Hole Transport Layer Materials for Perovskite Solar Cells

Abstract

Provided is a hole transport layer material that contributes to the thermal stability of a perovskite solar cell.　This hole transport layer material for a perovskite solar cell has a hole transport substance and an added substance represented by formula (1). R1, R2, and R3 are independently alkyl groups having at least 1 and at most 2 carbon atoms, and R4 is an ether group having at least 2 and at most 5 carbon atoms.

Description

Technical Field

[0001] This application relates to a hole transport layer material for perovskite solar cells.

Background Art

[0002] In recent years, perovskite solar cells in which the optoelectronic conversion layer is a perovskite crystal layer have attracted attention. In order to improve the optoelectronic conversion efficiency of perovskite solar cells, additives are used in the hole transport layer. Non-Patent Document 1 describes a hole transport layer in which LiTFSI (lithium bis(trifluoromethane)sulfonimide) is added to Spiro-OMeTAD (2,2′,7,7′-Tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9′-spirobifluorene). However, perovskite solar cells having a hole transport layer containing LiTFSI have poor thermal stability. An additive to the hole transport layer that contributes to the thermal stability of perovskite solar cells is required.

Prior Art Documents

Non-Patent Documents

[0003]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] This application has been made in view of such circumstances, and an object thereof is to provide a hole transport layer material that contributes to the thermal stability of perovskite solar cells.

Means for Solving the Problems

[0005] The hole transport layer material for a perovskite solar cell of this application has a hole transporting substance and an additive substance represented by the following general formula (1). In the following general formula (1), R1 , R 2 , and R 3 are each independently an alkyl group having 1 to 2 carbon atoms, and R 4 is an ether group having 2 to 5 carbon atoms.

[0006]

Chemical formula

[0007] The perovskite solar cell of the present application includes a transparent electrode layer, an electron transport layer, a perovskite crystal layer, a hole transport layer composed of the hole transport layer material of the present application, and an electrode layer.

Advantages of the Invention

[0008] The hole transport layer material of the perovskite solar cell of the present application contains the additive substance represented by the above general formula (1). Therefore, the perovskite solar cell using the hole transport layer material of the present application has excellent thermal stability.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0010] Hereinafter, based on embodiments and examples, a hole transport layer material and a perovskite solar cell of the present application will be described with reference to the drawings. Note that the hole transport layer material of the present application will be described as the material of the hole transport layer, which is a component of the perovskite solar cell of the present application. FIG. 1 schematically shows a cross section of a perovskite solar cell 10 according to an embodiment of the present application. The perovskite solar cell 10 includes a substrate 12, a transparent electrode layer 14, an electron transport layer 16, a perovskite crystal layer 18, a hole transport layer 20, and an electrode layer 22.

[0011] In addition to these components, the perovskite solar cell 10 may include (a) an anti-reflection film provided on the light incident side of the substrate 12, (b) an interface modification film or auxiliary layer provided at the interface between the electron transport layer 16 and the perovskite crystal layer 18, (c) an interface modification film or auxiliary layer provided at the interface between the perovskite crystal layer 18 and the hole transport layer 20, or (d) a sealing material or moisture getter material that protects the perovskite solar cell 10 from moisture in the atmosphere. Further, the perovskite solar cell may be an inverted structure solar cell in which the electron transport layer 16 and the hole transport layer 20 in the perovskite solar cell 10 are interchanged.

[0012] In this embodiment, the substrate 12 is a glass substrate, the transparent electrode layer 14 is an FTO (Fluorine-doped tin oxide) layer, the electron transport layer 16 is a tin oxide (SnO 2 ) layer composed of nanoparticles, the perovskite crystal layer 18 is a Cs 0.05 (FA 0.89 MA 0.11 ) 0.95 Pb(I 0.89 Br 0.11 ) 3 layer (FA is formamidinium, MA is Methylamine (the same hereinafter)), and the electrode layer 22 is a gold layer. The perovskite crystal layer 18 may be CH 3 NH 3 PbI 3 and CH(NH 2 ) 2 PbI 3 and the like.

[0013] The hole transport layer 20 is composed of a hole transport layer material. The hole transport layer material includes a hole transport substance, Spiro-OMeTAD, and an additive substance represented by the following general formula (1). In the following general formula (1), R 1 , R 2 , and R 3 are independently alkyl groups having 1 or more and 2 or less carbon atoms, and R 4 is an ether group having 2 or more and 5 or less carbon atoms. Since R 1 , R 2 , and R 3 are alkyl groups having 1 or more and 2 or less carbon atoms and R 4 is an ether group having 2 or more and 5 or less carbon atoms and has a small number of carbon atoms, phase separation between the hole transport substance and the additive substance in the hole transport layer due to the increased lipophilicity of the additive substance is suppressed. Also, since the number of carbon atoms of R 1 , R 2 , R 3 , and R 4 is small, deterioration of the electrical characteristics of the perovskite solar cell due to an increase in the electrical resistance of the additive substance is suppressed.

[0014]

Chemical formula

[0015] The hole transport layer material may contain substances other than the hole transport substance and the additive substance, such as a solvent that dissolves the hole transport substance and the additive substance. Also, the hole transport layer material preferably does not substantially contain Li. This is to prevent Li from diffusing within the perovskite solar cell 10 and reducing the thermal stability of the perovskite solar cell 10. That the hole transport layer material does not substantially contain Li means that the mass content of Li in the hole transport layer material is 2% or less. The mass content of Li in the hole transport layer material is preferably 1% or less, and more preferably 0.01% or less. Further, it is most preferable that Li is not contained in the hole transport layer material except in cases where it is unavoidably contained. Note that the mass content of Li in the hole transport layer material can be measured by mass spectrometry.

[0016] R 1 、R 2 、and R 3 are linear alkyl groups, and R 4 is preferably a linear ether group. Among these, R 1 and R 2 are methyl groups, R 3 is an ethyl group, and R 4 is more preferably a methoxyethyl group. The perovskite solar cell 10 is manufactured, for example, as follows. A transparent electrode layer 14 is formed on a substrate 12, an electron transport layer 16 is formed on the transparent electrode layer 14, a perovskite crystal layer 18 is formed on the electron transport layer 16, a hole transport layer 20 is formed on the perovskite crystal layer 18, and an electrode layer 22 is formed on the hole transport layer 20 using a spin coating method, a sputtering method, a vacuum evaporation method, a spray coating method, a die coating method, a gravure printing method, a screen printing method, or the like.

Example

[0017] 〔Fabrication of Perovskite Solar Cell〕 (Example 1) A 15 mass% aqueous dispersion of tin(IV) oxide (Alfa Aesar) was dropped and spin-coated on the FTO surface of FTO-coated glass (Nippon Sheet Glass Co., Ltd., NSG TEC 10) and dried at 150 °C for 1 hour to obtain a substrate on which a glass substrate, an FTO layer as a transparent electrode layer, and a tin oxide layer as an electron transport layer were laminated in this order. Then, the surface of the tin oxide of this substrate was treated with oxygen ions in oxygen plasma by the following procedure.

[0018] First, the substrate was placed on the lower electrode in the processing chamber of a plasma processing apparatus (diener, FEMTO (frequency of high-frequency power supply: 40 kHz, maximum power: 100 W)) so that the tin oxide layer faced the upper electrode. Next, in order to remove moisture and nitrogen in the air, the pressure in the processing chamber was reduced to 20 Pa or less by vacuum evacuation. Then, for plasma generation, oxygen gas was introduced into the processing chamber, the pressure in the processing chamber was maintained at 100 Pa, and 100 W of high-frequency power was supplied between the upper electrode and the lower electrode to perform plasma cleaning for 30 seconds.

[0019] Next, in order to remove the solvent contained in the substrate, the substrate was heated at 150 °C for 1 hour. Then, oxygen gas was introduced into the processing vessel, the pressure in the processing vessel was maintained at 100 Pa, 100 W of high-frequency power was supplied between the upper electrode and the lower electrode, the oxygen gas was plasmaized to generate oxygen plasma, and the surface of the tin oxide layer was treated with oxygen ions in the oxygen plasma for 30 seconds.

[0020] Next, 123 mg of FAI, PbI 2 : 382 mg, 14 mg of MABr, PbBr 2 : 36 mg, and 29 μL of a DMSO solution (1.5 M) of CsI were each dissolved to prepare a precursor solution of Cs 0.05 (FA 0.89 MA 0.11 ) 0.95 Pb(I 0.89 Br 0.11 ) 3 This precursor solution was spin-coated onto the surface-treated tin oxide layer at 1000 rpm for 10 seconds, and then a small amount of chlorobenzene was spin-coated at 6000 rpm for 20 seconds to obtain a uniform perovskite precursor thin film.

[0021] Next, it was heated at 100 °C for 1 hour using a hot plate to form a Cs 0.05 (FA 0.89 MA 0.11 ) 0.95 Pb(I 0.89 Br 0.11 ) 3 layer, and a laminate including a substrate, a transparent electrode layer, an electron transport layer, and a perovskite crystal layer was obtained. Then, 31 mg of Spiro-OMeTAD and 2 μL of N-ethyl-N-(2-methoxyethyl)-N,N-dimethylammonium = bis(trifluoromethanesulfonyl)imide (manufactured by Fujifilm Wako Pure Chemical Corporation) represented by the following chemical formula (2) were dissolved in 0.35 mL of chlorobenzene, and 11 μL of 4-tert-butylpyridine was added to obtain a hole transport layer precursor solution which is a hole transport layer material.

[0022]

Chem.

[0023] Next, the Cs of the laminate obtained above 0.05 (FA 0.89 MA 0.11 ) 0.95 Pb(I 0.89 Br 0.11 ) 3 layer was spin-coated with this hole transport layer precursor solution at 3000 rpm for 30 seconds. Then, it was dried at 65°C for 10 minutes to form a hole transport layer. A gold layer with a thickness of 50 nm was deposited on the surface of this hole transport layer using a vacuum evaporator to obtain a perovskite solar cell member. Note that this perovskite solar cell member corresponds to the perovskite solar cell described in the above embodiment. In the example, the perovskite solar cell is a combination of the perovskite solar cell member and the following housing member.

[0024] Next, a housing member was added to this perovskite solar cell member to obtain a perovskite solar cell. That is, calcium oxide 52 was supported at the center of the surface of the glass plate 50, and an ultraviolet curable adhesive 54 containing glass spheres with a diameter of 10 μm was applied as a spacer with a thickness of 0.05 mm and a width of 0.2 mm around it to obtain a sealing member. Then, in a nitrogen atmosphere, this sealing member was overlaid on the perovskite solar cell member obtained above, and ultraviolet light was irradiated to cure the adhesive 54, thereby fabricating the perovskite solar cell of Example 1. FIG. 2 schematically shows a cross section of this perovskite solar cell.

[0025] (Comparative Example 1) 61 mg of Spiro-OMeTAD and 10 mg of LiTFSI (Sigma-Aldrich) were dissolved in 0.7 mL of chlorobenzene, and 22 μL of 4-tert-butylpyridine was added to obtain a hole transport layer precursor solution. Otherwise, in the same manner as in Example 1, a perovskite solar cell of Comparative Example 1 was obtained.

[0026] (Comparative Example 2) Instead of 2 μL of N-ethyl-N-(2-methoxyethyl)-N,N-dimethylammonium bis(trifluoromethanesulfonyl)imide of Example 1, 1 μL of 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (manufactured by Fujifilm Wako Pure Chemical Corporation) represented by the following chemical formula (3) was used, and a perovskite solar cell of Comparative Example 2 was obtained in the same manner as in Example 1.

[0027]

Chemical formula

[0028] (Comparative Example 3) Instead of 2 μL of N-ethyl-N-(2-methoxyethyl)-N,N-dimethylammonium bis(trifluoromethanesulfonyl)imide of Example 1, 3 μL of tributylmethylammonium bis(trifluoromethanesulfonyl)imide (manufactured by Fujifilm Wako Pure Chemical Corporation) represented by the following chemical formula (4) was used, and a perovskite solar cell of Comparative Example 3 was obtained in the same manner as in Example 1.

[0029]

Chemical formula

[0030] (Comparative Example 4) Instead of 2 μL of N-ethyl-N-(2-methoxyethyl)-N,N-dimethylammonium bis(trifluoromethanesulfonyl)imide of Example 1, 5 μL of 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (manufactured by Fujifilm Wako Pure Chemical Corporation) represented by the following chemical formula (5) was used, and a perovskite solar cell of Comparative Example 4 was obtained in the same manner as in Example 1.

[0031]

Chemical formula

[0032] [Evaluation of Perovskite Solar Cell] (Initial characteristics) Using a solar simulator (OTENTO-SUN, manufactured by Spectral Instruments Co., Ltd.), AM1.5 simulated sunlight (intensity 1000 W / m 2 ) was irradiated onto the perovskite solar cells of Example 1 and Comparative Examples 1 to 4. From the curve plotting the current-voltage relationship with a source meter (Keithley 2400, manufactured by Keithley Instruments, Inc.), the short-circuit current density, open-circuit voltage, fill factor, and photoelectric conversion efficiency were determined. The results are shown in Table 1.

[0033]

Table 1

[0034] As shown in Table 1, the short-circuit current density, open-circuit voltage, fill factor, and photoelectric conversion efficiency of the perovskite solar cell of Example 1 were equivalent to those of the perovskite solar cell of Comparative Example 1. That is, a perovskite solar cell provided with a hole transport layer containing the additive N-ethyl-N-(2-methoxyethyl)-N,N-dimethylammonium = bis(trifluoromethanesulfonyl)imide (the above chemical formula (2)) exhibited initial characteristics equivalent to those of a perovskite solar cell provided with a hole transport layer containing the additive LiTFSI.

[0035] Also, the short-circuit current density, open-circuit voltage, fill factor, and photoelectric conversion efficiency of the perovskite solar cells of Comparative Examples 2 to 4 were smaller than those of the perovskite solar cell of Example 1. That is, simply adding a substance containing bis(trifluoromethanesulfonyl)imide anion to the hole transport layer was insufficient. By adding the additive represented by the above general formula (1) to the hole transport layer, good initial characteristics of the perovskite solar cell were obtained.

[0036] (Thermal stability) Using the perovskite solar cells of Example 1, Comparative Example 1, and Comparative Example 2, the change over time in the photoelectric conversion efficiency under the above initial characteristics was measured in the same manner as the method for obtaining the photoelectric conversion efficiency. The results are shown in Figure 3. As shown in Figure 3, in the perovskite solar cell of Example 1, the photoelectric conversion efficiency was 72.5% of the initial value even after 960 hours. In contrast, in the perovskite solar cell of Comparative Example 1, the photoelectric conversion efficiency decreased to 51.6% of the initial value after 960 hours.

[0037] That is, the perovskite solar cell provided with a hole transport layer containing N-ethyl-N-(2-methoxyethyl)-N,N-dimethylammonium = bis(trifluoromethanesulfonyl)imide (the above chemical formula (2)) as an additive substance was superior in thermal stability to the perovskite solar cell provided with a hole transport layer containing LiTFSI as an additive substance. In the perovskite solar cell of Comparative Example 2, the photoelectric conversion efficiency decreased to 16.4% of the initial value after 456 hours.

Explanation of Symbols

[0038] 10 Perovskite solar cell 12 Substrate 14 Transparent electrode layer 16 Electron transport layer 18 Perovskite crystal layer 20 Hole transport layer 22 Electrode layer

Claims

1. A hole transport layer material for a perovskite solar cell having a hole transporting material and an additive material represented by the following formula (1). 【Chemical 1】 The R1 and the R2 are methyl groups, the R3 is an ethyl group, and the R4 is a methoxyethyl group.

2. A perovskite solar cell having a transparent electrode layer, an electron transport layer, a perovskite crystal layer, a hole transport layer composed of the hole transport layer material according to Claim 1, and an electrode layer.

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