Mixed solvent, coating liquid, hole transport layer, preparation method of hole transport layer and photovoltaic cell

Abstract

The invention discloses a mixed solvent, a coating liquid, a hole transport layer, a preparation method of the hole transport layer and a photovoltaic cell, and relates to the technical field of photovoltaic cells. The mixed solvent comprises chloroform and propionic acid. Wherein the non-polar solvent chloroform with high saturated vapor pressure can improve the solubility of a non-polar unit in the hole transport material, and the polar solvent propionic acid with low saturated vapor pressure can dissolve the polar unit of the hole transport material, so that the hole transport material is uniformly dispersed in the mixed solvent. Furthermore, the mixed solvent is mixed with a hole transport material such as a carbazole phosphate self-assembly molecular material, so that the phosphate group of the carbazole phosphate self-assembly molecular material is preferentially arranged towards the substrate when the hole transport layer is prepared on the substrate; the anchoring rate of the carbazole phosphate self-assembly molecular material on the substrate is improved while agglomeration is reduced, so that a uniform, compact and high-coverage hole transport layer is prepared, and the performance of a photovoltaic cell is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of photovoltaic cells, and in particular to a mixed solvent, a coating solution, a hole transport layer, a preparation method thereof, and a photovoltaic cell. Background Art

[0002] The application of outdoor photovoltaics has grown rapidly in the past decade. However, the indoor application of photovoltaic devices is still in its infancy. The main application scenarios of indoor photovoltaics include wireless sensors, Internet of Things gateways, RFID information tags, calculators, clocks, etc. These applications are characterized by a large number, scattered distribution locations, low power (<0.1 mW), and DC drive. The power supply methods through the power grid, primary batteries, or secondary batteries cannot meet the requirements of service life, energy conservation, and environmental protection, while the ready-to-use indoor photovoltaic cells can better match these application scenarios. For future scenarios such as the industrial 4.0 smart factory and low-carbon intelligent office based on the Internet of Things, a large number of wireless sensors are required. Powering the supporting sensors through indoor photovoltaics can provide powerful help for reducing the overall energy consumption of the system. However, common photovoltaic devices, such as crystalline silicon, amorphous silicon, cadmium telluride and other solar cells, have low photoelectric conversion efficiency under indoor light. Fortunately, perovskite solar cells have shown extremely high weak light response efficiency. For example, the certified efficiency of small-area perovskite indoor photovoltaic devices has exceeded 43%, demonstrating great application potential.

[0003] However, the current preparation technology of perovskite indoor photovoltaic cells is mainly realized by a method combining solution method and vacuum coating method. Among them, the perovskite layer has been prepared by the solution method, but the hole transport layer mainly still relies on the vacuum coating method for preparation, which to a certain extent increases the preparation cost and time cost of the device, thus hindering its industrialization process.

[0004] Although there are currently some studies on preparing the hole transport layer by the solution method, there are still severe challenges in preparing the hole transport layer by the continuous solution method. The main reasons are as follows: 1) During the process of coating the hole transport material with a conventional solvent such as isopropanol (IPA) or N,N-dimethylformamide (DMF), the molecules of the hole transport material (such as carbazole phosphate-based self-assembled molecular materials) are extremely prone to aggregation phenomena, as shown in Figure 1 ; 2) The solvents used generally have the characteristics of low viscosity and high saturated vapor pressure, which makes it difficult to control the solution flow and the solvent leaving process. The above problems make the hole transport layer prepared based on the continuous solution method often show low uniformity, low coverage, and low reproducibility, thereby limiting the performance of the photovoltaic cell.

[0005] Therefore, the prior art still needs to be improved and developed. Summary of the Invention

[0006] Based on the deficiencies of the above-mentioned prior art, the object of the present invention is to provide a mixed solvent, a coating solution, a hole transport layer and its preparation method, and a photovoltaic cell, aiming to solve the problems of poor uniformity and low coverage of the hole transport layer prepared by the existing solution method.

[0007] The technical solution of the present invention is as follows:

[0008] In the first aspect of the present invention, a mixed solvent is provided, wherein the mixed solvent includes chloroform and propionic acid.

[0009] Optionally, the volume ratio of chloroform to propionic acid is 1:1 to 1.5:1.

[0010] In the second aspect of the present invention, a coating solution is provided, wherein the coating solution includes the mixed solvent as described above in the present invention and a hole transport material; the hole transport material includes a phosphonic acid carbazole-based self-assembled molecular material.

[0011] Optionally, the phosphonic acid carbazole-based self-assembled molecular material includes at least one of polyphosphonic acid carbazole, (2-(9H-carbazol-9-yl)ethyl)phosphonic acid, (4-(3,6-dimethyl-9H-carbazol-9-yl)butyl)phosphonic acid, 4-(7H-dibenzo(c,g)carbazol-7-yl)phenylphosphonic acid, and (2-(3,6-diiodo-9H-carbazol-9-yl)ethyl)phosphonic acid.

[0012] Optionally, in the coating solution, the concentration of the hole transport material is 0.5 to 2 mg / mL.

[0013] In the second aspect of the present invention, a preparation method of a hole transport layer is provided, which includes the following steps:

[0014] Coating with the coating solution as described above in the present invention, and after annealing, the hole transport layer is obtained.

[0015] Optionally, the coating includes one of blade coating and spin coating; and / or, the annealing temperature is 100 to 110 °C, and the annealing time is 10 to 15 minutes.

[0016] Optionally, the process parameters of the blade coating are: the blade coating speed is 4 to 6 mm·s -1 , and the blade coating height is 80 to 120 μm.

[0017] In the third aspect of the present invention, a hole transport layer is provided, wherein the hole transport layer is prepared by the preparation method as described above in the present invention.

[0018] In the fourth aspect of the present invention, a photovoltaic cell is provided, wherein the photovoltaic cell includes the hole transport layer as described above in the present invention.

[0019] Beneficial effects: In the present invention, chloroform, a non-polar solvent with a high saturated vapor pressure, can increase the solubility of non-polar units in the hole transport material, and propionic acid, a polar solvent with a low saturated vapor pressure, can dissolve the polar units of the hole transport material, enabling the hole transport material to be uniformly dispersed in the mixed solvent. Further, when the mixed solvent provided by the present invention is mixed with a hole transport material such as a carbazole phosphate-based self-assembled molecular material to prepare a hole transport layer on a substrate, the phosphate groups of the carbazole phosphate-based self-assembled molecular material can be preferentially oriented towards the substrate, reducing aggregation while increasing the anchoring rate of the carbazole phosphate-based self-assembled molecular material on the substrate, making the carbazole phosphate-based self-assembled molecular material uniformly cover (or homogenously distribute) on the substrate without aggregation and with a high coverage, thereby preparing a uniform, dense, and high-coverage hole transport layer, which is conducive to improving the performance of the photovoltaic cell. Description of the Drawings

[0020] Figure 1 It is a schematic diagram showing the aggregation phenomenon of the hole transport material during the process of coating the hole transport material with a conventional solvent in the prior art.

[0021] Figure 2 It is a graph of the saturated vapor pressure and solvent polarity of chloroform (CF), methanol (MeOH), formic acid (FA), and propionic acid (PA).

[0022] Figure 3 It is a schematic diagram of the mechanism for preparing a uniform and high-coverage hole transport layer using the mixed solvent in the embodiment of the present invention.

[0023] Figure 4 It is the O1s peak spectra of the Poly-4PACz / ITO / glass samples prepared in different comparative examples and Example 1. Among them, (a) is the Poly-4PACz / ITO / glass sample prepared in Comparative Example 1, (b) is the Poly-4PACz / ITO / glass sample prepared in Comparative Example 2, (c) is the Poly-4PACz / ITO / glass sample prepared in Comparative Example 3, and (d) is the Poly-4PACz / ITO / glass sample prepared in Example 1.

[0024] Figure 5KPFM test result diagrams of the hole transport layers prepared in different comparative examples and Example 1, wherein (a) is the potential distribution diagram of the hole transport layer prepared in Comparative Example 1, (b) is the statistical chart of the potential distribution corresponding to Figure (a), (c) is the potential distribution diagram of the hole transport layer prepared in Comparative Example 2, (d) is the statistical chart of the potential distribution corresponding to Figure (c), (e) is the potential distribution diagram of the hole transport layer prepared in Comparative Example 3, (f) is the statistical chart of the potential distribution corresponding to Figure (e), (g) is the potential distribution diagram of the hole transport layer prepared in Example 1, and (h) is the statistical chart of the potential distribution corresponding to Figure (g). Detailed implementation manners

[0025] The present invention provides a mixed solvent, a coating solution, a hole transport layer, a preparation method thereof and a photovoltaic cell. To make the objectives, technical solutions and effects of the present invention clearer and more definite, the present invention is further described in detail below. 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.

[0026] Unless otherwise defined, all technical terms and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the specification of the present invention are only for the purpose of describing specific implementation manners and are not intended to limit the present invention.

[0027] If the descriptions in the embodiments of the present invention involve "first", "second", etc., such descriptions of "first", "second", etc. are only for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the quantity of the indicated technical features.

[0028] An embodiment of the present invention provides a mixed solvent, wherein the mixed solvent includes chloroform (CF) and propionic acid (PA).

[0029] In the present invention, the non-polar solvent chloroform with a high saturated vapor pressure can increase the solubility of non-polar units in the hole transport material, and the polar solvent propionic acid with a low saturated vapor pressure can dissolve the polar units of the hole transport material, enabling the hole transport material to be uniformly dispersed in the mixed solvent. Moreover, the mixture of the non-polar solvent chloroform with a high saturated vapor pressure and the polar solvent propionic acid with a low saturated vapor pressure makes it easy to control the solution flow and solvent departure processes. Further, when the mixed solvent provided by the embodiments of the present invention is mixed with a hole transport material such as a carbazole phosphate-based self-assembled molecular material to prepare a hole transport layer on a substrate, the phosphate groups of the carbazole phosphate-based self-assembled molecular material can be preferentially arranged towards the substrate, reducing aggregation while increasing the anchoring rate of the carbazole phosphate-based self-assembled molecular material on the substrate, enabling the carbazole phosphate-based self-assembled molecular material to uniformly cover the substrate without agglomeration and with a high coverage, thereby preparing a uniform, dense, and highly covered hole transport layer, which is beneficial to improving the performance of the photovoltaic cell.

[0030] Here, taking a hole transport material (such as a carbazole phosphate-based self-assembled molecular material) and indium tin oxide (ITO) conductive glass as the substrate as an example, a detailed explanation will be given.

[0031] As Figure 2 shown, the non-polar solvent chloroform (CF) has a high saturated vapor pressure, and the polar solvent propionic acid (PA) has a low saturated vapor pressure. In the mixed solvent provided by the present invention, the non-polar solvent chloroform with a high saturated vapor pressure can increase the solubility of non-polar benzene ring units in the carbazole phosphate-based self-assembled molecular material, and the polar solvent propionic acid with a low saturated vapor pressure can dissolve the polar phosphate units of the carbazole phosphate-based self-assembled molecular material. This polar-non-polar co-solvent system provided by the present invention can promote the formation of a high-quality carbazole phosphate-based self-assembled molecular layer. As Figure 3 shown, in this mixed solvent (i.e., co-solvent) system, the carbazole phosphate-based self-assembled molecular material chains tend to adopt an extended conformation rather than a coiled structure. During the coating process, the non-polar solvent chloroform with a high saturated vapor pressure completely evaporates, and the remaining polar solvent propionic acid promotes the phosphate groups in the carbazole phosphate-based self-assembled molecular material to be preferentially arranged towards the ITO conductive glass. This reduces the aggregation of the carbazole phosphate-based self-assembled molecular material while significantly increasing the reactivity between the phosphonic acid anchoring groups and the surface of the hydroxyl-rich ITO conductive glass, increasing the anchoring rate of the carbazole phosphate-based self-assembled molecular material on the substrate, and then a uniform, non-agglomerated, dense, and highly covered carbazole phosphate-based self-assembled molecular material layer can be formed on the ITO conductive glass, thereby preparing a uniform, dense, and highly covered hole transport layer.

[0032] In some embodiments, the volume ratio of the chloroform to the propionic acid is 1:1 to 1.5:1. This ratio can achieve the preparation of a more uniform and dense high-quality hole transport layer. By way of example, the volume ratio of the chloroform to the propionic acid can be 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, or 1.5:1, etc.

[0033] An embodiment of the present invention also provides a coating solution, wherein the coating solution includes the mixed solvent and the hole transport material as described above in the embodiments of the present invention; the hole transport material includes a phosphonic acid carbazole-based self-assembled molecular material.

[0034] Using the coating solution provided by the embodiment of the present invention, a uniform and dense phosphonic acid carbazole-based self-assembled molecular material layer, that is, a hole transport layer, can be formed on the ITO conductive glass.

[0035] In some embodiments, the phosphonic acid carbazole-based self-assembled molecular material includes at least one of poly(4-phosphonic acid carbazole) (Poly-4PACZ), (2-(9H-carbazol-9-yl)ethyl)phosphonic acid (2PACZ), (4-(3,6-dimethyl-9H-carbazol-9-yl)butyl)phosphonic acid (Me-4PACZ), 4-(7H-dibenzo(c,g)carbazol-7-yl)phenylphosphonic acid (Bz-PhpPACZ), and (2-(3,6-diiodo-9H-carbazol-9-yl)ethyl)phosphonic acid (I-2PACZ), but is not limited thereto.

[0036] In some embodiments, in the coating solution, the concentration of the hole transport material is 0.5 to 2 mg / mL. For example, it can be 0.5 mg / mL, 0.6 mg / mL, 0.8 mg / mL, 0.85 mg / mL, 0.9 mg / mL, 0.95 mg / mL, 1 mg / mL, 1.2 mg / mL, 1.5 mg / mL, 1.8 mg / mL, or 2 mg / mL, etc. In the coating solution, if the concentration of the hole transport material is too high, stacking and agglomeration phenomena are likely to occur in the hole transport layer, and the deposition thickness is relatively thick; if the concentration of the hole transport material is too low, the coverage rate will be low. When the concentration of the hole transport material is 0.5 to 2 mg / mL, a high coverage rate can be ensured without stacking and agglomeration phenomena.

[0037] An embodiment of the present invention also provides a method for preparing a hole transport layer, which includes the following steps:

[0038] Coating with the coating solution as described above in the embodiments of the present invention, and after annealing, the hole transport layer is obtained.

[0039] The hole transport layer prepared by using the preparation method provided by the embodiment of the present invention has high uniformity, high density, and high coverage.

[0040] In some embodiments, the coating includes one of blade coating and spin coating. The blade coating method can be used to prepare a large-area hole transport layer, which is beneficial to the industrial production of photovoltaic cells.

[0041] In some embodiments, the annealing temperature is 100 - 110 °C and the annealing time is 10 - 15 minutes. By way of example, the annealing temperature can be 100 °C, 101 °C, 102 °C, 103 °C, 104 °C, 105 °C, 106 °C, 107 °C, 108 °C, 109 °C or 110 °C, etc., and the annealing time can be 10 minutes, 11 minutes, 12 minutes, 13 minutes, 14 minutes or 15 minutes, etc.

[0042] In some embodiments, the process parameters of the blade coating are as follows: the blade coating speed is 4 - 6 mm·s -1 , and the blade coating height is 80 - 120 μm. By way of example, the blade coating speed can be 4 mm·s -1 , 4.5 mm·s -1 , 5 mm·s -1 , 5.5 mm·s -1 or 6 mm·s -1 , etc., and the blade coating height can be 80 μm, 85 μm, 90 μm, 95 μm, 100 μm, 105 μm, 110 μm, 115 μm or 120 μm, etc.

[0043] The embodiment of the present invention also provides a hole transport layer, wherein the hole transport layer is prepared by using the preparation method as described above in the present invention.

[0044] The embodiment of the present invention also provides a photovoltaic cell, wherein the photovoltaic cell includes the hole transport layer as described above in the present invention.

[0045] In some embodiments, the photovoltaic cell is a perovskite photovoltaic cell (i.e., a perovskite solar cell), and the perovskite photovoltaic cell can be a normal structure or an inverted structure.

[0046] In some embodiments, the perovskite photovoltaic cell includes a transparent conductive oxide electrode, a hole transport layer, a perovskite light-absorbing layer, an electron transport layer and a metal electrode which are sequentially stacked.

[0047] In some embodiments, the transparent conductive oxide electrode includes an ITO electrode, a fluorine-doped tin oxide (FTO) electrode, etc., but is not limited thereto.

[0048] In some embodiments, the perovskite light-absorbing layer comprises a perovskite material, and the chemical formula of the perovskite material is ABX3, where A is at least one of methylammonium (MA) ion, formamidinium (FA) ion, cesium (Cs) ion, but not limited thereto; B is at least one of lead (Pb) ion, tin (Sn) ion, but not limited thereto; X is at least one of halide ions, pseudohalide ions, thiocyanate (SCN) ions, and the halide ions include but are not limited to at least one of iodine (I) ion, bromine (Br) ion.

[0049] In some embodiments, the thickness of the perovskite light-absorbing layer is 450 - 500 nm, and for example, it can be 450 nm, 460 nm, 470 nm, 480 nm, 490 nm or 500 nm, etc.

[0050] In some specific embodiments, the perovskite material comprises FA 0.7 Cs 0.3 Pb(I 0.6 Br 0.4 )3, FA 0.85 Cs 0.15 PbI 2.55 Br 0.45 or at least one of them.

[0051] In some embodiments, the electron transport layer comprises an electron transport material, and the electron transport material includes at least one of an organic electron transport material and an inorganic electron transport material. The organic electron transport material includes, poly(fullerene - xylene) (PFBO - C12), [6,6]-phenyl - C 61 - methyl butyrate (PCBM) and C 60 or at least one of them. The inorganic electron transport material includes at least one of titanium dioxide and tin dioxide, but not limited thereto.

[0052] In some embodiments, the thickness of the electron transport layer is 25 - 30 nm, and for example, it can be 25 nm, 26 nm, 27 nm, 28 nm, 29 nm or 30 nm, etc.

[0053] In some embodiments, the metal electrode is one of a gold electrode, a silver electrode and a copper electrode, but not limited thereto.

[0054] In some embodiments, the perovskite photovoltaic cell further comprises a hole blocking layer, and the hole blocking layer is located between the perovskite light-absorbing layer and the electron transport layer.

[0055] In some embodiments, the hole blocking layer comprises a hole blocking material, which includes at least one of 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP, also known as bathocuproine), 1,3,5-tris(1-phenyl-1H-benzoimidazol-2-yl)benzene (TPBI), but is not limited thereto.

[0056] The present invention will be further described below through specific embodiments.

[0057] In the following examples, unless otherwise specified, the raw materials used are commercially available products that can be obtained through commercial channels.

[0058] Example 1

[0059] This example provides a method for preparing a hole transport layer, which includes the following steps:

[0060] After scrubbing the ITO conductive glass (i.e., composed of a glass substrate and an ITO layer on the glass substrate) with dishwashing liquid, it is successively placed in deionized water, acetone, and isopropanol and ultrasonically cleaned for 15 minutes respectively. After the cleaning is completed, it is dried with N2, and then treated with ultraviolet ozone for 30 minutes to obtain the treated ITO glass;

[0061] Chloroform and propionic acid are mixed in a volume ratio of 1:1 and stirred at room temperature for 3 hours to obtain a mixed solvent;

[0062] Poly-4PACz is added to the above mixed solvent to prepare a coating solution with a Poly-4PACz concentration of 1 mg / mL;

[0063] Using the spin coating method, the spin coating process parameters are set as: the spin coating speed is 5 mm·s -1 , the spin coating height is 100 μm. The coating solution is spin-coated on the ITO layer of the treated ITO conductive glass, and then annealed on a heating table at 100 °C for 10 minutes. After cooling, a hole transport layer is obtained on the surface of the ITO conductive glass. Then, the ITO conductive glass and the hole transport layer on its surface are collectively denoted as the Poly-4PACz / ITO / glass sample.

[0064] Comparative Example 1

[0065] This comparative example provides a method for preparing a hole transport layer, which is only different from Example 1 in that Poly-4PACz is added to isopropanol and stirred at room temperature for 3 hours to prepare a coating solution with a Poly-4PACz concentration of 1 mg / mL.

[0066] Comparative Example 2

[0067] This comparative example provides a method for preparing a hole transport layer. The difference from Example 1 is only that Poly-4PACz is added to a mixed solution of chloroform and methanol (the volume ratio of chloroform to methanol is 1:1), stirred at room temperature for 3 hours, and a coating solution with a Poly-4PACz concentration of 1 mg / mL is prepared.

[0068] Comparative Example 3

[0069] This comparative example provides a method for preparing a hole transport layer. The difference from Example 1 is only that Poly-4PACz is added to a mixed solution of chloroform and formic acid (the volume ratio of chlorobenzene to formic acid is 1:1), stirred at room temperature for 3 hours, and a coating solution with a Poly-4PACz concentration of 1 mg / mL is prepared.

[0070] Test:

[0071] (1) The Poly-4PACz / ITO / glass samples prepared in Comparative Example 1, Comparative Example 2, Comparative Example 3 and Example 1 were subjected to X-ray photoelectron spectroscopy (XPS) test to obtain the O1s peak spectrum. By integrating the peak areas of P-O-In and P=O-In, the ratio of the sum of the peak areas of P-O-In and P=O-In to the O 1s peak area was obtained to compare the anchoring rate of the hole transport layer on the ITO conductive glass. The results are as Figure 4 shown. It can be seen that the peak areas of P-O-In and P=O-In of the Poly-4PACz / ITO / glass sample prepared based on the mixed solvent of chloroform and propionic acid in Example 1 are the largest, accounting for 53.9%. The ratio of the peak areas of P-O-In and P=O-In of the Poly-4PACz / ITO / glass sample prepared based on isopropanol in Comparative Example 1 is 19.3%. The ratio of the peak areas of P-O-In and P=O-In of the Poly-4PACz / ITO / glass sample prepared based on the mixed solution of chloroform and methanol in Comparative Example 2 is 22.7%. The ratio of the peak areas of P-O-In and P=O-In of the Poly-4PACz / ITO / glass sample prepared based on the mixed solution of chloroform and formic acid in Comparative Example 3 is 37.2%. This shows that the anchoring rate of the hole transport layer prepared based on the mixed solvent of chloroform and propionic acid on the ITO conductive glass in Example 1 is higher than that of the hole transport layers prepared based on isopropanol, chloroform and methanol, and chloroform and formic acid systems on the ITO conductive glass. That is, the mixed solution provided by the present invention can prepare a hole transport layer with a high coverage.

[0072] (2) The hole transport layers in the Poly-4PACz / ITO / glass samples prepared in Comparative Example 1, Comparative Example 2, Comparative Example 3 and Example 1 were subjected to KPFM (Kelvin probe force microscopy) test. The results are as Figure 5As shown. It can be seen that, compared with isopropanol in Comparative Example 1, chloroform and methanol in Comparative Example 2, and the hole transport layer prepared by the chloroform and formic acid system in Comparative Example 3, the hole transport layer prepared by the chloroform and propionic acid mixed solvent system in Example 1 shows a more uniform and dense distribution on the ITO conductive glass, and its surface potential difference is only about 100 mV. Using the mixed solvent provided by the present invention can reduce the aggregation of Poly-4PACz, and a uniform, dense and highly covered hole transport layer can be prepared.

[0073] Example 2

[0074] This example provides a perovskite photovoltaic cell, including an ITO conductive glass, a hole transport layer located on the ITO conductive glass, a perovskite light-absorbing layer located on the hole transport layer, an electron transport layer located on the perovskite light-absorbing layer, a hole blocking layer located on the electron transport layer, and an Ag electrode located on the hole blocking layer.

[0075] Among them, the thickness of the ITO layer in the ITO conductive glass is 200 nm;

[0076] The thickness of the hole transport layer is 5 nm, and it is prepared by the method of Example 1;

[0077] The thickness of the perovskite light-absorbing layer is 480 nm, and it is composed of FA 0.7 Cs 0.3 Pb(I 0.6 Br 0.4 )3;

[0078] The thickness of the electron transport layer is 30 nm, and it is composed of poly(fullerene-xylene);

[0079] The thickness of the hole blocking layer is 5 nm, and it is composed of 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline;

[0080] The thickness of the Ag electrode is 120 nm.

[0081] Comparative Example 4

[0082] This example provides a perovskite photovoltaic cell, which is only different from Example 2 in that the hole transport layer is prepared by the method of Comparative Example 1.

[0083] Comparative Example 5

[0084] This example provides a perovskite photovoltaic cell, which is only different from Example 2 in that the hole transport layer is prepared by the method of Comparative Example 2.

[0085] Comparative Example 6

[0086] This example provides a perovskite photovoltaic cell, which is only different from Example 2 in that the hole transport layer is prepared by the method of Comparative Example 3.

[0087] The perovskite photovoltaic cells in Example 2, Comparative Example 4, Comparative Example 5 and Comparative Example 6 were tested, and the results are shown in Table 1.

[0088] Table 1. Performance of perovskite photovoltaic cells

[0089]

[0090]

[0091] It can be seen that using the mixed solvent provided by the present invention to prepare the hole transport layer of the perovskite photovoltaic cell can improve the performance of the perovskite photovoltaic cell.

[0092] In summary, the present invention provides a mixed solvent, a coating solution, a hole transport layer and their preparation methods and photovoltaic cells. In the mixed solvent provided by the present invention, the non-polar solvent chloroform with a high saturated vapor pressure can increase the solubility of the non-polar benzene ring unit in the carbazole phosphate-based self-assembled molecular material; the polar solvent propionic acid with a low saturated vapor pressure can dissolve the polar phosphate unit of the carbazole phosphate-based self-assembled molecular material. And in this mixed solvent system, the chains of the carbazole phosphate-based self-assembled molecular material tend to adopt a long conformation rather than a coiled structure. During the coating process, the non-polar solvent chloroform with a high saturated vapor pressure completely evaporates, while the remaining polar solvent propionic acid promotes the preferential arrangement of the phosphate groups in the carbazole phosphate-based self-assembled molecular material towards the ITO conductive glass surface. While reducing the aggregation of the carbazole phosphate-based self-assembled molecular material, it significantly improves the reactivity between the phosphonic acid anchoring group and the surface of the hydroxyl-rich ITO conductive glass, and then a uniform, non-aggregated, dense (i.e., high coverage) carbazole phosphate-based self-assembled molecular material layer can be formed on the ITO conductive glass, thereby preparing a uniform, dense and high-coverage hole transport layer, which is beneficial to improving the performance of the photovoltaic cell.

[0093] It should be understood that the application of the present invention is not limited to the above examples. For those of ordinary skill in the art, improvements or changes can be made according to the above description, and all such improvements and changes should fall within the protection scope of the appended claims of the present invention.

Claims

1. A mixed solvent, characterized in that, The mixed solvent includes chloroform and propionic acid.

2. The mixed solvent according to claim 1, wherein The volume ratio of the chloroform to the propionic acid is 1:1 to 1.5:

1.

3. A coating liquid, characterized in that, The coating solution includes the mixed solvent described in claim 1 and a hole transport material; the hole transport material includes a phosphonic acid carbazole-based self-assembled molecular material.

4. The coating liquid according to claim 3, characterized in that, The phosphonic acid carbazole-based self-assembled molecular material includes at least one of poly(phosphonic acid carbazole), (2-(9H-carbazol-9-yl)ethyl)phosphonic acid, (4-(3,6-dimethyl-9H-carbazol-9-yl)butyl)phosphonic acid, 4-(7H-dibenzo(c,g)carbazol-7-yl)phenylphosphonic acid, and (2-(3,6-diiodo-9H-carbazol-9-yl)ethyl)phosphonic acid.

5. The coating liquid according to claim 4, characterized in that, In the coating solution, the concentration of the hole transport material is 0.5 to 2 mg / mL.

6. A method for preparing a hole transport layer, characterized in that, It includes the following steps: Coating is performed using the coating solution described in any one of claims 3-5, and after annealing, the hole transport layer is obtained.

7. The preparation method according to claim 6, characterized in that, The coating includes one of knife coating and spin coating; and / or The temperature of the annealing is 100 to 110 °C, and the time of the annealing is 10 to 15 minutes.

8. The preparation method according to claim 7, wherein The process parameters of the scraping coating are as follows: the scraping speed is 4-6 mm·s -1 , and the scraping height is 80-120 μm.

9. A hole transport layer, characterized in that, The hole transport layer is prepared by the preparation method described in any one of claims 6-8.

10. A photovoltaic cell, characterized in that, The photovoltaic cell includes the hole transport layer described in claim 9.

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