Perovskite active layer doped with carbazole-based small molecules, preparation method and application thereof

Abstract

The present invention discloses a perovskite active layer doped with a carbazole-based small molecule, and its preparation method and application. The preparation method includes: dissolving formamidinium iodide, cesium iodide, lead iodide, and methylammonium iodide in an organic solvent to obtain a cesium-formamidinium-methylammonium lead iodide alloy perovskite precursor solution of the ABX3 configuration; doping a carbazole-based small molecule dopant into the perovskite precursor solution; and preparing a carbazole-based small molecule-doped perovskite active layer by any one of spin coating, blade coating, or spray coating. By introducing the carbazole-based small molecule, the present invention effectively adjusts the energy level of the perovskite, improves the crystallinity of the perovskite thin film, and prepares a p-i-n type perovskite solar cell without a hole transport layer. The photoelectric conversion efficiency of the battery device prepared by this method exceeds 26.6%, and it exhibits excellent long-term operation stability.

Description

Technical Field

[0001] The present invention relates to the field of perovskite solar cells, and particularly to a perovskite active layer doped with carbazole-based small molecules, a preparation method thereof, and an application thereof. Background Art

[0002] With the continuous increase in the global demand for renewable energy and the growing awareness of environmental protection, the future development prospects of solar cells are very broad. A solar cell is an energy-saving device that directly converts solar radiation into electrical energy, and has the advantages of high energy utilization efficiency, low maintenance cost, high power supply stability, etc., and is a more green and sustainable power generation technology.

[0003] Perovskite solar cells have always been regarded as one of the most promising photovoltaic technologies, and have the advantages of solution preparation, low cost, high efficiency, flexible preparation, semi-transparency, etc., and have developed rapidly in the past decade. Among them, the p-i-n type perovskite solar cell has attracted extensive attention due to its simple manufacturing process, potential application in flexible devices, and good compatibility with tandem devices. At present, the power conversion efficiency of single-junction p-i-n type devices has reached as high as 27%. However, the traditional p-i-n type perovskite solar cell adopts a classical multi-layer heterostructure. This structure usually includes a perovskite light-absorbing layer sandwiched between a p-type carrier transport layer (HTL) and an n-type electron transport layer (ETL). Although this structure has achieved certain success to some extent, there are also some limitations. First, the deposition process of the multi-layer structure is time-consuming and energy-consuming, thus increasing the manufacturing cost. Second, common organic hole transport layers (such as PEDOT:PSS and PTAA) are prone to photo-, heat- and moisture-induced degradation; inorganic hole transport layers (such as nickel oxide) will react with perovskite, resulting in interface decomposition. In addition, most HTLs have the characteristics of being expensive and having complex synthesis. Under the combined action of these factors, the wide application and commercial development of p-i-n type perovskite solar cells are restricted. Therefore, preparing a device without a hole transport layer by doping perovskite with molecules is a more effective strategy. However, at present, the performance of p-i-n type perovskite solar cells without a hole transport layer is lower than that of perovskite solar cells with a hole transport layer. This is because the strategy without a hole transport layer is prone to the energy level matching problem between perovskite and the electrode, which is mainly attributed to problems such as the conductivity difference between perovskite and the transport layer, and it is difficult to regulate the conductive behavior of perovskite to make it have a carrier extraction ability comparable to that of the transport layer, resulting in a lower performance of p-i-n type perovskite solar cells without a hole transport layer.

[0004] Therefore, for p-i-n type perovskite solar cells without a hole transport layer, regulating the energy band structure of perovskite through molecular dopants to make it more compatible with the energy levels of the electrodes and improving the conductive behavior of perovskite to endow it with a carrier injection ability comparable to that of the transport layer are important research directions for solving their efficiency problems. Summary of the Invention

[0005] Based on this, the present invention provides a perovskite active layer doped with carbazole-based small molecules, its preparation method and application, to solve the problem that the p-i-n type perovskite solar cells without a hole transport layer in the prior art are difficult to effectively regulate the energy band structure of perovskite, resulting in a mismatch between the energy levels of the active layer and the electrodes, and further leading to poor performance of the p-i-n type perovskite solar cells without a hole transport layer.

[0006] To achieve the above object, the present invention provides a preparation method of a perovskite active layer doped with carbazole-based small molecules, which includes the following steps:

[0007] (1) Dissolve formamidinium iodide, methylammonium iodide, cesium iodide and lead iodide in an organic solvent, and shake to dissolve to obtain a perovskite precursor solution;

[0008] (2) Add a carbazole-based small molecule dopant to the perovskite precursor solution in step (1) to make a precursor solution containing the carbazole-based small molecule dopant, and the carbazole-based small molecule dopant is selected from the following structures:

[0009]

[0010] Wherein, B is an alkyl group, a benzene ring or a biphenyl; A is a phosphoric acid group, a carboxylic acid group or a boric acid group;

[0011] (3) Use the coating and film-forming process for the precursor solution containing the carbazole-based small molecule dopant in step (2) to prepare a cesium-formamidinium-methylammonium lead iodide alloy perovskite film with an ABX3 configuration, which is the perovskite active layer doped with the carbazole-based small molecule; in the ABX3 configuration, the A site is a blend of methylammonium ions, formamidinium ions and cesium ions, the B site is lead ions, and the X site is iodide ions.

[0012] As a further preferred technical solution of the present invention, the carbazole-based small molecule dopant is selected from one of the following structures:

[0013] .

[0014] As a further preferred technical solution of the present invention, the concentration of the carbazole-based small molecule dopant in the perovskite precursor solution is 0.05 - 15 mg / mL.

[0015] As a further preferred technical solution of the present invention, the organic solvent is selected from one or a mixture of several of DMF, DMSO, and NMP.

[0016] As a further preferred technical solution of the present invention, in step (3), the substrate used for coating the precursor solution doped with carbazole-based small molecules is ITO conductive glass or FTO conductive glass.

[0017] As a further preferred technical solution of the present invention, the thickness of the cesium-formamidinium-methylammonium lead iodide alloy perovskite film with the ABX3 configuration prepared in step (3) is 450 - 850 nm.

[0018] As a further preferred technical solution of the present invention, in step (3), after the precursor solution doped with carbazole-based small molecules is coated by any one of spin coating, blade coating, and spray coating, annealing treatment is carried out at 90 - 150 °C.

[0019] According to another aspect of the present invention, the present invention also provides a perovskite active layer doped with carbazole-based small molecules.

[0020] According to still another aspect of the present invention, the present invention also provides an application of a perovskite active layer doped with carbazole-based small molecules as a perovskite active layer in a p-i-n type perovskite solar cell. The p-i-n type perovskite solar cell includes a conductive glass, a perovskite active layer doped with carbazole-based small molecules, an interface passivation layer, an electron transport layer, and a metal electrode arranged in sequence.

[0021] Compared with the prior art, the present invention effectively regulates the energy band structure of perovskite and improves the conductive behavior of perovskite by introducing carbazole-based small molecules through doping, and obtains a perovskite active layer doped with carbazole-based small molecules with a carrier injection ability comparable to that of the transport layer and high crystallinity; moreover, for the p-i-n type perovskite solar cell using the perovskite active layer doped with carbazole-based small molecules, the open-circuit voltage and photoelectric conversion efficiency of the device are well improved, and excellent long-term operation stability is obtained.

[0022] The raw materials used for the perovskite active layer doped with carbazole-based small molecules and the p-i-n type perovskite solar cell without a hole transport layer prepared by the present invention are inexpensive and easy to obtain, and this method simplifies the device structure, has a simpler manufacturing process, and greatly reduces the production cost. In addition, this method is compatible with the preparation of large-area devices, flexible and tandem devices, and is suitable for industrial promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present invention will be further described in detail below with reference to the drawings and specific embodiments.

[0024] Figure 1Schematic flow chart of the preparation method of the perovskite thin film in the specific embodiment of the present invention, where: 1 is to drop the perovskite precursor solution containing a dopant on the ITO substrate; 2 is to deposit the perovskite thin film by spin coating; 3 is to drop the antisolvent; 4 is the annealing process.

[0025] Figure 2 Schematic diagram of the structure of the p-i-n type perovskite solar cell, where: 1 is the substrate; 2 is the perovskite active layer; 3 is the interface passivation layer; 4 is the electron transport layer; 5 is the metal electrode.

[0026] Figure 3 XRD pattern of the perovskite thin film before and after doping with the dopant in Example 1.

[0027] Figure 4 SEM image of the upper surface of the perovskite thin film before and after doping with the dopant in Example 1.

[0028] Figure 5 Steady-state fluorescence spectrum (PL) of the perovskite thin film before and after doping with the dopant in Example 1.

[0029] Figure 6 Time-resolved fluorescence spectrum (TRPL) of the perovskite thin film before and after doping with the dopant in Example 1.

[0030] Figure 7 Current-voltage characteristic curves of the perovskite solar cells prepared in the control example and Examples 1, 2, 3 and 4.

[0031] Figure 8 Long-term stability curve of the p-i-n type perovskite solar cell without a hole transport layer in Example 1.

[0032] The realization of the object, functional features and advantages of the present invention will be further described with reference to the embodiments and the accompanying drawings. Specific Embodiments

[0033] The following is a detailed description of the specific embodiments of the present invention with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only for the purpose of illustrating and explaining the present invention, and are not intended to limit the present invention.

[0034] Unless otherwise defined, the technical terms used in the following embodiments have the same meaning as commonly understood by those skilled in the art to which the present invention pertains. The test reagents used in the following embodiments are all conventional biochemical reagents unless otherwise specified; the experimental methods used are all conventional methods unless otherwise specified.

[0035] At present, in hole-transport-layer-free p-i-n perovskite solar cells, due to the mismatch between the energy band structure of the perovskite active layer and the energy levels of the electrodes, there is a huge open-circuit voltage loss at the bottom interface, which seriously affects the performance and stability of the hole-transport-layer-free p-i-n perovskite solar cells.

[0036] Aiming at the above problems, in the present invention, a dopant is added to the precursor solution to adjust the energy level structure of the perovskite to achieve the best energy level matching with the electrodes, improve the carrier extraction ability of the perovskite, thereby reducing the energy level mismatch at the bottom interface and increasing the open-circuit voltage of the device. In addition, the introduction of carbazole-based small molecules effectively improves the crystallinity of the perovskite film, is conducive to the formation of large-sized grains, reduces the grain boundaries in the bulk of the perovskite film, thereby reducing the carrier transport loss at the bottom interface and further increasing the photoelectric conversion efficiency of the p-i-n perovskite solar cell.

[0037] The precursor solution of the present invention is obtained by dissolving formamidinium iodide, methylammonium iodide, cesium iodide and lead iodide in a mixed solution of organic solvents and introducing 0.05 - 15 mg / mL of carbazole-based small molecules as dopants, and dissolving them by shaking. Then, the precursor solution is prepared into a carbazole-based small molecule-doped perovskite active layer with an ABX3 configuration by any one of spin coating, blade coating or spray coating.

[0038] Applying the above-prepared carbazole-based small molecule-doped perovskite active layer to a p-i-n perovskite solar cell, the thickness of the perovskite active layer is usually 450 - 850 nm, preferably 750 nm. As Figure 2 shown, the p-i-n type perovskite solar cell includes a conductive glass 1, a carbazole-based small molecule-doped perovskite active layer 2, an interface passivation layer 3, an electron transport layer 4 and a metal electrode 5.

[0039] In the present invention, by introducing carbazole-based small molecules as dopants into the precursor solution, the energy band structure of the perovskite active layer is effectively regulated, the best energy level alignment between the perovskite active layer and the electrodes is achieved, and further a p-i-n perovskite solar cell device with high photoelectric conversion efficiency is prepared. The packaged device has better operating stability under the conditions of humidity of 55 - 75% and 65 °C.

[0040] In order to enable those skilled in the art to better understand and implement the technical solutions of the present invention, the following will further elaborate on the present invention through specific embodiments.

[0041] Control example:

[0042] The steps for preparing a p-i-n perovskite solar cell based on an undoped perovskite active layer are as follows:

[0043] 1. Cleaning of conductive glass:

[0044] The transparent conductive glass ITO was ultrasonically cleaned with detergent, deionized water, and ethanol for 45 minutes each, twice. Before use, it was cleaned with oxygen plasma to remove surface organic substances and increase the concentration of hydroxyl groups on the ITO surface.

[0045] 2. Preparation of perovskite layer:

[0046] Combined Figure 1 As shown, 247.7 mg of formamidinium iodide (FAI), 20.8 mg of cesium iodide (CsI), 737.6 mg of lead iodide (PbI2), 12.7 mg of methylammonium iodide (MAI), 5.4 mg of chloroammonium chloride (MACl), and 22.3 mg of lead chloride (PbCl2) were dissolved in a mixed solvent of 200 μL of DMSO and 800 μL of DMF, and shaken for 3 hours to obtain a perovskite precursor solution. 40 μL of the prepared precursor solution was dropped onto the ITO conductive glass substrate, and a perovskite thin film was deposited by spin coating. The spin coating procedure was as follows: the acceleration was 2000 revolutions per second, and it was accelerated to 4000 rpm and spin coated for 30 s. 160 μL of chlorobenzene was dropped as an anti-solvent at the 5th second from the end of the program, and then annealed on a hot plate at 110 °C for 30 min.

[0047] 3. Deposition of interface passivation layer:

[0048] After the perovskite thin film was deposited, a bimolecular ammonium salt passivation layer was coated. The specific operation was as follows: 12 mM of 3-(methylthio)propylamine hydroiodide (3MTPAI) and 6 mM of propane-1,3-diammonium iodide (PDAI2) were dissolved in a mixed solvent with a volume ratio of isopropanol / chlorobenzene of 1:1, and the acceleration was 4500 revolutions per second, and spin coated at 4500 rpm for 25 s.

[0049] 4. Deposition of electron transport layer:

[0050] 30 nm of C 60 and 5 nm of BCP were sequentially deposited by vacuum evaporation. The vacuum degree during evaporation was less than 7×10 -4 Pa, and the evaporation rate was 0.1 - 0.5 Å / s.

[0051] 5. Deposition of metal electrode:

[0052] After the deposition of the electron transport layer was completed, 100 nm thick silver was deposited by the same process to complete the preparation of the p-i-n type perovskite solar cell device.

[0053] Performance and stability testing:

[0054] An iron sheet with a circular hole area of 0.074 cm 2 and a thickness of 0.1 mm was used as a light-shielding template. The current-voltage characteristic curve of the p-i-n type perovskite solar cell device was tested under AM 1.5 G illumination, and the results are as Figure 7 shown. The stability test was carried out in an environmental chamber with 60% humidity and 65 °C, and the results are as Figure 8 shown.

[0055] Example 1

[0056] A p-i-n type perovskite solar cell based on a perovskite active layer doped with a carbazole-based small molecule PBA was prepared, and the specific steps are as follows:

[0057] 1. Substrate cleaning: The same as the control example;

[0058] 2. Preparation of the perovskite layer: 247.7 mg of formamidinium iodide (FAI), 20.8 mg of cesium iodide (CsI), 737.6 mg of lead iodide (PbI2), 12.7 mg of methylammonium iodide (MAI), 5.4 mg of methylammonium chloride (MACl) and 22.3 mg of lead chloride (PbCl2) were dissolved in a mixed solvent of 200 μL of DMSO and 800 μL of DMF, and shaken for 3 hours to dissolve. Then 5 mg / mL of the carbazole-based small molecule PBA was doped into the above solution, and shaken for another 3 hours to dissolve, obtaining a perovskite precursor solution. 40 μL of the prepared precursor solution was dropped onto the ITO conductive glass substrate, and the perovskite thin film was deposited by spin coating. The spin coating procedure was as follows: the acceleration was 2000 revolutions per second, accelerated to 4000 rpm and spin coated for 30 s, 160 μL of chlorobenzene was dropped as an anti-solvent at the 5th second from the end of the program, and then annealed on a hot plate at 110 °C for 30 min.

[0059] 3. Deposition of the interface passivation layer: The same as the control example;

[0060] 4. Deposition of the electron transport layer: The same as the control example;

[0061] 5. Deposition of the metal electrode: The same as the control example;

[0062] Performance and stability tests:

[0063] The same test method as the control example was adopted. The test results of the current-voltage characteristics are as Figure 7 shown. It can be seen that compared with the control example, the performance of Example 1 was significantly improved to 25.7%. At the same time, the stability test results of the device are as Figure 8As shown, the long-term stability of the device is significantly improved. After 2000 hours of aging test, the device efficiency retains more than 95% of the original. By adding a dopant to the precursor solution, the optimal energy level matching between the perovskite and the electrode is achieved, improving the carrier extraction ability of the perovskite and increasing the open-circuit voltage of the device. At the same time, the introduction of the carbazole-based small molecule effectively improves the crystallinity of the perovskite film, reduces the carrier transport loss at the buried interface, and thus significantly improves the device performance and long-term operation stability.

[0064] The perovskite active layer before and after doping with the carbazole-based small molecule dopant was characterized by X-ray diffraction (XRD), as Figure 3 shown. Compared with the undoped perovskite, the perovskite doped with PBA has a narrower full width at half maximum and a higher diffraction peak intensity, and the signal of lead iodide weakens, indicating that the perovskite crystal quality is significantly improved after molecular doping.

[0065] The perovskite active layer before and after doping with the carbazole-based small molecule dopant was characterized by scanning electron microscopy (SEM), as Figure 2 and Figure 4 shown. The SEM images of the upper surface and cross-section of the perovskite film show that the grain size increases and the grain boundaries are significantly reduced in the vertical orientation after molecular doping.

[0066] The above perovskite film was characterized by steady-state fluorescence spectroscopy (PL) and time-resolved fluorescence spectroscopy (TRPL), as Figure 5 and Figure 6 shown. The PL peak intensity and lifetime of the perovskite film doped with the carbazole-based small molecule dopant are significantly enhanced, indicating that the non-radiative recombination is reduced and the bulk and interface defects of the perovskite are effectively passivated.

[0067] Example 2

[0068] 1. Substrate cleaning: The same as the control example;

[0069] 2. Electron transport layer deposition: The same as the control example;

[0070] 3. Perovskite layer preparation: The specific preparation method refers to Example 1, except that the carbazole-based small molecule dopant used in this example is Cz-PBA;

[0071] 4. Passivation layer deposition: The same as the control example;

[0072] 5. Hole transport layer preparation: The same as the control example;

[0073] 6. Metal electrode deposition: The same as the control example;

[0074] Adopting the same test method as the control example, the current-voltage characteristic test results are asFigure 7 As shown, under AM1.5G simulated sunlight irradiation, when scanning in the reverse direction, the short-circuit current of the device is 26.44 mA cm -2 , the open-circuit voltage is 1.188 V, the fill factor is 83.2%, and the photoelectric conversion efficiency is 26.0%.

[0075] Example 3

[0076] 1. Substrate cleaning: the same as the control example;

[0077] 2. Electron transport layer deposition: the same as the control example;

[0078] 3. Perovskite layer preparation: The specific preparation method refers to Example 1. The difference is that the carbazole-based small molecule dopant used in this example is BCz-PBA;

[0079] 4. Passivation layer deposition: the same as the control example;

[0080] 5. Hole transport layer preparation: the same as the control example;

[0081] 6. Metal electrode deposition: the same as the control example;

[0082] Adopt the same test method as the control example, and the performance test results are as Figure 7 shown. It can be seen that the optoelectronic performance of Example 3 is better than that of the control example, and its photoelectric conversion efficiency reaches 26.6%.

[0083] Example 4:

[0084] 1. Substrate cleaning: the same as the control example;

[0085] 2. Electron transport layer deposition: the same as the control example;

[0086] 3. Perovskite layer preparation: The specific preparation method refers to Example 1. The difference is that the carbazole-based small molecule dopant used in this example is N-ethylcarbazole;

[0087] 4. Passivation layer deposition: the same as the control example;

[0088] 5. Hole transport layer preparation: the same as the control example;

[0089] 6. Metal electrode deposition: the same as the control example;

[0090] Adopt the same test method as the control example, and the performance test results are as Figure 7As shown, it can be seen that the optoelectronic performance of Example 4 is significantly lower than that of the control example, and its optoelectronic conversion efficiency only reaches 20.2%. In addition, a large number of experiments were also carried out by replacing the type of carbazole-based small molecule dopant. It was found by comparison that only the carbazole-based small molecule with the following structure of the present invention has excellent optoelectronic performance and operating stability. The structure of this carbazole-based small molecule is as follows:

[0091]

[0092] Wherein, B is an alkyl group, a benzene ring or a biphenyl; A is a phosphate group, a carboxyl group or a borate group.

[0093] Although the specific embodiments of the present invention have been described above, those skilled in the art should understand that these are only examples, and various changes or modifications can be made to this embodiment without departing from the principle and essence of the present invention. The protection scope of the present invention is only defined by the appended claims.

Claims

1. A preparation method of a perovskite active layer doped with a carbazole-based small molecule for a hole-transport-layer-free p-i-n type perovskite solar cell, characterized in that, It includes the following steps: (1) Dissolve formamidinium iodide, methylammonium iodide, cesium iodide and lead iodide in an organic solvent, and shake to dissolve to obtain a perovskite precursor solution; (2) Add a carbazole-based small molecule dopant to the perovskite precursor solution in step (1) to prepare a precursor solution doped with a carbazole-based small molecule, and the carbazole-based small molecule dopant is selected from one of the following structures: ； (3) Prepare a cesium-formamidinium-methylammonium lead iodide alloy perovskite film with an ABX3 configuration by a coating process using the precursor solution doped with a carbazole-based small molecule in step (2), which is the perovskite active layer doped with a carbazole-based small molecule; in the ABX3 configuration, the A site is a blend of methylammonium ions, formamidinium ions and cesium ions, the B site is lead ions, and the X site is iodine ions.

2. The preparation method of the perovskite active layer doped with carbazole-based small molecules according to claim 1, wherein The concentration of the carbazole-based small molecule dopant in the perovskite precursor solution is 0.05 - 15 mg / mL.

3. The preparation method of the perovskite active layer doped with carbazole-based small molecules according to claim 1, wherein The organic solvent is selected from one or a mixture of DMF, DMSO, and NMP.

4. The preparation method of the perovskite active layer doped with carbazole-based small molecules according to claim 1, wherein, In step (3), the substrate used for coating the precursor solution doped with a carbazole-based small molecule is ITO conductive glass or FTO conductive glass.

5. The preparation method of the perovskite active layer doped with carbazole-based small molecules according to claim 1, wherein The thickness of the cesium-formamidinium-methylammonium lead iodide alloy perovskite film with an ABX3 configuration prepared in step (3) is 450 - 850 nm.

6. The preparation method of the perovskite active layer doped with carbazole-based small molecules according to claim 1, wherein, In step (3), after the precursor solution doped with a carbazole-based small molecule is coated by any one of spin coating, blade coating, and spray coating, annealing treatment is carried out at 90 - 150 °C.

7. A perovskite active layer doped with a carbazole-based small molecule, characterized in that, Prepared by using the method according to any one of claims 1 - 6.

8. Application of the perovskite active layer doped with a carbazole-based small molecule according to claim 7 as a perovskite active layer in a hole-transport-layer-free p-i-n type perovskite solar cell.

9. A hole-transport-layer-free p-i-n type perovskite solar cell, characterized in that, The hole-transport-layer-free p-i-n type perovskite solar cell includes conductive glass, an interface passivation layer, an electron transport layer, a metal electrode, and the perovskite active layer doped with a carbazole-based small molecule according to claim 7.

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