shown in Table 1 and Figure 2 Fig. 2 below, the trans- perovskite solar cell containing the hole transport layer prepared by the liquid-liquid interface transfer method has more excellent photoelectric performance. The open circuit voltage of the cell device perovskite solar cell No. 2 in Example 3 without using the liquid-liquid interface transfer method to prepare the hole transport layer is 1.08 V, the short circuit current is 24.49 mA / cm 2 , the fill factor is 78.16%, and the photoelectric conversion efficiency is 20.67%, while the cell device perovskite solar cell No. 1 in Example 2 using the liquid-liquid interface transfer method to prepare the hole transport layer has an open circuit voltage of 1.16 V, a short circuit current of 26.18 mA / cm 2 , a fill factor of 88.09%, and a photoelectric conversion efficiency of 24.32%. The test results show that the use of the liquid-liquid interface transfer method to prepare the self-assembled hole transport layer improves the open circuit voltage and photoelectric conversion efficiency of the perovskite solar cell device. Since the liquid-liquid interface transfer method is a self-assembly process in equilibrium, such continuous growth ensures that the obtained thin film has high crystallinity and uniform orientation, thereby improving the coverage and crystallinity of the thin film, and thus the photovoltaic performance of the device.

[0080] Table 1 (Performance parameters of perovskite solar cells)

[0081] Device Open circuit voltage (V) Short circuit current density (mA / cm 2 ) Fill factor (%) Photoelectric conversion efficiency (%) Control device 1.08 24.49 78.16 20.67 Target device 1.16 26.18 80.09 24.32

[0082] In addition, according to Figure 4 The stability test results show that the efficiency of the trans-perovskite solar cell device without using the liquid-liquid interface transfer method to prepare the hole transport layer has begun to decrease after running for 200 h, while the efficiency of the perovskite solar cell device No. 2 using the liquid-liquid interface transfer method to prepare the hole transport layer still maintains above 90% after being irradiated for 1000 h under a solar light intensity, wherein the test condition is that the device is packaged and in a nitrogen atmosphere. The above data results show that due to higher coverage and better crystallinity, the hole transport layer prepared by the liquid-liquid interface transfer method has fewer defect sites, and a long-term stable perovskite solar cell is obtained. Therefore, the method of using the liquid-liquid interface transfer method to prepare the hole transport layer can obtain a high-efficiency and stable perovskite solar cell, which provides a new idea for subsequent research and commercial development.

[0083] The above description is a detailed description of the preferred embodiments of the present application, but the embodiments are not intended to limit the scope of the patent application of the present application. Any equivalent changes or modifications made under the technical spirit of the present application should be included in the scope of the patent application of the present application.

Claims

1. A novel method for preparing a self-assembled hole transport layer, characterized in that: This method employs a liquid-liquid interface transfer technique to inject a hole transport solution into water for drag coating, followed by solution extraction to obtain the hole transport layer. The specific steps include: Weigh a certain amount of [4-(3,6-dimethyl-9H-carbazole-9-yl)butyl]phosphonic acid (Me-4PACz) powder, add an appropriate amount of ethanol (CH3CH2OH) solvent, and prepare a solution with a concentration of 0.5-5 mg / mL; Place the ITO conductive glass in a polytetrafluoroethylene water tank and add an appropriate amount of deionized water until the water completely covers the ITO conductive glass. Slowly pour the Me-4PACz solution into the water along one side of the PTFE water tank wall. The solution spreads rapidly on the water surface. Use a thin glass rod to drag the solution until it is completely spread on the water surface. After standing for 1-15 minutes, use a syringe to remove all the solution and deionized water. Remove the ITO conductive glass and spin-coat it with a certain amount of ethanol to obtain a self-assembled hole monolayer.

2. A solar cell, characterized in that: The structure of the solar cell, from bottom to top, includes: a transparent conductive substrate, a self-assembled hole transport layer, a perovskite layer, an electron transport layer, a buffer layer, and an electrode layer, wherein the hole transport layer is prepared using the hole transport layer preparation method as described in claim 1.

3. The solar cell according to claim 2, characterized in that: The light-absorbing material of the perovskite layer is ABX3, where A = CH3NH3, NH2CHNH2 or Cs; B = Pb or Sn; and X = I, Br, Cl, CN or SCN.

4. A method for preparing a solar cell as described in claim 3, characterized in that: The method includes the following steps: Prepare and process the transparent conductive glass substrate; A hole transport layer is formed on the transparent conductive substrate; A perovskite layer is formed on the hole transport layer; An electron transport layer is formed on the perovskite layer; A buffer layer is formed on the electron transport layer; An electrode layer is formed on the buffer layer; The hole transport layer is fabricated using a liquid-liquid interface transfer method, in which a hole transport solution is injected into water and dragged, and then the solution is extracted to obtain the final hole transport layer.

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