Solar cells and methods for manufacturing solar cells

Abstract

To improve the durability of solar cells.SOLUTION: A solar cell 1000 includes a support material 2, a photoelectric conversion element 1, and a sealing material 3. The photoelectric conversion element 1 is disposed inside a sealed space sealed by the support material 2 and the sealing material 3. The photoelectric conversion element 1 includes a first electrode, a photoelectric conversion layer, and a second electrode, in this order. The value obtained by dividing the amount of water vapor in the sealed space by the surface area of the face of the photoelectric conversion element facing the sealed space is 2.3×10-6 mol / m2 or more and 1.2×10-4 mol / m2 or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a solar cell and a method for manufacturing the solar cell.

[0002] In recent years, research and development of perovskite solar cells using a perovskite-type crystal represented by a composition formula ABX3 (where A is a monovalent cation, B is a divalent cation, and X is a halogen anion) and its similar structures (hereinafter referred to as "perovskite compounds") as a photoelectric conversion material have been advanced. Various efforts have been made to improve the photoelectric conversion efficiency and durability of perovskite solar cells.

[0003] In Non-Patent Document 1, it has been reported that water vapor in the atmosphere reacts with perovskite compounds, and thereby substances that do not contribute to power generation, such as lead iodide, methylammonium iodide, or hydrated compounds, are formed on the surface or grain boundaries of perovskite compounds.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Non-Patent Documents

Means for Solving the Problem

[0007] The solar cell of the present disclosure has a support a photoelectric conversion element, and a sealing material, and the photoelectric conversion element is disposed inside a sealed space sealed by the support and the sealing material, the photoelectric conversion element includes a first electrode, a photoelectric conversion layer, and a second electrode in this order, the value obtained by dividing the amount of water vapor in the sealed space by the surface area of the surface of the photoelectric conversion element facing the sealed space is 2.3×10 -6 mol / m 2 or more and 1.2×10 -4 mol / m 2 or less.

Advantage of the Invention

[0008] The present disclosure can improve the durability of a solar cell. ]>

Brief Description of the Drawings

[0009] [Figure 1] FIG. 1 is a diagram showing a schematic configuration of a solar cell 1000 according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a cross-sectional view showing a schematic configuration of a first configuration example of a photoelectric conversion element 1 in the solar cell 1000 according to an embodiment of the present disclosure. [Figure 3] FIG. 3 is a cross-sectional view showing a schematic configuration of a second configuration example of a photoelectric conversion element 1 in the solar cell 1000 according to an embodiment of the present disclosure. [Figure 4] FIG. 4 is a cross-sectional view showing a schematic configuration of a third configuration example of a photoelectric conversion element 1 in the solar cell 1000 according to an embodiment of the present disclosure. [Figure 5] FIG. 5 is a graph showing the dependence of the normalized photoelectric conversion efficiency of the solar cells of Example 1, Example 4, Example 6, and Comparative Example 1 on the water vapor concentration. [Figure 6]Figure 6 is a graph showing the dependence of the normalized photoelectric conversion efficiency of solar cells in Example 1, Example 4, Example 6, and Comparative Example 1 on the amount of water vapor. [Figure 7] Figure 7 is a graph showing the dependence of the normalized photoelectric conversion efficiency of solar cells in Example 2, Example 3, Example 5, Example 7, and Comparative Example 2 on water vapor concentration. [Figure 8] Figure 8 is a graph showing the dependence of the normalized photoelectric conversion efficiency of solar cells in Example 2, Example 3, Example 5, Example 7, and Comparative Example 2 on the amount of water vapor. [Modes for carrying out the invention]

[0010] <Knowledge that forms the basis of this disclosure> As reported in Non-Patent Document 1, lead-containing perovskite compounds react with water to form substances that do not contribute to power generation, such as lead iodide, methylammonium iodide, or hydrated compounds, on the surface or grain boundaries of the perovskite compound. These reaction products are highly insulating substances. Therefore, if a large amount of these reaction products is formed, the movement of photogenerated carriers is inhibited, which leads to a problem of reduced performance of perovskite solar cells. For this reason, perovskite solar cells are generally used in a nitrogen atmosphere with as little water as possible in the surroundings (for example, a water vapor concentration of 0.1 ppm or less by volume fraction). In this specification, all water vapor concentration and oxygen concentration mentioned below refer to the concentration by volume fraction.

[0011] Patent Document 1 discloses a perovskite solar cell having a sealed structure, in which oxygen and moisture are contained within the sealed space. It is disclosed that the heat resistance of the solar cell can be improved by controlling the oxygen concentration in the space to 5% or more and the moisture concentration (volume fraction) to 300 ppm or less. However, Non-Patent Document 1 reports on the effect of oxygen on solar cells, in addition to the degradation of solar cell properties due to water vapor as described above. Specifically, Non-Patent Document 1 discloses that the normalized photoelectric conversion efficiency after a light irradiation test of a perovskite solar cell decreases monotonically as the oxygen concentration around the solar cell increases from 1% to 20%, with the case where the oxygen concentration around the solar cell is 0% as the baseline. Thus, the decrease in light resistance at an oxygen concentration of 5% is reported in Non-Patent Document 1. Therefore, it is predicted that it will be difficult to achieve both thermal stability and photostability in the range of oxygen concentrations above 5%.

[0012] Non-patent document 2 discloses that the conductivity of a π-conjugated polymer, which is a hole transport material, is improved when water is coordinated near the main chain. However, there have been no reports to date of improved thermal stability and photostability due to water vapor, and the presence of water vapor has been considered a factor that reduces durability.

[0013] As described above, there were no reports indicating that the presence of water vapor contributes to improving the photostability and thermal stability, which are important in actual use.

[0014] In light of these prior art studies, the inventors conducted a detailed investigation into the threshold water vapor concentration, i.e., the water vapor concentration value at which the impact on the durability of the solar cell becomes significant, while keeping the oxygen concentration in the sealed space below 2 ppm. As a result, they found that an optimal range for the durability of the solar cell exists between a water vapor concentration of 0% and 1%. Specifically, in a solar cell having a sealed structure, it was found that the photoelectric conversion efficiency after the light irradiation test and the photoelectric conversion efficiency after the heat resistance test improve when the water vapor concentration in the sealed space is between 100 ppm and 5000 ppm. Furthermore, it was found that the photoelectric conversion efficiency after the light irradiation test and the photoelectric conversion efficiency after the heat resistance test improve even further when the water vapor concentration in the sealed space is between 100 ppm and 1000 ppm. Therefore, the photostability and thermal stability of the solar cell can be achieved simultaneously when the water vapor concentration in the sealed space is between 100 ppm and 5000 ppm, and can be further improved when the water vapor concentration in the sealed space is between 100 ppm and 1000 ppm.

[0015] <Embodiments of this Disclosure> A solar cell according to an embodiment of the present disclosure comprises a support material, a photoelectric conversion element, and a encapsulant. The photoelectric conversion element is located inside a sealed space sealed by the support material and the encapsulant. The photoelectric conversion element comprises a first electrode, a photoelectric conversion layer, and a second electrode in that order. The oxygen concentration in the sealed space is less than 10 ppm, and the water vapor concentration in the sealed space is 100 ppm or more and 5000 ppm or less.

[0016] With the above configuration, photodegradation and thermal degradation phenomena induced by defects in the photoelectric conversion material can be suppressed. Therefore, the durability of the solar cell can be improved.

[0017] Furthermore, if the photoelectric conversion element further comprises a hole transport layer, the water vapor concentration within the sealed space being within the above range suppresses the reaction of moisture with the photoelectric conversion material, while the moisture coordinates to the hole transport material, thereby improving the conductivity of the hole transport layer. This improves the conductivity of the solar cell. As a result, holes can be extracted efficiently, making recombination at the interface less likely. Therefore, if the photoelectric conversion element further comprises a hole transport layer, the durability of the solar cell can be further improved by the above configuration.

[0018] In the solar cell according to this embodiment, the water vapor concentration in the sealed space may be 100 ppm or more and 1000 ppm or less.

[0019] With the above configuration, structural changes in the photoelectric conversion material induced by heat and structural changes in the photoelectric conversion material induced by light become less likely to occur. Therefore, with the above configuration, the thermal stability and photostability of the solar cell can be further improved.

[0020] In the solar cell according to this embodiment, the water vapor concentration in the sealed space may be greater than 300 ppm.

[0021] As described above, the solar cell according to this embodiment has an oxygen concentration of less than 10 ppm in the sealed space. Having a low oxygen concentration of less than 10 ppm in the sealed space improves the light resistance of the solar cell, thus enabling both thermal stability and light stability. For further improvement of light resistance, the oxygen concentration in the sealed space may be 2 ppm or less.

[0022] The water vapor concentration within the sealed space can be measured using atmospheric pressure ionization mass spectrometry and gas chromatography. For example, using an atmospheric pressure ionization mass spectrometry (API-TDS600, manufactured by API Japan), a sample package (i.e., a solar cell module) is destroyed in a destruction chamber under a purified argon gas atmosphere. The gaseous components within the package (i.e., the gaseous components within the sealed space) are detected, and the gaseous components within the package are quantitatively measured using a separately prepared calibration curve. This allows for the measurement of the gaseous components within the sealed space. In addition to the destruction of the sample package in the destruction chamber described above, the gas within the sealed space can also be recovered by extracting it using a syringe.

[0023] The oxygen concentration in the sealed space can be measured using atmospheric pressure ionization mass spectrometers, gas chromatography, and electrochemical oxygen concentration meters, etc. The method for recovering the gas in the sealed space is the same as the method used for measuring the water vapor concentration described above.

[0024] Here, as an example, a method for flowing out the gas contained in the sealing space of the solar cell into a closed space such as the destruction chamber and measuring the water vapor concentration and oxygen concentration in the flowed-out gas by an atmospheric pressure ionization mass spectrometer will be described. For example, a solar cell module is placed in a chamber filled with an inert gas such as argon or krypton. By damaging the module in the chamber, the gas contained in the sealing space of the solar cell is allowed to flow out. Next, the gas in the chamber is quantitatively analyzed with an atmospheric pressure ionization mass spectrometer. By quantifying all the components in the gas in the chamber and calculating the ratio of oxygen in the total amount thereof, the oxygen concentration can be determined. Examples of gases other than water vapor and oxygen contained in the sealing space include inert gases such as nitrogen and noble gases, and carbon dioxide. Note that if the same type of inert gas that fills the chamber used for gas analysis is contained in the sealing space, accurate gas analysis may be difficult. Therefore, when the type of gas contained in the sealing space is unknown, two identical solar cell modules are prepared, and different types of inert gases are used as the inert gases that fill the chamber, and gas analysis is performed on the two solar cell modules according to the above procedure respectively. By comparing the two analysis results, the composition of the gas contained in the sealing space can be determined. The partial pressure of water vapor in the sealing space is 1×10 -4 atm or more and 5×10 -3 atm, or may be 1×10 -4 atm or more and 1×10 -3 atm.

[0025] According to the above configuration, it becomes easier to suppress the photo-degradation phenomenon and thermal degradation phenomenon induced by the defects of the photoelectric conversion material. Therefore, the durability of the solar cell can be improved.

[0026] When the solar cell of the present disclosure is manufactured under atmospheric pressure, the pressure in the sealing space becomes about atmospheric pressure. In this case, the partial pressure of water vapor in the sealing space is 1×10 -4 atm or more and 1×10 -3 atm.

[0027] The partial pressure of water vapor in the sealed space can be calculated from the ideal gas law by, for example, measuring the mass or molar concentration of the gas containing water vapor in the sealed space using the water vapor concentration measurement method described above, and then measuring the volume of the sealed space. The volume of the sealed space can be estimated, for example, by injecting liquid into the sealed space. Alternatively, it can be estimated by disassembling the solar cell and measuring the shape of the space. The various measurements described above are usually performed at room temperature, but this is not limited to this. That is, in order to take into account the effects of adsorption and desorption of gas in the sealed space, the measurements may be performed at a temperature that simulates the actual operating environment.

[0028] Modified examples of solar cells according to embodiments of this disclosure will be described below. Repetitive explanations may be omitted as appropriate.

[0029] As described above, the solar cell of this disclosure comprises a support material, a photoelectric conversion element, and a encapsulant, wherein the photoelectric conversion element is disposed inside a sealed space sealed by the support material and the encapsulant. The photoelectric conversion element comprises a first electrode, a photoelectric conversion layer, and a second electrode in this order. The amount of water vapor in the sealed space per unit surface area of ​​the surface of the photoelectric conversion element facing the sealed space is 2.3 × 10⁻⁶. -6 mol / m 2 The above and 1.2 × 10 -4 mol / m 2 The following is also acceptable: That is, the value obtained by dividing the amount of water vapor in the sealing space by the surface area of ​​the surface of the photoelectric conversion element facing the sealing space is 2.3 × 10⁻⁶. -6 mol / m 2 The above and 1.2 × 10 -4 mol / m 2 The following may also be used. This can suppress degradation of solar cells due to long-term operation.

[0030] To further suppress degradation of solar cells due to long-term operation, the amount of water vapor in the sealing space per unit surface area of ​​the surface facing the sealing space of the photoelectric conversion element is 2.3 × 10⁻⁶. -6 mol / m 2 The above and 2.3 × 10 -5 mol / m2 The following is also acceptable.

[0031] To suppress degradation due to oxygen, the amount of oxygen in the sealing space per unit surface area of ​​the surface facing the sealing space of the photoelectric conversion element is 7.0 × 10⁻⁶. -5 mol / m 2 The following is also acceptable: That is, the value obtained by dividing the amount of oxygen in the sealing space by the surface area of ​​the surface of the photoelectric conversion element facing the sealing space is 7.0 × 10 -5 mol / m 2 The following is also acceptable.

[0032] The photoelectric conversion element may have the main surface of the first electrode facing the support material, or the main surface of the second electrode facing the support material.

[0033] The solar cells of this disclosure can be manufactured, for example, by the following method.

[0034] First, a photoelectric conversion element is fabricated using the method described below.

[0035] The resulting photoelectric conversion element is sealed using a sealing material in a glove box with controlled oxygen concentration.

[0036] The oxygen concentration inside the glove box is less than 10 ppm by volume fraction, and the water vapor concentration is 100 ppm or more and 5000 ppm or less by volume fraction. Alternatively, the amount of water vapor in the sealing space per unit surface area of ​​the surface facing the sealing space of the photoelectric conversion element is 2.3 × 10⁻⁶. -6 mol / m 2 The above and 1.2 × 10 -4 mol / m 2 It has been adjusted to be as follows:

[0037] As a result, a solar cell with the desired oxygen and water vapor concentrations can be obtained.

[0038] As described above, a photoelectric conversion element comprising a first electrode, a photoelectric conversion layer, and a second electrode in this order may be sealed in an atmosphere having an oxygen concentration of less than 10 ppm by volume fraction and a water vapor concentration of 100 ppm or more and 5000 ppm or less by volume fraction to produce a solar cell.

[0039] Figure 1 is a diagram showing a schematic configuration of a solar cell 1000 according to an embodiment of the present disclosure.

[0040] The solar cell 1000 according to this embodiment comprises a photoelectric conversion element 1, a support material 2, and a sealing material 3. The photoelectric conversion element 1 is arranged inside a sealed space sealed by the support material 2 and the sealing material 3.

[0041] The photoelectric conversion element 1 may be in contact with the support material 2.

[0042] The support material 2 and the sealing material 3 may be made of the same material. This material may, for example, have a gas barrier function. This material may also be glass.

[0043] The photoelectric conversion element 1 will be described in more detail below using the first to third configuration examples. Note that the photoelectric conversion element 1 is not limited to the photoelectric conversion elements of the first to third configuration examples below.

[0044] Figure 2 is a cross-sectional view showing a schematic configuration of a first example of the photoelectric conversion element 1 in a solar cell 1000 according to an embodiment of the present disclosure.

[0045] The photoelectric conversion element 100 of the first configuration comprises a substrate 4, a first electrode 5, an electron transport layer 6, a photoelectric conversion layer 7, a hole transport layer 8, and a second electrode 9 in this order. As with the photoelectric conversion element 100 of the first configuration, the photoelectric conversion element 1 in the solar cell 1000 according to this embodiment may further include an electron transport layer between the first electrode and the photoelectric conversion layer, or it may further include a hole transport layer between the photoelectric conversion layer and the second electrode.

[0046] When light is shone on the photoelectric conversion element 100, the photoelectric conversion layer 7 absorbs the light, generating excited electrons and holes. These excited electrons move to the first electrode 5 through the electron transport layer 6. Meanwhile, the holes generated in the photoelectric conversion layer 7 move to the second electrode 9 via the hole transport layer 8. As a result, the photoelectric conversion element 100 can extract current from the first electrode 5, which acts as the negative electrode, and the second electrode 9, which acts as the positive electrode.

[0047] The photoelectric conversion element 100 may or may not have a substrate 4.

[0048] The photoelectric conversion element 100 may or may not have an electron transport layer 6. If the photoelectric conversion element 100 has an electron transport layer 6, electrons can be efficiently transferred to the first electrode 5. As a result, the photoelectric conversion element 100 can efficiently extract current.

[0049] The photoelectric conversion element 100 may or may not have a hole transport layer 8. If the photoelectric conversion element 100 has a hole transport layer 8, holes can be efficiently moved to the second electrode 9. As a result, the photoelectric conversion element 100 can efficiently extract current.

[0050] The photoelectric conversion element 100 can be fabricated, for example, by the following method.

[0051] First, a first electrode 5 is formed on the surface of the substrate 4 by chemical vapor deposition, sputtering, or the like. Next, an electron transport layer 6 is formed by chemical vapor deposition, sputtering, or a solution coating method. Next, a photoelectric conversion layer 7 is formed on the electron transport layer 6. The photoelectric conversion layer 7 may be formed by, for example, a solution coating method, printing method, or vapor deposition method. Alternatively, for example, a perovskite compound cut to a predetermined thickness may be placed on the electron transport layer 6 as the photoelectric conversion layer 7. Next, a hole transport layer 8 is formed on the photoelectric conversion layer 7 by chemical vapor deposition, sputtering, or a solution coating method. Next, a second electrode 9 is formed on the hole transport layer 8 by chemical vapor deposition, sputtering, or a solution coating method. The photoelectric conversion element 100 is thus obtained.

[0052] Figure 3 is a cross-sectional view showing a schematic configuration of a second example of the photoelectric conversion element 1 in a solar cell 1000 according to an embodiment of the present disclosure.

[0053] The photoelectric conversion element 200 of the second configuration comprises a substrate 4, a first electrode 5, an electron transport layer 6, a porous layer 10, a photoelectric conversion layer 7, a hole transport layer 8, and a second electrode 9 in this order. Like the photoelectric conversion element 200 of the second configuration, the photoelectric conversion element 1 in the solar cell 1000 according to this embodiment may further include a porous layer. The porous layer is disposed, for example, between the electron transport layer and the photoelectric conversion layer.

[0054] The porous layer 10 contains a porous material. The porous material contains voids.

[0055] The photoelectric conversion element 200 may or may not have a substrate 4.

[0056] The photoelectric conversion element 200 may or may not have an electron transport layer 6. If the photoelectric conversion element 200 does not have an electron transport layer 6, the porous layer 10 is placed between the first electrode 5 and the photoelectric conversion layer 7. If the photoelectric conversion element 200 has an electron transport layer 6, electrons can be efficiently transferred to the first electrode 5. As a result, the photoelectric conversion element 200 can efficiently extract current.

[0057] The photoelectric conversion element 200 may or may not have a hole transport layer 8. If the photoelectric conversion element 200 has a hole transport layer 8, holes can be efficiently moved to the second electrode 9. As a result, the photoelectric conversion element 200 can efficiently extract current.

[0058] Figure 4 is a cross-sectional view showing a schematic configuration of a third example of the photoelectric conversion element 1 in a solar cell 1000 according to an embodiment of the present disclosure.

[0059] The photoelectric conversion element 300 of the third configuration comprises a substrate 4, a first electrode 5, an electron transport layer 6, a porous layer 10, an intermediate layer 11, a photoelectric conversion layer 7, a hole transport layer 8, and a second electrode 9, in this order. As with the photoelectric conversion element 300 of the third configuration, the photoelectric conversion element 1 in the solar cell 1000 according to this embodiment may further include an intermediate layer. The intermediate layer is, for example, placed between the porous layer and the photoelectric conversion layer.

[0060] The photoelectric conversion element 300 may or may not have a substrate 4.

[0061] The photoelectric conversion element 300 may or may not have an electron transport layer 6. If the photoelectric conversion element 300 has an electron transport layer 6, electrons can be efficiently transferred to the first electrode 5. As a result, the photoelectric conversion element 300 can efficiently extract current.

[0062] The photoelectric conversion element 300 may or may not have a hole transport layer 8. If the photoelectric conversion element 300 has a hole transport layer 8, holes can be efficiently moved to the second electrode 9. As a result, the photoelectric conversion element 300 can efficiently extract current.

[0063] The photoelectric conversion element 300 may or may not have a porous layer 10. If the photoelectric conversion element 300 does not have a porous layer 10, the intermediate layer 11 is placed between the electron transport layer 6 and the photoelectric conversion layer 7.

[0064] The following provides a detailed explanation of each component of the photoelectric conversion element.

[0065] (Circuit board 4) The substrate 4 is an auxiliary component. The substrate 4 plays the role of holding each layer of the photoelectric conversion element. The substrate 4 can be formed from a transparent material. For example, a glass substrate or a plastic substrate can be used as the substrate 4. The plastic substrate may be, for example, a plastic film.

[0066] If the second electrode 9 is translucent, the substrate 4 may be made of a material that is not translucent. Such materials can include metals, ceramics, or resin materials with low translucency.

[0067] If the first electrode 5 has sufficient strength, the first electrode 5 can hold each layer, so the substrate 4 does not need to be provided.

[0068] (1st electrode 5) The first electrode 5 is conductive.

[0069] The first electrode 5 is translucent. For example, it transmits light from the visible region to the near-infrared region.

[0070] The first electrode 5 is composed of, for example, a transparent and conductive material. Examples of such materials are metal oxides or metal nitrides. Examples of such materials include (i) titanium oxide doped with at least one selected from the group consisting of lithium, magnesium, niobium, and fluorine; (ii) gallium oxide doped with at least one selected from the group consisting of tin and silicon; (iii) gallium nitride doped with at least one selected from the group consisting of silicon and oxygen; (iv) tin oxide doped with at least one selected from the group consisting of antimony and fluorine; (v) zinc oxide doped with at least one selected from the group consisting of boron, aluminum, gallium, and indium; (vi) indium-tin composite oxide; or (vii) composites thereof.

[0071] The first electrode 5 may be formed with a light-transmitting pattern. Examples of light-transmitting patterns include linear, wavy, grid-like, or perforated metal-like patterns with a large number of fine through-holes arranged regularly or irregularly. When the first electrode 5 has these patterns, light can pass through areas where there is no electrode material. Therefore, by providing a light-transmitting pattern, an opaque material can be used. Examples of opaque electrode materials include platinum, gold, silver, copper, aluminum, rhodium, indium, titanium, iron, nickel, tin, zinc, or alloys containing any of these. Conductive carbon materials may also be used as opaque electrode materials.

[0072] If the photoelectric conversion element does not have an electron transport layer 6, the first electrode 5 has blocking properties for holes from the photoelectric conversion layer 7. In this case, the first electrode 5 does not make ohmic contact with the photoelectric conversion layer 7. Furthermore, blocking properties for holes from the photoelectric conversion layer 7 refer to the property of allowing only electrons generated in the photoelectric conversion layer 7 to pass through, while preventing holes from passing through. The Fermi energy of a material having such properties is higher than the energy level at the top of the valence band of the photoelectric conversion layer 7. The Fermi energy of a material having such properties may also be higher than the Fermi energy of the photoelectric conversion layer 7. Aluminum is a specific example of such a material.

[0073] If the photoelectric conversion element includes an electron transport layer 6, the first electrode 5 does not need to have blocking properties for holes from the photoelectric conversion layer 7. In this case, the first electrode 5 may be made of a material capable of forming ohmic contact with the photoelectric conversion layer 7. In this case, the first electrode 5 may or may not be in ohmic contact with the photoelectric conversion layer 7.

[0074] The light transmittance of the first electrode 5 may be, for example, 50% or more, or 80% or more. The wavelength of light that the first electrode 5 should transmit depends on the absorption wavelength of the photoelectric conversion layer 7.

[0075] The thickness of the first electrode 5 may be, for example, 1 nm or more and 1000 nm or less.

[0076] (electron transport layer 6) The electron transport layer 6 includes a semiconductor. The electron transport layer 6 may be formed from a semiconductor with a band gap of 3.0 eV or more. This allows visible light and infrared light to be transmitted to the photoelectric conversion layer 7. An example of a semiconductor is an inorganic n-type semiconductor.

[0077] Examples of inorganic n-type semiconductors are metal oxides, metal nitrides, or perovskite oxides. Examples of metal oxides are oxides of Cd, Zn, In, Pb, Mo, W, Sb, Bi, Cu, Hg, Ti, Ag, Mn, Fe, V, Sn, Zr, Sr, Ga, Si, or Cr. Metal oxides are, for example, TiO2 or SnO2. Metal nitrides are, for example, GaN. Perovskite oxides are, for example, SrTiO3 or CaTiO3.

[0078] The electron transport layer 6 may contain a material with a band gap larger than 6.0 eV. Examples of such materials include (i) alkali metal or alkaline earth metal halides such as lithium fluoride and calcium fluoride, (ii) alkali metal oxides such as magnesium oxide, or (iii) silicon dioxide. In this case, the electron transport layer 6 may have a thickness of, for example, 10 nm or less to ensure electron transport.

[0079] The electron transport layer 6 may include multiple layers made of different materials.

[0080] (Photoelectric conversion layer 7) The photoelectric conversion layer 7 contains a photoelectric conversion material.

[0081] The photoelectric conversion material may be, for example, a perovskite compound. That is, the photoelectric conversion layer 7 may contain a perovskite compound. Perovskite compounds have a high light absorption coefficient in the wavelength range of the solar spectrum and high carrier mobility. Therefore, a photoelectric conversion element containing a perovskite compound has high photoelectric conversion efficiency.

[0082] Perovskite compounds are represented, for example, by the chemical formula ABX3, where A is a monovalent cation. Examples of monovalent cations are alkali metal cations or organic cations. An example of an alkali metal cation is potassium cation (K + ), cesium cation (Cs + ), or rubidium cation (Rb +) is an example of an organic cation, methylammonium cation (MA). + Or CH3NH3 + ), formamidinium cation (FA + or HC(NH2)2 + ), ethylammonium cation (CH3CH2NH3 + ), or guanidinium cation (CH6N3 + ) is a divalent cation. An example of a divalent cation is lead cation (Pb 2+ ) or tin cation (Sn 2+ ) is the case. X is a monovalent anion. Examples of monovalent anions are halogen anions. Each of the sites A, B, and X may be occupied by multiple types of ions.

[0083] The photoelectric conversion material may be, for example, a lead-containing perovskite compound.

[0084] The thickness of the photoelectric conversion layer 7 is, for example, 50 nm or more and 10 μm or less.

[0085] The photoelectric conversion layer 7 is formed, for example, by a solution coating method, a printing method, or a vapor deposition method. The photoelectric conversion layer 7 may also be formed by cutting out and arranging a perovskite compound.

[0086] The photoelectric conversion layer 7 may mainly contain a perovskite compound represented by the compositional formula ABX3. Here, "the photoelectric conversion layer 7 mainly contains a perovskite compound represented by the compositional formula ABX3" means that the photoelectric conversion layer 7 contains 90% by mass or more of the perovskite compound represented by the compositional formula ABX3. The photoelectric conversion layer 7 may contain 95% by mass or more of the perovskite compound represented by the compositional formula ABX3. The photoelectric conversion layer 7 may consist of a perovskite compound represented by the compositional formula ABX3. The photoelectric conversion layer 7 only needs to contain a perovskite compound represented by the compositional formula ABX3, and may contain defects or impurities.

[0087] The photoelectric conversion layer 7 may further contain other compounds different from the perovskite compound represented by the compositional formula ABX3. Examples of other different compounds include compounds having a Ruddlesden-Popper type layered perovskite structure.

[0088] (Hole transport layer 8) The hole transport layer 8 contains a hole transport material. The hole transport material is a material that transports holes. The hole transport material is, for example, an organic semiconductor or an inorganic semiconductor.

[0089] The hole transport layer 8 may contain an organic semiconductor. The organic semiconductor forms a good interface with the photoelectric conversion layer 7, suppressing the occurrence of interface defects during bonding. As a result, the photoelectric conversion element may have high photoelectric conversion efficiency and durability.

[0090] Examples of organic semiconductors include triphenylamine, triallylamine, phenylbenzidine, phenylenevinylene, tetrathiafulvalene, vinylnaphthalene, vinylcarbazole, thiophene, aniline, pyrrole, carbazole, triptycene, fluorene, azulene, pyrene, pentacene, perylene, acridine, or phthalocyanine.

[0091] Representative organic semiconductors used as hole transport materials include 2,2′,7,7′-tetrakis-(N,N-di-p-methoxyphenylamine)9,9′-spirobifluorene, poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (hereinafter also referred to as "PTAA"), poly(3-hexylthiophene-2,5-diyl), poly(3,4-ethylenedioxythiophene), or copper phthalocyanine. These organic semiconductors possess excellent hole transport properties. Therefore, they can improve the photoelectric conversion efficiency of photoelectric conversion elements.

[0092] The organic semiconductor may include at least one selected from the group consisting of 2,2′,7,7′-tetrakis-(N,N-di-p-methoxyphenylamine)9,9′-spirobifluorene and poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine].

[0093] Inorganic semiconductors used as hole transport materials are p-type semiconductors. Examples of inorganic semiconductors include Cu2O, CuGaO2, CuSCN, CuI, and NiO. x MoO x This is a carbon material such as V2O5 or graphene oxide, where x > 0.

[0094] The hole transport layer 8 may include multiple layers made of different materials. For example, multiple layers may be stacked such that the ionization potential of the hole transport layer 8 decreases sequentially with respect to the ionization potential of the photoelectric conversion layer 7. This improves the hole transport characteristics.

[0095] The thickness of the hole transport layer 8 may be 1 nm or more and 1000 nm or less, or 10 nm or more and 50 nm or less. This allows for sufficient hole transport characteristics to be achieved. Therefore, the low resistance of the solar cell can be maintained, and high photoelectric conversion efficiency can be realized.

[0096] The hole transport layer 8 is formed, for example, by coating, printing, or vapor deposition. This is similar to the photoelectric conversion layer 7. Examples of coating methods include doctor blade, bar coating, spray, dip coating, or spin coating. An example of a printing method is screen printing. If necessary, the hole transport layer 8 may be fabricated by mixing multiple materials and then pressurized or fired. If the material of the hole transport layer 8 is an organic low-molecular-weight substance or an inorganic semiconductor, the hole transport layer 8 can also be fabricated by vacuum deposition.

[0097] The hole transport layer 8 may contain additives in addition to the hole transport material to enhance conductivity. Examples of additives include supporting electrolytes, solvents, or dopants. Supporting electrolytes and solvents have the effect of stabilizing holes in the hole transport layer 8. Dopants have the effect of increasing the number of holes in the hole transport layer 8.

[0098] Examples of supporting electrolytes are ammonium salts, alkaline earth metal salts, or transition metal salts. Examples of ammonium salts are tetrabutylammonium perchlorate, tetraethylammonium hexafluoride phosphate, imidazolium salts, or pyridinium salts. Examples of alkali metal salts are lithium perchlorate or potassium borotetrafluoride. An example of an alkaline earth metal salt is bis(trifluoromethanesulfonyl)imidocalcium(II). Examples of transition metal salts are bis(trifluoromethanesulfonyl)imidozinc(II) or tris[4-tert-butyl-2-(1H-pyrazole-1-yl)pyridine]cobalt(III)tris(trifluoromethanesulfonyl)imide.

[0099] An example of a dopant is a fluorine-containing aromatic boron compound. An example of a fluorine-containing aromatic boron compound is tris(pentafluorophenyl)borane.

[0100] The solvent contained in the hole transport layer 8 may have excellent ionic conductivity. This solvent may be an aqueous solvent or an organic solvent. To further stabilize the solute, the solvent contained in the hole transport layer 8 may be an organic solvent. Examples of organic solvents are heterocyclic compound solvents such as tert-butylpyridine, pyridine, and n-methylpyrrolidone.

[0101] Ionic liquids may be used as solvents. Ionic liquids may be used alone or in mixtures with other solvents. Ionic liquids are desirable because they have low volatility and high flame retardancy.

[0102] Examples of ionic liquids include imidazolium-based liquids such as 1-ethyl-3-methylimidazolium tetracyanoborate, pyridine-based liquids, alicyclic amine-based liquids, aliphatic amine-based liquids, or azonium amine-based liquids.

[0103] The hole transport layer 8 may contain, as an additive, at least one selected from the group consisting of tert-butylpyridine, bis(trifluoromethanesulfonyl)imide calcium(II), bis(trifluoromethanesulfonyl)imide zinc(II), tris[4-tert-butyl-2-(1H-pyrazole-1-yl)pyridine]cobalt(III)tris(trifluoromethanesulfonyl)imide, and tris(pentafluorophenyl)borane. This improves the hole transport properties of the hole transport layer 8. Therefore, the photoelectric conversion efficiency of the photoelectric conversion element can be improved.

[0104] (2nd electrode 9) The second electrode 9 is conductive.

[0105] If the photoelectric conversion element does not have a hole transport layer 8, the second electrode 9 has blocking properties for electrons from the photoelectric conversion layer 7. In this case, the second electrode 9 does not make ohmic contact with the photoelectric conversion layer 7. Blocking properties for electrons from the photoelectric conversion layer 7 refer to the property of allowing only holes generated in the photoelectric conversion layer 7 to pass through, while preventing electrons from passing through. The Fermi energy of a material having such properties is lower than the energy level at the lower end of the conduction band of the photoelectric conversion layer 7. The Fermi energy of a material having such properties may also be lower than the Fermi energy of the photoelectric conversion layer 7. Specific materials include platinum, gold, or carbon materials such as graphene.

[0106] If the photoelectric conversion element includes a hole transport layer 8, the second electrode 9 does not need to block electrons from the photoelectric conversion layer 7. In this case, the second electrode 9 may be made of a material capable of forming ohmic contact with the photoelectric conversion layer 7. This allows the second electrode 9 to be made transparent.

[0107] Of the first electrode 5 and the second electrode 9, at least the electrode on the side into which light is incident only needs to be translucent. Therefore, one of the first electrode 5 and the second electrode 9 does not need to be translucent. In other words, one of the first electrode 5 and the second electrode 9 does not need to be made of a translucent material, nor does it need to have a pattern that includes an opening that transmits light.

[0108] (Porous layer 10) The porous layer 10 is formed on the electron transport layer 6, for example, by a coating method. If the photoelectric conversion element does not have an electron transport layer 6, it is formed on the first electrode 5.

[0109] The porous structure introduced by the porous layer 10 serves as the foundation for forming the photoelectric conversion layer 7. The porous layer 10 does not hinder the light absorption of the photoelectric conversion layer 7 or the electron transfer from the photoelectric conversion layer 7 to the electron transport layer 6.

[0110] The porous layer 10 includes a porous material.

[0111] Porous materials are formed, for example, by a series of insulating or semiconductor particles. Examples of insulating particles are aluminum oxide particles or silicon oxide particles. Examples of semiconductor particles are inorganic semiconductor particles. Examples of inorganic semiconductors are metal oxides, perovskite oxides of metallic elements, sulfides of metallic elements, or metal chalcogenides. Examples of metal oxides are oxides of Cd, Zn, In, Pb, Mo, W, Sb, Bi, Cu, Hg, Ti, Ag, Mn, Fe, V, Sn, Zr, Sr, Ga, Si, or Cr. An example of a metal oxide is TiO2. An example of a perovskite oxide of a metallic element is SrTiO3 or CaTiO3. Examples of sulfides of metallic elements are CdS, ZnS, In2S3, PbS, Mo2S, WS2, Sb2S3, Bi2S3, ZnCdS2, or Cu2S. Examples of metal chalcogenides include CsSe, In2Se3, WSe2, HgS, PbSe, or CdTe.

[0112] The thickness of the porous layer 10 may be 0.01 μm or more and 10 μm or less, or 0.05 μm or more and 1 μm or less.

[0113] The surface roughness of the porous layer 10 may be 10 or greater, or 100 or greater, given by the effective area / projected area. The projected area is the area of ​​the shadow cast behind an object when it is illuminated from directly in front. The effective area is the actual surface area of ​​the object. The effective area can be calculated from the volume obtained from the projected area and thickness of the object, and from the specific surface area and bulk density of the materials constituting the object. The specific surface area is measured, for example, by the nitrogen adsorption method.

[0114] The voids in the porous layer 10 are connected from one main surface of the porous layer 10 to the other main surface. That is, the voids in the porous layer 10 are connected from the main surface of the porous layer 10 in contact with the photoelectric conversion layer 7 to the main surface of the porous layer 10 in contact with the electron transport layer 6. As a result, the material of the photoelectric conversion layer 7 can fill the voids in the porous layer 10 and reach the electron transport layer 6. Therefore, even with the porous layer 10, electrons can be exchanged because the photoelectric conversion layer 7 and the electron transport layer 6 are in direct contact.

[0115] By providing the porous layer 10, the photoelectric conversion layer 7 can be easily formed. The porous layer 10 allows the material of the photoelectric conversion layer 7 to penetrate the voids in the porous layer 10, and the porous layer 10 acts as a scaffold for the photoelectric conversion layer 7. Therefore, the material of the photoelectric conversion layer 7 is less likely to be repelled or aggregated on the surface of the porous layer 10. Consequently, the photoelectric conversion layer 7 can be easily formed as a uniform film. The photoelectric conversion layer 7 can be formed by the coating method, printing method, or vapor deposition method described above.

[0116] The porous layer 10 is expected to cause light scattering, which increases the optical path length of light passing through the photoelectric conversion layer 7. An increase in optical path length is predicted to increase the amount of electrons and holes generated in the photoelectric conversion layer 7.

[0117] (Intermediate layer 11) The intermediate layer 11 is made of fullerene (C 60 ), C 60 Derivatives, or C 60 It includes a self-assembled monolayer (hereinafter also referred to as "C60SAM") having [a specific property]. Because electron collection is efficiently performed by the intermediate layer 11, the resistance loss when transporting electrons to the electron transport layer 6 is reduced.

[0118] C 60 An example of a derivative is [6,6]-Phenyl C 61 butyric acid methyl ester or [6,6]-Phenyl-C 61 Butyric acid is a butyl ester. An example of C60SAM is 4-(1′,5′-Dihydro-1′-methyl-2′H-[5,6]fullereno-C 60 -Ih-[1,9-c]pyrrol-2′-yl)benzoic acid, (1,2-Methanofullerene C 60 )-61-carboxylic acid, or C 60 It is pyrrolidine tris-acid.

[0119] The intermediate layer 11 is formed, for example, by a solution coating method, immersion method, printing method, or vapor deposition method.

[0120] The present disclosure will be described in more detail below with reference to examples and comparative examples.

[0121] In the examples and comparative examples, perovskite solar cells were fabricated, and their initial properties, properties after light resistance testing, and properties after heat resistance testing were evaluated.

[0122] The configurations of the photoelectric conversion elements in the solar cells of Examples 1, 4, and 6, and Comparative Example 1, are as follows. • Substrate: Glass substrate (thickness: 0.7mm) • First electrode: Transparent electrode (indium-tin composite oxide layer) (thickness: 100 nm) • Electron transport layer: Titanium oxide (TiO2) (thickness: 30 nm) • Porous layer: A mixed layer of mesoporous titanium oxide (TiO2) (thickness: 150 nm) and the material of the photoelectric conversion layer described below. • Photoelectric conversion layer: A layer mainly containing HC(NH2)2PbI3 (thickness: 500nm) • Hole transport layer: Layer containing phenethylammonium iodide (manufactured by greatcellSolar) / Layer mainly containing PTAA (however, lithium bis(trifluoromethanesulfonyl)imide (manufactured by Sigma-Aldrich) and 4-tert-butylpyridine are included as additives) (thickness: 50 nm) • Second electrode: Au (thickness: 200 nm)

[0123] The configurations of the photoelectric conversion elements in the solar cells of Examples 2, 3, 5, and 7, and Comparative Example 2, are as follows. • Substrate: Glass substrate (thickness: 0.7mm) • First electrode: Transparent electrode (indium-tin composite oxide layer) (thickness: 100 nm) • Electron transport layer: Titanium oxide (TiO2) (thickness: 30 nm) • Porous layer: Mesoporous structure titanium oxide (TiO2) ·Middle layer: 4-(1′,5′-Dihydro-1′-methyl-2′H-[5,6]fullereno-C 60 -Ih-[1,9-c]pyrrol-2′-yl)benzoic acid (i.e., C60SAM) (manufactured by Sigma-Aldrich) (thickness: 50 nm (thickness including mesoporous structure titanium oxide)), further containing photoelectric conversion layer material in the voids. • Photoelectric conversion layer: A layer mainly containing HC(NH2)2PbI3 (thickness: 500nm) • Hole transport layer: Layer containing n-butylammonium bromide (manufactured by greatcellSolar) / Layer mainly containing PTAA (however, tris(pentafluorophenyl)borane (manufactured by Tokyo Chemical Industry Co., Ltd.) is included as an additive) • Second electrode: Au (thickness: 200 nm)

[0124] As described above, the photoelectric conversion elements in the solar cells of Examples 1, 4, and 6, and Comparative Example 1, were the photoelectric conversion elements of the second configuration example shown in Figure 3. Furthermore, the photoelectric conversion elements in the solar cells of Examples 2, 3, 5, and 7, and Comparative Example 2, were the photoelectric conversion elements of the third configuration example shown in Figure 4.

[0125] <Fabrication of photoelectric conversion elements> (Example 1) First, a glass substrate with a thickness of 0.7 mm was prepared. This substrate serves as a support material in the solar cell of this disclosure.

[0126] A layer of indium-tin composite oxide was formed on the substrate by sputtering. In this way, the first electrode was formed.

[0127] Next, a layer of titanium oxide was formed on the first electrode by sputtering. In this way, an electron transport layer was formed.

[0128] After applying 30NR-D (manufactured by Great Cell Solar) to the electron transport layer using a spin-coating method, a layer of titanium oxide with a mesoporous structure was formed by firing at 500°C for 30 minutes. In this way, a porous layer was formed.

[0129] Next, the substrate, which had formed a porous layer, was immersed in a C60SAM solution for 30 minutes and then removed. Here, the C60SAM solution was a mixed solution of tetrahydrofuran (manufactured by Fujifilm Wako Pure Chemical Industries) and ethanol (manufactured by Fujifilm Wako Pure Chemical Industries) in a 1:1 volume ratio, to which C60SAM was added at a concentration of 1 × 10⁻⁶. -5 The solution was obtained by adding it to a concentration of mol / L. After thoroughly rinsing the removed substrate with ethanol solution, it was annealed on a hot plate at 100°C for 30 minutes. After annealing, the substrate was allowed to cool naturally to room temperature to obtain a substrate modified with C60SAM. In this way, an intermediate layer was formed.

[0130] Next, a raw material solution for the photoelectric conversion material was applied by spin coating to form a photoelectric conversion layer containing a perovskite compound. The raw material solution contained 0.92 mol / L lead(II) iodide (manufactured by Tokyo Chemical Industry Co., Ltd.), 0.17 mol / L lead(II) bromide (manufactured by Tokyo Chemical Industry Co., Ltd.), 0.83 mol / L formamidinium iodide (manufactured by GreatCell Solar Co., Ltd.), 0.17 mol / L methylammonium bromide (manufactured by GreatCell Solar Co., Ltd.), 0.05 mol / L cesium iodide (manufactured by Iwatani Corporation), and 0.05 mol / L rubidium iodide (manufactured by Iwatani Corporation). The solvent for this solution was a mixture of dimethyl sulfoxide (manufactured by Acros) and N,N-dimethylformamide (manufactured by Acros). The mixing ratio (DMSO:DMF) of dimethyl sulfoxide (DMSO) and N,N-dimethylformamide (DMF) in this raw material solution was 1:4 by volume.

[0131] Next, a hole transport layer was formed on the photoelectric conversion layer. An isopropyl alcohol (Acros Organics) solution containing 1 g / L of phenethylammonium iodide (greatcellSolar) was prepared and spin-coated onto the photoelectric conversion layer. This formed a layer containing phenethylammonium iodide. Subsequently, a layer mainly containing PTAA was formed by spin-coating a solution containing PTAA. The solvent for the PTAA-containing solution was toluene (Acros). The PTAA-containing solution contained 10 g / L of PTAA, lithium bis(trifluoromethanesulfonyl)imide, and 4-tert-butylpyridine.

[0132] Next, a second electrode 9 was formed on the hole transport layer by vacuum deposition of an Au film. Thus, a photoelectric conversion element was obtained on the glass substrate, which served as the support material.

[0133] Next, the photoelectric conversion element according to Example 1 was sealed in a glove box where the water vapor concentration was adjusted to 100 ppm. Here, the oxygen concentration in the glove box was 2 ppm or less. The photoelectric conversion element according to Example 1 was sealed with UV-curable resin, a cover glass, and a glass substrate. That is, a photoelectric conversion element comprising a first electrode, an electron transport layer, a porous layer, a photoelectric conversion layer, a hole transport layer, and a second electrode was sealed with UV-curable resin, a cover glass, and a glass substrate. Thus, a solar cell according to Example 1 was obtained. In the photoelectric conversion element according to Example 1, the water vapor concentration in the sealing space was 100 ppm, and the oxygen concentration was 2 ppm or less.

[0134] (Example 2) A solar cell was fabricated using the same method as in Example 1, except that the materials used for forming the intermediate layer and fabricating the hole transport layer were different. The materials used for forming the intermediate layer and the hole transport layer are described below.

[0135] The intermediate layer was formed using the following procedure. A substrate formed up to the porous layer using the same method as in Example 1 was immersed in a C60SAM solution for 30 minutes and then removed. Here, the C60SAM solution was prepared by mixing tetrahydrofuran (manufactured by Fujifilm Wako Pure Chemical Industries) and ethanol (manufactured by Fujifilm Wako Pure Chemical Industries) in a 1:1 volume ratio and adding C60SAM to a concentration of 1 × 10⁻⁶. -5 The solution was obtained by adding it to a concentration of mol / L. After thoroughly rinsing the removed substrate with ethanol solution, it was annealed on a hot plate at 100°C for 30 minutes. After annealing, the substrate was allowed to cool naturally to room temperature to obtain a substrate modified with C60SAM. In this way, an intermediate layer was formed.

[0136] For forming the n-butylammonium bromide-containing hole transport layer, n-butylammonium bromide (manufactured by greatcellSolar) was used instead of phenethylammonium iodide in the phenethylammonium iodide-containing solution used in Example 1. Furthermore, for forming the layer mainly containing PTAA, tris(pentafluorophenyl)borane was used instead of lithium bis(trifluoromethanesulfonyl)imide and 4-tert-butylpyridine in the PTAA-containing solution used in Example 1. Otherwise, the hole transport layer was formed in the same manner as in Example 1.

[0137] As described above, a solar cell according to Example 2 was obtained.

[0138] (Example 3) In Example 3, the photoelectric conversion element was sealed in a glove box where the water vapor concentration was adjusted to 500 ppm. Aside from this, the procedure was the same as in Example 2, and the solar cell according to Example 3 was obtained.

[0139] (Example 4) In Example 4, the photoelectric conversion element was sealed in a glove box where the water vapor concentration was adjusted to 1000 ppm. Apart from this, the solar cell according to Example 4 was obtained in the same manner as in Example 1.

[0140] (Example 5) In Example 5, the photoelectric conversion element was sealed in a glove box where the water vapor concentration was adjusted to 1000 ppm. Apart from this, the solar cell according to Example 5 was obtained in the same manner as in Example 2.

[0141] (Example 6) In Example 6, the photoelectric conversion element was sealed in a glove box where the water vapor concentration was adjusted to 5000 ppm. Apart from this, the solar cell according to Example 6 was obtained in the same manner as in Example 1.

[0142] (Example 7) In Example 7, the photoelectric conversion element was sealed in a glove box where the water vapor concentration was adjusted to 5000 ppm. Apart from this, the solar cell according to Example 7 was obtained in the same manner as in Example 2.

[0143] (Comparative Example 1) In Comparative Example 1, the photoelectric conversion element was sealed in a glove box with a water vapor concentration adjusted to 10 ppm. Apart from this, the solar cell according to Comparative Example 1 was obtained in the same manner as in Example 1.

[0144] (Comparative Example 2) In Comparative Example 2, the photoelectric conversion element was sealed in a glove box with a water vapor concentration adjusted to 10 ppm. Apart from this, the solar cell according to Comparative Example 2 was obtained in the same manner as in Example 2.

[0145] <Measurement of photoelectric conversion efficiency> The photoelectric conversion efficiency of solar cells was measured for Examples 1 to 7 and Comparative Examples 1 to 2.

[0146] The photoelectric conversion efficiency of the solar cell was measured in the initial state, after light resistance testing, and after heat resistance testing, using an electrochemical analyzer (ALS440B, BAS) and a xenon light source (BPS X300BA, Spectrometer). Before measurement, the light intensity was measured using a silicon photodiode at 1 Sun (100 mW / cm²). 2 The device was calibrated to ). The voltage sweep rate was set to 100 mV / s, and the current-voltage characteristics were measured. No pre-adjustments such as light irradiation or prolonged application of forward bias were performed before the start of the measurement. To fix the effective area and reduce the effect of scattered light, the aperture was set to 0.1 cm. 2 With the solar cell masked with a black mask, light was irradiated from the mask / substrate side. The output under the current / voltage conditions that maximized power was defined as the photoelectric conversion efficiency. The photoelectric conversion efficiency was measured at room temperature under dry air (<2%RH).

[0147] <Lightfastness Test> Lightfastness tests were conducted on the solar cells according to Examples 1 to 7 and Comparative Examples 1 to 2. In the lightfastness tests, the output values ​​were measured while maintaining the voltage and current of the solar cell near the operating point where the output was maximum. Light equivalent to 1 Sun was irradiated from the substrate side for 90 hours while maintaining the substrate temperature at 50°C. After the lightfastness tests, the photoelectric conversion efficiency of the solar cells was measured using the method described above.

[0148] <Heat resistance test> A heat resistance test was conducted on the solar cells according to Examples 1 to 7 and Comparative Examples 1 to 2. The solar cells were maintained at 85°C for 190 hours in a constant temperature chamber. After the heat resistance test, the photoelectric conversion efficiency of the solar cells was measured using the method described above.

[0149] The experimental results described above, namely the measurement results of the photoelectric conversion efficiency of the solar cell in the initial state, after the light resistance test, and after the heat resistance test, are shown in Table 1. In the table, the additives contained in the raw material solution of the hole transport layer are denoted as "LiTFSI" for lithium bis(trifluoromethanesulfonyl)imide and "TPFPB" for tris(pentafluorophenyl)borane. In addition, in order to evaluate the difference in efficiency due to water vapor concentration, the rate of decrease in efficiency relative to the maximum efficiency of each additive is shown in Table 1. The rate of decrease in efficiency relative to the maximum efficiency of each additive is labeled as "rate of decrease in conversion efficiency" in the table.

[0150] [Table 1]

[0151] To compare the effect of water vapor concentration on durability after light resistance and heat resistance tests for each additive, the normalized photoelectric conversion efficiency was calculated using the photoelectric conversion efficiency at the water vapor concentration that showed the maximum efficiency after the tests as a baseline.

[0152] Figure 5 is a graph showing the dependence of the normalized photoelectric conversion efficiency on water vapor concentration for solar cells of Example 1, Example 4, Example 6, and Comparative Example 1. Specifically, Figure 5 is a graph showing the dependence of the normalized photoelectric conversion efficiency on water vapor concentration when the additive in the hole transport layer is LiTFSI.

[0153] Figure 6 is a graph showing the dependence of the normalized photoelectric conversion efficiency on the amount of water vapor in the solar cells of Example 1, Example 4, Example 6, and Comparative Example 1. Specifically, Figure 6 is a graph showing the dependence of the normalized photoelectric conversion efficiency on the amount of water vapor when the additive in the hole transport layer is LiTFSI. In Figure 6, the horizontal axis of Figure 5 has been converted from the water vapor concentration in the sealing space to the amount of water vapor divided by the surface area of ​​the surface of the photoelectric conversion element facing the sealing space.

[0154] Figure 7 is a graph showing the dependence of the normalized photoelectric conversion efficiency on water vapor concentration for solar cells of Example 2, Example 3, Example 5, Example 7, and Comparative Example 2. Specifically, Figure 7 is a graph showing the dependence of the normalized photoelectric conversion efficiency on water vapor concentration when the additive in the hole transport layer is TFPPB.

[0155] Figure 8 is a graph showing the dependence of the normalized photoelectric conversion efficiency on the amount of water vapor in the solar cells of Examples 2, 3, 5, 7, and Comparative Example 2. Specifically, Figure 8 shows the dependence of the normalized photoelectric conversion efficiency on the amount of water vapor when the additive in the hole transport layer is LiTFSI. In Figure 8, the horizontal axis of Figure 7 has been converted from the water vapor concentration in the sealing space to the amount of water vapor divided by the surface area of ​​the surface of the photoelectric conversion element facing the sealing space.

[0156] The volume of the sealing space in the solar cells of the examples and comparative examples is approximately 1.4 × 10⁻⁶. -7 m 3 Therefore, the surface area of ​​the face of the photoelectric conversion element facing the sealing space is 2.6 × 10⁻⁶. -4 m 2 That was the case.

[0157] <Effect of water vapor concentration on initial solar cell characteristics> As shown in Table 1, the initial photoelectric conversion efficiency did not show significant differences when the water vapor concentration in the sealed space was 5000 ppm or less, and was stable without light irradiation or heating.

[0158] <Effect of water vapor concentration on solar cell characteristics after lightfastness testing> As shown in Table 1, Figure 5, and Figure 7, the photoelectric conversion efficiency after the lightfastness test was found to be good in the range of water vapor concentration in the sealed space between 100 ppm and 5000 ppm. On the other hand, the decrease in photoelectric conversion efficiency was significant in the low water vapor concentration region of 10 ppm and when the additive was lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). From the graph in Figure 5, it can be inferred that in the concentration region exceeding 5000 ppm, the photoelectric conversion efficiency decreases even further than the photoelectric conversion efficiency at 5000 ppm. When the water vapor concentration exceeds 5000 ppm, it is thought that a large amount of decomposition products of the perovskite compound (e.g., metal iodides) are generated on the surface and / or grain boundaries of the perovskite compound due to degradation phenomena induced by excess moisture, thereby inhibiting carrier transport. On the other hand, when the water vapor concentration is 5000 ppm or less, it is thought that the above-mentioned decomposition products contribute to the termination of defects in the perovskite compound, thereby suppressing the photodegradation phenomenon induced by defects in the photoelectric conversion material and thus suppressing the decrease in photoelectric conversion efficiency. However, when the water vapor concentration is 10 ppm or less, it is thought that the defects under light irradiation are not sufficiently terminated, the conductivity of PTAA decreases, the hole transport efficiency decreases, and the solar cell characteristics deteriorate due to carrier recombination by defect levels. Furthermore, the rate of efficiency decrease was large when lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was used as an additive to PTAA. This is thought to be because, compared to when TFPPB, a strong acceptor molecule, is used as an additive, the amount of LiTFSI doping is small, so the increased resistance of PTAA due to the low water vapor concentration is more pronounced, and the effect of increased recombination due to the degradation of the perovskite compound becomes larger.

[0159] <Effect of water vapor concentration on solar cell characteristics after heat resistance testing> As shown in Table 1, Figure 5, and Figure 7, the photoelectric conversion efficiency after the heat resistance test was found to be good in the range of water vapor concentration in the sealed space between 100 ppm and 5000 ppm. On the other hand, the rate of decrease in photoelectric conversion efficiency was large in the low water vapor concentration region of 10 ppm. The reason for the existence of an optimal water vapor concentration range is the same for both the light resistance test and the heat resistance test. However, unlike the light resistance test, in the heat resistance test, the rate of decrease in photoelectric conversion efficiency was large when the additive was tris(pentafluorophenyl)borane. This is thought to be because the doping ability of tris(pentafluorophenyl)borane decreases under heated conditions, and the difference in the high conductivity effect of moisture on PTAA becomes apparent. Therefore, as the energy of the light irradiated in the lightfastness test and the heating temperature in the heat resistance test increase, new defects may be generated depending on the activation energy of various defects. Furthermore, when the water vapor concentration is low, the conductivity of PTAA decreases, reducing the hole extraction efficiency, which increases the probability of defect recombination and reduces the photoelectric conversion efficiency. However, since the conditions for the lightfastness test and heat resistance test in this embodiment were set assuming actual operation outdoors, the range of optimal water vapor concentration found in the embodiment for improving the durability of the solar cell remains unchanged.

[0160] Based on the above results, it was confirmed that the photostability and thermal stability of the solar cell disclosed herein can be achieved simultaneously when the water vapor concentration in the sealed space is in the range of 100 ppm or more and 5000 ppm or less. [Industrial applicability]

[0161] This disclosure can significantly improve the durability of solar cells and has extremely high potential for industrial application. [Explanation of symbols]

[0162] 1. Photoelectric conversion element 2 Support material 3. Sealing material 4 circuit boards 5 1st electrode 6 Electron transport layer 7 Photoelectric conversion layer 8 Hole transport layer 9 Second electrode 10 Porous layer 11. Middle Class 100, 200, 300 photoelectric conversion elements 1000 solar cells

Claims

1. supporting material, Photoelectric conversion element, and A sealing material is provided, The photoelectric conversion element is placed inside the sealed space sealed by the support material and the sealing material. The aforementioned photoelectric conversion element comprises a first electrode, a photoelectric conversion layer, and a second electrode in this order. The photoelectric conversion layer comprises a perovskite compound, The value obtained by dividing the amount of water vapor in the sealing space by the surface area of ​​the surface of the photoelectric conversion element facing the sealing space is 2.3 × 10 -6 mol / m 2 The above and 2.3 × 10⁻⁵ mol / m³ 2 The following is: Solar cell.

2. The oxygen concentration in the sealed space is less than 10 ppm by volume fraction. The solar cell according to claim 1.

3. The partial pressure of water vapor in the sealed space is 1 × 10 -4 atm or more and 5 x 10 -3 It is ATM. The solar cell according to claim 1.

4. The perovskite compound contains lead. The solar cell according to claim 1.

5. The photoelectric conversion element further comprises a hole transport layer disposed between the photoelectric conversion layer and the second electrode, The hole transport layer includes an organic semiconductor. The solar cell according to claim 1.

6. The organic semiconductor comprises at least one selected from the group consisting of 2,2',7,7'-tetrakis-(N,N-di-p-methoxyphenylamine)9,9'-spirobiflourene and poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine]. The solar cell according to claim 5.

7. The hole transport layer further comprises an additive. The solar cell according to claim 5 or 6.

8. The additive comprises at least one selected from the group consisting of tert-butylpyridine, bis(trifluoromethanesulfonyl)imide calcium (II), bis(trifluoromethanesulfonyl)imide zinc (II), tris[4-tert-butyl-2-(1H-pyrazole-1-yl)pyridine]cobalt(III)tris(trifluoromethanesulfonyl)imide, and tris(pentafluorophenyl)borane. The solar cell according to claim 7.

9. A photoelectric conversion element comprising a first electrode, a photoelectric conversion layer containing a perovskite compound, and a second electrode in this order, wherein the amount of water vapor in the sealing space per unit surface area of ​​the surface of the photoelectric conversion element facing the sealing space is 2.3 × 10 -6 mol / m 2 The above and 2.3 × 10⁻⁵ mol / m³ 2 In an atmosphere adjusted to the following, including sealing: A method for manufacturing solar cells.

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